Airway management: desaturation in obesity: 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 · Airway management: desaturation in obesity

Sample item

Why does a morbidly obese patient desaturate within minutes of apnoea despite preoxygenation?

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

The answer and the reasoning

A. Reduced functional residual capacity with raised oxygen consumption

Chest wall and abdominal weight reduce the functional residual capacity, which is the oxygen store, while oxygen consumption is increased. The ramped position and apnoeic oxygenation extend the safe apnoea time.

Option by option

  • A. Reduced functional residual capacity with raised oxygen consumption (correct)

    Correct. A small oxygen reserve with high consumption leads to rapid desaturation.

  • B. Raised haemoglobin affinity for oxygen

    Haemoglobin affinity is not altered by obesity.

  • C. Increased dead space in the airway

    Increased dead space affects carbon dioxide clearance, not the oxygen reserve.

  • D. Reduced diffusion across the alveolar membrane

    Membrane diffusion is not the main problem.

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 A, Reduced functional residual capacity with raised oxygen consumption. Chest wall and abdominal weight reduce the functional residual capacity, which is the oxygen store, while oxygen consumption is increased.

Why is "Raised haemoglobin affinity for oxygen" not the answer?

Haemoglobin affinity is not altered by obesity.

Why is "Increased dead space in the airway" not the answer?

Increased dead space affects carbon dioxide clearance, not the oxygen reserve.

Why is "Reduced diffusion across the alveolar membrane" not the answer?

Membrane diffusion is not the main problem.

What concept does this question test?

It tests Airway management: desaturation in obesity in Anaesthesia. The ramped position and apnoeic oxygenation extend the safe apnoea time.

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 Airway management: desaturation in obesity?

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.