Certified Pulmonary Function Technologist (CPFT) Practice Exam

What happens to SaO2 if it is usually not at 100%?

1. It has no effect on CaO2

2. It may decrease CaO2

3. It always increases CaO2

4. It validates hemoglobin levels

The correct answer is: It may decrease CaO2

In the context of oxygen transport in the blood, when SaO2 (arterial oxygen saturation) is not at 100%, it indicates that the hemoglobin is not fully saturated with oxygen. This will affect the total oxygen content of the blood, known as CaO2 (arterial oxygen content). The correct response highlights that lower levels of SaO2 can lead to a decrease in CaO2. This is because CaO2 is determined not only by the concentration of hemoglobin in the blood but also by the oxygen saturation level of that hemoglobin. If SaO2 is low, it means that a smaller proportion of hemoglobin is bound to oxygen, thereby reducing the overall amount of oxygen carried by the blood. In this scenario, if SaO2 is less than 100%, the available hemoglobin to bind oxygen is less effective, which can significantly lower the CaO2 despite potentially normal hemoglobin levels. Hence, knowing the SaO2 is crucial for assessing how well oxygen is being transported through the bloodstream. The other choices do not accurately reflect the relationship between SaO2 and CaO2. An option suggesting no effect on CaO2 disregards the direct relationship between saturation and total oxygen content. Similarly,