Neuraxial opioids: intrathecal morphine: 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 · Neuraxial opioids: intrathecal morphine

Sample item

A patient given intrathecal morphine 100 micrograms develops respiratory depression 12 hours later. Why?

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

The answer and the reasoning

B. Hydrophilic morphine spreads rostrally in CSF to the brainstem

Morphine is hydrophilic and remains in CSF for a long time, reaching the respiratory centres up to 12 to 24 hours later, so monitoring must continue overnight. Pruritus, urinary retention and nausea are also common.

Option by option

  • A. Hepatic accumulation

    Hepatic accumulation does not account for a delayed event.

  • B. Hydrophilic morphine spreads rostrally in CSF to the brainstem (correct)

    Correct. Rostral spread causes delayed depression.

  • C. Rapid redistribution to fat

    Fat redistribution is the course of lipophilic drugs.

  • D. Residual spinal block

    Residual spinal block does not depress respiration at this time.

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 B, Hydrophilic morphine spreads rostrally in CSF to the brainstem. Morphine is hydrophilic and remains in CSF for a long time, reaching the respiratory centres up to 12 to 24 hours later, so monitoring must continue overnight.

Why is "Hepatic accumulation" not the answer?

Hepatic accumulation does not account for a delayed event.

Why is "Rapid redistribution to fat" not the answer?

Fat redistribution is the course of lipophilic drugs.

Why is "Residual spinal block" not the answer?

Residual spinal block does not depress respiration at this time.

What concept does this question test?

It tests Neuraxial opioids: intrathecal morphine in Anaesthesia. Pruritus, urinary retention and nausea are also common.

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 Neuraxial opioids: intrathecal morphine?

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.