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Methemoglobinaemia — NDEB AFK MCQ

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ModerateBiomedical SciencesMethemoglobinaemiaNDEB AFK

A 38-year-old develops cyanosis and shortness of breath after receiving a high dose of prilocaine for multiple restorations. Pulse oximetry remains low despite oxygen, and blood appears chocolate-brown. What is the most likely cause/mechanism?

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Correct answer: A — Oxidation of haemoglobin iron to the ferric state

Prilocaine can precipitate methemoglobinaemia, in which haemoglobin iron is oxidised to the ferric state and cannot carry oxygen effectively. Oxygen alone may not correct the saturation reading because the problem is haemoglobin function. The pearl is to recognise persistent cyanosis after certain local anaesthetics and arrange urgent medical management.

Reference: Canadian dental pharmacology reference texts; NDEB KSAs 2024