Tracheobronchial Tear

Etiology

The trachea is a relatively elastic structure made up of about 16 to 20 cartilaginous rings and is positioned and protected, given its vicinity to the sternum, rib cage, and vertebral column. The etiology for tracheobronchial tears includes penetrating and blunt trauma, and also iatrogenic injuries. Motor vehicle collisions represent more than half of the cases of penetrating and blunt traumas, causing tracheobronchial injury.

Penetrating injuries are more likely to cause a tracheobronchial tear than blunt trauma, and gunshot wounds are more common penetrating injuries than stab wounds.[3] Blunt injuries are the less likely cause for tracheobronchial tear though the mortality is higher when compared with penetrating trauma.

Gunshot wounds generally cause injury to the cervical portion of the trachea, though any point of trachea could be injured. Stab injuries almost always involve the cervical part of the trachea. Blunt trauma to the cervical trachea could result indirectly from hyperextension injuries occurring while weightlifting or sudden deceleration during motor vehicle accidents. Direct cervical tracheal injuries result from wire strangulation while snow biking, seat belt, steering wheel, and dashboard injuries during the vehicular crash. Complex injuries involving both the above mechanisms could also happen in vehicular motor accidents as in "padded dashboard syndrome."[4] The thyroid and cricoid cartilages are most commonly involved in cervical tracheal injuries, and the area of disruption in severe injury is between the cricoid cartilage and trachea. Calcified laryngeal cartilages in adults are more likely to sustain fractures. In contrast, the flexible laryngeal cartilages are less likely injured in children when the entire brunt of trauma is targeted on the larynx.

The lower thoracic trachea is often involved in blunt injuries, and the associated multiple severe injuries compound the higher mortality. Blunt trauma during motor vehicle accidents causes damage to the intrathoracic trachea, carina, and the main bronchi. The carina is the most fixed area in the airway system and hence is very likely affected by the shear stress forces during sudden deceleration. Thus blunt injuries are much more common in the lower trachea, which may vary from a partial horizontal tear to a complete separation. The vertical tear could go upwards from the carinal injury. The lower tracheal injury could extend to one or both bronchi resulting in a partial or complete laceration. Intra thoracic trachea usually gets injured with high energy trauma though low energy blows are also known to inflict injury. Most blunt bronchial injuries occur on the right side, likely due to the bulkier right lung and a shorter right main bronchus. Kiser el published a study in 2001, which showed the site of bronchial injury is almost always within 2 cm from the carina in three-fourths of the patients.[5]

Iatrogenic causes for tracheobronchial injury or tear is increasingly reported in airway instrumentations (e.g., endotracheal intubation, rigid bronchoscopy), diagnostic-transbronchial needle aspiration (TBNA) via endobronchial ultrasound (EBUS) and therapeutic airway interventions, e.g., tracheostomy (open as well as percutaneous dilatational), metallic airway stent deployment and removal, balloon bronchoplasty, and head and neck, thyroid, and esophageal surgeries. Most iatrogenic injuries occur in the posterior membranous portion of the trachea.[6] The endotracheal tube related injury causes a longitudinal tear in the membranous regions in the cervical as well as the thoracic trachea. In contrast, cuff inflation-related injuries occur in the proximal trachea.

The risk factors for iatrogenic tracheobronchial tear could be divided into mechanical and anatomical factors. The mechanical factors could be procedural or instrumentation related causes that are most modifiable. The etiologies for the former include inexperienced operator for the given procedure and increased attempts at intubation, and causes for the latter include the use of stylet during intubation, use of large-sized tracheal tubes, double-lumen tube, larger balloon diameters during bronchoplasty and inadequate tube care after intubation. The anatomical risks for tracheobronchial injury include tracheal diverticula, distorted anatomy, tracheal bronchus, congenital tracheobronchomegaly, female gender, age above 65 years, inhaled steroids, and inflamed trachea. A review found female sex, age above 65 years, and emergency intubations as most non-modifiable factors.[7]

Epidemiology

It is difficult to determine the exact incidence of penetrating or blunt trauma, causing tracheobronchial tears since most victims would not survive to hospital admission. The overall incidence of tracheobronchial injury in post mortem series was 2% to 3%, which includes the victims who died at the spot.[8][9] Penetrating injuries cause more tracheobronchial injuries in comparison with blunt trauma.[2][10] Penetrating neck injuries account for up to 6% tracheobronchial injuries, whereas about 1-2% of penetrating thoracic trauma causes tracheobronchial injury.

 In a 20 year study on airway structures published in 1992 identified transverse tears in 74% of the patients (of which 4% being in the cervical trachea, and 12% in the intrathoracic trachea with the remaining injuries in the right main bronchus, left main bronchus and lobar bronchus (25,17 and 16% in that order), vertical tears in 18% (6.5% in the cervical trachea,10% in the intrathoracic trachea and 1.5% main bronchi) with the remaining 8% being complex injuries involving trachea and right or both main bronchi.[11] A German study done over five years and published in 2009 identified 1033 tracheobronchial injuries, of which 41.5% were identified as non-iatrogenic, and the remaining 58.4% were iatrogenic.[12] Almost 64.3% of the non-iatrogenic traumas were blunt traumas with the remaining injuries being penetrating wounds, bullet wounds, and miscellaneous etiologies. 

Survival in blunt trauma is expected to be less than with penetrating injury since multiple severe associated injuries are much more common in the former. Study on 104 patients with tracheobronchial injury over 15 years showed an overall mortality of 23%, and the mortality in a blunt injury being twice more than penetrating tracheobronchial injury (36 versus 16%).[2] The incidence of tracheobronchial injury in patients brought to emergency with blunt trauma is 0.5 to 2%.[3]

It is much difficult to determine the incidence of iatrogenic tracheobronchial tears since most often, they are under detected or under-reported. The incidence of tracheobronchial injury with a single-lumen endotracheal tube is about  0.005 %, and the double-lumen tube is between 0.005% to 0.19% [7][13][14][15]. Posterior tracheal wall perforation occurs in 1% of patients during percutaneous dilatational tracheostomy. In the German study mentioned above, among the iatrogenic causes, endotracheal intubation/mechanical ventilation constituted 61.5%, almost 30% were related to dilatational tracheostomy, and the remaining injuries were related to endoscopic interventions.[12] Airway injury occurs in about 1 to 1.8% in esophageal surgeries involving trans thoracic & transabdominal approach.[16]

Pathophysiology

Penetrating injury most commonly involves the anterior trachea involving the cartilages or the ligamentous areas between the cartilages. Stab wounds are penetrating injuries almost always confined to the cervical trachea, whereas gunshot wounds could disrupt trachea or bronchi at any contact point. Blunt trauma causes tracheobronchial tears due to blow, shear stress, or burst mechanisms. Blunt trauma application of a large amount of energy to the anterior chest will push the lungs laterally & separates the bronchi from the relatively immobile carina. Carina is the most fixed part of the airway system in the chest and hence has an increased propensity to be inflicted by shear forces resulting from sudden deceleration. The sudden rise in airway pressure against closed glottis after a crush injury will result in the rupture of the airway whenever the pressure exceeds the tissue elasticity.

History and Physical

Though the location of airway tear will determine the presenting symptoms and signs, and also the optimal modality for identification, many patients present with non-specific symptoms irrespective of the site of injury. The common symptoms include breathing difficulty, stridor, and respiratory failure due to airway blockage, subcutaneous emphysema, hoarseness of voice or aphonia, hemoptysis, and other symptoms due to associated injury.

The most common presenting signs in tracheobronchial injury include subcutaneous emphysema 35% to 85%) and pneumothorax (20% to 50%). Hence the classic signs that have been described, which should trigger the suspicion of tracheobronchial injury in the appropriate settings, include subcutaneous emphysema, pneumomediastinum, and pneumothorax. Damage to proximal structures, including thoracic trachea and large bronchi, presents with pneumomediastinum with subcutaneous air, whereas more distal injury will result in pneumothorax and subcutaneous air. A raspy mediastinal crunch synchronizing with a heartbeat could be heard in mediastinal emphysema. Persistent air leak or non-resolving pneumothorax after an intercostal tube insertion should raise the suspicion of a tracheobronchial tear in a trauma setting.

Pneumoperitoneum is known to result after blunt chest injuries involving the rupture of the trachea, and right main bronchus. The mediastinal air is thought to enter the abdomen via transesophageal or aortic hiatus. Post extubation respiratory symptoms could be the initial presentation of an unnoticed tracheal tear, which must have been sealed initially by the inflated endotracheal tube cuff. The tracheal tear gets reopened once the patient is extubated, thereby manifesting airway related symptoms. Detection of air leak from a penetrating neck wound and its disappearance after intubation is classically described in tracheal injury.

Evaluation

A definitive diagnosis of tracheobronchial tear is usually made on clinical findings at initial evaluation or surgical exploration or findings at a bronchoscopic fiberoptic assessment in suspected cases. However, tracheobronchial injuries could easily be missed in 25% to 68% of the patients, and the following imaging modalities might throw more clues to enhance the suspicion, especially in chest and neck trauma.

Chest radiographs would be normal in about 10% of the patients where the tracheobronchial tear/injury does not extend beyond the peri tracheal or peri-bronchial connective tissue, or spontaneous sealing of a minor tear has occurred due to fibrin formation. The most common site of tracheobronchial tear is at the level of carina where the mediastinum is fixed and hence vulnerable to shear stress. Tears within the mediastinal pleura cause pneumomediastinum and tear beyond the mediastinal pleura causes pneumothorax. The right main bronchial injury is most likely expected to produce a pneumothorax, whereas the tear on the left main bronchus is more likely to produce a pneumomediastinum. This is due to the longer course of left main bronchus in the mediastinum. Fallen-lung sign is seen in severely injured patients due to the partial or complete detachment of the main bronchus resulting in the relocation of the lung in the lateral dependent position, unlike the typical collapse of the lung towards the hilum in usual pneumothorax.

Other classic descriptions include the incorrect position of an endotracheal tube, overdistension of a cuff, and persistent pneumothorax after intercostal tube placement. Abnormal hyoid bone elevation (above the third cervical vertebra) could occur due to contraction and upward pull of suprahyoid muscle whenever a cervical tracheal tear results in rupture of the infrahyoid muscle. However, the most specific radiologic signs for a tracheobronchial tear are the location of the endotracheal tube beyond the expected tracheal anatomy and the fallen-lung sign.

CT scan is much more sensitive and specific in delineating tracheobronchial injury and is the non-invasive investigation of choice. It would be able to identify subtle pneumothoraces, mediastinal emphysema, and active bleeding in an injured airway. Detection of air in the wall of the trachea or bronchus is a helpful finding in the diagnosis of the tracheobronchial tear. It has got added advantage of helping to detect associated critical injuries to the heart and great vessels. MPR/3D reconstructed images in the long axis of airways, or virtual endoscopy could help evaluation in a more precise manner. CT scans would be falsely negative in subtle injuries. Fiberoptic bronchoscopy may throw more light in such circumstances.

Though the advantage of MRI includes a multiplanar display, high tissue contrast, reduced risk for contrast-induced nephropathy, and no risk for radiation, these advantages are easily offset by the need for preparation, increased scanning time with enhanced risks involved in monitoring the unstable trauma patients. Moreover, MRI is not available universally.

Nuclear imaging will not be of any help, especially in minor injuries. Varying findings are noted depending on the severity of injuries. If there is a partial or complete airway obstruction with an intact vascular supply, evidence of V/Q mismatch would be present with the physiological response of diminished blood supply. Angiography would be of any help only if the tracheobronchial tear is actively bleeding. However, angiography will help in the determination of associated vascular injuries.

The gold standard for the detection of tracheal tear/injury is fiberoptic bronchoscopy.[17] Fiberoptic bronchoscopy can also aid in the initial safe management of the airway in suspected or proved tracheobronchial injuries, as explained below.

Treatment / Management

Securing a safe airway is a crucial aspect of emergency management of patients with suspected or proved tracheobronchial tears. However, tracheobronchial injuries are often not detected or suspected before the decision to intubation is made. The practice of rapid sequence intubation often prompted by hemodynamic instability or respiratory distress should be avoided in patients with tracheobronchial injury since intubation in a torn or disrupted airway causes further damage to the air passage with a high likelihood of making a false passage. Spontaneous breathing is promoted in such a setting until a safe airway is established.

A 2014 newsletter by the American Society of Anesthesiologists outlines an algorithm for disrupted airway, which underscores the need to maintain spontaneous breathing in such settings until a safe airway is ensured. Fiberoptic bronchoscopic intubation is the ideal measure in such settings since it can visualize the airway clearly and can suction out clots and secretions, helping in the safe placement of the tube. Moreover, fiberoptic bronchoscopy does not require neck extension, which makes it ideal in any suspected or confirmed cervical spine injury settings. The fiberoptic bronchoscopic placement re ensures that the cuff is distal to the injured airway. If the injury is at the level of carina or one of the main bronchi, the endoscope could guide the positioning of the tube into the uninjured bronchus and help in initiating single lung ventilation. However, fiberoptic bronchoscopy will not be able to visualize the airway clearly whenever there is active bleeding, or there is a distal collapse of the airway. A restless, unstable, or uncooperative trauma patient with hemodynamic compromise makes the procedure extremely challenging under normal sedation. Rigid bronchoscope under inhalational anesthesia at the operation theatre would be ideal in such a condition since it can also remove clots and secretions much more effectively. Moreover, an endoscopic intervention could help in patching the airway defect (if any) at least temporarily. However, rigid bronchoscopy needs an extension of the neck and is contraindicated even in a suspected cervical spine injury.

In cases of severe tracheal injury where larynx and proximal trachea are completely transected, and transoral intubation is challenging to achieve, the airway should be grasped via the cervical wound and tracheostomy tube needs to be introduced therein. Emergency bedside open tracheostomy may have to be performed by a surgeon with the tracheostomy tube passed through the injured trachea to preserve the tracheal length when reconstruction procedure is to be undertaken in the future. Since the trachea has anatomical proximity to numerous vital structures in the cervicothoracic region, it is imperative that the injuries to these nearby structures need to be ruled out soon after a safe airway is established. Severe concomitant injuries to these vital structures determine the overall survival. Hence injuries to the vocal cords, esophagus, vertebral body and spinal cord, lungs, ribs, sternum and clavicle, carotid arteries, jugular veins, and great vessels need to be specifically looked for.

If the tear is extending to the carina, single-lung ventilation has to be considered with the endoscopic placement of the endotracheal tube to the uninjured bronchus. The high airway pressures and positive end-expiratory pressures should be avoided during ventilation in the airway injured patients. Extracorporeal membrane oxygenation (ECMO) needs to be considered for patients unable to ventilate as a bridge to recovery or a definitive repair either surgically or bronchoscopically.

The vast majority of patients with tracheobronchial injuries are best managed with surgical intervention. Conservative management to allow spontaneous healing often results in stenosis at a later stage. If the stenosis is detected bronchoscopically, an initial dilation will open up the airway and drain the secretions for a short period. However, the definitive surgery is delayed until four to six months in such cases until the scar tissue gets matured. A bronchial sleeve resection with a pedicled tissue flap is often required in the management of late stenosis. Laryngeal & vocal cord injuries have to be thoroughly assessed with appropriate measures before attempting the repair of injured cervical trachea. However, there appears to be a recent paradigm shift towards minimally invasive modalities (e.g., stent placement), especially in iatrogenic injuries or in high-risk patients for surgical repair.[18][15]

The decision regarding surgical repair for acute tracheobronchial tear, in general, is based on the risk for airway obstruction, massive air leak, and mediastinal infections.[19] Most experts opt for surgical repair when the tracheal tear is more than 4 cm. Emergency surgical intervention is indicated in the presence of esophageal prolapse into the tracheobronchial lumen, inability to ventilate, and detection of tracheobronchial injury intraoperatively. The conservative approach is adopted if the tear is less than 2 cm.  A tracheal tear between 2 to 4 cm in length is managed by taking into account the clinical condition, comorbid factors, anatomy, and the degree of local expertise available.

Few experts advocate conservative management in self-ventilating patients or the ones on minimal mechanical ventilatory support without evidence of mediastinal or esophageal injury. This approach is probably more applicable to iatrogenic tracheobronchial injuries, which are often single, unlike the tracheobronchial injuries in blunt or penetrating trauma, which are much more severe and are associated with multiple life-threatening concomitant injuries. Surgical management is indicated in such iatrogenic injuries after a failed trial of conservative management in the form of worsening pneumomediastinum, subcutaneous emphysema or pneumothorax with persistent air leak, or unexpanded lung even after intercostal tube placement. 

The select group of patients, especially the one with posterior wall laceration/tear after iatrogenic injuries (e.g., endotracheal intubation, percutaneous tracheostomy), are managed successfully with conservative management.[20][21][20][19] The posterior tracheobronchial tear could be managed conservatively in the presence of minimal pneumomediastinum which is non-progressive, absence of mediastinitis, evacuation of pneumothorax feasible without a persistent large air leak, absence of esophageal injury, ability to maintain ventilation, and ability to place the endotracheal cuff distant to the site of injury with ventilation feasible with minimal positive end-expiratory pressure.(B2)

Surgical principles in the management of tracheobronchial tear include obtaining optimal exposure, conservative debridement ensuring the preservation of adequate airway length for future reconstruction, preservation of laterally oriented tracheal blood supply, buttressing the repair, and consideration for a tracheostomy, especially in polytrauma patients. Basic principles of cervical tracheal injury include a collar incision followed by anterior mobilization of the trachea up to the level of carina with taking precautions as not to injure the laterally placed blood supply. Knots are placed outside the trachea to prevent the formation of granulomas.

A post-operative tracheostomy is often required due to the high incidence of unilateral or bilateral recurrent laryngeal nerve injury incomplete tracheal transactions, which occur below the level of the cricoid cartilage. But an anastomosis with minimal tension is often possible in such circumstances. In associated esophageal injury, the esophagus is repaired first with flap placement, and the tracheal repair is performed only at the end of the procedure. A thoracotomy will be required in intrathoracic tracheal repair. The right fourth intercostal approach is used to access the lower trachea, carina, and right main bronchus where a left fourth intercostal thoracotomy is done to access left main bronchus. A transsternal approach (median sternotomy) is made in patients who have lower tracheal and carinal injuries along with spinal injuries, with the latter precluding thoracotomy positioning. All the above repairs should be visualized by bronchoscopy before leaving the surgical suite. It is imperative to ensure that the cuff of the endotracheal tube is not placed near the area of repair in intubated patients.

Cardilo et al. proposed a morphologic classification for tracheal wall injuries during endotracheal intubation to guide non-surgical management.[22] Few experts have extrapolated the above classification to other iatrogenic tracheal injuries, too.[15] Level 1 is mucosal or submucosal injury; level 2 represents further extension with muscular wall involvement with subcutaneous or mediastinal emphysema, level 3-A represents complete laceration with herniation of esophageal or mediastinal soft tissue, and 3-B represents all the above findings plus esophageal injury or mediastinitis. Level 3-A and 3-B represent a definite indication for surgery. Level 1 could undergo conservative management with the management of level 2 chosen on a case to case basis.

Broad-spectrum antibiotics are administered in such conservatively managed patients for a week though clinical data to support this measure is lacking at this stage. Routine antibiotic protocols are applied to surgically managed patients. Schaefer-Fuhrman classification also has been applied to laryngotracheal trauma to identify those patients who could be managed non-operatively. Though most experts believe that primary surgical repair is the treatment of choice in tracheal injuries, there is another group of experts who find no difference between primary surgical versus conservative management in the management of select types of iatrogenic tracheobronchial injuries.[23][18](B3)

In patients who are at high risk for surgical intervention due to multiple comorbidities, including a moderate to severe underlying cardiopulmonary disability could be managed with self-expandable metallic stents (SEMS), which could mechanically cover the defect, and incite local inflammatory response to cover the area by granulation tissues. These stents could be removed after 4 to 6 weeks after an endoscopic reevaluation of the injury. The benefits of this intervention far outweigh the possible stent-related complications. In certain patients, surgery also could be considered at a later stage after this bridging intervention. Madden BP et al. used endobronchial glue injection with stenting in tracheal lacerations less than 5 mm.[24] Endoluminal repair has been performed in patients who could withstand jet insufflation and who have posterior wall attachments.[6]

Differential Diagnosis

Pneumomediastinum, subcutaneous emphysema, and pneumothorax could result not only from injuries to the tracheobronchial tree but also secondary to injuries to the larynx, pulmonary parenchyma, and esophagus. Air could also enter the thorax from outside via chest wall trauma, and also via transdiaphragmatic spread from the abdomen. With blunt and penetrating injuries contributing significantly to tracheobronchial tear, it is crucial to carefully evaluate for concomitant injuries to carotid arteries, jugular veins, aorta, pulmonary trunk and recurrent laryngeal and vagal nerve injuries in chest/neck trauma settings. All those associated injuries discussed above could cause shock, sepsis, pneumonia, atelectasis, bronchiectasis, stroke, and multiorgan dysfunction, which could significantly increase the mortality in tracheobronchial injury.

Prognosis

The prognosis depends on the clinical condition of the patient, the severity of the injury, the time of detection, concomitant injuries, and finally, the type of repair undertaken. Almost 80% of the patients with tracheobronchial injuries in blunt trauma die before reaching a medical facility. One major compounding reason could be associated with concomitant injuries, which by themselves are lethal. However, the mortality of traumatic tracheobronchial injury has decreased significantly from 36% before 1950 to 9% in 2001.[25] A 2009 systematic review by Minambres et al. identified male gender at an increased risk of mortality in tracheobronchial injuries; this finding could be related to the etiology for respiratory failure rather than the injury itself.[7]

Superimposed mediastinitis, delayed diagnosis before undergoing a surgical correction, and surgical repair in critically ill patients increases mortality significantly. Up to 80% of mortality is observed in critically ill patients undergoing repair. Patients should also be followed up for the development of stenosis in all airway injuries until complete healing occurs. Health expenditures are significant for periodic monitoring of such patients who may require therapeutic endoscopic dilatations during the follow-up.

Complications

The complications of tracheobronchial tear depend upon the type and the severity of the injury. Almost 80% of patients with tracheobronchial injuries with blunt trauma dies either at the site or on the way to the hospital. The mortality is compounded by concomitant severe injuries the patient sustains in blunt trauma. Post-traumatic tracheobronchial injuries could present with subtle asymptomatic lesions to severe respiratory distress and respiratory failure. The tracheal injury could result in sudden airway collapse. Subcutaneous emphysema, pneumomediastinum, and pneumothorax are common presentations and complications—infections and sepsis with multiorgan dysfunction compound the mortality risk. Long-standing collapse or bronchiectasis following airway injuries could substantially reduce the pulmonary reserve.

Iatrogenic tracheal injuries could cause esophageal and mediastinal injuries, including life-threatening mediastinitis. Untreated airway injuries often result in late stenosis. Cuff pressure-related injuries could vary from simple mucosal lacerations, which could progress to tracheal stenosis or tracheoesophageal fistula. Complications of surgically corrected tracheobronchial injury include anastomotic separation, brachial artery fistula with sudden life-threatening bleeding. Strictures, fistula, and hoarseness of voice due to recurrent laryngeal nerve palsy could also complicate the treatment. Few known complications of endoscopic management with stenting include infections, migration of stent, tracheal stenosis secondary to granulation tissue, metal fatigue, and mucous formation with blockage.

Almost 50% to 70% of the tracheobronchial tears are missed initially and could present later on with breathing difficulty, stridor, and recurrent infections. The mortality in initially missed injuries with subsequent need for surgery is high.