Inhalational anaesthetics: pharmacokinetics: 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 · Inhalational anaesthetics: pharmacokinetics

Sample item

When nitrous oxide is given in high concentration together with a volatile agent during induction, the alveolar concentration of the volatile agent rises faster than expected. This is called:

AThe Haldane effectBThe Bohr effectCDiffusion hypoxiaDThe second gas effect

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

The answer and the reasoning

D. The second gas effect

Rapid uptake of a large volume of nitrous oxide from the alveoli concentrates the remaining gases, including the volatile agent, and increases inspiratory flow, so the second gas rises in concentration faster. The concentration effect is the related principle for the first gas. Diffusion hypoxia is the opposite event at the end of anaesthesia, when nitrous oxide rapidly leaves the blood and dilutes alveolar oxygen.

Option by option

A. The Haldane effect
The Haldane effect describes how deoxygenation increases carbon dioxide carriage.
B. The Bohr effect
The Bohr effect is the shift of the oxygen-haemoglobin curve caused by carbon dioxide and pH.
C. Diffusion hypoxia
Diffusion hypoxia occurs on emergence from nitrous oxide and is unrelated to induction.
D. The second gas effect (correct)
Correct. Uptake of the first gas speeds the rise of the second gas.

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 D, The second gas effect. Rapid uptake of a large volume of nitrous oxide from the alveoli concentrates the remaining gases, including the volatile agent, and increases inspiratory flow, so the second gas rises in concentration faster.

Why is "The Haldane effect" not the answer?

The Haldane effect describes how deoxygenation increases carbon dioxide carriage.

Why is "The Bohr effect" not the answer?

The Bohr effect is the shift of the oxygen-haemoglobin curve caused by carbon dioxide and pH.

Why is "Diffusion hypoxia" not the answer?

Diffusion hypoxia occurs on emergence from nitrous oxide and is unrelated to induction.

What concept does this question test?

It tests Inhalational anaesthetics: pharmacokinetics in Anaesthesia. The concentration effect is the related principle for the first gas. Diffusion hypoxia is the opposite event at the end of anaesthesia, when nitrous oxide rapidly leaves the blood and dilutes alveolar oxygen.

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 Inhalational anaesthetics: pharmacokinetics?

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.