Brain Tissue Oxygenation and Cerebral Metabolic Patterns in Focal and Diffuse Traumatic Brain Injury

Abstract

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 (BtipO2) would add information with the potential of improving patient outcome. The aim of this study was to examine BtipO2 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, BtipO2, 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 BtipO2 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 BtipO2 <5 mmHg, indicating increased vulnerability of the brain at this level.Conclusion: Monitoring of BtipO2 adds important information in addition to traditional ICP and CPP surveillance. Because of the different metabolic responses to very low BtipO2 in the individual patient groups we submit that brain tissue oximetry is a complementary tool rather than an alternative to MD monitoring.

Pathophysiology and Clinical Management of Moderate and Severe Traumatic Brain Injury in the ICU

“…Placement of the device on the side of the lesion (injured hemisphere) yields quite different results compared with placement on the contralateral (noninjured) hemisphere, and needs to be studied further. 26 Near-infrared spectroscopy is a promising newer noninvasive technique that may have additional uses, such as in the assessment of cerebral autoregulation. 9 Jugular venous bulb oximetry measures SjvO 2 (oxygen saturation at the jugular bulb), allowing assessment of global brain oxygenation as opposed to more focal or regional assessment with PBtO 2 probes.…”

Lactate Shuttling and Lactate use as Fuel after Traumatic Brain Injury: Metabolic Considerations

“…6 Poor outcome after TBI is associated with low oxygen, glucose, pyruvate levels, high LPR, and elevated glutamate and glycerol levels, particularly when changes have longer duration and higher magnitude. [7][8][9][10] Probe Site Microdialysis catheter location is important, e.g., in gray or white matter ipsilateral or contralateral to the injury because metabolite level changes are larger in lesioned or penumbral zones compared with distant 'normal' tissue. [10][11][12] Also, gray and white matter exhibit different magnitudes and time courses of responses (i) to hypoxia for lactate and pyruvate in immature brain, 13 and (ii) to ischemia and reperfusion for the decline in direct current potential and levels of extracellular [Ca 2+ ], adenosine, inosine, hypoxanthine, glutamate, and GABA in adult brain, with white matter being usually less negatively affected.…”

“…[7][8][9][10] Probe Site Microdialysis catheter location is important, e.g., in gray or white matter ipsilateral or contralateral to the injury because metabolite level changes are larger in lesioned or penumbral zones compared with distant 'normal' tissue. [10][11][12] Also, gray and white matter exhibit different magnitudes and time courses of responses (i) to hypoxia for lactate and pyruvate in immature brain, 13 and (ii) to ischemia and reperfusion for the decline in direct current potential and levels of extracellular [Ca 2+ ], adenosine, inosine, hypoxanthine, glutamate, and GABA in adult brain, with white matter being usually less negatively affected. [14][15][16] Because white matter has approximately two-to fourfold lower metabolic and blood flow rates than gray matter, synaptic activity and excitatory neurotransmission (and excitotoxic damage) predominate in neuropil, and white matter is enriched with axons and oligodendroglia, caution must be applied when extrapolating data derived from small extracellular fluid volumes sampled by microdialysis (frequently placed in 'normal' white matter) to other brain regions.…”

End Points of Traumatic Brain Injury Resuscitation

“…In addition to following ICP and CPP trends, brain tissue oxygenation (BtipO 2 ) may add information regarding end points of TBI resuscitation. By monitoring levels of BtipO 2 , it is hypothesized that CPP levels can be optimized on an individual basis [23]. After a TBI, the partial pressure of oxygen in brain tissue (PbrO 2 ) increases with elevations in CPP; this increase relative to an increase in arterial PO 2 is termed brain tissue oxygenation.…”

“…Brain oxygen tension can be continuously measured with an invasive sensor probe, such as Clark-type electrode. Normal PbrO 2 ranges between 35 and 50 mmHg, suggesting that ischemic thresholds lie between 5 and 20 mmHg; the true cutoff level is still under investigation [23,24]. As more studies show that using brain tissue oximetry in addition to ICP and CPP monitoring leads to better outcomes, the evidence to include brain tissue oximetry as a means to determine end point resuscitation in TBI is increasing [24].…”