Extracellular amino acid changes in patients during reversible cerebral ischaemia

This study investigated the changes in extracellular chemistry during reversible human cerebral ischaemia. Delayed analysis was performed on samples taken from a subgroup of patients during aneurysm surgery previously reported. Frozen microdialysis samples from 14 patients who had all undergone temporary clipping of the ipsilateral internal carotid artery (ICA) were analysed for another 15 amino acids with HPLC and for glycerol with CMA-600. Changes were characterised according to whether cerebral tissue oxygen pressure (PBO2) decreases were brief or prolonged. Brief ICA clipping (maximum duration of 16 minutes) in 11 patients was not associated with changes in amino acids or glycerol. Cerebral ischaemia, defined by a PBO2 decrease below 1.1 kPa for at least 30 minutes during ICA occlusion, occurred in 3 patients. None of whom developed an infarct in the monitored region. This prolonged reversible ischaemia was associated with transient delayed increases in gamma-amino butyric acid (GABA) as well as glutamate and glycerol, each by two-to-three folds. This study demonstrates detectable transient increases in human extracellular glutamate, GABA and glycerol during identified periods of reversible cerebral ischaemia, maximal 30-60 minutes after onset of ischaemia, but not in other amino acids detected by HPLC.