A method and apparatus for non-invasively determining a blood oxygen saturation level and/or the presence of fecal matter within a subjects lower GI tissue is provided. The method includes the steps of: a) providing a spectrophotometric sensor operable to transmit light into the subjects tissue, and to sense the light b) sensing the subjects lower GI Tissue Using the Sensor, and Producing signal data from sensing the subjects tissue c) processing the signal data, including determining the presence of one or more wavelength dependent light absorbing materials not present within blood within the subjects lower GI tract from the signal data and d) determining the blood oxygen saturation level and/or presence of fecal matter within the subjects lower GI tissue, including accounting for the presence of the wavelength dependent light absorbing material not present within blood within the subjects lower GI tract determined using the signal data.
