The apparatus has a mixing device for mixing medical gas i.e. oxygen, with air sucked by a blower (1). A gas line (10) for the medical gas and an air line (11) are led into a common breathing gas line (12). A junction of the gas line into the common breathing gas line is provided downstream of the blower. The gas line comprises a control valve (8) i.e. proportional valve, for variable setting of gas flow. Another control valve (4) i.e. proportional valve, for metering respiratory gas is provided in the common breathing gas line. An independent claim is also included for a method for operating a respirator and/or anesthesia apparatus.
