///2009 Abstract Details
2009 Abstract Details2019-08-03T15:55:31-06:00

Up-down determination of the ED90 of oxytocin infusions for the prevention of postpartum uterine atony in parturients undergoing cesarean delivery

Abstract Number: 155
Abstract Type: Original Research

Anna C Chaplin BSc1 ; Ronald B George MD FRCPC2; Dolores M McKeen MD MSc FRCPC3; Lynne McLeod MD FRCSC4

Introduction: Boluses of oxytocin may be associated with hypotension and myocardial ischemia. An oxytocin infusion of the lowest effective dose may reduce the side effects. This study determines the minimum effective dose (ED90) of infusions of oxytocin for the prevention of uterine atony and the need for additional uterotonics in low risk parturients presenting for elective cesarean.

Methods: With REB approval participants were eligible if; 1) full term 2) ASA class I & II 3) ≥18 years of age. Forty-two subjects were recruited. The spinal technique was standardized; 12 mg bupivacaine, 10 - 20 mcg fentanyl, and 100 - 200 mcg morphine. After delivery of the baby a blinded infusion of oxytocin was administered. The initial dose of oxytocin infusion was 0.4 IU/min. Three minutes after delivery, the obstetrician rated uterine contraction as satisfactory or unsatisfactory. Unsatisfactory resulted in the usual management of uterine atony (additional oxytocin bolus, ergometrine, or carboprost). The subsequent dose for the next subject was based upon the response of the preceding patient in the usual biased coin up-and-down method. If during the initial 3 minute assessment, uterine contraction / tone is judged as unsatisfactory (i.e. there is a need to administer additional uterotonics), the dose is stepped up in the next patient. If satisfactory (i.e. no uterine atony is observed and there is no need for additional uterotonics), the next patient is randomized with probability of 0.10 to the next lower dose and with probability 0.90 to the same dose. The dosing change was in increments of 0.1 IU/min. The ED90 and 95% confidence intervals were calculated using the maximum likelihood estimation.

Results: Mean age was 31.5 5.1 years, BMI was 31.8 5.1 and the median parity was 1 [IQR 1-2]. The dosage of oxytocin ranged from 0.1 - 0.4 IU/min. There were 7 (17.5%) subjects in whom uterine tone was judged inadequate, as judged by the surgeon and or the need to administer additional uterotonic medications. The figure demonstrates the oxytocin infusion doses assigned and subsequent dose assignment based upon uterine tone assessment. There were no oxytocin side effects. A nonparametric estimation of the dose at which 90% of women were judged to have satisfactory uterine tone was 0.273 IU / minute. This study shows that the current dose of 0.4 IU / minute infusion rate is higher than the ED90 dose of 0.273 IU per minute to prevent postpartum uterine atony.

SOAP 2009