The effects of anesthesia on cerebral tissue oxygen tension: use of EPR oximetry to make repeated measurements.

While very useful data can be obtained from measurements of pO2 within various compartments of the vascular system, such measurements do not necessarily provide accurate information on the pO2 in the brain. Anesthetics can significantly affect the tissue pO2 in the brain by several mechanisms involving both delivery and utilization. Electron Paramagnetic Resonance (EPR or ESR) oximetry has the potential for non-invasively carrying out repeated direct measurements of pO2 in tissues during the course of anesthesia. In this paper we describe the use of EPR oximetry for studying the influence of anesthesia on tissue pO2, and present illustrative results from experiments with five different anesthetics in rats. The results indicate that the tissue O2 can be measured directly using EPR oximetry, and data can be obtained non-invasively during the course of anesthesia.