Background: Using brachial plexus blocks as regional anaesthetic is standard procedure for upper limb surgery. Although a retro-clavicular brachial plexus block has just been proposed, another technique has not been thoroughly evaluated. This single-blinded, randomized, controlled experiment looked at whether the retroclavicular technique had a higher success rate than the supraclavicular approach. Methods: This experimental study was conducted in the Department of Anaesthesia, National Institute of Traumatology and Orthopaedic Rehabilitation (NITOR), Dhaka, Bangladesh From June 2019 to June 2021. The physical state of one hundred and twenty ASA members there was randomization of 1-3 patients having distal surgery on their upper limbs to receive a 30 mL 1:1 mixture of mepivacaine and ropivacaine, which was administered as a single injection without repositioning the needle tip, using ultrasound guidance for the retroclavicular or supraclavicular brachial plexus block. In the 30 minutes following local anaesthetic injection, the primary outcome was block success rate defined as a composite score of 14 points, including sensory and motor components, inclusive. Additionally, secondary outcomes were the number of needles used, the time it took to obtain an opioid, the amount of oxycodone taken, and the patient's postoperative pain level (on a numeric rating range of 0-10). Results: Success rates were 98.3% [95% confidence interval (CI): 90.8%, 99.9%] and 98.3% [95% CI: 90.9%, 99.9%] in the supraclavicular and retroclavicular groups, respectively (P¼0.99). The mean needling time was reduced in the supra- clavicular group [supraclavicular: 5.0 (95% CI: 4.7, 5.4) min; retroclavicular: 6.0 (95% CI: 5.4, 6.6) min; P¼0.006]. The mean time to first opioid request was similar between groups [supraclavicular: 439 (95% CI: 399, 479) min; retroclavicular: 447 (95% CI: 397, 498) min; P¼0.19] as were oxycodone consumption [supraclavicular: 10.0 (95% CI: 6.5, 13.5 mg; ...............