ED50 and ED95 of intrathecal hyperbaric ropivacaine for parturients undergoing cesarean section with prophylactic infusion of phenylephrine A Prospective dose-finding Study

Background: Studies have reported that the ED50 of intrathecal ropivacaine was increased when using prophylactic infusion of phenylephrine to prevent spinal-induced hypotension. However, ED95 is more meaningful to clinical practice than ED50. Therefore, we conducted this study to determine the 95% effective dose (ED95) of intrathecal hyperbaric ropivacaine for cesarean section in parturients receiving prophylactic infusion of phenylephrine to prevent spinal-induced hypotension. Methods: A hundred of healthy parturients undergoing elective cesarean section under combined spinal-epidural anesthesia (CSEA) were enrolled in this randomized, double-blinded, dose-ranging study. Patients were randomly assigned to receive 7, 9, 11, 13 or 15mg intrathecal hyperbaric ropivacaine respectively. The prophylactic phenylephrine infusion (50mg/min) was initiated immediately at the same time of spinal injection. Successful spinal anesthesia was defined as a T5 sensory level achieved within 10 min after intrathecal drug administration and no epidural supplement was required during the surgery. The ED95 was calculated with Probit analysis. Results: The ED95 of intrathecal ropivacaine with 5 mu g sufentanil for successful anesthesia was 15.2mg (95% CI, 13.5-18.8 mg), when receiving prophylactic infusion of phenylephrine. Conclusion: Under the conditions of the present study, the ED95 of intrathecal hyperbaric ropivacaine for successful spinal anesthesia for cesarean section in healthy parturient receiving prophylactic infusion of phenylephrine was 15.2mg.