Minimum Effective Concentration/Volue Of Ropivaine For Ultrasound Supraclavicular Brachial Plexus Block

Background Supraclavicular block(SCB), often referred to as "spinal of the arm",which typically produces a complete and dense block of toe brachial plexus,lost its popularity due to a high risk of pneumotoorax. By dramatically decreasing toe risk of pleural puncture in SCB,ultrasound guidance(USG) has revolutionized the practice of regional anesthesia and contributed to the renaissance of this technique.By enabling the operators to visualize the needle,nerves,pleura and important surrounding structures under real-time ultrasound guidance, USG-SCB has the advantages of anesthetic efficiency,low incidence of block-related compHcations and convenience for educating purposes. Also by simultaneous observation of the local anesthetic(LA) spread,the doto of LA can be reduced Wiile ensuring toe block effectiveness,thereby reducing the incidence of adverse drug reactions(local anesthetic systemic toxicity, local neurotoxicity,etc.) and promoting a safer block.In order to prevent excessive administration of potentially toxic doses of LA as well as achieving a painless surgery, determination of minimum effective concentration and minimum effective volume is important for a peripheral nerve block(PNB). Ropivaciune isa long-acting amide LA, most frequently used for PNB in China To date, this is the first study investigating the appropriate concentration and volume of ropivacaine fbr USG-SCB.The study was carried out using a biased coin design (BCD) up-and-down method (UDM), exploring the appropriate concentration and volume combination of ropivacaine for USG-SCB for young (18 to 40 years old) and middle-aged (41 to 65 years old) adults by studying the minimum effective concentration in 90%of subjects (MEC90) and minimum effective volume in 90% of subjects (MEV90).Methods and Results1. Minimum Effective Concentration (MEC90) of Ropivacaine for Ultrasound-Guided Supraclavicular BlockMethods. A minimum of 45 patients undergoing elective surgery of the elbow, forearm, wrist, or hand were included in each age group. All the patients received double-injection US-guided SCB using ropivacaine 40mL. The study was based on BCD-UDM, where the concentration of ropivacaine administered to each patient depended on the response of the previous one. In case of failure, the ropivacaine concentration was increased by 0.025% in the next subject. If the previous patient had a successful block, the next subject was randomized to a lower concentration (with a decrement of 0.025%), with a probability of 0.11, or the same concentration, with a probability of 0.89. Success was defined as a complete sensory blockade of the brachial plexus 30 minutes after the block together with pain-free surgery. The patients’responses were analyzed to estimate the MEC90 by isotonic regression, with the 95% confidence interval (CI) calculated by bootstrapping method.Results. A total of 102 patients were included in the study, with 51 subjects in each age group, and none of them had pneumothorax, vascular puncture or any other severe complications. The MEC90 of ropivacaine for double-injection USG-SCB of young and middle-aged adult patients were estimated to be 0.273%(95% CI 0.240%-0.296%) and 0.257%(95% CI 0.241%-0.280%), respectively. By extrapolation to minimum effective concentration in 99%of subjects (MEC99) and pooled adjacent violators algorithm (PAVA) adjusted responses, it would be optimal to choose ropivacaine 0.325% and 0.275% for patients aged 18 to 40 years and 41 to 65 years, respectively.2. Minimum Effective Volume (MEV90) of Ropivacaine for Ultrasound-Guided Supraclavicular BlockMethods. A minimum of 45 patients undergoing elective surgery of the elbow, forearm, wrist, or hand were included in each age group. All the patients in young and middle-aged group received double-injection US-guided SCB using 0.325% and 0.275% ropivacaine, respectively. The study was based on BCD-UDM, where the volume of ropivacaine administered to each patient depended on the response of the previous one. In case of failure, the ropivacaine volume was increased by 2.0mL in the next subject. If the previous patient had a successful block, the next subject was randomized to a lower volume (with a decrement of 2.0mL), with a probability of 0.11, or the same volume, with a probability of 0.89. Success was defined as a complete sensory blockade of the brachial plexus 30 minutes after the block together with pain-free surgery. The patients’responses were analyzed to estimate the MEV90 by isotonic regression, with the 95% confidence interval (CI) calculated by bootstrapping method.Results. A total of 106 patients were included in the study, with 53 subjects in each age group, and none of them had pneumothorax, vascular puncture or any other severe complications. The MEV90 of ropivacaine for double-injection USG-SCB of young and middle-aged adult patients were estimated to be 29.5mL (95% CI 27.6-31.6mL) and 30.2mL (95% CI 28.2-34.1mL), respectively. By extrapolation to minimum effective volume in 99%of subjects (MEV99) and PAVA-adjusted responses, it would be optimal to choose ropivacaine 32.0mL for patients of both age groups.ConclusionFor adult patients 18-65 years old undergoing elective unilateral upper extremity surgery, in order to reach a balance between block efficacy and safety, the optimal concentration and volume of ropivacaine for double-injection supraclavicular brachial plexus block are 0.325% 32mL for patients 18-40 years old, and 0.275% 32mL for patients 41-65 years old.