Pain and regional anaesthesia03 / 13
Hip arthroplasty in sleep apnoea: neuraxial opioid safety71-year-old man, 112 kg, BMI 37, for elective right total hip arthroplasty under spinal anaesthesia
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Know this first
- Intrathecal morphine 50–150 mcg gives 12–24 h of analgesia; delayed respiratory depression is the risk.
- OSA: favour regional over systemic opioids, no background PCA infusion, continuous oximetry.
- Bradycardia: atropine 1 mg every 3–5 min to 3 mg.
- Severe hypotension with bradycardia under spinal: early adrenaline 0.1–1 mcg/kg.
- Naloxone lasts 15–45 min, so long-acting opioids need repeat doses or an infusion.
The patient
71-year-old man, 112 kg, BMI 37, for elective right total hip arthroplasty under spinal anaesthesia.
Severe obstructive sleep apnoea on home CPAP; hypertension.
Drugs: amlodipine, ramipril.
Vitals: BP 146/84, HR 64, SpO2 95% on air, RR 14.
The examiner asks
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Consider
What are your considerations?
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- A 71-year-old, obese, with severe OSA treated by CPAP, for elective hip arthroplasty under spinal. Patient
- At 71 I record his cognition and frailty now, so delirium after his hip surgery is recognised.
- His OSA makes him prone to opioid-induced apnoea, so the whole plan spares opioids. Disease
Plan
How will you manage his analgesia?
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- Multimodal base: regular paracetamol 1 g 6-hourly, plus an NSAID if his kidneys allow, plus a block. Disease
- Fascia iliaca or PENG block for his hip, to cut his systemic opioid needs. Surgery
- Intrathecal morphine only after weighing it: 50–150 mcg lasts 12–24 hours, with delayed apnoea risk. Disease
- If I give it, I use the low end and he goes to a monitored bed.
- Any PCA runs without a background infusion.
- His own CPAP comes in and goes on whenever he sleeps. After surgery
- Continuous oximetry; nurses check RR, breathing depth and conscious level without waking him.
Crisis
Five minutes after the spinal, BP is 78/40 and HR 38. He is nauseated but talking. What do you do?
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- Bradycardia algorithm: HR 38 with hypotension soon after his spinal; I call for help. (Crisis)
- I check the block height; a high block can also weaken his breathing.
- Atropine 1 mg IV; I can give it every 3–5 minutes, 3 mg in total.
- Ephedrine boluses for pressure, not phenylephrine, whose reflex slowing he can't afford; plus fluid.
- If both stay severe, adrenaline early in small doses, 0.1–1 mcg/kg.
- Still unresponsive: an adrenaline infusion at 2–10 mcg/min.
Crisis
At 03:00 on the ward he is hard to rouse, RR 6, SpO2 84% on 2 L. His CPAP was never put on. What do you do?
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- Opioid respiratory depression from his intrathecal morphine, made worse by untreated OSA. Crisis
- Call for help, rouse him, open his airway and give oxygen by bag-mask.
- Naloxone 40 mcg IV every 2 minutes, to 200 mcg, aiming for breathing, not full reversal.
- Naloxone lasts 15–45 minutes, far less than his morphine, so I start an infusion.
- CPAP on once he's awake, and he moves to a monitored bed. After surgery
Fatal mistakes
- Neuraxial morphine followed by an unmonitored ward bed.
- Leaving his CPAP off after surgery.
- A large naloxone bolus instead of titrated doses.
- Delaying adrenaline when severe bradycardia and hypotension follow the spinal.
Checked against: Barash 9e · Miller 10e
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