Local anesthetic volume in ultrasound-guided interscalene block and opioid consumption during shoulder arthroscopic surgery A retrospective comparative study

Interscalene block (ISB) is commonly performed for regional anesthesia in shoulder surgery. Ultrasound-guided ISB enables visualization of the local anesthetic spread and a reduction in local anesthetic volume. However, little is known about the appropriate local anesthetic dose for surgical anesthesia without sedation or general anesthesia. The purpose of our study was to evaluate the appropriate local anesthetic volume by comparing intraoperative analgesics and hemodynamic changes in ISB in arthroscopic shoulder surgery. Overall, 1007 patients were divided into groups 1, 2, and 3 according to the following volume of local anesthetics: 10-19, 20-29, and 30-40 mL, respectively. The use of intraoperative analgesics and sedatives, and the reduction in intraoperative maximum blood pressure and heart rate were compared through retrospective analysis. Fentanyl was used in 55.6% of patients in group 1, which was significantly higher than in those groups 2 and 3 (22.3% and 30.7%, respectively); furthermore, it was also higher than those in groups 2 and 3 in dose-specific comparisons (P < .05). The percent of the maximum reduction in intraoperative systolic blood pressure and heart rate in group 3 was significantly higher than those in groups 1 and 2. Ephedrine administration was lower in group 2 than that in other groups (P < .05). The incidence of hypotensive bradycardic events was lowest (9.1%) at the local anesthetic volume of 24 mL as revealed by the quadratic regression analysis (R-2 = 0.313, P = .003). Decreasing the local anesthetic volume to less than 20 mL for ultrasound-guided ISB as the sole anesthesia increases the opioid consumption during shoulder arthroscopic surgery. Local anesthetics >30 mL or increased opioid consumption with <20 mL of local anesthetics could increase the risk of cardiovascular instability intraoperatively. Our findings indicate that 24 mL of local anesthetic could be used to lower the incidence of hypotensive bradycardic events.