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NIRS and the InSpectra™ StO2
Oxygenation Monitor
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.

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The InSpectra™ StO2 Tissue Oxygenation Monitor provides a direct, absolute measurement of hemoglobin oxygen saturation in tissue (StO2), providing trauma teams the ability to measure tissue oxygenation and monitor it during resuscitation. It is the only tissue oxygenation monitor designed for trauma environments. The InSpectra StO2 Tissue Oxygenation Monitor uses near infrared light to illuminate tissue, and then analyzes the returned light to produce a quantitative measurement of oxygen saturation in the tissue's microcirculation.

The StO2 Trauma Study researched the role that tissue oxygen saturation monitoring could play in hemorrhagic shock and resuscitation. Study results demonstrate that StO2 measurements less than 75% may indicate serious hypoperfusion in trauma patients and that StO2 functions as well as base deficit in indicating hypoperfusion in trauma patients.