Abstract: Objective To determine the median effective concentration (EC50) and 95% effective concentration (EC95) of ropivacaine for ultrasound-guided llioinguinal, lliohypogastric and genitocruralnerve block in aged patients with inguinal hernia. Methods Thirty-five male patients, American Society of Anesthesiologists physical status Ⅱ or Ⅲ, body mass index 19-27 kg/m2 , aged 65-79 yr, scheduled for elective unilateral tension-free inguinal hernia repair were included in this study. Patients received an ultrasound-guided llioinguinal, lliohypogastric, and genitocrural nerve block. After successful location 10 mL ropivacaine was injected at each puncture point. The sensory block of the areas innervated by the nerves were assessed by pin-prick test. The painless of the areas innervated by target nerves (VAS=0) at the beginning of operation was regarded as the effective block. The concentration of ropivacaine was determined by Dixon up-and-down method. The initial concentration was 0.3%. When the block was effective, the next patient was given the low first-order concentration, on the contrary, the patient was given the high first-order concentration. The ratio between the adjacent concentrations was 1∶1.1. The EC50, EC95 and their 95% confidence interval (CI) were calculated by probit analysis. Results Eighteen (51.4%) in a total of 35 patients received a successful nerve block.The EC50 of ropivacaine was 0.263% (95%CI: 0.248%-0.280%) and the EC95 was 0.348% (95%CI: 0.323%-0.371%). Conclusion The EC50 and EC95 of ropivacaine for ultrasound-guided llioinguinal, lliohypogastric and genitocrural nerve block are 0.263% and 0.348% in aged patients with inguinal hernia respectively.

Key words: nerve block, hernia, inguinal, aged, ultrasonography, dose-response relationship, drug, ropivacaine; genitocruralnerve