Below-knee amputation on dual antiplatelets, and phantom pain76-year-old man, 68 kg, for left below-knee amputation for critical limb ischaemia with rest pain

The patient

The examiner asks

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1. Consider

   What are your considerations?

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   • A 76-year-old with critical ischaemia, diabetes and recent stents on dual antiplatelets, for amputation. Patient
   • At 76, with vascular disease and diabetes, I record his cognition now; delirium risk rises after 60.
   • Chronic pain follows 50–80% of amputations, and his severe pain beforehand raises his risk. Disease

2. Prepare

   Take me through his cardiac risk before the amputation.

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   • Urgency: critical limb ischaemia is time-sensitive surgery; it can't wait months for workup. Stem trigger
   • Active cardiac conditions? None: no acute coronary syndrome, decompensated failure, severe valve disease or fast arrhythmia. Disease
   • RCRI 2, coronary disease and insulin; a below-knee amputation isn't a high-risk procedure. About 8% risk.
   • Functional capacity: rest pain stops him walking, and disability of any cause counts as under 4 METs.
   • Decision: elevated risk, but revascularisation wouldn't help; 4 months after stenting allows time-sensitive surgery. Proceed.

3. Prepare

   How do you prepare him before surgery?

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   • His rest pain is 8/10 on oxycodone; poorly controlled pain before surgery raises his chronic pain risk. Disease
   • So I improve his analgesia now, rather than waiting for theatre.
   • At 4 months I ask cardiology whether clopidogrel can pause; aspirin continues regardless.
   • Glucose 11 mmol/L: his insulin continues, with glucose checks through surgery. Patient
   • I warn him about phantom sensations and pain beforehand, so they don't frighten him. After surgery

4. Plan

   What is your anaesthetic and analgesic plan?

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   • Unless clopidogrel has been off 5–7 days, he can't have a neuraxial block. Disease
   • So no spinal or epidural: GA, with a perineural catheter for analgesia.
   • A popliteal sciatic catheter: a compressible site, acceptable on his antiplatelets. It cuts opioid use. Surgery
   • His oxycodone continues as baseline, with short-acting opioid added for surgery. Disease
   • Ketamine, roughly 0.25 mg/kg as a bolus, then 0.05–0.35 mg/kg/h; gabapentin at a renal-adjusted dose.
   • Paracetamol 1 g 6-hourly as the base of his regimen.

5. Crisis

   On day five he has burning, cramping pain in the missing foot and sharp pain at the stump; pain 9/10. BP 150/85, HR 96, temperature 37.9°C. What do you do?

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   • I separate phantom pain, phantom sensation and stump pain; each needs its own answer. Crisis
   • Stump first: fever makes me look for ischaemia, infection or haematoma in the wound.
   • Sharp, localised stump pain can come from a neuroma on the cut nerve.
   • Phantom pain: morphine, gabapentin and ketamine all have short-term benefit.
   • Mirror therapy with the physiotherapists and the rehabilitation team. After surgery
   • If it persists: a tricyclic or duloxetine, reviewed in pain clinic.