Physiology: apnoeic oxygenation: 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 · Physiology: apnoeic oxygenation

Sample item

How does nasal oxygen delivered during apnoea help maintain saturation?

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

The answer and the reasoning

D. Oxygen is absorbed from the alveoli faster than CO2 enters, drawing gas into the lungs

During apnoea, oxygen uptake of about 250 mL/min exceeds CO2 excretion into alveoli, which creates a negative pressure that draws oxygen from the patent airway. Nasal prongs or high-flow nasal oxygen can therefore prolong safe apnoea time, but CO2 still rises. It is a supplement to preoxygenation.

Option by option

  • A. It reduces oxygen consumption

    Consumption is not altered.

  • B. It prevents all desaturation indefinitely

    Desaturation is delayed but not prevented indefinitely.

  • C. It eliminates CO2 effectively

    CO2 continues to accumulate.

  • D. Oxygen is absorbed from the alveoli faster than CO2 enters, drawing gas into the lungs (correct)

    Correct. Net alveolar gas uptake draws oxygen down the airway.

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, Oxygen is absorbed from the alveoli faster than CO2 enters, drawing gas into the lungs. During apnoea, oxygen uptake of about 250 mL/min exceeds CO2 excretion into alveoli, which creates a negative pressure that draws oxygen from the patent airway.

Why is "It reduces oxygen consumption" not the answer?

Consumption is not altered.

Why is "It prevents all desaturation indefinitely" not the answer?

Desaturation is delayed but not prevented indefinitely.

Why is "It eliminates CO2 effectively" not the answer?

CO2 continues to accumulate.

What concept does this question test?

It tests Physiology: apnoeic oxygenation in Anaesthesia. Nasal prongs or high-flow nasal oxygen can therefore prolong safe apnoea time, but CO2 still rises. It is a supplement to preoxygenation.

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 Physiology: apnoeic oxygenation?

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.