The invention relates to a method and a device for ventilating a patient while taking into consideration a respiratory gas additive admixture. A ventilating device is proposed which substantially consists of a base device, a breathing tube, and a contact device and in which a respiratory gas additive volumetric flow rate provided by an external respiratory gas additive source is introduced into the contact device and at least partly mixed with the respiratory gas volumetric flow rate provided by the base device. By continuously feeding the respiratory gas additive volumetric flow rate directly into the contact device or into a breathing tube section which adjoins the contact device, and thus into the respiratory gas volumetric flow rate to be dispensed to the patients lungs in a cyclical manner, it is possible to enrich the additive concentration to any concentration or to completely replace the additive concentration during the expiration process, in which the respiratory gas volumetric flow rate is zero in an ideal monitoring process.
