DOSE-RANGE EFFECTS OF CLONIDINE ADDED TO LIDOCAINE FOR BRACHIAL-PLEXUS BLOCK

Background: Although addition of clonidine to local anesthetics can pr olong pain relief after peripheral nerve block, a dose-range effect ha s not been determined, Methods: Fifty-six outpatients undergoing carpa l tunnel release were randomly assigned to receive in a double-blind f ashion 45 ml of a mixture containing either 400 mg lidocaine plus sali ne or 400 mg lidocaine plus 30, 90 or 300 mu g clonidine for axillary nerve block, In each group (n = 14), blocks were evaluated at regular time intervals to determine sensory and motor functions in the five ne rve regions of the hand and forearm, Also, adequacy of the block for s urgery, postoperative pain intensity, and side effects were evaluated. Results: Compared with saline, each dose of clonidine reduced the ons et time of sensory block and extended the field of adequate anesthesia , Ten minutes after injection, 30 mu g clonidine was more effective th an 90 mu g clonidine in producing sensory blockade, Sedation occurred with clonidine 30 and 300 mu g, Clonidine reduced the use of supplemen tary intravenous anesthetic agents for surgery and produced dose-depen dent prolongation of analgesia, reaching a mean 770 min (range, 190-14 40 min) for the largest dose, Clonidine also produced a dose-dependent decrease in systolic arterial pressure of up to -22.5% (range, -6.0-2 9.9%) of baseline. With clonidine, 300 mu g, three patients had mean a rterial pressure of < 55 mmHg; four patients had episodes of arterial oxyhemoglobin saturation of <90%, and two others were not discharged b ecause of hypotension. Conclusion: This study suggests that a small do se of clonidine enhances the quality of the peripheral blocks from lid ocaine and limits the classical alpha(2)-agonist side effects to sedat ion.