The InSpectra StO2 Tissue Oxygenation Monitor functions as a tissue oxygen saturation monitor by sending light through the skin into underlying tissues and taking measurements of the light after it travels through the tissues. The measurement of hemoglobin oxygen saturation in tissue is based on spectrophotometric principles that relate light absorption to chemical concentration. The absorption spectra of oxygenated and deoxygenated hemoglobin are well characterized and provide a means to calculate the ratio of oxygenated hemoglobin to total hemoglobin. When measured in the microcirculation of a volume of tissue, this is expressed as percent tissue oxygen saturation (St02).
The InSpectra StO2 Tissue Oxygenation Monitor measures tissue absorbance values between 680-800 nm, and transforms these values using a scaled second derivative equation to provide a tissue spectral measurement that is robust to total hemoglobin and optical path length changes. The depth of tissue measured by the InSpectra StO2 System is directly related to the distance between the illumination fibers and detection fibers: studies have shown that with 15mm sensor spacing, approximately 95% of the detected optical signal is from a depth of 0-14mm.