A method and a control program for operating an anesthesia apparatus, as well as an anesthesia apparatus (12), which operates according to the method are provided. The anesthesia apparatus includes a breathing gas feed unit (22) intended for displacing a breathing gas volume in a breathing circuit (10). A piston (23) brings about the displacement of the breathing gas. Switching over between a first mode of operation and a second mode of operation during the return of the piston (23) allows for a presetting of a corresponding piston return velocity. The piston return velocity depends on a volume flow in an exhalation branch (34) of the breathing circuit (10) in the first mode of operation. The piston return velocity depends on a minimally necessary piston return velocity in the second mode of operation.
