The invention relates to a device, with which one is to prevent a patient who breathes on Ms own and who desires a lower CO2-partial-pressure than is achieved by the set Ventilation from tiring. It comprises the following means for the regulation of a changing intensity of a mechanical Ventilation: • means for determining a target frequency RRsp, • means for determining a spontaneous frequency RRspont • means for comparing the spontaneous frequency RRspont with the target frequency RRsp. wherein adapting a Ventilation target value (% MinVol, V′gAsp) on account of the result of the comparison of the spontaneous frequency RRspont with the target frequency RRsp and • means for adapting the parameters determining the intensity of the Ventilation, on account of the Ventilation target value (% MinVol, V′gAsp). This so-called pump support System (PSS) is activated (PSS on) when the patient breathes in an adequately spontaneous manner (Criterion 1). With an insufficient individual activity of the patient, his behavior is taken as a basis for the control of the regulation. The control or regulation of the Ventilation is assumed by a fixed setting of a Ventilation target value (% MinVol), or a CO2-controller, as soon as the patient breathes in a manner which is not spontaneous enough.
