Clinical significance of CSF glutamate concentrations following severe traumatic brain injury in humans

Glutamate excitotoxicity is a putative mechanism of secondary damage after traumatic brain injury (TBI). No relationship between glutamate release and clinical status has been shown in humans, however. We hypothesize a dose-response relationship between CSF glutamate concentrations and severity of injury, electrophysiological deterioration as measured by somatosensory evoked potential amplitudes, and clinical outcome. From August 1991 to March 1996, intensive monitoring of 55 patients with severe TBI (GCS < or = 8 after resuscitation) included twice daily CSF glutamate levels and hourly somatosensory evoked potentials (SSEPs) for an average of 5 days. Clinical outcomes were survival/nonsurvival and Glasgow outcome score (GOS) at 3 months or more post-injury. Glutamate levels were not associated with severity of injury, electrophysiological deterioration, or clinical outcome. Neither peak nor mean glutamate levels significantly improved a simple logistic regression model which used only age and presence of bilaterally unreactive pupils to predict survival. Using this methodology CSF glutamate concentrations did not display a dose-response relationship to severity of injury, electrophysiological deterioration, or predict clinical outcomes following TBI in a group of 55 patients. An early effect of glutamate, an effect dependent on time of exposure to glutamate or other modulating effects cannot be ruled out.