Preeclampsia — Management & Delivery
Magnesium sulfate saves lives in preeclampsia — but its therapeutic window sits dangerously close to respiratory arrest. Knowing where that line falls is the entire game.
Core Concept
Once preeclampsia is identified, the definitive cure is delivery, but management bridges the gap. Magnesium sulfate is the first-line drug for seizure prophylaxis — not to lower blood pressure. The loading dose is typically 4–6 g IV over 15–30 minutes, followed by a maintenance infusion of 1–2 g/hr. Therapeutic serum magnesium is 4–7 mEq/L (approximately 5–9 mg/dL). Toxicity follows a predictable ladder: loss of deep tendon reflexes (DTRs) at 7–10 mEq/L, respiratory depression at 10–13 mEq/L, and cardiac arrest above 15 mEq/L. Before every assessment you check three things: DTRs present, respiratory rate ≥12, and urine output ≥30 mL/hr. If any fails, hold the infusion and notify the provider. Calcium gluconate 1 g IV is the antidote — keep it at the bedside. For blood pressure control, IV labetalol or hydralazine is used when systolic ≥160 or diastolic ≥110 mmHg. The goal is not normotension — it is preventing stroke by reducing severe-range pressures. The environment should be low-stimulation: dim lights, minimal noise, side rails padded, suction at bedside. Seizure precautions remain in place during labor and typically 24–48 hours postpartum, because eclampsia can occur after delivery.
Watch Out For
Magnesium sulfate prevents seizures; it does not treat hypertension — students commonly confuse these roles. Don't mix up calcium gluconate (magnesium antidote) with calcium chloride (more caustic, not the standard bedside rescue drug for mag toxicity). Loss of DTRs is the earliest toxicity sign and comes before respiratory depression — if reflexes are absent, the mag is already too high.
Clinical Pearl
Patellar reflex gone = magnesium too far gone. Check DTRs before you check anything else — no reflexes means stop the drip and grab the calcium gluconate.
Test Your Knowledge
3 quick questions — see how well you understood Preeclampsia — Management & Delivery