Effects of magnesium sulfate tocolysis on maternal mental status

Objective: Magnesium sulfate is the most commonly used agent for tocolysis in the management of preterm labor. Anecdotally both clinicians and patients have noted alterations in mental status of women receiving high doses of magnesium infusion, and central nervous system depression including lethargy and depression of deep tendon reflexes has been documented. Our hypothesis is that intravenous magnesium sulfate at tocolytic doses significantly affects maternal mental status.Materials and Methods: Eligibility criteria included admission or transport to University Hospital between 25 and 34 weeks gestation with an initial episode of spontaneous premature labor. Patients were consented and given an initial mental status examination prior to magnesium sulfate infusion. Those patients transported to University Hospital diagnosed with premature labor and already on magnesium were consented and given an initial mental status examination at the time of arrival. Once a therapeutic level of magnesium was documented a repeat mental status examination was performed, with a third examination performed 24 hours after the magnesium infusion has been discontinued. As a control group pregnant women hospitalized for premature rupture of the membranes not in labor had the examinations performed initially, after 24 hours of hospitalization, and again after 72 hours of hospitalization. Exclusion criteria included underlying mental illness, administration of other medications that might affect mental status, cervical dilation greater than 4 cm, clinical evidence of chorioamnionitis, or the presence of any significant abnormalities in the fetal heart rate tracing. The mental status examination consisted of the mini mental state exam, the comprehension portion of the Wechsler Adult Intelligence Scale, and the Bender-Gestalt Indicator. The results of these examinations were scored in a blinded fashion by a psychiatrist.Results: There were 22 patients in the study group and 9 patients in the control group. There were no differences in the age, gravidity, parity, or gestational age of the two groups. Out of a possible 102 points, the mean mental status scores were as follows:The mean serum magnesium level at the time of therapy was 5.1 mg/dL. The time required for response to the Wechsler test was significantly different although the scoring of the comprehension was unchanged (15.2 +/- 3.6 min vs 22.3 +/- 4.7 min, P <.05).Conclusions: This prospective blinded study reveals no differences in maternal mental status during magnesium sulfate infusion at the levels recorded in our study. There was an increase in the length of time required to answer the comprehension and judgment portion of the examination. These findings have significant clinical implications suggesting that patients on magnesium sulfate can make appropriate judgments and can, therefore, participate in clinical discussions and trials.