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Acute intermittent porphyria for urgent wrist fixation24-year-old woman, 56 kg, for urgent fixation of a displaced distal radius fracture

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Know this first

  • Triggers: drugs, fasting, dehydration, stress, infection and hormonal change.
  • Propofol, opioids, volatiles and muscle relaxants are safe; thiopental, etomidate and ketamine are not.
  • Hyponatraemia occurs in 40% of attacks; seizures can follow.
  • Severe attack: haem therapy first, not after a trial of glucose.

The patient

24-year-old woman, 56 kg, for urgent fixation of a displaced distal radius fracture; fasting since last night. Acute intermittent porphyria with two past attacks of abdominal pain and confusion, the last a year ago. Drugs: combined oral contraceptive pill. Vitals: BP 124/78, HR 92, SpO2 99% on air, RR 16. Na+ 138 mmol/L.

The examiner asks

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  1. Consider

    What are the issues?

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    • A 24-year-old with acute intermittent porphyria and two past attacks, for urgent wrist fixation. Patient
    • My worry is an acute attack: pain, autonomic swings, low sodium, weakness and seizures. Disease
    • Her triggers today: fasting, dehydration, pain, stress, infection and the wrong drugs. Stem trigger
    • Her combined pill is a hormonal trigger; I check it and every planned drug on the porphyria database.
    • Weakness in an attack can reach her breathing muscles; respiratory failure occurs in up to 20%. Disease

  2. Prepare

    How will you prepare her?

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    • Shortest fast possible; she has fasted overnight, so a glucose-containing infusion starts now. Stem trigger
    • A full neurological examination before any block, so existing neuropathy is on record. Disease
    • Baseline sodium, potassium, calcium and magnesium.
    • Safe choices fixed in advance for each class: antibiotic, antiemetic, analgesic and anticonvulsant. Stem trigger
    • Midazolam for her anxiety and early analgesia; stress alone can set off an attack.

  3. Plan

    What anaesthetic will you give?

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    • No neuropathy found, so a brachial plexus block is my first choice; local anaesthetics are safe. Disease
    • If general: propofol, fentanyl, rocuronium and sevoflurane, all considered safe.
    • No thiopental, etomidate or ketamine; they can provoke her attack. Stem trigger
    • Close blood pressure watch, since autonomic lability is common in porphyria. Disease
    • Ondansetron for nausea; paracetamol and opioids for pain, but no ketorolac. After surgery

  4. Crisis

    On day one she becomes confused, then has a generalised seizure. BP 168/100, HR 128, SpO2 93%, Na+ 119 mmol/L. What do you do?

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    • An acute porphyric attack with a hyponatraemic seizure; airway, oxygen and help first. Crisis
    • Midazolam 1–5 mg IV to stop the seizure; propofol is the safe alternative.
    • No phenytoin or barbiturates; both can drive her attack.
    • 3% saline 100 mL for the seizing hyponatraemia, repeated once or twice if needed.
    • Then her sodium rises no more than 10 mmol/L over the first day.
    • Haem arginate now for a severe attack, with carbohydrate and fluids; her pill is stopped.
    • Beta-blocker for her tachycardia and hypertension; ICU to watch her strength and cranial nerves. After surgery

Fatal mistakes

  • Phenytoin or a barbiturate to treat her seizure.
  • Thiopental or etomidate at induction.
  • Trying glucose alone and holding back haem when her attack is severe.

Checked against: Stoelting 8e · Barash 9e · Miller 10e

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