The poisonous effect of carbon monoxide stems from its competition for the same binding site as oxygen. Hemoglobin unloads more oxygen into the tissues that need it most. NOAA Scuba Hematologic Disqualifications Hematological Sickle cell anemia should be disqualifying. Leukemia or pre-leukemia manifesting as myelofibrosis and polycythemia should be disqualifying. Intoxication that has caused methemoglobinemia should be disqualifying.
All physicians know that hemoglobin carries oxygen and that anemia can lead to severe hypoxemia.
Tissues have to have a certain amount of oxygen per minute in order to live, a need met by oxygen content , not oxygen pressure. The oxygen carrying capacity of one gram of hemoglobin is 1.34 ml. Conversely, patients can have a normal PaO2 and be profoundly hypoxemic by virtue of a reduced CaO2. Obviously, however, the lower the hemoglobin content the lower the oxygen content. It is not unusual to see priority placed on improving a chronically hypoxemic patient's low PaO2 when a blood transfusion would be far more beneficial.