Respiratory physiology and ventilation: curriculum recognition: 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 · Respiratory physiology and ventilation: curriculum recognition

Sample item

In a paralysed patient on controlled ventilation with constant CO2 production, the volume of fresh gas reaching perfused alveoli each minute is doubled. What happens to the arterial PaCO2?

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

The answer and the reasoning

D. Falls to about half

PaCO2 is directly proportional to CO2 production and inversely proportional to alveolar ventilation. Doubling the effective ventilation therefore halves the PaCO2 when production is constant. Oxygenation is much less sensitive to the same change.

Option by option

  • A. Rises slightly

    A rise would occur with reduced ventilation, not increased ventilation.

  • B. Doubles

    Doubling would follow halving the ventilation, not doubling it.

  • C. Remains unchanged

    PaCO2 changes whenever alveolar ventilation changes at constant production.

  • D. Falls to about half (correct)

    Correct. PaCO2 varies inversely with alveolar ventilation.

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, Falls to about half. PaCO2 is directly proportional to CO2 production and inversely proportional to alveolar ventilation.

Why is "Rises slightly" not the answer?

A rise would occur with reduced ventilation, not increased ventilation.

Why is "Doubles" not the answer?

Doubling would follow halving the ventilation, not doubling it.

Why is "Remains unchanged" not the answer?

PaCO2 changes whenever alveolar ventilation changes at constant production.

What concept does this question test?

It tests Respiratory physiology and ventilation: curriculum recognition in Anaesthesia. Doubling the effective ventilation therefore halves the PaCO2 when production is constant. Oxygenation is much less sensitive to the same change.

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 Respiratory physiology and ventilation: curriculum recognition?

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.