Physiology: preoxygenation: 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: preoxygenation

Sample item

What is the principle of preoxygenation before induction?

ALowering oxygen consumptionBIncreasing dissolved oxygen in plasma onlyCReplacing the nitrogen in the functional residual capacity with oxygen to extend safe apnoea timeDReducing the functional residual capacity

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

The answer and the reasoning

C. Replacing the nitrogen in the functional residual capacity with oxygen to extend safe apnoea time

Breathing 100 percent oxygen for about 3 minutes of tidal breathing, or 8 deep breaths, denitrogenates the lungs. The oxygen stored in the functional residual capacity then sustains oxygenation for several minutes of apnoea. Head-up positioning increases the reserve.

Option by option

A. Lowering oxygen consumption
Consumption is not changed.
B. Increasing dissolved oxygen in plasma only
Dissolved oxygen is a minor contributor.
C. Replacing the nitrogen in the functional residual capacity with oxygen to extend safe apnoea time (correct)
Correct. The lungs become an oxygen reservoir.
D. Reducing the functional residual capacity
A larger, not smaller, functional residual capacity is helpful.

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 C, Replacing the nitrogen in the functional residual capacity with oxygen to extend safe apnoea time. Breathing 100 percent oxygen for about 3 minutes of tidal breathing, or 8 deep breaths, denitrogenates the lungs.

Why is "Lowering oxygen consumption" not the answer?

Consumption is not changed.

Why is "Increasing dissolved oxygen in plasma only" not the answer?

Dissolved oxygen is a minor contributor.

Why is "Reducing the functional residual capacity" not the answer?

A larger, not smaller, functional residual capacity is helpful.

What concept does this question test?

It tests Physiology: preoxygenation in Anaesthesia. The oxygen stored in the functional residual capacity then sustains oxygenation for several minutes of apnoea. Head-up positioning increases the reserve.

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: preoxygenation?

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.