Brain ischemia detected by tissue-PO2 measurement and the lactate-oxygen index in head injury

The aim of the study was to find out whether there is a correlation between the tissue-pO2 (ti-pO2) measurement and the lactate-oxygen index (mLOI). Both methods are to be considered as methods to detect brain ischemia. We studied 7 patients after severe head injury (GCS < 8) with a jugular bulb catheter and a tissue pO2 probe. Possible ischemia was defined with ti-pO2 below 10 mm Hg and mLOI above 0.08. 67 pairs of ti-pO2 and corresponding mLOI were found. In 5 cases out of the 7 cases with a ti-pO2 below 10 we found a pathological mLOI above 0.08. In 11 cases with pathological mLOI values, however, we found only 6 cases of decreased ti-pO2. The absolute values did not correlate. The sensitivity to predict normal values is above 85% with both methods. The specifity to predict ischemia is low (< 72%). The reason is the fact, that ti-pO2 is a local method in contrast to the mLOI values. In cases of diffuse brain injury without major contusions there should be a correlation between ti-pO2 and the mLOI.