Background and Aims Continuous interscalene brachial plexus block (ISB) provides superior analgesic benefits in major shoulder surgery but has a high risk of hemidiaphragmatic paresis (HDP). Using proximal longitudinal oblique (PLO) approach, catheter can be placed without interfering with surgical site, and the local anesthetic can be injected more distally. We expected supraclavicular brachial plexus block using PLO approach (PLO-SCB) would provide equivalent analgesia compared with ISB while sparing the phrenic nerve.

Methods Patients were randomly allocated to receive continuous PLO-SCB (n = 40) or continuous ISB (n = 40) after low-volume single-shot injection. The primary outcomes were HDP incidence and worst pain scores. Secondary outcomes included respiratory function, postoperative analgesic consumption, sensory and motor function, and complications. This study was appoved by the Institutional Review Board of Asan Medical Center.

Results Incidence of HDP was significantly lower in the PLO-SCB group than in the ISB group at 30 min after block (28 of 38 [73.7%] vs. 0 of 38 [0%]; p<0.001) and 24 h after surgery (18 of 38 [47.4%] vs. 9 of 38 [23.7%]; P=0.002). Pain scores measured immediately (1 [0,2] vs. 1 [0,1]; p=0.06), and 24 h after surgery (6 [4,8] vs. 5 [3,7]; p=0.199) were similar between the two groups.

Conclusions Continuous PLO-SCB showed minimal effect on phrenic nerve function while providing equivalent analgesia to continuous ISB in patients undergoing arthroscopic shoulder surgery. For single-shot injection, low-volume PLO-SCB achieves a 0% rate of HDP while maintaining analgesia. PLO-SCB could be applied even in patients with a high risk of postoperative respiratory complications.