A Comparison of Anesthetic Quality Between Interscalene Block and Superior Trunk Block for Arthroscopic Shoulder Surgery: A Randomized Controlled Trial

Background: Interscalene block is the most commonly used nerve block for shoulder surgery, and superior trunk block has been investigated as a phrenic-sparing alternative. This randomized controlled trial compared ultrasound-guided interscalene block and superior trunk block as anesthesia for arthroscopic shoulder surgery. Objectives: Our aims were to determine the superiority of anesthesia quality and compare the risk of hemidiaphragmatic paralysis between these 2 blocks. Study Design: A randomized, controlled trial. Setting: Department of Anesthesiology and Pain Medicine, Korea University Anam Hospital. Methods: Forty-eight patients undergoing elective arthroscopic shoulder surgery under an ultrasound guided brachial plexus block were randomized to receive either an interscalene block (ISB group, n = 24) or a superior trunk block (STB group, n = 24) for surgery. Ten milliliters of 2% lidocaine and 10 mL of 0.75% ropivacaine were used as local anesthesia in both brachial plexus block groups (total 20 mL). In the ISB group, the local anesthesia was injected between the C5–C6 root and at the upper part of C5 with equally divided doses. In the STB group, the local anesthesia was injected into the anterior and posterior parts of the superior trunk with equally divided doses. Sensory blockade of each trocar’s insulting site (supraclavicular, axillary, and suprascapular nerve areas) and motor blockade of the axillary nerve (shoulder abduction) and the suprascapular nerve (shoulder external rotation) were assessed by a blinded observer at 5-minute intervals for 30 minutes after the block. Anesthesia quality was assessed using 3 grades (excellent/insufficient/failure). The blinded investigator also assessed the grade of hemidiaphragmatic paralysis (normal/partial/complete) by comparing pre- and postoperative chest radiographs. Primary outcome variables were anesthesia grade and rate of hemidiaphragmatic paralysis. Secondary outcome variables were performance time and anesthesia onset time. Results: The anesthetic grade was significantly different between the 2 groups (22/2/0 in the ISB group vs. 16/3/5 in the STB group, P = 0.046). Both groups displayed equivalent incidence of hemidiaphragmatic paralysis (12/6/6 in the ISB group vs. 7/14/3 in the STB group, P = 0.063). No intergroup differences were found in terms of performance time and anesthesia onset time. Limitations: Our sensory and motor function test was not applied to the subscapular nerve, which serves internal rotation of the humeral head so may be difficult to evaluate in patients with rotator cuff tears. We assessed the diaphragmatic movement by chest radiographs instead of by ultrasound. Conclusions: The superior trunk block provided lower quality of surgical anesthesia than the interscalene block and did not effectively decrease the risk of hemidiaphragmatic paralysis during arthroscopic shoulder surgery for rotator cuff syndrome. Key words: Brachial plexus block, hemidiaphragmatic paralysis, interscalene block, superior trunk block, ultrasound