RESUMEN
Abstract Background: Ultra-low-dose Spinal Anesthesia (SA) is the practice of employing minimal doses of intrathecal agents so that only the roots that supply a specific area are anesthetized. The aim of this study was to compare the effectiveness and safety of ultra-low-dose spinal anesthesia with that of Perineal Blocks (PB). Methods: A two-arm, parallel, double-blind randomized controlled trial comparing two anesthetic techniques (SA and PB) for hemorrhoidectomy and anal fistula surgery was performed. The primary outcomes were postoperative pain, complementation and/or conversion of anesthesia, and hemodynamic changes. Results: Fifty-nine patients were included in the final analysis. The mean pain values were similar in the first 48 h in both groups (p > 0.05). The individuals allocated to the SA group did not need anesthetic complementation; however, those in the PB group required it considerably (SA group, 0% vs. PB group, 25%; p = 0.005). Hemodynamic changes were more pronounced after PB: during all surgical times, the PB group showed lower MAP values and higher HR values (p < 0.05). Postoperative urinary retention rates were similar between both groups (SA group 0% vs. PB group 3.1%, p = 0.354). Conclusion: SA and PB are similarly effective in pain control during the first 48 h after hemorrhoidec-tomy and anal fistula surgery. Although surgical time was shorter among patients in the PB group, the SA technique may be preferable as it avoids the need for additional anesthesia. Furthermore, the group that received perineal blocks was under sedation with a considerable dose of propofol.