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Etiology and incidence of brain dysfunction after cardiac surgery
1Department of Anesthesia, University Campus, London Health Sciences Center, Ontario, Canada.
Insights
Central nervous system complications after cardiopulmonary bypass (CPB) are common, especially in older adults. Age and aortic atherosclerosis increase risks, but strategies like alpha-stat management and aprotinin may reduce brain injury.
Area of Science:
- Neurology
- Cardiovascular Surgery
- Geriatrics
Background:
- Central nervous system (CNS) complications following cardiopulmonary bypass (CPB) may be underestimated, particularly in elderly patients.
- Older individuals (>70 years) with severe aortic atherosclerosis face documented risks of embolic neurologic events and stroke during CPB.
- Subtle CNS dysfunction persists in many CPB patients for up to a year post-surgery, despite a low incidence of overt perioperative stroke.
Purpose of the Study:
- To review the incidence and severity of cerebral injury during CPB.
- To examine the impact of patient age and ascending aorta atherosclerosis on neurological outcomes.
- To discuss diagnostic methods and potential preventative strategies for CPB-induced brain injury.
Main Methods:
- Review of existing literature on CPB-related neurological complications.
- Discussion of diagnostic tools: transesophageal echocardiography, epiaortic imaging, transcranial Doppler, and retinal fluorescein angiography.
- Analysis of pH management strategies (pH-stat vs. alpha-stat) and the role of aprotinin.
Main Results:
- Age is the most significant predictor of neurological sequelae after CPB.
- Ascending aorta atherosclerosis severity correlates with increased embolic risk.
- Alpha-stat management showed improved cognitive outcomes in patients on bypass >90 minutes.
- Aprotinin significantly reduced perioperative stroke incidence in clinical trials.
Conclusions:
- Further research is needed for therapeutic and preventative strategies against brain injury during CPB, especially in the elderly.
- Aprotinin and anti-inflammatory agents may mitigate CPB-induced organ dysfunction by suppressing injury-related enzymes and leukocyte activation.
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.