their collapse. even when only one side of the chest is injured, inflammation may also affect the other lung. uninjured lung tissue may develop edema, thickening of the septa of the alveoli, and other changes. if this inflammation is severe enough, it can lead to dysfunction of the lungs like that seen in acute respiratory distress syndrome. ventilation/perfusion mismatch normally, the ratio of ventilation to perfusion is about one-to-one; the volume of air entering the alveoli (ventilation) is about equal to that of blood in the capillaries around them (perfusion). this ratio is reduced in pulmonary contusion; fluid-filled alveoli cannot fill with air, oxygen does not fully saturate the hemoglobin, and the blood leaves the lung without being fully oxygenated. insufficient inflation of the lungs, which can result from inadequate mechanical ventilation or an associated injury such as flail chest, can also contribute to the ventilation/perfusion mismatch. as the mismatch between ventilation and perfusion grows, blood oxygen saturation is reduced. pulmonary hypoxic vasoconstriction, in which blood vessels near the hypoxic alveoli constrict (narrow their diameter) in response to the lowered oxygen levels, can occur in pulmonary contusion. the vascular resistance increases in the contused part of the lung, leading to a decrease in the amount of blood that flows into it, directing blood to better-ventilated areas. although reducing blood flow to the unventilated alveoli is a way to compensate for the fact that blood passing unventilated alveoli is not oxygenated, the oxygenation of the blood remains lower than normal. if it is severe enough, the hypoxemia resulting from fluid in the alveoli cannot be corrected just by giving supplemental oxygen; this problem is the cause of a large portion of the fatalities that result from trauma. diagnosis to diagnose pulmonary contusion, health professionals use clues from a physical examination, information about the event that caused the injury, and radiography. laboratory findings may also be used; for example, arterial blood gasses may show insufficient oxygen and excessive carbon dioxide even in someone receiving supplemental oxygen. however, blood gas levels may show no abnormality early in the course of pulmonary contusion. x-ray a chest x-ray showing right sided (seen on the left of the picture) pulmonary contusion associated with rib fractures and subcutaneous emphysema chest x-ray is the most common method used for diagnosis, and may be used to confirm a diagnosis already made using clinical signs. consolidated areas appear white on an x-ray film. contusion is not typically restricted by the anatomical boundaries of the lobes or segments of the lung. the x-ray appearance of pulmonary contusion is similar to that of aspiration, and the presence of hemothorax or pneumothorax may obscure the contusion on a radiograph. signs of contusion that progress after 48 hours post-injury are likely to be actually due to aspiration, pneumonia, or ards. although chest radiography is an important part of the diagnosis, it is often not sensitive enough to detect the condition early after the injury. in a third of cases, pulmonary contusion is not visible on the first chest radiograph performed. it takes an average of six hours for the characteristic white regions to show up on a chest x-ray, and the contusion may not become apparent for 48 hours. when a pulmonary contusion is apparent in an x-ray, it suggests that the trauma to the chest was severe and that a ct scan might reveal other injuries that were missed with x-ray. computed tomography a chest ct scan revealing pulmonary contusions, pneumothorax, and pseudocysts computed tomography (ct scanning) is a more sensitive test for pulmonary contusion, and it can identify abdominal, chest, or other injuries that accompany the contusion. in one study, chest x-ray detected pulmonary contusions in 16.3% of people with serious blunt trauma, while ct detected them in 31.2% of the same people. unlike x-ray, ct scanning can detect the contusion almost immediately after the injury. however, in both x-ray and ct a contusion may become more visible over the first 24–48 hours after trauma as bleeding and edema into lung tissues progress. ct scanning also helps determine the size of a contusion, which is useful in determining whether a patient needs mechanical ventilation; a larger volume of contused lung on ct scan is associated with an increased likelihood that ventilation will be needed. ct scans also help differentiate between contusion and pulmonary hematoma, which may be difficult to tell apart otherwise. however, pulmonary contusions that are visible on ct but not chest x-ray are usually not severe enough to affect outcome or treatment. ultrasound an ultrasound image showing early pulmonary contusion, at this moment not visible on radiography. lung swelling is seen as vertical white lines, the "b-lines". pulmonary ultrasound, performed at the bedside or on the accident scene, is being explored as a diagnosis for pulmonary contusion. its use is still not widespread, being limited to facilities which are comfortable with its use for other applications, like pneumothorax, airway management, and hemothorax. accuracy has been found to be comparable to ct scanning. prevention prevention of pulmonary contusion is similar to that of other chest trauma. airbags in combination with seat belts can protect vehicle occupants by preventing the chest from striking the interior of the vehicle during a collision, and by distributing forces involved in the crash more evenly across the body. however, in rare cases, an airbag causes pulmonary contusion in a person who is not properly positioned when it deploys. child restraints such as carseats protect children in vehicle collisions from pulmonary contusion. equipment exists for use in some sports to prevent chest and lung injury; for example, in softball the catcher is equipped with a chest protector. athletes who do not wear such equipment, such as basketball players, can be trained to protect their chests from impacts. protective garments can also prevent pulmonary contusion in explosions. although traditional body armor made from rigid plates or other heavy materials protects from projectiles generated by a blast, it does not protect against pulmonary contusion, because it does not prevent the blast's shock wave from being transferred to the lung. special body armor has been designed for military personnel at high risk for blast injuries; these garments can prevent a shock wave from being propagated across the chest wall to the lung, and thus protect wearers from blast lung injuries. these garments alternate layers of materials with high and low acoustic impedance (the product of a material's density and a wave's velocity through it) in order to "decouple" the blast wave, preventing its propagation into the tissues. treatment no treatment is known to speed the healing of a pulmonary contusion; the main care is supportive. attempts are made to discover injuries accompanying the contusion, to prevent additional injury, and to provide supportive care while waiting for the contusion to heal. monitoring, including keeping track of fluid balance, respiratory function, and oxygen saturation using pulse oximetry is also required as the patient's condition may progressively worsen. monitoring for complications such as pneumonia and acute respiratory distress syndrome is of critical importance. treatment aims to prevent respiratory failure and to ensure adequate blood oxygenation. supplemental oxygen can be given and it may be warmed and humidified. when the contusion does not respond to other treatments, extracorporeal membranous oxygenation may be used, pumping blood from the body into a machine that oxygenates it and removes carbon dioxide prior to pumping it back in. ventilation mechanical ventilation may be required if pulmonary contusion causes inadequate oxygenation. positive pressure ventilation, in which air is forced into the lungs, is needed when oxygenation is significantly impaired. noninvasive positive pressure ventilation including continuous positive airway pressure (cpap) and bi-level positive airway pressure (bipap), may be used to improve oxygenation and treat atelectasis: air is blown into the airways at a prescribed pressure via a face mask. noninvasive ventilation has advantages over invasive methods because it does not carry the risk of infection that intubation does, and it allows normal coughing, swallowing, and speech. however, the technique may cause complications; it may force air into the stomach or cause aspiration of stomach contents, especially when level of consciousness is decreased. people with signs of inadequate respiration or oxygenation may need to be intubated and mechanically ventilated. mechanical ventilation aims to reduce pulmonary edema and increase oxygenation. ventilation can reopen collapsed alveoli, but it is harmful for them to be repeatedly opened, and positive pressure ventilation can also damage the lung by overinflating it. intubation is normally reserved for when respiratory problems occur, but most significant contusions do require intubation, and it may be done early in anticipation of this need. people with pulmonary contusion who are especially likely to need ventilation include those with prior severe lung disease or kidney problems; the elderly; those with a lowered level of consciousness; those with low blood oxygen or high carbon dioxide levels; and those who will undergo operations with anesthesia. larger contusions have been correlated with a need for ventilation for longer periods of time. pulmonary contusion or its complications such as acute respiratory distress syndrome may cause lungs to lose compliance (stiffen), so higher pressures may be needed to give normal amounts of air and oxygenate the blood adequately. positive end-expiratory pressure (peep), which delivers air at a given pressure at the end of the expiratory cycle, can reduce edema and keep alveoli from collapsing. peep is considered necessary with mechanical ventilation; however, if the pressure is too great it can expand the size of the contusion and injure the lung. when the compliance of the injured lung differs significantly from that of the uninjured one, the lungs can be ventilated independently with two ventilators in order to deliver air at different pressures; this helps avoid injury from overinflation while providing adequate ventilation. fluid therapy the administration of fluid therapy in individuals with pulmonary contusion is controversial. excessive fluid in the circulatory system (hypervolemia) can worsen hypoxia because it can cause fluid leakage from injured capillaries (pulmonary edema), which are more permeable than normal. however, low blood volume (hypovolemia) resulting from insufficient fluid has an even worse impact, potentially causing hypovolemic shock; for people who have lost large amounts of blood, fluid resuscitation is necessary. a lot of the evidence supporting the idea that fluids should be withheld from people with pulmonary contusion came from animal studies, not clinical trials with humans; human studies have had conflicting findings on whether fluid resuscitation worsens the condition. current recommendations suggest giving enough fluid to ensure sufficient blood flow but not giving any more fluid than necessary. for people who do require large amounts of intravenous fluid, a catheter may be placed in the pulmonary artery to measure the pressure within it. measuring pulmonary artery pressure allows the clinician to give enough fluids to prevent shock without exacerbating edema. diuretics, drugs that increase urine output to reduce excessive fluid in the system, can be used when fluid overload does occur, as long as there is not a significant risk of shock. furosemide, a diuretic used in the treatment of pulmonary contusion, also relaxes the smooth muscle in the veins of the lungs, thereby decreasing pulmonary venous resistance and reducing the pressure in the pulmonary capillaries. supportive care retaining secretions in the airways can worsen hypoxia and lead to infections. thus, an important part of treatment is pulmonary toilet, the use of suction, deep breathing, coughing, and other methods to remove material such as mucus and blood from the airways. chest physical therapy makes use of techniques such as breathing exercises, stimulation of coughing, suctioning, percussion, movement, vibration, and drainage to rid the lungs of secretions, increase oxygenation, and expand collapsed parts of the lungs. people with pulmonary contusion, especially those who do not respond well to other treatments, may be positioned with the uninjured lung lower than the injured one to improve oxygenation. inadequate pulmonary toilet can result in pneumonia. people who do develop infections are given antibiotics. no studies have yet shown a benefit of using antibiotics as a preventative measure before infection occurs, although some doctors do recommend prophylactic antibiotic use even without scientific evidence of its benefit. however, this can cause the development of antibiotic resistant strains of bacteria, so giving antibiotics without a clear need is normally discouraged. for people who are at especially high risk