Onset times and duration of analgesic effect of various concentrations of local anesthetic solutions in standardized volume used for brachial plexus blocks

Visualization of the nerve structures of brachial plexus allows anesthesiologists to use a lower dose of local anesthetics. The content of this low dose is not unequivocal, consequently, the pharmacokinetics of local anesthetics used by various authors are difficult to compare. In this study, the onset times and duration of the analgesic effect of local anesthetic mixture solutions used for brachial plexus blocks are investigated and the quality of anesthesia is compared. 85 unpremedicated American Society of Anesthesiologist physical status I-III, 19-83-year-old patients scheduled for upper limb trauma surgery are assigned to four groups for the axillary-supraclavicular block with lidocaine 1% and bupivacaine 0,5% 1:1 mixture (Group LB) or bupivacaine 0.33% (Group BS) or lidocaine 0,66% (Group LS) or bupivacaine 0.5% and lidocaine 1% 2:1 mixture (Group BL). 0.4 ml/kg was administered to the four groups. The onset time was significantly shorter in the lidocaine group (LS 13.0 ± 1.02) than in the other study groups (LB 16.64 ± 0.89; BS 17.21 ± 0.74; BL 16.92 ± 0.51 min ±SEM, p = 0.002). No differences were observed in the onset times between LB, BS, and BL groups (p > 0.05). Statistical differences were found in the duration of local anesthetics between LB (392.9 ± 20.4), BS (546.4 ± 14.9), LS (172.85 ± 7.8), and BL (458.7 ± 11.9 min ±SEM, p = 0.001). Lidocaine does not shorten the onset times, but significantly decreases the duration of action of bupivacaine when used in mixture solutions. Lidocaine exhibits a good quality of block in the applied dose, while other solutions have excellent quality. Bupivacaine without lidocaine has the longest duration of action to achieve the longest postoperative analgesia.