(425) Duration of High-Dose Postpartum Oxytocin Infusion and Postpartum Bleeding Outcomes in Individuals Undergoing Vaginal Delivery

Objective: High-dose prophylactic postpartum (PP) oxytocin (80 IU) has been suggested to reduce postpartum hemorrhage (PPH); however the optimal infusion duration is unknown. We sought to compare rates of PPH and other bleeding outcomes between high-dose (80 IU) oxytocin infused over 1 versus 4 hours.

Study Design: Secondary analysis of a database of all vaginal deliveries >22 weeks at a large academic referral center (1/1/2013-12/31/2018). Our institution’s protocol for PP oxytocin infusion was altered on 10/15/2015 for vaginal deliveries only from 80 IU/500 mL over 1 hour to 80 IU/500 mL over 4 hours with initial 100 mL bolus prior to 4 hour infusion. All vaginal deliveries with available outcomes were included. Patients were categorized as receiving oxytocin over 1 versus 4 hours, individually confirmed in the medication administration record. Primary outcome was a composite of estimated blood loss (EBL) >1000 mL, 2nd line uterotonic use, and any blood transfusion (secondary outcomes in Figure). Generalized estimating equation models were used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CI) using the 4 hour group as referent.

Results: Of 16,793 deliveries, 12,092 met inclusion criteria: 5,675 received 80U oxytocin for 1-hour (47%), 6,417 (53%) for 4-hours. There were multiple differences in baseline characteristics between groups (Table). Compared to the 4-hour group, the 1-hour group had increased odds of the primary composite (aOR 1.21, 95% CI 1.03-1.42), driven by an increase in 2nd line uterotonic use (aOR 1.39,1.16-1.67) (Figure). While there was no difference in EBL >1000 mL or blood transfusion, the 1-hour group had increased odds of HCT decline >6% (aOR 1.83, 1.33-2.54).

Conclusion: Infusion of PP high-dose oxytocin over 1 hour compared to 4 hours is associated with increased odds of postpartum bleeding – mainly 2nd-line uterotonic use and HCT decline > 6%. Given that 2nd line uterotonic use is clinician dependent, further investigation, utilizing less subjective outcomes such as transfusion, is needed to further define optimal high-dose oxytocin duration.