Intravenous and inhalational agents: carbon monoxide from dry absorbent: 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 · Intravenous and inhalational agents: carbon monoxide from dry absorbent

Sample item

Several children operated on first on a Monday morning under desflurane through circle systems wake with headache and drowsiness. Pulse oximetry is normal, but co-oximetry shows an abnormal haemoglobin fraction. What explains this?

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

The answer and the reasoning

D. Degradation of desflurane by desiccated strong-base absorbent produces carbon monoxide

Dry carbon dioxide absorbent, which is more likely after gas flows over a weekend, degrades desflurane, enflurane and isoflurane to carbon monoxide, especially with barium hydroxide or potassium hydroxide absorbents. Pulse oximetry misreads carboxyhaemoglobin as oxyhaemoglobin, so co-oximetry is needed.

Option by option

  • A. A vaporiser fault delivering carbon monoxide

    A vaporiser fault does not produce carbon monoxide.

  • B. Exhaust gas from the scavenging system entering the circuit

    Scavenging exhaust does not return to the patient circuit in a correctly working system.

  • C. Compound A formed from desflurane in soda lime

    Compound A is a product of sevoflurane, not of desflurane.

  • D. Degradation of desflurane by desiccated strong-base absorbent produces carbon monoxide (correct)

    Correct. Desiccated absorbent turns the agent into carbon monoxide, which pulse oximetry does not detect.

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 Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Degradation of desflurane by desiccated strong-base absorbent produces carbon monoxide. Dry carbon dioxide absorbent, which is more likely after gas flows over a weekend, degrades desflurane, enflurane and isoflurane to carbon monoxide, especially with barium hydroxide or potassium hydroxide absorbents.

Why is "A vaporiser fault delivering carbon monoxide" not the answer?

A vaporiser fault does not produce carbon monoxide.

Why is "Exhaust gas from the scavenging system entering the circuit" not the answer?

Scavenging exhaust does not return to the patient circuit in a correctly working system.

Why is "Compound A formed from desflurane in soda lime" not the answer?

Compound A is a product of sevoflurane, not of desflurane.

What concept does this question test?

It tests Intravenous and inhalational agents: carbon monoxide from dry absorbent in Anaesthesia. Pulse oximetry misreads carboxyhaemoglobin as oxyhaemoglobin, so co-oximetry is needed.

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 Intravenous and inhalational agents: carbon monoxide from dry absorbent?

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.