Brain tissue oxygenation and cerebral metabolic patterns in focal and diffuse traumatic brain injury

Introduction: Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. There are reasons to believe that knowledge of brain tissue oxygenation (BtipO(2)) would add information with the potential of improving patient outcome. The aim of this study was to examine B(ti)pO(2) and cerebral metabolism using the Neurovent-PTO probe and cerebral microdialysis (MD) in TBI patients. Methods: Twenty-three severe TBI patients with monitoring of physiological parameters, ICP CPP B(ti)pO(2), and MD for biomarkers of energy metabolism (glucose, lactate, and pyruvate) and cellular distress (glutamate, glycerol) were included. Patients were grouped according to injury type (focal/diffuse) and placement of the Neurovent-PTO probe and MD catheter (injured/non-injured hemisphere). Results: We observed different patterns in B(ti)pO(2) and MD biomarkers in diffuse and focal injury where placement of the probe also influenced the results (ipsilateral/contralateral). In all groups, despite fairly normal levels of ICP and CPP, increased MD levels of glutamate, glycerol, or the L/P ratio were observed at B(ti)pO(2) <5 mmHg, indicating increased vulnerability of the brain at this level. Conclusion: Monitoring of B(ti)pO(2) adds important information in addition to traditional ICP and CPP surveillance. Because of the different metabolic responses to very low B(ti)pO(2) in the individual patient groups we submit that brain tissue oximetry is a complementary tool rather than an alternative to MD monitoring.