Does calcium chloride help restore maternal blood pressure and uterine blood flow during hemorrhagic hypotension in hypermagnesemic gravid ewes?

Magnesium sulfate worsens maternal hypotension and fetal oxygenation during hemorrhage in gravid ewes. The purpose of this study was to determine whether calcium chloride administration is a useful adjunct to blood transfusion during hemorrhagic hypotension in hypermagnesemic gravid ewes. Sixteen experiments were performed in eight chronically instrumented animals between 0.8 and 0.9 of timed gestation. The experimental sequence included (a) T = 0: magnesium sulfate 4 g IV; (b) T = 5: infusion of magnesium sulfate 4 g/h IV; (c) T = 90: maternal hemorrhage 20 mL/kg over 55 min; (d) T = 147: calcium chloride 10 mg/kg or normal saline (NS-control) 0.1 mL/kg IV; (e) T = 160: transfusion of collected maternal blood over 55 min. Magnesium sulfate alone slightly decreased maternal mean arterial pressure (P = 0.002) and increased uterine blood flow (P = 0.0001) in both groups before hemorrhage. During hemorrhage, maternal mean arterial pressure, cardiac output, and uterine blood flow, and fetal PO2 and pH all decreased sharply (P = 0.0001). Cardiac output increased (P = 0.0005) modestly just after the intravenous bolus of calcium chloride. Maternal mean arterial pressure was significantly higher (P = 0.03) during transfusion in the calcium chloride group than in the NS-control group, but only after mean arterial pressure was near baseline measurements. Maternal uterine blood flow and fetal PO2 and pH responses over time were similar in the two groups. We conclude that intravenous administration of calcium chloride (10 mg/kg) transiently increased cardiac output during hemorrhagic hypotension and slightly increased mean arterial pressure during transfusion in hypermagnesemic gravid ewes.(ABSTRACT TRUNCATED AT 250 WORDS)