Monitoring of electroencephalogram during open-heart surgery. A prospective analysis of 118 cases.

The electroencephalogram (EEG) was prospectively analyzed in 118 consecutive open-heart procedures. In 96 patients (81%) the records were normal whereas in 22 patients (19%) the EEG showed slow wave activity and decreased electrical voltage. In 16 of these patients the EEG abnormality was transient or only of mild degree. In 10 of this group of patients the abnormality occurred with the institution of total cardiopulmonary bypass (CPB) and returned to normal within 2 minutes. In four other patients the abnormalities were mild, persisted to the end of the CPB, and then returned to normal; in two patients the EEG abnormalities developed in the last half of CPB and then returned to normal. In the remaining six patients the EEG was grossly abnormal. In one of these patients the abnormality was secondary to a previous stroke. In five patients, however, the EEG alerted the surgeon to an otherwise unsuspected poor cerebral blood flow. A serious neurologic insult was probably prevented by identifying and correcting the mechanical cause.