Hemoglobin is the molecule in the blood responsible for transporting oxygen through the bloodstream and throughout the body. Hemoglobin has a high affinity for oxygen, but its affinity for carbon monoxide is much greater.
When oxygen and carbon monoxide are present in the room, carbon monoxide will bind to the hemoglobin, halting oxygen delivery and causing suffocation.
The only way to outcompete carbon monoxide for hemoglobin binding spots is to oversaturate the body with oxygen. When a patient is in an environment filled with 100% oxygen, carbon monoxide and other harmful gases will literally be forced out of the body.