Purpose The most significant feature of acute respira tory distress syndrome (ARDS) lung is reduced end-e xpiratory lung volume (EELV).Lung protective ventilat ion was performed to reduce ventilator induced lung in jury(VILI),which is primarily due to unphysiological lun g strain (the ratio between tidal volume and EELV) an d lung stress (the transpulmonary pressure).