A 30-year-old woman at 34 weeks of gestation presents to the emergency department with severe preeclampsia. Her blood pressure is 168/110 mmHg, and she has significant proteinuria (4+ on dipstick) and mild headaches. She is admitted to the obstetric ward and started on magnesium sulfate for seizure prophylaxis and antihypertensive therapy. The magnesium sulfate infusion is initiated with a loading dose of 4 g intravenously over 30 minutes, followed by a maintenance dose of 2 g/hour. Her reflexes and vital signs are monitored hourly, and she initially responds well to the therapy. After 8 hours of infusion, the patient begins to report nausea and generalized weakness. The nurse notes that her respiratory rate has decreased to 10 breaths per minute, and her deep tendon reflexes are absent on examination. The patient also complains of flushing and mild dizziness. Concerned about possible magnesium toxicity, the medical team orders immediate serum magnesium levels. At what serum magnesium level do this patient’s current symptoms and signs typically occur?
