Effect of crystalloid co-loading infusion rate on the dose requirements of prophylactic phenylephrine for preventing hypotension following spinal anesthesia for cesarean delivery

Abstract

Abstract Background Intravenous fluid administration and prophylactic vasopressor infusion are main methods for prevention spinal anesthesia-induced hypotension (SAIH) in cesarean delivery. The evidence regarding the impact of different volumes of crystalloid solution on the phenylephrine infusion dosage for preventing spinal anesthesia-induced hypotension remains inconclusive. In this study, we aimed to compare the median effective dose (ED50) of phenylephrine for preventing SAIH, while 10 or 20 mL/kg/h of crystalloid solution was coloaded. Methods Eighty healthy partrients undergoing elective cesarean delivery under combined spinal-epidural anesthesia were enrolled in the study. Subjects were randomly assigned to receive either 10 mL/kg/h (group 10) or 20 mL/kg/h (group 20) of lactated Ringer's solution. The first patient in each group received 0.5 µg/kg/min of phenylephrine infusion immediately after intrathecal injection. The dose of phenylephrine for the next patient varied with increments or decrements of 0.05 µg/kg/min based on the response of the previous patient. The ED50 of phenylephrine infusion to prevent spinal-induced hypotension for cesarean delivery were estimated using modified up-down sequential analysis with probit analysis applied as a backup sensitive analysis. Results The ED50 values for preventing SAIH were 0.30 µg/kg/min (95% CI, 0.29–0.32 µg/kg/min) for group 10, and 0.19 µg/kg/min (95% CI, 0.16–0.22µg/kg/min) for group 20, respectively. The estimated relative potency for phenylephrine in group 10 compared to group 20 was determined to be 1.52 (95%CI, 1.24–1.97), showing that there was a significant difference in the ED50 values between the two groups. Conclusion A negative correlation was found between the volume of liquid cohydration and the dose of preventive vasopressor in preventing spinal anesthesia-induced hypotension during cesarean delivery under the condition of this study. The combination of intravenous fluid administration and prophylactic vasopressor may be more suitable for the prevention of hypotension following spinal anesthesia.