Thoracic anaesthesia: 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 · Thoracic anaesthesia

Sample item

A patient with a right lower lobe lesion undergoing lobectomy has one-lung ventilation with a double-lumen tube. The saturation falls shortly after the left lung is ventilated alone. Which physiological mechanism normally limits shunting through the collapsed lung?

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

The answer and the reasoning

C. Hypoxic pulmonary vasoconstriction

In the collapsed lung, alveolar hypoxia causes pulmonary arteriolar vasoconstriction that diverts blood to the ventilated lung and limits shunt. Volatile anaesthetics above about 1 MAC, vasodilators and some conditions blunt this response. Shunt falls as a result, and further measures include CPAP to the non-dependent lung and PEEP to the dependent lung.

Option by option

  • A. Reduced cardiac output

    A fall in cardiac output worsens hypoxaemia rather than limiting shunt.

  • B. Alveolar hyperventilation of the non-dependent lung

    The collapsed lung is not ventilated at all, so it cannot hyperventilate.

  • C. Hypoxic pulmonary vasoconstriction (correct)

    Correct. Hypoxic pulmonary vasoconstriction diverts blood from the collapsed lung.

  • D. Increased hypoxic drive from carotid bodies only

    Carotid chemoreceptor drive affects ventilation but does not redirect pulmonary blood flow.

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.

More Anaesthesia questions

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is C, Hypoxic pulmonary vasoconstriction. In the collapsed lung, alveolar hypoxia causes pulmonary arteriolar vasoconstriction that diverts blood to the ventilated lung and limits shunt.

Why is "Reduced cardiac output" not the answer?

A fall in cardiac output worsens hypoxaemia rather than limiting shunt.

Why is "Alveolar hyperventilation of the non-dependent lung" not the answer?

The collapsed lung is not ventilated at all, so it cannot hyperventilate.

Why is "Increased hypoxic drive from carotid bodies only" not the answer?

Carotid chemoreceptor drive affects ventilation but does not redirect pulmonary blood flow.

What concept does this question test?

It tests Thoracic anaesthesia in Anaesthesia. Volatile anaesthetics above about 1 MAC, vasodilators and some conditions blunt this response. Shunt falls as a result, and further measures include CPAP to the non-dependent lung and PEEP to the dependent lung.

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 Thoracic anaesthesia?

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.