A pregnant patient receiving magnesium sulfate therapy is being monitored. Which finding indicates magnesium toxicity?

Appeared in: NORCET 10 Prelims-2026

Explanation

A urine output of 10 mL/hr is significantly below the normal threshold of 30 mL/hr, indicating oliguria.
Magnesium is excreted by the kidneys, so low urine output causes the drug to accumulate in the body.
Oliguria is a primary and critical sign of impending magnesium toxicity, as it signals impaired renal clearance.
This accumulation can lead to severe complications, including respiratory depression and cardiac arrest.

Option A: A deep tendon reflex (DTR) of +3 indicates hyperreflexia (exaggerated reflexes). This is a sign of worsening preeclampsia, the very condition magnesium sulfate is used to treat.
Option B: A fetal heart rate (FHR) of 138 beats per minute is within the normal range for a fetus (110-160 bpm).
Option C: A respiratory rate of 17 breaths per minute is within the normal adult range (12-20 breaths/min).

Visual 1: Infographic: The 'BURP' mnemonic for magnesium toxicity (Blood pressure, Urine output, Respiratory rate, Patellar reflex).
Visual 2: Chart: A table comparing the signs of worsening preeclampsia (e.g., hyperreflexia) with the signs of magnesium toxicity (e.g., hyporeflexia, oliguria, respiratory depression).

Clinical Relevance

Nursing practice connection: Use the key finding related to Recognition of magnesium sulfate toxicity signs during pregnancy to guide bedside assessment, documentation, and the next nursing action.
Magnesium sulfate is a high-alert medication. Nurses must monitor patients receiving it vigilantly for signs of toxicity, as it can rapidly become life-threatening.
The standard nursing assessment for a patient on magnesium sulfate includes checking vital signs, deep tendon reflexes, and urine output at least hourly.
The antidote for magnesium toxicity, calcium gluconate, should always be readily available at the bedside whenever a patient is receiving a magnesium sulfate infusion.

How to Approach the Question

First, identify the core of the question: it asks for a sign of toxicity from magnesium sulfate.
Recall the mechanism and primary adverse effects of magnesium sulfate. It's a CNS depressant excreted by the kidneys.
Evaluate each option against the known signs of magnesium toxicity.
Option A (DTR +3): This is hyperreflexia, a sign of preeclampsia, not toxicity. Toxicity causes hyporeflexia.
Option B (FHR 138): This is a normal fetal heart rate.
Option C (RR 17): This is a normal respiratory rate. Toxicity causes respiratory depression (<12).

Concept Tested & Keywords

Concept Tested: Recognition of magnesium sulfate toxicity signs during pregnancy.
Stem keywords: magnesium sulfate, pregnant patient, magnesium toxicity
Lead-in keywords: indicates
Clinical cues: The patient is receiving magnesium sulfate, a high-alert medication requiring close monitoring.

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