Monitoring: methaemoglobinaemia and 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: methaemoglobinaemia and pulse oximetry

Sample item

In significant methaemoglobinaemia, the pulse oximeter reading tends towards which value?

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

The answer and the reasoning

B. About 85%

Methaemoglobin absorbs both wavelengths almost equally, driving the red to infrared ratio towards 1, which corresponds to a saturation of about 85%. The patient looks cyanosed despite a good PaO2.

Option by option

  • A. 60%

    60% is too low for the typical value.

  • B. About 85% (correct)

    Correct. Readings converge to about 85%.

  • C. 100%

    100% is not the typical pattern.

  • D. 40%

    40% is far too low.

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 B, About 85%. Methaemoglobin absorbs both wavelengths almost equally, driving the red to infrared ratio towards 1, which corresponds to a saturation of about 85%.

Why is "60%" not the answer?

60% is too low for the typical value.

Why is "100%" not the answer?

100% is not the typical pattern.

Why is "40%" not the answer?

40% is far too low.

What concept does this question test?

It tests Monitoring: methaemoglobinaemia and pulse oximetry in Anaesthesia. The patient looks cyanosed despite a good PaO2.

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 Monitoring: methaemoglobinaemia and 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.