Effects of Thoracic Epidural Anesthesia on Systemic and Myocardial Oxygen Supply/Demand Balance during Coronary Occlusion in Dogs

Chung, Hyung Kuen; Lim, Hae Ja

Abstract

BACKGROUND: A thoracic epidural combined with general anesthesia may reduce the oxygen demand of the heart by cardiac sympathetic blockade, but it may also reduce the systemic and cardiac oxygen delivery due to hypoperfusion which is critical to patients with significant coronary lesions. This study was done to investigate the effects of thoracic epidural anesthesia on the systemic and cardiac oxygen supply/demand balance during coronary occlusion in dogs. METHODS: In 10 dogs, the left circumflex coronary artery was occluded, and then thoracic epidural anesthesia was given at the T5-6 or T6-7 level with 5 ml of 0.5% bupivacaine to block T1-T12 through the surgically introduced epidural catheter. Hemodynamic parameters and arterial, mixed venous and coronary sinus blood samples were obtained at baseline and 30 minutes after coronary occlusion. The same parameters were also measured at 30, 60, 90, 120 and 150 minutes after the epidural blockade. An epicardial 2D-echocardiogram was done by a cardiologist at baseline, 30 minutes after occlusion and 1 hour after the epidural blockade. RESULTS: Systemic oxygen delivery (O2 flux) was decreased after epidural anesthesia (p < 0.05), but oxygen consumption (VO2) was maintained throughout the experimental periods. Although the systemic oxygen extraction ratio (O2ER) was not changed, cardiac O2ER was increased at 90, 120 and 150 minutes after epidural anesthesia (p < 0.05). The end-diastolic noncontractile area of the left ventricle was increased, pulmonary capillary wedge pressure was increased 90 minutes after epidural anesthesia and cardiac output was decreased 120 minutes after epidural anesthesia (p < 0.05). CONCLSIONS: In the experimental canine model of coronary occlusion, thoracic epidural anesthesia induces diminished systemic oxygen delivery without deteriorating oxygen supply/demand balance. However, as PsO2 and SsO2 diminished and the noncontractile left ventricular area increased after epidural anesthesia in the setting of acute coronary occlusion, perioperative use of thoracic epidural anesthesia in patients of coronary disease should be done carefully in order not to aggravate myocardial ischemia.