Comparison of three methods for determining oxygen saturation in arterial blood

Oxygen saturation was determined by direct measurement with the Van Slyke method, an oximeter, and by indirect measurement with a pO2 electrode with conversion of oxygen tension to oxygen saturation. All three methods correlated well when the oxygen saturation was above 94 per cent. Below this value both the oximeter measurement and the saturation value calculated from the oxygen tension significantly overestimated the oxygen saturation as determined by the Van Slyke method. It appears from our data that when the saturation is less than 94 per cent, the absolute values for O2 saturation continue to be accurately determined with a Van Slyke, but the other two methods in this range are, at best, only useful in detecting gross changes in oxygen saturation.