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 15 mg intrathecal hyperbaric ropivacaine respectively. The prophylactic phenylephrine infusion (50 μg/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 μg sufentanil for successful anesthesia was 15.2 mg (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 15.2 mg.