Oxygen radicals in cardiac surgery.

Most cardiac surgical procedures require the use of prolonged induced myocardial ischemia. Experimental models of global myocardial ischemia which mimic cardiac surgical techniques have been developed to investigate the possibility of oxygen free radical development during prolonged myocardial ischemia or upon reperfusion. In such experiments, various free radical scavenging agents, including superoxide dismutase, catalase, and mannitol, have been shown to improve the tolerance of the heart to protracted global ischemia. Use of these agents has improved cardiac functional recovery and has attenuated the biochemical and structural changes which occur due to prolonged ischemia and reflow. In a recently developed porcine experimental model, the effects of preexisting regional myocardial ischemia with superimposed global ischemia and reperfusion have been studied, with free radical scavenging agents administered in an attempt to reduce myocardial infarction and improve regional functional recovery. In most such studies completed to date, free radical scavenging agents have resulted in better myocardial preservation, suggesting, at least indirectly, that there may be an oxygen free radical-mediated component of the ischemia-reperfusion injury seen in such models. Techniques for directly measuring myocardial oxygen free radical levels may allow for early clarification of the development of such toxic species in the clinical cardiac surgical setting.