Median Effective Concentration Of Ropivacaine Producing Sensory-motor Separation When Used For Femoral Nerve Block Performed Under Ultrasound Guidance

Objective:To determine the median effective concentration(EC₅₀)of ropivacaine producing sensory-motor separation when used for femora l nerve block performed under ultrasound guidance.Methods:American Society of Anesthesiologists physical status I-II patients of both sexes,aged 18-64 yr,with body mass index of 18-30kg/m²,scheduled for elective unilateral arthroscopic knee surgery the first ti me under general anesthesia,were enrolled in this study.Femoral nerve bl ock was performed under ultrasound guidance.After successful location,ro pivacaine 22 ml was injected with the initial concentration of 0.2%,and the concentration gradient between the two consecutive was 0.02%.The EC₅₀ of ropivacaine was determined by up-and–down sequential method.The positive response was considered as sensory block without motor bl ock.The negative response was considered as sensory and motor block.When a negative response was found,the concentration was decreased in the next patient.When a positive response occurred,the concentration wa s increased in the next patient.Probit analysis was used to calculate the EC₅₀ and 95%confidence interval of ropivacaine producing sensory-mot or separation when used for femoral nerve block which was performed under ultrasound guidance.Results:The EC₅₀ of ropivacaine producing sensory-motor separatio n was 0.188%,and the 95%confidence interval was 0.173%～0.203%wh en used for ultrasound-guided femoral nerve block.Conclusions:The EC₅₀ of ropivacaine producing sensory-motor separ ation is 0.188%when used for femoral nerve block performed under ultr asound guidance.