A chest drainage system, including a circulation assembly having an intake for taking fluid into the system and an exhaust for exhausting fluid out of the system. An intake flow device is configured to selectively control fluid flow through the intake and an exhaust flow device is configured to selectively controlling fluid flow through the exhaust. The circulation assembly has a first configuration and a second configuration such that transitioning between the first and second configurations during operation of the circulation assembly displaces at least a portion of fluid within the system with fluid from outside the system via the intake and the exhaust. A sensor is arranged in fluid communication with the fluid within the system and configured to detect a concentration of a reference fluid in the fluid in the system.