Pulse oximetry in horses

The clinical usefulness of two pulse oximeters was evaluated at two probe sites in nine anesthetized horses. The hemoglobin saturation determined by the pulse oximeters (SaOx) was compared with the hemoglobin saturation calculated from the measured arterial oxygen tension (SaO2). The mean and standard deviation (SD) were calculated from the differences in saturation measurements, over the saturation range of 80% to 100%, for each oximeter used at the tongue probe site and for one oximeter used at the ear. The oximeter results tended to underestimate the SaO2 with mean differences of -3.7% on the tongue and -6.0% on the ear. The limits of agreement were defined as the mean difference +/- 2 SD. Each oximeter used at the tongue produced limits of agreement of +1% to -8%, which meant that 95% of the SaOx values were 1 percentage point above or 8 percentage points below the SaO2. The variability of the differences and limits of agreement were larger when the ear was used as the probe site and at saturations less than 80%. Although both oximeters tended to underestimate the SaO2, they appeared to be clinically useful in detecting changes in arterial hemoglobin saturation.