A pressure-isolating component for an oxygenator 20 of an extracorporeal ventilation system has an oxygenation gas inlet GI for supply of oxygenation gas, an exhaust chamber 1, and exhaust ports 28 permitting gas passage from the exhaust chamber 1 to the oxygenator exterior 2. The pressure isolating component 40 comprises a pressure relief arrangement activating at a pressure relief threshold and is thereby configured to inhibit pressure equalising between the exhaust chamber 1 and the oxygenator 20 exterior unless the pressure in the exhaust chamber 1 exceeds the pressure relief threshold and thereby causes the pressure-relief arrangement to activate and permit pressure equalising between the exhaust chamber 1 and the oxygenator exterior 2. The component 40 is provided as a cap to fit over the exhaust ports 28, and has duckbill valves 42 which open when the pressure in the oxygenator chamber exceeds their pressure relief threshold.
