A client with severe preeclampsia is receiving magnesium sulfate by continuous IV infusion. Which assessment finding would indicate that the medication should be discontinued?

• A. Absence of deep tendon reflexes
• B. Respiratory rate of 16 breaths per minute
• C. Urinary output of 45 mL during the past hour
• D. Decrease in blood pressure from 180/100 mm Hg to 150/90 mm Hg

Answer: (A)

Magnesium sulfate is used to prevent seizures in severe preeclampsia, but it depresses neuromuscular function as levels rise. The earliest reliable sign of toxicity is the loss of deep tendon reflexes. When reflexes disappear, it indicates the medication is accumulating to a dangerous level, and the infusion should be stopped immediately. Have calcium gluconate available as the antidote and monitor the patient closely for airway, breathing, and hemodynamics.

The other findings shown are not signs of magnesium toxicity. A respiratory rate of 16 is normal and compatible with safe breathing. Urine output of 45 mL in an hour indicates adequate kidney function and fluid clearance. A blood pressure decrease from 180/100 to 150/90 reflects clinical improvement in hypertension rather than a toxicity issue.