Radiologic considerations in the adult respiratory distress syndrome

ARDS is the clinical consequence of acute lung injury that results in increased-permeability edema. Distinct pathophysiologic stages are reflected in the radiographic evolution of the syndrome. Diffuse microatelectasis, proteinaceous edema fluid, and multifocal in situ pulmonary vascular occlusions characterize the acute stages of injury and result in the appearance of diffuse consolidations and occasional pleural effusions on the radiograph. In the chronic organizing stage of ARDS, the physiologic consequences of subsiding edema and tissue repair may be reflected by a transition to stable interstitial patterns. There is a high frequency of complications related to the decreased compliance of the injured lung that lead to interstitial emphysema and other barotraumatic complications. Survivors of ARDS exhibit various degrees of physiologic impairment and radiographic abnormality that may improve during the first year after survival. The relations between various indices of the severity of ARDS and the ultimate outcome are emerging. Debate continues about the specificity of the chest radiograph in distinguishing increased-permeability edema from hydrostatic edema. In fact, interstitial patterns and pleural effusions are observed in both. Nonetheless, the chest radiograph is a pivotal tool for monitoring patients at risk of serious morbidity from nosocomial lung infection, barotrauma, and the complications accompanying the use of invasive devices. It is hoped that as we develop a more uniform consensus on the clinical definition of ARDS and begin to classify patients according to specific clinical or physiologic observations, chest radiographic observation will acquire greater diagnostic and prognostic significance in these critically ill patients.