The Effect of Thoracic Epidural Block on the Defibrillation Threshold and Neuroendocrine Responses in Dogs

Chung, Mee Young; Lee, Byung Ho; Chea, Jun Seuk; Kim, Chang Jae; Park, Kyoung Hee

Abstract

BACKGROUND: Epidural block is known to block sympathetic efferent nerve fiber, resulting in the decrease of catecholamine. We examined the effects of thoracic epidural block on DFT, neuroendocrine responses and hemodynamic changes in dogs.
METHODS
Twenty one dogs were divided into three groups. The control group (N = 7) was anesthesized with only alpha-chloralose for general anesthesia, and a high thoracic epidural (T; N = 7) while the thoracolumbar epidural groups (TL; N = 7) were put under general anesthesia with high thoracic or thoracolumbar epidural blocks, respectively. The DFT was determined at 30 mins after surgical manipulation in the control group and at 10 mins after the epidural blocks in the two epidural groups. Four hemodynamic variables, catecholamine, cAMP and lactate were measured at 30 mins after the surgical manipulation (resting period), at 10 mins after epidural blocks and after defibrillation.
RESULTS
1) The DFT levels were significantly higher in the T (6.4 +/- 2.2 J) and TL groups (11.2 +/- 9.3 J) than in the control group (3.2 +/- 1.6 J)(P < 0.05). In the TL group, epinephrine-induced second DFT was lower (3.0 +/- 1.5 J) than the first DFT (11.2 +/- 9.3 J)(P < 0.05). 2) Catecholamine levels and hemodynamic variables including heart rate, mean arterial pressure, and cardiac output significantly decreased in the TL group compared with the control group after epidural block and defibrillation (P < 0.05). The DFT showed a significant correlation with plasma epinephrine levels after the epidural block (r = 0.56, P < 0.05).
CONCLUSIONS
Our results show, an increase in transmyocardial DFT by the epidural block which may be caused by a decrease in catecholamine, especially epinephrine.