Lung injury comes from a variety of causes. There are many causes, but let’s boil it down to the basics: oxygen.
Too much = ventilator-induced lung injury
Too little = hypoxemia
In the past, large tidal volumes were used to prevent collapse of the alveoli and to deliver more oxygen. Volumes as large at 10-15 ml/kg ideal body weight were used. But, these caused stress fractures in the alveolar-capillary interface. These days lower tidal volumes of 6-8 ml/kg of ideal body weight are used for lung protection.
Oxygen free radicals
Large amounts of oxygen is bad due to its status as a free radical. It is reduced in a series of one electron reactions. The intermediates are free radicals that are highly reactive.
Types of trauma in ventilator-induced lung injury
Barotrauma — alveolar fractures from high pressure
Volutrauma — alveolar fractures from high volumes