A process and system are provided for clearing modes of operation of a medical engineering device, especially modes of operation on a respirator (1), such as IMV (Intermittent Mandatory Ventilation, CPAP (Continuous Positive Airway Pressure) or HFV (High-Frequency Ventilation). The clearing is performed with an external electronic, optical or magnetic storage medium, e.g., a chip card (2), on which data that determine the available modes of operation and optionally the duration of their availability are present. The data on the chip card (2) are read by a writing and reading unit (3) of the respirator (1). The data may be coded, the duration of availability of a mode of respiration may be controlled by keeping a time log (9) on the chip card, and the corresponding time periods are debited from the time log (9) each time a certain mode of operation is used.