Acute Respiratory Distress Syndrome

Adult respiratory distress syndrome (ARDS) is a clinical diagnosis of diffuse lung injury leading to severe hypoxemia in spite of high inspired oxygen concentrations. Histologically, ARDS manifests as diffuse alveolar damage (DAD). Intrapulmonary causes of ARDS include pneumonia, inhalational injuries, aspiration, and chest trauma. Extrapulmonary or systemic causes include sepsis, multi-organ failure, transfusion reaction, pancreatitis, and drug toxicity. The early exudative phase occurs within 72 hours of the precipitating cause, and usually manifests with diffuse bilateral airspace opacities. The organizing phase occurs later, with a dependent gradient of consolidation worse in the posterior lower lungs; bronchial dilatation may develop rapidly. In survivors, the lung may return to a relatively normal state, or may develop fibrosis. Fibrosis is often more severe in the anterior portions of the lungs due to the protective effect of the typically posterior, dependent consolidation and atelectasis of ARDS. Imaging findings of ARDS may appear in patients with progressive dyspnea and tachypnea who require mechanical ventilation. Pneumothorax may occur in patients with ARDS due to barotrauma, with minimal loss of volume of the ipsilateral lung due to its increased density and decreased compliance