Relationship between Excitatory Amino Acid Release and Outcome after Severe Human Head Injury

In previous studies, Katayama and our group have documented a massive increase in excitatory amino acid release following traumatic brain injury, in both rat fluid percussion, and humans [2,5]. To test the hypothesis that the magnitude of this "Excitotoxic Surge" plays a significant role in determining 6-month patient outcome. We have studied 83 consecutive severely head injured patients at the Medical College of Virginia for inclusion into this study. A microdialysis probe was placed within the cortex to continuously measure dialysate excitatory amino acids (Glutamate and Aspartate), along with several other analytes for approximately 5 days after injury. ICP, CPP, and MABP measurements were also time linked with each analyte measurement to create a neurochemical, clinical, and physiological "prolile" for each patient. Outcome was determined by follow up using the Glasgow 6-Month outcome scale. A very strong correlation existed between the release of the EAA's glutamate and aspartate after TBI (p < 0.0001). Patients with significantly elevated mean glutamate values for the entire monitoring period were most likely to exhibit elevated levels of ICP. The magnitude of glutamate released significantly correlates with 6-month patient outcome (p = 0.0234). When patients were subdivided by the CT diagnosis of lesion type, we found that those patients with contusions displayed the highest overall of EAA's.