Tracheal and tracheobronchial tree injuries

Incidence and mechanisms of injury

Injury to the tracheobronchial tree occurs in both penetrating and blunt chest trauma. Many victims die prior to emergency care from associated injuries to vital structures, hemorrhage, tension pneumothorax, or respiratory insufficiency. Thus, a substantial number of diagnoses are established only after death. At other times, the diagnosis is not readily apparent and is not made until late symptoms indicating tracheobronchial injury have developed. Thus, the true incidence of injury to the tracheobronchial tree is difficult to discern. In a review of autopsies of 1,178 persons dying from blunt trauma to the chest, Bertelsen and Howitz found that tracheobronchial disruptions occurred in only 33 patients, for an incidence of 2.8%; 27 of these died immediately. In a review of survivors and nonsurvivors, Campbell reported on 15,136 patients diagnosed with blunt chest trauma. Forty-nine (0.3%) had a tracheobronchial injury. This series showed an extremely high mortality (67%) but did not describe the severity of associated injuries. Asensio in a review of the literature described the incidence in penetrating neck trauma with 331 of 4193 patients (8%) presenting with laryngotracheal injuries. Greater than 80% of blunt tracheobronchial ruptures occur within 2.5 cm of the carina. Mainstem bronchi are injured in 86% of patients and distal bronchi in only 9.3%, while complex injuries are seen in 8%.

Penetrating injury is a straightforward mechanism and consists basically of the hole created by the path of a knife or bullet. Iatrogenic injuries during airway instrumentation are also seen. Knife wounds occur almost exclusively in the cervical trachea, whereas gunshot wounds occur at any point along the tracheobronchial tree. Intrathoracic injury to the tracheobronchial tree occurs more commonly from blunt trauma but may also result from bullet wounds. These injuries occur at a higher incidence when the projectile crosses the mediastinum. Associated injuries to other mediastinal structures, including the heart, great vessels, and esophagus, are common and contribute significantly to morbidity and mortality. There are several mechanisms by which blunt trauma may injure the trachea and bronchus, including direct blow, sheer stress, and burst injury. A direct blow to the neck may produce a “clothesline”-type injury, crushing the cervical trachea against the vertebral bodies and transecting the tracheal rings or cricoid cartilage. Shear forces on the trachea create damage at its relatively fixed points, the cricoid and the carina. A common factor in burst injury along the tracheobronchial tree is rapid anteroposterior compression of the thorax. This compression causes a simultaneous expansion in the lateral thoracic diameter, and the negative intrapleural pressure stretches the lungs laterally along with the chest wall, thereby placing traction on the carina. When the plasticity of the tracheobronchial tree is exceeded, the lungs are pulled apart and the bronchi avulsed. Closure of the glottis before impact may convert the trachea into a rigid tube with increased intratracheal pressure, which may cause a linear tear or blowout of the membranous portion of the trachea or cause a complex disruption of the trachea and bronchi. As predicted by the law of LaPlace, this type of burst injury occurs where the airway diameter is greatest, usually within 2.5 cm of the carina, but may occur anywhere along the airway. A combination of these mechanisms is probably responsible for producing most injuries. Given the protected nature of these structures, a significant amount of high-energy transfer is usually required to create these injuries.

Diagnosis