In acute respiratory distress syndrome, computed tomography (CT) typically demonstrates symmetric ground-glass opacity and gravity-dependent consolidation when patients are positioned supine. Moreover, CT findings may vary according to the evolutional stage of the disease over time. The slope of the pressure-volume curve, which is a direct or indirect measure of lung recruitment rather than a measure of the characteristics of the respiratory mechanics of a portion of the aerated lung, indicates the potential for recruitment. The lung recruitment maneuver is performed by maintaining a sustained increase in airway pressure with the goal of opening collapsed alveoli, after which sufficient positive end-expiratory pressure is applied to maintain the alveoli in an open state. Alveolar recruitment resulting from continuous positive airway pressure occurs predominantly in nondependent and cephalic lung regions and is more limited in the diaphragmatic region or even negative (alveolar derecruitment) caudal to the diaphragmatic cupola. By partially relieving cardiac and abdominal compression, positioning patients in prone and semirecumbent positions may reopen dependent and caudal lung regions and improve gas exchange. The mean CT attenuation of a given region is equivalent to its aeration. Computed tomography, especially helical CT, may help to assess alveolar recruitment and lung overinflation by providing information on whole-lung attenuation.
From the *Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; and †Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Supported by grant R11-2002-103 from Korea Science and Engineering Foundation.
Presented as an educational exhibit at the 2003 Radiological Society of North America (RSNA) Scientific Assembly.
Reprints: Dr. Kyung Soo Lee, Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50, Ilwon-Dong, Kangnam-Ku, Seoul 135–710, Korea (e-mail: email@example.com).