Determination of gas exchange device performance

A system comprising:

• a gas exchange device for transferring blood gases between blood in a circulatory system of a patient and a gas flow passing through the gas exchange device, the gas flow entering the gas exchange device as an inlet gas and exiting the gas exchange device as an exhaust gas;
• a carbon dioxide sensor configured to generate sensor data indicating a carbon dioxide concentration FeCO2 in the exhaust gas;
• and
• a control unit configured to:
• determine a flow rate of carbon dioxide VeCO2 in the exhaust gas based on the carbon dioxide concentration FeCO2 in the exhaust gas and a flow rate Qe of the exhaust gas;
• determine a flow rate of carbon dioxide VgCO2 transferred to the gas flow based on a difference between the flow rate of carbon dioxide VeCO2 in the exhaust gas and a flow rate of carbon dioxide VsCO2 in the inlet gas;
• and
• determine a performance of the gas exchange device based on the flow rate of carbon dioxide VgCO2 transferred to the gas flow and a reference flow rate VrefCO2;
• wherein the reference flow rate is based on at least one of:
• a flow rate of blood through the gas exchange device Qb, and a flow rate of the gas flow Qs.