HYPOTHERMIA INFLUENCES TIME-COURSE OF INTRACRANIAL-PRESSURE, BRAIN TEMPERATURE, EEC AND MICROCIRCULATION DURING ISCHEMIA-REPERFUSION

Time-related effects of hypothermia on intracranial pressure (ICP), br ain (Tbr) and rectal temperature (Tc), cortical (LDF) and subcortical microcirculation (ti-pO(2)) were assessed following a unilateral ballo on induced epidural focal mass lesion in rats. Results of injured but normothermia animals (Group A, n = 6) were compared with hypothermia a nimals (Group B, n = 6). Parameters were recorded during balloon expan sion (BD to an ICP of 60 mmHg followed by a period of sustained inflat ion (SI) of 30 +/- 2 min. Animals in Group B were then cooled to 31.7 +/- 0.4 degrees C (Tbr) during SI. After reperfusion animals were moni tored 178 +/- 4 min. The study protocol concluded with a rewarming pha se of the hypothermic animals. Balloon expansion led to a Gushing resp onse and flattening of the EEG In both groups Tbr decreased during inf lation of the balloon 0.5-0.8 degrees C below Tc and during SI in Grou p A 1.7 degrees C below Tc. During SI and reperfusion Tbr decreased be low Tc in Group A but remained above Tc in Group B (p < 0.003). During sustained inflation LDF decreased in group A to 21% and in Group B to 45% of baseline values. After 178 +/- 4 min of reperfusion LDF reache d 68% of baseline values in Group A and 97% in Group B (p < 0.001). Du ring sustained inflation ti-pO(2) showed median values of 0.8 mmHg in Group A and 5.5 mmHg in Group B. After reperfusion ti-pO(2) reached no rmal values in both groups (p < 0.3) but ti-pO(2) showed 18% higher va lues before rewarming. After reperfusion the secondary increase of ICP was reduced (p < 0.006) and CPP was improved by 20% in Group B. EEG r estored quicker in Group B than Group A (106 +/- 11 min vs. 188 +/- 25 min). Intra-ischemic hypothermia improved cerebral microcirculation, prevented a secondary increase of ICP and improved restoration of EEG after ischemia-reperfusion.