ECMO loop not removing CO2 properly

I have a script that sets up an ECMO loop and is supposed to remove CO2 from the blood that passes through the ECMO circuit. However I noticed that the aorta’s pCO2 does not change based on the rate of CO2 removal from the ECMO loop. It only changes when the blood flow rate is changed. Have I setup the CO2 removal incorrectly? This is my code:

settings.get_substance_concentration(“CarbonDioxide”).get_concentration().set_value(list(results)[31] - 0.00013555, MassPerVolumeUnit.g_Per_dL)

Where results[31] is the CO2 concentration from the ECMO blood sampling port.