Impact of adding dexmedetomidine to various lidocaine concentrations in the interscalene brachial plexus block for upper limb surgery

Background. The interscalene brachial plexus block is widely used in orthopedic surgery for procedures on the proximal upper limb. However, the main concern remains the systemic toxicity of local anesthetics due to the use of their high concentrations. The purpose of the study was to investigate the effect of adding dexmedetomidine to lidocaine solutions of different concentrations in the interscalene brachial plexus block by examining the onset time and duration of motor block and analgesia. Materials and methods. The study included 75 patients who underwent elective upper limb surgery under interscalene brachial plexus block. They were divided into three groups (n = 25 each): control group I (L1%), group II (Dex L1%), and group III (Dex L0.5%). In group I, the brachial plexus block was performed using a 1% lidocaine solution with the addition of 50 mcg of epinephrine (1 : 400,000). In group II, 50 mcg of dexmedetomidine was added to the same solution, while group III (Dex L0.5%) used a 0.5% lidocaine solution combined with 50 mcg of dexmedetomidine. The duration of analgesia, motor function of the upper limb, hemodynamic changes, and side effects were assessed. Results. Preoperatively, the time of complete motor block onset (Me [25 %; 75 %]) in groups L1% and Dex L1% was 12.5 [10.0; 15.0] minutes, which was slightly shorter than in group Dex L0.5% (15.0 [15.0; 20.0] minutes; p = 0.06). The duration of complete motor block was longest in the Dex L1% group (330 [270; 440] minutes) compared to the Dex L0.5% group (305 [235; 348] minutes; p = 0.25) and the L1% group (185 [180; 255] minutes; p < 0.002). The duration of analgesia in the Dex L1% group (460 [330; 480] minutes) was significantly longer than in the Dex L0.5% group (305 [248; 425] minutes; p = 0.35) and the L1% group (270 [210; 333] minutes; p = 0.018), with no statistically significant difference between Dex L0.5% and L1% groups (p = 0.29). The heart rate was significantly reduced at the start and the end of surgery compared to baseline in the Dex L1% and Dex L0.5% groups. Systolic blood pressure was significantly reduced in all groups at all stages compared to baseline. Conclusions. The addition of dexmedetomidine prolongs both motor block and analgesia after interscalene brachial plexus block and allows the lidocaine concentration to be reduced to 0.5 % without compromising efficacy.