Respiratory system: effect of PEEP: practice question

A Physiology 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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Physiology · Respiratory system: effect of PEEP

Sample item

Positive end-expiratory pressure improves oxygenation in acute respiratory distress syndrome mainly by which mechanism?

AIncreasing anatomical dead spaceBRecruiting collapsed alveoli and raising FRC to cut shuntCLowering the work of exhalation by increasing elastic recoilDIncreasing venous return and cardiac output

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

The answer and the reasoning

B. Recruiting collapsed alveoli and raising FRC to cut shunt

In ARDS, many alveoli are collapsed or flooded, and perfusion of these units produces shunt. PEEP keeps alveoli open at end-expiration, which raises the functional residual capacity, improves compliance and reduces shunt. Its drawbacks are a fall in venous return and the risk of overdistension.

Option by option

A. Increasing anatomical dead space
PEEP does not improve oxygenation by raising dead space, which would worsen gas exchange.
B. Recruiting collapsed alveoli and raising FRC to cut shunt (correct)
Correct. Keeping alveoli open reduces shunt and raises FRC.
C. Lowering the work of exhalation by increasing elastic recoil
PEEP does not increase elastic recoil, and its benefit is on oxygenation.
D. Increasing venous return and cardiac output
PEEP tends to reduce venous return and cardiac output, which is a side effect.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Recruiting collapsed alveoli and raising FRC to cut shunt. In ARDS, many alveoli are collapsed or flooded, and perfusion of these units produces shunt.

Why is "Increasing anatomical dead space" not the answer?

PEEP does not improve oxygenation by raising dead space, which would worsen gas exchange.

Why is "Lowering the work of exhalation by increasing elastic recoil" not the answer?

PEEP does not increase elastic recoil, and its benefit is on oxygenation.

Why is "Increasing venous return and cardiac output" not the answer?

PEEP tends to reduce venous return and cardiac output, which is a side effect.

What concept does this question test?

It tests Respiratory system: effect of PEEP in Physiology. PEEP keeps alveoli open at end-expiration, which raises the functional residual capacity, improves compliance and reduces shunt. Its drawbacks are a fall in venous return and the risk of overdistension.

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 system: effect of PEEP?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.