Pre-anaesthetic assessment and perioperative principles: curriculum recognition: 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 · Pre-anaesthetic assessment and perioperative principles: curriculum recognition

Sample item

A 38-year-old man with a BMI of 46 kg/m2 is preoxygenated and then made apnoeic for intubation. His saturation falls within about two minutes, much faster than in a lean adult. Which physiological change mainly explains this?

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

The answer and the reasoning

B. Low functional residual capacity with raised oxygen consumption

In obesity the chest wall and abdominal mass reduce functional residual capacity, especially when supine and anaesthetised, so the oxygen store in the lungs is small. Oxygen consumption is also raised. Head-up positioning and CPAP preoxygenation lengthen the safe apnoea time.

Option by option

  • A. Raised lung compliance causing alveolar overdistension

    Compliance is reduced, not raised, in obesity.

  • B. Low functional residual capacity with raised oxygen consumption (correct)

    Correct. A small oxygen reserve and higher consumption cause rapid desaturation.

  • C. Reduced cardiac output with normal lung volumes

    Cardiac output is usually raised in obesity, and lung volumes are reduced.

  • D. Increased haemoglobin affinity for oxygen

    Haemoglobin affinity for oxygen is not altered by obesity.

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, Low functional residual capacity with raised oxygen consumption. In obesity the chest wall and abdominal mass reduce functional residual capacity, especially when supine and anaesthetised, so the oxygen store in the lungs is small.

Why is "Raised lung compliance causing alveolar overdistension" not the answer?

Compliance is reduced, not raised, in obesity.

Why is "Reduced cardiac output with normal lung volumes" not the answer?

Cardiac output is usually raised in obesity, and lung volumes are reduced.

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

Haemoglobin affinity for oxygen is not altered by obesity.

What concept does this question test?

It tests Pre-anaesthetic assessment and perioperative principles: curriculum recognition in Anaesthesia. Oxygen consumption is also raised. Head-up positioning and CPAP preoxygenation lengthen the safe apnoea time.

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 Pre-anaesthetic assessment and perioperative principles: curriculum recognition?

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.