Muscle relaxants: hypercapnia and failed reversal: 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: hypercapnia and failed reversal

Sample item

Half an hour after rocuronium, a ventilated patient still shows fade on train-of-four stimulation. Neostigmine with glycopyrrolate was given 10 minutes ago and twitch height has barely improved. Arterial gas shows pH 7.18 and PaCO2 78 mmHg. What is the best next step?

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

The answer and the reasoning

A. Increase ventilation to correct the respiratory acidosis and reassess

Respiratory acidosis potentiates non-depolarising block and opposes reversal by anticholinesterases. Correcting the hypercapnia restores the response, whereas extra neostigmine only adds muscarinic effects once its ceiling effect is reached. Always correct acid-base and temperature problems before blaming the drug.

Option by option

  • A. Increase ventilation to correct the respiratory acidosis and reassess (correct)

    Correct. Acidosis deepens non-depolarising block and weakens neostigmine, so correcting it is the logical step.

  • B. Give edrophonium together with atropine

    Edrophonium is a weaker anticholinesterase and fails for the same reason as neostigmine.

  • C. Give a small dose of suxamethonium to hasten recovery

    Suxamethonium given on top of a non-depolarising block is unpredictable and does not treat the cause.

  • D. Repeat neostigmine at double the first dose

    Neostigmine has a ceiling effect, so a larger dose adds side effects without more reversal.

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 A, Increase ventilation to correct the respiratory acidosis and reassess. Respiratory acidosis potentiates non-depolarising block and opposes reversal by anticholinesterases.

Why is "Give edrophonium together with atropine" not the answer?

Edrophonium is a weaker anticholinesterase and fails for the same reason as neostigmine.

Why is "Give a small dose of suxamethonium to hasten recovery" not the answer?

Suxamethonium given on top of a non-depolarising block is unpredictable and does not treat the cause.

Why is "Repeat neostigmine at double the first dose" not the answer?

Neostigmine has a ceiling effect, so a larger dose adds side effects without more reversal.

What concept does this question test?

It tests Muscle relaxants: hypercapnia and failed reversal in Anaesthesia. Correcting the hypercapnia restores the response, whereas extra neostigmine only adds muscarinic effects once its ceiling effect is reached. Always correct acid-base and temperature problems before blaming the drug.

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 Muscle relaxants: hypercapnia and failed reversal?

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.