• Linda Boonstra, CarvalhoJose C AJCADepartment of Anesthesia and Pain Management, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.Department of Obstetrics and Gynecology Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada., William Turner, Kristi Downey, Xiang Y Ye, Jackie Thomas, and Mrinalini Balki.
• Department of Anesthesia and Pain Management, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
• Can J Anaesth. 2024 Oct 1; 71 (10): 136313711363-1371.

PurposeThe 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.MethodsWe 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.ResultsWe 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.ConclusionBased 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 RegistrationClinicalTrials.gov ( NCT04946006 ); first submitted 25 June 2021.© 2024. Canadian Anesthesiologists' Society.

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