Etiology
One major causative factor is the over stretching of the airways and alveoli(volutrauma). During mechanical ventilation, the flow of gas into the lung will take the path of least resistance. Areas of the lung that are collapsed (atelectasis) or filled with secretions will be underinflated, while those areas that are relatively normal will be overinflated. These areas will become over distended and injured. This may be reduced by using smaller tidal volumes.
During positive pressure ventilation, atelectatic regions will inflate, however the alveoli will be unstable and will collapse during the expiratory phase of the breath(atelectrauma). This repeated alveolar collapse and expansion (RACE) is thought to cause VALI. By opening the lung and keeping the lung open RACE (and VALI) is reduced.
Another possible ventilator associated lung injury is known as biotrauma. Biotrauma involves the lung suffering injury from any mediators of the inflammatory response or from bacteremia.
Read more about this topic: Ventilator-associated Lung Injury