Inhalational agents: 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 · Inhalational agents

Sample item

A patient with a known untreated pneumothorax needs emergency anaesthesia before a chest drain can be placed. Which agent should be avoided, and why?

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

The answer and the reasoning

D. Nitrous oxide, because it enters the air-filled space faster than nitrogen leaves

Nitrous oxide is far more soluble in blood than nitrogen, so it diffuses into closed gas spaces much faster than nitrogen can diffuse out. A pneumothorax, obstructed bowel, air embolism or middle ear can therefore expand. Nitrous oxide should be avoided in these settings.

Option by option

  • A. Sevoflurane, because it is a bronchial irritant

    Sevoflurane is non-irritant and is a bronchodilator, and it does not expand air spaces.

  • B. Propofol, because it is lipid soluble and enters air spaces

    Propofol does not enter gas spaces or change their volume.

  • C. Ketamine, because it causes bronchoconstriction

    Ketamine tends to cause bronchodilatation and does not expand air spaces.

  • D. Nitrous oxide, because it enters the air-filled space faster than nitrogen leaves (correct)

    Correct. Its diffusion into the closed space enlarges a pneumothorax and may produce a tension pneumothorax.

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.

More Anaesthesia questions

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Nitrous oxide, because it enters the air-filled space faster than nitrogen leaves. Nitrous oxide is far more soluble in blood than nitrogen, so it diffuses into closed gas spaces much faster than nitrogen can diffuse out.

Why is "Sevoflurane, because it is a bronchial irritant" not the answer?

Sevoflurane is non-irritant and is a bronchodilator, and it does not expand air spaces.

Why is "Propofol, because it is lipid soluble and enters air spaces" not the answer?

Propofol does not enter gas spaces or change their volume.

Why is "Ketamine, because it causes bronchoconstriction" not the answer?

Ketamine tends to cause bronchodilatation and does not expand air spaces.

What concept does this question test?

It tests Inhalational agents in Anaesthesia. A pneumothorax, obstructed bowel, air embolism or middle ear can therefore expand. Nitrous oxide should be avoided in these settings.

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 Inhalational agents?

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.