[Near-infrared monitoring of cerebral oxygenation during cerebral ischemia].

The objective of this study was to assess the relationship between the changes in the redox state of cytochrome oxidase (Cyt. ox.) and those of spontaneous EEG activity and cellular energy state during cerebral ischemia and recirculation. We induced 5-min forebrain ischemia by occluding the bilateral common carotid arteries in anesthetized gerbils. Redox changes of Cyt. ox. were monitored with near-infrared spectroscopy (NIRS) through the experiments. Cortical energy metabolites, ATP, ADP, and AMP, were also measured with high performance liquid chromatography (HPLC) during ischemia and recirculation. Ischemia immediately caused a rapid reduction of Cyt. ox., which paralleled to deterioration of spontaneous EEG activity and preceded significant changes in cellular energy state. Re-oxygenation of Cyt. ox. was observed just after recirculation, and paralleled to the recovery of cellular energy state. Spontaneous EEG activity did not recover even when all other NIRS parameters almost recovered during recirculation after 5-min ischemia. During clamping of the carotid artery, NIRS findings also correlated with those of somatosensory evoked potential (SEP). We concluded that, by means of monitoring redox changes of Cyt. ox., NIRS can detect non-invasively critical neuronal hypoxia prior to a significant impariment of cellular energy state caused by cerebral ischemia, and that NIRS can also detect recovery of oxidative phosphorylation during recirculation, which cannot be observed on EEG.