EEG changes during open heart surgery on infants aged 6 months or less: relationship to early neurologic morbidity

In a prospective study, we analyzed the intraoperative electroencephalographic (EEG) changes during open heart surgery with deep hypothermia in 66 infants aged 6 months or younger, 70% of whom were neonates. Suppression of amplitude and continuity at the nadir of temperature reduction and following rewarming, and the appearance of periodic paroxysmal activity, was compared with neurologic abnormalities before and following operation, patient characteristics, and operation variables. EEG changes disclosed no relationship to abnormal neurologic findings, age at operation, type of anesthetic, duration of cardiopulmonary bypass (CPB), duration of low-flow CPB or cooling, temperature at circulatory arrest (HCA) or low flow, or nasopharyngeal-venous return temperature differences. EEG suppression following rewarming was associated with the use of thiopentone and duration of HCA. Use of thiopentone was also related to decreased levels of alertness at the end of the first postoperative week. We could not demonstrate any association between operation variables, including duration of HCA, and postoperative neurologic findings which include abnormalities of tone, alertness, seizures, generalized pyramidal signs, choreoathetosis, and hemiparesis. Severe hypotonia before operation was associated with continuing severe hypotonia during the postoperative period. EEG changes during cooling for open heart surgery on infants appear to be physiologic, and these plus EEG suppression following HCA or low-flow CPB are not useful predictors of early neurologic morbidity.