Preeclampsia is new high blood pressure after 20 weeks of pregnancy with protein in the urine or organ damage, and magnesium sulfate is given to prevent seizures. The kidneys clear magnesium, so too much of it, especially with low urine output, can stop reflexes, breathing and the heart.
Key symptoms
- Headache, vision changes and upper belly pain from preeclampsia
- Flushing, warmth and nausea as magnesium rises
- Muscle weakness and drowsiness
- Slurred speech and shallow breathing with severe toxicity
What you find on exam
- Blood pressure, often 160/110 mmHg or higher in severe disease
- Deep tendon reflexes: a lost knee jerk is an early sign of toxicity
- Respiratory rate below 12 and falling oxygen saturation
- Urine output below 30 mL per hour
Tests
- Serum magnesium: target 4.8 to 8.4 mg/dL; reflexes fade above about 9.6, breathing slows above about 12
- Creatinine, liver enzymes and platelets
- Urine protein-to-creatinine ratio
- Fetal heart rate monitoring
Treatment basics
- Stop the magnesium infusion right away
- Give calcium gluconate 1 g IV over a few minutes
- Support breathing: oxygen, bag-mask or intubation if needed
- Treat severe blood pressure with labetalol, hydralazine or nifedipine
- Delivery is the definitive cure for preeclampsia
Red flags
- Respiratory rate below 12 or apnea
- Absent reflexes or heart rhythm changes
- Seizure, which signals eclampsia
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Sources: NCCPA PANCE Content Blueprint; NCSBN 2026 NCLEX-RN Test Plan; Open RN, Nursing Pharmacology 2e. Written by Making Synapses. Making Synapses is not affiliated with these organizations.