Does the Estimation of Light Attenuation in Tissue Increase the Accuracy of Reflectance Pulse Oximetry at Low Oxygen Saturations In Vivo?

A new technique was validated in vivo in reflectance pulse oximetry for measuring low oxygen saturations. Two pairs of light emitter/detector diodes allow for estimation of light attenuation (LA) in tissue, which is assumed to be responsible for the inaccuracy of pulse oximetry at less than 70% arterial oxygen saturation. For validation, 17 newborn piglets were desaturated stepwise from 21% to 1.25% inspiratory oxygen concentration during general anesthesia, and arterial oxygen saturation was measured with the reflectance pulse oximeter adjusted for LA in tissue, with a standard transmission pulse oximeter and a hemoximeter. LA in tissue could be quantified and was different between snout and foreleg (probability level (p) < 0.05). At arterial oxygen saturations above 70%, the bias between the methods was at 0%-l% and the variability 4%-5%. From 2% to 100% arterial oxygen saturation, the reflectance pulse oximeter estimated oxyhemoglobin saturation more accurately than a conventional transmission pulse oximeter (p < 0.05). At low oxygen saturations below 70%, the bias and variability of the reflectance pulse oximeter calibration were closer to the hemoximeter measurements than the transmission pulse oximeter (p < 0.05). The variability of the reflectance pulse oximeter was slightly lower than the traditional oximeter by taking into account the LA in tissue (9% versus 11%-15%, ns), and thus, the quality of the individual calibration lines improved (correlation coefficient, p < 0.05).