Certified Transport Registered Nurse Certification Practice Exam

In a left shift on the oxygen-hemoglobin dissociation curve, how is SPO2 affected?

1. It will be increased

2. It will be decreased

3. It remains unchanged

4. It will fluctuate unpredictably

The correct answer is: It will be increased

A left shift in the oxygen-hemoglobin dissociation curve indicates an increased affinity of hemoglobin for oxygen. This means that at a given partial pressure of oxygen (PaO2), hemoglobin will bind more oxygen and release less of it to the tissues. When hemoglobin has a higher affinity for oxygen, the saturation of hemoglobin with oxygen, denoted as SPO2, will be increased because hemoglobin is able to hold onto oxygen more effectively. Therefore, even if the oxygen levels in the blood remain the same, the increased affinity leads to a higher concentration of oxygenated hemoglobin at lower PaO2 levels. This physiological response is important in various clinical scenarios, such as during respiratory alkalosis or in cases of exposure to certain chemicals or conditions that promote a left shift. Thus, the correct understanding of a left shift's impact on SPO2 is that it results in an increased level of saturation, as correctly identified in the answer provided.