Spectral analysis of the EEG during hypothermic cardiopulmonary bypass

In 39 patients undergoing aorto-coronary-bypass grafting, spectral analysis of the EEG (compressed spectral array: CSA) and calculation of spectral edge frequency (SEF) were performed. The effects of different temperatures and of perfusion pressure (PP) were analyzed. Predictable patterns were observed. During cooling on cardiopulmonary bypass (CPB), linear regression analysis revealed a close correlation between SEF and tympanic membrane (Tty) or nasopharyngeal temperature (Tnp). During rewarming, a nonlinear correlation between SEF and Tty or Tnp was found. Rectal temperature as well as blood temperature in the arterial or venous line of the oxygenator seemed to be less useful. The independence of SEF and PP was demonstrated during the whole procedure. At the onset of CPB, after correction of the aortic clamp for performance of the aortic anastomosis and after removal of the aortic clamp, bilateral EEG slowing of varying duration occurred in 20 patients. Comparison of mean SEF before and after CPB revealed a difference of about 5 Hz. In no patient were major neurological abnormalities observed postoperatively.