Which condition would cause a rightward shift of the oxyhemoglobin dissociation curve?

Which condition would cause a rightward shift of the oxyhemoglobin dissociation curve?

• A. Methemoglobinemia
• B. Carboxyhemoglobinemia
• C. Hypothermia
• D. Pregnancy

Answer: (D)

A rightward shift of the oxyhemoglobin dissociation curve means hemoglobin has a lower affinity for oxygen and will release it more readily to tissues. Conditions that cause this include higher temperature, higher carbon dioxide, lower pH (acidosis), and increased 2,3-bisphosphoglycerate (2,3-BPG) in red cells. In pregnancy, maternal physiology adapts to improve oxygen delivery to the fetus. One key change is an increase in 2,3-BPG within red blood cells, which lowers hemoglobin’s O2 affinity. This, along with placental CO2 and local metabolic changes, promotes oxygen unloading from maternal hemoglobin to the placenta and fetus. That combination pushes the curve to the right. Methemoglobinemia and carboxyhemoglobinemia alter oxygen delivery differently: carboxyhemoglobin binding (CO) increases the affinity of the remaining normal hemoglobin for oxygen, tending to shift the curve to the left; methemoglobinemia reduces overall oxygen-carrying capacity and doesn’t produce the same rightward shift in the normal Hb population. Hypothermia lowers metabolic demand and shifts the curve to the left as well. Therefore, pregnancy is the condition that would cause a rightward shift.

A rightward shift of the oxyhemoglobin dissociation curve means hemoglobin has a lower affinity for oxygen and will release it more readily to tissues. Conditions that cause this include higher temperature, higher carbon dioxide, lower pH (acidosis), and increased 2,3-bisphosphoglycerate (2,3-BPG) in red cells. In pregnancy, maternal physiology adapts to improve oxygen delivery to the fetus. One key change is an increase in 2,3-BPG within red blood cells, which lowers hemoglobin’s O2 affinity. This, along with placental CO2 and local metabolic changes, promotes oxygen unloading from maternal hemoglobin to the placenta and fetus. That combination pushes the curve to the right.

Methemoglobinemia and carboxyhemoglobinemia alter oxygen delivery differently: carboxyhemoglobin binding (CO) increases the affinity of the remaining normal hemoglobin for oxygen, tending to shift the curve to the left; methemoglobinemia reduces overall oxygen-carrying capacity and doesn’t produce the same rightward shift in the normal Hb population. Hypothermia lowers metabolic demand and shifts the curve to the left as well. Therefore, pregnancy is the condition that would cause a rightward shift.