Complications and emergencies: hyperventilation and potassium: 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 · Complications and emergencies: hyperventilation and potassium

Sample item

A patient is mechanically hyperventilated to a PaCO2 of 20 mmHg during neurosurgery, and the serum potassium falls. What is the mechanism?

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

The answer and the reasoning

C. Alkalosis shifts potassium into cells in exchange for hydrogen ions

Alkalosis moves hydrogen ions out of cells and potassium in, lowering the plasma level without a change in total body potassium. The effect reverses when the alkalosis corrects, so hypokalaemia from hyperventilation is not treated with large doses of potassium.

Option by option

  • A. Increased renal potassium excretion within minutes

    Renal losses do not change this rapidly.

  • B. Dilution by crystalloid infusion

    Crystalloid dilution is minor and unrelated to the ventilator setting.

  • C. Alkalosis shifts potassium into cells in exchange for hydrogen ions (correct)

    Correct. Transcellular shift explains the fall.

  • D. Insulin release due to hypocapnia

    Hypocapnia does not trigger insulin release.

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 C, Alkalosis shifts potassium into cells in exchange for hydrogen ions. Alkalosis moves hydrogen ions out of cells and potassium in, lowering the plasma level without a change in total body potassium.

Why is "Increased renal potassium excretion within minutes" not the answer?

Renal losses do not change this rapidly.

Why is "Dilution by crystalloid infusion" not the answer?

Crystalloid dilution is minor and unrelated to the ventilator setting.

Why is "Insulin release due to hypocapnia" not the answer?

Hypocapnia does not trigger insulin release.

What concept does this question test?

It tests Complications and emergencies: hyperventilation and potassium in Anaesthesia. The effect reverses when the alkalosis corrects, so hypokalaemia from hyperventilation is not treated with large doses of potassium.

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 Complications and emergencies: hyperventilation and potassium?

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.