Double-blind, randomized comparison of the effect of carbetocin and oxytocin on intraoperative blood loss and uterine tone of patients undergoing cesarean section.

Objectives: A double-blind randomized study involving pregnant women undergoing cesarean section was conducted to compare the effectiveness of a single 100 micrograms intravenous injection of the long-acting oxytocin analog, carbetocin, with that of a standard infusion of oxytocin with respect to intraoperative blood loss. The two treatments also were compared for safety and ability to maintain adequate uterine tone.

Study Design: The study drug was administered to 57 women during elective cesarean section after placental delivery; blood was collected until abdominal closure. Intraoperative blood loss was calculated with a sensitive colorimetric method. Position, tone of the fundus, and vital signs were assessed up to 24 hours after the operation. The need for additional uterotonic agents was recorded.

Results: A single 100 micrograms intravenous injection of carbetocin was as effective as a continuous 16 hour infusion of oxytocin in controlling intraoperative blood loss after placental delivery. Mean blood loss after carbetocin administration was 29 ml less than after oxytocin administration (p = 0.3). Subset analysis deleting two patients who received oxytocic intervention in the operating room and one extreme outlier revealed a mean blood loss of 41 ml less in the carbetocin group (p = 0.14) with lower variances (p = 0.02). The percentage of patients with blood loss of 200 ml or less was greater with carbetocin (79% vs 53%; p = 0.041). Carbetocin enhanced early postpartum uterine involution. The fundus was below the umbilicus in more patients who received carbetocin at 0, 2, 3, and 24 hours on the ward (p < 0.05). There were no significant differences in uterine tone or type or amount of lochia. Additional oxytocin was used to treat three patients for postpartum hemorrhage or persistent uterine atony. All interventions were in the oxytocin group. Vital signs and hematologic values were comparable in each group, confirming similar safety profiles.

Conclusions: A single 100 micrograms intravenous injection of carbetocin is as effective and more reliable than a standard continuous infusion of oxytocin in maintaining adequate uterine tone and preventing excessive intraoperative blood loss during cesarean section after delivery of the placenta. Patients receiving carbetocin required less intervention. Carbetocin was well tolerated.