Multiparametric monitoring of brain oxygen balance under experimental and clinical conditions

In order to evaluate the relationship between brain oxygen supply and demand (O₂ balance) in real time, it is necessary to use a multiparametric monitoring approach. Cerebral blood flow (CBF) is a representative parameter of O₂ supply. The extracellular level of K⁺ is a reliable indicator of O₂ demand since more than 60% of the energy consumed by the brain is utilized by active transport processes. Mitochondrial NADH redox state can represent the balance between O₂ supply and demand. In order to monitor the brain of experimental animals or patients, we constructed the multiparametric assembly (MPA) and the following parameters were monitored simultaneously and in real time: CBF, CBV, NADH redox state, extracellular K⁺, DC potential, EEG, tissue temperature and ICP. Animals were exposed to hypoxia, ischemia, hypercapnia, hyperoxia and spreading depression (SD) and the relative changes in CBF and NADH were calculated and found to be significant indicators of brain energy state. Monitoring these two parameters increases the possibility of differentiating between various pathophysiological states. Each added parameter increases the power of diagnosis and determination of the functional state of the brain. Preliminary results obtained in patients monitored in the ICU or in the OR show that the responses to hypercapnia, spreading depression or ischemia are similar to those measured in experimental animals.