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Methaemoglobinaemia after IVRA — FRCA Primary MCQ

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ModeratePharmacologyMethaemoglobinaemia after IVRAFRCA Primary

After intravenous regional anaesthesia, cyanosis develops with high PaO2 and a pulse oximeter reading near 85%. Which drug is most likely?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Prilocaine

Prilocaine can cause methaemoglobinaemia through o-toluidine metabolites. Nitrous oxide is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Glycopyrronium is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Ephedrine is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Suxamethonium is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA pharmacology, link the clinical effect to the receptor, distribution or elimination mechanism rather than memorising isolated facts.

Reference: Peck, Hill & Williams Pharmacology for Anaesthesia and Intensive Care; BNF; Primary FRCA textbooks