A method and apparatus for non-invasively determining a blood oxygen saturation level within an organ of a subject using direct application of a near infrared spectrophotometric sensor is provided. The method includes the steps of: a) transmitting a light signal directly into the subject's organ using the sensor； b) sensing a first intensity of the light signal and a second intensity of the light signal, after the light signal travels a predetermined distance through the organ of the subject； c) determining an attenuation of the light signal along multiple different wavelengths using the sensed first intensity and sensed second intensity； d) determining a difference in attenuation of the light signal between wavelengths； and e) determining the blood oxygen saturation level within the subject's organ using the difference in attenuation between wavelengths.
