A method and apparatus for non-invasively determining the blood oxygensaturation level within a subjects tissue is provided. The method includes:providing anear infrared spectrophotometric sensor transmits light along a plurality ofwavelengthsinto the subjects tissue sensing the light transmitted into the subjectstissue using thesensor, and producing signal data representative of the light sensed from thesubjectstissue processing the signal data to account for physical characteristics ofthe subjectand determining the blood oxygen saturation level within the subjects tissueusing adifference in attenuation between the wavelengths. The apparatus includes asensoroperably connected to a processor. The sensor transmits light along aplurality ofwavelengths into the subjects tissue, and produces signal data representativeof the lightsensed from the subjects tissue. The processor processes the signal data withanalgorithm to account for the physical characteristics of the subject beingsensed.
