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Effects of exogenous pre-delivery oxytocin dosing on post-partum uterotonic use
Abstract Number: T 24
Abstract Type: Original Research
Background: Prolonged infusion of oxytocin has been has been shown to desensitize the oxytocin receptors on the myometrium.(1, 2) With the increased incidence of post-partum hemorrhage (PPH) mainly from uterine atony (3), what role does the total dose of oxytocin contribute? We analyzed pre-delivery oxytocin exposure using a more sensitive tool, Area Under the Curve (AUC) and postpartum uterotonic use in primigravid women admitted for spontaneous labor and who received oxytocin for augmentation of labor.
Methods: After IRB approval, a manual retrospective medical chart review was performed for calendar year 2008. Inclusion criteria was primigravid women aged >18 years who were admitted with a gestational age >36 weeks for spontaneous labor and received exogenous pre-delivery oxytocin to augment their labor. The dosage rate and time interval of oxytocin administration prior to delivery was used to calculate a total predelivery oxytocin area under the curve (AUC). Patients were then divided into quartiles based on their pre-delivery oxytocin AUC exposure. The patient’s medication administration record was also reviewed for use of uterotonics i.e., methylergonovine, misoprostol, or carboprost tromethamine. PPH data was also collected based on the American College of Obstetricians and Gynecologist definition, estimated blood loss greater than 500ml for vaginal delivery or 1000ml for cesarean section, blood transfusion, or a change in hematocrit from pre-delivery to postpartum greater than 10%. Chi-square analysis was done to compare the oxytocin exposure to use of uterotonics, where p<0.05 was considered statistically significant.
Results: 228 patients who meet the inclusion criteria and analyzed. Patient demographics were similar among quartiles, however the higher predelivery oxytocin exposure was associated with longer labor. Chi-square analysis showed statistical significance P<.003 for higher use of uterotonic use with higher pre-delivery exposure to oxytocin. Quartiles for oxytocin AUC low to high respectively were: 1/57(1.7%), 2/56(3.6%), 5/56 (8.9%), and 11/57(19.3%) The PPH rate was not statistically different amongst the quartiles.
Conclusion: Prolonged exposure to oxytocin has been shown in-vivo to desensitize the oxytocin receptors on the myometrium. We have shown that higher pre-delivery oxytocin AUC exposure increases the need for uterotonic administration, suggesting the phenomenon of greater acute down-regulation of the oxytocin receptors. The anesthesiologist and OB need to be vigilant and commit adequate resources for postpartum uterine atony events in the face of higher dose oxytocin administration.
1. J Reprod Fertil 2000; 120:91-7.
2. Am J Physiol Endocrinol Metab 2011; 300:E468-77.
3. Am J Obstet Gynecol 2010; 202:353 e1-6.