Bifrontal measurements of brain tissue-PO2 in comatose patients

The purpose of this study was to compare brain tissue-PO2 (PtiO2) in lesioned vs. non-lesioned brain tissue. PtiO2 was monitored bifrontally with a "Clark"-type microcatheter in patients following severe head injury (n = 6) and subarachnoid hemorrhage (SAH) (n = 1) from day 2 to day 12 posttrauma/post SAH. Mean arterial blood pressure, intracranial pressure (ICP), cerebral perfusion pressure and end-tidal CO2 were monitored. Data were stored and analyzed by a multimodal cerebral monitoring system. The CT of five patients was classified as "diffuse injury" and of one patients as "evacuated mass lesion". The patient with SAH (Hunt and Hess IV) had a concomitant intracerebral hematoma which was removed. In all cases, one catheter was placed close to the lesion, while the other was situated in an area with no visible pathology. For analysis, bifrontal PtiO2 data were taken from both on-line monitoring and O2 reactivity tests (FiO2 1.0 for 10 min). Two different patterns were identified: periods of concordance (22% of recordings) and periods in which PtiO2 was lower in lesioned cerebral white matter (78%) but always running parallel. In the latter case, O2-reactivity response was markedly reduced on the lesioned side. Our findings demonstrate a decreased PtiO2 and a reduced O2 reactivity in contused or infarcted brain tissue. Future studies have to clarify which PtiO2 is more important to be used as a guide for therapy.