Regional & Pain, the reference

Shoulder skin gets its nerve supply from two plexuses. The brachial plexus roots C5, C6 and C7 supply most of it, and an interscalene injection reliably reaches these. The cap and front of the shoulder are supplied by the supraclavicular nerves. These are cutaneous branches of the cervical plexus from C3 and C4, and modest interscalene volumes often miss them. You therefore need to add those roots. The lower brachial plexus roots mainly supply the forearm and hand, so the shoulder does not need them.

Omitting supraclavicular, adding hand-supply nerves. Tempting because shoulder surgery uses a brachial plexus block, so people list the plexus roots. It fails twice: it omits the C3–C4 supraclavicular supply to the top and front of the shoulder, and it adds a lower root that supplies the hand, not the shoulder.

Interscalene spread usually reaches C5–C7, supplying most but not all shoulder skin. The C3–C4 roots supplying the anterior shoulder are often spared. Complete anaesthesia for shoulder arthroscopy may need an added superficial cervical plexus block, whose supraclavicular branches supply shoulder skin.

Sources: Mayo reviewBarash 9e

Visceral organs receive spinal nerve supply from segments well above their overlying skin, so the block must reach the organ's own segment, not just the incision. The prostate, bladder neck and bladder are supplied at T10, so a T10 block is needed to abolish sensation from resection. Handling or pulling on the testis hurts unless the block reaches T10, despite the scrotal incision. Caesarean section involves handling the peritoneum, supplied at T4; any lower level leaves the mother feeling intra-abdominal traction.

Confusing scrotal skin with testis visceral pain. An orchidectomy incision is in the scrotum, well below the umbilicus, so a low lumbar level looks like enough. But pulling on the testis sends pain through segments much higher than the scrotal skin. Only a block reaching T10 prevents it.

A T10 level is enough for TURP because it blocks sensation from the prostate and bladder neck. Any testicular traction needs a T10 block. Caesarean section needs surgical anaesthesia up to T4. The peritoneum is supplied at T4, and the bladder and uterus at T10.

Sources: Miller 10eMayo reviewBarash 9e

You choose the catheter site from where the skin incision is, not from where the organ is. An open nephrectomy uses a subcostal or flank incision across the middle of the abdomen. A catheter placed at the segments that match that incision puts the local anaesthetic where the wound pain comes from. This pain is severe and lasts days. It stops the patient breathing deeply, coughing and moving, which leads to atelectasis and chest infection. That is why good segmental epidural cover matters.

Matching visceral segment to incision location. The kidney's visceral nerves enter the cord at the low thoracic and upper lumbar segments, so a low catheter feels right. But the pain that stops the patient breathing comes from the flank incision in the mid-thoracic dermatomes. A catheter this low mostly blocks segments below the wound.

Miller's gives recommended catheter sites by incision location. Middle abdominal operations such as nephrectomy and cystoprostatectomy get T7–10. Open subcostal nephrectomy causes severe, prolonged pain that impairs breathing and coughing, so postoperative epidural analgesia is recommended.

Sources: Miller 10e

When the uterus contracts and the cervix and lower segment dilate, visceral nociceptors fire. Their afferent fibres run backwards with the sympathetic chain. They then pass through the rami communicantes and the mixed spinal nerves and reach the cord only at the lower thoracic and first lumbar segments. Because these fibres are visceral, the pain is vague, diffuse and poorly localised. It is relieved by interrupting that thoracolumbar band of segments, not the sacral roots.

Confusing kidney afferent level with uterine. It looks right because it names thoracolumbar segments that overlap the uterine band, and kidney pain feels like deep loin visceral pain. But the range is shifted down the cord. The only organ-to-segment pairing the source firmly supports is the uterus at T10 to L1.

First-stage labour pain is visceral and poorly localised. It arises from stretching of the cervix and lower segment plus the contractions. Its afferents accompany sympathetic fibres and join the cord via rami communicantes of T10, T11, T12 and L1.

Sources: Faust

Blocks above the clavicle place local anaesthetic around the roots and trunks. Spread from there often paralyses the diaphragm on the same side, and a patient with little pulmonary reserve tolerates this poorly. Most of the shoulder's sensation comes from two terminal branches: the suprascapular nerve (about 70%) and the axillary nerve (about 20%). Blocking these branches further out covers most of the shoulder and leaves the phrenic nerve alone. Even the suprascapular block by itself carries less phrenic risk than a proximal plexus block.

Underestimating phrenic palsy risk in COPD. Supraclavicular block seems a safe middle ground, being further from the neck than interscalene block with fewer side effects. Yet it still fails: phrenic palsy is less common but clinically significant, so the diaphragm of a patient with COPD is not reliably protected.

Interscalene block paralyses the ipsilateral phrenic nerve and should be avoided in severe COPD. Phrenic palsy after supraclavicular block is rarer but important. Suprascapular block carries less phrenic risk; suprascapular and axillary nerves together supply most of the shoulder.

Sources: FaustBarash 9eStoelting 8e

An early report blamed spinal anaesthesia for postoperative MS relapse; the theory was that a leaky blood–brain barrier and demyelinated cord leave fibres exposed to local anaesthetic neurotoxicity, so Miller still advises against routine spinal. Later cohorts found relapse rates similar after spinal, epidural or no neuraxial block, and Miller, Stoelting and Barash accept neuraxial use as safe. The caution therefore survives as modification: lower dose and concentration or epidural, expect a longer block, counsel about relapse. Diplopia, ataxia and leg weakness signal brainstem and cord plaques.

Confusing Guillain-Barré peripheral with MS central. Guillain-Barré is also demyelinating and causes leg weakness, so it looks equally risky. But it attacks peripheral nerves, not the cord, and neuraxial anaesthesia remains in common use for it, including in labour; blurred vision with ataxia points to the central plaques of MS.

Spinal block was implicated in postoperative MS exacerbation and is usually discouraged, yet any link to relapse lacks evidence. Blocks may last longer, so use lower dose and concentration spinal or choose epidural. Brainstem and cord lesions cause diplopia, ataxia and weakness.

Sources: Miller 10eBarash 9e

Residual anticoagulant effect of enoxaparin rises with dose, so twice-daily treatment doses leave far more anti-Xa activity than thromboprophylactic doses. Needle or catheter placement while activity persists risks spinal or epidural haematoma, so the gap after the last treatment dose must be longer. Pregnancy and labour do not relax this. If the full gap cannot be met, measure residual anti-Xa activity to confirm sufficient clearance. This matters most in elderly patients and those with poor renal clearance, who eliminate the drug slowly.

Using prophylactic interval for therapeutic dose. Twelve hours is the wait after thromboprophylactic enoxaparin, so it is the figure most people remember. Seventy milligrams twice daily is weight-based treatment dosing, about 1 mg/kg. It leaves much more residual anti-Xa activity, so the longer 24-hour wait applies.

Reviews and the obstetric anaesthesia consensus advise at least 24 hours after therapeutic enoxaparin (1 mg/kg twice daily) before neuraxial puncture. Current guidance suggests an anti-Xa level if under 24 hours, especially over age 75 or CrCl 30 or less, accepting 0.1 IU/mL or less.

Sources: Mayo reviewOutside our books: SOAP consensus statement on the anesthetic management of pregnant and postpartum women receiving thromboprophylaxis or higher dose anticoagulants (2018)Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)

LMWH has a predictable half-life, so waiting a fixed number of half-lives lets its anti-Xa effect wear off without testing. No residual anti-Xa level has been proven safe, so a lab result cannot replace the interval. Clearance slows in older patients and in renal failure, and residual activity can last beyond 24 h in older patients with comorbid disease. So if a block is planned within 24 h, consider an anti-Xa level and accept ≤0.1 IU/mL, particularly when age is over 75 or CrCl is ≤30.

Measuring anti-Xa level instead of timing. Anti Xa factor is tempting because LMWH acts on factor Xa, so measuring it feels direct. But no safe residual level is established, and guidance times the block from the last dose. A level is only an optional adjunct when proceeding within 24 h. It is not a routine prerequisite.

Standard texts set block delay by dose; obstetric guidance prefers half-life-based intervals over laboratory cut-offs. The newest regional guidance keeps the 24 h rule but suggests considering anti-Xa ≤0.1 IU/mL when under 24 h, especially in elderly or renally impaired patients.

Sources: Miller 10eOutside our books: SOAP consensus statement on the anesthetic management of pregnant and postpartum women receiving thromboprophylaxis or higher dose anticoagulants (2018)Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)

Prophylactic subcutaneous heparin has a slight, brief effect: most patients show no measurable aPTT change, and any change normalises within 4 to 6 hours. Waiting that long before needle insertion or catheter removal lets residue fade; a normal coagulation screen can substitute. Restart splits: ASRA, Barash and Miller allow the next prophylactic dose without delay after removal; ASRA's own 1 hour rule is for intravenous heparin, which AAGBI, ESA and SOAP extend to subcutaneous prophylaxis, so 1 hour satisfies all.

Applying the 4 to 6 hour gap after removal. It looks like the mirror image of the pre-block hold, so people assume the same gap applies afterwards. No guideline asks for that: US sources allow next prophylactic dose without delay; UK, European and obstetric guidance need 1 hour. The 4 to 6 hour interval belongs before puncture or removal.

Guidelines advise a four to six hour gap after low-dose heparin before needle insertion, or normal coagulation; catheter removal follows the same interval. Standard tests often stay unchanged at these doses. ASRA permits immediate redosing after removal; obstetric guidance waits at least an hour.

Sources: Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)Outside our books: SOAP consensus statement on the anesthetic management of pregnant and postpartum women receiving thromboprophylaxis or higher dose anticoagulants (2018)

The wait before a neuraxial block depends on the heparin dose. A larger subcutaneous dose gives a bigger and longer-lasting anticoagulant effect. That leaves more residual effect when the needle goes in, and a higher risk of spinal or epidural haematoma. The standard low-dose regimen of 5,000 units needs only 4–6 h. The intermediate regimen needs 12 h plus a coagulation check. Therapeutic dosing needs 24 h. Match the interval to the actual dose, not just to the drug.

Applying prophylactic interval to intermediate-dose heparin. Many people remember the familiar 4–6 h window for prophylactic heparin, and some texts give it without mentioning dose. That interval only covers the low-dose 5,000-unit regimen. At 7,500 units twice daily the patient is in the intermediate band, which needs a longer interval.

Regional anaesthesia guidance and a major textbook agree. Twice-daily subcutaneous heparin at 7,500–10,000 units needs at least 12 h before neuraxial block, and normal coagulation must be confirmed. Lower doses need 4–6 h. Therapeutic doses need 24 h.

Sources: Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)Barash 9e

Pain procedure guidance uses a wait of five half-lives, not the shorter wait used for routine neuraxial blocks. This is because patients having pain procedures carry extra bleeding risk: they are often elderly, may have spinal stenosis, and some procedures are surgical in nature. For rivaroxaban, five half-lives adds up to about 3 days. A spinal haematoma was reported after only an 18-hour gap, which supports the longer wait.

Using prophylactic rivaroxaban interval for therapeutic. One day looks right because the newer regional anaesthesia guidance allows a 24-hour stop for low-dose (prophylactic) rivaroxaban. That figure does not fit this patient. Atrial fibrillation needs full anticoagulant dosing, and a spinal pain procedure is high risk, so the five-half-life rule applies.

The pain-procedure guidance says to allow 5 half-lives, which is 3 days, between the last rivaroxaban dose and the procedure. It says to restart the drug 24 hours afterwards. It cites a spinal haematoma after an 18-hour interval as the reason for the longer gap.

Sources: Outside our books: Interventional spine and pain procedures in patients on antiplatelet and anticoagulant medications (second edition): ASRA/ESRA/AAPM/INS/NANS/WIP guidelines (2018)Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)

Taking out an epidural catheter is a neuraxial manipulation, just like putting one in. It can injure epidural vessels and cause a spinal haematoma. So the catheter comes out only after the prophylactic dose has been held and the drug's effect has fallen. Once it is out, the next dose is delayed briefly so the puncture track can seal before anticoagulant activity rises again. The delay is timed from removal. How long the drug was held beforehand does not change it.

Expecting symmetrical pre- and post-removal timing. It looks symmetrical, but the 12-hour pre-removal hold is what makes removal safe. Afterwards, guidelines ask for only a short delay before prophylaxis restarts. People wrongly expect the same wait; a longer delay adds nothing for routine prophylactic dosing.

Regional and obstetric anaesthesia guidance agrees. Take out the catheter at least 12 hours after a prophylactic dose, then wait at least 4 hours after removal before the next dose. If blood appears when the catheter is placed, postoperative dosing is delayed to 24 hours.

Sources: Outside our books: SOAP consensus statement on the anesthetic management of pregnant and postpartum women receiving thromboprophylaxis or higher dose anticoagulants (2018)Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)Mayo reviewOutside our books: Interventional spine and pain procedures in patients on antiplatelet and anticoagulant medications (second edition): ASRA/ESRA/AAPM/INS/NANS/WIP guidelines (2018)

Thrombolytic drugs leave a systemic lytic state that outlasts the procedure. Moving a catheter in the epidural space during that state risks a spinal haematoma. Fibrinogen is one of the slowest clotting factors to recover. When the fibrinogen level has returned, that is good evidence the drug's effect has worn off, so removal is timed to that recovery rather than done at once. Bleeding can still show itself after the catheter is out, so frequent neurological checks continue afterwards.

Removing catheter before lysis has cleared. Removing the catheter straight away feels right because the team wants to start long-term antiplatelet therapy, and catheters normally come out before antithrombotic drugs restart. But right after lysis the lytic effect is still present. You must show it has cleared first.

Current ASRA guidance sets no fixed removal time. Measure fibrinogen to detect residual thrombolytic effect and time removal, then check neurology frequently for at least 48 hours. An earlier pain-procedures guideline permits leaving the catheter in, removing it after 48 hours or 2 half-lives.

Sources: Outside our books: Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: ASRA Pain Medicine evidence-based guidelines (2025)Outside our books: Interventional spine and pain procedures in patients on antiplatelet and anticoagulant medications (second edition): ASRA/ESRA/AAPM/INS/NANS/WIP guidelines (2018)

Neuropathic pain comes from damaged or abnormal nerves, not from inflamed tissue. Tricyclics and SNRIs raise monoamine levels and strengthen the descending inhibitory pathways that damp pain signalling in the spinal cord. Tricyclics are the stronger class but have more side effects. SNRIs or gabapentinoids are often chosen because they are better tolerated. Opioids are pushed down the ladder because of misuse risk.

Starting strong opioid for neuropathic pain. A strong opioid feels like the natural choice for persistent, severe pain. In neuropathic pain, however, opioids are third line, behind topical agents and tramadol. They also carry a real risk of misuse, so they are never the first drug to start.

First-line drugs for neuropathic pain are antiepileptics, SNRIs and tricyclics. Topical agents and tramadol are second line, and opioids are third. Tricyclics work better than SNRIs, but duloxetine is favoured in diabetic neuropathy for tolerability. Gabapentinoids may be preferred when side effects and misuse matter.

Sources: Barash 9eStoelting 8e

Fibromyalgia is a chronic widespread pain syndrome. It is managed with a multidisciplinary plan rather than a single hands-on intervention. The supported non-drug treatments are active ones: teaching the patient about the condition, supportive care, gentle low-impact physical training, and cognitive and operant behavioural therapy, which change how the patient thinks about and responds to pain. Drug therapy is added where needed.

Acupuncture as sensible complementary fibromyalgia treatment. Acupuncture seems a sensible complementary pain treatment, and some guidelines give it weak, low-quality support. It fails because the textbooks' effective non-drug list for fibromyalgia is education, low-impact exercise and cognitive and operant behavioural therapy; neither acupuncture nor massage is on it. Guidelines strongly recommend only exercise.

Effective non-drug management includes education, supportive therapy, low-intensity low-impact exercise programmes, and cognitive and operant behavioural therapy. A specialist pain society panel recommended a multidisciplinary approach combining education, physical training, cognitive behavioural strategies and drug treatment.

Sources: Barash 9eStoelting 8e

Blocking the sympathetic chain separates pain sustained by sympathetic activity from pain that is not, so relief identifies a sympathetically maintained component. Allodynia with trophic, sweating and vasomotor change after limb injury is CRPS, even if the arm is cold and pale, and still merits the block. Barash counts blocks as therapy: brief relief opens a window for physiotherapy, and a series follows if the first gives over 50% relief. Faust, the more cautious current source, makes occupational therapy the mainstay, so blocks serve rehabilitation, never replace it.

Using somatic block for sympathetic testing. Interscalene block numbs the whole arm, so it looks like the obvious regional choice for arm pain. It blocks somatic nerves, though, so relief cannot show whether the pain depends on sympathetic outflow. Only a sympathetic (stellate) block answers that diagnostic question.

Faust uses stellate block diagnostically to tell sympathetically maintained from independent pain and calls occupational therapy the treatment mainstay; Barash lists allodynia with trophic and vasomotor change as CRPS and repeats sympathetic blocks after over 50% first-block relief to enable physiotherapy.

Sources: FaustBarash 9e

In many patients nobody can pin down where mechanical back pain comes from, so a film or scan cannot prove the cause and does not change treatment. Uncomplicated pain is expected to settle. The plan is reassurance, keeping active and self-management. Keep imaging for when the result would change care: red flags pointing to serious disease, or radiculopathy.

Ordering dynamic films without red flags. Dynamic films look targeted because bending and twisting bring on the pain, and instability sounds like a reasonable cause. But plain radiography is usually not appropriate without red flags. The cause often cannot be found anyway, and any result would leave the conservative plan the same.

NICE advises against routine imaging outside specialist care. ACR rates lumbar radiography usually not appropriate as first imaging for acute back pain without red flags. Stoelting says the cause is often uncertain. Low-risk patients need reassurance, advice to keep active and self-management.

Sources: Outside our books: Low back pain and sciatica in over 16s: assessment and management (2016)Outside our books: ACR Appropriateness Criteria: Low Back Pain (2021)Stoelting 8e

Once the carotid is clamped, the hemisphere on that side relies on collateral flow. An awake patient's responsiveness and behaviour show at once whether that flow is enough. New confusion, agitation or unresponsiveness means ischaemia. Because deficits are seen directly, the surgeon can shunt only patients who show them. Under general anaesthesia, without this check, everyone may be shunted as a blind precaution. Indirect monitors are then needed, and inserting a shunt adds its own embolic risk.

Expecting respiratory benefit in carotid surgery. Regional techniques do reduce lung complications in other vascular surgery, so this sounds right. For carotid surgery, though, the patient must stay cooperative and lie flat for a long time. Significant lung disease can rule out the awake approach, and a respiratory benefit is not one of its cited advantages.

Awake assessment is seen as the most sensitive way to detect poor cerebral perfusion. It reduces shunt use and saves the cost of indirect monitors. The technique needs a cooperative patient who can lie flat, and chronic lung disease may rule people out.

Sources: Miller 10eBarash 9e

Under spinal the patient stays awake, so their mental state works as a live monitor. When irrigation fluid is absorbed, sodium and osmolality fall, and the first signs are restlessness and confusion. An awake patient shows these early, while general anaesthesia hides them. If the block is kept no higher than T9, a bladder perforation shows up as pain. The neuraxial block also lowers the risk of venous thrombosis and reduces bleeding. It does not stop irrigation fluid from being absorbed.

Thinking spinal anaesthesia prevents TURP syndrome. Spinal anaesthesia is closely linked with TURP syndrome, so it is easy to assume it prevents it. It does not. Fluid is absorbed the same way under either technique. Spinal only helps you spot the syndrome sooner, because the patient's changing mental state can be watched.

The texts list three benefits of spinal: earlier recognition of electrolyte upset shown by changes in mental state, fewer deep vein thromboses, and less blood loss. Keeping the patient awake lets early signs of TURP syndrome be seen. Cardiac outcomes are similar with either technique.

Sources: FaustMiller 10e

Bleeding from the surgical bed depends on the venous pressure behind it. A regional block lowers central and peripheral venous pressures, reducing oozing beyond any fall in blood loss. Positive pressure ventilation raises venous pressure and adds to bleeding. The cited comparison set epidural, and combined epidural-general anaesthesia with spontaneous breathing, against ventilated general anaesthesia, blaming ventilation's raised venous pressure for the extra bleeding. As the block itself lowers venous pressure, epidural should still bleed less than spontaneously breathing general anaesthesia, though that pairing is not tested directly.

Equal bleeding when general anaesthesia is spontaneous. If the general anaesthetic patient also breathes spontaneously, the ventilation effect seems to cancel, so equal bleeding looks logical. That pairing is not tested directly, but regional anaesthesia lowers central and peripheral venous pressure in its own right, and reduced blood loss remains a listed advantage over general anaesthesia.

Epidural with spontaneous breathing lowers blood loss; reduced bleeding is an advantage of regional over general anaesthesia. Where regional techniques cut bleeding, lower central and peripheral venous pressures are the proposed reason; raised venous pressure from controlled ventilation likely explained extra bleeding under general anaesthesia.

Sources: Barash 9eMiller 10e

Stimuli below a high lesion, such as surgical traction on a contracted limb, fire spinal sympathetic reflexes that the brain can no longer damp, causing surges in pressure and reflex spasms. A spinal drops a dense block across every root below its level, including the large sacral roots, so the reflex never starts, regardless of sedation. An epidural may spare sacral roots and its level is hard to confirm. Only deep general anaesthesia blunts the reflex; a femoral block misses much of the limb's input.

Choosing GA over neuraxial in paralysis. An LMA-based general anaesthetic feels safe and avoids an awkward neuraxial puncture in a paralysed, deformed patient. But light anaesthesia leaves the reflex arc below the lesion active, so surgical stimulation can still trigger severe hypertension and spasms.

Spinal anaesthesia can prevent autonomic hyperreflexia. It blocks the large sacral roots more dependably than an epidural, and return of cerebrospinal fluid confirms placement. Difficult access and low baseline pressure after cord injury rarely cause problems in practice.

Sources: Mayo reviewFaust

The cervical plexus splits early. Its motor branches stay deep, while its purely sensory branches run laterally and come to the surface together behind the sternocleidomastoid. One of these, the great auricular nerve, climbs over the mandibular angle, the parotid and the lower pinna. The lesser occipital nerve supplies skin behind the ear. Putting local anaesthetic superficially at the point where these branches emerge numbs this skin. The block does not need to reach the deep motor branches.

Confusing cervical with brachial plexus block. Interscalene is a familiar neck block placed near the scalene muscles, so it seems anatomically close. But it targets the brachial plexus for shoulder and upper-limb surgery. The skin over the mandibular angle and lower ear belongs to the sensory branches of the cervical plexus.

The sensory branches of the cervical plexus surface at the border of the sternocleidomastoid and supply the skin of the neck. The great auricular nerve reaches the mandibular region, parotid and pinna. The superficial block anaesthetises it along with the lesser occipital nerve.

Sources: Miller 10eBarash 9e

The interscalene approach places local anaesthetic high in the neck, where the plexus is still roots and trunks. This blankets the upper plexus that supplies the shoulder and proximal humerus. The lower trunk is often missed, which matters for hand and ulnar-border surgery but not for the shoulder. Lower approaches reach the plexus after it has divided into divisions, cords or branches, so they are aimed further down the limb. The cost is ipsilateral phrenic block, which can occur in every patient for as long as the block lasts.

Choosing supraclavicular over interscalene for shoulder. Supraclavicular block also reaches the shoulder and proximal arm, so it looks like an equally good answer. The texts still name the interscalene approach as the best fit for shoulder surgery. The supraclavicular block acts lower, at trunks and divisions, and lies close to the pleura.

The interscalene route acts at root and trunk level and is described as best suited to shoulder operations. A continuous interscalene catheter supports discharge after rotator cuff repair. Phrenic paresis may affect all patients.

Sources: FaustMiller 10eMayo review

The superficial block alone gives surgical anaesthesia comparable to deep or combined blocks. The deep block adds no benefit. It needs a needle near the cervical roots, which brings more serious needle-related harm. The local anaesthetic can also reach the motor fibres to the diaphragm. Healthy patients can breathe with one paralysed hemidiaphragm because the accessory and intercostal muscles take over. Patients with poor respiratory reserve cannot, so they become short of breath and their oxygen saturation falls during surgery.

Preferring deep cervical over superficial approach. A deep block is tempting because it is a recognised technique for one-sided neck anaesthesia and seems more thorough. It works no better than the superficial block. It also causes more serious needle complications and risks weakening the diaphragm, which a patient with obstructive lung disease tolerates poorly.

A superficial block works as well as a deep or combined block for carotid surgery. A large review found more serious needle-related complications with deep blocks. Anaesthetic spreading to the cervical plexus can reach the diaphragm's motor supply, causing problems in respiratory insufficiency.

Sources: Barash 9eMiller 10e

The infraorbital nerve is a maxillary branch of the trigeminal nerve, not the facial nerve. It supplies the lip being repaired, so blocking it gives targeted analgesia. The age matters: the lip is closed at 6 to 12 weeks and the palate later, at 9 to 14 months, so a baby this young is usually having the lip repaired. The supraorbital nerve is one of the scalp nerves blocked for craniotomy. It does not reach the cleft.

Using supraorbital instead of infraorbital block. Supraorbital sounds like the mirror image of the infraorbital block, so people mix them up. It is a scalp nerve blocked for craniotomy and does not supply the lip or palate being repaired, so it gives no analgesia for cleft surgery.

Infraorbital and suprazygomatic maxillary blocks are the usual cleft lip and palate blocks, the maxillary one needing expertise. Infraorbital blocks give effective lip-repair analgesia; lips are repaired at 6 to 12 weeks, palates at 9 to 14 months; supraorbital belongs to craniotomy.

Sources: Barash 9eStoelting 8eMiller 10e

Paravertebral local anaesthetic reaches the spinal nerves where they leave the spine. This blocks several intercostal nerves at once, mostly on the operated side, and little spreads into the epidural space. As a result, the widespread two-sided sympathetic block of an epidural is avoided. Pain relief matches epidural local anaesthetic. Hypotension, nausea and urinary retention are less common, fewer blocks fail and the risk of a spinal haematoma is lower. A catheter infusion keeps the block going through the painful early days after surgery.

Using lumbar epidural for thoracic surgery. An epidural infusion is a standard thoracotomy technique, so it looks like the natural step up from failing PCA. But a lumbar catheter sits far below the chest wall segments that carry the pain, so the drug misses them. Even epidural opioids work best when given at thoracic level.

Paravertebral block, single-shot or continuous catheter, gives analgesia equal to or better than thoracic epidural and is a valuable alternative, with fewer failed blocks, lower haematoma risk, and less hypotension, nausea and urinary retention. Epidural opioids work best at thoracic level.

Sources: Miller 10eBarash 9e

The lower abdominal wall is supplied by thoracoabdominal segmental nerves plus the ilioinguinal and iliohypogastric nerves. These lie in the plane separating transversus abdominis from internal oblique. One injection into that fascial layer reaches several of them at once and avoids the neuraxial route completely. For groin surgery its weakness is poor cover of the genitofemoral nerve's genital branch, so a targeted ilioinguinal–iliohypogastric block does better there.

Using lateral serratus for lower abdominal. A serratus block is also a truncal fascial plane block used when neuraxial routes are unavailable, so it sounds equivalent. But it spreads over the lateral chest wall, well above the dermatomes of a groin or lower abdominal incision. It adds block risk without giving useful analgesia there.

Barash recommends truncal blocks, including TAP, for patients unsuitable for neuraxial blocks, and ilioinguinal–iliohypogastric blocks for hernia repair. Miller presents TAP as a single-injection plane technique, and found ilioinguinal–iliohypogastric block gave better paediatric hernia analgesia, probably because TAP poorly covers the genitofemoral genital branch.

Sources: Barash 9eMiller 10e

The great toe gets sensation from several nerves. The posterior tibial nerve supplies the plantar skin and the superficial peroneal supplies the dorsum. It spares the first web space, which the deep peroneal supplies. The saphenous nerve can reach the medial base of the toe. Only the saphenous comes from the femoral nerve; the others are sciatic branches. A sciatic block in the popliteal fossa therefore catches all of those branches at once, and only the saphenous needs adding.

Forgetting posterior tibial great toe plantar. The two peroneal nerves cover the dorsum and first web space, so blocking both feels complete. It is not: the posterior tibial nerve supplies the plantar skin of the great toe. With this pair alone, the underside of the toe can still feel pain during amputation.

The great toe is supplied by the deep peroneal, posterior tibial and superficial peroneal nerves, and sometimes the saphenous, so block all four. Foot surgery can use an ankle block or popliteal sciatic block, adding a saphenous block to cover the medial foot.

Sources: Mayo reviewBarash 9eMiller 10e

Nearly the whole foot and ankle is supplied by sciatic nerve branches: the posterior tibial, sural, deep peroneal and superficial peroneal nerves. A single popliteal fossa injection around the sciatic trunk, close to its bifurcation, anaesthetises all of them. It therefore provides most of the pain relief and lowers opioid requirements, which is particularly relevant in an opioid-tolerant patient. The saphenous nerve arises from the femoral nerve and supplies only the skin over the medial leg and ankle, so it is blocked as a supplementary procedure.

Using saphenous block alone for ankle. The saphenous nerve does reach the ankle, and it is often added to a popliteal block, so it sounds right. But it only supplies a strip of medial skin. On its own it misses most of the ankle, which the sciatic nerve supplies.

The foot and ankle are supplied by sciatic branches plus the saphenous nerve, which comes from the femoral nerve. A popliteal sciatic block reduces pain and opioid use after foot and ankle surgery. A saphenous block is often added for the medial side.

Sources: Miller 10eBarash 9e

Diathermy current at the lateral bladder wall can directly stimulate the obturator nerve, causing violent thigh adductor contraction and dangerous sudden movement during resection. Barash's urology chapter says neuraxial block to T9–T10 prevents the reflex, but prefers muscle relaxation under general anaesthesia. Its regional chapter names obturator nerve block as the preventive. Jerks still occur under a working spinal, so reconcile the views: keep the spinal and add an obturator block, not a femoral one, for lateral wall lesions. Otherwise use general anaesthesia with neuromuscular blockade.

Using femoral block for obturator adduction. The femoral nerve is the familiar big thigh nerve and the usual lower-limb block, so it seems right for a leg jerk. But the movement is adduction, which the obturator nerve drives. The cautery excites the obturator nerve at the lateral wall, so a femoral block leaves the spasm untouched.

Barash says lateral-wall electrocautery can stimulate the obturator nerve, causing violent ipsilateral thigh contraction. It prefers general anaesthesia with muscle relaxation, and states a T9–T10 neuraxial block prevents the reflex. Elsewhere it names obturator nerve block as effective prevention.

Sources: Barash 9e

Local anaesthetic injected at the sacral hiatus spreads upward through the epidural space. The more volume given per kilogram, the more segments it reaches. Concentration sets the density of the block and the total milligrams: use dilute solutions such as 0.2% ropivacaine or 0.125–0.25% bupivacaine. Volume sets how high the block goes. Penile surgery needs only sacral roots. A groin incision needs lumbar cover, so hernia repair needs the larger volume. Always quote the dose in mL/kg of the dilute solution, not mg/kg.

Using 0.5 mL/kg for inguinal incision. 0.5 is the first number in the scheme and is close to the penile or circumcision dose, so it looks like 'the caudal dose'. But it blocks only the sacral dermatomes. That is too low for an inguinal incision, which needs lumbar spread at 1 mL/kg.

Caudal volume follows the required block level: 0.5 mL/kg covers sacral dermatomes, 1 mL/kg lumbar, 1.25 mL/kg lower thoracic. For groin incisions, give 1 mL/kg dilute bupivacaine or 0.2% ropivacaine, up to 20 mL. A general hernia caudal is 0.8–1 mL/kg.

Sources: Barash 9eFaust

Stoelting makes caudal analgesia the routine choice for hypospadias repair, and Miller doses it per kilogram. A fixed volume is therefore not a dose; in an older child the weight-based volume is much larger. NSAIDs do not decide the case. Barash warns that any NSAID may cause severe bronchospasm in asthmatics; Faust concentrates the life-threatening reaction in aspirin-induced asthma. Taken together, an earlier uneventful ibuprofen course neither clears nor condemns NSAIDs, so the choice rests on the operation, which calls for a routine caudal block.

Using oral analgesia instead of caudal. It is tempting because the child has already taken ibuprofen safely, so the asthma worry seems answered. It fails because that history is not the deciding point: combined oral analgesics suit mild-to-moderate pain, whereas hypospadias repair warrants a routine caudal block.

Caudal block is the standard analgesic technique for hypospadias surgery, using a paediatric volume of 0.5–1 mL/kg of a 0.25% solution. Barash warns that any NSAID may trigger serious bronchospasm in patients with asthma, and Faust links the life-threatening reaction specifically to aspirin-sensitive asthma.

Sources: Stoelting 8eMiller 10eBarash 9eFaust

The patch gives steady background opioid, so routinely it stays on into theatre to cover baseline needs. Major surgery makes skin absorption unreliable: warming blankets or heat over the patch can raise fentanyl uptake several-fold, and uptake can also fall unexpectedly, risking overdose or inadequate analgesia. Both major texts therefore remove the patch for major surgery, or when heavy bleeding or sepsis is likely, and start a continuous IV opioid infusion as soon as the patient reaches theatre, leaving no gap. Barash adds short-acting opioids for breakthrough pain.

Stopping fentanyl patch early before theatre. It sounds like the recommended swap to an IV opioid infusion, so it feels safe. But the books keep the patch until theatre and start the infusion on arrival there for major cases. Switching a day early matches neither source's timing.

Patches usually stay on as baseline cover. For major surgery, or real bleeding or sepsis risk, both texts remove the patch and give an IV infusion. One warns that warming multiplies uptake and starts the background infusion on arrival in theatre.

Sources: Barash 9eMiller 10e

In a tolerant patient, the regular opioid only keeps things as they were before surgery. It prevents withdrawal but gives no cover for new incisional pain. Tolerance also means these patients need 3 to 4 times what an opioid-naive patient needs for the same acute pain. Surgical pain must therefore be treated with extra short-acting doses on top of the baseline. When choosing between regimens, add up each regimen's regular daily total. Pick the one that best matches the pre-operative daily dose, then check that rescue doses are also prescribed.

Underdosing opioid baseline in tolerance. It feels safe as a cautious, frequent dose. However, 100 mg twice daily totals twice the 100 mg dose. Twenty milligrams every four hours totals below baseline, reducing it. Thirty milligrams every four hours gives the total closest to baseline among the options.

The textbooks say to continue the home opioid regimen and add short-acting oral or intravenous opioid for postoperative needs. Chronic users need three to four times the acute-pain dose of naive patients. Once eating, patients can take regular sustained-release morphine plus immediate-release opioid as needed.

Sources: Barash 9eFaustMiller 10e

Tolerance to one opioid transfers only partly to another. Switching agents can therefore restore analgesic responsiveness in a patient who has become tolerant. Because cross-tolerance is incomplete, the new drug is effectively more potent than a conversion calculation predicts, so the starting dose must be reduced. Methadone is a frequent choice for this switch. Conversion from morphine to methadone needs particular caution.

Choosing hydromorphone over methadone for rotation. Hydromorphone is a familiar potent opioid, so it seems a natural agent to switch to. The source, however, names methadone as the usual choice for rotation. That makes methadone the best answer.

Rotation is described as valuable for restoring analgesic sensitivity in very tolerant patients, and methadone is named as a common agent for it. Incomplete cross-tolerance means the new opioid's dose ends up lower than calculated. Morphine-to-methadone conversion needs particular care.

Sources: Barash 9e

The methadone ratio tables are built on daily oral morphine, not IV morphine. Oral morphine is less available to the body than IV morphine, so 10 mg IV matches about 30 mg by mouth. Methadone's strength compared with morphine is not fixed. The ratio curves upwards as the morphine dose rises, from 3:1 at low doses to 20:1 above 1,000 mg/day. At low daily doses a divisor of three is safe. Using a bigger ratio at high doses stops methadone from building up to a dangerous level.

Stopping at first calculation step. Thirty milligrams is the correct oral morphine equivalent of the IV dose, and the textbook's worked example for the low-dose band is 30 mg of methadone. Someone who does the first step and then stops, or copies the example, picks this. That is three times the right methadone dose.

The textbook lists 10 mg IV morphine as equal to 30 mg oral morphine. For daily oral morphine under 100 mg, the oral morphine-to-methadone ratio is 3:1. The ratio curves upwards to 20:1 above 1,000 mg/day, so seek expert advice before converting.

Sources: Barash 9e

A basal rate delivers opioid whether or not the patient presses. Drowsy patients stop pressing, but the infusion keeps running. That removes the built-in safety of demand dosing. In opioid-naive adults it adds opioid and respiratory events, not better analgesia. Older age compounds the risk. Barash lists basal rate among settings available in every PCA mode. Miller's does not recommend it routinely in opioid-naive adults. It reserves it for opioid-tolerant or paediatric patients. So the pump offers it, but standard practice leaves it off.

Switching drug without removing background infusion. Pethidine is a poor PCA choice because its toxic metabolite accumulates. Switching drugs therefore looks like the fix. But the drowsiness comes from opioid given regardless of demand. A new drug on the same basal rate still sedates. Remove the background infusion first.

Barash counts basal rate as a variable in all PCA modes. Miller's advises against it routinely in opioid-naive adults. It only raises opioid use and respiratory events. Miller's also names it, with advanced age, as a respiratory depression risk.

Sources: Miller 10eBarash 9e

A PCA pump gives only what its settings allow: the bolus, the lockout and a cumulative limit per period. Her usage equals the standard limit, so the pump has stopped and pressing gives nothing; raising the limit restores access. Too small a bolus leaves pain, too large risks respiratory depression, so escalate once she is rousable and pressing more often than doses arrive. Faust lists a basal infusion, but Miller ties background infusions to respiratory depression, so in opioid-naive adults adjust bolus, lockout or limit first.

Lengthening lockout instead of shortening it. Lengthening the lockout sounds like a safe, cautious change, and it is a real PCA setting, just like the correct fix. But it lets fewer boluses through each hour, so a patient already in uncontrolled pain gets even less opioid. The lockout should be shortened, not lengthened.

Faust: frequent unanswered presses mean analgesic needs are not being met. The fixes are a shorter lockout, a larger demand dose, a basal infusion, or a combination. Miller: too small a demand dose causes inadequate analgesia, and a background infusion adds to respiratory-depression risk.

Sources: FaustMiller 10e

Children vary widely in how they handle morphine and how they respond to it, so no fixed dose reliably fits. Small intravenous increments, repeated until the child is comfortable, control pain quickly without overshooting into overdose. A maintenance regimen given alone builds an effective level too slowly. Loading boluses therefore come first, and maintenance analgesia starts only once pain is controlled. Pethidine now has almost no perioperative role apart from treating shivering, so it is not a first-line rescue analgesic.

Starting infusion without initial bolus first. It is the right drug and sounds controlled and safe. But a low-rate infusion with no loading dose takes a long time to reach an analgesic level. A child already in severe pain needs titrated IV boluses first. Any infusion or PCA is started only after that.

Paediatric texts give morphine as 50–100 mcg/kg intraoperatively and 50 mcg/kg per postoperative dose. Doses are titrated because individual response varies widely. Loading boluses are repeated until the patient is comfortable before maintenance starts. Pethidine is rarely used except for shivering.

Sources: Barash 9eMiller 10eFaust

Surgical pain has several mechanisms, so one drug class rarely controls it. Local anaesthetic at the site of pain, by wound infiltration, peripheral nerve block or neuraxial block, stops pain signals from that region; Miller rates this above systemic opioids. Stoelting's spine-surgery section names no regional technique. It favours low-dose ketamine to reduce opioid requirements and limit opioid-induced hyperalgesia, and warns that NSAIDs raise bleeding risk and may impair fusion. The plan safe under both sources is a site-specific technique where feasible, ketamine as an adjunct, and no NSAIDs.

Using systemic ketamine instead of regional. The spine-surgery text recommends low-dose ketamine, so it looks made for fusion surgery. But it is a systemic adjunct that lowers opioid needs. It does not give the targeted regional analgesia that the general text rates above systemic opioids, and that regional technique is the core of a multimodal plan.

Miller lists local anaesthetic techniques among multimodal strategies and says epidural and peripheral local anaesthetic analgesia is site-specific and better than systemic opioids. Stoelting, writing on spine surgery, suggests low-dose ketamine to reduce opioid use and cautions against NSAIDs at fusion sites.

Sources: Miller 10eStoelting 8e

Intrathecal morphine goes straight into the cerebrospinal fluid beside the spinal cord opioid receptors. An epidural dose must first cross the dura before it reaches those receptors, so the intrathecal route needs only a small fraction of the epidural dose. Morphine is water-soluble, so it stays in the cerebrospinal fluid and acts for a long time. A single spinal injection therefore covers the first postoperative day. This makes the dose band narrow: too little gives no benefit, and systemic-sized amounts would be dangerous.

Using slipped decimal in intrathecal morphine. It is tempting because intrathecal doses feel tiny, and lipophilic spinal opioids such as fentanyl are given in tens of micrograms. It fails because this is a slipped decimal. At a tenth of the recommended morphine range it gives inadequate analgesia after arthroplasty.

Intrathecal morphine at 0.1 to 0.3 mg gives the same effect as 1 to 5 mg given epidurally. By either route, analgesia lasts 12 to 24 hours. For inpatients having knee replacement, 100 μg intrathecally is the recommended dose.

Sources: Mayo reviewBarash 9e

Ketamine uncouples limbic from cortical processing. The patient neither registers the painful stimulus nor remembers it, and the airway can be left alone. That suits a brief, intensely painful bedside procedure. Titrated IV opioids handle the continuous pain of the acute phase. Pushing opioid boluses high enough to cover a dressing change risks respiratory depression, tolerance and hyperalgesia. So opioids stay as the background, and ketamine covers the procedure.

Using escalating opioid for burn dressing. Miller's names IV morphine among the potent opioids for acute burn pain, so it looks like the textbook answer. That advice is for the background analgesic. For the dressing change itself, Miller's picks ketamine, because escalating opioid doses carry respiratory depression and tolerance.

Miller's names titrated IV opioids such as morphine as the mainstay in the acute phase. For brief procedures such as dressing changes, ketamine is possibly the agent of choice, as the airway need not be manipulated. Escalating opioid doses cause respiratory depression and tolerance.

Sources: Miller 10e

NNT is the number of patients who must receive a drug for one of them to reach a set outcome. Here the outcome is at least half of their pain relieved. A lower figure means a more effective drug, so analgesics can be ranked on one scale. A perfect analgesic would work in everyone treated. Morphine works in about every third patient, which puts it level with oxycodone preparations and far ahead of oral codeine.

Overestimating morphine efficacy as gold standard. The first figure is tempting because morphine is seen as the gold-standard analgesic, so people expect near-perfect efficacy. The league table gives a higher value. A standard parenteral dose does not halve pain in most patients, which puts morphine level with oral oxycodone rather than well ahead of it.

Both sources give intramuscular morphine 10 mg an NNT of 2.9 (CI 2.6–3.6) for postoperative pain, defined as relief of moderate to severe pain by more than 50%. Oral codeine 60 mg scores 16.7; morphine's number needed to harm is 9.1.

Sources: Miller 10eBarash 9e

A transforaminal needle lies in the foramen beside segmental arteries supplying the cord. Particulate steroid entering one of these vessels can embolise to the brain or cord, or the artery can spasm. Dexamethasone is non-particulate, so it avoids this. Barash gives a consensus rule against particulate steroid here. A later registry report, also cited in Barash, found similar adverse events with both types, but included non-transforaminal injections, so the cervical rule stands. Interlaminar access is limited to the lowest interspaces; transforaminal injection is done at the symptomatic level.

Betamethasone particles safer than other steroids. Betamethasone has the smallest particles of the depot steroids, so it looks like a safer compromise. It is still particulate, and particulate steroid is excluded from cervical transforaminal injection. Only particle-free dexamethasone removes the embolic risk to the brain and cord.

Particulate steroid should not be used for cervical transforaminal injection, as injury may arise from particle embolisation to brain or cord, or segmental artery spasm; dexamethasone is often preferred. A 2021 report found equal adverse events with both types, but included non-transforaminal injections.

Sources: Barash 9eFaust

A secondary form, for example from a tumour, can cause the same brief electric attacks, set off by brushing teeth or shaving, as the classical form. Some features suggest a secondary cause: younger age, sensory loss in the face, or pain on both sides. These features are insensitive, though. A typical history and a normal examination therefore do not reassure you. Only imaging can tell the two apart, so a scan belongs in the early work-up for everyone.

Dental referral for typical trigeminal neuralgia triggers. Brushing-triggered pain suggests a dental cause, but brief electric shocks provoked by light touch are typical of trigeminal neuralgia, not tooth disease. The next step is imaging to look for a secondary cause, not dental referral.

European neurology guidance says to scan every patient with MRI to look for a secondary cause. No clinical profile reliably rules one out, and the absence of warning features does not either. If MRI is unavailable or contraindicated, consider contrast CT to look for tumours.

Sources: Outside our books: European Academy of Neurology guideline on trigeminal neuralgia (2019)

Corticosteroid placed in the epidural space inhibits phospholipase A2. This dampens local inflammation and also directly reduces nociception. Much refractory back pain comes from a nerve root inflamed by mechanical or chemical injury. Depositing the drug beside that root treats the inflamed site in a way that tablets cannot. The gain is therefore largest when a radicular component is present. Purely axial, non-specific back pain gains little, which explains why the UK guideline advises against injections for back pain on its own.

Surgery appropriate after tablets fail conservatively. Operating seems the natural escalation once tablets have failed. However, decompression is kept for symptoms that persist after every conservative option, including injection, or for a significant motor deficit. The less invasive epidural steroid comes before surgery.

Barash lets clinicians consider epidural steroid for spine pain that non-interventional care has not helped, and explains its action through phospholipase A2 inhibition. Stoelting adds that inflamed nerve-root pain may respond. NICE tells clinicians not to offer spinal injections for low back pain.

Sources: Barash 9eStoelting 8eOutside our books: Low back pain and sciatica in over 16s: assessment and management (2016)

In a diabetic, neuropathic pain points to diabetic painful neuropathy, whose management Barash heads with tight glucose control; it treats the chronic nerve ischaemia rather than giving quick relief. The offered drugs fail here. Miller says antipyretic analgesics are not indicated in neuropathic pain, though paracetamol stays first-line for ordinary back pain; duloxetine, which Barash finds effective for neuropathic back pain, is not offered. COX-2 inhibitors are avoided after stroke. Epidural steroid disturbs blood glucose control in diabetes, so it is ruled out.

Paracetamol first-line neuropathic pain treatment. Paracetamol is a familiar, safe first drug for ordinary back pain. It also avoids NSAID and COX-2 risks after a stroke, so 4 g/day looks sensible. But it is not a neuropathic-pain drug. Once the pain is called neuropathic in a diabetic, glucose control is the answer offered.

Barash puts tight glucose control first for painful diabetic neuropathy and finds duloxetine effective for neuropathic back pain. Miller: antipyretic analgesics are not indicated in neuropathic pain. COX-2 inhibitors are not advised after stroke. Glucocorticoids disturb glucose control in diabetes.

Sources: Barash 9eFaustMiller 10e

Patients with fibromyalgia have low levels of the main noradrenaline metabolite in their cerebrospinal fluid. This points to a central shortage of monoamines that regulate pain. Drugs that increase both serotonin and noradrenaline correct this shortage, which explains why SNRIs such as milnacipran and duloxetine help. Tricyclics and tramadol help for the same reason. Pregabalin works by a different mechanism and adds to the effect. Drug treatment works best as one part of a wider programme that also includes non-drug measures.

Ketamine effective for fibromyalgia central sensitisation. Ketamine is tempting because fibromyalgia involves central sensitisation, and NMDA antagonists are used for difficult pain. However, the sources do not list it as an effective fibromyalgia drug. It does not correct the serotonin and noradrenaline shortage that the recommended agents target.

The sources recommend combining drug and non-drug treatment. Effective drugs include the SNRIs milnacipran and duloxetine, pregabalin, gabapentin, amitriptyline and sodium oxybate. Milnacipran gives moderate pain relief. Pregabalin taken with duloxetine gives the best results.

Sources: Barash 9e

CRPS causes trophic changes as well as pain, so its drug list goes beyond ordinary analgesics. Calcitonin sits in the bone-pain adjuvant group with bisphosphonates, and both appear on the CRPS medication list; one text grades its evidence as weak but still names it. Given by injection, it remains a drug treatment, not a procedure. That suits a patient who improved after a sympathetic block but declines more procedures, when the alternatives are a plain NSAID, an opioid, or a spasticity drug with no oral CRPS evidence.

Oral baclofen for CRPS-related dystonia. Baclofen tempts because it sits on neuropathic adjuvant lists and CRPS can cause dystonia. Its only CRPS evidence is intrathecal baclofen for CRPS-related dystonia, an implanted pump this patient has declined. Oral baclofen is on no CRPS treatment list in the books, whereas calcitonin is.

CRPS is managed with sympathetic blocks, physiotherapy and medication: oral gabapentin, memantine and alendronate; calcitonin by intramuscular or subcutaneous injection. One book lists calcitonin among drugs with less conclusive evidence and notes some evidence for intrathecal baclofen in CRPS-related dystonia.

Sources: Barash 9eFaust

The stellate ganglion carries sympathetic outflow to the head, neck, upper limb and heart. Blocking it removes sympathetic drive to that area. This relieves pain that sympathetic activity keeps going, as in regional pain syndromes and acute zoster, and it releases vasoconstriction in the arm. A Horner syndrome on the same side shows the sympathetic chain has been blocked and the needle is in the right place.

Lumbar sympathetic block treats arm CRPS. Lumbar sympathetic block is tempting because it is also a sympathetic block used for regional pain syndromes. But it only reaches the lower limb. It cannot treat pain in the arm or zoster of the face. For those, you need the cervicothoracic chain, which is the stellate ganglion.

The pain indications listed are regional pain syndromes types I and II, zoster of the face and neck (including ophthalmic zoster), refractory angina and phantom limb pain. Vascular indications include Raynaud, vasospasm, scleroderma and frostbite. A Horner syndrome confirms the block is correctly placed.

Sources: FaustMiller 10e

Pain from abdominal and pelvic cancers is visceral. It travels with sympathetic fibres through the plexuses in front of the spine. Destroying the right plexus with alcohol or phenol cuts off this pain, so the patient needs less opioid and has fewer opioid side effects such as nausea and constipation. The pancreas and other upper abdominal organs send pain through the coeliac plexus. Pelvic organs send pain through the superior hypogastric plexus. The block also removes sympathetic tone, so expect hypotension, especially in volume-depleted patients.

Superior hypogastric block treats limb ischaemia. It is tempting because it is also a sympathetic block at a lumbar level. But it blocks the lumbar sympathetic chain that supplies the lower limb. It is used for limb ischaemia and circulatory problems, not for pain from pelvic organs.

Coeliac plexus neurolysis is the most effective option for visceral pain from pancreatic cancer, and hypotension is a known complication. Pelvic cancer pain is treated with superior hypogastric block. Neurolysis of the visceral sympathetic system relieves pain, reduces opioid use and improves quality of life.

Sources: Miller 10eStoelting 8eBarash 9e

Two questions, two answers. Approval: the first US device label covered chronic trunk and limb pain from failed back surgery and intractable back and leg pain; CRPS was added later, so Barash names both, and failed back surgery remains the commonest use. Benefit: stimulation suits peripheral neuropathic pain best, and CRPS is the classic responder, with a systematic review grading CRPS type I evidence at its top level. Radicular leg pain after back surgery has a randomised trial base at least as large, so this ranking is a teaching convention.

Radiculopathy as the best responder. Radiculopathy tempts because it is a common real-world use, and one textbook names lumbar radiculopathy alongside failed back surgery syndrome as the commonest indication. On the device label it appears only as a cause within back and leg pain, while CRPS, a peripheral neuropathic state, is the classic best responder.

Barash says US approval covers failed back surgery syndrome, intractable back and leg pain and CRPS. It calls failed back surgery the commonest indication and says stimulation suits peripheral neuropathic pain best. The original device label named failed back surgery and back and leg pain.

Sources: Barash 9eOutside our books: Summary of Safety and Effectiveness: PRECISION Spinal Cord Stimulator System (2004)

The leads go into the epidural space and are then steered sideways through the foramen onto the ganglion itself. This means stimulation reaches single dermatomes. It can cover small distal areas such as the foot, which conventional dorsal column stimulation covers poorly, and the paraesthesia hardly changes with posture. CRPS usually causes focal, distal limb pain, so this targeted approach suits it. The trial behind the approval compared DRG stimulation with conventional stimulation in CRPS patients only.

DRG stimulation effective for failed back surgery. Failed back surgery syndrome is the classic indication for spinal neuromodulation, and DRG leads also enter the epidural space. However, DRG approval rests on a CRPS trial and covers only CRPS lower-limb pain. Axial back and radicular pain belong to conventional or high-frequency spinal cord stimulation.

The FDA label covers moderate to severe chronic intractable lower-limb pain in adults with CRPS types I and II. In a randomised CRPS trial, DRG stimulation succeeded in 81.2% of patients versus 55.7% with traditional stimulation, with more accurate paraesthesia placement over the painful area.

Sources: Outside our books: Summary of Safety and Effectiveness Data: Axium Neurostimulator System (2016)Barash 9eFaust

A nerve depolarises more easily when the needle tip is the cathode. Stimulating through the cathode takes roughly half the current that anodal stimulation needs, so the correct polarity gives a clear motor twitch at lower current. Because current is concentrated at the uninsulated needle tip, it is the tip that matters. With a constant-current stimulator, where the surface electrode sits on the body makes no difference.

Cathodal placement reduces peripheral nerve stimulator doses. It is tempting because precise needle placement sounds as if it should let you use less drug. But the lead arrangement is about how well the current excites the nerve, not about volume. The sources link cathodal preference to better depolarisation, not to a dose reduction.

Making the needle the cathode, with the red pole as ground, gives better depolarisation; cathodal stimulation is about twice as effective as anodal. With constant-current devices, ground placement is irrelevant. Stimulating needles and catheters have increased continuous peripheral nerve block success rates.

Sources: Barash 9eMiller 10e

Transducer frequency trades sharpness against depth. Shorter wavelengths resolve fine detail along the beam, so nerves, fascial planes and the needle shaft stand out crisply. Tissue absorbs high-frequency energy quickly, so the signal weakens as it travels further in. When the target lies just beneath the skin, extra penetration adds nothing and resolution is what counts. Only deep targets justify longer wavelengths that reach them, at the cost of a blurrier picture.

Lower frequencies better for superficial ultrasound targets. Lower frequency sounds more powerful or wider-viewing, and it is correct for deep work such as neuraxial scanning. Close to the skin it only sacrifices resolution. The nerve and needle blur, and there is no depth gain to make up for it.

Higher frequencies suit structures near the surface and lower frequencies suit deeper ones. High frequency gives better axial resolution but fades rapidly with depth. That is why most peripheral blocks rely on high-frequency linear transducers when the nerves lie just under the skin.

Sources: Miller 10eFaust

The trunks cluster on the first rib lateral to the subclavian artery, with lung just below. Keeping the rib shadow over the pleura means a needle that goes too deep hits bone rather than lung. Local anaesthetic often spreads to the nearby phrenic nerve and takes effect as the block sets up, so early hypoxaemia is usually diaphragmatic. Pneumothorax is uncommon and usually delayed, but it can present during needling. Examine for it, and avoid this block when any respiratory compromise is intolerable.

Pneumothorax most common supraclavicular block complication. Pneumothorax is the complication people link most closely with this block, so desaturation seems to confirm it. But it is rare and usually shows up after surgery. Paralysis of the diaphragm from phrenic spread affects about half of patients and starts as the block takes effect.

Faust gives pneumothorax as 0.5% to 6%, usually presenting postoperatively, with phrenic block in 50%–60%. The Mayo review gives phrenic block as 30%-60% and warns that pneumothorax may cause cough, chest pain or breathlessness during needling, or be delayed up to 24 hours.

Sources: Barash 9eFaustMayo review

The motor branches to sartorius leave the femoral nerve just below the inguinal ligament, above and in front of the usual block point. So a sartorius response picks up a superficial, anterior twig rather than the main trunk. Local anaesthetic placed there can miss the fibres that supply the knee. The deeper quadriceps component lifts the patella. When that twitch appears and then vanishes once injection starts, the needle tip is beside the main nerve.

Superficial sartorius response indicates correct femoral placement. It sounds like a needle-position error, so it looks like a failure mechanism. In fact the deeper, posterior component that drives the quadriceps and lifts the patella is the endpoint you want. Stimulating it confirms correct placement. The block fails when you inject on the superficial, anterior sartorius response.

A sartorius twitch without patellar movement means the needle is too anterior and superficial, because sartorial branches leave the nerve before the block site. Advance deeper until a quadriceps response with patellar twitch appears at 0.5 mA; it should disappear once local anaesthetic goes in.

Sources: Mayo reviewBarash 9e

The probe sits on the anterior axillary fold, so the top of the screen is anterior (skin) and the bottom is posterior (deep). Around the artery, the nerves heading for the front of the arm lie anteriorly. These are the median nerve, anteromedial, and the musculocutaneous nerve, anterolateral. The radial nerve belongs to the posterior compartment, so it runs behind the artery and appears beneath it on the image. It lies just above the conjoint tendon of latissimus dorsi and teres major, which forms the deep floor of the bundle.

Ulnar nerve deep to axillary artery. In the anatomical description, the ulnar nerve is posterior as well as medial, so people read 'posterior' as 'below the artery'. On ultrasound, though, the ulnar nerve usually sits medial and superficial to the artery. The nerve that is truly deep to the artery is the radial.

The terminal nerves surround the artery: median anteromedial, ulnar posteromedial, musculocutaneous anterolateral, radial posterolateral. On ultrasound, median and ulnar nerves lie superficial to the artery, radial deep. The block is performed at the conjoint tendon, beneath the bundle.

Sources: Barash 9eMiller 10e

How easily a fibre is blocked depends on its size and myelination. Preganglionic sympathetic B fibres are small and only thinly myelinated, so they stop conducting at drug exposures that leave other fibres working. Among sensory fibres, the unmyelinated C fibres that carry cold sensation fail early. Sensory nerves as a group are in the middle. Heavily myelinated motor fibres hold out longest. So the usual order of loss is autonomic, then sensory, then motor.

Temperature sensation blocked before autonomic fibres. Temperature is tempting because Barash's classic sequence starts with loss of temperature sensation, and cold-carrying C fibres are the earliest sensory fibres to go. That list only covers sensory and motor modalities and leaves out autonomic fibres. When sympathetic or autonomic is offered, it comes before temperature.

Miller: preganglionic sympathetic B fibres are the most sensitive, and cold-carrying C fibres go early among sensory fibres. Faust: autonomic loss comes before sensory, then motor. Barash's pharmacology sequence starts with temperature, then proprioception, motor, sharp pain and light touch, but leaves out autonomic fibres.

Sources: Miller 10eFaustBarash 9e

Local anaesthetic blocks thin fibres before thick ones. Cold travels in small unmyelinated C fibres, which are blocked earliest. Pinprick uses thin myelinated A-delta fibres and is lost next. Touch uses the larger A-beta fibres, which are the last sensory fibres to fail. So ice, alcohol or ethyl chloride shows a working block and its spread soonest. Pinch or touch catches up later and will underestimate a block that is still developing.

Pinch best early indicator of block level. Pinch feels right because Barash lists pinprick and pinch as recognised block-monitoring tools. They do work, but touch uses the largest sensory fibres, which block last. Pinch therefore lags cold and underestimates early spread, so it is not the best early test.

Miller says cold sensation is usually lost first, tested with ethyl chloride, ice or alcohol. Pinprick follows, tested with a non-skin-breaking needle. Touch fibres are affected last. Barash lists both cold and touch (pinprick, pinch) as traditional monitoring tools.

Sources: Miller 10eBarash 9e

The modified Bromage scale grades lumbosacral motor block by how many leg movements are lost as the block deepens. The straight-leg raise is lost first, which is grade 1. Losing knee movement as well makes it grade 2, when only the feet can move. Grade 3 means no movement of the limb at all. Grade 0 means no motor block. To score, ask which movements are still possible, then pick the lowest grade that fits.

Inability to raise leg indicates grade 2 blockade. People often think that being unable to lift the leg means a dense block and choose a higher grade. Grade 2 also needs loss of knee movement. Here the knee still moves, so the block is only grade 1.

The modified Bromage scale is the usual way to measure motor block, though it covers only lumbosacral fibres. Its grades run from 0, no block, up to 3, complete block. Losing only the straight-leg raise is grade 1. Losing knee movement too is grade 2.

Sources: Miller 10e

A true post-dural puncture headache comes from cerebrospinal fluid leaking through the dural hole. When the patient is upright, intracranial fluid volume falls and the brain sags, stretching pain-sensitive meninges. The pain therefore gets worse on sitting and eases on lying flat. A headache that posture does not change lacks this sign. If it also copies her familiar one-sided migraine with photophobia, her usual headache disorder is the likely cause. That responds to serotonin 5-HT1B/1D agonists, which act on neurovascular headache pathways.

Non-positional post-dural headache needs blood patch. A blood patch is tempting because the headache followed a dural puncture, and a patch is the definitive treatment for post-dural puncture headache. But that headache is postural. A non-positional headache identical to her usual migraine is not caused by a fluid leak, so a patch treats the wrong diagnosis.

Textbooks describe post-dural puncture headache as worse on standing and relieved lying flat. They list migraine among its differential diagnoses and advise excluding benign headaches such as migraine before treating a leak. Triptans are described as effective for migraine.

Sources: Barash 9eMiller 10e

The spinal needle leaves a hole in the dura, and cerebrospinal fluid leaks out through it. The more fluid is lost, the more likely and the worse the headache. That is why larger needles, cutting tips and repeated punctures raise the risk. The headache typically sits at the front or back of the head. It gets worse when the patient sits or stands and eases when they lie flat. Younger adults and women are affected more often, so a young woman is a typical patient.

Caffeine withdrawal causes postural post-spinal headache. Caffeine withdrawal is a real cause of headache after surgery in a fasted patient, so it sounds plausible. But it has nothing to do with the dural puncture. The spinal, the timing in the first few days and the patient's profile all point to a dural leak instead.

Post-dural puncture headache is frontal or occipital, worse upright and relieved by lying flat. Over 90% of cases begin within 3 days of puncture. It is commoner in younger adults and women, and is caused by cerebrospinal fluid leaking through the dural hole.

Sources: Miller 10eMayo review

The dural hole lets CSF escape, so cranial CSF pressure falls. The ear's fluid compartment communicates with cranial CSF through the cochlear aqueduct, so the pressure drop passes straight into it and disturbs hearing, typically as transient low-frequency loss. The leak is the upstream trigger. The direct cause of the deafness is the fall in fluid pressure within the ear. Larger needles leave bigger holes and leak more, so the risk is lower with finer-gauge spinal needles.

Cranial nerve lesion causes post-dural hearing loss. Cranial nerve involvement, such as diplopia, is a recognised consequence of low CSF pressure after dural puncture, so a nerve lesion seems a natural explanation. However, muffled hearing with post-dural puncture headache is attributed to pressure loss through the cochlear aqueduct, not to nerve damage.

One text attributes hearing loss after subarachnoid block to lowered CSF pressure acting on inner ear function, with less risk from finer needles. Another says muffled hearing reflects a pressure fall transmitted from cranial CSF through the cochlear aqueduct, not cranial nerve involvement.

Sources: Barash 9eMiller 10e

The lateral femoral cutaneous nerve has no motor fibres, so injury to it affects sensation only. Patients get burning pain, dysaesthesia or numbness over the lateral thigh, and power is normal. The nerve runs under the inguinal ligament close to the anterior superior iliac spine. Prolonged hip flexion, such as long pushing in labour, stretches the ligament, which can compress the nerve or starve it of blood. Cases after childbirth come from positioning, not from the epidural. A femoral nerve lesion is different: it weakens knee extension.

Femoral neuropathy causes only sensory lateral thigh. Femoral neuropathy is tempting because it is as common after childbirth and has the same hip-flexion cause. But the femoral nerve also supplies the knee extensors, so injury to it causes weakness. Lateral thigh sensory loss with normal power rules it out.

The lateral femoral cutaneous nerve is purely sensory and can be trapped under the inguinal ligament near the anterior superior iliac spine, giving burning lateral thigh pain and sensory loss without motor deficit. Postpartum, it and femoral neuropathy are commonest, attributed to extreme hip flexion.

Sources: Stoelting 8eFaustMiller 10e

The sciatic nerve gives rise to the common peroneal nerve. It runs close to the surface around the head of the fibula, so it lies against bone with little protection. A leg-brace frame can press it there, and correcting a marked valgus knee can stretch it. This nerve supplies the muscles that lift the ankle, evert the foot and extend the toes. When it is damaged, the patient cannot dorsiflex and the foot drops.

Tibial nerve blocks cause foot drop. The tibial nerve is the other major division of the sciatic nerve and runs behind the knee, so it looks like a natural suspect after knee surgery. It does not control dorsiflexion, though. A block of the tibial nerve alone gives knee analgesia without foot drop.

Leg-support frames compress the common peroneal nerve against the fibular head. Palsy is a known complication of large valgus knee corrections, causing foot drop with loss of dorsiflexion, eversion and toe extension. A selective tibial block avoids foot drop.

Sources: Mayo reviewMiller 10eBarash 9e

The median nerve enters the hand beneath the transverse carpal ligament. There it can be squeezed against the carpal bones, causing a compression neuropathy. It supplies sensation to the palmar side of the lateral three and a half digits, so the pain and paraesthesia follow the thumb, index finger and middle finger. Its motor fibres supply the short thenar muscles, namely abductor and flexor pollicis brevis and opponens. Chronic compression therefore wastes the thenar eminence and weakens thumb opposition.

Ulnar nerve causes thenar wasting thumb pain. The ulnar nerve is the other nerve classically linked with wasting of the small hand muscles, so people pick it by reflex. Its territory is the little-finger side of the hand, though. It does not explain thenar wasting with symptoms affecting the thumb, index finger and middle finger.

Compression under the transverse carpal ligament produces recurrent wrist and hand pain and paraesthesia over the index and middle fingers and thumb. The same nerve innervates the short thenar muscles that abduct, flex and oppose the thumb.

Sources: Stoelting 8eMayo review

Injury and inflammation sensitise nociceptors inside damaged tissue, so a stimulus there that already stings a little causes more pain than expected: primary hyperalgesia. Around the wound, harmless stimuli begin to hurt: secondary hyperalgesia or allodynia. Allodynia means pain from something never painful, such as light touch or clothing. Dysaesthesia is an unpleasant abnormal sensation, such as pins-and-needles after nerve injury, not provoked pain. For mild heat on a burn, Faust counts it as an injury-site stimulus, so primary hyperalgesia; Barash and IASP count warmth as painless, so allodynia.

Allodynia for mild heat on a burn. Mild heat seems harmless, so allodynia tempts, and it is a defensible reading: Barash's sunburn-shower example and the IASP definition treat warmth as painless. Faust, however, classes a mildly aversive stimulus at the injury site as primary hyperalgesia, the intended answer when the cue stresses the injured area.

At an injury, a mildly aversive stimulus feels more intense, primary hyperalgesia, because peripheral nociceptors are sensitised; nearby, harmless stimuli turn aversive. After sunburn, warm water or a towel's touch may hurt. Allodynia is pain from a normally painless stimulus; dysaesthesia, an unpleasant abnormal sensation.

Sources: FaustBarash 9eMayo review

With repeated exposure the patient responds less to the opioid, so a fixed dose gives less relief. Raising the dose makes up for this and brings back analgesia. Dependence is a separate adaptation that only shows as withdrawal when the drug is stopped, cut quickly or reversed with an antagonist. Addiction is compulsive use despite harm. Hyperalgesia means the patient has become more sensitive to pain itself, not less responsive to the drug.

Opioid-induced hyperalgesia shows simple dose escalation. Hyperalgesia tempts because opioid-induced hyperalgesia also pushes chronic users towards higher doses. But it means pain sensitivity has increased, so giving more opioid does not cleanly solve it. When a bigger dose simply abolishes the pain, the cause is reduced response to the drug, which is tolerance.

Tolerance is a weaker effect from an unchanged dose, or a need for bigger doses for the same effect, as the patient responds less to the opioid. Dependence shows as withdrawal, addiction is compulsive use despite harm, and hyperalgesia is increased pain sensitivity.

Sources: Miller 10eFaust

Fibromyalgia is diagnosed clinically. The doctor scores how widely the pain is spread across the body and how severe the symptoms are. Scans and blood tests play no part in the diagnosis. The diagnosis also requires that no other condition explains the symptoms. So a normal MRI and normal tests do not argue against it; they are part of making it. Once the diagnosis is made, the patient needs structured treatment across several disciplines. It is not a label that justifies a psychiatric referral or dismissing the patient.

Localised myofascial trigger points cause widespread pain. Muscle tenderness to finger pressure sounds like a myofascial problem, so this option looks attractive. It fails because the pain here is spread across the whole body, well beyond any single muscle region. Widespread pain with no other disorder to explain it matches the fibromyalgia criteria.

The diagnosis is made from a widespread pain index and a symptom severity score. Symptoms must be present for at least 3 months, with no other disorder that explains them. An expert panel recommends combined care: education, exercise, cognitive behavioural therapy and drugs.

Sources: Stoelting 8e

The Budapest criteria define CRPS by a cluster of features rather than a single finding. The pain must be out of proportion to the original trauma. The patient must report at least 1 symptom in 3 of the 4 domains (sensory, vasomotor, sudomotor/oedema, motor/trophic), and the clinician must see 1 sign in 2 or more domains. Type I follows injury without nerve damage; type II follows injury to a named nerve. No test confirms CRPS, so any diagnosis that better explains the picture must be ruled out first.

Plexopathy causes disproportionate pain with autonomic changes. Plexopathy is tempting because the limb was injured and a nerve lesion can cause pain and weakness. But it does not account for the swelling and autonomic change. Disproportionate pain, oedema and poor function after a limb injury make up the CRPS pattern.

The diagnosis needs ongoing pain that is out of proportion to the inciting event, plus features across the sensory, vasomotor, sudomotor/oedema and motor/trophic groups. Oedema and reduced range of motion are named explicitly. No other diagnosis should explain the picture better. The diagnosis is clinical.

Sources: FaustStoelting 8e

The pain follows the sensory map of the trigeminal nerve. It stays within one or more of its divisions, most often the mandibular, and affects one side only. Attacks are short, stabbing bursts, not constant aching. Because this is neuropathic pain, harmless touch can cause pain (allodynia). Everyday touching of the face on the affected side, such as washing, brushing teeth or shaving, can therefore set off an attack. Short attacks, a set nerve territory and a touch trigger together point to this diagnosis.

Post-herpetic neuralgia causes brief electric pain. It is tempting because it is also a facial neuralgia. But post-herpetic pain is usually a steady burning pain following a shingles rash, not separate electric shocks lasting seconds and triggered by touch, and the history mentions no rash.

Tic douloureux causes short, severe, stabbing, paroxysmal, electric facial pain on one side, confined to trigeminal divisions and most often mandibular. Attacks start spontaneously or are triggered by sensory stimulation of the affected side. It is neuropathic pain with allodynia.

Sources: Stoelting 8eBarash 9e

After primary varicella (chickenpox), the virus is not cleared. It stays dormant in the dorsal root ganglion of a sensory nerve for many years. Later, often as immunity changes with age, it reactivates and travels outward along that one sensory nerve to the skin. The vesicles and the pain are therefore confined to that nerve's dermatome, for example a band across the chest wall or breast from a thoracic root. The pain is neuropathic because the nerve itself is inflamed.

Not recognising dormant zoster reactivation mechanism. It sounds right because the rash is acute and zoster-related, but it is not a recognised diagnosis and misses the mechanism. The condition is reactivation of dormant virus. Complex regional pain syndrome is also wrong: it causes regional pain without a vesicular rash in one dermatome.

Latent varicella–zoster virus, dormant in the dorsal root ganglion after primary infection, reactivates, most often after the sixth decade. It travels along the sensory fibre to the skin, causing a very painful dermatomal eruption.

Sources: Barash 9eFaust

The medial branch nerves carry pain from the facet joints. Numbing them for a short time with local anaesthetic works as a test: if the patient's usual pain goes away, the facet joints are the likely source. Leaning back (extension) and standing load the facet joints, which is why these movements bring on the pain. History and examination alone cannot confirm the diagnosis. A positive block also picks out patients who are likely to benefit from radiofrequency ablation of the same nerves.

Medial branch nerve block localises spinal root. It sounds right because a medial branch block is a nerve block, so a nerve problem seems likely. But the medial branch serves the facet joint, not the spinal nerve root. Root irritation causes pain that spreads down the leg, not axial pain brought on by extension.

Facet syndrome is diagnosed by combining the history, the examination and a positive response to diagnostic medial branch blocks or facet joint injections. Guidelines prefer medial branch blocks over intra-articular injections for selecting patients for radiofrequency ablation. Intra-articular injections fail more often.

Sources: Barash 9e

Both types produce the same picture of burning pain with sensory, motor, autonomic and trophic change. Wasting, skin changes and hair changes therefore occur in either type and cannot tell them apart. The classification rests only on cause. Type I, formerly reflex sympathetic dystrophy, follows tissue trauma with no nerve lesion. Type II, causalgia, is defined by an earlier injury to a specific nerve or one of its major branches.

Surgical trauma distinguishes CRPS type 1 type 2. Surgery is a well-known trigger for CRPS, so it looks like a plausible way to separate the types. It fails because operations, fractures and other trauma can start either type. What defines type II is damage to a nerve, not whether the injury was surgical.

Type II CRPS (formerly causalgia) has the same sensory, motor, autonomic and trophic features as type I (formerly reflex sympathetic dystrophy), differing only by a preceding nerve injury. Previous surgery is a risk factor for CRPS generally.

Sources: Barash 9eMayo review

Local anaesthetic that enters an epidural vein, or a dose too large for body weight, reaches the circulation directly. The brain is usually affected first. Blocking inhibitory pathways unmasks excitation, so tinnitus, dizziness, restlessness and agitation appear, and cardiovascular collapse can follow. The classic sequence is inconsistent, so cardiovascular signs may dominate. In children, Barash's rule of thumb is 2 mg/kg per bupivacaine bolus; it also gives a caudal or epidural ceiling of 4 mg/kg in older children, 2 mg/kg in infants, that other texts do not give.

Intrathecal spread causes tinnitus and agitation. Fast hypotension and bradycardia after an epidural dose suggest intrathecal spread with block of the cardiac accelerator fibres. But a total spinal reaches the brainstem and causes apnoea and unconsciousness. It does not cause tinnitus or agitation. Excitation of the brain points to drug in the bloodstream.

Epidurals cause systemic toxicity mainly through accidental intravenous injection. Early features are tinnitus, dizziness and agitation; seizures and circulatory collapse occur in only some patients. Barash: bolus rule of thumb 2 mg/kg; caudal or epidural ceiling 4 mg/kg in older children, 2 mg/kg in infants.

Sources: Miller 10eFaustBarash 9e

Local anaesthetic effects on the brain rise with plasma concentration. Barash puts tongue and circumoral numbness, with a metallic taste, at the lowest toxic levels. Restlessness, vertigo, tinnitus and trouble focusing come only as levels climb, and twitching and seizures come after that. Faust lists tinnitus and perioral numbness together as initial signs without ranking them. Mayo starts with light-headedness, dizziness and tongue numbness. Miller warns that only 60% of patients follow the classic minor-to-major sequence, so treat any minor symptom as a warning that levels are rising.

Tinnitus earliest sign local anaesthetic toxicity. Tinnitus is the best-remembered symptom of toxicity, and Faust names it first in a list of initial signs that is not in order. Barash places it at higher plasma levels than circumoral numbness, so the numbness comes first.

Barash: tongue and circumoral numbness with a metallic taste at low levels, tinnitus as levels rise. Mayo: light-headedness, dizziness and tongue numbness first. Faust: tinnitus and perioral numbness both initial signs, not ranked. Miller: only 60% follow the classic sequence.

Sources: Barash 9eFaustMiller 10eMayo review

Uncontrolled convulsions sharply raise metabolic demand. The resulting metabolic acidosis makes resuscitation harder, so seizures must be stopped quickly. Benzodiazepines are the preferred terminating agents. Large doses of propofol should be avoided, particularly when the circulation is unstable, because they can worsen the cardiovascular compromise. If seizures prove intractable, a small dose of suxamethonium stops the muscle activity, which limits acidosis and hypoxaemia while oxygenation and lipid therapy continue.

Phenytoin first-line LAST seizure management. Phenytoin feels like the 'proper' anticonvulsant because it is familiar from status epilepticus protocols. In general seizure pathways, however, it is a second-line drug given after a benzodiazepine. The LAST checklist names benzodiazepines, not phenytoin, for seizure control.

The ASRA checklist prefers benzodiazepines for seizure control and cautions against large propofol doses in unstable patients. It suggests intravenous midazolam 1 to 5 mg, and considers small-dose suxamethonium when seizures are intractable.

Sources: Mayo reviewBarash 9e

The bolus is dosed by weight at 1.5 mL/kg of ideal body weight. At about 70 kg that works out to roughly 100 mL, so heavier adults get a fixed 100 mL cap rather than a larger weight-scaled dose. Only the 20% emulsion is the rescue product. The 10% lipid that carries propofol cannot replace it. The larger volumes belong to the infusion that follows the bolus, not to the first push.

10% lipid emulsion 150ml bolus LAST treatment. It looks right because the volume is close to the follow-on infusion and 10% lipid is familiar from propofol. It is wrong on both counts: rescue needs 20% emulsion, and the first bolus stops at 100 mL. The bigger volume is the infusion given afterwards.

Use 20% lipid, not propofol's 10%: give a rapid bolus of 1.5 mL/kg ideal body weight (maximum 100 mL in adults) over 2-3 min. Then infuse, for example, about 250 mL over 15-20 min above 70 kg.

Sources: FaustMiller 10eOutside our books: ASRA Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version (2020)Barash 9e

In LAST the heart is already poisoned and prone to arrhythmia. A full resuscitation dose of adrenaline can turn it into a malignant rhythm, so give it in small titrated boluses. Vasopressin, calcium blockade and beta blockade have been linked to worse haemodynamics. Lidocaine is itself a local anaesthetic that blocks sodium channels, so it adds to the toxicity. That leaves amiodarone as the antiarrhythmic of choice. Seizures are a separate branch: stop them with a benzodiazepine, and use propofol only in small doses when nothing else is available.

Ephedrine corrects LAST myocardial depression. Barash's textbook says ephedrine or adrenaline can correct mild myocardial depression, so ephedrine feels safe. The ASRA LAST checklist names only small-dose adrenaline for LAST arrhythmia or hypotension. Adrenaline is correct under both sources, so choose it.

The ASRA checklist and a major textbook agree: start adrenaline below 1 mcg/kg, as larger boluses risk malignant arrhythmias. Avoid vasopressin, calcium-channel blockers, beta-blockers and further local anaesthetic. Treat ventricular arrhythmias with amiodarone. Prefer a benzodiazepine for seizures; use propofol only in low doses.

Sources: Outside our books: ASRA Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version (2020)Barash 9e

How long you observe depends on the most severe system that was involved, not on how quickly the patient recovered. If toxicity stayed in the CNS, for example a seizure, the shorter period applies. Once the heart is involved, the longer period applies even when there were also neurological features. That includes ECG changes such as QRS widening, arrhythmia or haemodynamic instability. The sources give that period as a range. When a question asks for the minimum, answer with the lower end of the range, not the upper end.

Seizure resolution requires only 2-hour monitoring. The patient had neurological symptoms and recovered fully with lipid and no arrest, so the seizure period seems to fit. But QRS change is a cardiovascular sign. That moves the patient into the longer period, and its minimum is 4 hours, not 2.

Both the review text and the ASRA checklist set the observation period by severity. It is at least 2 hours when toxicity stayed limited to a seizure or other CNS event. It rises to at least 4 to 6 hours once cardiovascular instability has occurred.

Sources: Mayo reviewOutside our books: ASRA Pain Medicine Local Anesthetic Systemic Toxicity checklist: 2020 version (2020)

Respiratory depression after neuraxial opioid mainly follows higher dose, older age, sleep apnoea and added systemic opioids or sedatives. Hyperbaric solution sinks with gravity, so a head-down spine carries block and drug toward the brainstem. Miller finds tilt alone does not always spread hyperbaric bupivacaine, but tilt with hips flexed flattens the lordosis and does; Barash treats obesity's built-in tilt as a high-block risk. Avoiding tilt suits both. Injection rate has no consistent effect on block height, so head-down tilt is the position to avoid.

Rapid injection spreads hyperbaric spinal block. Fast injection feels like it should drive drug further up the theca, so it tempts. But injection rate has not consistently changed block height, and a slower push may even spread more; gravity acting on a hyperbaric solution in head-down tilt is what moves drug cephalad.

Miller: head-down tilt alone does not always widen hyperbaric spread, but combined with hip flexion it does; injection rate has no consistent effect. Barash: obesity creates a head-down effect, so a chest ramp prevents high block. Miller's opioid risk factors: dose, age, sedatives, sleep apnoea.

Sources: Miller 10eBarash 9e

How high a block rises depends on factors that push local anaesthetic cephalad. Two of them are giving a spinal after a failed epidural and the size of the intrathecal dose. That means a standard dose can climb much higher than intended. An epidural top-up that reaches the subarachnoid space through an unrecognised puncture or a migrated catheter does the same. Extensive sympathetic block causes hypotension and bradycardia. Spread to thoracic and cervical roots causes dyspnoea and difficulty speaking.

Systemic toxicity from intrathecal epidural top-up. Toxicity is tempting because a large epidural dose has just been given. But systemic toxicity comes from drug entering a vein, not from a small intrathecal dose. The real danger is intrathecal drug spreading far higher than planned, causing hypotension and difficulty breathing.

Miller lists spinal after failed epidural, and dose given, as factors raising block height. Barash describes intrathecal epidural drug causing rapid block ascent, dyspnoea, hypotension and bradycardia. Faust reserves general anaesthesia for contraindicated neuraxial block or emergency delivery.

Sources: Miller 10eBarash 9eFaust

Infants have little resting sympathetic tone, so the sympathectomy from a neuraxial block barely lowers their blood pressure or heart rate. As the block rises it paralyses the intercostals, then the diaphragm through the C3–5 roots, and finally the brainstem respiratory centres. Breathing therefore fails and the child desaturates. When a caudal (epidural) dose enters the subarachnoid space, the spinal block develops fast. In older children, sympathetic and cardiac accelerator blockade can then add bradycardia and hypotension to the respiratory arrest.

Hypotension earliest sign spinal blockade infants. In adults, hypotension is the classic early sign of a high spinal because sympathectomy unmasks vasodilatation. Infants lack that resting sympathetic tone, so their pressure holds while the rising block stops breathing. Apnoea and desaturation come first.

Paediatric texts state that total spinal in infants, whether from a deliberate spinal or a misplaced epidural, shows up as apnoea rather than hypotension because sympathetic tone is low. Bradycardia and hypotension are uncommon. An epidural dose given intrathecally produces a rapid spinal block.

Sources: Barash 9eMayo reviewMiller 10e

The optic nerve sheath gives a direct path from the orbital cone to the cerebrospinal fluid. Local anaesthetic can reach the subdural or subarachnoid space in two ways: the needle tip injects into the sheath, or the drug tracks backwards along it. There it progressively anaesthetises the brainstem. This depresses consciousness and breathing and can paralyse cranial nerves, including those of the unblocked eye. It starts within seconds to minutes. Because the orbital dose is small, blood levels stay low, so systemic toxicity cannot explain the picture.

Systemic toxicity causes brainstem retrobulbar apnoea. It is tempting because systemic local anaesthetic toxicity can also depress the brain and cause apnoea. But the orbital dose is too small to have systemic effects, even if all of it enters a vein. Injection into an artery causes excitation and seizures, not quiet obtundation.

Local anaesthetic reaches the subdural or subarachnoid space in two ways: injected into the optic nerve sheath, or tracking backwards along it. This causes progressive brainstem anaesthesia, with unconsciousness and apnoea within minutes. The small orbital dose makes systemic effects unlikely even if given intravenously.

Sources: Miller 10eBarash 9eFaust

In the sitting position blood pools in the veins, so venous return falls. Sympathectomy with hypovolaemia after a spinal has the same effect. The result is a small ventricle that keeps contracting forcefully around very little blood. This paradoxically activates mechanoreceptors inside the heart. The reflex then abruptly withdraws sympathetic drive and increases vagal output. So the heart slows and the vessels dilate together, instead of the expected compensatory tachycardia. The result is profound hypotension and bradycardia, which can progress to collapse.

Bainbridge reflex causes hypotension and bradycardia. Bainbridge is the other well-known reflex set off by how full the heart is, so it sounds right. But it speeds the heart when atrial filling increases. Here venous return has fallen and the heart slows, which fits a vagal inhibitory reflex from an underfilled ventricle.

Textbooks report severe hypotension and bradycardia in awake, sitting shoulder patients under interscalene block. They put this down to reduced venous return stimulating mechanoreceptors inside the heart. The same reflex is proposed for profound bradycardia and collapse after spinal anaesthesia, especially with hypovolaemia.

Sources: Miller 10e

Clonidine stimulates alpha-2 receptors on both sides of the synapse in the spinal dorsal horn, which lengthens the block and adds analgesia. Alpha-2 agonists given centrally also sedate and depress the circulation. Barash reports more hypotension, bradycardia and nausea after 150 mcg. Miller cites a systematic review that found the hypotension was not linked to dose and that bradycardia was no more common. Taken together: sedation reliably produces hypotension, while bradycardia may occur but is not certain.

Assumes opioid side effect profile. Opioids are the most familiar spinal adjunct, so people reach for them. Their typical side effects are pruritus, nausea and respiratory depression, not a drop in blood pressure. Clonidine causes neither pruritus nor respiratory depression. Its hypotension and sedation come from alpha-2 agonism.

Neuraxial clonidine acts on dorsal horn alpha-2 receptors, causing analgesia, sedation, and reduced blood pressure and heart rate. Barash reports more hypotension, bradycardia and nausea at 150 mcg. Miller's systematic review found hypotension not dose-related and no increase in bradycardia.

Sources: Miller 10eBarash 9e

A spinal block removes sympathetic tone. Veins and arterioles dilate, and a high block can also slow the heart. Ephedrine acts on both alpha and beta receptors, so it restores vascular tone and supports heart rate and output. That fixes more of the problem than a pure vasoconstrictor does. In pregnancy the priority is the fetus. Phenylephrine reaches the fetus less and causes less fetal acidosis, so it has replaced ephedrine there. If severe hypotension and severe bradycardia occur together, the patient is heading towards arrest and needs adrenaline early.

Assumes strongest vasopressor works best. Noradrenaline feels like the strongest vasopressor, so it seems the safe pick for any fall in blood pressure. The neuraxial texts instead recommend ephedrine or small phenylephrine boluses for the usual mild to moderate fall, and adrenaline for a crisis. They never recommend noradrenaline for this.

Ephedrine, a mixed agonist, is more suitable than a pure alpha agonist for the circulatory effects of neuraxial block. Mild to moderate falls respond to ephedrine or phenylephrine. Severe hypotension with bradycardia needs adrenaline promptly. In pregnancy, phenylephrine causes less fetal transfer and less acidosis.

Sources: Miller 10e

The sympathetic fibres that supply the eye run down the cord just beneath the pia, close to the surface. Local anaesthetic can reach them even when the sensory level stays well below the neck. Losing sympathetic tone to the eye gives a small pupil, a drooping lid and no sweating on that side. This comes from the spread of the block. It is not nerve injury, compression or toxicity, so it needs no intervention.

Removes catheter for benign sympathetic effect. Removing the catheter seems safe for a new neurological sign, but these eye signs are a harmless sympathetic effect of the block. Removal only loses labour or caesarean analgesia. Reserve urgent investigation for red flags, such as back pain with unexpected paralysis, which suggest a haematoma.

The review calls eye sympathetic blockade after a lumbar epidural harmless. It is seen occasionally even when the dermatome level is modest, probably because the descending sympathetic fibres lie superficially under the pia. A haematoma work-up is kept for back pain with unexpected paralysis.

Sources: Mayo review

Intrathecal morphine goes straight to opioid receptors in the dorsal horn. There it weakens the inhibitory control that normally holds back itch-transmitting neurones. So itch is released at the spinal level, not triggered in the skin. Parenteral morphine is different: it causes itch by releasing histamine from mast cells. The opioid can also spread upwards to medullary sites, which may add facial itch. Opioid antagonists and mixed agonist-antagonists relieve the itch. The substantia gelatinosa is the superficial dorsal horn, so an answer naming that site fits.

Confuses inhibition with disinhibition mechanism. It is tempting because spinal inhibition and the word disinhibition bring GABA to mind. But the itch comes from losing inhibitory tone, the opposite of boosting it. Strengthening GABA inhibition would damp itch signalling, not cause it. The drug acting here is an opioid on opioid receptors.

Neuraxial opioid itch comes from neuronal disinhibition in the spinal dorsal horn. Parenteral morphine instead releases histamine. Peripheral histamine is not the cause. Proposed central contributors include a medullary itch centre and blocking of inhibitory transmitters. Naloxone, naltrexone, nalbuphine and droperidol appear to work.

Sources: Miller 10eFaust

The bladder depends on the sacral roots S2 to S4. Local anaesthetic reaching these roots weakens the detrusor, so the bladder cannot empty. Intrathecal opioid lowers detrusor contraction further and dulls the feeling of needing to void. The bladder can fill without the patient noticing until discomfort shows as anxiety or agitation. Normal voiding comes back on its own only when the sensory block falls below S2–3.

Mistakes retention for abscess development. It is tempting because of the neuraxial puncture and the back pain. But an abscess does not explain a full lower abdomen straight after surgery in recovery. The patient also has no fever and normal vital signs. The bladder finding points to retention.

Retention happens in up to one-third of patients after a neuraxial block. Blocking the sacral roots weakens the detrusor. Neuraxial opioids reduce its contraction and the urge to void. Bladder function returns once the sensory level falls below S2–3.

Sources: Miller 10e

Herpes simplex stays latent in sensory ganglia and is held in check by the host immune response. Morphine suppresses immunity. It blunts antibody production, alters immune-cell activation and changes cytokine output. With that control weakened, the latent virus can reactivate and oral lesions recur. Epidural morphine is widely used for pain relief after caesarean section, so this is where the association shows up in practice. Local anaesthetics carry no such link.

Assumes effect applies to all opioids. Fentanyl is also a neuraxial opioid given in labour, so someone may assume any opioid will do. The documented association, and the immunosuppressive mechanism described, are specific to morphine. The sources do not implicate fentanyl.

Morphine's immunosuppressive effects have been shown to reactivate latent herpes simplex. Epidural morphine given for analgesia after caesarean section is significantly associated with oral herpes reactivation in obstetric patients. Herpes simplex recrudescence is listed as an adverse effect of neuraxial analgesia.

Sources: Outside our books: Opioids and viral infections: a double-edged sword (2016)Outside our books: Effects of systemic and neuraxial morphine on the immune system (2019)Faust

Blood from the needle or catheter collects quickly inside the rigid vertebral canal. The expanding mass causes intense, localised back pain early, often within hours. An abscess needs time for infection to develop. Its back pain builds over days, radicular pain follows about 3 days later, and fever is common. Both are space-occupying lesions that can go on to compress the cord, so early imaging decides the diagnosis and the timing of decompression.

Attributes acute pain to abscess. An abscess is the other feared space-occupying lesion after neuraxial block, and it also causes severe back pain. But it develops over days, usually with fever and later radicular pain. Severe pain only hours after the block, without fever, points to bleeding instead.

Severe back pain is the hallmark of epidural haematoma. With abscess, radicular pain appears about 3 days after back pain begins, and fever is common but rare with haematoma. This suggests a space-occupying lesion needing urgent MRI. Transient neurological symptoms follow spinal lidocaine.

Sources: Mayo reviewMiller 10e

Epidural haematoma occupies space in a rigid bony canal, compressing the cord and nerve roots and causing ischaemia. Warning signs are back pain, a block that is prolonged or recurs after wearing off, and bladder or bowel failure. These indicate compression, not lingering drug effect. Saddle numbness with sphincter loss suggests cauda equina syndrome; if asked for the cause, name the compressing lesion. The deficit becomes permanent unless the clot is imaged and removed quickly.

Misattributes acute deficit to abscess. An abscess is also a compressing epidural lesion after neuraxial block and gives the same deficits, so it looks like a match. But it develops over days, with fever and a raised white count. Afebrile weakness that appears hours after the block points to a haematoma.

A haematoma can form within 12 hours of the procedure; an abscess takes days, with fever and leukocytosis. Back pain, prolonged block and sphincter dysfunction suggest an intracanal lesion and need urgent MRI. Treatment is decompressive laminectomy within 8 hours.

Sources: Mayo reviewMiller 10e

Bilateral flaccid weakness is not expected with dilute bupivacaine, which mainly blocks sensation. Two explanations must be considered: the epidural catheter may have migrated into the subarachnoid space, or a haematoma or abscess may be compressing the spinal cord. Bleeding is more likely with coagulopathy or difficult or traumatic insertion. Cord compression causes ischaemic injury, and the longer it persists, the less reversible it becomes. Outcome is much better if decompression occurs within 8 hours of paralysis starting, timed from when weakness is first noticed.

Underestimates timeline for dense block reversal. It is tempting because Miller's says most motor block wears off about two hours after the infusion stops. That applies to expected, modest block. Profound bilateral paralysis after several insertion attempts is out of proportion, and waiting two hours eats into the time window for decompression.

Miller's: most motor block settles about 2 hours after stopping the infusion, but persistent or worsening block needs prompt assessment for haematoma, abscess or intrathecal migration. Mayo: disproportionate weakness signals cord compression; image with MRI, consult neurosurgery; decompression within 8 hours improves recovery.

Sources: Mayo reviewMiller 10e

The needle or catheter tract can carry the patient's own skin bacteria into the epidural space, and a catheter left in place keeps that route open longer. Pus takes days to collect, so an abscess presents later than a haematoma, with systemic signs: fever and a raised white count. It progresses from local back pain to radicular pain, then motor, sensory or sphincter loss, and finally paraplegia. Streptococcus viridans from the operator's mouth classically causes meningitis after a spinal, not abscess; hence operators wear masks.

Confuses coloniser with pathogenic organism. Staphylococcus epidermidis lives on skin and colonises catheters, so 'skin flora' seems to point to it. But it has low virulence and causes only a small minority of these abscesses. The skin organism that forms pus and causes most epidural abscesses is Staphylococcus aureus.

The sources say a haematoma can appear within hours, but an abscess takes days and brings fever and leucocytosis. Staphylococci from the patient's skin are a leading cause of epidural infection. Oral streptococci cause infection after a spinal. Symptoms progress in stages, ending in paraplegia.

Sources: Miller 10eMayo reviewBarash 9e

The setting decides, and two Miller chapters cover the two settings. After a peripheral block, a significant deficit that persists needs a neurologist to grade it and nerve conduction studies now for diagnosis and prognosis; EMG is a poor first test because spontaneous denervation activity takes 1 to 4 weeks to appear. After labour, most peripheral neuropathies heal with time, so an isolated foot drop is re-examined later with outpatient neurology follow-up. Barash keeps imaging for compressive lesions, since imaging shows structure, not nerve function.

Treats anatomic imaging as functional test. CT feels like the thorough, objective step for a deficit in the operated limb, but it images anatomy, not nerve function. Imaging is kept for suspected compressive lesions after neuraxial blocks: severe back pain, a persistent or recurrent block, bowel or bladder upset. A peripheral block produces none.

Miller advises consultation and neurophysiological testing, including nerve conduction studies, for significant post-block injuries. It expects most postpartum neuropathies to heal, with outpatient neurology follow-up. EMG spontaneous denervation activity takes 1 to 4 weeks. Barash's mass-lesion warnings: severe back pain, persisting block, sphincter dysfunction.

Sources: Miller 10eBarash 9e

The roots of the cauda equina are long and only thinly myelinated, so they are exposed to anything placed in the subarachnoid space. If local anaesthetic does not mix evenly in the cerebrospinal fluid, it collects in dependent parts of the lumbosacral sac. The sacral roots are then soaked in a high concentration, which damages them directly. Slow injection through a fine spinal catheter makes this worse. Hyperbaric solutions and concentrated agents given as a single injection can do it too.

Confuses epidural approach with intrathecal drug. Caudal block feels like the right answer because it targets the sacral roots and suits perianal surgery. But a caudal block puts drug in the epidural space, outside the dura. This syndrome comes from drug pooling in the subarachnoid space. A saddle spinal is the intrathecal technique used for haemorrhoidectomy.

Lasting weakness and sensory loss is a rare complication of spinal anaesthesia, caused by local anaesthetic pooling in dependent subarachnoid space. Fine catheters increase pooling around lumbosacral roots, exposing them to high concentrations. Symptoms include saddle anaesthesia and loss of bladder and bowel control.

Sources: FaustMayo reviewMiller 10e

Local anaesthetic entering CSF produces a total spinal from little drug: sympathetic outflow is lost, giving hypotension and bradycardia, and respiratory muscles are paralysed, so hypoxia is immediate. Vertebral artery injection sends drug straight to the brain, causing seizures and unconsciousness. At the sixth level the vertebral artery sits deep in the transverse process canal. A needle sliding lateral and deep off the target tubercle meets the emerging root, causing arm paraesthesia. A correctly placed block may slow the heart by blocking cardiac accelerator fibres.

Misattributes neuraxial symptoms to artery. Vertebral artery injection is the famous dangerous stellate complication and does cause abrupt collapse, so it feels right for any sudden change. But drug delivered to the brain shows as seizure and loss of consciousness; bradycardia with apnoea and hypotension points to CSF spread producing a total spinal.

Reviews list total spinal from intradural injection and vertebral artery injection with seizure as the severe risks; intrathecal spread causes hypotension, bradycardia and respiratory paralysis. Pneumothorax is about 1%, recurrent laryngeal block is common, and brachial plexus block and cardioaccelerator block are uncommon.

Sources: Mayo reviewFaustBarash 9e

The needle deposits local anaesthetic at root and trunk level in the interval between anterior scalene and middle scalene muscles, not beside sternocleidomastoid. The spread also blocks the ipsilateral phrenic nerve, so hemidiaphragm paresis accompanies nearly every block and can compromise patients with poor lung reserve. The inferior trunk, C8–T1, is reached unreliably, so ulnar territory is often left unblocked. Hence the block suits shoulder surgery but is unreliable for forearm or hand work without a separate ulnar block.

Overlooks incomplete ulnar coverage distally. One text lists the forearm among its indications, so this sounds right. But the inferior trunk is often incompletely blocked, leaving the ulnar side uncovered. Forearm and hand surgery usually need an extra ulnar block, so the block is really a shoulder block.

The texts place the plexus between the anterior and middle scalenes, list ulnar sparing, and report phrenic paresis in up to 100% of blocks. The books give no percentage, only 'often'; of the statements offered, the ulnar-sparing one is the only one not contradicted.

Sources: Mayo reviewFaustMiller 10e

The vertebral artery runs close to the brachial plexus roots, deep to them in the interscalene region. If local anaesthetic goes into this vessel, it travels straight into the brain's circulation without first being diluted in the systemic blood volume. Even a very small dose can therefore reach a toxic level in the brain within seconds and cause convulsions. Careful aspiration and small incremental injections help prevent it. Phrenic nerve block happens with almost every interscalene block, but a working diaphragm on the other side usually makes up for it.

Underestimates vertebral artery severity risk. It is tempting because it happens with nearly every interscalene block and can cause respiratory failure. But it is an expected side effect, and healthy patients usually have no symptoms. It only becomes dangerous when respiratory reserve is already borderline, so it is not the most serious immediate complication.

Injection into the vertebral artery sends local anaesthetic directly to the brain and can cause an immediate convulsion. Aspiration and incremental dosing help avoid this. The phrenic nerve is blocked 100% of the time, but healthy patients seldom notice it.

Sources: Mayo reviewBarash 9e

Blocking the coeliac plexus removes the sympathetic supply to the abdominal viscera. Losing sympathetic tone reduces preload, so blood pools on standing and blood pressure falls; giving fluid beforehand helps. Parasympathetic input to the gut is then unopposed, which speeds gut motility and causes transient diarrhoea. The plexus wraps around the aorta, so the needle can cause retroperitoneal bleeding and, rarely, paraplegia. The plexus supplies all abdominal viscera apart from the left colon and pelvis, so it is the right target for pancreatic cancer pain.

Dismisses unopposed vagal effect incorrectly. Diarrhoea seems an odd result of a nerve block, and these patients are usually constipated from opioids, so it looks like the odd one out. In fact the unopposed vagal tone makes diarrhoea one of the commonest effects. Air embolism is the item missing from every complication list.

Common effects are back pain, diarrhoea and orthostatic hypotension; complications include retroperitoneal haematoma and paraplegia. Hypotension reflects reduced preload after sympathectomy, preventable by fluid loading. Diarrhoea reflects unopposed parasympathetic gut activity. The plexus supplies all abdominal viscera except the left colon and pelvis.

Sources: Barash 9eMayo review

Severity depends on how deep the needle goes and what it strikes. A superficial vessel bleeds into lid and periorbital tissue outside the closed orbital space, so the result is mainly cosmetic. An arterial bleed behind the globe fills a confined orbit. Intraocular pressure climbs, the eye is pushed forward and its blood supply is threatened, putting vision at risk. A needle entering the globe damages the eye directly.

Underestimates cardiovascular reflex as trivial. People often think of the reflex as a transient intraoperative nuisance, so it feels minor. It is a systemic cardiovascular event, not a cosmetic one. The only outcome the source describes as merely unsightly is the superficial bruise around the orbit.

Complications of needle-based eye blocks can be local or systemic and may cause blindness or death. Superficial bleeding leaves only an unsightly bruise around the orbit. Arterial retrobulbar bleeding sharply raises eye pressure and causes proptosis. Globe perforation is listed as a major complication.

Sources: Barash 9e

Opioids depress breathing at a higher receptor occupancy than the level needed for pain relief. So small doses of the antagonist, given into a vein or muscle and titrated to the breathing rate, can restore ventilation without removing analgesia. Large resuscitation-sized boluses remove analgesia at once. They can cause a pain- and catecholamine-driven surge with hypertension and myocardial ischaemia, and they can cause severe withdrawal in opioid-dependent patients. A cautious starting dose that can be repeated is therefore the safer choice.

Misapplies out-of-hospital protocol to hospital. Nasal naloxone is promoted by guidelines for first responders and lay rescuers, but a hospital PCA patient has trained staff and venous access. The recommended starting dose is framed for IV or IM use, allowing small, titrated reversal. The nasal spray is a convenience for use outside hospital.

Resuscitation guidance suggests a modest empiric naloxone starting dose, given IV or IM, to avoid severe withdrawal. Nasal or IM naloxone is suggested for lay rescuers. Anaesthesia texts say careful titration reverses respiratory depression while keeping analgesia, but large boluses risk hypertension and ischaemia.

Sources: Miller 10eBarash 9e

EMLA contains prilocaine. The liver breaks prilocaine down to O-toluidine, an oxidant that turns haemoglobin into methaemoglobin, which cannot carry oxygen normally. Spreading the cream over a large area of skin lets enough drug be absorbed to raise methaemoglobin to a harmful level. Methaemoglobin also misleads the pulse oximeter, so the reading levels off at 84% to 86% whatever the real oxygenation. That is why the patient looks blue but the oximeter reading barely moves. Methylene blue is the specific treatment.

Treats methaemoglobinaemia as lipid toxicity. Headache, nausea and agitation after a large dose of local anaesthetic suggest systemic toxicity, and lipid emulsion is the rescue treatment for that. But cyanosis with a saturation stuck in the mid-eighties points to oxidised haemoglobin, and lipid emulsion does not reverse that.

Large doses of prilocaine can cause methaemoglobinaemia through its O-toluidine metabolite, so generous EMLA application needs caution. Pulse oximetry levels off at 84% to 86%. Treatment is intravenous methylene blue 1 mg/kg.

Sources: FaustMiller 10eBarash 9e

Early in development the cord fills the whole canal. The vertebral column then grows faster than the cord, its nerve roots and the dura around them, so the cord and sac seem to move up the canal. The difference is biggest at birth. By the end of the first year the lower ends have reached their adult positions. After that, a caudal or spinal needle at a given vertebral level has adult anatomy around it.

Confuses adult and neonatal anatomy. It sounds right because infants are known to have a lower sac, and this looks like a reasonable halfway point. It fits neither age, though. The newborn sac reaches S3–S4, and by one year it has already risen to the adult S2 level.

One textbook places the newborn conus at L3–L4 and the dura at S3–S4, reaching adult levels (conus L1, sac S2) by the end of the first year. A review text gives the newborn sac as S3–S4 and the adult sac as S1–S2.

Sources: Miller 10eMayo review

In the embryo the cord fills the whole canal. The vertebral column then grows faster than the cord, so the conus sits lower at birth and rises to its adult level by the end of the first year. Needles are aimed below the conus. The margin matters because clinicians who count spaces by feel often choose an interspace higher than they meant to. As a result, a planned L2–L3 puncture can reach the conus.

Applies neonatal cord level to adults. L3 is the newborn cord level, so it sounds familiar. By the end of the first year the column has outgrown the cord, and the adult conus sits at L1–L2. L3 lies below the adult conus, which is why the lower lumbar spaces are the usual puncture sites.

The cord ends at L1–L2; midline spinals usually go at L3–L4 or L4–L5. At birth the conus ends at L3 or L4 and the dura at S3 or S4. Adult levels, conus L1 and sac S2, come by the end of the first year.

Sources: Miller 10eBarash 9e

The sacral hiatus is a V-shaped opening framed by the two sacral cornua. The sacrococcygeal ligament, which continues the ligamentum flavum, covers it. The posterior superior iliac spines are bony points that are easy to feel, so the triangle guides the fingers down to the cornua. The needle then passes through skin and that ligament, and the loss of resistance shows it has entered the caudal canal. The triangle is only approximate and does not help when the cornua cannot be felt.

Confuses anterior with posterior spine landmarks. The anterior superior iliac spine is the more familiar pelvic landmark and its name is almost the same. But the caudal triangle is built on the back of the pelvis, from the two posterior spines. The ischial tuberosity and greater trochanter are not part of this triangle either.

Both textbooks place the hiatus between the cornua, at the tip of an equilateral triangle whose base joins the posterior superior iliac spines. The sacrococcygeal ligament covers it. One textbook warns that the triangle does not help when palpation fails.

Sources: Barash 9eMiller 10e

An intrathecal dose of local anaesthetic spreads within the lumbosacral CSF. The smaller that fluid volume, the higher the same dose reaches, so the effective dose is lower. CSF volume explains about 80% of the variation in peak block height and in regression of block. Volume falls when raised abdominal pressure pushes soft tissue into the intervertebral foramina and displaces CSF, as in obesity. Apart from body weight, no bedside body measurement predicts CSF volume, so a high block can be hard to foresee.

Overstates needle direction influence dramatically. Pointing the needle orifice towards the head is a genuine, listed technique factor for cephalad spread, so it looks correct. But it is a minor influence. CSF volume, together with baricity, is the dominant determinant and accounts for most of the variation in block height.

Lumbosacral CSF volume is estimated to explain 80% of variability in peak block height and regression. With baricity, it is the most important determinant of spread. Volume is lower with higher BMI and with raised abdominal pressure, which displaces CSF.

Sources: Miller 10eBarash 9e

Local anaesthetic spreads up and down the epidural space by bulk flow, so whatever keeps the injected volume inside the canal makes the block spread further. With age, less solution escapes sideways through the intervertebral foramina, so more of each millilitre travels along the canal. The ageing epidural space is also more compliant, and the text names this as a second reason for wider spread. A given dose therefore covers more segments, so reduce the volume in elderly patients, especially for thoracic catheters.

Reverses compliance-age relationship direction. A stiff, low-compliance space sounds as if it should force solution further, and the question points you towards age-related change. But the source says compliance goes up with age, and a more compliant space increases spread. Stiffness is the wrong direction.

The text gives two reasons for greater spread with age: less local anaesthetic escapes through the foramina, and the epidural space becomes more compliant. The age effect is strongest in thoracic epidurals, where one study found elderly patients needed 40% less volume.

Sources: Miller 10e

For these amides, potency follows lipid solubility. A more lipophilic drug enters the nerve membrane more easily, so a smaller amount gives the same block. Ropivacaine is much less lipid-soluble than bupivacaine, so it needs a higher concentration for the same effect. Its apparent motor-sparing may simply reflect this lower potency. Levobupivacaine is the S-enantiomer of bupivacaine and behaves almost the same physically, so any potency gap is small. Miller's finds it slightly weaker. Faust's table treats the two as equal. In both, ropivacaine is the weakest.

Treats potency as equivalent across agents. This is tempting because all three are long-acting amides with similar clinical profiles. One textbook table also gives bupivacaine and levobupivacaine the same potency. It fails because every source ranks ropivacaine as weaker, so it needs a higher equipotent concentration.

Levobupivacaine is slightly less potent than bupivacaine. Ropivacaine is also slightly less potent, at about 1:1.3–1.5 for regional anaesthesia, and 40% less potent epidurally. Equipotent doses: 0.5% bupivacaine, 0.5% levobupivacaine, 0.75% ropivacaine. Ropivacaine is weakest; bupivacaine is at least joint strongest.

Sources: Miller 10eFaust

The epidural space is only where the drug is deposited. The drug has to reach neural tissue to block conduction. As the spinal nerve roots cross the epidural space, their dural covering is thin, so the drug reaches the axons easily there. Only a small fraction crosses the dura into the subarachnoid space to reach deeper structures. The segmental block therefore starts at the roots.

Overestimates dural permeability and penetration. It sounds right because the dorsal horn is where many analgesic mechanisms work, so it seems a natural target for any central block. But little epidural local anaesthetic crosses the dura. The main action is on the roots as they pass through the epidural space, not in the cord.

Local anaesthetic given into the epidural space acts mainly at the spinal nerve roots, where the dura mater is thin. Only a small amount of the drug crosses the dura into the subarachnoid space.

Sources: Faust

How long a block lasts depends on the drug and on where it is injected. Bupivacaine given into the subarachnoid space wears off sooner than the same drug given epidurally or by infiltration. Adding adrenaline to the intrathecal dose makes the block last about 50% longer. So the adrenaline-free spinal figure is the baseline, and a longer range applies only when adrenaline is added.

Confuses infiltration with intrathecal duration. It overlaps the upper end of the true range, and its upper limit matches the figure quoted for bupivacaine infiltration with adrenaline, so it looks familiar. However, the textbooks give 90 to 200 minutes for a plain spinal, not this range.

The review states that bupivacaine spinal without adrenaline lasts 90 to 200 minutes, and adding adrenaline makes it last about 50% longer. With adrenaline, bupivacaine epidural block lasts 180 to 350 minutes and infiltration 180 to 240 minutes.

Sources: Mayo review

The saphenous nerve comes off the femoral nerve high in the femoral triangle. It then runs down the subsartorial canal alongside the femoral artery, under sartorius. Local anaesthetic placed beside that artery, deep to the vastoadductor membrane, therefore reaches the saphenous nerve and also the nerve to vastus medialis. The tibial, peroneal and sural nerves come from the sciatic nerve, which runs separately at the back of the limb, so they are never in the canal and are not blocked.

Misattributes plexus origin to femoral. Its name contains 'femoral' and it supplies thigh skin, so it looks like a femoral branch that should sit in the canal. In fact it is a separate branch of the lumbar plexus, not arising from the femoral nerve, and it does not run in the adductor canal.

The saphenous nerve leaves the femoral nerve in the femoral triangle and runs down the adductor canal with the femoral artery. Injection there also covers the nerve to vastus medialis. It is the only nerve to the foot not from the sciatic nerve.

Sources: Barash 9eMiller 10eMayo reviewFaust

The sciatic nerve collects anterior rami from L4 to S3. The ventral divisions form the tibial trunk and the dorsal divisions form the common peroneal. Further down, these give rise to the posterior tibial, sural, superficial peroneal and deep peroneal nerves, so almost all sensation below the knee is sciatic. The saphenous nerve is the exception. It comes down from the femoral nerve along the inner leg to the medial malleolus. A sciatic block therefore leaves that medial strip with sensation unless the saphenous is blocked separately.

Confuses tibial nerve sole cutaneous supply. The tibia forms the inner shin, so the tibial nerve sounds as if it should supply the medial leg. It is tempting for that reason. But the tibial nerve is a sciatic branch, so a working sciatic or popliteal block has already blocked it. Only the femoral-derived saphenous nerve escapes.

Posterior tibial, sural and both peroneal nerves reaching the ankle and foot come from the sciatic (anterior rami L4–S3). Only the saphenous is femoral, supplying the medial lower leg to the medial malleolus.

Sources: Mayo reviewMiller 10eBarash 9e

The nerve is a small branch of the lumbar plexus. It leaves the psoas at its lateral edge, crosses towards the anterior superior iliac spine, then passes through the inguinal ligament into the thigh. It carries only skin sensation. Damage, such as stretch or ischaemia at the ligament during prolonged hip flexion, therefore causes numbness or painful dysaesthesia over the outer front of the thigh but never weakness. This separates it from the larger mixed nerves of the plexus.

Extends purely cutaneous nerve root origin. L2-L4 is the familiar root value for the femoral and obturator nerves, so people attach it to every lumbar plexus branch. Those nerves are mixed motor and sensory. The purely cutaneous lateral femoral nerve takes a narrower origin that stops at L3.

The lumbar plexus gives the lateral femoral cutaneous nerve from L2-L3, while the obturator and femoral nerves come from L2-L4. It emerges lateral to psoas and crosses the inguinal ligament. Injury causes anterolateral thigh sensory loss without motor deficit.

Sources: Mayo reviewFaustBarash 9e

Descending through the plexus, the roots unite between the scalene muscles to form trunks. At the outer border of the first rib, behind the clavicle, each trunk divides into anterior and posterior divisions. In the axilla, these recombine as cords around the axillary artery. A supraclavicular block therefore reaches the plexus where trunks become divisions. Nerve tissue is closely compacted here, so a low volume of local anaesthetic spreads quickly and dependably. An infraclavicular block, by contrast, encounters structures already formed into cords.

Confuses divisions with trunks position. Divisions are tempting because they sit right behind the clavicle, and one textbook table lists the supraclavicular level as divisions. But the supraclavicular injection sits at the junction of trunks and divisions, and trunks is the accepted single answer. Below the clavicle, the divisions have already merged into cords.

Interscalene block works at roots and trunks but misses the inferior trunk. Supraclavicular block works at the distal trunks and proximal divisions, where the plexus is compact. Infraclavicular block works at the cords, beside the axillary artery at the level of the coracoid.

Sources: Mayo reviewBarash 9eMiller 10e

A tendon reflex tests the spinal segments that supply the muscle being stretched. Tapping the patellar tendon stretches quadriceps. The femoral nerve supplies quadriceps from L2, L3 and L4, so the reflex sits in the middle of that range. Tibialis anterior, at the front of the leg, takes L4, L5 and S1, so L4 is the root it shares with the knee jerk. Gastrocnemius and soleus plantar flex through the tibial nerve from S1 and S2. Gluteus maximus draws on L5, S1 and S2.

Swaps lumbar and sacral root levels. L5–S1 is the root pair people link with the ankle jerk and with plantar flexion, so it is easy to swap in by reflex. The knee jerk comes from quadriceps, which is supplied well above the sacral roots.

The muscle innervation table puts quadriceps (knee extension) on the femoral nerve from L2–L4. Tibialis anterior (dorsiflexion) takes L4, L5 and S1. Gastrocnemius and soleus (plantar flexion) take S1–S2 via the tibial nerve. Gluteus maximus takes L5, S1 and S2.

Sources: Stoelting 8e

The subcostal, ilioinguinal and iliohypogastric nerves supply the anterolateral abdominal wall. They run a long way in the fascial layer that separates internal oblique from transversus abdominis. Filling that layer bathes all of them with one injection. Drug placed inside a muscle, or in the gap between the two obliques, does not reach them. On ultrasound the wall looks like a three-layer cake. External oblique is the top layer, internal oblique the middle and transversus abdominis the deepest. The target lies between the lower two.

Misplaces target layer within abdominal wall. This is the first gap between muscles that the needle reaches, so it feels like the right place. The nerves do not run there. They lie one layer deeper, just above transversus abdominis, so drug left between the obliques gives poor analgesia.

The sources say the abdominal wall nerves run between internal oblique and transversus abdominis, so drug goes into that plane and not into muscle. The subcostal, ilioinguinal and iliohypogastric nerves all run through it. Ultrasound shows three stacked muscles, with nerves entering that deepest plane.

Sources: Mayo reviewMiller 10e

The interscalene groove lies over the plexus, just lateral to the belly of anterior scalene. The clavicular head is the lateral part of sternocleidomastoid. If you roll your fingers posterolaterally off its lateral edge, they cross anterior scalene and drop into the groove. The cricoid sets the level at C6. Lifting the head makes the muscle edge stand out. A deep breath contracts the scalenes, which makes the groove deeper and easier to feel.

Locates groove at wrong muscular region. The sternal head is the most visible part of the muscle, so 'behind the sternocleidomastoid' can suggest it. However, the groove is found by moving posterolaterally from the lateral border, the clavicular edge. The sternal head is too medial, so a needle behind it is not over the scalenes.

The groove sits just posterior to the outer edge of the muscle's clavicular part, at cricoid level (C6). You find it by moving your fingers posterolaterally across anterior scalene. Contracting the scalenes makes it deeper.

Sources: Barash 9eFaustMiller 10e

The erector spinae plane is a fascial layer between the front surface of the erector spinae muscle and the bony transverse process. Injecting there lifts the muscle away from the bone and opens this plane. Local anaesthetic then spreads up and down the continuous plane across several vertebral levels. It is thought to reach the posterior and anterior branches of the spinal nerves as well as sympathetic fibres. This explains how a superficial posterior injection can give both somatic and visceral analgesia.

Overstates depth of neural spread. The block eases visceral pain, so an internal organ can look like a plausible target. It is not. The needle stops on the bony transverse process. Any visceral relief comes from local anaesthetic spreading to spinal nerve branches and sympathetic fibres.

The textbooks place local anaesthetic under the erector spinae muscle, lying on the bony surface of the transverse process. Correct needle placement shows as linear spread between muscle and bone. Bone contact gives a clearer endpoint than a paravertebral block does.

Sources: Miller 10eBarash 9e

The posterior angle is the most prominent point along the back of each rib, so it is easy to feel. It gives the needle a reliable bony target at a set distance from the spine. Because the landmark is a named, palpable point, the injection site stays the same from one level to the next. A vague description of where the needle sits relative to the rib cannot do that. Lateral and more medial approaches exist, but the rib angle is the standard reference.

Omits specific rib angle location. It sounds right because many chest-wall procedures go over the upper border of a rib to avoid the neurovascular bundle. But it does not say where along the rib to inject. The books place this block at the palpable posterior rib angle.

Intercostal blocks are injected along the sharp posterior rib angle, palpable 5–7 cm from the midline. Alternatives are a lateral approach at 8–10 cm, or a medial approach just beyond the transverse processes.

Sources: Barash 9e

The preganglionic cell bodies sit in the intermediolateral grey column. That column exists only in the thoracic and upper lumbar cord segments. Their myelinated axons leave through the ventral roots and white rami to reach the paravertebral chain. Inside the chain they can run up or down before they synapse. Grey rami then send postganglionic fibres out with spinal nerves at every level. So sympathetic fibres reach the head, neck and pelvis, but they all start in the thoracolumbar cord.

Confuses craniosacral with sympathetic distribution. Craniosacral is tempting because it is the other named autonomic outflow pattern, and sympathetic effects clearly reach the head and pelvis. It is wrong because those fibres only get there by travelling along the chain. Their cell bodies are never in the brainstem or the sacral cord.

Sympathetic preganglionic cell bodies lie in the intermediolateral grey matter of cord segments T1 to L2 (L3 in some texts), hence "thoracolumbar system". Fibres enter the chain and are distributed with spinal nerves at all levels.

Sources: Barash 9e

Sympathetic relay stations lie close to the spinal cord, either along the vertebral chain or in front of the vertebral column in the abdomen. The myelinated preganglionic axon therefore has only a short way to travel. The long postganglionic axon then carries the signal out to distant effectors. Each preganglionic fibre branches to many postganglionic neurons, so activation spreads widely and produces a diffuse, mass response. The postganglionic terminals release noradrenaline.

Assigns parasympathetic relay to sympathetic. It sounds like a real autonomic relay in the head. However, cranial ganglia belong to the craniosacral parasympathetic outflow, whose ganglia sit near their target organs. Sympathetic preganglionic fibres relay in chain ganglia or in abdominal prevertebral ganglia such as the coeliac. Thyroid and carotid body are not ganglia.

Short myelinated preganglionic fibres leave through the anterior roots and white rami. They synapse in ganglia outside the neuraxis, including the unpaired prevertebral coeliac and mesenteric ganglia. Each preganglionic fibre reaches many postganglionic neurons, and those neurons' terminals release noradrenaline.

Sources: FaustBarash 9e

Preganglionic sympathetic fibres pass the chain ganglia without synapsing and end directly on the chromaffin cells, where they release acetylcholine. The chromaffin cells come from neural tissue and do the job of the postganglionic neuron. They do not release a transmitter at a synapse. They release catecholamines into the blood, where these act as hormones. The medulla also has phenylethanolamine-N-methyltransferase, an enzyme that converts noradrenaline to adrenaline. That is why adrenaline is most of what it releases. Acetylcholine goes into the medulla; it is not something the medulla secretes.

Confuses neurotransmitter at chromaffin synapse. This option is tempting because acetylcholine really is released at the adrenal medulla, and adrenaline really is the medulla's main product. But the acetylcholine comes from the preganglionic nerve ending and acts on the chromaffin cell. The chromaffin cell itself releases only catecholamines: adrenaline and noradrenaline.

The medulla makes and secretes adrenaline (80%) and noradrenaline (20%). Cholinergic preganglionic fibres run straight to the chromaffin cells. These cells act like postganglionic neurons, but what they release works as a hormone, not a neurotransmitter.

Sources: Barash 9e

The C6 tubercle is the bony anterior projection of the C6 transverse process. It is the most prominent cervical tubercle, lies at cricoid level and is palpable beside the cricoid. The ganglion lies one level lower, anterior to the first rib at C7, with the C6 tubercle directly above it. The needle is aimed at this palpable bone. Ultrasound also identifies C6 first, then slides down to C7. The tubercle lies under the carotid, so "medial to the carotid" describes the needle path after retraction, not fixed anatomy.

Conflates ganglion location with tubercle level. This is tempting because the stellate ganglion itself lies at C7 and the carotid is pulled aside during the block. But the question asks where the tubercle is, and the tubercle belongs to the C6 transverse process. C7 is the ganglion's level, one vertebra lower.

The cricoid cartilage and the C6 transverse process anterior tubercle, its most prominent one, are neck landmarks. The ganglion lies at C7 in front of the first rib, below Chassaignac's tubercle. Ultrasound scans C6, then C7.

Sources: Miller 10eFaustBarash 9e

A wider axon and a myelin sheath both speed up impulse conduction. A-alpha fibres are thick, myelinated motor fibres to skeletal muscle, so they sit at the top for both size and speed. A-beta fibres carry touch and proprioception and share the same top velocity band. C fibres are the thinnest and have no myelin, so they conduct slowest. Their free nerve endings respond to thermal, chemical and noxious stimuli. That makes them the main route for heat sensation and dull pain.

A-beta carries heat sensation. A-beta is a sensory fibre coming from the skin, so it seems a natural choice for a skin sensation like heat. But it carries touch and proprioception, not temperature. Heat travels in the thin fibres: C fibres and, to a lesser extent, A-delta.

Large myelinated A fibres serve speed-dependent motor and sensory tasks. A-alpha motor fibres are widest; A-alpha and A-beta conduct fastest. Thin unmyelinated C fibres conduct slowly, carrying pain, temperature and autonomic signals via free endings responsive to thermal stimuli.

Sources: Miller 10eMayo reviewBarash 9e

Pain has two parts. The sensory-discriminative part tells you where the pain is and how strong it is. The affective part is the suffering, fear and autonomic arousal. Second-order spinal neurons relay to the thalamus. From there the signal spreads to cortical areas that locate the stimulus, and to limbic structures such as the amygdala and cingulate that give it emotional weight and drive the stress response. Large myelinated Aβ fibres normally carry touch. They can take on a nociceptive role once sensitisation sets in.

Cerebellum as a pain relay. The cerebellum receives much sensory input, so it looks like a plausible relay. The textbook pain network runs thalamus, insula, cingulate, limbic structures, prefrontal cortex; no book lists the cerebellum. Imaging shows cerebellar activity during pain, so call it 'not part of the pathway', not 'uninvolved'.

In volunteers given painful heat, activation spread from thalamus through insula and cingulate to prefrontal cortex. Thalamus relays nociceptive input to amygdala and somatosensory cortex. Spinoamygdalar pathways drive emotional and autonomic pain responses. Aβ fibres carry nociceptive signals in chronic pain.

Sources: Barash 9e

Primary afferent A and C fibres end in the dorsal horn and synapse there on second-order neurons. Several influences meet at this synapse. Local interneurons release inhibitory transmitters. Endogenous opioid circuits act before and after the synapse. Descending fibres from the brainstem bring serotonin and noradrenaline and act on dorsal horn neurons. Together these can damp or amplify the signal before it ascends. That is why spinal opioids and spinal cord stimulation work at this level.

Thalamus is main pain modulation site. The thalamus is tempting because it is a well-known processing centre and holds the cell bodies of the third-order neurons. It passes the signal up to the cortex. The textbooks, however, name the spinal dorsal horn as the most common site where the signal is altered.

The textbooks name the spinal dorsal horn as the most frequent site of pain modulation, and say it can either inhibit or enhance the signal. Peripheral nociceptive input and descending modulatory input combine there. Brainstem stimulation suppresses nociceptive dorsal horn neurons.

Sources: Barash 9eMiller 10e

Pain triggers nociceptor activation, and that sets off a sympathetic surge and inhibitory spinal reflexes. The overall effect is to switch organs off rather than speed them up. Gut motility slows into ileus, urine output falls and the bladder retains. Clotting risk rises because the patient is immobile and weak. So the expected picture is tachycardia, splinting with atelectasis, a stalled gut, retained urine and venous clots. Loose stools, a large urine output or a bleeding tendency do not fit it.

Pain causes haemorrhage. Bleeding is tempting because clotting is on the list of affected systems. But the effect runs the other way: pain and immobility raise the risk of thrombosis, not haemorrhage.

Poorly managed acute pain raises the risk of oliguria and urinary retention, postoperative ileus and thromboembolism. It works through sympathetic activation and inhibitory spinal reflexes that slow the return of gut function. Immobility adds to the clot risk.

Sources: Barash 9eMiller 10e