Investigation of Extracellular Amino Acid Release in Children with Severe Head Injury using Microdialysis. A Pilot Study

Microdialysis has been used to investigate the pathophysiology of severe head injury in adults. No similar data exist, however, for children. As part of routine neuromonitoring, five children with severe, closed head injury (GCS <8) were fitted with a microdialysis probe (CMA 70) at the time of intracranial pressure bolt insertion. Samples were collected at hourly intervals prior to analysis of amino acids by High Performance Liquid Chromatography. In contrast to adult patients, glutamate and aspartate did not correlate with structural amino acid levels and were inversely related to glutamine levels, suggesting that excitatory aminoacid release in children with severe head injury is likely to be an active process rather than an effect of indiscriminate cell destruction and that glutamate levels extracellularly may also depend on glutamate uptake and metabolism. The nitric oxide metabolite citrulline remained at similar levels in different patients throughout the monitoring period, indicating that nitric oxide metabolism may not follow the pattern of glutamate release. Our study is suggesting that amino acid release in severe head injury in children may not correspond to the recognised patterns from cell culture and animal studies and may also differ from that in adults.