Unilateral spinal block for outpatient knee arthroscopy: A dose-finding study

Study Objective: To evaluate the onset time, success rate, and recovery profile of unilateral spinal anesthesia produced with 4 mg, 6 mg, and 8 ing of 0.5% hyperbaric bupivacaine. Design: Prospective, randomized, blinded study Setting: Outpatient anesthesia unit at a University Hospital. Patients: 90 ASA physical status I and H outpatients, who were scheduled for elective knee arthroscopy. Interventions: After standard intravenous midazolam premedication (0.05 mg/kg) and crystalloid infusion (7 mL/kg) were given, patients were placed in the lateral decubitus position on the operative side, and randomly allocated to receive spinal block with either 4 ing (Group 4, n = 30), 6 ing (Group 6, n = 30), or 8 mg (Group 8, n = 30) of 0.5 % hyperbaric bupivacaine injected slowly (3 mL/min) with the needle orifice directed toward the dependent side using a 25-gauge Whitacre needle. The lateral decubitus position was. maintained for 15 minutes. Measurements and Main Results: The onset time of surgical block was 13 +/- 5 minutes in Group 4 and 10 +/- 4 minutes in Group 6 (p = 0.006), and 9 +/- 4 minutes in Group 8 (p = 0.002). The maximum level of sensory block on the operative and nonoperative sides was, respectively, T-10 (T-12-T-6) and / (/-L-2) in Group 4 (p = 0.0005), T-8 (T-12-T-6) and / (/-L-5) in Group 6 (p = 0.0005), and T-7 (T-12-T-5) and (/-T-10) in Group 8 (p = 0.0005). A strictly unilateral sensory block, was observed in 2 7 Group 4 patients (90 %), 28 Group 6 patients (93 %) and 23 Group 8 patients (77 %) (p = 0. 28). Complete unilateral motor block was observed in 29 Group 4 patients (97%), 28 Group 6 patients (93 %), and 28 Group 8 patients (93 %) (p = 0. 80). No failed blocks were reported. Complete regression of spinal anesthesia required 71 - 20 minutes in Group 4 (range: 40 to I 10 min), 82 +/- 25 minutes in Group 6 (range: 30 to 160 min), and 97 +/- 3 7 minutes in Group 8 (range: 50 to 120 min) (p = 0. 003). Conclusions: Hyperbaric bupivacaine 4 ing injected slowly through pencil-point directional needles in patients who are maintained in the lateral decubitus position for 15 minutes provided a surgical block that was mostly restricted to the operative side and adequate to perform knee arthroscopy, with a faster recovery profile than when a 6 mg or 8 mg dose was used. (C) 2003 by Elsevier Inc.