Breathing assistance apparatus for supplying a respiratory gas to a patient during a cardiopulmonary resuscitation comprising: - a respiratory gas source for supplying a respiratory gas to said patient during a cardiopulmonary resuscitation, - means for measuring CO 2 content for taking measurements of CO 2 concentration produced by the patient, and supplying signals for measuring CO 2 content to signal and control processing means, - signal and control processing means configured for processing the CO 2 content measurement signals coming from the CO 2 content measurement means, and - at least one user graphic interface, characterised in that: - the signal and control processing means are configured for: a) processing CO 2 content measurement means corresponding to measurements taken by the CO 2 content measurement means for a given time period (dt), and extracting a plurality of CO 2 content peak values from it (EtCO2 _1, EtCO 2_2, EtCO2 _3,..., EtCO2_x), b) selecting the maximum value (Vmax) of CO 2 content among said plurality of CO 2 content peak values (EtCO2_ 1, EtCO2_ 2, EtCO2_ 3,..., EtCO2_x) measured for said given time period (dt), c) repeating steps a) and b) for obtaining several successive maximum values (Vmax) of CO 2 content measured over a time window (Ft) comprising several successive time periods (dt), d) calculating at least one average value (Vmoy) of CO 2 content from the maximum values (Vmax) of CO 2 content obtained over the time window (Ft), and e) transmitting said at least one average value (Vmoy) of CO 2 content to the user graphic interface, - and the user graphic interface is configured for displaying said at least one average value (Vmoy) of CO 2 content. - a respiratory gas source for supplying a respiratory gas to said patient during a cardiopulmonary resuscitation, - means for measuring CO 2 content for taking measurements of CO 2 concentration produced by the patient, and supplying signals for measuring CO 2 content to signal and control processing means, - signal and control processing means configured for processing the CO 2 content measurement signals coming from the CO 2 content measurement means, and - at least one user graphic interface, - the signal and control processing means are configured for: a) processing CO 2 content measurement means corresponding to measurements taken by the CO 2 content measurement means for a given time period (dt), and extracting a plurality of CO 2 content peak values from it (EtCO2 _1, EtCO 2_2, EtCO2 _3,..., EtCO2_x), b) selecting the maximum value (Vmax) of CO 2 content among said plurality of CO 2 content peak values (EtCO2_ 1, EtCO2_ 2, EtCO2_ 3,..., EtCO2_x) measured for said given time period (dt), c) repeating steps a) and b) for obtaining several successive maximum values (Vmax) of CO 2 content measured over a time window (Ft) comprising several successive time periods (dt), d) calculating at least one average value (Vmoy) of CO 2 content from the maximum values (Vmax) of CO 2 content obtained over the time window (Ft), and e) transmitting said at least one average value (Vmoy) of CO 2 content to the user graphic interface, a) processing CO 2 content measurement means corresponding to measurements taken by the CO 2 content measurement means for a given time period (dt), and extracting a plurality of CO 2 content peak values from it (EtCO2 _1, EtCO 2_2, EtCO2 _3,..., EtCO2_x), b) selecting the maximum value (Vmax) of CO 2 content among said plurality of CO 2 content peak values (EtCO2_ 1, EtCO2_ 2, EtCO2_ 3,..., EtCO2_x) measured for said given time period (dt), c) repeating steps a) and b) for obtaining several successive maximum values (Vmax) of CO 2 content measured over a time window (Ft) comprising several successive time periods (dt), d) calculating at least one average value (Vmoy) of CO 2 content from the maximum values (Vmax) of CO 2 content obtained over the time window (Ft), and e) transmitting said at least one average value (Vmoy) of CO 2 content to the user graphic interface, - and the user graphic interface is configured for displaying said at least one average value (Vmoy) of CO 2 content.