Microemboli and Neurologic Dysfunction After Cardiovascular Surgery

Several recent studies have shown that cardiac surgery poses significant risks for negative neurologic and neu ropsychological outcome. Death and major stroke have become uncommon consequences of cardiac surgery, but more than two-thirds of the patients show evidence of neuropsychological dysfunction postoperatively. The mechanisms contributing to postcardiopulmonary bypass neuropsychological deficits are uncertain, and potentially there are many possible causative factors that may play a significant role in perioperative neuro logic injury. However, two major interrelated factors, hypoperfusion and emboli, are suggested as probable culprits. Perfusion is important because the level of global and focal cerebral blood flow during periods of high embolic risk will determine the amount of brain embolization as well as the localization of the lesions. Ultrasonically detected macroemboli have been re ported to be the best predictor of neurobehavioral outcome. Microemboli found in autopsy specimens may also be important predictors of negative outcome. The relationship between microemboli and changes in brain function, as detected by magnetic resonance spectroscopy, may provide further insight into the prob ability of the clinical expression of a neurobehavioral dysfunction after cardiac surgery. The incidence and severity of neuropsychological defi cits after cardiac surgery appear to be related to the delivery of macroemboli. The composition of the embo lus may be the most important determinant of the level and volume of focal injury, but the time of occurrence (ie, rewarming) of macroemboli during cardiopulmo nary bypass may also be important in determining the effect of emboli on neuropsychological outcome. How ever, the key variable in the manifestation of neurobe havioral dysfunction remains the location of the lesion site.