Neurologic Sequelae Associated With Deep Hypothermic Circulatory Arrest

Background. Earlier studies of the incidence of neurologic disturbances after deep hypothermic circulatory arrest produced conflicting results. This article reviews the results of the Boston Circulatory Arrest Study, and another study undertaken to compare neurologic outcome in infants after deep hypothermic circulatory arrest using alpha-stat and pH-stat strategies. Methods. The study population in the Boston Circulatory Arrest Study consisted of 171 infants less than 3 months of age. Neurologic outcomes were evaluated perioperatively, at 1 year, and at 4 years. The study population in the alpha-stat versus pH-stat study consisted of 182 infants no older than 9 months of age. Patients were evaluated for postoperative electroencephalographic (EEG) and clinical seizures, recovery time to first EEG activity, and postoperative mortality and morbidity. Results. After about 30 minutes of circulatory arrest there was increasing probability of perioperative clinical seizures, EEG seizures, and increased time to recovery of EEG activity. One-year evaluations showed a significant relation of duration of circulatory arrest to lowered psychomotor developmental index and increased neurologic abnormalities. Four-year evaluations showed no difference between low-flow and circulatory-arrest patients in results of neurologic examination or in full-scale general IQ, although there was an effect of circulatory arrest duration on various subscores of cognitive function. Compared with the pH-stat strategy, the alpha-stat strategy tended to be associated with more EEG seizures and higher postoperative morbidity and mortality, and was significantly associated with longer recovery time to first EEG activity. Conclusions. These studies strongly suggest that in infants undergoing open heart operations for complex congenital heart defects, low-flow bypass is associated with better neurologic outcome than is circulatory arrest and that the pH-stat strategy is associated with a better outcome than the alpha-stat strategy when circulatory arrest is used.