The apparatus (1) for the measurement of carbon dioxide in a working gas comprising: - one oxygenation device (2) of an extracorporeal blood flow provided with at least one entry (3) and one outlet (4) for a working gas (16) used to supply oxygen and/or to remove CO2 from the blood flow； - one measuring device (5) provided with at least one inlet (6) of the working gas (16) coming out of the oxygenation device (2) and configured to measure the level of carbon dioxide present inside the working gas (16)； - one connecting line (7) for the connection of the outlet (4) to the inlet (6) adapted to convey the working gas (16) coming out of the oxygenation device (2) entering the measuring device (5)； - outflow means (8) of the condensate (15) formed by the working gas (16) along the connecting line (7) on the outside thereof； where the outflow means (8) comprise at least one branch line (9) communicating on one side with the connecting line (7) and on the opposite side with the external environment, the branch line (9) being at room pressure.
