Comparison of the anesthesia effect of ultrasound-guided middle and low interscalene brachial plexus block: a randomized, controlled, non-inferiority trial

BACKGROUND: Ultrasound-guided low interscalene brachial plexus block (LISB) can provide satisfactory anesthesia for surgery at or below the elbow. However, the anesthesia effect of ultrasound-guided middle interscalene brachial plexus block (MISB) has not been fully investigated. We hypothesized that MISB provides a non-inferior anesthesia effect to LISB for surgery at or below the elbow. METHODS: A total of 82 patients with ASA I-III (18–65 years) scheduled for elective surgery at or below the elbow were randomized to the MISB group or the LISB group equally, located 1/2 or 2/3 of the caudal distance from C6 to the clavicle. Both groups were administered 15 mL 0.5% ropivacaine at the lower part of the brachial plexus with the first injection and equivalent volume at the upper part with the second injection. RESULTS: For the primary outcome, 92.3% in the MISB group experienced successful anesthesia compared to 94.6% in the LISB group [difference: –2.3%, 95% confidence interval (CI) –13.4% to 8.8%], exceeding the predefined non-inferiority margin -15%. For the secondary outcomes, the incidence of pleura suppression for the first injection (7.7% vs. 45.9%, P < 0.001) and the time to perform the block (9.9 ± 1.3 vs. 10.7 ± 1.3 min, P = 0.006) were significantly less in MISB compared to LISB. No significant differences were observed in the consumption of perioperative rescue analgesics, VAS score, and adverse events within the two groups. CONCLUSIONS: MISB provides a non-inferior anesthesia effect to LISB for surgery at or below the elbow. TRIAL REGISTRATION: Chinese Clinical Trial Register (identifier: ChiCTR2100054196).