Pulmonary contusion epidemiology and demographics

Epidemiology
The severity ranges from mild to deadly—small contusions may have little or no impact on the patient's health—yet pulmonary contusion is the most common type of potentially lethal chest trauma. It occurs in 30–75% of severe chest injuries. With an estimated mortality rate of 14–40%, pulmonary contusion plays a key role in determining whether an individual will die or suffer serious ill effects as the result of trauma. Pulmonary contusion is usually accompanied by other injuries. Although associated injuries are often the cause of death, pulmonary contusion is thought to cause death directly in a quarter to half of cases. Children are at especially high risk for the injury because the relative flexibility of their bones prevents the chest wall from absorbing force from an impact, causing it to be transmitted instead to the lung. Pulmonary contusion is associated with complications includingpneumonia and acute respiratory distress syndrome, and it can cause long-term respiratory disability.

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 withthoracic 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 mortality rate of pulmonary contusion is estimated to range from 14–40%, 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. An accompanying flail chest increases the morbidityand mortality to more than twice that of pulmonary contusion alone. Pulmonary contusion is thought to be the direct cause of death in a quarter to a half of people with polytrauma who die.

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%.

Since their chest walls are more flexible, children are more vulnerable to pulmonary contusion than adults are, and it is more common in children than in adults for that reason. Children in forceful impacts suffer twice as many pulmonary contusions as adults with similar injury mechanisms, yet have proportionately fewer rib fractures. Pulmonary contusion has been found in 53% of children with significant chest injuries (those requiring hospitalization). The rates of certain types of injury mechanisms differ between children and adults; for example, children are more often hit by cars when they are pedestrians. Differences in the bodies of children and adults also 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 to multiple body systems. 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.