Disorders of the Respiratory Tract Caused by Trauma




Abstract


Thoracic trauma, although rare in children, can lead to significant morbidity and mortality. Most are sustained due to blunt mechanisms, with motor vehicle accidents being most common. Due to chest wall pliability, pulmonary contusions are more common than fractures, which are typically seen later in life. Other potential injuries are pneumothorax, hemothorax, tracheobronchial injury, cardiac/great vessel injury, esophageal injury, and diaphragmatic rupture. Thoracic trauma may also be associated with head, abdominal, pelvic, and/or spine trauma. Early diagnosis and prompt treatment during the “golden hour” can help mitigate the potential short- and long-term complications of chest trauma.




Keywords

trauma, chest, pneumothorax, hemothorax, flail chest

 




General Considerations


Traumatic thoracic injury in infants and children is uncommon; it is usually secondary to blunt mechanisms and is often managed nonoperatively. Penetrating injuries, such as stab and gunshot wounds are, fortunately, rare, but they usually require some sort of operative intervention, and result in increased morbidity and mortality.


More than 75% of pediatric blunt chest trauma is due to automobile accidents, with the remainder resulting from sports injuries, nonaccidental trauma, and falls from heights. Children involved in automobile accidents tend to be pedestrians rather than occupants of vehicles. The complete spectrum of chest trauma includes pneumothorax, hemothorax, destruction of the integrity of the chest wall and diaphragm, thoracic visceral damage, and combined thoracoabdominal injuries. The mortality rate from thoracic trauma has been reported to be approximately 26%, and can be as high as 33% when penetrating injuries are involved. Overall, recent literature suggests that the mortality rate for childhood thoracic trauma has decreased. Thoracic trauma is frequently associated with head, abdominal, and spine trauma, making the mortality rate higher in this combined scenario.


Pediatric deaths may occur in the prehospital setting and are usually secondary to hemorrhagic shock or cardiopulmonary arrest related to a tension pneumothorax or cardiac tamponade. The mortality and morbidity rate can be improved if the patient is transferred to a tertiary level pediatric trauma center and managed within “the golden hour” described by the Advanced Trauma Life Support (ATLS) guidelines.


Most blunt thoracic injuries in children can be managed without operative intervention. This often involves significant respiratory support, including analgesia, assisted ventilation, and aggressive physiotherapy. As in adults, the significance of thoracic trauma results from the concomitant pulmonary, cardiac, and systemic dysfunction that follows. In the pediatric age group, because of chest wall plasticity, profound physiologic aberrations can occur in the absence of fractures. Respiratory and circulatory dysfunction secondary to chest injury is frequently complicated by blood loss and hypotension. Hypotension from hemorrhage can usually be managed through volume replacement; algorithmic therapy is monitored and refined by serial determination of blood pressures, hematocrit, central venous pressure, blood gases, and, if necessary, blood volume. Restoration of the normal cardiopulmonary function fundamentally depends on a clean airway, intact chest and diaphragm, and unrestricted cardiopulmonary dynamics. The primary and secondary surveys recommended by the ATLS guidelines are mandatory in pediatric trauma as well. If the patient is hemodynamically stable with a significant mechanism of injury, computed tomography (CT) of the chest should be considered to search for undetected injuries if felt that they would alter the clinical approach. Otherwise, chest radiography is typically adequate and avoids the radiation risk.


The long-term outcome of thoracic trauma in children has not been well studied. A single European study addressed the 5-year outcome of thoracic trauma in children; they concluded that most injuries resolve without significant late sequelae.




Features of the Pediatric Thorax


The thorax of a child is different from that of an adult from both an anatomic and a physiologic point of view. The pediatric chest is typically more rounded with less developed musculature. This characteristic, together with a more flexible and elastic rib cage, results in a very compliant chest. The ribs and sternum of a child can thus support a significant amount of blunt force without fracture. Deformability is such that the anterior and posterior curvatures of the ribs can contact each other without fracture. Therefore, blunt injury to the chest presents a diagnostic challenge since obvious external signs of injury may be minor, chest radiographs may be normal, and yet the visceral structures may still have sustained serious injury.


Additionally, the mediastinum is relatively mobile and thus less susceptible to the rapid acceleration and deceleration forces commonly experienced in blunt trauma. Increased mediastinal mobility, together with the absence of preexisting vascular disease in children, make injuries to the mediastinum and great vessels less frequent than in adults. On the other hand, conditions such as tension pneumothorax or hemothorax are very poorly tolerated and must be recognized and addressed emergently.


Physiological compensation to trauma is different in children when compared with adults; the cardiovascular and pulmonary reserves are much less in children. Tachycardia may be the only compensatory mechanism in children who present with hypovolemic shock, even with 30% loss of estimated blood volume. Hypotension will only occur in the very late stage, just before cardiac arrest. The pulmonary reserve can be seriously affected by massive gastric distention, a very common finding in pediatric trauma. Prompt insertion of a nasogastric tube is recommended since many children will develop gastric distention due to aerophagia following any type of trauma.




Sternal Fractures


Fractures of the sternum in infancy and childhood follow high-compression crush injuries and are usually associated with other thoracic and orthopedic injuries. Interestingly, one series has reported sternal fractures as the result of surprisingly minor trauma. The most common injury identified in this report was an isolated anterior cortical fracture.


On physical examination, there is local tenderness, ecchymosis, and sometimes a concavity or paradoxical respiratory movement. The sternal segments are typically well aligned without much displacement. Dyspnea, cyanosis, arrhythmias (most commonly sinus tachycardia), and hypotension may be evidence of an underlying cardiac contusion. Radiographic demonstration of fractures is most commonly by chest x-ray or CT scan, although ultrasound is being used more frequently with high sensitivity/specificity.


Children with traumatic injury of the sternum should be admitted to the intensive care unit given the increased risk for arrhythmias. Cardiac tamponade and blunt myocardial damage must be ruled out by various studies, including serial electrocardiography, echocardiography, and careful monitoring of vital signs. Although cardiac enzymes were once used as a screening tool, their use has been abandoned due to low sensitivity and specificity.


If the bony deformity is minimal, there is no specific treatment indicated. Markedly displaced fragments are reduced under general anesthesia by a closed or open technique in order to prevent a traumatic pectus excavatum. Violent paradoxical respirations can be controlled by assisted mechanical respiration through an endotracheal tube, or rarely by operative fixation of rib fragments.




Rib Fractures and Flail Chest


Rib fractures are unusual in children because of the extreme flexibility of the osseous and cartilaginous framework of the thorax. The upper ribs are protected by the scapula and related muscles, and the lower ones are quite resilient. As such, rib fractures are present in only about 3% of all children admitted with thoracic injury. Predictably, children with more than one rib fracture are more likely to have sustained multisystem trauma; crush and direct-blow injuries are the usual etiologic factors. Multiple fractures of the middle ribs are almost diagnostic of nonaccidental trauma.


Multiple rib fractures resulting in the destruction of the integrity of the thoracic skeleton can cause the paradoxical motion of the “flail chest” ( Fig. 73.1 ). The unsupported area of the chest moves inward with inspiration and outward with expiration; these paradoxical respiratory excursions inexorably lead to dyspnea ( Fig. 73.2 ). The explosive expiration of coughing is dissipated and made ineffectual by the paradoxical movement and intercostal pain. In effect, the ideal preparation for acute respiratory distress syndrome—airway obstruction, atelectasis, and pneumonia—has been established.




Fig. 73.1


An illustration of five ribs broken in two places, with loss of chest wall stability and resultant paradoxical or “flail chest” wall.



Fig. 73.2


(A–D) A diagram of the action of a normal chest compared with that of a “flail chest” during phases of the respiratory cycle.


The clinical picture includes local pain that is aggravated by motion. Tenderness is elicited by pressure applied directly over the fracture or elsewhere on the same rib. The fracture site may be edematous and ecchymotic. The clinical manifestations may range from these minimal findings with simple, restricted fractures to severe ventilatory distress with underlying lung injury. Chest radiographs demonstrate the extent and displacement of the fractures and hint at underlying visceral damage.


The treatment of uncomplicated fractures requires pain control to allow unrestricted respiration. With severe fractures, the alleviation of pain and the restoration of cough are important and can be provided by analgesics, physiotherapy, and intermittent positive-pressure breathing. Thoracostomy tubes should be inserted promptly for pneumothorax and hemothorax, and shock should be managed by appropriate resuscitation. There are a few small studies to suggest that surgical fixation results in a reduction in pneumonia, chest deformity, tracheostomy, duration of mechanical ventilation, and length of intensive care unit (ICU) stay.


Paradoxical respiratory excursions with flail chest must be promptly brought under control, sometimes requiring mechanical positive pressure ventilation to help prevent respiratory distress syndrome. In some cases, a thoracic epidural anesthetic may be useful to provide appropriate analgesia and achieve effective ventilation. Although not routinely used, surgical stabilization in severe flail chest has been shown to lower the incidence of pneumonia, shorten the ICU stay, reduce ventilatory requirement, and reduce overall hospital cost.


Tracheostomy in Chest Wall Injury


Controlled mechanical ventilation is an essential component for respiratory insufficiency in the setting of thoracic trauma. Despite vigorous therapy, secretions may be troublesome, and are managed using intermittent tracheal suctioning or bronchoscopy. There is evidence that tracheostomy in children can be avoided by long-term intubation in many cases. However, prolonged intubation has become the most important indication for tracheostomy, since it allows an avenue for the control of secretions, diminishes ventilatory dead space, and obtains control of an obstructed airway ( Fig. 73.3 ).




Fig. 73.3


Techniques of tracheostomy performed over an oral endotracheal tube. Note the transverse skin incision (A) and the suture on the lower tracheal flaps to facilitate subsequent tube changes (C). (B) The anatomy of the area. (D) The tube in place.


During the first year of life, tracheostomy is a particularly morbid operation. Common complications are pneumomediastinum, pneumothorax, tracheal stenosis, and tracheomalacia. Secretions may be difficult to aspirate, as the small tracheostomy tube easily becomes plugged. Distal infection, often with staphylococci, is poorly handled by such young patients. In addition, withdrawal of the tracheostomy tube is a precarious and unpredictable endeavor. Nevertheless, even in this age group, tracheostomy can be lifesaving in specific instances of chest trauma.


The decision for tracheostomy in cases of chest injury can often be made if there is (1) a mechanically obstructed airway that cannot be managed more conservatively, (2) flail chest, or (3) prolonged endotracheal intubation. Unstable, paradoxical chest wall movement can be controlled for long periods by assisted positive pressure respiration through a short, uncuffed Silastic tracheostomy tube.




Traumatic Pneumothorax


Pneumothorax is one of the most common consequences of thoracic trauma and is identified in approximately 12%–50% of chest trauma patients admitted to hospital. Pneumothorax is potentially fatal and requires specific maneuvers to prevent or reverse a malignant chain of events.


The creation of a tension pneumothorax requires a valvular mechanism through which the amount of air entering the pleural space exceeds the amount escaping it. The positive intrapleural pressure is initially dissipated by a mediastinal shift, which compresses the opposite lung and can result in ipsilateral pulmonary collapse and angulation of the great vessels entering and leaving the heart. Intrapleural tension can be increased by traumatic hemothorax, and respiratory exchange and cardiac output are thus critically diminished.


The etiologic possibilities, in addition to chest wall and lung trauma, include rupture of the esophagus, pulmonary cyst, emphysematous lobe, and postoperative bronchial fistula. These latter sources of tension pneumothorax almost always require thoracotomy for control.


The clinical findings may include external evidence of a wound, tachypnea, dyspnea, cyanosis with hyperresonance, the absence or transmission of breath sounds, and displacement of the trachea and apical cardiac impulse. The hemithoraces may be asymmetric, with the involved side appearing larger and hyperresonant.


A confirmatory radiograph is comforting but often cannot be afforded in this thoracic emergency. Chest tube insertion is indicated for a tension pneumothorax or simple pneumothorax associated with respiratory distress or shock. Prompt relief and pulmonary expansion can be anticipated if the source of the intrapleural air has been controlled. A traumatic valvular defect in the chest wall can be occluded. If the pulmonary air leak persists or recurs, the possibility of tension pneumothorax is circumvented by the insertion of one or more intercostal tubes connected to water-seal drainage with low-pressure suction. Most instances of traumatic tension pneumothorax require tube drainage for permanent decompression, although needle aspiration is indispensable for emergency management. Stubborn bronchopleural fistulas that continue to remain widely patent despite adequate intercostal tube drainage may need thoracotomy and repair or resection of the affected lung segment.


An open pneumothorax (“sucking” chest wound) in which atmospheric air has direct, unimpeded entrance into and exit from the pleural space is a second, equally urgent, thoracic emergency. This pathology is almost always due to a large traumatic wound. Ingress of air during inspiration and egress during expiration produce an extreme degree of paradoxical respiration and mediastinal flutter, which is partially regulated by the size of the chest wall defect in comparison with the circumference of the trachea. If a considerable segment of chest wall is open, more air is exchanged at this site than through the trachea, because the pressures are similar. Inspiration collapses the ipsilateral lung and drives its alveolar air into the opposite side. During expiration, the air returns across the carina. In addition, the mediastinum becomes a widely swinging pendulum compressing the uninjured lung on inspiration and the lung on the injured side during expiration ( Fig. 73.4 ). Obviously, under these circumstances, little effective ventilation is taking place because of the tremendous increase in the pulmonary dead space and the decrease in tidal volumes. A totally ineffective cough completes the clinical picture. The diagnosis is readily made by inspection of the thoracic wound and the peculiar sound of air rushing in and coming out of the wound.




Fig. 73.4


(A–D) Changes in the normal respiratory pattern brought about by an open, sucking thoracic wall injury.


Emergency management of this critical situation includes prompt occlusion of the chest wall defect by sterile dressings ( Fig. 73.5 ) and measures to prevent conversion of this open pneumothorax into an equally threatening tension pneumothorax, which can occur if the underlying visceral pleura has been injured. Pleural decompression by closed intercostal tube drainage is essential. When immediate chest tube is not available (i.e., in the prehospital setting), closure of the wound with an occlusive dressing sealed on three sides is appropriate. This acts as a one-way valve allowing air to escape from the pleural space on expiration but sealing and preventing further air entry on inspiration. After systemic stabilization, more formal surgical débridement, reconstruction, and closure of the chest wound can be done in the operating room.




Fig. 73.5


A temporary occlusive chest wall dressing applied to a sucking wound with underwater intercostal chest tube drainage. Once the period of emergency is over, operative debridement and closure of the chest wound is necessary.




Hemothorax


Blood in the pleural cavity is perhaps the most common sequel of thoracic trauma, regardless of type. Depending on the speed of the hemorrhage, it can be life threatening. Bleeding sources are abundant, with either systemic (high pressure) or pulmonary (low pressure) sources. Systemic bleeding usually originates in the chest wall from the intercostal vessels. Hemorrhage from pulmonary vessels is usually self-limiting unless major tributaries have been transected. It is important to note that a child can accumulate about 40% of his/her blood volume in the chest.


The immediate findings are those of blood loss compounded by respiratory distress. The trachea and apical impulse may be dislocated, the percussion note is flat, and the breath sounds are indistinct. The actual diagnosis is confirmed by thoracentesis if time allows after adequate radiographic studies.


Management of hemothorax is accomplished by total evacuation of air and blood with a large-bore chest tube. Most often, the evacuation of blood will obliterate the pleural space, and pleural apposition will tamponade parenchymal bleeding. Small-volume hemothorax may be safely observed as long as cardiorespiratory mechanics are not altered. A simple formula to define the need for urgent thoracotomy is a bloody chest tube output of more than 1 mL/kg per minute with associated hemodynamic instability despite rigorous resuscitation. The surgeon’s common sense is crucial in this setting, and if one suspects either persistent or voluminous bleeding, an operation should be performed.


Clotting, loculation, and infection may supervene despite vigorous initial therapy. A retained hemothorax can eventually result in empyema. Publications from the adult literature support early thoracoscopy and drainage of the retained hemothorax in order to avoid late infections. As with management of parapneumonic effusions, use of thrombolytics (tissue plasminogen activator [tPA]) is well established to assist with clot dissolution. Unevacuated intrapleural blood eventually clots and can become organized fibrous tissue (fibrothorax). With the development of a fibrothorax, the lung becomes incarcerated and the chest wall is immobilized, chronically altering cardiorespiratory dynamics. Empyema from secondary contamination is always a threat when the pleural space is filled with blood. Patients rarely eventually require thoracotomy and decortication.

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Jul 3, 2019 | Posted by in RESPIRATORY | Comments Off on Disorders of the Respiratory Tract Caused by Trauma
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