Oxytocin Requirements at Elective Cesarean Delivery: A Dose-Finding Study

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Abstract
Oxytocin is frequently used by intravenous bolus and infusion to minimize blood loss and prevent postpartum hemorrhage at cesarean delivery. Current dosing regimens are arbitrary whereas large doses may pose a serious risk to the mother. The purpose of this study was to estimate the minimum effective intravenous bolus dose of oxytocin (ED90) required for adequate uterine contraction at elective cesarean in nonlaboring women. A randomized, single-blinded study was undertaken in 40 healthy term pregnant women presenting for elective cesarean under spinal anesthesia. Oxytocin was administered by bolus according to a biased coin up-and-down sequential allocation scheme with increments or decrements of 0.5 IU. Uterine contraction was assessed by the obstetrician, who was blinded to the dose of oxytocin, as either satisfactory or unsatisfactory. After achieving sustained uterine contraction, an infusion of 40 mU/min of oxytocin was started. Oxytocin-induced adverse effects and intraoperative complications were recorded and blood loss was estimated. Data were interpreted by parametric analysis based on logistic regression model and nonparametric analyses at 95% confidence intervals (CIs). The ED90 of oxytocin as determined by logistic regression model fitted to the data was estimated to be 0.35 IU (95% CI 0.18-0.52 IU), with nonparametric estimates of 97.1% (95% CI 84.9-99.8%) response rate at 0.5 IU, and 100% (95% CI 92.2-100%) at 1.0 IU. The estimated blood loss was 693 +/- 487 mL (mean +/- standard deviation). The bolus dose of oxytocin used at elective cesarean deliveries in nonlaboring women can be significantly reduced while maintaining effective uterine contraction. Alteration in practice will likely reduce the potential adverse effects of this drug when given in large bolus doses, but may require modification of the techniques to remove the placenta.