Patent ID: 8371298

Claim:
A ventilator for ventilation of a patient, comprising an inhalation gas circuit that provides breathing air comprising a mixture of N2 and O2 to the patient and an exhalation gas circuit that receives exhaled air from the patient, and a gas outlet for said exhaled air, and a control unit configured to calculate the end expiratory lung volume, EELV, of a patient being ventilated by the ventilator, based on the expired volume per breathing cycle, and a composition measuring unit configured to obtain a measurement of a quantity that varies linearly with the N2/O2 composition in the expired gas, said measuring unit being arranged near the gas outlet, the control unit being configured to determine the change in the N2/O2 composition in the expired gas between a first point in time (t 1 ) at which the N2/O2 composition of the breathing gas is changed from a first fixed composition to a second fixed composition, and a second point in time (t 2 ) at which the N2/O2 composition of the expired gas in at least two subsequent breaths is substantially stable, and said control unit being further configured to calculate, said EELV based on the measurement of the quantity that varies linearly with the N2/O2 composition in the expired gas, and the change in the N2/O2 composition exhaled and the total gas volume, for each breath between the first and the second points in time t 1 and t 2 .