Maternal health: magnesium sulphate toxicity: practice question

A PSM 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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PSM · Maternal health: magnesium sulphate toxicity

Sample item

A woman with eclampsia is on the Pritchard regimen of magnesium sulphate. Before the next maintenance dose, her respiratory rate is 18 per minute, urine output is 50 mL per hour and the patellar reflex is absent. What should be done?

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

The answer and the reasoning

D. Withhold the next dose and monitor closely

Loss of the patellar reflex is the earliest sign of magnesium toxicity, appearing before respiratory depression and cardiac arrest. The next dose is withheld when the reflex is absent, respiratory rate is below 16 per minute or urine output is below 30 mL per hour. Calcium gluconate 1 g intravenously is given as the antidote if respiratory depression or arrest occurs.

Option by option

  • A. Double the next dose to prevent a seizure

    Doubling the dose would worsen toxicity.

  • B. Give 10% calcium gluconate immediately

    Calcium gluconate is the antidote for respiratory depression and is not needed with normal respiration.

  • C. Give the next dose as scheduled

    Continuing as scheduled risks respiratory depression and cardiac arrest.

  • D. Withhold the next dose and monitor closely (correct)

    Correct. An absent patellar reflex means the next dose must be held and the patient observed.

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.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, Withhold the next dose and monitor closely. Loss of the patellar reflex is the earliest sign of magnesium toxicity, appearing before respiratory depression and cardiac arrest.

Why is "Double the next dose to prevent a seizure" not the answer?

Doubling the dose would worsen toxicity.

Why is "Give 10% calcium gluconate immediately" not the answer?

Calcium gluconate is the antidote for respiratory depression and is not needed with normal respiration.

Why is "Give the next dose as scheduled" not the answer?

Continuing as scheduled risks respiratory depression and cardiac arrest.

What concept does this question test?

It tests Maternal health: magnesium sulphate toxicity in PSM. The next dose is withheld when the reflex is absent, respiratory rate is below 16 per minute or urine output is below 30 mL per hour. Calcium gluconate 1 g intravenously is given as the antidote if respiratory depression or arrest occurs.

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 Maternal health: magnesium sulphate toxicity?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.