Assessment of Brain Oxygenation: A Comparison Between an Oxygen Electrode and Near-Infrared Spectrophotometry

The inability of the brain to withstand more than a brief period of hypoxia is often the limiting factor determining survival for a variety of clinical conditions, most notably the adult respiratory distress syndrome and the hypoxic-hypotension related to major trauma. The capability for continuously and non-invasively monitoring cerebral oxygen availability within the mitochondria would be extremely desirable. Prior to the introduction of nearinfrared spectrophotometry (niroscopy) by Jöbsis (1977) such a capability did not exist. Subsequent work (Proctor et al., 1982) demonstrated the feasibility of monitoring cerebral cytochrome a,a3 redox states using in vivo spectrophotometry in a variety of experimental models, designed to mimic frequently encountered clinical conditions. An immediate problem became the interpretation and validation of the data in terms of a more conventional and commonly accepted method of assessing tissue oxygenation. As one of a series of investigations designed to clarify the role of niroscopy with regard to future applications, the present study correlates cytochrome a,a3 redox state and the intracerebral hemoglobin (HbO2) as measured by niroscopy with simultaneously performed measurements of cerebral cortex surface Po2 obtained using a Polarographic oxygen electrode