Accuracy of pulse oximetry during arterial oxyhemoglobin desaturation in dogs

An animal model was developed to evaluate the accuracy of pulse oximetry over a wide range of oxyhemoglobin desaturation. The fractional inspired oxygen concentration was varied from 0.03-1.0 in five anesthetized dogs. One hundred and twelve simultaneous pulse oximeter oxygen saturation measurements (SpO2) and IL 282 CO-Oximeter arterial oxygen saturation (SaO2) measurements were made. Variance of SpO2 was increased for SaO2 less than 22%. Linear regression analysis of the data for SaO2 greater than 22% produced the equation y = 0.93x + 9.8 (r2 = 0.97). The mean difference between SpO2 and SaO2 was +5.5% +/- 4.2% (SD) over the range of 22-100%. Spectral analyses of oxygenated (O2Hb) and reduced (RHb) canine and human hemoglobins were performed. The absorption spectra of canine O2Hb and RHb were nearly identical to those of human O2Hb and RHb. Therefore, 1) SpO2 measurements in dogs at SaO2 greater than 22% are relatively accurate, and 2) hemoglobin absorption characteristics support the contention that such canine pulse oximeter studies can be extrapolated to humans.