Lidocaine plasma levels following two techniques of obturator nerve block

Abstract

Study Objectives: To assess plasma levels and the potential toxicity of lidocaine following two different approaches to the obturator nerve. Design: Prospective, randomized, clinical trial. Setting: Operating rooms of a university hospital. Patients: 45 ASA physical status I, II, and III patients over 40 years of age, and undergoing transurethral resection of urinary bladder tumors. Interventions: A prospective study compared lidocaine plasma levels following direct and indirect (3-in-1) obturator nerve block using lidocaine 1.5% plus 1:200,000 epinephrine. Patients with unilateral urinary bladder tumors were randomized to receive direct obturator nerve block with 15 ml of lidocaine (Group A, n = 20), while those with bilateral tumors received a bilateral direct obturator nerve block with 30 ml (2 × 15 ml) of lidocaine (Group B, n = 12). A third group of patients with unilateral bladder tumors received 3-in-1 (indirect) obturator nerve block with 40 ml of lidocaine (Group C, n = 17). Plasma lidocaine concentration was determined every 5 minutes for 30 minutes, and at 45, 60, and 90 minutes after the block. Measurements and Main Results: In Group A, mean (±SD) peak plasma lidocaine level of 1.35 ± 0.5 μg/ml (range 0.61 to 2.41 μg/ml) occurred 45 minutes after injection. In Group B, a peak of 3.63 ± 2.07 μg/ml (0.75 to 7.21 μg/ml) occurred 15 minutes after injection. Mean peak level in Group C of 2.08 ± 0.77 μg/ml (0.84 to 3.21 μg/ml) occurred 60 minutes after injection. Lidocaine concentrations were significantly higher in Groups B and C than in Group A, and they were higher in Group B than in Group C. No patient had any signs of symptoms of local anesthetic toxicity. Conclusions: Despite a lower total dose of lidocaine administered (450 mg), higher mean and peak plasma levels were reached sooner with bilateral direct obturator nerve block compared with the indirect obturator nerve block (600 mg), indicating a faster blood absorption of lidocaine following direct block. Both types of obturator nerve block prevented adductor muscle contraction in a large percentage of cases.