Five Unit Bolus Oxytocin at Cesarean Delivery in Women at Risk of Atony

Abstract

I.v. bolus oxytocin is used routinely during cesarean delivery to prevent postpartum hemorrhage. Its adverse hemodynamic effects are well known, resulting in a recent change in dose from 10 IU to 5. Whether a 5 IU bolus has any advantages over infusion alone is unclear. We tested the hypothesis that a 5 IU i.v. bolus of oxytocin before the initiation of a continuous infusion decreases the need for additional uterotonic drugs in the first 24 hours after delivery in women with risk factors for uterine atony undergoing cesarean delivery, compared with infusion alone. A prospective, randomized, double-blind, controlled trial was conducted in 143 subjects undergoing cesarean delivery with at least 1 risk factor for uterine atony. Subjects received 5 IU bolus of oxytocin or normal saline i.v. over 30 seconds after umbilical cord clamping. All subjects received an infusion of 40 IU oxytocin in 500 mL normal saline over 30 minutes, followed by 20 IU in 1 L over 8 hours. The primary outcome was the need for additional uterotonics in the first 24 hours after delivery. Secondary outcomes included uterine tone as assessed by the surgeon (5-point Likert scale: 0 = "floppy," 4 = "rock hard"), estimated blood loss, side effects of bolus administration, and the oxytocin bolus-placental delivery interval. There was no difference in the need for additional uterotonic drugs in the first 24 hours between groups. There was a significant difference in uterine tone immediately after placental delivery (P < 0.01) (2.8 in the oxytocin group [95% confidence interval 2.6-3.0] vs 2.2 in the saline group [95% confidence interval 1.8-2.5]), which disappeared after 5 minutes. There were no differences in observed or reported side effects between groups. We found that a 5 IU i.v. bolus of oxytocin added to an infusion did not alter the need for additional uterotonic drugs to prevent or treat postpartum hemorrhage in the first 24 hours in women undergoing cesarean delivery with risk factors for uterine atony, despite causing an initial stronger uterine contraction. Our study was not powered to find a difference in side effects between groups. These results suggest that an oxytocin infusion may be adequate without the need for a bolus, even in high-risk patients.