Pharmacodynamics of different local anesthetics administered intrathecally for caesarean section

Abstract

Objective To investigate tbe pharmacodynamics of different local anesthetics administered intrathecally for caesarean section. Methods Ninety-six parturients with singleton term pregnancies undergoing caesarean section under combined spinal-epidural anesthesia were enrolled in this study. The patients were randomly divided into 3 groups （ n = 32 each ） and received intrathecal （ IT ） 0.5 % bupivacaine, 0.5 % levobnpivacaine and 0.5 % ropivacalne respectively. The initial doses was 9 mg in all 3 groups. The ratio of two successive doses was 0.9. If the upper sensory block reached T7 or above and there was no need for additional dose in the 45 min after the initial dose, the IT analgesia was considered to be effective. The median effective dose （ ED50 ）, the 95 % effective dose （ ED95 ） and 95 % confidence interval （95 % CI） were calculated by Dixon. Results The EDs0 and ED95 and 95% CI of bupivacalne were 6.15 （95% CI 5.48-6.68） mg and 7.62 （95% CI 6.91- 11.82） rag; of levobupivacaine were 8.06 （95% CI 7.46-8.62） mg and 9.59 （95% CI 8.86-13.42） mg; of ropivacaine were 10.55 （95%CI 9.73-11.49） mg and 12.80 （95%CI 11.66-21.42） rag. The relative potency ratio between bupivacaine, levobupivacaine and rupivacaine is 1.00： 0.76：0.58. Conclusion The relative potency ratio between bupivacalne, levobupivacaine and rupivacaine is 1.00 ： 0.76 ： 0.58. Key words: Bupivacaine ; Amides ; Dose-response relationship, drug; Cesarean section ; Injections, spinal