Inhalational agents: Entonox: 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: Entonox

Sample item

Entonox is a 50:50 mixture of nitrous oxide and oxygen. What happens at temperatures below minus 6 degrees C?

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

The answer and the reasoning

D. The gases separate (Poynting effect)

Below its pseudocritical temperature of -5.5 degrees C, nitrous oxide liquefies and separates from oxygen, so the first gas delivered is oxygen and later nitrous oxide-rich, which risks a hypoxic mixture. Cylinders should be stored warm and inverted before use.

Option by option

  • A. Nitrous oxide polymerises

    Nitrous oxide does not polymerise.

  • B. Pressure rises sharply

    Pressure falls, not rises.

  • C. The mixture explodes

    Entonox does not explode, though it supports combustion.

  • D. The gases separate (Poynting effect) (correct)

    Correct. Separation is called the Poynting effect.

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 D, The gases separate (Poynting effect). Below its pseudocritical temperature of -5.

Why is "Nitrous oxide polymerises" not the answer?

Nitrous oxide does not polymerise.

Why is "Pressure rises sharply" not the answer?

Pressure falls, not rises.

Why is "The mixture explodes" not the answer?

Entonox does not explode, though it supports combustion.

What concept does this question test?

It tests Inhalational agents: Entonox in Anaesthesia. 5 degrees C, nitrous oxide liquefies and separates from oxygen, so the first gas delivered is oxygen and later nitrous oxide-rich, which risks a hypoxic mixture. Cylinders should be stored warm and inverted before use.

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 Inhalational agents: Entonox?

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.