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Ondansetron Does Not Prevent Spinal Hypotension But Reduces Total Vasopressor Requirements in Women Undergoing Cesarean Delivery
Abstract Number: T-10
Abstract Type: Original Research
Introduction: Ondansetron is used to prevent and treat nausea, vomiting and pruritus in obstetrics (1). Another potential indication, recently described, is prevention of spinal hypotension during cesarean delivery (CD) under spinal anesthesia (2). The aim of this study was to determine the efficacy of ondansetron in spinal hypotension prevention, and to evaluate if the effect was dose-dependent and correlated with blood levels of ondansetron.
Methods: 40 healthy women undergoing CD were randomly assigned to receive 4 or 8 mg IV ondansetron for a prospective, open-label pharmacokinetic study. Maternal blood was sampled at 7, 15 and 40 min after ondansetron administration. This data was then combined with a dataset collected retrospectively from medical records of 125 women undergoing CD who did not receive ondansetron. All women were healthy parturients with term singleton pregnancies having elective CD with spinal anesthesia (1.6 ml 0.75% bupivacaine, fentanyl 10 mcg, morphine 100-200 mcg). Outcome measures included phenylephrine use (first 20 minutes and total use during CD), blood pressure, heart rate, fluid requirements, and estimated blood loss (EBL).
Results: There was no difference between groups for phenylephrine use in the first 20 min (419 ± 279 in ondansetron group vs. 370 ± 275 mcg in no ondansetron group, p=0.336). However, total phenylephrine requirements were less (1008 ± 759 vs. 1518 ± 1000 mcg) in women receiving ondansetron (p<0.001). We found no difference in blood pressure measurements (p=0.56), heart rates (p=0.07), fluid requirements (p=0.922) or EBL (p=0.622). There was no dose effect when comparing 4 and 8 mg ondansetron doses, and no significant correlations between ondansetron blood concentration AUC and phenylephrine requirements were found (Figure).
Conclusions: Our results found that ondansetron does not prevent hypotension or early vasopressor use after spinal anesthesia for CD, suggesting a limited role of ondansetron for spinal hypotension prevention (3). A significant decrease in the total, but not early (first 20 minutes), phenylephrine requirements suggests ondansetron may have a potential role in blood pressure maintenance later on during CD, perhaps due to counteracting the hypotension side-effect of oxytocin.
1. Anesth Analg 2009;109:174-82
2. Int J Obstet Anesth 2012;21,24-28
3. Int J Obstet Anesth 2014;23(2):138-43