Which condition will cause a leftward shift of the oxygen dissociation curve?

• A. Respiratory Alkalosis
• B. Therapeutic Hypothermia
• C. Increased DPG
• D. Right Shift

Answer: (A)

When Hb binds oxygen, the curve can shift left or right to reflect changes in Hb’s affinity for oxygen. A leftward shift means Hb holds onto O2 more tightly, increasing its loading in the lungs but making unloading to tissues harder. Respiratory alkalosis increases blood pH and lowers CO2, which reduces hydrogen ion availability on hemoglobin and shifts the curve left (the Bohr effect). This makes oxygen binding to Hb more favorable. While cooler temperatures (therapeutic hypothermia) can also cause a left shift, the classic exam association for a leftward shift due to a condition is respiratory alkalosis. Conversely, increased 2,3-BPG lowers Hb’s affinity and shifts the curve to the right, and a rightward shift describes the opposite direction.