Airway management: nitrous oxide and cuff pressure: 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 · Airway management: nitrous oxide and cuff pressure

Sample item

During a 5-hour operation with 66 percent nitrous oxide in oxygen, the cuff pressure of the tracheal tube rises from 25 to above 50 cm H2O. What explains this?

AWarming of air inside the cuffBNitrous oxide diffuses into the cuff faster than nitrogen leaves itCProgressive tracheal oedemaDAbsorption of plasticiser from the cuff

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

The answer and the reasoning

B. Nitrous oxide diffuses into the cuff faster than nitrogen leaves it

Nitrous oxide is far more soluble than nitrogen, so it enters air-filled cuffs faster than nitrogen diffuses out, raising pressure. High cuff pressure reduces mucosal blood flow and can cause ischaemic damage. Cuff pressure should be monitored or the cuff filled with saline, and kept below about 30 cm H2O.

Option by option

A. Warming of air inside the cuff
Warming gives a small change at most and cannot double the pressure.
B. Nitrous oxide diffuses into the cuff faster than nitrogen leaves it (correct)
Correct. The gas diffuses into the cuff down its concentration gradient faster than nitrogen leaves it.
C. Progressive tracheal oedema
Oedema narrows the lumen but does not change pressure measured inside the cuff.
D. Absorption of plasticiser from the cuff
Plasticiser absorption does not raise cuff pressure.

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 B, Nitrous oxide diffuses into the cuff faster than nitrogen leaves it. Nitrous oxide is far more soluble than nitrogen, so it enters air-filled cuffs faster than nitrogen diffuses out, raising pressure.

Why is "Warming of air inside the cuff" not the answer?

Warming gives a small change at most and cannot double the pressure.

Why is "Progressive tracheal oedema" not the answer?

Oedema narrows the lumen but does not change pressure measured inside the cuff.

Why is "Absorption of plasticiser from the cuff" not the answer?

Plasticiser absorption does not raise cuff pressure.

What concept does this question test?

It tests Airway management: nitrous oxide and cuff pressure in Anaesthesia. High cuff pressure reduces mucosal blood flow and can cause ischaemic damage. Cuff pressure should be monitored or the cuff filled with saline, and kept below about 30 cm H2O.

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 Airway management: nitrous oxide and cuff pressure?

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.