Carboxyhemoglobin (British English: Carboxyhaemoglobin) (COHb) is a stable complex of carbon monoxide and hemoglobin that forms in red blood cells upon contact with carbon monoxide (CO). Large quantities of CO hinders the ability of Hb to deliver oxygen to the body.OHb has a half-life in the blood of 4 to 6 hours. This time can be reduced to 70 to 35 minutes with administration of pure oxygen (the lower number applying when oxygen is administered with 4 to 5% CO2 to cause hyperventilation).