Abstract: An anesthetic respiratory system which is switchable between half-open and half-closed modes of operation improved with respect to the conspicuousness and operational safety. A CO.sub.2 absorber is arranged in an expiration branch and is formed as a switching element detachable from connection points which are secured to a respirator housing. One point of connection of the absorber comprises a shut-off element positively actuated by the switching element, which upon removal of the absorber interrupts the ring line and establishes separate inspiration and expiration respiration branches. The second point of connection of the absorber is open upon removal and it lies behind the controllable outlet valve.