Comparison of brain tissue metabolic changes during ischemia at 35 degrees and 18 degrees C.
BACKGROUND
We evaluated brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2) and pH during ischemia with brain temperature at 35 degrees and 18 degrees C in the same patient.


METHODS
Surgery was performed in a 60-year-old woman to clip a large aneurysm in the left internal carotid artery (ICA). A Paratrend 7 probe measuring PO2, PCO2, and pH was inserted into tissue at risk for ischemia during ICA occlusion and brain protection was provided with 9% desflurane. One week later, hypothermic circulatory arrest with brain temperature at 18 degrees C was performed for aneurysm clipping and tissue measurements were obtained during ischemia and rewarming.


RESULTS
At 35 degrees C, ICA occlusion 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 acidosis at the end of the ischemic period. During hypothermic circulatory 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 H+ increase during hypothermic arrest was one-third of that seen during ischemia at 35 degrees C. During rewarming from profound hypothermia, two phases of recovery from acidosis were observed, one during CO2 clearance and one after tissue reoxygenation. Recovery of acidosis occurred sooner at 18 degrees C than at 35 degrees C.


CONCLUSIONS
These results show that tissue acidosis develops more slowly and recovers more rapidly with hypothermic ischemia. This may be an important mechanism of reduced ischemic injury during hypothermia.
Hoffman
W E
WE
Department of Anesthesiology, University of Illinois at Chicago, USA.
Charbel
F T
FT
Munoz
L
L
Ausman
J I
JI
D001921:Brain / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism; D013696:Temperature
D002245:Carbon Dioxide; D010100:Oxygen