COMPARISON OF BRAIN-TISSUE METABOLIC CHANGES DURING ISCHEMIA AT 35-DEGREES AND 18-DEGREES-C

BACKGROUND We evaluated brain tissue oxygen pressure (PO2), carbon dio xide pressure (PCO2) and pH during ischemia with brain temperature at 35 degrees and 18 degrees C in the same patient, METHODS Surgery was p erformed in a 60-year-old woman to clip a large aneurysm in the left i nternal carotid artery (ICA). A Paratrend 7 probe measuring PO2, PCO2, and pH was inserted into tissue at risk for ischemia during ICA occlu sion and brain protection was provided with 9% desflurane, One week la ter, hypothermic circulatory arrest with brain temperature at 18 degre es C was performed for aneurysm clipping and tissue measurements were obtained during ischemia and rewarming. RESULTS At 35 degrees C, ICA o cclusion for 16 minutes produced tissue hypoxia (PO2 = 0) and acidosis (pH = 6.70), The rate of increase of hydrogen ion (H+) reached 50 nEq .L-1.min(-1) during ICA occlusion and there was a slow recovery of aci dosis at the end of the ischemic period, During hypothermic circulator y arrest, tissue PO2 was sensitive to decreases in blood pressure and decreased rapidly during exsanguination. Although tissue pH decreased to 6.5 with 30 min of no pump flow, the rate of Ht increase during hyp othermic arrest was one-third of that seen during ischemia at 35 degre es C, During rewarming from profound hypothermia, two phases of recove ry from acidosis were observed, one during CO2 clearance and one after tissue reoxygenation, Recovery of acidosis occurred sooner at 18 degr ees C than at 35 degrees C. CONCLUSIONS These results show that tissue acidosis develops more slowly and recovers move rapidly with hypother mic ischemia, This may be an important mechanism of reduced ischemic i njury during hypothermia. (C) 1998 by Elsevier Science Inc.