Carbon monoxide effect on O2 dissociation curve is

Carbon monoxide (CO) combines with hemoglobin at the same point on the hemoglobin molecule as does O2; it can, therefore, displace O2 from the hemoglobin, thereby decreasing the O2-carrying capacity of blood. Fuher, it binds with about 250 times as much tenacity as O2.The presence of HbF and carbon monoxide (CO) shift the curve to the left, increasing the oxygen affinity of hemoglobin.Ref: Guyton; 13th edition; Chapter 41; Transpo of Oxygen and Carbon Dioxide in Blood and Tissue Fluids