Thoracic epidural anesthesia reduces infarct size in a canine model of myocardial ischemia and reperfusion injury

Objective: To determine the effects of thoracic epidural anesthesia on myoc ardial infarct size, regional myocardial blood flow (RMBF), and plasma nore pinephrine in an anesthetized canine model of ischemia reperfusion injury w ith infarction. Design: Blinded, randomized, placebo-controlled animal study. Setting: Experiments were performed in the cardiothoracic research laborato ry at Wake Forest University Baptist Medical Center. Participants: Anesthetized, open-chest mongrel dogs were used in these stud ies. Methods: Dogs were instrumented for measurement of aortic pressure (AP) and left ventricular systolic pressure (LVSP), dP/dt, and RMBF. Epidural cathe ters were inserted at thoracic segment T5. Three groups received epidural 0 .5% bupivacaine: low-dose (0 = 7; 0.3 mg/kg bolus, 0.15 mg/kg/h), mid-dose (0 = 7; 0.6 mg/kg bolus, 0.3 mg/kg/h), high-dose (0 = 7; 1.2 mg/kg bolus, 0 .6 mg/kg/h). The vehicle (VEH) group received epidural saline. Bolus follow ed by maintenance infusions began 30 minutes before the onset of ischemia ( 60 min) and continued through reperfusion (180 min). Results: Myocardial infarct size was significantly reduced in the high-dose group versus the VEH and low-dose groups (p < 0.05). After initiation of t he mid and high dose, AP, LVSP, and dP/dt decreased 7% to 16% (high v VEH; p < 0.05). VEH dogs showed a 130% increase from control in early postischem ic RMBF. There was a dose-dependent attenuation in this reflow response: 72 %, 31%, and 6% increase in RMBF in the low, mid, and high groups, relative to controls (p < 0.05 high v VEH). Although there was no significant differ ence in plasma norepinephrine, fewer surges occurred in the high-dose group . Conclusions: Thoracic epidural anesthesia reduces infarct size and postisch emic hyperemia in a model of ischemia reperfusion injury. Copyright (C) 199 9 by W.B. Saunders Company.