DIFFERENTIAL-EFFECTS OF MAGNESIUM ON SELECTED MEASURES OF VASCULAR-RESISTANCE IN PREECLAMPSIA

Objective: The purpose of this investigation was to further define the hemodynamic effect of magnesium sulfate (MgSO4) on stroke systemic va scular resistance index. Study Design: This prospective observational study was performed in 20 preeclamptic patients (12 severe, 8 mild) he modynamically monitored in the lateral recumbent position by thoracic electrical bioimpedance (BoMed, Irvine, California) prior to and durin g high dose magnesium sulfate bolus infusion. Mean arterial pressure, systemic vascular resistance index, cardiac index, stroke index, and h eart rate, were recorded at base line and during magnesium sulfate inf usion. Stroke systemic vascular resistance index was calculated as the product of heart rate and systemic vascular resistance index. Hemodyn amic values were recorded at base line (after 10 min of lateral recumb ency), 30 min, and 1 h after beginning magnesium sulfate therapy. Magn esium sulfate therapy consisted of a 5-g bolus over 20 min followed by 3 g/h of continuous infusion. All patients received a standard crysta lloid infusion. Results: Twenty preeclamptic patients (12 severe, 8 mi ld) at 33.4 +/- 3.9 ((X) over bar +/- SD) weeks gestation were enrolle d. The base line systemic vascular resistance index was 2704 +/- 720 ( (X) over bar +/- SD) F . ohm m(2). MgSO4 therapy resulted in a signifi cant drop in systemic vascular resistance index. The baseline stroke s ystemic vascular resistance index was 224,044 +/- 83,656 ((X) over bar +/- SD) F . ohm m(2). bt, which did not significantly change after Mg SO4 therapy. A significant increase in heart rate resulted in a signif icantly increased cardiac index. Conclusion: Magnesium sulfate infusio n significantly lowers systemic vascular resistance index (systemic va scular resistance/(min) but not stroke systemic vascular resistance in dex/beat) in preeclampsia.