Studies of tissue PO2 in normal and pathological human brain cortex.

Brain cortex PO2 was measured after craniotomy and opening of the dura mater in 26 patients. We determined the brain tissue PO2 under standard narcotic conditions and after changing arterial PO2 and PCO2. Patients were divided into two groups (normal and pathological), depending on the aspect of their cortex on Ct/MRI and intraoperative appearance of the cortex. No statistical significantly difference was seen between tissue PO2 of the normal and the pathological group. A significant difference was seen only between the normal group and a subgroup with brain swelling (p = 0.0344). In the normal group no correlation was seen between tissue PO2 and arterial PO2 (r = 0.1541, p = 0.3076), whereas in the pathological group and especially in the oedema subgroup there was a highly significant correlation between tissue PO2 and PaO2 (r = 0.754, p = 0.0015 and r = 0.888, p = 0.0007). Breathing 100% oxygen changed tissue PO2 to 137.8 or 352 mmHg in the normal or the pathological group, respectively. Again, there was no correlation between tissue PO2 and PaO2 in the normal group (r = 0.1071, p = 0.392), whereas this correlation was significant in the pathological and the oedema subgroup (r = 0.6291, p = 0.0473 and r = 0.8385, p = 0.0185). This is evidence for regulatory mechanisms of tissue PO2. During hyperventilation no significant difference in tissue PO2 between the normal and the pathological group was seen. Low tissue PO2 values, however, indicate a risk for inducing ischemia.