The 90% minimum effective volume of 0.5 ropivacaine for Ultrasound-guided femoral nerve block: A biased coin up-and-down design.

Abstract

Abstract Background:The ultrasound-guided femoral nerve block is commonly employed in lower limb surgeries; however, there is presently a paucity of precise research regarding the optimal dosage of local anesthetic agents. This study aims to determine the 90% minimum effective volume (MEV90) for ultrasound-guided femoral nerve block. Methods: All patients received an ultrasound-guided femoral nerve block with 0.5% ropivacaine at an initial volume of 0.12 mL/mm2 of cross-sectional nerve area. In cases of a successful block, the next patient received the same volume with a probability of 0.89, and the volume was decreased by 0.04 mL/mm2 of cross-sectional nerve area with a probability of 0.11. In the event of block failure, the volume was increased by 0.02 mL/mm2 cross-sectional nerve area. Following 45 successful block cases, the MEV90 of local anesthetic was determined using the centered isotonic regression method. Results: Centred isotonic regression analysis revealed that the MEV90 for the femoral nerve block is 0.182 mL/mm2, with a 95% confidence interval ranging from 0.160 to 0.278 mL/mm2. Conclusions:The application of 0.182 mL/mm2 of 0.5% ropivacaine allows for precise dosing, resulting in a femoral nerve block effect and concurrently reducing the potential for local anesthetic poisoning. Trial registration：We registered the study prospectively at chinese Clinical Trial Registry(https://www.chictr.org.cn)(Ref. No. ChiCTR2300077426，Date of Registration:2023-11-08 )