Background: The 90% effective dose (ED90) of oxytocin infusion has been previously estimated to be 16.2 IU h- 1. However, bolus administration of oxytocin prior to the infusion may decrease the infusion dose required. The aim of this study was to estimate the ED95 for oxytocin infusion after a bolus at elective caesarean delivery (CD) in nonlaboring parturients.
Methods: We performed a randomized, triple blinded study in 150 healthy termparturients scheduled for elective CD under epidural anaesthesia. After delivery of the infant and i.v. administration of 1 IU oxytocin as a bolus, Participants were randomized to receive oxytocin infusion at a rate of 0, 1, 2, 3, 5, or 8 IU h- 1, to be given for a total of 1 h. Uterine tone assessed by the blinded obstetrician as either adequate or inadequate. Secondary outcomes included estimated blood loss (EBL), requirement for supplemental uterotonic agents, and development of side effects.
Results: The 95% effective dose (ED95) of oxytocin infusion was estimated to be 7.72 IU h- 1 (95% confidence interval 5.80-12.67 IU h- 1). With increasing oxytocin infusion rate, the proportion of parturients who needed rescue oxytocin bolus or secondary uterotonic agents decreased. No significant among-group differences in the EBL and oxytocin-related side effects were observed.
Conclusions: In parturients who receive a 1 IU bolus of oxytocin during elective cesarean delivery, an infusion rate of oxytocin at 7.72 IU h- 1 will produce adequate uterine tone in 95% of parturients. These results suggest that the total dose of oxytocin administered in the postpartum period can be decreased when administered as an infusion after oxytocin bolus.
Keywords: Caesarean section; Oxytocin; Postpartum haemorrhage prevention.