Muscle relaxants: volatile agents potentiate block: 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 · Muscle relaxants: volatile agents potentiate block

Sample item

During a long laparotomy under 1.5 MAC sevoflurane, the interval between rocuronium top-ups is much longer than it was in an earlier case under propofol infusion. What is the best explanation?

ASevoflurane inhibits plasma cholinesteraseBVolatile agents potentiate non-depolarising blockCSevoflurane displaces rocuronium from plasma proteins into muscleDSevoflurane increases the number of junctional receptors

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

The answer and the reasoning

B. Volatile agents potentiate non-depolarising block

Inhalational agents, especially sevoflurane, desflurane and isoflurane, enhance non-depolarising block in a dose-dependent way, so less relaxant is needed than under intravenous anaesthesia. The effect is partly central and partly at the postjunctional membrane. The anaesthetist must therefore adjust relaxant doses to the technique.

Option by option

A. Sevoflurane inhibits plasma cholinesterase
Rocuronium is cleared by liver and kidney and does not depend on plasma cholinesterase.
B. Volatile agents potentiate non-depolarising block (correct)
Correct. Volatile agents add to the block, lengthening the effect of each dose.
C. Sevoflurane displaces rocuronium from plasma proteins into muscle
Protein-binding displacement is not a recognised action of sevoflurane on relaxants.
D. Sevoflurane increases the number of junctional receptors
More receptors would make the patient resistant, the opposite of what was seen.

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 B, Volatile agents potentiate non-depolarising block. Inhalational agents, especially sevoflurane, desflurane and isoflurane, enhance non-depolarising block in a dose-dependent way, so less relaxant is needed than under intravenous anaesthesia.

Why is "Sevoflurane inhibits plasma cholinesterase" not the answer?

Rocuronium is cleared by liver and kidney and does not depend on plasma cholinesterase.

Why is "Sevoflurane displaces rocuronium from plasma proteins into muscle" not the answer?

Protein-binding displacement is not a recognised action of sevoflurane on relaxants.

Why is "Sevoflurane increases the number of junctional receptors" not the answer?

More receptors would make the patient resistant, the opposite of what was seen.

What concept does this question test?

It tests Muscle relaxants: volatile agents potentiate block in Anaesthesia. The effect is partly central and partly at the postjunctional membrane. The anaesthetist must therefore adjust relaxant doses to the technique.

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 Muscle relaxants: volatile agents potentiate block?

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.