The device has two different adjustable pressure levels. A higher level for inspiration and a lower level for expiration. Trigger device The respiration trigger detects the patients efforts to breath in and out and signals these efforts to the control device. A flow-based trigger is integrated which can be set separately for inspiration and expiriation. While the pressure increases during inspiration it decreases during expiration. In connection with an optimum slope adjustment this results in a ventilation which is very comfortable for the patient and which gives the patient the impression as if the device is following the natural respiration without delay. The BILEVEL-devices offer two levels of pressure (I-pressure and E-pressure). The triggers which are separately adjustable for inspiration and expiration are particularly well suited to shallow breathing and effectively avoids undesirable selftriggering. The inspiration trigger controlled by volume and the expiration trigger controlled by flow are adjustable in three settings.