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Korean Journal of Anesthesiology 1995;29(5):583-593.
DOI: https://doi.org/10.4097/kjae.1995.29.5.583   
The Effects of Thoracic Epidural Anesthesia on Myocardial and Systemic Circulation after Coronary Artery Occlusion in Dogs.
Seong Ho Chang, Hae Ja Lim, Hee Dong Yoon, Young Hoon Kim, Young Kee Kim
1Department of Anesthesiology, College of Medicine, Korea University, Seoul, Korea.
2Department of Internal Medicine, College of Medicine, Korea University, Seoul, Korea.
3Department of Clinical Pathology, College of Medicine, Korea University, Seoul, Korea.
Abstract
Thoracic epidural combined with general anesthesia is used for thoracic and upper abdominal surgery and postoperative pain control. This technique has advantages of reducing the hemodynamic demand on the heart because of cardiac sympathetic block and stable intraoperative hemodynamics, but it may have a potential hazard of reducing coronary perfusion pressure due to hypotension. Decreased coronary perfusion pressure may be critical hazard to coronary insufficiency patients, but coronary vascular resistance may be decreased also due to blockade of sympathetic coronary constriction. This study was done to investigate the effect of thoracic epidural anesthesia on myocardial and systemic circulation during coronary occlusion limiting flow to 50% of preocclusive value. Comnary occlusion of left circumflex coronary artery was achieved with hydraulic vascular occluder with blood flow meter distal to occluder in 20 dogs. Five of them were dead during preparation. Coronary stenosis was maintained for 30 minutes, then epidural anesthesia was done with 0.5% bupivacaine (bupiva group) or saline (saline group) 5 ml through the surgically introduced epidural catheter. Arterial, mixed venous and coronary sinus blood was collected for the measurement of metabolites and myocardial and systemic oxygen comsumption and extraction ratio. Hemodynamic parameters and blood samples were obtained before(control), 30 minutes after stenosis(stenosis), 15, 30, 60, 90 and 120 minutes after epidural blockade. The results were as follows; The thoracic epidural block caused decrease in blood pressure, heart rate, cardiac index, level of free fatty acid and glucose, and increase in lactic acid level of mixed veous and coronary sinus blood, myocardial oxygen extraction ratio, arterio-venous oxygen content difference, and systemic oxygen extraction ratio. In conclusion the high thoracic epidural block may cause hypotension thus decrease oxygen supply to myocardium but the degree of which is less than that of total body, in the dogs with acute coronary stenosis. The reason is that the high thoracic epidural block decrease myocardial oxygen consumption, and make effective distribution of blood flow in ischemic myocardium, but the normal myocardium has the highest oxygen extraction in the body, so the high thoracic epidural block in coronary stenosis may cause ill effect on myocardial oxygen equlibrium.
Key Words: Thoracic epidural anesthesia(TEA); Coronary artery stenosis; Myocardial oxygen consumption; Myocardial oxygen extraction ratio; Hemodynamic parameters


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