The Median Effective Dose of Phenylephrine Infusion for Prevention of Spinal-Induced Hypotension During Cesarean Delivery in the 15° Left-Tilt vs. Supine Positions: A Randomised Control Study

Background: Left uterine displacement is presumed to decrease vasopressor requirements during cesarean delivery due to decreased aortocaval compression, but studies have been equivocal. Our primary aim was to determine the median effective dose (ED 5 0 ) of prophylactic phenylephrine infusion in two positions— 15° left lateral tilt versus supine—which remains unknown during elective cesarean delivery under combined spinal-epidural anesthesia. We hypothesized that a 15° left tilt would reduce phenylephrine requirements. Methods: Eighty pregnant women were randomly allocated to be positioned either at a 15° left tilt (group L) or supine (group S) during elective cesarean delivery. A Prophylactic phenylephrine was started immediately after intrathecal injection. In each group, the first patient received phenylephrine infusion at 0.5 μg/kg/min. Each subsequent patient received an infusion with an incremental dose of 0.05 μg/kg/min above or below the initial dose, depending on the response of the preceding patient. ED50 values for phenylephrine were calculated using the up-down sequential methodology and compared using relative median potency ratios. Results: The ED50 of a phenylephrine infusion was 0.33 μg/kg/min (95% confidence interval (CI), 0.23 to 0.39 μg/kg/min) in group L and 0.30 μg/kg/min (95% CI, 0.22 to 0.37 μg/kg/min) in group S. The relative median potency for phenylephrine in group L vs. group S was 1.06 (95% CI, 0.86 to 1.45). Conclusion: A 15 left tilt did not significantly alter phenylephrine requirements; therefore, routine use of tilt solely to reduce vasopressor need may not be necessary. Keywords: phenylephrine, spinal anesthesia, hypotension, cesarean delivery, left-tilt, supine