Atelectasis is a very common condition seen in the ICU, with an appearance varying from normal to patchy areas of linear opacity to segmental and lobar collapse.
When air bronchograms are absent, mucous plugging or other endobronchial lesions should be considered ( Fig, 1). Otherwise, other etiologies, including pneumonia, aspiration, and contusion, should be considered. The distinction between atelectasis and pneumonia can be difficult, but an associated pneumonia should be considered after 3 to 4 days in the postoperative patient, and even sooner in the immune-compromised patient.
Fiq. 1 Mucous plug. The right mainstem bronchus is occluded (arrows), the trachea is shifted to the right, and there is almost complete atelectasis of the right lung. (Reproduced with permission from Woi.reILi199.4).)
The diagnosis of infectious pneumonia is difficult and requires the correlation of clinical and laboratory findings with the chest radiograph appearance, often of a segmental or larger pattern of parenchymal opacification with air bronchograms present. The diagnosis of aspiration pneumonia, unless observed, is often radiographic based on the appearance of a new localized parenchymal opacification that is not due to atelectasis alone ( SiJverstein..etiia/ 1993) (Fig 2).
Fig. 2 Aspiration pneumonia. The patient is an alcoholic with witnessed aspiration and bilateral parenchymal opacification in the middle and upper lung fields. Aspiration into the superior segments of the lower lobes and the apical and posterior segments of the upper lobes is common in the supine patient. Notice also the endotracheal tube near the right mainstem bronchial orifice.
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