EFFECTS OF MAGNESIUM-SULFATE ON THE FETAL HEART-RATE RESPONSE DURING ACUTE HYPOXEMIA IN GOATS

OBJECTIVE: The effects of magnesium sulfate on fetal heart rate (FHR) responses during acute hypoxemia in goats were investigated. METHODS: The FHR responses due to hypoxemia during magnesium sulfate infusion ( Mg study) were compared with those during vehicle infusion (controls) in six chronically instrumented goat fetuses at 125-130 days' gestatio n. RESULTS: Four-hour infusions of magnesium sulfate significantly inc reased fetal plasma concentrations of magnesium from 2.3 to 6.5 mg/dL. During the hypoxemic period, the fetal arterial oxygen pressure was s ignificantly decreased from 29.0 +/- 2.5 to 24.6 +/- 2.6 torr in the c ontrols, and from 28.9 +/- 3.9 to 13.7 +/- 4.7 torr during the Mg stud y. Neither arterial carbon dioxide pressure nor pH was significantly a ltered. In the controls, FHR was significantly decreased by hypoxemia, accompanied by increases in variability. lit the Mg study, FHR was no t significantly, decreased by hypoxemia. Acute hypoxemia also increase d the FHR variability during magnesium infusion, which was significant ly reduced compared with those in the control population. CONCLUSION: Magnesium sulfate masks FHR-slowing responses during acute hypoxemia i n fetal goats.