Many etiologic factors have been associated with ARDS, including shock, fat embolism, fluid overload, oxygen toxicity, fluid aspiration, narcotic overdose, disseminated intravascular coagulation, multiple transfusions, inhalation of toxic gases, diffuse pulmonary infection, and systemic reactions to sepsis, pancreatitis, and massive trauma or burns. ARDS is characterized clinically by dyspnea, tachypnea, tachycardia, cyanosis, and hypoxemia. The lung compliance is decreased so that the lung is stiffer and more difficult to ventilate.
Chest radiographs show signs of bilateral interstitial and alveolar edema.
Cardiac filling pressures are normal, and the pulmonary capillary wedge pressure is below 18 torr. The syndrome has four phases that characterize its progression. Phase I, injury and resuscitation, occurs immediately after the initial injury, infection, or hemorrhage, when the patient has usually been administered large volumes of IV fluids or whole blood and perhaps cardiopulmonary resuscitation. Although alkalosis may be present, there is no sign of respiratory distress. In Phase II, circulation is stabilized, and tissue perfusion returns to normal.