Although the brain is the organ most sensitive to total bodily ischemia, and probably also most sensitive to the deleterious effects of cardiopulmonary bypass, it is also the most difficult organ in which to quantitate function accurately. Clinical studies allow sensitive neuropsychometric testing, as discussed elsewhere in this issue (see Wernovsky et al, p. 308). This is not possible in studies using animals. Even testing of gross neurological integrity in animals is complicated by the associated dysfunction of other organs which accompanies the insult of cardiopulmonary bypass with or without circulatory arrest on the whole body. For example, how should one evaluate an animal undergoing neurological testing which is unable to walk or eat, perhaps because of severe cardiorespiratory or gastrointestinal dysfunction following cardiopulmonary bypass and circulatory arrest. What is the contribution of neurological dysfunction to this state? Most importantly, how is the animal scored which does not survive, even though this may be a result of multiorgan dysfunction?

Over the past two decades, advances in equipment used for cardiopulmonary bypass and in operative techniques have resulted in a tremendous decrease in the mortality of patients undergoing surgical repair of congenital heart disease utilizing hypothermic circulatory arrest. Despite the widespread use of hypothermic arrest, opinion is not unanimous with regard to its safety. Previous studies which have examined neurological outcome following repair of congenital heart disease in infancy have generally agreed that when the period of arrest exceeds 60 minutes, there is increasing risk of cerebral injury.