The invention relates to a device for the automated determination of the PEEP of a patient. Said device comprises sensors and a suitable electronic system for determining a pressure-volume characteristic curve during a P/V manoeuvre. The electronic system is designed in such a way as to generate, specifically in terms of breathing pressure, the difference between ' lung volume during exhalation (Vdef)' and ' lung volume during inhalation (Vinf)', and to determine the maximum value of said difference. The breathing pressure is then determined, for which the volume difference has a value definedin relation to the maximum value of the volume difference. The device calculates a PEEP value on the basis of said determined breathing pressure value.