Blood entering the oxygenator will be fully saturated with oxygen. The contribution this makes to systemic oxygenation is dependent on extracorporeal blood flow relative to the patient’s cardiac output. The fully saturated blood from the oxygenator mixes with deoxygenated venous return (which has not passed through the oxygenator) to return to the right atrium. The closer the extracorporeal blood flow to cardiac output (and therefore venous return), the greater the proportion of blood entering the pulmonary artery which has been oxygenated, and
the higher the oxygen content of the mixed blood.
The native lungs initially provide minimal contribution to gas exchange, thus blood entering the pulmonary artery will have same oxygen content as the left sided circulation.
Oxygenation is primarily controlled by manipulating extracorporeal blood flow but is affected by recirculation haemoglobin concentration and membrane efficiency. Recirculation is where reinfused oxygenated blood is withdrawn through the drainage cannula without passing through the systemic circulation.
