[Use of intracerebral microdialysis in severe traumatic brain injury]

Brain microdialysis (MD) is a well-established technique to monitor the chemistry of the extracellular space in the brain during neurointensive care. MD may be useful in severe cases of traumatic brain injury (TBI) in which monitoring of intracranial pressure and cerebral perfusion pressure is required. Lactate/pyruvate (L/P) ratio, glucose, glutamate, and glycerol can be measured using a bedside device. The L/P ratio is a sensitive marker of changes in the redox state of cells caused by ischemia. Glycerol is an integral component of cell membranes. Loss of energy due to ischemia eventually leads to an influx of calcium and a decomposition of cell membranes, which liberates glycerol into the interstitial fluid. Thus the L/P ratio and glycerol have become the most important markers of ischemia and cell membrane damage. As the primary source of energy, glucose is an important marker of changes in brain metabolism and the glutamate level is an indirect marker of cell damage. We have monitored MD together with intracranial pressure (ICP) for 55 to 287 (142±74) hours in 8 severe TBI patients. No complications were observed in relation to MD and ICP monitoring. Our preliminary results indicate that MD L/P ratios are higher and more fluctuated in poor outcome patients compared to those in favorable outcome patients. MD in association with other brain monitoring techniques is safe and may be useful in preventing and relieving secondary ischemic injury, predicting outcome and guiding therapy after severe TBI. However, the value of MD as a tool in routine neurointensive care decision-making remains unclear.