Intravenous and inhalational agents: nitrous oxide in tympanoplasty: 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: nitrous oxide in tympanoplasty

Sample item

A patient undergoing tympanoplasty with a tympanic membrane graft is given nitrous oxide. Why is this undesirable?

AIt diffuses into the closed middle ear faster than nitrogen leaves, raising pressure and risking graft displacementBIt dissolves the graft materialCIt causes a fall in middle ear pressure that retracts the graftDIt irritates the eustachian tube mucosa and closes it permanently

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

The answer and the reasoning

A. It diffuses into the closed middle ear faster than nitrogen leaves, raising pressure and risking graft displacement

Nitrous oxide is far more soluble than nitrogen, so it enters closed air-filled cavities faster than nitrogen leaves. In the middle ear the pressure rises and may displace a graft, and on stopping the gas the pressure falls sharply. It is therefore avoided or stopped before the graft is placed.

Option by option

A. It diffuses into the closed middle ear faster than nitrogen leaves, raising pressure and risking graft displacement (correct)
Correct. Inward diffusion of the gas raises middle ear pressure.
B. It dissolves the graft material
Nitrous oxide has no effect on graft tissue.
C. It causes a fall in middle ear pressure that retracts the graft
Pressure rises during administration; the fall comes only after the gas is withdrawn.
D. It irritates the eustachian tube mucosa and closes it permanently
It does not permanently close the eustachian tube.

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, It diffuses into the closed middle ear faster than nitrogen leaves, raising pressure and risking graft displacement. Nitrous oxide is far more soluble than nitrogen, so it enters closed air-filled cavities faster than nitrogen leaves.

Why is "It dissolves the graft material" not the answer?

Nitrous oxide has no effect on graft tissue.

Why is "It causes a fall in middle ear pressure that retracts the graft" not the answer?

Pressure rises during administration; the fall comes only after the gas is withdrawn.

Why is "It irritates the eustachian tube mucosa and closes it permanently" not the answer?

It does not permanently close the eustachian tube.

What concept does this question test?

It tests Intravenous and inhalational agents: nitrous oxide in tympanoplasty in Anaesthesia. In the middle ear the pressure rises and may displace a graft, and on stopping the gas the pressure falls sharply. It is therefore avoided or stopped before the graft is placed.

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 Intravenous and inhalational agents: nitrous oxide in tympanoplasty?

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.