Brain Tissue Oxygenation Levels and Barbiturate Coma Therapy in Severe Traumatic Head Injury

Introduction: The purpose of this study was to determine changes in high energy (hypoxanthine, inosine, adenosine) and metabolic (lactate, pyruvate) metabolites as well as amino acids (aspartate, glutamate, GABA) in a fluid percussion model of cerebral trauma. Significant changes occur during the first 2 hours postinjury and little clinical information is available in this time frame. These events may be important determinants of long-term outcome. Methods: Following induction of anesthesia, Sprague-Dawley rats were intubated and artificially ventilated. Femoral arterial and venous catheters were placed and burr holes were made in the skull for the fluid percussion mount, laser Doppler fibers, and a microdialysis probe. Arterial blood pressure and blood gases were monitored. Microdialysis samples were collected from two hours preto two hours post-injury. Cerebral perfusion was monitored continuously. Fluid percussion was effected at 2 atmospheres, a moderate injury. Results: Increases were seen in the following metabolites in response to the injury: Hypoxanthine (p < 0.01), Inosine (p < 0.01), Adenosine (p < 0.01), Lactate (p < 0.01), Aspartate (p < 0.01), Glutamate (p < 0.02), GABA (p < 0.001). There was no change in pyruvate concentration. Cerebral perfusion decreased by 40% and remained decreased for the 2 hour post-injury period. Conclusion: Significant early changes occur in the metabolic state and the availability of high energmetabolites. There is a general increase in deleterious excitatory amino acids concomitant with a decrease in cerebral perfusion. These changes may support the formation of free radicals, particularly the highly reactive oxygen species. These alterations and their timing should be considered when devising a treatment protocol. PB 03 BRAIN TISSUE OXYGENATION LEVELS AND BARBITURATE COMA THERAPY IN SEVERE TRAUMATIC HEAD INJURY J Daniel Thorat, I Ng (Singapore)