Intravenous and inhalational agents: thiopentone in hypoalbuminaemia: 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 in hypoalbuminaemia

Sample item

A malnourished 55-year-old man with serum albumin 20 g/L and uraemia receives the usual 5 mg/kg of thiopentone and becomes deeply anaesthetised with marked hypotension. What is the mechanism?

AIncreased hepatic metabolism produces a toxic active metaboliteBImpaired renal excretion, as the drug is cleared unchanged by the kidneyCReduced protein binding raises the free, active fraction of this highly bound drugDComplete absence of redistribution into muscle and fat

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

The answer and the reasoning

C. Reduced protein binding raises the free, active fraction of this highly bound drug

Thiopentone is about 80 percent protein bound, so low albumin and uraemia raise the unbound fraction, and the same dose has a larger effect. Doses are reduced in hypoalbuminaemia, shock and the elderly.

Option by option

A. Increased hepatic metabolism produces a toxic active metabolite
Thiopentone is not converted into a toxic active metabolite by increased metabolism.
B. Impaired renal excretion, as the drug is cleared unchanged by the kidney
Thiopentone is metabolised by the liver and little is excreted unchanged.
C. Reduced protein binding raises the free, active fraction of this highly bound drug (correct)
Correct. More free drug means a larger effect from the same dose.
D. Complete absence of redistribution into muscle and fat
Redistribution still occurs; it is the protein binding that explains the exaggerated response.

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 C, Reduced protein binding raises the free, active fraction of this highly bound drug. Thiopentone is about 80 percent protein bound, so low albumin and uraemia raise the unbound fraction, and the same dose has a larger effect.

Why is "Increased hepatic metabolism produces a toxic active metabolite" not the answer?

Thiopentone is not converted into a toxic active metabolite by increased metabolism.

Why is "Impaired renal excretion, as the drug is cleared unchanged by the kid…" not the answer?

Thiopentone is metabolised by the liver and little is excreted unchanged.

Why is "Complete absence of redistribution into muscle and fat" not the answer?

Redistribution still occurs; it is the protein binding that explains the exaggerated response.

What concept does this question test?

It tests Intravenous and inhalational agents: thiopentone in hypoalbuminaemia in Anaesthesia. Doses are reduced in hypoalbuminaemia, shock and the elderly.

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 Intravenous and inhalational agents: thiopentone in hypoalbuminaemia?

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.