Monitoring brain PO₂, PCO₂, and ph during graded levels of hypoxemia in rabbits

Brain ischemia and hypoxia are of concern when they occur following traumatic brain injury because they frequently result in potentially preventable secondary brain damage. In this study, we examined the ability of an implantable catheter (Paratrend 7; Diametrics Medical, St. Paul, MN) to continuously measure brain tissue pH, PCO₂, and PO₂ during graded levels of hypoxia. Values obtained from this catheter were compared with simultaneous measurements of arterial and sagittal sinus blood. As expected, there was a good correlation between the changes in pH, PCO₂, and PO₂ in brain tissue and sagittal sinus blood. Brain tissue PO₂ was numerically lower than sagittal sinus blood at all inspired levels of oxygen. These data suggest that the Paratrend 7 may be useful in monitoring brain tissue oxygen tension in patients at risk for regional cerebral ischemia and hypoxia.