Different mechanisms of atelectasis formation require different treatment strategies.

Several strategies have been developed to treat atelectasis, including positive end-expiratory pressure and deep inspirations. However, in some patients these recruitment strategies fail to improve lung function. Therefore, the authors studied whether recruitment maneuvers could resolve atelectasis following either passive airway closure or active bronchconstriction. Aerated lung areas were measured in 5 dogs at baseline, and after airway closure with either a bronchial blocker, or administration of methacholine, followed by deep inspiration. Finally, bronchoconstriction was reversed pharmacologically. Bronchial occlusion reduced aerated lung areas, which were reopened by deep inspirations. Following methacholine, aerated lung areas were also significantly reduced; however, deep inspirations had no significant effect. Passive atelectasis was easily resolved by deep inspirations. In contrast, active airway constriction that leads to atelectasis could not be overcome with recruitment maneuvers.