Minimum Effective Dose of Ropivacaine 0.5% for Ultrasound-guided Interscalene Block Targeting the C7 Nerve Root in Hand and Forearm Surgery

Overview

Inter muscular groove brachial plexus block is a commonly used peripheral nerve block technique in clinical practice, commonly used for anesthesia and analgesia in clavicle, shoulder, and humeral surgeries. Intermuscular groove block is achieved by injecting local anesthetics between the anterior and middle scalene muscles in order to block the anterior branches of the cervical nerve that pass through this gap, including the anterior branches of the cervical 5 (C5), cervical 6 (C6), and cervical 7 (C7) spinal nerves. The classic technique of intermuscular groove block involves puncturing the thyroid cartilage horizontally into the intermuscular groove. This area is roughly equivalent to the level of the anterior branch of the C5/C6 nerve root. The classic ultrasound-guided intermuscular groove block also involves puncturing the needle to the level of the C5/C6 anterior branch for drug injection. After injection, local anesthetics mainly wrap around C5, C6, and some C7 nerve roots. According to the range of spinal nerve innervation, its blocking range is located in the shoulder, the anterior, posterior, and lateral sides of the upper arm, the anterior, posterior, and lateral sides of the forearm, and the two and a half fingers on the radial side. Therefore, intermuscular groove block is mainly used for shoulder, humerus, and clavicle surgery. Due to incomplete ulnar block, it is not recommended for surgery on the elbow joint and its distal end. Scholars have found that using C5 as the puncture target to implement intermuscular groove block and administering 10ml of 0.75% ropivacaine, the success rate of ulnar nerve block is 19%. The success rate of ulnar nerve block with C6 as the puncture target was 93% when 10ml of 0.75% ropivacaine was administered. This suggests that blockade methods closer to the tail muscle groove on the tail side have a higher success rate for blocking the C7, C8, and T1 nerve roots. In our clinical work, we found that when performing intermuscular groove block with C7 nerve root as the puncture target, local anesthetics not only stably wrap around C7 nerve root, but also spread to wrap around C5 and C6 nerve roots on the head side, and spread to the deep surface of the brachial plexus trunk on the tail side. Local anesthetic diffusion can also be seen in some patients at the brachial plexus bundle in the intercostal space. From the perspective of local anesthetic diffusion patterns, intermuscular groove block targeting the C7 nerve root may cover the anterior branches of C5, C6, C7, C8, and T1 nerve roots, achieving complete brachial plexus block. In the preliminary exploratory clinical work, the patient underwent C7 nerve root intermuscular groove brachial plexus block. Through sensory testing, it was found that the musculocutaneous nerve, medial forearm nerve, radial nerve, median nerve, and ulnar nerve could all be stably blocked, and the forearm and hand surgeries were successfully completed under nerve block. Preliminary clinical practice suggests that C7 intermuscular groove block can be used for forearm and hand surgery. Successful C7 intermuscular groove block relies on the diffusion and wrapping of local anesthetics around the anterior branches of C5, C6, and C7 nerve roots, as well as the inferior trunk of the brachial plexus (or the anterior branches of C8 and T1 nerve roots). Therefore, we designed this study to determine the amount of local anesthetic required to achieve stable forearm and hand block during C7 intermuscular groove block.