Abstract: A canister (10) is provided for use with an anaesthesia and resuscitation machine. The canister (10) includes a canister body (12) defining an interior (41) for holding carbon dioxide absorbent (114). A unidirectional expiratory valve (40) is integrally mounted to the canister body (12) through which a patient gas can pass into the canister body interior (41), and a unidirectional inspiratory valve (42) is provided through which the patient gas can pass out of the canister body interior (41). An overflow orifice (102) extends through the canister body, through which the patient gas can pass. A unidirectinal overflow valve (150) is coupled to the overflow orifice (102) for permitting a controlled flow of patient gas therethrough to maintain the desired patient gas pressure within the interior (41) of the canister body (12).