Median effective concentration of ropivacaine producing sensory-motor separation when used for femoral nerve block performed under ultrasound guidance / 中华麻醉学杂志

ABSTRACT

Objective:To determine the median effective concentration (EC 50) of ropivacaine producing sensory-motor separation when used for femoral nerve block performed under ultrasound guidance. Methods:American Society of Anesthesiologists physical status Ⅰ-Ⅲ patients of both sexes, aged 18-64 yr, with body mass index of 18-30 kg/m 2, scheduled for elective arthroscopic knee surgery under general anesthesia, were enrolled in this study. Femoral nerve block was performed under ultrasound guidance.After successful location, ropivacaine 22 ml was injected with the initial concentration of 0.50%, and the ratio between the two consecutive concentrations was 1.1.The EC 50 of ropivacaine was determined by up-and-down sequential method.The positive response was considered as sensory block without motor block.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 was increased in the next patient.Probit analysis was used to calculate the EC 50 and 95% confidence interval of ropivacaine producing sensory-motor separation when used for femoral nerve block which was performed under ultrasound guidance. Results:The EC 50 of ropivacaine producing sensory-motor separation was 0.186%, and the 95% confidence interval was 0.155%-0.205% when used for ultrasound-guided femoral nerve block. Conclusion:The EC 50 of ropivacaine producing sensory-motor separation is 0.186% when used for femoral nerve block performed under ultrasound guidance.