The effect of adding clonidine as an adjuvant to lidocaine with epinephrine for ultrasound guided axillary brachial plexus block

Objectives: Adjuvants have been widely used with local anaesthetics to improve the characteristics of the peripheral nerve blocks. Previously, studies comparing block onset time and duration using epinephrine and clonidine admixture to local anaesthetics using conventional techniques yielded inconsistent results. We proposed to evaluate the effects of adding clonidine to lidocaine with epinephrine for ultrasound guided axillary brachial plexus block (USgABPB) on the onset and duration of sensory and motor block. Material and methods: After obtaining Clinical Research Ethics Committee approval and registered at https://clinicaltrials.gov, Twenty-four patients were randomly assigned to receive an ultrasoundguided axillary brachial plexus block with either 20 mL of lidocaine 2% with epinephrine plus 2 mL of 0.9% normal saline (Group 1) or 20 mL of lidocaine 2% with 1:200,000 epinephrine plus 2 mL containing clonidine 1 μg/kg in 0.9% normal saline (Group 2). The primary endpoint was overall onset time of sensory and motor block. Secondary outcomes included overall duration of sensory and motor block. Results: The patient demographics were similar between the two groups. There were no block failures or systemic adverse events noted in either group. The overall onset time of sensory and motor block was significantly shorter in Group 2 (Table 1) and the overall duration of block was significantly longer in Group 2 (Table 2). The median (Interquartile range) time to first request of supplementary analgesia was 318 (303-469) min in Group 2 versus 209 (166-268) mins in Group 1 (P < 0.001). The haemodynamic paramteres and sedation score showed no significant difference between the groups. Conclusion: In USgABPB, addition of clonidine 1μg/kg to lidocaine with epinephrine resulted in faster onset of sensory and motor block, prolonged duration of block and longer time to first request of postoperative analgesia.