MATERNAL OXYGEN DESATURATION WITH INTRAVENOUS MAGNESIUM THERAPY

Objective: To describe the occurrence, treatment, and outcome of mater nal oxygen desaturation during magnesium sulfate therapy. Methods: A p ost hoc analysis of a randomized double-blind trial, designed to deter mine if mothers at risk for premature delivery treated with phenobarbi tal and vitamin K had less frequent intracranial hemorrhage in their n ewborns, was done. A subset of these patients at imminent risk for del ivery received both intravenous magnesium sulfate and intravenous stud y drug (phenobarbital or placebo) and was monitored with maternal oxyg en saturation monitoring. Results: One hundred one women (29%) in the trial had pulse oximetry; 47 were assigned to placebo and 54 to the tr eatment group. The placebo and treatment groups had the following simi larities: mean lowest oxygen saturation by pulse oximeter (93.4% +/- 3 .0 compared with 93.1% +/- 3.3), mean highest magnesium levels (6.3 mE q/L +/- 1.5 compared with 6.2 mEq/L +/- 0.9), frequencies of desaturat ion events defined as oxygen saturation below 90% (11% compared with 1 1%), gestational age at delivery, birth weight, Apgar scores, and cord arterial pH. Using regression analysis, multiple gestation was the on ly one of 14 independent variables associated with low maternal oxygen saturation. Preeclampsia was not associated with a greater risk of de saturation. The statistical power of this study is limited by its smal l sample sizes. Conclusion: Maternal oxygen desaturation occurs common ly with intravenous magnesium therapy, does not occur more frequently with simultaneous administration of intravenous phenobarbital, and doe s not cause decompensation in maternal or fetal status. Multiple gesta tion may be associated with lower maternal oxygen saturation. (C) 1997 by The American College of Obstetricians and Gynecologists.