Clonidine as adjuvant for mepivacaine, ropivacaine and bupivacaine in axillary, perivascular brachial plexus block

Purpose: To evaluate the effects of clonidine on three local anesthetics (m epivacaine 1%, ropivacaine 0.75% and bupivacaine 0.5%) with comparable pote ncy and almost the same concentration-response relationship. Methods: One hundred and twenty trauma-patients were randomly allocated int o six groups. In the control-groups (Mo/Ro/Bo) brachial plexus was performe d using 40 mL of local anesthetic plus 1 mL of NaCL 0.9%. In the clonidine- groups (Mc/Rc/Bc) brachial plexus was performed using each 40 mL of drug pl us 1 mL (0. 150 mg) of clonidine. Onset-time and the duration of the sensor y block were recorded. Data are expressed as mean +/- SD. Results: According to the average sensory block determined by a visual anal og scale in the median, ulnar and radial nerve distributions and ranging fr om 100 (no sensory blockade) to 0 (complete sensory blockade), both mepi-gr oups showed a rapid onset(at 10 min: Mo 20 +/- 15 /Mc 19 +/- 14; at 30 min: -Mo 3 +/- 4 / Mc 5 +/- 4). The ropi-and bupi- groups both had a longer ons et time (at 10 min: -Ro 23 +/- 19 / Rc 25 +/- 22 /Bo 24 +/- 15; at 30 min - Ro/ 0 +/- 6/ Rc 11 +/- 6 / Bo 12 +/- 4). The onset time in group Bc was sig nificantly prolonged (at 10 min: -45 +/- 21; at 30 min: -20 +/- 6). Duratio n of motor blockade was prolonged by clonidine only in the mepivacaine and bupivacaine groups; (in minutes: Mo 212 +/- 47 -Mc 468 +/- 62; Ro 702 +/- 5 2 -Rc 712 +/- 82; Bo 728 +/- 36 -Bc 972 +/- 72). Conclusion: The present study shows that the addition of clonidine has a di fferent impact on each of the three local anesthetics investigated in terms of onset and duration of block.