Method for operating an anesthesia apparatus, anesthesia apparatus operating according to the method and computer program for implementing the method

An anesthesia apparatus comprising:

• a breathing circuit;
• a breathing gas feed unit for displacing a breathing gas volume in the breathing circuit, the breathing gas feed unit comprising a piston bringing about the displacement of the breathing gas;
• and
• a control unit with associated memory, the control unit being operatively connected to the breathing gas feed unit, the control unit with associated memory being configured to:
• automatically switch over between at least one breathing gas feed unit first mode of operation and a breathing gas feed unit second mode of operation during a return of the piston to preset a corresponding piston return velocity;
• and
• provide the piston return velocity to depend on a volume flow in an exhalation branch of the breathing circuit in the first mode of operation;
• and
• provide the piston return velocity to depend on a minimally necessary piston return velocity in the second mode of operation;
• a fresh gas dispensing device operatively connected to the breathing gas feed unit and operatively connected to the control unit, wherein the control unit with associated memory selects the breathing gas feed unit first mode of operation or the breathing gas feed unit second mode of operation and switches over between the breathing gas feed unit first mode of operation or the breathing gas feed unit second mode of operation depending upon a setting of the fresh gas dispensing device for a fresh gas feed into the breathing circuit;
• wherein the control unit with associated memory has preset or receives limit values and sets the fresh gas feed into the breathing circuit as a function of the limit values for the selection of the first mode of operation or the second mode of operation and for the switching between the first mode of operation and the second mode of operation;
• wherein a switchover takes place between the first mode of operation and the second mode of operation based on an interpolation related to the limit values.

A method for operating an anesthesia apparatus comprising a breathing gas feed unit for displacing a breathing gas volume in a breathing circuit, wherein the breathing gas feed unit comprises a piston bringing about the displacement of the breathing gas, the method comprising the steps of:

• automatically switching over between at least one first mode of operation and a second mode of operation during a return of the piston to preset a corresponding piston return velocity;
• and
• providing the piston return velocity to depend on a volume flow in an exhalation branch of the breathing circuit in the first mode of operation;
• and
• providing the piston return velocity to depend on a minimally necessary piston return velocity in the second mode of operation;
• wherein a zero position of the piston of the breathing gas feed unit is changed incrementally as a function of a volume reserve and an applied inspiratory tidal volume;
• wherein the zero position of the piston and a changed volume reserve resulting from a change in the zero position of the piston are changed asymmetrically, such that a possible reduction of the volume reserve is smaller from one ventilation cycle to a next ventilation cycle than a possible increase in the volume reserve.