Arterial oxyhemoglobin saturation is related to P o 2 . P o 2 at 50% saturation (P 50 ) is normally 27 mm Hg. The dissociation curve is shifted to the right by increased hydrogen ion (H + ) concentration, increased RBC 2,3-diphosphoglycerate (DPG), increased temperature (T), and increased P co 2 . Decreased levels of H + , DPG, temperature, and P co 2 shift the curve to the left. Hb characterized by a rightward shifting of the curve has a decreased affinity for oxygen, and Hb characterized by a leftward shifting of the curve has an increased affinity for oxygen.