The effects of clonidine on ropivacaine 0.75% in axillary perivascular brachial plexus block

Introduction: The new long-acting local anesthetic ropivacaine is a chemica l congener of bupivacaine and mepivacaine. The admixture of clonidine to lo cal anesthetics in peripheral nerve block has been reported to result in a prolonged block. The aim of the present study was to evaluate the effects o f clonidine added to ropivacaine on onset, duration and quality of brachial plexus block. Methods: Patients were randomly allocated into two groups. In group I brach ial plexus was performed using 40 mi of ropivacaine 0.75% plus 1 mi of NaCL 0.9%, and in group II brachial plexus was performed using 40 mi of ropivac aine 0.75% plus 1 mi (0.150 mg) of clonidine. Onset of sensory and motor bl ock of radial, ulnar, median and musculocutaneous nerve were recorded. Moto r block was evaluated by quantification of muscle force, according to a rat ing scale from 6 (normal contraction force) to a (complete paralysis). Sens ory block was evaluated by testing response to a pinprick in the associated innervation areas. Finally, the duration of the sensory block was register ed. Data were expressed in mean+/-SD. For statistical analysis a Student t- test was used. A P-value of less than or equal to 0.05 was considered as st atistically significant. Results: The duration of blockade was without significant difference betwee n the groups. Group I: 718+/-90 min; Group II: 727+/-117 min. There was no intergroup difference in sensory and motor onset or in quality of blockade. Conclusion: The addition of clonidine to ropivacaine 0.75% does not lead to any advantage of block of the brachial plexus when compared with pure ropi vacaine 0.75%.