ABSTRACT
Cerebral metabolism can be divided into basal and active metabolism. Active electroencephalogram(EEG) represents electrophysiologic activity of the brain and become flat when such an activity is abolished. Hypothermia can protect ischemic cerebral damage by reducing cerebral metabolic rate. Profound hypothermia could induce a slow or flat EEG. It can be assumed that the cessation of brain electrical activity appear far faster in the case of cerebral ischemia combined with brain cooling than simple ischemia. To prove this assumption, we carried out this study to determine if selective brain cooling shortens time to onset of a flat electroencephalogram(EEG) after cerebral ischemia. Rabbits were anesthetized with halothane and oxygen. Brain was selectively cooled by intracarotid infusion with saline at 37degrees C (normothermic group) and 18degrees C (hypothermic group). Cerebral ischemia was induced for 2 minutes with a simultaneous clamping of contralateral carotid artery and induced hypatension. In 22 of 28(79%) episodes a flat EEG was identified, and occurred an average 10+/-1 sec in the hypothermic group, 14+/-I sec in the normothermic group. Time to onset of a flat EEG was significantly faster in the hypothermic group than normothermic group(p=0.02). These pattems may be recognized as an indication of metabolic suppression of hypothermia during cerebral ischemia.