An oxygenation system for a ventilation system comprises an inlet for receiving oxygenation gas at an oxygenation gas flow rate into an oxygenator, and an exhaust gas remover to remove exhaust gas at an exhaust gas flow rate from the oxygenator, and one or more flow controllers for controlling the exhaust gas flow rate relative to the oxygenation gas flow rate. This allows the amount of total gas entering the oxygenator and the amount of total gas removed from the oxygenator to be controlled with greater accuracy.
