Preoperative assessment: MAO inhibitor and vasopressors: 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 · Preoperative assessment: MAO inhibitor and vasopressors

Sample item

A woman on long-term phenelzine for depression becomes hypotensive after spinal anaesthesia. A usual dose of ephedrine is followed by a dangerous rise in blood pressure with severe headache. Which mechanism best explains the exaggerated response?

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

The answer and the reasoning

D. Ephedrine releases stored noradrenaline, which is not broken down because monoamine oxidase is inhibited

Ephedrine is an indirect sympathomimetic that works by releasing noradrenaline from nerve terminals. With monoamine oxidase inhibited, stores are large and the released transmitter is not degraded, causing a hypertensive crisis. A small dose of a direct-acting agent such as phenylephrine is safer.

Option by option

  • A. Phenelzine inhibits plasma cholinesterase, so ephedrine is not metabolised

    Plasma cholinesterase has no role in ephedrine metabolism.

  • B. Phenelzine blocks beta receptors, leaving ephedrine's alpha effect unopposed

    Phenelzine does not block beta receptors; it inhibits an enzyme.

  • C. Phenelzine up-regulates alpha-1 receptors, so ephedrine acts directly on them

    Phenelzine does not up-regulate alpha receptors, and ephedrine acts mainly indirectly.

  • D. Ephedrine releases stored noradrenaline, which is not broken down because monoamine oxidase is inhibited (correct)

    Correct. Indirect agents cause a large release of transmitter that cannot be degraded.

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, Ephedrine releases stored noradrenaline, which is not broken down because monoamine oxidase is inhibited. Ephedrine is an indirect sympathomimetic that works by releasing noradrenaline from nerve terminals.

Why is "Phenelzine inhibits plasma cholinesterase, so ephedrine is not metabo…" not the answer?

Plasma cholinesterase has no role in ephedrine metabolism.

Why is "Phenelzine blocks beta receptors, leaving ephedrine's alpha effect un…" not the answer?

Phenelzine does not block beta receptors; it inhibits an enzyme.

Why is "Phenelzine up-regulates alpha-1 receptors, so ephedrine acts directly…" not the answer?

Phenelzine does not up-regulate alpha receptors, and ephedrine acts mainly indirectly.

What concept does this question test?

It tests Preoperative assessment: MAO inhibitor and vasopressors in Anaesthesia. With monoamine oxidase inhibited, stores are large and the released transmitter is not degraded, causing a hypertensive crisis. A small dose of a direct-acting agent such as phenylephrine is safer.

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 Preoperative assessment: MAO inhibitor and vasopressors?

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.