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Carbon monoxide poisoning — SCE Acute Medicine MCQ

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ModerateToxicology and OverdoseCarbon monoxide poisoningSCE Acute Medicine

A 31-year-old woman is assessed on the acute medical unit. She has headache, dizziness and collapse after a faulty boiler alarm. Pulse oximetry reads 99% but blood gas co-oximetry shows carboxyhaemoglobin 24%. Initial assessment includes relevant observations, bedside tests and urgent blood results. What is the most likely diagnosis?

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Correct answer: E — Carbon monoxide poisoning

Carbon monoxide poisoning is the best answer because normal pulse oximetry does not exclude carbon monoxide poisoning because it cannot distinguish oxyhaemoglobin from carboxyhaemoglobin. Upper gastrointestinal bleeding is plausible, but it is less appropriate for the physiology or timing described in this stem. The other distractors either fit a neighbouring presentation, delay definitive treatment, or miss the key immediate risk. Clinical pearl: Co-oximetry is required when CO poisoning is suspected.

Reference: https://www.gov.uk/government/organisations/uk-health-security-agency#acute-medicine-order-41-1