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PULMONARY LACERATION

PULMONARY LACERATION

Rapid deceleration from blunt thoracic trauma may produce shearing forces that lacerate the lung. Other causes include missiles, knives, and fractured ribs that directly lacerate the lung and lung hyperinflation from such causes as blast injuries and diving accidents. Lung lacerations usually manifest as hemopneumothoraxes requiring early tube thoracostomy. A persistent air leak is common but typically seals as the lung becomes fully reexpanded. With more extensive injuries requiring endotracheal intubation and positive-pressure ventilation, however, there is a risk of life-threatening acute bronchovenous air embolism. The typical scenario is a patient who is hypovolemic and requires semi-urgent endotracheal intubation for moderate hypoxemia but develops acute cardiac deterioration. As pressure in the airway is increased, air is forced from disrupted terminal bronchi into an adjacent injured pulmonary vein, which conveys the air bubbles into the left side of the heart and ultimately into the coronary or carotid systems. The hypovolemic patient is more susceptible to air embolism because of decreased pulmonary venous pressure, thus increasing the gradient from the airway. Symptomatic coronary air embolus mandates resuscitative thoracotomy with pulmonary hilar cross-clamping and vigorous internal cardiac massage. Air should be vented from the left ventricle and ascending aorta. Ongoing air leak from the injured lung is usually managed with staple tractotomy (i.e., linear stapling is performed on both sides of the torn lung as an alternative to anatomic resection). Pulmonary tractotomy is particularly useful when required for persistent air leaks from multiple lobes caused by a gunshot wound, avoiding the necessity for emergent pneumonectomy, which is often poorly tolerated because of right ventricular failure.

PULMONARY LACERATION
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Cavitation of the lung is a variant of pulmonary laceration that occurs after blunt trauma. The cavitation represents bursting of the lung parenchyma without disruption of the visceral pleural and is likely caused by a combination of increased airway pressure and a shearing stress, which exceed the elasticity of the lung. Bleeding into the lung occurs, causing a hematoma, which appears as a poorly defined density on chest radiography but becomes more defined within the next 2 weeks after injury. Cystic cavitation of the hematoma may then develop. Several terms have been used to describe this entity; perhaps the most widely recognized is posttraumatic pneumatocele. The initial chest radiograph typically shows a cavity with air or air and fluid with adjacent radiodensity caused by lung hemorrhage. The vast majority of pneumatoceles resolve uneventfully, but occasional y, a lung resection is required for secondary infection.