The invention relates to a respiratory assistance apparatus (1) such as a medical ventilator, comprising a gas circuit (2, 16) with at least one inhalation branch (2) able to carry a respiratory gas intended to be administered to a patient under cardiac arrest during cardio pulmonary resuscitation； measurement means (6) suited to and designed for measuring at least one parameter indicative of said flow of gas and converting said at least one parameter indicative of said flow of gas into at least one signal indicative of said flow of gas； and a signal processing and control means (5, 8) suited to and designed for processing said at least one signal indicative of the flow of gas supplied by the measurement means (6) and deducing from said at least one signal indicative of the flow of gas information relating to the phases of compression and relaxation of a cardiac massage on the patient under cardiac arrest and controlling the motorised micro blower (40) and exhalation valve (19) accordingly in response to the phases detected.
