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

A 60-year-old smoker has SpO2 91 percent on room air with PaCO2 of 38 mmHg and a widened alveolar-arterial gradient. Oxygen by mask partly corrects the hypoxaemia, and the chest radiograph shows hyperinflation with airway secretions. Which mechanism is mainly responsible?

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

The answer and the reasoning

A. Ventilation-perfusion mismatch

Uneven airflow relative to blood flow is the commonest cause of hypoxaemia in lung disease and responds to supplemental oxygen. Hypoventilation would raise the PaCO2 with a normal gradient. A true shunt responds poorly to oxygen.

Option by option

  • A. Ventilation-perfusion mismatch (correct)

    Correct. A normal PaCO2, a wide gradient and a partial response to oxygen fit mismatch.

  • B. Alveolar hypoventilation

    Hypoventilation raises the PaCO2 and leaves the alveolar-arterial gradient normal.

  • C. Anatomical right-to-left shunt

    A true shunt is largely unresponsive to a higher inspired oxygen concentration.

  • D. Diffusion limitation

    Diffusion limitation is rarely the sole cause at rest and does not fit this picture.

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 A, Ventilation-perfusion mismatch. Uneven airflow relative to blood flow is the commonest cause of hypoxaemia in lung disease and responds to supplemental oxygen.

Why is "Alveolar hypoventilation" not the answer?

Hypoventilation raises the PaCO2 and leaves the alveolar-arterial gradient normal.

Why is "Anatomical right-to-left shunt" not the answer?

A true shunt is largely unresponsive to a higher inspired oxygen concentration.

Why is "Diffusion limitation" not the answer?

Diffusion limitation is rarely the sole cause at rest and does not fit this picture.

What concept does this question test?

It tests Respiratory physiology and ventilation: curriculum recognition in Anaesthesia. Hypoventilation would raise the PaCO2 with a normal gradient. A true shunt responds poorly to oxygen.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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.