Certified Ambulatory Perianesthesia Nurse (CAPA) Practice Exam

If a patient has a low arterial O2 content despite an SpO2 reading of 100%, what condition might the perianesthesia nurse suspect?

1. Hypovolemia

2. A low Hgb level

3. Hyperthermia

4. An elevated HCT

The correct answer is: A low Hgb level

When a patient presents with low arterial oxygen content despite an SpO2 reading of 100%, it is crucial to differentiate the concept of oxygen saturation from overall oxygen content. Oxygen content in the blood is determined not just by the saturation of hemoglobin with oxygen, but also by the amount of hemoglobin available to carry that oxygen. A low hemoglobin level could lead to insufficient oxygen being transported in the blood, even if the hemoglobin that is present is fully saturated with oxygen. This scenario is particularly common in conditions such as anemia, where there are fewer red blood cells or a lower level of hemoglobin available. Thus, even at 100% saturation, the total arterial oxygen content would remain low due to a decreased amount of hemoglobin to bind oxygen. In contrast, while other conditions on the list, such as hypovolemia or hyperthermia, could have some effect on oxygenation, they would not typically lead to a scenario where arterial oxygen content is low while SpO2 remains at 100%. An elevated hematocrit (HCT) does not lead to low arterial O2 content either, as it indicates a higher proportion of blood volume is made up of red cells, which could correlate with higher total oxygen content.