Supplementary Material

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Background: Preoperative interscalene brachial plexus block (ISB) has been shown to reduce postoperative nausea and vomiting after shoulder arthroscopy performed under general anesthesia (GA), possibly via reduced consumption of opioids. Postoperative urinary retention (POUR) is another adverse effect after GA with higher incidence among the elderly patients. The aim of this study is to investigate the effect of preoperative ISB on POUR.

Methods: A historical cohort analysis of patients receiving shoulder arthroscopy under GA was conducted. Included patients were allocated to ISB + GA or GA only group. The difference in incidence of POUR between groups were explored as well as intraoperative requirement of inhaled anesthetics and fentanyl. Potential risk factors of POUR were also assessed with multivariate logistic regression analysis.

Results: There are 229 patients in ISB + GA group and 169 patients in GA only group. Patient characteristics shows no difference between groups. ISB + GA group required lower concentration of inhaled anesthetics (fraction of minimum alveolar concentration (fMAC) 0.71 (0.16) vs. 0.93 (0.15), p < 0.001) and less total fentanyl dose (mcg kg-1, 1.9 (0.7) vs. 2.7 (1.1), p < 0.001). The incidence of POUR is lower in ISB + GA group than GA only group (3.9% vs. 10%, p = 0.02) aswell as the incidence of postoperative nausea (28.4% vs. 39%, p = 0.03), and postoperative vomiting (16.2% vs. 25%, p = 0.03). Multivariate analysis reveals increased age and intraoperative fentanyl dose are associated with increased POUR.

Conclusion: Preoperative ISB is associated with decreased consumption of intraoperative opioids, which may contribute to a reduced incidence of POUR.