Abstract
BACKGROUND: The superior trunk block (STB) has been proposed as an alternative to interscalene block for reducing the risk of hemidiaphragmatic paralysis (HDP) while maintaining adequate analgesia. However, the optimal local anesthetic dosage for STB has not been established. This study aimed to evaluate whether a low dose of ropivacaine could effectively provide surgical anesthesia, reduce the incidence of complete and partial HDP, and improve anesthetic safety and patient comfort during shoulder arthroscopy. METHODS: Eighty-eight patients scheduled for shoulder arthroscopy were enrolled and randomly allocated in a 1:1 ratio to either a low-dose group (LD group; 10 mL of 0.25% ropivacaine) or a conventional-dose group (CD group; 15 mL of 0.5% ropivacaine). The primary outcome was the incidence of HDP assessed at 3 h post-block. Secondary outcomes included rates of successful surgical anesthesia, pain scores, opioid consumption, duration and onset time of the block, handgrip strength, and patient satisfaction. RESULTS: The incidence of complete and partial HDP at 3 h post-STB was significantly lower in the LD group than in the CD group (31.8% vs. 84.1%, p < 0.001), with an absolute risk reduction of 52.3% (95% CI: 34.8% to 69.8%). All patients in both groups successfully underwent surgery without conversion to general anesthesia with tracheal intubation or requiring supplemental intraoperative analgesia. The overall patient satisfaction score was significantly higher in the LD group compared to the CD group (p = 0.003). However, patients in the LD group reported higher pain scores at 12 h post-block (p = 0.044), exhibited a shorter duration of sensory block (p = 0.001) compared to the CD group. CONCLUSIONS: These findings indicate that a low-dose ropivacaine regimen (10 mL of 0.25%) for STB significantly reduces the incidence of HDP while still providing sufficient surgical anesthesia. However, this approach may be associated with reduced efficacy in postoperative analgesia. TRIAL REGISTRATION: This trial was registered at the Chinese Clinical Trial Registry (No. ChiCTR2000036608).