Favorable hemodynamic effects of magnesium sulfate in preeclampsia

OBJECTIVE: Our purpose was to evaluate the hemodynamic effects of magnesium sulfate in preeclamptic and preterm labor patients. STUDY DESIGN: Fifteen preeclamptic patients at 32.4 ± 3.3 (mean ± SD) weeksʹ gestation and 11 preterm labor patients (31.3 ± 2.8 weeks) were hemodynamically monitored in the lateral recumbent position by thoracic electrical bioimpedance (BoMed, Irvine, Calif.) before and during high-dose magnesium sulfate bolus and infusion. Cardiac index, systemic vascular resistance index, mean arterial pressure, heart rate, and stroke index were all recorded at baseline and during magnesium sulfate infusion. All patients received a standard crystalloid infusion. Data analysis continued until the patient received epidural placement or other antihypertensive therapy or was delivered. RESULTS: At baseline the systemic vascular resistance index was 2465 ± 718 F • ohm/m2 and the cardiac index was 3.6 ± 1.0 L/min/m2 for the preeclamptic patients. These were significantly different compared with the preterm labor patients, who had a systemic vascular resistance index of 1377 ± 563 F • ohm/m2 and 4.6 ± 1.2 L/min/m2. Magnesium sulfate infusion resulted in a rapid, sustained fall in systemic vascular resistance and a rise in cardiac index in the preeclamptic patient. This effect was evident at least 4 hours after initiation of the bolus and infusion. In the preterm labor patients the hemodynamic effects of magnesium sulfate were minimal and were noted only during the magnesium sulfate bolus. CONCLUSION: Magnesium sulfate infusion appears to have a prolonged hemodynamic effect in the preeclamptic patient. Sustained reduction in systemic vascular resistance and an increase in cardiac index is found in patients with preeclampsia but not in preterm labor.