Deep hypothermic circulatory arrest: II. Changes in electroencephalogram and evoked potentials during rewarming

Background.. Electrophysiologic studies during rewarming after deep hypothe rmic circulatory arrest probe the state of the brain during this critical p eriod and may provide insight into the neurological effects of circulatory arrest and the neurologic outcome. Methods. Electroencephalogram (EEG) and evoked potentials were monitored du ring rewarming in 109 patients undergoing aortic surgery with hypothermic c irculatory arrest. Results. The sequence of neurophysiologic events during rewarming did not m irror the events during cooling. The evoked potentials recovered first foll owed by EEG burst-suppression and then continuous EEG. The time to recovery of the evoked potentials N20-P22 complex was significantly correlated with the time of circulatory arrest even in patients without postoperative neur ologic deficits (r = 0.37, (p = 0.002). The nasopharyngeal temperatures at which continuous EEG activity and the N20-P22 complex returned were strongl y correlated (r = 0.44, p = 0.0002; r = 0.41, p = 0.00003) with postoperati ve neurologic impairment. Specifically, the relative risk for postoperative neurologic impairment increased by a factor of 1.56 (95% CI 1.1 to 2.2) fo r every degree increase in temperature at which the EEG first became contin uous. Conclusions. No trend toward shortened recovery times or improved neurologi c outcome was noted with lower temperatures at circulatory arrest, indicati ng that the process of cooling to electrocerebral silence produced a relati vely uniform degree of cerebral protection, independent of the actual nasop haryngeal temperature. (Ann Thorac Surg 2001;71:22-8) (C) 2001 by The Socie ty of Thoracic Surgeons.