True about Hb dissociation curve is
Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2, and thus less delivery of O2 to tissues.
Shift to left seen in
-        Increased pH
-        Decreased 2,3 DPG, temperature, PCO2
-        HbF (Fetal)
Shift to right seen in
-        Decreased pH
-        Increased 2,3DPG, temperature, PCO2
-        HbS (Sickle cell)
Acidosis shifts O2 dissociation curve to right
↑CO2 shifts the curve to left
Hypoxia shifts curve to left
2, 3 DPG has no effect on curve