Thoracic Trauma

Etiology

Thoracic trauma is broadly categorized by mechanism into blunt or penetrating trauma. The most common cause of blunt chest trauma is motor vehicle collisions (MVC) which account for up to 80% of injuries. Other causes include falls, vehicles striking pedestrians, acts of violence, and blast injuries. The majority of penetrating trauma is due to gunshots and stabbings, which together account for 20% of all major trauma in the United States.[2]

Epidemiology

Blunt chest trauma is more common than penetrating trauma and directly comprises 20 to 25% of trauma deaths. Among patients presenting after motor vehicle collisions, higher morbidity and mortality are associated with high-speed collisions and with a lack of seat belt use. Poorer outcomes are also seen in patients with advanced age and higher injury severity scores (ISS). Despite its higher incidence, less than 10% of patients suffering blunt trauma to the thorax require operative intervention, whereas 15 to 30% of patients sustaining penetrating chest injuries will need operative intervention. Penetrating chest trauma is associated with higher overall mortality. Incidence varies based on geographic location, predominating in urban areas, those prone to interpersonal violence, and areas of conflict.

Pathophysiology

Anatomic Considerations and Pathophysiology

The major components of the chest wall are the rib cage, costal cartilage, and intercostal musculature. The blood supply and innervation to the chest wall are supplied by neurovascular bundles, comprising an intercostal artery, vein, and nerve that course at the inferior border of each rib. Deep to the rib cage, the parietal pleura makes up the inner lining of the chest wall. It receives somatic innervation from the intercostal nerves and therefore contains pain fibers. A layer of visceral pleura covers the intrathoracic structures. The potential space between the visceral and parietal layers is termed the pleural space and normally contains a small volume of hypotonic fluid, approximately 0.3 mL/kg, which undergoes constant turnover at a rate of 0.15 mL/kg per hour.[3]. This pleural fluid is produced by the parietal pleura itself and reabsorbed by pleural lymphatics. When lymphatic reabsorption is overwhelmed, pleural effusion occurs.

The chest wall serves 2 main purposes. First, it functions to facilitate respiration. Contraction of the diaphragm and intercostal muscles during inspiration increases intrathoracic volume, thus decreasing intrathoracic pressure, allowing the passive flow of air into the lungs. The reverse occurs during expiration. The diaphragm and intercostals return to their relaxed positions resulting in an increase in intrathoracic pressure, which forces air out of the lungs. The chest wall also protects intrathoracic structures from external injury. The sternum and clavicles provide additional structural support to the anterior thorax. They are dense bones that serve as points of attachment for the pectoralis major and minor muscles and therefore require significant force to fracture. Similarly, the scapulas which overlie the superior aspect of the posterior chest wall provide an added protective barrier to trauma.

The mediastinum comprises the heart, thoracic aorta, trachea, and esophagus and is anatomically located in the center of the chest between the right and left hemithoraces. It is bordered by the sternum anteriorly, vertebral column posteriorly, and parietal pleura and lungs bilaterally and extends from the thoracic inlet superiorly to the diaphragm inferiorly. The most common isolated mediastinal injury in blunt trauma is an injury to the aorta, which can range in severity from an intimal laceration to complete aortic transection. In penetrating trauma, all the mediastinal structures are equally susceptible, and the injury sustained depends on the anatomic location of the penetrating wound and its trajectory. Of particular importance is an injury within the "cardiac box" whose boundaries are the midclavicular lines laterally, the clavicles superiorly, and the xiphoid process inferiorly. Trauma in this region is associated with an increased risk of penetrating cardiac injury and the development of cardiac tamponade, and rapid clinical decompensation.

Morbidity and mortality associated with thoracic trauma are due to the disruption of respiration, circulation, or both. Respiratory compromise can occur due to direct injury to the airway or lungs, as is the case with pulmonary contusions, or from interference in the mechanics of breathing, as with rib fractures. The common outcome is the development of ventilation-perfusion mismatch and decreased pulmonary compliance. This then results in hypoventilation and hypoxia, which may necessitate intubation. Circulatory compromise occurs in the setting of significant blood loss, decreased venous return, or direct cardiac injury. Intrathoracic bleeding most commonly manifests as hemothorax in both blunt and penetrating trauma, and a massive hemothorax can lead to hypotension and hemodynamic shock.

History and Physical

The initial evaluation of a trauma patient is based on the ATLS protocol. This begins with an assessment of the patient's airway, breathing, and circulation (ABCs) during the primary survey, typically in that order. The initial evaluation of the patient who has sustained blunt or penetrating thoracic trauma is similar and geared toward the rapid identification of immediately life-threatening conditions, namely tension pneumothorax, cardiac tamponade, aortic injury, massive hemothorax, and tracheobronchial disruption. The clinician must pay careful attention to the patient's appearance on arrival to the trauma bay. Signs of respiratory distress, agitation, diaphoresis, or unwillingness to lay flat suggest underlying cardiopulmonary injuries, such as tension pneumothorax or cardiac tamponade, in which case the breathing or circulation portions of the primary survey would need to be addressed and intervened upon first, as indicated. Intubating such patients may exacerbate the pneumothorax or hypotension and lead to cardiovascular collapse due to the increased intrathoracic pressure generated by positive pressure ventilation. Therefore, if time and personnel allow, these interventions should be performed while the patient is prepared for intubation. However, assessment of the airway is generally performed first to establish patency and evaluate the need for intubation. The assessment of breathing begins at the trachea, which is inspected and palpated to ensure that it is midline and not deviated. The chest wall in then inspected for asymmetry, auscultated for breath sounds, and palpated for tenderness, crepitus, and to detect flail segments. In assessing circulation, hypotension in the setting of thoracic trauma should raise suspicion for tension pneumothorax or tamponade, which need urgent intervention before further evaluation of the patient can proceed.

Evaluation

Ultrasound

Sonographic evaluation of the abdomen and thorax using the focused assessment with sonography in trauma (FAST) exam is important in the initial phase of the trauma assessment. Per ATLS guidelines, it is ideally performed during the circulation portion of the primary survey to allow for the rapid detection of pathologic pericardial, intraperitoneal, or intrathoracic free fluid. Hemothorax can be identified using the standard flank views where the most dependent portions of the pleural spaces can be imaged. The extended FAST (E-FAST) exam employs additional chest views to evaluate for pneumothorax. The linear ultrasound transducer probe (5 to 10 MHz) is utilized as opposed to the standard curvilinear probe (2.5 to 5 MHz) as the higher frequency enhances visualization of the pleural space. The exam typically begins in the third or fourth intercostal space in the midclavicular line, and evaluation is based on the presence or absence of the parietal and visceral pleura sliding past each other, termed lung sliding.[4] Absent lung sliding suggests the presence of a pneumothorax. Several signs have also been described to aid in the diagnosis, most importantly the lung point sign, where both lung sliding and the absence of lung sliding are visualized in the same sonographic window. The lung point sign has a sensitivity of over 66% and is 100% specific for pneumothorax.

Chest X-ray

Most thoracic injuries can be evaluated by physical exam and chest radiograph. A chest x-ray is fast, easy to obtain, inexpensive, and often readily accessible. Any patient who undergoes an intervention in the trauma bay should have a repeat chest x-ray performed to ensure the adequacy of the procedure. An initial chest x-ray is recommended in any patient who presents after blunt thoracic trauma, but it is not mandatory if the trauma is minor and the patient is not manifesting any physical signs to suggest underlying injury. Based on the NEXUS chest decision rules, patients younger than 60 years old who have no chest pain or tenderness, no distracting injuries or intoxication, and whose mechanism did not involve rapid deceleration do not need a routine chest x-ray.[5] All criteria being met, there is a low likelihood of clinically significant intrathoracic injury, with a negative predictive value of 99%. However, if the patient meets any individual criterion, chest radiography should be performed. Conversely, physical exam alone has not been shown to have adequate diagnostic sensitivity, particularly for pneumothorax, in penetrating trauma patients. Therefore, all patients who suffer penetrating injuries need evaluation with a chest x-ray since many, up to 20%, with negative physical findings will have hemothorax or pneumothorax.

Cross-Sectional Imaging

The use of CT scans in the evaluation of trauma patients has significantly increased. Compared to chest x-ray, chest CT has greater sensitivity for detecting a pneumothorax or hemothorax and also allows for evaluation of the rib cage, the mediastinum, the lung parenchyma, and the aorta. In blunt trauma, the decision to obtain chest CT should be based on physical findings, injury mechanism, and clinical judgment. Patients who are hemodynamically stable with a normal chest x-ray and no sternal, thoracic spinal, or scapular tenderness are unlikely to have a significant intrathoracic injury to warrant CT, as shown by NEXUS.[6] Scanning based on mechanism remains controversial. However, recent studies have also reported a substantial number of patients, up to 19%, with significant underlying injury despite having no clinical symptoms or abnormal findings on chest x-ray.[7] High-risk mechanisms include high-energy deceleration MVC over 30 mph with frontal or lateral impact, MVC with ejection, falls over 7.62 meters (25 feet), and direct chest impact. Therefore, current recommendations are to obtain CT imaging in symptomatic patients and those presenting after high-risk mechanism regardless of symptomatology or chest x-ray findings. In penetrating trauma, there are several indications for CT scanning other than the clinician's judgment. All cases in which the penetrating object crosses the midline need CT scans as there is an increased risk for mediastinal injury in these patients. Patients with symptoms concerning for underlying tracheobronchial, esophageal, or vascular injury or those with symptoms that cannot be adequately explained by chest x-ray require further investigation.

Esophagography, Esophagoscopy, and Bronchoscopy

An esophageal injury is often difficult to diagnose because it lacks specific symptoms. It is rare in blunt trauma and typically occurs in the setting of severe polytrauma, which further complicates the diagnosis. When present, patients may have cervical subcutaneous emphysema, neck hematoma, or bloody aspirate from a gastric tube, none of which are specific. A chest x-ray may demonstrate pneumomediastinum or pleural effusion prompting CT, but definitive diagnosis requires esophagram or endoscopy. Water-soluble esophagram is typically performed first, followed by barium esophagram if suspicion remains. Endoscopy is generally less favored in the acute setting due to fear of exacerbating an existing injury. A tracheobronchial injury is rare in blunt trauma, present in less than 1% of patients, and is seen in the setting of severe high-risk mechanisms. Injuries usually occur within 1cm of the carina and are more common in the right mainstem bronchus as it is less flexible. In penetrating trauma, an esophageal injury is often associated with concomitant tracheal injury due to proximity, and these patients require workup for both. Patients with persistent pneumothorax after tube thoracostomy, a large air leak after, difficulty ventilating, and those with transmediastinal penetrating trauma should all undergo expeditious flexible bronchoscopy.

Treatment / Management

Life-threatening injuries diagnosed during the initial trauma evaluation require prompt intervention. Still, the most common injuries due to thoracic trauma are pneumothorax and hemothorax, which are definitively managed in 80% of cases with tube thoracostomy. The size of the chest tube used is a clinical decision based on the pathology seen on a chest x-ray. If both pneumothorax and hemothorax are present, a size 28-Fr or 32-Fr chest tube is usually considered as this will facilitate the evacuation of both air and blood while minimizing the chance of the tube obstructing due to clot. If no effusion is present, small-bore catheters are appropriate, although many trauma clinicians will still opt for formal chest tubes instead. Occult pneumothorax is a pneumothorax that is seen on CT but not on a chest x-ray. They are incidentally found in 2 to 10% of trauma patients who undergo chest CT. Patients can be observed if the pneumothorax is less than 8 mm.[8] However, occult pneumothoraces are associated with a 5% to 10% risk of expansion and should, therefore, be monitored closely. Patients whose pneumothoraces expand or those who become symptomatic warrant tube thoracostomy.(B2)

Chest wall injuries are common in blunt thoracic trauma, and the vast majority are treated non-operatively. Most of these injuries are seen in the setting of MVCs, especially when patients are seat-belted or sustain frontal impact to the steering wheel. Rib fractures are found in up to 10% of all trauma patients and 30% of patients presenting with chest trauma. Sternal fractures and scapula fractures are less common, accounting for 8% and 3.5%, respectively, of blunt thoracic trauma patients[9]. Rib fractures are diagnosed clinically or radiographically, typically on initial chest x-ray. Patients will complain of pain and dyspnea and, on physical exam, may be found to have tenderness, crepitus, or diminished breath sounds. The latter signs should raise suspicion for underlying pneumothorax. Patients with less than three rib fractures and no associated injuries are appropriate candidates for outpatient management with oral analgesics. However, consideration for outpatient management should be on a case-by-case basis. Patients over the age of 65 and those who are unable to maintain an oxygen saturation of 92% or have an incentive spirometer volume of less than 15 mL/kg should be admitted for respiratory monitoring.[10] All patients with three or more rib fractures or those with displaced fractures are at increased risk for pulmonary complications, such as contusions, pneumonia, and delayed hemothorax, and therefore require admission. Initial management involves providing adequate analgesia, thoracostomy drainage if indicated, and respiratory care, including incentive spirometry. Early and effective pain control is the mainstay of management and is achieved through a multimodal approach. Pain management begins with standing acetaminophen and NSAIDs with opioids administered as needed. Demand-only patient-controlled analgesia (PCA) with opioids is effective when pain is more severe, but patients should be transitioned to oral narcotics as they clinically improve. In patients with multiple or displaced rib fractures and those with pain refractory to pharmacologic management, regional anesthesia techniques are employed. These include the placement of epidural catheters, paravertebral blocks, and intercostal nerve blocks. The EAST trauma guidelines advocate for the use of epidural anesthesia in patients with greater than three rib fractures or patients with fewer fractures but who are over 65 years old or have a significant history of cardiopulmonary disease.[11] Compared to other forms of analgesia, a continuous epidural infusion has not been shown to reduce the need for mechanical ventilation, length of intensive care unit (ICU) stay, or mortality but has been shown to decrease the duration of mechanical ventilation. Paravertebral catheters administer a local anesthetic to the paravertebral space and have comparable efficacy to epidural catheters but with a lower rate of causing systemic hypotension. Surgical rib fixation is reserved for patients in whom adequate analgesia cannot be achieved due to fracture severity and those with impending respiratory failure. It is ideally performed within 48 to 72 hours of injury.(B2)

Flail chest occurs when 3 or more contiguous ribs are fractured in at least 2 locations. This leads to the paradoxical movement of the flail segment during respiration. The injury itself is usually not the cause of respiratory compromise. Respiratory failure in these patients typically results from the underlying presence of a pulmonary contusion. Pulmonary contusions themselves usually progress over the first 12 to 24 hours post-injury, in which time worsening hypoventilation and hypoxemia may necessitate intubation. Initial chest x-ray usually underestimates the degree to which the lung parenchyma is damaged, and patients with pulmonary contusions should, therefore, be admitted and serially monitored for signs of impending decompensation.

Tension pneumothorax is the presumed diagnosis when patients present with chest trauma, respiratory distress, and hypotension. A physical exam will also demonstrate specific clinical signs, such as tracheal deviation away from the affected side, decreased or absent breath sounds on the affected side, and subcutaneous emphysema on the affected side. If recognized in the field, immediate decompression using a 14-gauge needle placed in the second intercostal space in the midclavicular line is indicated. It should be noted that recent data suggests that needle decompression through the fifth intercostal space in the anterior axillary line correlates with a lower chance of failure (16.7%) due to body habitus compared to the midclavicular line placement (42.5%).[12] Once in the emergency department, patients who have undergone needle decompression in the field must then undergo immediate tube thoracostomy for definitive management.(B2)

Massive hemothorax is defined as greater than 1500 mL of blood in the adult population. Although the volume of blood in the pleural space may be estimated on a chest radiograph, the most reliable means for quantification is by tube thoracostomy. In blunt trauma, it is most commonly due to multiple rib fractures with associated lacerated intercostal arteries. However, bleeding can also be due to lung parenchymal lacerations, in which case there is usually an associated air leak. In the setting of penetrating injury, great vessel or pulmonary hilar vessel injury should be suspected. Regardless of the etiology, massive hemothorax is an indication for operative intervention, but the patient's condition should first be stabilized with tube thoracostomy to facilitate lung re-expansion.

Cardiac tamponade is most common after penetrating injury but can also occur due to blunt myocardial rupture, particularly of the atrial appendage. Acutely, less than 100 mL of blood in the pericardial space can cause tamponade. As the pressure in the pericardium rises to match that of the injured chamber, right atrial pressure is overcome, and this leads to decreased filling and reduced right ventricular preload. The classic Beck's triad of muffled heart sounds, jugular venous distention, and hypotension might not be appreciated in the trauma setting due to the often loud environment and the presence of hypovolemia. Patients presenting with hypotension and chest trauma must, therefore, be approached with a high level of suspicion. In the hemodynamically unstable patient, a pericardial drain is placed in the trauma bay under ultrasound guidance. This procedure is successful in approximately 80% of patients and provides sufficient stabilization for transport to the operating room for sternotomy.

Penetrating trauma causes over 90% of great vessel injury compared to blunt trauma. The incidence of blunt aortic injury (BAI) ranges between 1.5 to 2% of patients involved in high-energy blunt trauma, particularly rapid deceleration MVCs, which account for 80% of blunt aortic injuries.[13] Most patients who suffer BAI die in the field from aortic transection. The patients who survive transport to the hospital are those who have sustained contained ruptures or dissections. Undiagnosed injury at the time of presentation significantly increases the chance of rupture in the first 24 hours. Clinical signs are neither sensitive nor specific to diagnose BAI in the hemodynamically stable patient. Therefore, patients who present after high-risk mechanism need to be approached with a high index of suspicion. Initial evaluation involves a chest x-ray which may show a widened mediastinum, an indistinct aortic knob, abnormal aortic contour, pleural blood above the left lung apex referred to as "apical capping," or displacement of the left mainstem bronchus to the right. These findings are not pathognomonic but indicate the need for further testing by CT angiography. A transesophageal echocardiogram (TEE) also serves as an important imaging modality, particularly in patients who are too unstable for transport to CT. TEE has a sensitivity and specificity comparable to that of CTA, and it has the added benefit of being able to be performed on the operating room table. Initial management of aortic injury consists of strict blood pressure and heart rate control with an SBP goal of less than 100 mm Hg and HR less than 100 per minute with intravenous beta-blockade while awaiting surgery. Definitive repair is by either open surgery via left thoracotomy or endovascular repair. Endovascular techniques in BAI have become increasingly popular, and stenting is now the mainstay of management, with success rates ranging from 80% to 100%.[14](A1)

Thoracotomy in the operating room has several indications in thoracic trauma. Most commonly, patients with massive hemothorax over 1500 mL and those with over 200 mL per hr of chest tube output over 3 consecutive hours require an operation. Additionally, those with cardiac tamponade, great vessel injury, massive air leak after thoracostomy placement, diagnosed tracheobronchial injury, and open pneumothorax need surgical repair. However, minimally invasive techniques using video-assisted thoracoscopic surgery (VATS) have been increasingly utilized in hemodynamically stable patients after both blunt and penetrating thoracic trauma. Several series have demonstrated favorable outcomes using VATS, with improved postoperative pain compared to thoracotomy and a shorter duration of thoracostomy drainage.[15] The most common indication is retained hemothorax after thoracostomy, but VATS has also been employed in the management of persistent pneumothorax as well as traumatic diaphragmatic injury.

The utility of resuscitative emergency department resuscitative thoracotomy has been a topic of controversy for many years. Studies have shown that outcomes are based on the location of major injury and whether signs of life are present on arrival. Overall, the survival rate after resuscitative thoracotomy in penetrating trauma is 8.8% versus just 1.4% in blunt trauma. The most favorable outcomes are seen in patients with penetrating cardiac injury who present with signs of life, with an overall survival rate of 19.4%.[16] Conversely, patients who sustain blunt chest trauma have an overall survival rate of 4.6% if signs of life are present on arrival versus 0.7% without. Resuscitative thoracotomy is therefore warranted in patients who present with vital signs or have a history of signs of life in the field.[17][18] General indications are as follows:(B2)

• Witnessed penetrating thoracic trauma with less than 15 minutes of prehospital CPR
• Witnessed blunt thoracic trauma with less than 10 minutes of prehospital CPR
• Witnessed penetrating trauma to the neck or extremities with less than 5 minutes of prehospital CPR
• Persistent, severe post-injury hypotension (systolic blood pressure less than 60 mm Hg) due to cardiac tamponade or massive intrathoracic, intraabdominal, extremity, or cervical hemorrhage.

Differential Diagnosis

The spectrum of injury in blunt trauma is diverse as multiple structures within the thorax may sustain damage simultaneously. Injury can result from direct trauma to the thorax, rapid acceleration or deceleration, crush, or blasts. A patient's external appearance may be deceiving. Injuries to chest wall structures, particularly the ribs, are frequent in blunt trauma and are readily diagnosed clinically or radiographically. Life-threatening injuries may be present with no obvious external signs of significant trauma, and these patients must be approached with a high index of suspicion. High-speed MVCs, lack of a seatbelt, extensive vehicle damage or steering wheel deformity, concomitant head, abdominal, or major bony injuries, and chest wall bruising are all factors associated with a higher risk of underlying thoracic injury. Penetrating trauma, by definition, results in a violation of the chest wall. The damage sustained to intrathoracic structures is based on the trajectory of the penetrating object. Hemodynamic instability suggests cardiac tamponade, great vessel injury with massive hemothorax, or tension pneumothorax. In stable patients, hemothorax and pneumothorax are common injuries and should rapidly be diagnosed. Further workup should be performed in stable patients if there is suspicion for underlying esophageal or tracheobronchial injury, particularly when wounds are present within the anatomic borders of the "cardiac box."

Prognosis

The prognosis for thoracic trauma can vary widely, given that thoracic injuries can range from simple rib fractures to pneumothoraces to direct penetrating cardiac injuries. Ultimately the degree and mechanism of injury combined with the patient's underlying comorbidities determine the prognosis of a patient who has suffered thoracic trauma.

Complications

The chances of a major complication can range from minimal for simple rib fractures to very likely if a major intervention is required or the degree of injury is significant. Given the number of vital structures in the chest, complications can frequently be significant, including damage to the vagus or phrenic nerves, the thoracic duct, or critical vascular structures with concomitant complications arising. The degree and mechanism of injury and the interventions taken to address them ultimately determine the type and severity of complications that may arise.