Monitoring: pulse oximetry: 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 · Monitoring: pulse oximetry

Sample item

A pulse oximeter continues to display 99% during apnea immediately after preoxygenation. Which limitation best explains why ventilation failure may initially be missed?

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

The answer and the reasoning

D. Oximetry measures oxygenation, not carbon dioxide elimination

Pulse oximetry estimates arterial oxygen saturation, which may remain normal for a time after preoxygenation despite absent ventilation. Capnography detects exhaled carbon dioxide and is more immediate for recognizing apnea or disconnection.

Option by option

  • A. Oximetry directly measures tidal volume

    Tidal volume requires other clinical or respiratory measurements.

  • B. Oximetry is unaffected by supplemental oxygen

    Supplemental oxygen can delay desaturation and mask hypoventilation on oximetry.

  • C. Oximetry measures neuromuscular recovery

    Neuromuscular recovery is assessed with quantitative or qualitative nerve stimulation.

  • D. Oximetry measures oxygenation, not carbon dioxide elimination (correct)

    Correct. Saturation can lag behind apnea, particularly when oxygen stores are high.

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, Oximetry measures oxygenation, not carbon dioxide elimination. Pulse oximetry estimates arterial oxygen saturation, which may remain normal for a time after preoxygenation despite absent ventilation.

Why is "Oximetry directly measures tidal volume" not the answer?

Tidal volume requires other clinical or respiratory measurements.

Why is "Oximetry is unaffected by supplemental oxygen" not the answer?

Supplemental oxygen can delay desaturation and mask hypoventilation on oximetry.

Why is "Oximetry measures neuromuscular recovery" not the answer?

Neuromuscular recovery is assessed with quantitative or qualitative nerve stimulation.

What concept does this question test?

It tests Monitoring: pulse oximetry in Anaesthesia. Capnography detects exhaled carbon dioxide and is more immediate for recognizing apnea or disconnection.

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 Monitoring: pulse oximetry?

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.