Intravenous and inhalational agents: tube cuff pressure with nitrous oxide: 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: tube cuff pressure with nitrous oxide

Sample item

During a three-hour anaesthetic with 66 percent nitrous oxide, the pilot balloon feels tighter and cuff pressure is above 40 cm H2O. What is the explanation?

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

The answer and the reasoning

B. Nitrous oxide diffuses into the air-filled cuff, increasing its volume and pressure

Nitrous oxide diffuses into the air-filled cuff faster than nitrogen diffuses out, so cuff pressure rises and can exceed capillary perfusion pressure of the tracheal mucosa. Cuff pressure is monitored and kept at 20 to 30 cm H2O, or the cuff is filled with the gas mixture.

Option by option

  • A. Warming of the tube softens it and tightens the cuff

    Warming the tube does not significantly raise the pressure.

  • B. Nitrous oxide diffuses into the air-filled cuff, increasing its volume and pressure (correct)

    Correct. Inward diffusion of nitrous oxide expands the cuff.

  • C. The tube has migrated into a bronchus

    Bronchial migration affects ventilation, not the cuff pressure.

  • D. Airway secretions are compressing the cuff

    Secretions outside the cuff do not change the pressure within it.

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 B, Nitrous oxide diffuses into the air-filled cuff, increasing its volume and pressure. Nitrous oxide diffuses into the air-filled cuff faster than nitrogen diffuses out, so cuff pressure rises and can exceed capillary perfusion pressure of the tracheal mucosa.

Why is "Warming of the tube softens it and tightens the cuff" not the answer?

Warming the tube does not significantly raise the pressure.

Why is "The tube has migrated into a bronchus" not the answer?

Bronchial migration affects ventilation, not the cuff pressure.

Why is "Airway secretions are compressing the cuff" not the answer?

Secretions outside the cuff do not change the pressure within it.

What concept does this question test?

It tests Intravenous and inhalational agents: tube cuff pressure with nitrous oxide in Anaesthesia. Cuff pressure is monitored and kept at 20 to 30 cm H2O, or the cuff is filled with the gas mixture.

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: tube cuff pressure with nitrous oxide?

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.