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Suspected carbon monoxide poisoning — MRCEM SBA MCQ

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EasyToxicology and environmental emergenciesSuspected carbon monoxide poisoningMRCEM SBA

A 38-year-old man presents to the emergency department with headache and nausea after spending the night in a flat with a faulty gas boiler. His partner has developed similar symptoms. Both have left the flat. He is alert and has had no syncope or chest pain. His SpO₂ is 99% on air, and he has not yet received oxygen. What is the most appropriate immediate management plan?

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

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Correct answer: C — Start reservoir-mask oxygen; request urgent venous carboxyhaemoglobin measurement.

Headache and nausea in two people who shared a flat with a faulty gas boiler make carbon monoxide poisoning likely. The SpO₂ of 99% does not exclude it: a standard pulse oximeter cannot distinguish carboxyhaemoglobin from oxyhaemoglobin. Give high-concentration oxygen immediately, irrespective of the displayed saturation, and obtain an urgent venous sample for carboxyhaemoglobin measurement. Treatment must not wait for the result. ([gov.uk](https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf)) A requests the appropriate test but delays oxygen. B gives appropriate oxygen but substitutes standard pulse oximetry for a measurement it cannot provide. D obtains the appropriate sample but uses a saturation target that is unreliable in this poisoning. E gives appropriate initial oxygen, but immediate hyperbaric transfer is not established by this presentation; further clinical assessment and specialist advice are appropriate if severe poisoning is suspected. His partner also requires assessment, and both must be warned not to use the suspect appliance pending safety checks. ([gov.uk](https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf))

Reference: UKHSA, Carbon monoxide: incident management — Clinical decontamination and first aid (May 2022) — https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf UKHSA, Diagnosing Poisoning: Carbon Monoxide (CO) (2015) — https://assets.publishing.service.gov.uk/media/5a7568fb40f0b6360e473e60/CO_diagnosis_algorithm_2015.pdf