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

Which wavelengths are used by a conventional two-wavelength pulse oximeter?

A660 nm red and 940 nm infraredB250 nm and 300 nmC400 nm and 500 nmD1200 nm and 1500 nm

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

The answer and the reasoning

A. 660 nm red and 940 nm infrared

Oxyhaemoglobin absorbs more infrared (940 nm) and deoxyhaemoglobin more red light (660 nm). The ratio of pulsatile absorbances provides saturation.

Option by option

A. 660 nm red and 940 nm infrared (correct)
Correct. Red 660 nm and infrared 940 nm are used.
B. 250 nm and 300 nm
These are ultraviolet wavelengths.
C. 400 nm and 500 nm
Those wavelengths are in the blue and green range.
D. 1200 nm and 1500 nm
These are far infrared wavelengths.

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.

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is A, 660 nm red and 940 nm infrared. Oxyhaemoglobin absorbs more infrared (940 nm) and deoxyhaemoglobin more red light (660 nm).

Why is "250 nm and 300 nm" not the answer?

These are ultraviolet wavelengths.

Why is "400 nm and 500 nm" not the answer?

Those wavelengths are in the blue and green range.

Why is "1200 nm and 1500 nm" not the answer?

These are far infrared wavelengths.

What concept does this question test?

It tests Monitoring: pulse oximetry in Anaesthesia. The ratio of pulsatile absorbances provides saturation.

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.