Respiratory failure in multiple-trauma patients can be studied in two ways. First, at the moment of the trauma, failure of ventilatory function can occur, necessitating immediate action to resolve it. Second, during the stay in the intensive care unit (ICU), when the patient is receiving mechanical ventilation, several trauma-associated conditions have the potential of producing respiratory failure and sometimes acute respiratory distress syndrome (ARDS). Upon initial evaluation of the trauma patient, the airway should be assessed, to ascertain patency. However, airway patency alone does not ensure adequate ventilation. Visual inspection and palpation of chest may reveal injuries to the chest wall that may acutely compromise ventilation. Later in the evolution of a multiple-trauma patient's course during ICU stay, ARDS may occur as a result of a direct lung injury, as well as from the systemic sequelae of extrathoracic injury or disease encountered in the multiple-injured patient. Many of the conditions diagnosed at the initial survey are considered stand-alone risk factors for respiratory failure. After trauma, the initial lung injury is usually at the capillary level rather than the alveolar level; however, the pathologic evolution of both injuries is indistinguishable. The major initial damage to the pulmonary epithelial surface causes alveolar flooding and collapse, but eventually the capillary endothelium may also be involved. When there are no other medical problems, the prognosis is fairly good, but if bacterial infection supervenes or if the patient is debilitated, the outlook becomes grim.