Median effective dose of 0.5% ropivacaine for ultrasound-guided adductor canal saphenous nerve block

Objective To determine the median effective dose (ED50) of 0.5% ropivacaine for ultrasound-guided adductor canal saphenous nerve block. Methods Twenty-three patients of both sexes, aged 18-45 yr, weighing 50-85 kg, of American Society of Anesthesiologists physical statusⅠ or Ⅱ, scheduled for elective arthroscopic meniscectomy, received an ultrasound-guided adductor canal saphenous nerve block.After successful location, 0.5% ropivacaine was injected.The sensory block of the area innervated by the saphenous nerve was assessed by pin-prick test.The dose of ropivacaine was determined by up-and-down technique.The initial dose of ropivacaine was set at 18 ml.Each time the dose increased/decreased in the next patient according to whether or not the sensory block of the area innervated by the saphenous nerve was complete, and the ratio between the two successive doses was 1∶1.2.The ED50 and 95% confidence interval of 0.5% ropivacaine for adductor canal saphenous nerve block were calculated by probit analysis. Results The ED50 (95% confidence interval) of 0.5% ropivacaine for ultrasound-guided adductor canal saphenous nerve block was 10.7 (8.8-12.2) ml. Conclusion The ED50 of 0.5% ropivacaine for ultrasound-guided adductor canal saphenous nerve block is 10.7 ml. Key words: Amides; Nerve block; Dose-response relationship, drug; Ultrasonography