Neonatal Nurse Practitioner Practice Exam

Which factors contribute to a left shift in the oxygen-hemoglobin dissociation curve?

1. Increase in temperature and CO2

2. Decrease in pH and increase in 2-3DPG

3. Decrease in CO2 and alkalosis

4. Increase in 2-3DPG and acidosis

The correct answer is: Decrease in CO2 and alkalosis

A left shift in the oxygen-hemoglobin dissociation curve indicates that hemoglobin has a higher affinity for oxygen, meaning that it holds onto oxygen more tightly and releases it less readily to the tissues. Multiple factors can influence this shift. The correct answer highlights that a decrease in carbon dioxide (CO2) levels and the presence of alkalosis (an increase in blood pH) promote this left shift. When CO2 levels decrease, there is less carbonic acid formed, which in turn leads to a higher pH. The Bohr effect explains that under conditions of higher CO2 and lower pH (more acidic), hemoglobin releases oxygen more readily. Conversely, with lower CO2 and higher pH (more alkaline), hemoglobin’s affinity for oxygen increases, resulting in a left shift on the curve. In contrast, conditions such as increased temperature and CO2 levels or a decrease in pH would lead to a right shift, where hemoglobin's affinity for oxygen decreases, thus facilitating oxygen release to the tissues. Similarly, increasing levels of 2,3-DPG, which is produced during glycolysis and acts as a metabolic regulator, also contribute to a right shift when levels rise, as it decreases hemoglobin's affinity for oxygen.