Postcesarean Oxytocin Boluses of Low Benefit


BANFF, ALTA. — The routine practice of giving oxytocin boluses to reduce the risk of postpartum hemorrhage appears to be of limited benefit even in high-risk patients after cesarean section, as long as an appropriate oxytocin infusion is given, according to the first randomized, placebo-controlled trial of the practice, said Dr. Kylie King from Maitland (Australia) Hospital.

The practice of administering oxytocin boluses has recently come under scrutiny. “Although the adverse hemodynamic effects [of oxytocin boluses] are well documented, one recently reported death associated with a 10-U bolus in the U.K. has prompted a change in dose from 10 to 5 units given slowly,” she said at the annual meeting of the Society for Obstetric Anesthesia and Perinatology. “This begs the question: Is a bolus necessary? Is 5 U the right dose? How slowly should it be given? And might an infusion be sufficient?”

Her study, which was conducted at British Columbia Women's Hospital in Vancouver, compared 143 subjects: 70 received an intravenous 5-U bolus of oxytocin, and 73 received normal saline, given over 30 seconds following cesarean section and cord clamping.

Both groups also received an identical infusion of 40 U of oxytocin in 500 mL of normal saline over 30 minutes, followed by 20 U of oxytocin in 1 L of saline over the next 8 hours.

“Our hypothesis was that the bolus, given in addition to the infusion, would reduce the need for additional drugs to contract the uterus,” said Dr. King. Because previous studies have suggested that oxytocin may have little or no effect in a low-risk population, study subjects were specifically selected as being high risk for postpartum hemorrhage. “Multiple gestations and macrosomia were the most common risk factors.”

Overall, 53% of the cesarean sections were elective, with 47% classified as emergency procedures. The need for additional uterotonics was high—between 30% and 40% overall—confirming that the population was indeed high risk, but need for more uterotonics was similar in both groups as assessed by a surgeon who was blinded to the patients' randomization. In addition, there was no difference between groups in the secondary outcomes of estimated blood loss, need for blood transfusion or hypotension.

“Even in a high-risk group, a 5-U bolus is of limited additional benefit provided that an adequate infusion is given,” concluded Dr. King. “Getting a stronger initial contraction at 1 minute doesn't reduce the need for additional uterotonics over the next 24 hours.”

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