Etiology and incidence of brain dysfunction after cardiac surgery

Abstract

The frequency and severity of central nervous system complications in patients undergoing cardiopulmonary bypass (CPB) may be greater than previously thought, particularly in the older population. The risks of embolic neurologic complications and stroke in the population older than 70 years from a severely atherosclerotic ascending aorta are well documented. Moreover, while the majority of CPB patients do not experience perioperative stroke, a high incidence of more subtle central nervous system dysfunction has been demonstrated to persist for up to 1 year after surgery. This report reviews the incidence and severity of cerebral injury during CPB and the effects of both age and the severely atherosclerotic ascending aorta on adverse neurologic outcomes. It discusses perioperative diagnostic methods, including transesophageal echocardiography, periaortic echocardiography, transcranial Doppler, and retinal fluorescein angiography, and the benefit of pH management. Ischemic brain injury resulting from activation of injury-related enzymes as part of the systemic inflammatory response is briefly reviewed. Age has been shown to be the strongest predictor of neurologic sequelae in patients undergoing CPB. The risk of embolic complications in the brain also increases in proportion to the degree of atherosclerosis in the ascending aorta, which is age-related. Transesophageal echocardiography has been found to be only partly useful in diagnosing these lesions or in guiding surgical manipulations in comparison with epiaortic imaging, which is more discreet. Transcranial Doppler and retinal fluorescein angiography have provided further evidence of microemboli during surgical manipulations. In a 316-patient prospective study, we found no differences in outcome between pH-stat and alpha-stat strategies during moderate hypothermic CPB, except in patients who were on bypass for more than 90 minutes. Approximately 90% of these had a significant reduction in cognitive impairment with the alpha-stat method. Aprotinin, a serine protease inhibitor, has been found in two separate, randomized, placebo-controlled trials to significantly lower incidences of perioperative stroke. Further study to develop therapeutic and preemptive strategies for prevention of brain injury is required, especially in the elderly. Aprotinin and other modalities aimed at suppressing the inflammatory response to CPB may offer hope because they act to suppress injury-provoking enzymes and leukocyte activation that are, in part, responsible for organ system dysfunction following CPB.