Spontaneous intermittent generalized attenuations (SIGAs) are defined as a transient decrease in amplitude of electroencephalography (EEG) activity in response to a physiologic process, external stimuli, or as a result of a pathologic condition. We seek to investigate their relationship to clinical outcomes. Demographic information, modified Rankin Scale (mRS), and clinical information were noted on 22 consecutive patients with SIGAs on their EEG. 12 of the 22 patients (54.5%) died, and 12 patients (54.5%) were admitted to the intensive care unit or coronary care unit. Future studies should attempt to prospectively compare outcomes among patients with SIGAs against a control group.

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?

Cerebral hypothermia is the principal means of protecting the brain during cardiac surgery, permitting periods of reduced perfusion and/or circulatory arrest. For example, at 10–20°C, circulatory arrest for 45–75 minutes is tolerated in animals without subsequent behavioral or histopathologic evidence of neurologic injury. Nevertheless, clinically, die protective effect of hypothermia is far from complete. In children undergoing hypothermic circulatory arrest under equivalent conditions, coma, seizures, choreoathetosis, and developmental retardation are recognized as potential neurologic sequels, occurring widi a combined incidence of 10-30%. Neurologic complications (stroke, neuropsychologic change) also occur with distressing frequency in adults undergoing cardiac surgery, even in the absence of circulatory arrest. An improved understanding of the physiology of cerebral hypothermia during cardiopulmonary bypass and hypothermic arrest is needed to improve upon these results. This review will address current concepts and controversies regarding flow of blood to the brain and its metabolism during hypothermic cardiopulmonary bypass and their relationship to current techniques for cerebral protection.

With substantial effort and research devoted to improving surgical techniques and myocardial protection, superb results have been achieved for repair of complex congenital heart defects in children. As a result, investigative efforts now have begun to examine the quality of life for patients surviving these operations. Because these neonates and infants are exposed to severe physiologic extremes of temperature (15–18 °C) and severe alterations from normal perfusion (total circulatory arrest), the nature of long-term neuropsychological outcome has been a prominent concern. Recent preliminary reports suggest that transient and permanent neuropsychologic injury occur in as many as 25% of all infants undergoing hypothermic cardiopulmonary bypass with circulatory arrest.'Since improved surgical techniques have significantly reduced rates of operative mortality and cardiac morbidity, one of the greatest risks remaining for the patient with congenital heart disease may be long term neuropsychologic and developmental abnormalities.

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.