Inhalational agents: second gas effect: 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 agents: second gas effect

Sample item

What is the second gas effect?

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

The answer and the reasoning

C. Rapid uptake of nitrous oxide at induction raises the alveolar concentration of a co-administered volatile agent

Fast uptake of a high concentration of nitrous oxide concentrates the remaining second gas in the alveoli and increases its alveolar fraction. It speeds induction slightly.

Option by option

  • A. Prolonged emergence due to nitrous oxide

    Prolonged emergence is not the second gas effect.

  • B. Reduced uptake of volatile agents when given with oxygen

    Oxygen does not reduce volatile uptake.

  • C. Rapid uptake of nitrous oxide at induction raises the alveolar concentration of a co-administered volatile agent (correct)

    Correct. This is the definition of second gas effect.

  • D. Reduction of MAC by opioids

    MAC reduction by opioids is a different interaction.

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 C, Rapid uptake of nitrous oxide at induction raises the alveolar concentration of a co-administered volatile agent. Fast uptake of a high concentration of nitrous oxide concentrates the remaining second gas in the alveoli and increases its alveolar fraction.

Why is "Prolonged emergence due to nitrous oxide" not the answer?

Prolonged emergence is not the second gas effect.

Why is "Reduced uptake of volatile agents when given with oxygen" not the answer?

Oxygen does not reduce volatile uptake.

Why is "Reduction of MAC by opioids" not the answer?

MAC reduction by opioids is a different interaction.

What concept does this question test?

It tests Inhalational agents: second gas effect in Anaesthesia. It speeds induction slightly.

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 agents: second gas effect?

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.