of developing infections, the sputum can be cultured to test for the presence of infection-causing bacteria; when they are present, antibiotics are used. pain control is another means to facilitate the elimination of secretions. a chest wall injury can make coughing painful, increasing the likelihood that secretions will accumulate in the airways. chest injuries also contribute to hypoventilation (inadequate breathing) because the chest wall movement involved in breathing adequately is painful. insufficient expansion of the chest may lead to atelectasis, further reducing oxygenation of the blood. analgesics (pain medications) can be given to reduce pain. injection of anesthetics into nerves in the chest wall, called nerve blockade, is another approach to pain management; this does not depress respiration the way some pain medications can. prognosis this ct scan, taken 22 days after pulmonary contusion with major chest trauma, shows that the contusion has completely resolved. pulmonary contusion usually resolves itself without causing permanent complications; however it may also have long-term ill effects on respiratory function. most contusions resolve in five to seven days after the injury. signs detectable by radiography are usually gone within 10 days after the injury—when they are not, other conditions, such as pneumonia, are the likely cause. chronic lung disease correlates with the size of the contusion and can interfere with an individual's ability to return to work. fibrosis of the lungs can occur, resulting in dyspnea (shortness of breath), low blood oxygenation, and reduced functional residual capacity for as long as six years after the injury. as late as four years post-injury, decreased functional residual capacity has been found in most pulmonary contusion patients studied. during the six months after pulmonary contusion, up to 90% of people have difficulty breathing. in some cases, dyspnea persists for an indefinite period. contusion can also permanently reduce the compliance of the lungs. complications a chest x-ray showing acute respiratory distress syndrome pulmonary contusion can result in respiratory failure—about half of such cases occur within a few hours of the initial trauma. other severe complications, including infections and acute respiratory distress syndrome (ards) occur in up to half of cases. elderly people and those who have heart, lung, or kidney disease prior to the injury are more likely to stay longer in hospital and have complications from the injury. complications occur in 55% of people with heart or lung disease and 13% of those without. of people with pulmonary contusion alone, 17% develop ards, while 78% of people with at least two additional injuries develop the condition. a larger contusion is associated with an increased risk. in one study, 82% of people with 20% or more of the lung volume affected developed ards, while only 22% of people with less than 20% did so. pneumonia, another potential complication, develops in as many as 20% of people with pulmonary contusion. contused lungs are less able to remove bacteria than uninjured lungs, predisposing them to infection. intubation and mechanical ventilation further increase the risk of developing pneumonia; the tube is passed through the nose or mouth into the airways, potentially tracking bacteria from the mouth or sinuses into them. also, intubation prevents coughing, which would clear bacteria-laden secretions from the airways, and secretions pool near the tube's cuff and allow bacteria to grow. the sooner the endotracheal tube is removed, the lower the risk of pneumonia, but if it is removed too early and has to be put back in, the risk of pneumonia rises. people who are at risk for pulmonary aspiration (e.g. those with lowered level of consciousness due to head injuries) are especially likely to get pneumonia. as with ards, the chances of developing pneumonia increase with the size of the contusion. children and adults have been found to have similar rates of complication with pneumonia and ards. associated injuries severe pulmonary contusion with pneumothorax and hemothorax following severe chest trauma a large amount of force is required to cause pulmonary contusion; a person injured with such force is likely to have other types of injuries as well. in fact, pulmonary contusion can be used to gauge the severity of trauma. up to three quarters of cases are accompanied by other chest injuries, the most common of these being hemothorax and pneumothorax. flail chest is usually associated with significant pulmonary contusion, and the contusion, rather than the chest wall injury, is often the main cause of respiratory failure in people with these injuries. other indications of thoracic trauma may be associated, including fracture of the sternum and bruising of the chest wall. over half of fractures of the scapula are associated with pulmonary contusion. the contusion is frequently found underlying fracture sites. when accompanied by a fracture, it is usually concentrated into a specific location—the contusion is more diffuse when there is no fracture. pulmonary lacerations may result from the same blunt or penetrating forces that cause contusion. lacerations can result in pulmonary hematomas; these are reported to develop in 4–11% of pulmonary contusions. epidemiology pulmonary contusion is found in 30–75% of severe cases of chest injury, making it the most common serious injury to occur in association with thoracic trauma. of people who have multiple injuries with an injury severity score of over 15, pulmonary contusion occurs in about 17%. it is difficult to determine the death rate (mortality) because pulmonary contusion rarely occurs by itself. usually, deaths of people with pulmonary contusion result from other injuries, commonly traumatic brain injury. it is controversial whether pulmonary contusion with flail chest is a major factor in mortality on its own or whether it merely contributes to mortality in people with multiple injuries. the estimated mortality rate of pulmonary contusion ranges from 14 to 40%, depending on the severity of the contusion itself and on associated injuries. when the contusions are small, they do not normally increase the chance of death or poor outcome for people with blunt chest trauma; however, these chances increase with the size of the contusion. one study found that 35% of people with multiple significant injuries including pulmonary contusion die. in another study, 11% of people with pulmonary contusion alone died, while the number rose to 22% in those with additional injuries. pulmonary contusion is thought to be the direct cause of death in a quarter to a half of people with multiple injuries (polytrauma) who die. an accompanying flail chest increases the morbidity and mortality to more than twice that of pulmonary contusion alone. pulmonary contusion is the most common cause of death among vehicle occupants involved in accidents, and it is thought to contribute significantly in about a quarter of deaths resulting from vehicle collisions. as vehicle use has increased, so has the number of auto accidents, and with it the number of chest injuries. however an increase in the number of airbags installed in modern cars may be decreasing the incidence of pulmonary contusion. use of child restraint systems has brought the approximate incidence of pulmonary contusion in children in vehicle accidents from 22% to 10%. differences in the bodies of children and adults lead to different manifestations of pulmonary contusion and associated injuries; for example, children have less body mass, so the same force is more likely to lead to trauma in multiple body systems. since their chest walls are more flexible, children are more vulnerable to pulmonary contusion than adults are, and thus suffer from the injury more commonly. pulmonary contusion has been found in 53% of children with chest injuries requiring hospitalization. children in forceful impacts suffer twice as many pulmonary contusions as adults with similar injury mechanisms, yet have proportionately fewer rib fractures. the rates of certain types of injury mechanisms differ between children and adults; for example, children are more often hit by cars as pedestrians. some differences in children's physiology might be advantageous (for example they are less likely to have other medical conditions), and thus they have been predicted to have a better outcome. however, despite these differences, children with pulmonary contusion have similar mortality rates to adults. history giovanni battista morgagni, credited with having first described lung trauma without chest wall trauma in 1761, the italian anatomist giovanni battista morgagni was first to describe a lung injury that was not accompanied by injury to the chest wall overlying it. nonetheless, it was the french military surgeon guillaume dupuytren who is thought to have coined the term pulmonary contusion in the 19th century. it still was not until the early 20th century that pulmonary contusion and its clinical significance began to receive wide recognition. with the use of explosives during world war i came many casualties with no external signs of chest injury but with significant bleeding in the lungs. studies of world war i injuries by d.r. hooker showed that pulmonary contusion was an important part of the concussive injury that results from explosions. pulmonary contusion received further attention during world war ii, when the bombings of britain caused blast injuries and associated respiratory problems in both soldiers and civilians. also during this time, studies with animals placed at varying distances from a blast showed that protective gear could prevent lung injuries. these findings suggested that an impact to the outside of the chest wall was responsible for the internal lesions. in 1945, studies identified a phenomenon termed "wet lung", in which the lungs accumulated fluid and were simultaneously less able to remove it. they attributed the respiratory failure often seen in blunt chest trauma in part to excessive fluid resuscitation, and the question of whether and how much to administer fluids has remained controversial ever since. during the vietnam war, combat again provided the opportunity for study of pulmonary contusion; research during this conflict played an important role in the development of the modern understanding of its treatment. the condition also began to be more widely recognized in a non-combat context in the 1960s, and symptoms and typical findings with imaging techniques such as x-ray were described. before the 1960s, it was believed that the respiratory insufficiency seen in flail chest was due to "paradoxical motion" of the flail segment of the chest wall (the flail segment moves in the opposite direction as the chest wall during respiration), so treatment was aimed at managing the chest wall injury, not the pulmonary contusion. for example, positive pressure ventilation was used to stabilize the flail segment from within the chest. it was first proposed in 1965 that this respiratory insufficiency is most often due to injury of the lung rather than to the chest wall, and a group led by j.k. trinkle confirmed this hypothesis in 1975. hence the modern treatment prioritizes the management of pulmonary contusion. animal studies performed in the late 1960s and 1970s shed light on the pathophysiological processes involved in pulmonary contusion. studies in the 1990s revealed a link between pulmonary contusion and persistent respiratory difficulty for years after the injury in people in whom the injury coexisted with flail chest. in the next decade studies demonstrated that function in contused lungs improves for years after the injury.