Thoracic Trauma

Published on 26/02/2015 by admin

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Last modified 26/02/2015

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Thoracic Trauma

Trauma is an important cause of morbidity and mortality in children. Although it accounts for a minority of trauma injuries (4–25%), thoracic trauma is associated with a 20-fold increase in mortality when compared with injured children without thoracic trauma.1–10 Isolated thoracic trauma in a child is associated with a mortality rate of approximately 5%, which is largely due to penetrating trauma.1 However, children with head trauma, thoracic trauma, and abdominal trauma can have a mortality rate that approaches 40%.

Epidemiologic studies have reported a two to threefold higher incidence of thoracic trauma in boys as compared with girls.9–15 Most injuries (80–95%) are the result of blunt trauma, typically resulting from a traffic accident in which the child is a passenger or pedestrian.2,10 Not surprisingly, many children will have involvement of other organ systems with a high injury severity score (ISS). When penetrating trauma occurs, older children and adolescents are more likely to be the victims and there is a higher mortality rate.5

Contusion or laceration of the pulmonary parenchyma is the most common thoracic injury and may be associated with rib fractures and pneumothorax or hemothorax. Injuries to other organs such as the tracheobronchial tree (<1%), esophagus (<1%), aorta (<1%), diaphragm (4%), and heart (6%) are uncommon, but not insignificant.12

Anatomy and Physiology

Children have unique anatomic and physiologic properties that are salient to the diagnosis and management of chest injuries. As in any trauma patient, sequential management of the airway, breathing, and circulation is of primary importance. The pediatric airway may be complicated by numerous factors. The head of an infant is proportionally much larger than that of an adult, thus predisposing to neck flexion and occlusion of the airway in the supine position. The larger tongue and soft palate, as well as the more anterior glottis, can make the airway difficult to visualize. The child’s trachea is shorter relative to body size, and narrower and more easily compressed compared with an adult. The subglottic region is the narrowest part of the trachea in children. Because of its small cross-sectional diameter, the pediatric airway is more susceptible to plugging with mucus or minimal airway edema.

The chest wall is more compliant in children, with less muscle mass for soft tissue protection. This allows a greater transmission of energy to underlying organs when injury occurs. The thinner chest wall also allows for easier transmission of breath sounds, which may obscure the diagnosis of a hemothorax or pneumothorax. Children are also at an increased risk for hypoxia owing to their higher oxygen consumption per unit body mass and their lower functional residual capacity to total lung volume ratio.

When assessing circulation, it is important to note that the mediastinum is more mobile in children than in older patients. This is particularly true in young children. Unilateral changes in thoracic pressure, as occurs from a pneumothorax, can lead to a tension pneumothorax. This can shift the mediastinum such that venous return is markedly reduced. The pathophysiologic effect is similar to hypovolemic shock, and this response is more pronounced than is typically seen in an adult.

Children compensate for a decrease in cardiac output by increasing their heart rate. In infants, improvement in stroke volume provides little in the way of compensation for hypotension. Infants and children also have a higher body surface area to weight ratio than adults, which predisposes them to hypothermia. This, in turn, may complicate the assessment of perfusion.

Specific Injuries and Management

Thoracic injuries in children can be categorized by location as seen in Box 15-1.

Chest Wall

Rib Fractures

Young children have a compliant thorax and do not begin to resemble adults until around 8 to 10 years of age. As a consequence, rib fractures are relatively uncommon in young children and occur more frequently in adolescents. Rib fractures are often suspected on physical examination and are identified on a chest radiograph (CXR) during the initial assessment. Independently, rib fractures are infrequently a cause of major morbidity or mortality, but are indicators of significant energy transfer.16 If a rib fracture is found in a child younger than 3 years, nonaccidental trauma (NAT) should be considered.17,18 Bone scans and bone surveys are useful in diagnosing remote fractures of the bony thorax in abused children, and follow-up studies improve identification of these injuries.19 In older children, rib fractures should draw attention to the risk of an associated underlying injury. Fractures and dislocations of the bony thorax and joints may cause significant long-term pain. In addition to pneumothorax and hemothorax, children with first rib fractures may have fractures of the clavicle, central nervous system injury, facial fractures, pelvic fractures, extremity injuries, and major vascular trauma.20,21 When children present with multiple rib fractures, the mortality has been reported to be as high as 42%.21 A careful survey of the child must be performed to look for significant injuries in other regions of the body.

The management of rib fractures is typically supportive. Attention to adequate pain relief will prevent atelectasis and pneumonia. Because rib fractures can be associated with a hemothorax or pneumothorax, immediate drainage of fluid, blood, or air via a chest tube or catheter is appropriate.

Flail Chest

Due to the increased pliability of the chest wall, multiple rib fractures in series (flail chest) are not commonly seen in younger children.22 As a result of the wide age and size range, the treatment of flail chest in children, whether surgical or nonsurgical, adds a level of complexity when compared to adults. Chest wall dynamics and physiology differ significantly in infants compared to teenagers. Furthermore, flail chest has been identified in the neonatal period which increases the complexity of management of these patients.23

When flail chest occurs, the patient’s respiratory effort can be depressed due to a paradoxical motion of the flail segment. The large force required to produce this injury invariably results in injury to the underlying lung, which contributes to the respiratory compromise. Like other thoracic injuries, treatment is tailored to avoid respiratory depression and pneumonia.24 Adequate pain control, supplemental oxygen, chest physiotherapy, and continuous positive-pressure ventilation are non-invasive treatment modalities utilized in these patients.

In selected adults, operative correction of the flail chest has been shown to decrease morbidity, time on the ventilator, intensive care stay, and hospital costs.25,26 Since thoracic operations can be performed in injured children with minimal morbidity and mortality, similar results should be expected.14 Indications for operative management include failure to wean from mechanical ventilation. Other indications for thoracotomy are flail chest with no associated contusion, severe dyspnea, and severe chest deformity, among others.27,28

There is no standard operative approach for correction of a flail chest. Currently used techniques include wire cerclage, clamping, screw fixation, and intramedullary fixation.29 The use of absorbable plates for rib trauma has also been described with good results.30 The optimal surgical treatment in children is unclear given the required future growth of a child’s thoracic cavity. A multidisciplinary approach between pediatric surgeons, orthopedic surgeons, and critical care physicians is important.

Open Pneumothorax

Open pneumothorax (sucking chest wound) occurs when there is a gaping defect in the chest wall, and typically is caused by a blast injury, a severe avulsion injury, or an impalement (Fig. 15-1). This is not often seen in children but can be life threatening when it occurs. The negative pressure in the pleural cavity created by spontaneous breathing sucks air into the thorax. Air trapping results in collapse of the ipsilateral lung and mediastinal shift, similar to a tension pneumothorax. Treatment requires placement of an occlusive dressing to prevent further air from entering the chest cavity as well as chest tube or catheter insertion to drain a hemo/pneumothorax that may have developed.

Traumatic Asphyxia

Traumatic asphyxia is typically caused by a large compressive force against the chest wall combined with deep inspiration against a closed glottis (Valsalva maneuver). The increased thoracic pressure compresses the right atrium, excludes blood return from the superior vena cava, and results in rupture of venules and capillaries about the face and head.31 Patients will exhibit conjunctival hemorrhages, facial swelling, and petechial hemorrhages on the face and upper chest. Although severe cases may result in loss of vision or other permanent neurologic sequelae, the morbidity and mortality associated with traumatic asphyxia is generally related to the associated injuries. The majority of children who survive have good outcomes.32,33

Pleural Cavity and Pulmonary Parenchyma

Pneumothorax–Pulmonary Lacerations

Pneumothorax may occur with a penetrating injury to the chest wall or air leak into the pleural space from a pulmonary laceration or disruption of the proximal airway. It is a relatively common finding in children with blunt and penetrating thoracic trauma. The air leak may dissect under the pleura to cause pneumomediastinum and subcutaneous emphysema. A simple pneumothorax is often asymptomatic because the lack of increased intrathoracic pressure limits the recognition of symptoms. For this reason, a screening CXR is an important component in the evaluation of thoracic injury in children. Air within the pleural cavity can layer anteriorly, posteriorly, or in the subpulmonic space. A simple pneumothorax can be easily missed on chest film, but can be found on a subsequent computed tomographic (CT) scan.34 However, a recent study analyzing the utility of CT scan as a screening modality to replace initial CXR concluded that although a CT scan is highly sensitive, it should not be used as a primary imaging tool given its cost and the acceptable sensitivity of routine CXR.35 Ultrasonography (US) is another diagnostic modality that has been shown to be nearly as sensitive as CT in determining the presence of an occult pneumothorax and has gained wide acceptance as a screening tool.36,37

The need for intervention in the presence of a simple pneumothorax will depend on its severity and the child’s clinical condition. Some authors have suggested that if the volume of the pneumothorax is greater than 20% of the pleural space, then drainage is needed.38 Although insertion of a chest tube can be considered appropriate in almost every circumstance of traumatic pneumothorax, there are alternatives to conventional chest tubes, such as pigtail catheters.39 Additionally, there may be a benefit in treating with supplemental oxygen alone. The rationale for this therapy is that atmospheric gas (78% nitrogen) comprises the majority of the entrapped air collection. If the nitrogen level in the blood is ‘washed out’ by increased inspired oxygen, a nitrogen gradient will be created that will cause accelerated absorption of the air. Oxygen can be delivered by way of nasal cannula, a hood, or a mask. Treatment with supplemental oxygen may be required for 24 to 48 hours.

In contrast, a tension pneumothorax is a life-threatening condition that requires expeditious decompression. A tension pneumothorax likely causes symptoms initially from hypoxemia and later from increased intrapleural pressure with subsequent decreased venous return and cardiovascular collapse.40 If the clinician suspects a tension pneumothorax in a patient with appropriate signs and symptoms, it is reasonable to proceed with decompression without waiting for a CXR. If rapid drainage of intrapleural air cannot be accomplished with a needle, insertion of a pigtail catheter or a chest tube should be performed. A tension pneumothorax treated initially with needle decompression will require chest tube or pigtail catheter insertion due to the continuing collection of air under pressure in the involved hemithorax. If one or both lungs have been compressed for a long time, re-expansion pulmonary edema may develop.41

Systemic air embolism can occur with any pulmonary parenchymal injury and increased intrabronchial pressure, creating a bronchopulmonary venous fistula.42 This is most often seen when positive-pressure ventilation is required to support the injured patient. Sudden neurologic findings or cardiovascular decompensation may be the initial sign that air has embolized to the coronary or cerebral vessels. If this complication is recognized, steps should be taken to prevent further air embolism. If possible, the removal of the intravascular air should be considered. Treatment options include tube thoracostomy, but more often an emergency thoracotomy will provide immediate reversal of the physiology promoting the air embolism. The hilum of the lung should be occluded to prevent further escape of air into the venous system, and operative control of the bronchial–venous interface should be obtained. The mortality associated with this complication is high.

Hemothorax

Hemothorax can result from blunt or penetrating injury to any of the intrathoracic vessels, the chest wall vessels, the pleura, or the pulmonary parenchyma. Occasionally, a rib fracture can lacerate an intercostal vessel or the lung. Rarely, the aorta or vena cava may be injured by pressure or shearing. Unless the volume of blood is large, a hemothorax may be asymptomatic. Smaller volumes may be more easily detected on CT scan, which also allows for measurement of Hounsfield density to aid in the diagnosis.43 Each hemithorax can hold approximately 40% of a child’s blood volume and it is difficult to estimate the amount of blood loss on a CXR.44 Prompt chest tube placement allows for evacuation of the blood from the pleural space and re-expansion of the lung. It also allows the surgeon to assess the volume of blood loss and whether the hemorrhage is ongoing.

There are instances in which an operation may be needed to stop ongoing intrathoracic bleeding. After tube thoracostomy, the immediate blood return of 15 mL/kg, or ongoing losses of 2–3 mL/kg/h for 3 or more hours, are indicators for thoracic exploration.45,46 If undrained, the hemothorax can become organized with the development of a fibrothorax that can cause a restrictive lung defect. This predisposes to atelectasis, ventilation–perfusion mismatching, and subsequent pneumonia.

Residual blood is also an excellent culture medium, and empyema and sepsis can result from infection of an undrained hemothorax. Tube thoracostomy may not adequately evacuate an organizing post-traumatic hemothorax in up to 12% of patients.47 In this situation, thoracoscopy may be useful to evacuate the residual clot. Patients who undergo early thoracoscopy may experience less morbidity.48,49 However, there are also data to suggest that thrombolytic therapy is equally effective in treating a chronic hemothorax.47 The use of intrapleural tissue plasminogen activator (tPA) has also been used for the treatment of traumatic residual hemothoraces and other parapneumonic processes with good results.50,51