Preventing Brain Injury After Cardiopulmonary Bypass Will Require More Than Just Dialing Up the Pressure
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Article, see p 1770
Brain injury remains an important and potentially preventable complication of cardiac surgery. Although clinically overt strokes occur in a minority of patients, studies using frequent neurological assessments after surgery have found a much higher rate than had been previously appreciated.1 Even more commonly, patients manifest nonfocal or nonspecific neurological signs and symptoms of brain dysfunction such as encephalopathy, seizure, delirium, or postoperative cognitive impairment, at least some of which are also attributable to acute infarct. Recent investigations using perioperative magnetic resonance diffusion-weighted imaging (DWI) have demonstrated that cerebral infarction is frequently present after cardiac operations and interventions even in the absence of overt stroke.1,2 These findings have led a research consortium guideline to recommend combining neurological examinations, neurocognitive testing, and brain imaging in clinical trials designed to assess neurological outcomes after cardiac procedures to fully characterize the incidence, severity, and clinical sequelae of perioperative brain injury.3
Perioperative cerebral infarction associated with cardiac operations can be attributed to preexisting vascular disease, transient hypercoagulability, procedure-related thromboembolism, hypoperfusion, or a combination of these factors. Among these mechanisms, hypoperfusion stands out as an obvious modifiable risk factor. Early observational studies found an association between the incidence and severity of postoperative brain damage and low mean arterial pressure (MAP) during cardiopulmonary bypass (CPB).4,5 Subsequent brain imaging studies suggested that up to 48% of cardiac surgical patients with postoperative stroke had infarction in the watershed regions of the brain and that hypotension was a risk factor for stroke.6 Furthermore, although thromboembolism is an important mechanism for stroke, hypotension may exacerbate these injuries by impairing “washout” or clearance of microemboli.7 However, randomized controlled studies8–10 and observational studies11,12 have yielded inconclusive or conflicting results on the effect of …