True about Hb dissociation curve:
Oxygen-hemoglobin dissociation curve is shifted to right in the following conditions: 

Decrease in partial pressure of oxygen.
 Increase in partial pressure of carbon dioxide (Bohr effect).
Increase in hydrogen ion concentration and decrease in pH (acidity). 
Increased body temperature. 
Excess of 2,3-diphosphoglycerate (DPG) in RBC. It is also called 2,3-biphosphoglycerate (BPG). DPG is a byproduct in Embden-Meyer-hof pathway of carbohydrate metabolism. It combines with β-chains of hemoglobin. In conditions like muscular exercise and in high attitude, the DPG increases in RBC. So, the oxygen-hemoglobin dissociation curve shifts to right to a great extent.
Acidosis shifts O2 dissociation curve to right
Increased CO2 shifts the curve to left
Hypoxia shifts curve to left
2,3 DPG has no effect on curve