Comparison between two different concentrations of a fixed dose of ropivacaine in interscalene brachial plexus block for pain management after arthroscopic shoulder surgery: a randomized clinical trial

Background: Only a few studies have evaluated the differences between varying concentrations of a fixed dose of local anesthetics. This study was conducted to compare the effects of two different concentrations of a fixed dose of ropivacaine used in ultrasound-guided interscalene brachial plexus block. Methods: This prospective, randomized, double-blind study included 62 patients who underwent arthroscopic surgery under general anesthesia. The patients were randomly assigned to receive ultrasound-guided interscalene block with 75 mg of ropivacaine at one of two concentrations: 0.75% (10 ml; group C) or 0.375% (20 ml; group V). Time to onset of sensory blockade, degree of blockade, pulmonary function changes, analgesic duration of the interscalene block, postoperative opioid requirement within 24 h, postoperative pain scores, satisfaction, and incidence of complications were recorded. Results: Although the time to onset of sensory blockade was shorter for group C (P = 0.015), successful blockade was achieved at 30 min after the interscalene block in both groups. The analgesic duration of the interscalene block was not significantly different between the groups. The amount of opioid used within 24 h after surgery was significantly reduced for group V compared with group C (P = 0.016). The rest of the parameters did not show any significant differences between the two groups.Conclusion: Compared with 10 ml of 0.75% ropivacaine, interscalene block with 20 ml of 0.375% ropivacaine could be effective for the reduction of postoperative opioid requirement within 24 h after surgery despite it might not prolong the analgesic duration.