Observing the dose-response relationship of ropivacaine for spinal anesthesia on cesarean section

Objective To evaluate effect of ropivacaine used in spinal anesthesia on cesarean section.Methods One hundred patients undergoing elective cesarean section were randomly divided into 4 groups:group A (ropivacaine 15 mg) ,group B (ropivacaine 17.5 mg),group C (ropivacaine 20mg) and group D (ropivacaine 22.5mg). All the groups were punctured in L2-3 interspace,then ropivacaine was injected into the subarachnoid space. The sensory block level,Bromage score were recorded. The degree of pain was evaluated using visual analogue scales(VAS). The relaxiation of the abdominal wall muscle was evaluated by the surgeon. Adverse reactions after anesthesia were recorded. The doses of ropivacaine for effective analgesia in 50% and 95% of patients (ED50 and ED95) and 95% confidence interval (CI) were calculated by Probit method. Results As the dose increased,motor block onset time shortened gradually,Bromage score increased gradually,sensory and motor recovery time is prolonged gradually. Analgesic efficacy of group A-D were 36%,64%,96%,100%. The incidence rate of very loose abdominal wall evaluated by the surgeon were 24%,48%,92%,100% respectively. Adverse reactions after anesthesia were fewer. The ED50 of ropivacaine was 15.95 mg(95% CI 15.31-16.62 mg) and ED95 18.76 mg(95% CI 17.67-19.54 mg).Conclusion The ED50 ,ED95 of ropivacaine used in spinal anesthesia for cesarean section was 15.95 mg and 18.76 mg.