• Mrinalini Balki, Michael Ronayne, Sharon Davies, Shafagh Fallah, John Kingdom, Rory Windrim, and José C A Carvalho.
• Department of Anesthesia and Pain Management, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada. mrinalini.balki@uhn.on.ca
• Obstet Gynecol. 2006 Jan 1;107(1):45-50.

ObjectiveTo estimate the minimum effective intravenous dose of oxytocin required for adequate uterine contraction after cesarean delivery for labor arrest.MethodsA randomized single-blinded study was undertaken in 30 parturients undergoing cesarean deliveries under epidural anesthesia for labor arrest despite intravenous oxytocin augmentation. Oxytocin was administered as a slow intravenous bolus immediately after delivery of the infant, according to a biased coin up-down sequential allocation scheme. After assisted spontaneous delivery of the placenta, the obstetrician, blinded to the oxytocin dose, assessed uterine contraction as either satisfactory or unsatisfactory. Additional boluses of oxytocin were administered as required, followed by a maintenance infusion. Data were interpreted and analyzed by a logistic regression model at 95% confidence intervals.ResultsAll patients received oxytocin infusions at a mean +/- standard deviation of 9.8 +/- 6.3 hours before cesarean delivery (maximum infusion dose 10.3 +/- 8.2 mU/min). The minimum effective dose of oxytocin required to produce adequate uterine response in 90% of women (ED90) was estimated to be 2.99 IU (95% confidence interval 2.32-3.67). The estimated blood loss was 1,178 +/- 716 mL.ConclusionWomen requiring cesarean delivery for labor arrest after oxytocin augmentation require approximately 3 IU rapid intravenous infusion of oxytocin to achieve effective uterine contraction after delivery. This dose is 9 times more than previously reported after elective cesarean delivery in nonlaboring women at term, suggesting oxytocin receptor desensitization from exogenous oxytocin administration during labor. Therefore, alternative uterotonic agents, rather than additional oxytocin, may achieve superior uterine contraction and control of blood loss during cesarean delivery for labor arrest.Level Of EvidenceI.

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