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ED90 of third stage labor oxytocin infusion for parturients undergoing cesarean delivery for labor dystocia.
Abstract Number: O2 3
Abstract Type: Original Research
Background: Previous studies have found the ED90 for oxytocin infusion to prevent uterine atony in non-laboring women undergoing elective cesarean delivery (CD) to be 15 to 21 IU/h [1,2]. We hypothesized that laboring parturients receiving intrapartum oxytocin, who then undergo CD for labor dystocia, will have a higher ED90 compare to a non-laboring parturients.
Method: Inclusion criteria included non-obese, ASA 2 parturients who required intrapartum CD after peripartum exposure to oxytocin under epidural anesthesia (experimental) or elective CD under spinal anesthesia (control). The first subject in each group started with an infusion rate of oxytocin 18 IU/h. At 4 minutes, the obstetrician, who was blinded to the oxytocin dose, assessed the uterine tone as adequate or not. The dose for the next subject was based on the response of the preceding subject. If the initial subject had inadequate uterine tone, the oxytocin infusion rate was increased by 2 IU/h for the next subject. If the subject had adequate uterine tone, the next subject either received a lower dose by 2 IU/h (chance 1/10) or the same dose (chance 9/10). Biased coin allocation was determined by drawing black and white marbles (ratio 1:9) out of an opaque bag prior to initiation of the study and concealing the allocation in sequentially numbered opaque envelops. The primary outcome was successful uterine tone at 4 minutes and any time after. Secondary outcomes were need for additional uterotonic, estimated blood loss and postpartum hemoglobin values.
Results: The estimated ED90 in the experimental group was 49 IU / h (95% confidence interval [CI] 38-70 IU / h) compared to 19 IU / h (95% confidence interval [CI] 17-32 IU / h) in the control group, P < 0.001. 47% of the subjects in the experimental group required additional uterotonic versus 2.6% in the control group, P < 0.001. The mean (± SD) estimated blood loss were 1115 ± 502 mL and 700 ± 238 mL in the experimental and control group respectively, P < 0.001.
Conclusion: The ED90 for oxytocin infusion during the third stage of labor is significantly higher in parturients receiving intrapartum oxytocin administration who require CD for labor dystocia compared with parturients undergoing elective CD. These results are consistent with previous reports of oxytocin resistance, which may further increase the risk of postpartum hemorrhage in this patient population.
1 George RB. Can J Anesth 2010
2 Carvalho JC. Obstet Gynecol 2004