Advanced Patient Assessment Practice Exam

Which of the following shifts the oxyhemoglobin dissociation curve to the left?

1. Increased PaCO2

2. Increased body temperature

3. Decreased pH

4. Fetal hemoglobin

The correct answer is: Fetal hemoglobin

The oxyhemoglobin dissociation curve represents the relationship between the partial pressure of oxygen (PaO2) and the hemoglobin saturation with oxygen (SaO2). A leftward shift in this curve indicates an increase in hemoglobin's affinity for oxygen, meaning that hemoglobin holds onto oxygen more tightly and is less willing to release it to the tissues. Fetal hemoglobin is known to cause a leftward shift of the oxyhemoglobin dissociation curve. This is primarily due to its unique structural characteristics, which allow fetal hemoglobin to bind oxygen more effectively than adult hemoglobin in the presence of low partial pressures of oxygen, such as those found in the placenta. This higher affinity is essential for effective oxygen uptake from maternal blood, ensuring that the fetus receives sufficient oxygen for its growth and metabolism. The other variables mentioned, such as increased carbon dioxide (PaCO2), increased body temperature, and decreased pH (which corresponds to an increase in metabolic acidosis), typically cause a rightward shift in the dissociation curve. This rightward shift indicates a decreased affinity of hemoglobin for oxygen, facilitating the release of oxygen to the tissues that are actively metabolizing and producing more carbon dioxide and acids. Thus, fetal hemoglobin is the only factor