Complications and emergencies: carbon monoxide poisoning treatment: practice question

A Anaesthesia 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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Anaesthesia · Complications and emergencies: carbon monoxide poisoning treatment

Sample item

A man rescued from an enclosed house fire is drowsy with a headache. SpO2 reads 99 percent on room air and co-oximetry shows a carboxyhaemoglobin level of 30 percent. What is the most appropriate immediate treatment?

A100 percent oxygen via a non-rebreather maskBIntravenous methylene blue to displace carbon monoxideCObservation on room air as saturation is normalDA sodium bicarbonate infusion to correct acidosis

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

The answer and the reasoning

A. 100 percent oxygen via a non-rebreather mask

A standard pulse oximeter reads carboxyhaemoglobin as oxyhaemoglobin, so the saturation is falsely normal. Carbon monoxide binds haemoglobin about 200 times more tightly than oxygen, and high-flow oxygen shortens its half-life from several hours on air to about an hour. Hyperbaric oxygen is considered in severe cases.

Option by option

A. 100 percent oxygen via a non-rebreather mask (correct)
Correct. The highest possible FiO2 competes with carbon monoxide for haemoglobin and speeds its elimination.
B. Intravenous methylene blue to displace carbon monoxide
Methylene blue treats methaemoglobinaemia and does not remove carbon monoxide from haemoglobin.
C. Observation on room air as saturation is normal
A normal pulse oximeter reading is unreliable here, and leaving the patient on air prolongs carbon monoxide binding.
D. A sodium bicarbonate infusion to correct acidosis
Bicarbonate treats metabolic acidosis and has no effect on carboxyhaemoglobin.

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.

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is A, 100 percent oxygen via a non-rebreather mask. A standard pulse oximeter reads carboxyhaemoglobin as oxyhaemoglobin, so the saturation is falsely normal.

Why is "Intravenous methylene blue to displace carbon monoxide" not the answer?

Methylene blue treats methaemoglobinaemia and does not remove carbon monoxide from haemoglobin.

Why is "Observation on room air as saturation is normal" not the answer?

A normal pulse oximeter reading is unreliable here, and leaving the patient on air prolongs carbon monoxide binding.

Why is "A sodium bicarbonate infusion to correct acidosis" not the answer?

Bicarbonate treats metabolic acidosis and has no effect on carboxyhaemoglobin.

What concept does this question test?

It tests Complications and emergencies: carbon monoxide poisoning treatment in Anaesthesia. Carbon monoxide binds haemoglobin about 200 times more tightly than oxygen, and high-flow oxygen shortens its half-life from several hours on air to about an hour. Hyperbaric oxygen is considered in severe cases.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Complications and emergencies: carbon monoxide poisoning treatment?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia 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.