• W Erlacher, C Schuschnig, H Koinig, P Marhofer, M Melischek, N Mayer, and S Kapral.
• Department of Anaesthesia and Intensive Care, Hospital Lainz, Vienna, Austria. Wolfgang.Erlacher@univie.ac.at
• Can J Anaesth. 2001 Jun 1;48(6):522-5.

PurposeTo evaluate the effects of clonidine on three local anesthetics (mepivacaine 1%, ropivacaine 0.75% and bupivacaine 0.5%) with comparable potency and almost the same concentration-response relationship.MethodsOne hundred and twenty trauma-patients were randomly allocated into six groups. In the control-groups (Mo/Ro/Bo) brachial plexus was performed 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 plus 1 mL (0.150 mg) of clonidine. Onset-time and the duration of the sensory block were recorded. Data are expressed as mean +/- SD.ResultsAccording to the average sensory block determined by a visual analog scale in the median, ulnar and radial nerve distributions and ranging from 100 (no sensory blockade) to 0 (complete sensory blockade), both mepi-groups 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 onset time (at 10 min: -Ro 23 +/- 19/Rc 25 +/- 22/Bo 24 +/- 15; at 30 min -Ro 10 +/- 6/ Rc 11 +/- 6 /Bo 12 +/- 4). The onset time in group-Bc was significantly prolonged (at 10 min: -45 +/- 21; at 30 min: -20 +/- 6). Duration of motor blockade was prolonged by clonidine only in the mepivacaine and bupivacaine groups; (in minutes: Mo 212 +/- 47 -Mc 468 +/- 62; Ro 702 +/- 52 -Rc 712 +/- 82; Bo 728 +/- 36 -Bc 972 +/- 72).ConclusionThe present study shows that the addition of clonidine has a different impact on each of the three local anesthetics investigated in terms of onset and duration of block.

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