Median effective dose of intrathecal hyperbaric and hypobaric ropivacaine for cesarean section

Abstract

Objective To determine the median effective dose (ED50) of intrathecal (IT) hyperbaric and hypobaric ropivacaine for elective cesarean section.Methods Forty parturients aged 20-40 yr at full term undergoing elective cesarean section under combined spinal-epidural anesthesia were randomized to receive IT 0.5 ％ hyperbaric (group HR) and hypobaric ropivacaine (group LR) ( n =20 each).The initial dose was 9 mg and the dose was increased/decreased by 1 mg in the next parturient using an up-and-down sequential allocation technique.Analgesia was considered acceptable if adequate analgesia reached T7 or higher in response to pin prick until 20 min after IT ropivacaine and no supplemental epidural analgesic was required during the operation.ED50 and 95％confidence interval (CI) were calculated.Results The ED50 and 95 ％ CI were 9.34 mg (95 ％ CI 8.34-10.46mg) for 0.5％ hyperbaric ropivacaine and 9.64 mg (95％ CI 8.90-10.44 mg) for 0.5％ hypobaric ropivacaine.Conclusion Baricity has no effect on the efficacy of IT ropivacaine for cesarean section. Key words: Amides; Specific gravity; Anesthesia, spinal; Cesarean section; Dose-response relationship, drug