Block Facilitatory Effects of Perineural Dexmedetomidine in Supraclavicular Brachial Plexus Block with Ropivacaine: Does Dexmedetomidine Has Perineural Site of Action? A Randomized, Controlled and Triple Blind Study

Although nerve block facilitatory effects of dexmedetomidine when used as a perineural adjunct to local anesthetics in supraclavicular brachial plexus blocks are well recognized in multiple studies, but whether this action is at directly on peripheral nerve fibers or is at central level after systemic absorption is unclear. Aim of this study was to evaluate the effect of adding dexmedetomidine 1 microgram/kg to ropivacaine 0.5% in supraclavicular brachial plexus block in terms of duration of analgesia and 24hour cumulative analgesic requirement and to test the hypothesis whether the effect of dexmedetomidine, is due to direct local action on nerve plexus or is centrally mediated after systemic absorption.

105 patients of ASA grade I and II of either sex undergoing upper limb orthopedic surgeries were divided in 3 groups of 35 patients in each group. Group Rc (control group) received supraclavicular block with 30ml of 0.5% ropivacaine and intravenous infusion of 30ml of normal saline; group RDexP received supraclavicular block with 30ml solution of 0.5% ropivacaine+ dexmedetomidine 1mcg/kg and intravenous infusion of 30ml of normal saline; and group RDexIV received supraclavicular block with 30ml of 0.5% ropivacaine and intravenous infusion of 30ml of normal saline solution containing dexmedetomidine 1mcg/kg. Primary outcome was duration of analgesia and 24hour cumulative analgesic requirement.

The demographic data were comparable in all three groups. Duration of analgesia was longest in group RDexP followed by group RDexIV and least in control group. 24hour cumulative analgesic requirement was least in group RDexP and maximum in group R. 2 patients, one from each group RDexP and group RDexIV reported bradycardia and 6 patients from group RDexIV reported hypotension.

We conclude that action of dexmedetomidine is most probably peripheral on brachial plexus nerve fibers directly rather than centrally mediated after systemic absorption.