pulmonary contusion pulmonary contusion a pulmonary contusion, also known as lung contusion, is a bruise of the lung, caused by chest trauma. as a result of damage to capillaries, blood and other fluids accumulate in the lung tissue. the excess fluid interferes with gas exchange, potentially leading to inadequate oxygen levels (hypoxia). unlike pulmonary laceration, another type of lung injury, pulmonary contusion does not involve a cut or tear of the lung tissue. pulmonary contusion or lung contusionother nameslung contusiona ct scan showing a pulmonary contusion (red arrow) accompanied by a rib fracture (purple arrow)specialtyemergency medicine a pulmonary contusion is usually caused directly by blunt trauma but can also result from explosion injuries or a shock wave associated with penetrating trauma. with the use of explosives during world wars i and ii, pulmonary contusion resulting from blasts gained recognition. in the 1960s its occurrence in civilians began to receive wider recognition, in which cases it is usually caused by traffic accidents. the use of seat belts and airbags reduces the risk to vehicle occupants. diagnosis is made by studying the cause of the injury, physical examination and chest radiography. typical signs and symptoms include direct effects of the physical trauma, such as chest pain and coughing up blood, as well as signs that the body is not receiving enough oxygen, such as cyanosis. the contusion frequently heals on its own with supportive care. often nothing more than supplemental oxygen and close monitoring is needed; however, intensive care may be required. for example, if breathing is severely compromised, mechanical ventilation may be necessary. fluid replacement may be required to ensure adequate blood volume, but fluids are given carefully since fluid overload can worsen pulmonary edema, which may be lethal. the severity ranges from mild to severe: small contusions may have little or no impact on health, yet pulmonary contusion is the most common type of potentially lethal chest trauma. it occurs in 30–75% of severe chest injuries. the risk of death following a pulmonary contusion is between 14 and 40%. 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 including pneumonia and acute respiratory distress syndrome, and it can cause long-term respiratory disability. classification the alveoli pulmonary contusion and laceration are injuries to the lung tissue. pulmonary laceration, in which lung tissue is torn or cut, differs from pulmonary contusion in that the former involves disruption of the macroscopic architecture of the lung, while the latter does not. when lacerations fill with blood, the result is pulmonary hematoma, a collection of blood within the lung tissue. contusion involves hemorrhage in the alveoli (tiny air-filled sacs responsible for absorbing oxygen), but a hematoma is a discrete clot of blood not interspersed with lung tissue. a collapsed lung can result when the pleural cavity (the space outside the lung) accumulates blood (hemothorax) or air (pneumothorax) or both (hemopneumothorax). these conditions do not inherently involve damage to the lung tissue itself, but they may be associated with it. injuries to the chest wall are also distinct from but may be associated with lung injuries. chest wall injuries include rib fractures and flail chest, in which multiple ribs are broken so that a segment of the ribcage is detached from the rest of the chest wall and moves independently. signs and symptoms presentation may be subtle; people with mild contusion may have no symptoms at all. however, pulmonary contusion is frequently associated with signs (objective indications) and symptoms (subjective states), including those indicative of the lung injury itself and of accompanying injuries. because gas exchange is impaired, signs of low blood oxygen saturation, such as low concentrations of oxygen in arterial blood gas and cyanosis (bluish color of the skin and mucous membranes) are commonly associated. dyspnea (painful breathing or difficulty breathing) is commonly seen, and tolerance for exercise may be lowered. rapid breathing and a rapid heart rate are other signs. with more severe contusions, breath sounds heard through a stethoscope may be decreased, or rales (an abnormal crackling sound in the chest accompanying breathing) may be present. people with severe contusions may have bronchorrhea (the production of watery sputum). wheezing and coughing are other signs. coughing up blood or bloody sputum is present in up to half of cases. cardiac output (the volume of blood pumped by the heart) may be reduced, and hypotension (low blood pressure) is frequently present. the area of the chest wall near the contusion may be tender or painful due to associated chest wall injury. signs and symptoms take time to develop, and as many as half of cases are asymptomatic at the initial presentation. the more severe the injury, the more quickly symptoms become apparent. in severe cases, symptoms may occur as quickly as three or four hours after the trauma. hypoxemia (low oxygen concentration in the arterial blood) typically becomes progressively worse over 24–48 hours after injury. in general, pulmonary contusion tends to worsen slowly over a few days, but it may also cause rapid deterioration or death if untreated. causes motor vehicle collisions are the most common cause of pulmonary contusion. pulmonary contusion is the most common injury found in blunt chest trauma, occurring in 25–35% of cases. it is usually caused by the rapid deceleration that results when the moving chest strikes a fixed object. about 70% of cases result from motor vehicle collisions, most often when the chest strikes the inside of the car. falls, assaults, and sports injuries are other causes. pulmonary contusion can also be caused by explosions; the organs most vulnerable to blast injuries are those that contain gas, such as the lungs. blast lung is severe pulmonary contusion, bleeding, or edema with damage to alveoli and blood vessels, or a combination of these. this is the primary cause of death among people who initially survive an explosion. unlike other mechanisms of injury in which pulmonary contusion is often found alongside other injuries, explosions can cause pulmonary contusion without damage to the chest wall. in addition to blunt trauma, penetrating trauma can cause pulmonary contusion. contusion resulting from penetration by a rapidly moving projectile usually surrounds the path along which the projectile traveled through the tissue. the pressure wave forces tissue out of the way, creating a temporary cavity; the tissue readily moves back into place, but it is damaged. pulmonary contusions that accompany gun and knife wounds are not usually severe enough to have a major effect on outcome; penetrating trauma causes less widespread lung damage than does blunt trauma. an exception is shotgun wounds, which can seriously damage large areas of lung tissue through a blast injury mechanism. mechanism the physical processes behind pulmonary contusion are poorly understood. however, it is known that lung tissue can be crushed when the chest wall bends inward on impact. three other possible mechanisms have been suggested: the inertial effect, the spalling effect, and the implosion effect. in the inertial effect, the lighter alveolar tissue is sheared from the heavier hilar structures, an effect similar to diffuse axonal injury in head injury. it results from the fact that different tissues have different densities, and therefore different rates of acceleration or deceleration. in the spalling effect, lung tissue bursts or is sheared where a shock wave meets the lung tissue, at interfaces between gas and liquid. the alveolar walls form such a gas-liquid interface with the air in the alveoli. the spalling effect occurs in areas with large differences in density; particles of the denser tissue are spalled (thrown) into the less dense particles. the implosion effect occurs when a pressure wave passes through a tissue containing bubbles of gas: the bubbles first implode, then rebound and expand beyond their original volume. the air bubbles cause many tiny explosions, resulting in tissue damage; the overexpansion of gas bubbles stretches and tears alveoli. this effect is thought to occur microscopically when the pressure in the airways increases sharply. contusion usually occurs on the lung directly under the site of impact, but, as with traumatic brain injury, a contrecoup contusion may occur at the site opposite the impact as well. a blow to the front of the chest may cause contusion on the back of the lungs because a shock wave travels through the chest and hits the curved back of the chest wall; this reflects the energy onto the back of the lungs, concentrating it. (a similar mechanism may occur at the front of the lungs when the back is struck.) the amount of energy transferred to the lung is determined in a large part by the compliance (flexibility) of the chest wall. children's chests are more flexible because their ribs are more elastic and there is less ossification of their intercostal cartilage. therefore, their chest walls bend, absorbing less of the force and transmitting more of it to the underlying organs. an adult's more bony chest wall absorbs more of the force itself rather than transmitting it. thus children commonly get pulmonary contusions without fractures overlying them, while elderly people are more likely to develop fractures than contusions. one study found that pulmonary contusions were accompanied by fractures 62% of the time in children and 80% of the time in adults. pathophysiology normally, oxygen and carbon dioxide diffuse across the capillary and alveolar membranes and the interstitial space (top). fluid impairs this diffusion, resulting in less oxygenated blood (bottom). pulmonary contusion results in bleeding and fluid leakage into lung tissue, which can become stiffened and lose its normal elasticity. the water content of the lung increases over the first 72 hours after injury, potentially leading to frank pulmonary edema in more serious cases. as a result of these and other pathological processes, pulmonary contusion progresses over time and can cause hypoxia (insufficient oxygen). bleeding and edema in contusions, torn capillaries leak fluid into the tissues around them. the membrane between alveoli and capillaries is torn; damage to this capillary–alveolar membrane and small blood vessels causes blood and fluids to leak into the alveoli and the interstitial space (the space surrounding cells) of the lung. with more severe trauma, there is a greater amount of edema, bleeding, and tearing of the alveoli. pulmonary contusion is characterized by microhemorrhages (tiny bleeds) that occur when the alveoli are traumatically separated from airway structures and blood vessels. blood initially collects in the interstitial space, and then edema occurs by an hour or two after injury. an area of bleeding in the contused lung is commonly surrounded by an area of edema. in normal gas exchange, carbon dioxide diffuses across the endothelium of the capillaries, the interstitial space, and across the alveolar epithelium; oxygen diffuses in the other direction. fluid accumulation interferes with gas exchange, and can cause the alveoli to fill with proteins and collapse due to edema and bleeding. the larger the area of the injury, the more severe respiratory compromise will be. consolidation and collapse pulmonary contusion can cause parts of the lung to consolidate, alveoli to collapse, and atelectasis (partial or total lung collapse) to occur. consolidation occurs when the parts of the lung that are normally filled with air fill with material from the pathological condition, such as blood. over a period of hours after the injury, the alveoli in the injured area thicken and may become consolidated. a decrease in the amount of surfactant produced also contributes to the collapse and consolidation of alveoli; inactivation of surfactant increases their surface tension. reduced production of surfactant can also occur in surrounding tissue that was not originally injured. inflammation of the lungs, which can result when components of blood enter the tissue due to contusion, can also cause parts of the lung to collapse. macrophages, neutrophils, and other inflammatory cells and blood components can enter the lung tissue and release factors that lead to inflammation, increasing the likelihood of respiratory failure. in response to inflammation, excess mucus is produced, potentially plugging parts of the lung and leading to