[Sympathetic block in dogs by a local anesthetic with addition of clonidine].

BACKGROUND

The aim of this study is to examine the duration and magnitude of vasodilating effect induced by sympathetic block with the addition of different concentrations of clonidine to mepivacaine.

METHODS

In dogs, mean arterial pressure (MAP), heart rate (HR), and right as well as left brachial artery blood flow (BABF) were measured before and after stellate ganglion block (SGB) used as sympathetic block. The experimental protocol was designed as follows: 1) Group 1: left SGB using 0.5% mepivacaine 1 ml (n = 6), 2) Group 2: left SGB using the addition of clonidine 0.5 microgram to 0.5% mepivacaine 1 ml (n = 6), 3) Group 3: left SGB using the addition of clonidine 5 micrograms to 0.5% mepivacaine 1 ml (n = 6).

RESULTS

MAP showed no significant change throughout the study in the groups 1 and 2. In the group 3, MAP was lower than that of the group 1. HR showed no significant change throughout the study in the three groups. Left BABF increased significantly after left SGB in the three groups. The duration of increased BABF in the group 2 was the longest, and that in the group 3 was the shortest among them. Right BABF after left SGB decreased significantly throughout the study in the three groups, and the magnitude of the decrease in BABF in the group 3 was the highest among them.

CONCLUSION

Sympathetic block with the addition of clonidine to local anesthetics increases both duration and magnitude of its vasodilating effect. However, sympathetic block with the addition of higher doses of clonidine to local anesthetics may induce shorter duration and lower magnitude of vasodilating effect compared with local anesthetics alone.