Burns: carbon monoxide poisoning: practice question

A General Surgery question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Surgery · Burns: carbon monoxide poisoning

Sample item

A 24-year-old woman from a smoke-filled kitchen fire has headache, confusion and nausea. Pulse oximetry reads 99% on room air, and the carboxyhaemoglobin is 30%. What is the immediate treatment?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. 100% oxygen through a non-rebreather mask

Carbon monoxide binds haemoglobin with about 200 times the affinity of oxygen, and standard pulse oximeters cannot distinguish carboxyhaemoglobin from oxyhaemoglobin, so readings are falsely normal. High-flow 100% oxygen shortens the half-life of carboxyhaemoglobin from about 4 to 5 hours on room air to roughly an hour. Hyperbaric oxygen is considered in severe cases.

Option by option

  • A. Room air since the saturation is normal

    A normal oximetry reading is misleading and does not exclude toxicity.

  • B. 100% oxygen through a non-rebreather mask (correct)

    Correct. 100% oxygen speeds the dissociation of carbon monoxide from haemoglobin.

  • C. Intravenous hydroxocobalamin for isolated carbon monoxide poisoning

    Hydroxocobalamin is the antidote for cyanide toxicity and has no role in isolated carbon monoxide poisoning.

  • D. Intravenous methylene blue

    Methylene blue treats methaemoglobinaemia and not carboxyhaemoglobinaemia.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this General Surgery question

What is the answer to this General Surgery question?

The best answer is B, 100% oxygen through a non-rebreather mask. Carbon monoxide binds haemoglobin with about 200 times the affinity of oxygen, and standard pulse oximeters cannot distinguish carboxyhaemoglobin from oxyhaemoglobin, so readings are falsely normal.

Why is "Room air since the saturation is normal" not the answer?

A normal oximetry reading is misleading and does not exclude toxicity.

Why is "Intravenous hydroxocobalamin for isolated carbon monoxide poisoning" not the answer?

Hydroxocobalamin is the antidote for cyanide toxicity and has no role in isolated carbon monoxide poisoning.

Why is "Intravenous methylene blue" not the answer?

Methylene blue treats methaemoglobinaemia and not carboxyhaemoglobinaemia.

What concept does this question test?

It tests Burns: carbon monoxide poisoning in General Surgery. High-flow 100% oxygen shortens the half-life of carboxyhaemoglobin from about 4 to 5 hours on room air to roughly an hour. Hyperbaric oxygen is considered in severe cases.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Burns: carbon monoxide poisoning?

Learn classic signs and eponyms alongside what they diagnose. Then use the flashcards and the other General Surgery questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.