Addition of clonidine increases duration and magnitude of vasodilative effect induced by sympathetic block with mepivacaine in dogs

Background and objectives: The aim of this study is to examine the duration and magnitude of vasodilative effect induced by sympathetic block with the addition of clonidine to mepivacaine. Methods: We measured mean arterial pressure (MAP), heart rate (HR), and rig ht and left brachial artery blood flow (BABF) before and after stellate gan glion block (SGB) in dogs. The experimental protocol was designed as follow s: (1) left SGB using 1.0 mL 0.5% mepivacaine (n = 6) and (2) left SGB usin g the addition of clonidine 0.5 mug to 1.0 mL 0.5% mepivacaine (n = 6). Results: MAP and HR did not change significantly throughout the study in ei ther group. Left SGB with mepivacaine increased left BABF significantly fro m 10 minutes through 50 minutes after SGB (baseline, 100%; peak at 10 minut es after SGB, 176% +/- 28%; P < .01). Left SGB with the addition of clonidi ne to mepivacaine induced a significant increase of left BABF from 10 minut es through 70 minutes after SGB (baseline, 100%; peak at 10 minutes after S GB, 223% +/- 42%; P < .01). The values of left BABF after SGB with the addi tion of clonidine to mepivacaine were significantly higher than those of SG B with mepivacaine alone from 10 minutes through 80 minutes after SGB (P < .05). Right BABF decreased significantly after SGB throughout the study in both groups. Conclusions: The addition of clonidine increases both duration and magnitud e of the vasodilative effect induced by sympathetic block over that caused by mepivacaine alone.