Which assessment is MOST important to monitor in a patient receiving magnesium sulfate for seizure prophylaxis in preeclampsia?

• A. Check deep tendon reflexes
• B. Observe for vaginal bleeding
• C. Check the respiratory rate
• D. Note the urine output

Answer: (C)

Monitoring respiratory status is essential when a patient is receiving magnesium sulfate for seizure prevention in preeclampsia because magnesium can depress the respiratory center. Respiratory depression is the most dangerous sign of magnesium toxicity, and catching a decline in breathing early can prevent life-threatening consequences. If the respiratory rate falls or breathing becomes shallow, withhold magnesium sulfate and promptly notify the provider; have calcium gluconate available as the antidote and be prepared to assist ventilation if needed.

Deep tendon reflexes are an important toxicity indicator—loss of reflexes suggests rising magnesium levels—but they don’t carry the same immediate risk to life as impaired respiration. Urine output reflects kidney function and magnesium excretion, and vaginal bleeding is a concern in preeclampsia overall, but neither directly signals magnesium toxicity as acutely as respiratory status.