An interface mechanism is provided that removably unites a carbon dioxide absorption canister with a patient breathing circuit on a ventilator. The interface mechanism includes a cradle that is moveably positioned between a first position and a second position, wherein in the first position, the canister is coupled to the cradle and the cradle is positioned such that the canister is in fluid communication with the breathing circuit. In the second position, the canister is removable from the cradle and the cradle extends at an angle from the patient breathing circuit. The interface mechanism advantageously provides visual indication when the canister is removed and the breathing circuit is operating as a closed loop system, without CO.sub.2 filtration. The mechanism also facilitates efficient and accurate fluid connection between the carbon dioxide absorption canister and the breathing circuit.