The computed tomography (CT) scan can be used to measure the lung weight-volume and to determine the degree of inflation (not aerated, poorly aerated, well aerated, over aerated tissue).
The change in weight of each lung compartment (non-aerated, poorly aerated, well-aerated and over-aerated) between the two positions is always expressed as a percentage change compared to the total lung weight.
By the changes in the CT values, the lung was divided into hyperinflated, normally aerated, poorly aerated and nonaerated regions.
Lung aeration was assessed by a radiologist who was blinded to group identity by measuring normally aerated, poorly aerated, nonaerated, and overinflated lung volumes as previously described [ 22].
The statistical analysis evidenced no effect of the sequence of ventilation modes on the hyperaerated, normally aerated, poorly aerated, and nonaerated compartments at end-expiration.
Dependent atelectatic regions are poorly aerated while nondependent aerated regions are ventilated with relatively high tidal volume (HTV).
It is important to note that the recruitment was associated with an increase in poorly aerated and normally aerated lung volume.
Recruitment maneuvers (RM) can be defined as a voluntary strategy to increase the transpulmonary pressure (PL) transiently with the goal to reopen those alveolar units that are not aerated or poorly aerated but reopenable.
Furthermore, at each PEEP step the tidal re-aeration was calculated as the difference between end-expiratory and end-inspiratory poorly aerated and non-aerated areas [ 12].
Poorly aerated and non-aerated areas, which were visually identified, were assumed to be areas of lung injury [ 16].
The increase in resting lung volume was mainly related to a redistribution of aeration: a minor decrease in non-aerated lung tissue (3%), a major decrease in poorly aerated tissue (17%) and a major increase (20%) in well-aerated tissue.
