Brain Parenchyma/pO 2 Catheter Interface: A Histopathological Study in the Rat

Local cerebral oxygenation can be monitored continuously using an intraparenchymal Clark-type PO2 sensitive catheter. Measured values of brain tissue pO₂ (PbrO₂) not only depend on the clinically interesting balance between oxygen offer and demand, but also on catheter properties and characteristics of the probe tissue interface. Microdamage surrounding pO₂-sensitive needles, inserted into various tissues, has been reported; we evaluated histologic changes at the probe tissue interface after insertion of pO₂ probes, suitable for clinical use, in the rat brain. The effect of insertion of the probe itself (mechanical damage), the application of micropotential during the measurements, and the effect of time was evaluated using digital image analysis of H&E-stained histological slices. Surrounding the probe tract, a zone of edema with an average radius of 126.8 μm was seen; microhemorrhages with an average surface area of 56.2 × 10³ μm² were observed in nearly all cases. The area of edema and the presence of microhemorrhages were not influenced by performed measurements or by time. Intraventricular blood was observed in 10 of 19 rats studied. Measured low PbrO₂ values were related to the presence of a microhemorrhage in either probe tract or ventricles. Tissue damage due to the measurements is negligible, and the amount of edema itself does not influence the accuracy or response time of the pO₂ probe. Low PbrO₂ readings, however, could be caused by local microhemorrhages, undetectable on CT or MRI.