Extracellular glutamate and aspartate in head injured patients

Eighty-six patients in coma from a severe head injury underwent monitoring of extracellular concentrations of glutamate and aspartate by a microdialysis technique during the first few days after injury. The median value for glutamate was 7.4 microM (interquartile range 3.6-18.8 microM). The median value for aspartate was 2.4 microM (interquartile range 1.1-5.0 microM). Average values for the dialysate concentrations of glutamate and aspartate, were closely related to outcome (p < .001 and p = .002, respectively). Patients who died of their head injury had significantly higher dialysate glutamate and aspartate concentrations compared to patients who recovered to a Glasgow Outcome Score of good recovery or moderate disability. Dialysate glutamate and aspartate levels were also significantly related to type of injury (p = .008 and p = .004, respectively). The highest values were found in patients with gunshot wounds, followed by patients with evacuated and unevacuated mass lesions. Patients with diffuse injuries had the lowest values of glutamate and aspartate. These results suggest that excitatory amino acids may play a role in the evolution of injury to the brain after trauma.