Validation and improvements of an algorithm for the determination of hemoglobin oxygenations, based on spectral data recorded by a tissue spectrophotometer.

The tissue spectrometer EMPHO allows measurements of absolute hemoglobin oxygenation values, non-invasively at any hemoglobin-perfused tissue, simply by applying visible light on the surface of the organs under investigation. The hemoglobin oxygenation-algorithm is based on Kubelka-Munk-Theory for tackling both, absorbance and scattering phenomena. Broad-band tissue spectra of backscattered light serves as data basis for the analysis. In this study the algorithm was tested for measurements in highly scattering media, in Intralipid(R), where erythrocytes were added step by step. The hemoglobin concentration in the suspension varied from 0.01 to 1.0 [g hb/dl of suspension], which corresponds to the range of hemoglobin concentrations physiologically found in various types of tissue. The oxygenation was changed from 0% to 100% by using a hollow-fibre oxygenator. The costly study revealed that the algorithm works with high accuracy at a middle hemoglobin-concentration of 0.3 g/dl. The error of calculation was smaller than 2% of the absolute HbO(2) value. The statistics proved that errors were larger at the highest acid lowest values of hemoglobin concentration. It could clearly be shown that the error can be minimized to 1% by application of new gold-standard hemoglobin spectra of 0% and 100% oxygenation.