Histologic Studies of Brain Microemboli in Humans and Dogs After Cardiopulmonary Bypass

Emboli become lodged in the brains of patients undergoing cardiopulmonary bypass (CPB) and can cause death, stroke, or more subtle neurological and neuropsychological deficits. Using a specialized vascular stain (for alkaline phosphatase) in autopsy tissues from the brains of patients who underwent CPB shortly before death, we found large numbers of microemboli. All of these microemboli contain lipid, some contain small birefringent particles, and some may contain aluminum or silicon. Within a few weeks after CPB, most of the microemboli had disappeared from the brain tissues, but some persisted for at least 6 months. After several days, the endothelial cells of some of the vessels containing microemboli showed subtle damage in the form of loss of alkaline phosphatase reactivity, and some vessels appeared to be degenerating. Sometimes the surrounding neuropil also showed degeneration. Since skin and muscle biopsies can be readily obtained before, during, and after CPB, we investigated their suitability as surrogate tissues for brain; however, they were unsuitable because they had so few microemboli. By injecting microspheres into dogs at various times during CPB, we have investigated the timing of the production of microemboli. We are also exploring the use of rat brains to trap microemboli from the injected blood of patients undergoing CPB. (ECHOCARDIOGRAPHY, Volume 13, September 1996)