1. Breathing apparatus comprising (a) a generator (140) of the pressure operable to create a flow of breathing gas under pressure for supplying the patients airways (b) an interface (180) of the patient, adapted to the breathing gas flow direction under pressure the patients airways, the patient interface comprises a clearance volume (c) one or more sensors (142) adapted to generate output signals conveying information related to the flow rate and / or pressure in the interface patsie NTA and (d) one or more processors (110) configured to execute computer program modules, wherein the computer program modules comprise (i) a control module (111) configured to control pressure generator to generate a respiratory gas stream at a pressure of at least partially to the patients lungs mechanically ventilated (ii) module (112) determining parameters capable of: (1) determining on the basis of output signals generated during exhalation, the exhaled tidal volume and about EMA leak during exhalation, and (2) determining on the basis of output signals generated during a subsequent inspiration, inspiratory tidal volume iobema leaks during inspiration and (iii) a module (113) estimates configured to estimate the proportion of inhaled oxygen during the subsequent inhalation based on the first comparison exhaled tidal volume to the sum of the volume of dead space and leak volume during exhalation and further, based on the second comparison inspiratory tidal volume with the sum of the volume of dead space and leak volume at vdohe.2. breathing device1. Дыхательное устройство, содержащее(a) генератор (140) давления, выполненный с возможностью создания потока дыхательного газа под давлением для подачи в дыхательные пути пациента(b) интерфейс (180) пациента, выполненный с возможностью направления потока дыхательного газа под давлением в дыхательные пути пациента, при этом интерфейс пациента содержит объем мертвого пространства(c) один или более датчиков (142), выполненных с возможностью
