Early Administration of Magnesium Sulfate during Open Fetal Myelomeningocele Repair Reduces the Dose of Inhalational Anesthesia

INTRODUCTION: Optimal uterine relaxation is achieved through higher minimum alveolar concentration (MAC) of inhalational anesthetics, increasing risks to mother and fetus. Our objective was to determine if earlier administration of magnesium sulfate would reduce the requirement of inhalational anesthetics in fetal myelomeningocele repair. MATERIALS AND METHODS: Prospective observational study of fetal myelomeningocele repair was performed from September 2011 to August 2017. Groups compared were: (1) magnesium sulfate at uterine closure; (2) magnesium sulfate at maternal skin incision. Maternal demographics, anesthetic agents, intraoperative complications, and pregnancy outcomes were reviewed. A Student t test was used for analysis. RESULTS: There were 30 cases in group 1 and 21 cases in group 2. There was no difference in gestational age at intervention (24.92 ± 0.62 vs. 25.22 ± 0.47 weeks, p = 0.07) or at delivery (34.83 ± 2.77 vs. 33.98 ± 3.83 weeks, p = 0.38) between groups 1 and 2, respectively. The maximum MAC of sevoflurane was significantly lower in group 2 (1.84 ± 0.25 vs. 1.05 ± 0.28, p < 0.0001). There was no difference in the average dose of phenylephrine used. DISCUSSION: Magnesium sulfate infusion initiated earlier in open fetal surgery reduces the total anesthetic exposure to the fetus.