Does an Earlier or Late Intravenous Injection of Ondansetron Affect the Dose of Phenylephrine Needed to Prevent Spinal-Anesthesia Induced Hypotension in Cesarean Sections?

backgroundThere was controversy about ondansetron can reduce the incidence of spinal-induced hypotension and decrease the consumption of vasopressor in cesarean delivery with spinal anesthesia. We hypothesized that different timing of ondansetron administration may contribute to the controversy. Therefore, we aimed to determine the effect of different timing of ondansetron administration on the dose requirement of preventing phenylephrine via comparing the ED

methodsSeventy-five parturients were finally enrolled in this prospective, randomized, double-blinded dose finding study. Ondansetron or placebo was administered 5 min or 15 min before intrathecal injection. Up-down allocation method was used to determine the dose of prophylactic phenylephrine for each parturient in the three groups. The initial infusion rate of first patient was 0.5 µg/kg/min. Then, the rate for next patient was varied with increasing or decreasing of 0.05 μg/kg/min according to the response of the previous patient. An effective dose was defined as no hypotension occurred during the study period. An ineffective dose was defined as hypotension occurred during the study period. Study period in this study is from intrathecal injection to neonatal delivery. ED

resultsThe ED

conclusionAn earlier administration of 4 mg prophylactic ondansetron contributed no benefits for lowing the dose of prophylactic phenylephrine compared to a late administration, but can decrease the dose of preventing phenylephrine in patients undergoing cesarean delivery with combined spinal-epidural anesthesia. This finding may be useful for clinical practice and further studies.