Intravenous and inhalational agents: thiopentone and muscle relaxant in one line: 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 · Intravenous and inhalational agents: thiopentone and muscle relaxant in one line

Sample item

Soon after thiopentone induction, rocuronium is injected through the same cannula without a flush, and the line turns cloudy with a white precipitate. What is the reason?

AAlkaline thiopentone solution, pH about 10.5, precipitates when mixed with an acidic drugBRocuronium is lipid-soluble and separates from the aqueous phaseCLight degrades thiopentone in the tubing into an insoluble compoundDBacterial contamination of the cannula hub formed a biofilm

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

The answer and the reasoning

A. Alkaline thiopentone solution, pH about 10.5, precipitates when mixed with an acidic drug

Thiopentone is prepared as a strongly alkaline sodium salt. When mixed in a line with acidic drugs such as muscle relaxants, the free acid of thiopentone precipitates and can block the cannula or embolise. The line is flushed between drugs.

Option by option

A. Alkaline thiopentone solution, pH about 10.5, precipitates when mixed with an acidic drug (correct)
Correct. The alkaline solution precipitates on contact with an acidic drug.
B. Rocuronium is lipid-soluble and separates from the aqueous phase
Rocuronium is an aqueous solution, and the precipitate comes from thiopentone.
C. Light degrades thiopentone in the tubing into an insoluble compound
Brief light exposure does not produce a precipitate in the line.
D. Bacterial contamination of the cannula hub formed a biofilm
Contamination would not produce an immediate cloudy precipitate between two drugs.

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 A, Alkaline thiopentone solution, pH about 10.5, precipitates when mixed with an acidic drug. Thiopentone is prepared as a strongly alkaline sodium salt.

Why is "Rocuronium is lipid-soluble and separates from the aqueous phase" not the answer?

Rocuronium is an aqueous solution, and the precipitate comes from thiopentone.

Why is "Light degrades thiopentone in the tubing into an insoluble compound" not the answer?

Brief light exposure does not produce a precipitate in the line.

Why is "Bacterial contamination of the cannula hub formed a biofilm" not the answer?

Contamination would not produce an immediate cloudy precipitate between two drugs.

What concept does this question test?

It tests Intravenous and inhalational agents: thiopentone and muscle relaxant in one line in Anaesthesia. When mixed in a line with acidic drugs such as muscle relaxants, the free acid of thiopentone precipitates and can block the cannula or embolise. The line is flushed between drugs.

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 Intravenous and inhalational agents: thiopentone and muscle relaxant in one line?

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.