Summary response:
The Tissue Hemoglobin Index (THI) measurement is an indicator of signal strength based on the measure of the total amount of hemoglobin present in the monitored tissue. A THI greater than 5.0 indicates sufficient hemoglobin to obtain an adequate StO2 signal in most circumstances. Values lower than 5.0 indicate a weaker hemoglobin signal in which case the accuracy of the StO2 value may be reduced.
Background:
Tissue Hemoglobin Index (THI) is reported as a number in the range of 1-99 by the InSpectraTM StO2 Tissue Oxygenation Monitor. It is a quantified value that corresponds to the amount of hemoglobin present within the volume of tissue monitored by the patient contact sensor. Because the volume of tissue illuminated is comprised of both extra vascular and vascular tissue, THI values are not the same as the blood hemoglobin concentration, but rather represent the total tissue concentration of hemoglobin.
Work is currently ongoing to further explore the clinical utility of the THI parameter, with experiments being conducted that include in vitro, ex vivo animal, and human volunteer studies.
References
Skarda DE, Mulier KE, Myers DE, Taylor JH, Beilman GJ. Dynamic near-infrared spectroscopy measurements in patients with severe sepsis. Shock. In press.
Mulier KE, Skarda DE, Taylor JH, Myers DE, McGraw MK, Gallea BL, Beilman GJ. Near-infrared spectroscopy in patients with severe sepsis: correlations with invasive hemodynamic measurements. Surg Infect. In press.
Myers D, unpublished data Hutchinson Technology 2006.