Maintenance infusion rate of oxytocin after initial 1-IU bolus for elective Cesarean delivery: a dose-finding study.

Purpose: The purpose of our study was to determine the minimum effective dose of oxytocin maintenance infusion required to maintain adequate uterine tone in 90% of patients (ED₉₀) after administration of the initial bolus at elective Cesarean delivery (CD) under spinal anesthesia.

Methods: We conducted a prospective, double-blind dose-finding study with biased coin up-down design. Immediately after delivery, a 1-IU oxytocin bolus was administered, followed by a maintenance infusion. The obstetrician assessed the uterine tone by palpation as satisfactory or unsatisfactory. In case of unsatisfactory response, the dose for the next patient was increased by 2 IU·hr^-1. For satisfactory response, the dose for the next patient was either decreased by 2 IU·hr^-1 with a probability of 1/9, or remained unchanged. The primary outcome was a satisfactory uterine tone from five minutes after delivery until discharge from postanesthesia care unit. The secondary outcomes were blood loss, need for additional uterotonics, and side effects.

Results: We analyzed data for 40 patients. The ED₉₀ of oxytocin maintenance infusion was 4.5 IU·hr^-1 (95% confidence interval, 3.3 to 5.5) based on the isotonic regression estimator. The median [interquartile range] blood loss was 861 [553-1,181] mL; 18% received additional uterotonics, and 38% developed hypotension post delivery.

Conclusion: Based on the results of this dose-finding study, we recommend a maintenance infusion rate of 4.5 IU·hr^-1 following an oxytocin bolus of 1 IU for adequate uterine tone in pregnant patients undergoing elective CDs. This infusion rate is four-fold lower than that required without an initial bolus.

Study registration: ClinicalTrials.gov ( NCT04946006 ); first submitted 25 June 2021.