A review of risk factors for adverse neurologic outcome after cardiac surgery.

Although the incidence of overt sequelae has traditionally been higher in patients undergoing isolated intracardiac procedures such as valve replacement or repair, recent studies show that the incidence of stroke for intracardiac procedures now approximates that for isolated coronary artery bypass grafting (CABG), in the range of 1 to 4%. In both intracardiac and extracardiac surgery, macroemboli (>200 microm in diameter) and microemboli (<40 microm in diameter) seem to be responsible for most neurologic complications. The risk of overt stroke is clearly increased in patients who undergo more complicated, combined procedures such as CABG plus valve replacement or CABG plus carotid endarterectomy. For isolated CABG, preoperative risk factors include advanced patient age, proximal aortic atherosclerosis, hypertension, previous stroke or transient ischemic attack, diabetes, and female gender. One area of controversy and current research concerns whether hypothermia is better than normothermia during cardiopulmonary bypass (CPB). Another debatable issue is whether CPB itself results in neurologic damage, owing to nonpulsatile perfusion, complement activation and the "inflammatory response," or a greater propensity for platelet activation and aggregation into microemboli in this setting. Strategies for preventing adverse neurologic outcome (new paradigms for managing intra-aortic plaque and controlling the cerebral reperfusion temperature) and for acute intervention (using specific cerebral protective agents) are under investigation. Further research into techniques for preventing or mitigating cerebral injury, particularly in high-risk patients, is clearly mandated.