Suspected carbon monoxide poisoning — MRCEM SBA MCQ

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EasyResuscitation and critical illnessSuspected carbon monoxide poisoningMRCEM SBA

A 42-year-old man is brought to the emergency department after being found confused in a closed garage with a petrol generator running. He has a headache and nausea. His GCS is 14/15, blood pressure is 128/76 mmHg, capillary glucose is 5.6 mmol/L and SpO₂ is 99% on air. He is breathing adequately and has not yet received oxygen. Which immediate management plan is most appropriate?

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Correct answer: A — Give oxygen at 15 L/min via a reservoir mask and obtain venous blood for carboxyhaemoglobin measurement now.

The enclosed-space generator exposure, headache and confusion make carbon monoxide poisoning a serious concern. His reassuring SpO₂ does not exclude it: an ordinary pulse oximeter cannot distinguish carboxyhaemoglobin from oxyhaemoglobin. UKHSA guidance recommends high-concentration oxygen immediately, irrespective of the displayed saturation, and urgent arterial or venous carboxyhaemoglobin measurement. Oxygen should not be delayed while the sample is taken. ([assets.publishing.service.gov.uk](https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf)) B offers the right diagnostic test but insufficient oxygen for suspected poisoning; low-flow oxygen would be appropriate for a different indication requiring modest supplementation. C supplies appropriate oxygen, but arterial oxygen tension alone does not measure carboxyhaemoglobin; an arterial sample would be suitable if carboxyhaemoglobin were measured on it. D correctly seeks carboxyhaemoglobin but wrongly treats the normal SpO₂ as a reason to withhold oxygen. E starts appropriate treatment but needlessly postpones the urgent measurement; carboxyhaemoglobin falls after removal from exposure and with oxygen treatment. The patient also needs continued assessment, including cardiac rhythm evaluation, while the result and clinical course are reviewed. ([assets.publishing.service.gov.uk](https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf))

Reference: UKHSA, Carbon monoxide: incident management (May 2022) — https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/337629/CARBON_MONOXIDE_Incident_management_v3-1.pdf UKHSA, Carbon monoxide: toxicological overview (24 May 2022) — https://www.gov.uk/government/publications/carbon-monoxide-properties-incident-management-and-toxicology/carbon-monoxide-toxicological-overview