THORACIC EPIDURAL-ANESTHESIA ATTENUATES HALOTHANE-INDUCED MYOCARDIAL SENSITIZATION TO DYSRHYTHMOGENIC EFFECT OF EPINEPHRINE IN DOGS

Background: The autonomic nervous system plays a critical role in the central modulation of cardiac dysrhythmias. Because sympathetic blockade by thoracic epidural anesthesia has been documented to protect patients from various stress responses, the authors speculate that epidural anesthesia can attenuate the dysrhythmogenic interaction between halothane and epinephrine. Methods: In adult mongrel dogs anesthetized with halothane, the dysrhythmogenic dose (DD) of epinephrine, defined as the smallest dose producing four or more premature ventricular contractions within a 15-s period, was determined in the presence of thoracic epidural mepivacaine or saline. To address the effect of circulating mepivacaine after epidural administration, the authors examined the DD of epinephrine in the presence of intravenous mepivacaine. They also investigated the effect of thoracic epidural anesthesia in bilaterally vagotomized dogs. Results: Epidural mepivacaine significantly increased the DD of epinephrine compared with epidural saline. However, intravenous mepivacaine did not affect the DD of epinephrine, even when the plasma concentration of mepivacaine during the dysrhythmias was twice that in the epidural mepivacaine group, The beneficial effect of epidural mepivacaine was not seen in bilaterally vagotomized dogs. Conclusions: Thoracic epidural anesthesia attenuated the myocardial sensitization by halothane, and vagal activity had an essential role in this action.