Neurologic sequelae after cardiopulmonary bypass have a multi-factorial etiology. Although it is typically thought that a neurologic dysfunction means a focal lesion, symptoms of a brain disorder can be initiated by metabolic disruption such as from hyper- or hypoglycemia, hypercalcemia, renal and hepatic injury, fatigue, and anesthesia. However, one of the most important causes of acute neurologic dysfunction is edema. Brain swelling is associated with the systemic inflammatory response and the passage of deformable microemboli. The larger question is whether acute symptoms associated with brain swelling because of a breakdown of the blood-brain barrier contributes to a long-term negative outcome caused by cell loss.