Perineural versus intravenous clonidine as an adjuvant to Bupivacaine in supraclavicular Brachial plexus block

Background
Clonidine has been used as an adjuvant in Brachial plexus block (BPB) to enhance its quality and duration. However, whether, clonidine in BPB acts perineurally or via systemic absorption is not entirely clear.
Methods
Ninety-three patients of either sex, ASA I and II, aged 18–70 years, undergoing lower end humerus fracture fixation were included in the study. Patients were randomized into 3 groups. All the patients received brachial plexus block using nerve stimulator with 28 ml 0.5% Bupivacaine and 2 ml of NS/NS with clonidine. In the first group (Bc) 2 mcg/kg of clonidine was added to the anaesthesia solution and 10 ml of NS was injected intravenously; second group (Bivc) received clonidine 2 mcg/kg diluted up to 10 ml by intravenous route with 28 ml of 0.5% Bupivacaine and 2 ml of NS in the block; third group (B) received 28 ml of 0.5% Bupivacaine with 2 ml of NS in the block and 10 ml of NS intravenously, as placebo. Onset and duration of sensorimotor block, hemodynamic variables, duration of analgesia, level of sedation and adverse effects were noted.
Results
Onset of sensory blockade was faster in group Bc (7 ± 0.720 min) compared to group B (11.46 ± 1.138 min) and Bivc (11.46 ± 1.170 min) (p < 0.001). Onset of motor block was faster in group Bc (16.43 ± 1.136 min) compared to group B (22.75 ± 1.456 min) and Bivc (22.25 ± 1.295 min) (p < 0.001). The mean durations of analgesia were recorded as 1160.71 ± 53.259 min in group Bc, 454.64 ± 14.07 min in Group Bivc and 442.50 ± 18.634 min in group B.
Conclusion
Addition of clonidine 2mcg/kg to 28 ml of 0.5% bupivacaine in brachial plexus blocks results in a faster onset, increased duration of block and longer postoperative pain relief when compared to bupivacaine alone. These advantages are not observed when the same dose of clonidine is injected intravenously.