Patients Undergoing Cesarean Delivery After Exposure to Oxytocin During Labor Require Higher Postpartum Oxytocin...

Experts recommend postpartum oxytocin to prevent uterine atony and hemorrhage, but oxytocin may be associated with dose-dependent adverse effects, and the correct dose of postpartum oxytocin has yet to be determined. The effective dose in 90% of patients (ED90) of oxytocin after cesarean delivery may be higher in patients exposed to oxytocin during labor compared to patients unexposed. We therefore undertook this study to compare postpartum oxytocin requirements in patients exposed to oxytocin prior to cesarean delivery versus those not exposed, when all were treated according to a specific institutional protocol.

In this retrospective chart review, we reviewed medical records of patients who underwent cesarean delivery under neuraxial anesthesia and noted demographic data, relevant comorbidities, and oxytocin exposure, infusion rate, and duration prior to delivery. Patients exposed to oxytocin before cesarean (OXY+ group) were compared to those not exposed (OXY- group). The primary outcome variable was highest infusion rate of postpartum oxytocin required per institutional protocol. Secondary outcomes included estimated blood loss, proportion of patients with postpartum hemorrhage, and proportions who received other uterotonic medications or red blood cell transfusion.

OXY+ patients were more likely to be nulliparous and had higher estimated gestational age and neonatal weight than OXY- patients. They also had higher incidence of chorioamnionitis and lower incidence of multiple gestation. OXY+ patients required a high postpartum oxytocin infusion rate more often than OXY- patients (adjusted odds ratio 1.94 [95% confidence interval, 1.19-3.15; P = .008]). They also received other uterotonic agents more commonly. Estimated blood loss, hemorrhage rates, and transfusion rates did not differ between groups.

Reported increases in the ED90 of postpartum oxytocin after oxytocin exposure during labor appear to be clinically significant. We have therefore altered our institutional protocol so that women preexposed to oxytocin routinely receive higher initial postpartum oxytocin infusion rates.