High cerebral perfusion pressure improves low values of local brain tissue O2 tension (PtiO2) in focal lesions

Arterial hypertension is widely applied to improve regional cerebral blood flow (rCBF). We measured local brain tissue O2 pressure (PtiO2) in low density lesions at computerized tomography (CT) of the head before and after manipulation of mean arterial pressure (MAP) in order to increase cerebral perfusion pressure (CPP). Nine patients, 7 subarachnoid hemorrhage (SAH), 1 severe head injury, 1 meningeoma, were included in our study. A flexible polarographic microcatheter for PtiO2 measurement was placed at the border of the low density area found at CT. PtiO2 was continuously measured for 615 hours. Hypoperfusion in low density areas was detected by perfusional single photon emission computed tomography (SPECT). We recorded 22 episodes of induced or spontaneous increase of MAP. Initial PtiO2 regularly improved after the CPP increase (r2 0.74 in induced episodes). Low PtiO2 showed a greater percent increase for unitary changes of CPP than normal-high PtiO2. Baseline PtiO2 below 20 mm Hg was associated with normal CPPs; 5 readings of PtiO2 below 20 mm Hg normalized when a higher CPP was obtained. Our results show that in ischemic areas PtiO2 is dependent on CPP suggesting both a derangement of pressure autoregulation and high regional cerebrovascular resistences (CVRs). Low PtiO2 was associated with normal CPP, thus indicating that CPP could be an inadequate estimate of rCBF in focal ischemic areas. Arterial hypertension, capable of increasing CPP above normal values, appeared useful in normalizing tissue oxygenation in ischemic areas.