Chapter 19: Chest Trauma

Although the chest wall can absorb significant amounts of trauma without serious injury to the patient, chest trauma is a frequent indication for critical care and mechanical ventilation. Unlike other disease states requiring mechanical ventilation (eg, chronic obstructive pulmonary disease [COPD]), patients suffering chest trauma are typically young and previously healthy and an increasing number are being managed with noninvasive approaches.

Blunt Chest Trauma

With blunt chest trauma, there are often no exterior signs or symptoms of injury to the chest. Clinical entities associated with blunt chest trauma include fractures, pulmonary contusion, tracheobronchial injury, myocardial and vascular injury, esophageal perforation, and diaphragmatic injury. Fractures can involve the ribs, sternum, vertebrae, clavicles, or scapulae. Of these, rib fractures are the most common. Rib fractures without flailing can be painful, resulting in splinting, atelectasis, and hypoxemia due to ventilation/perfusion mismatching. Isolated rib fractures almost never necessitate mechanical ventilation unless they are associated with other injuries such as pulmonary contusion. Flail chest is a loss of stability of the rib cage caused by multiple rib fractures, which frequently results in significant ventilatory disturbances due to underlying damage to the lung parenchyma, inefficient expansion of the thorax due to paradoxical movement of the chest wall, and pain leading to hypoventilation. Until recently, it was common practice to internally stabilize the rib cage in patients with flail chest by use of positive pressure ventilation and positive end-expiratory pressure (PEEP). Many patients with flail chest are now adequately managed without intubation and mechanical ventilation. This is particularly the case with appropriate pain control and noninvasive ventilation (NIV). It is now generally accepted that mechanical ventilation is only required for patients with flail chest if one of the following is present: shock, closed head injury, need for immediate operation, severe pulmonary dysfunction, or deteriorating respiratory status.

Pulmonary contusion results from high impact blunt chest trauma, which produces leakage of blood and protein from the vascular to the interstitial and alveolar space of the lungs. Clinically, pulmonary contusion is similar in presentation and treatment to acute respiratory distress syndrome (ARDS). If the contusion is localized, high levels of PEEP may produce a paradoxical decrease in arterial oxygenation because blood may be diverted from normal to the injured lung increasing shunt fraction. Mild to moderate forms of pulmonary contusion may not require intubation, and hypoxemia can be adequately treated with oxygen and mask continuous positive airway pressure (CPAP) or NIV.

Tracheobronchial injuries most often occur near the trachea or near the origin of the mainstem bronchi. If they are small and do not result in pneumothorax, these may heal spontaneously. Tracheobronchial injuries that result in large air leaks and pneumothorax require surgical repair. Patients with tracheobronchial injuries may require mechanical ventilation following thoracotomy, particularly if other injuries compromising pulmonary function are present.

Myocardial injuries associated with blunt chest trauma are most often in the form of myocardial contusion. Myocardial contusion can result in arrhythmias, but rarely results in cardiac failure. The need for mechanical ventilation is rare in patients with myocardial contusion who do not have other associated injuries such as rib fractures and pulmonary contusion. Injuries to the thoracic vasculature can result in significant hypotension and the need for emergent thoracotomy. Patients with these injuries typically have multiple chest injuries and require mechanical ventilation.

Diaphragm injury secondary to blunt chest injury is very rare. This injury almost always requires operative repair. Patients with diaphragmatic injury may require postoperative mechanical ventilation and may be difficult to wean due to diaphragmatic weakness.

Penetrating Chest Trauma

Penetrating injuries can affect the lungs, the heart, and/or the vasculature, and almost always require surgical intervention. When associated with tension pneumothorax and/or significant blood loss, penetrating injuries can be immediately life-threatening. A tension pneumothorax can be rapidly corrected by insertion of a chest tube, and mechanical ventilation may not be required. Many penetrating chest injuries require extensive surgical repair, and mechanical ventilation is frequently required postoperatively.

Indications

Indications for mechanical ventilation in patients with chest trauma are listed in Table 19-1. None of these indications are absolute, and each is dependent on the corresponding level of respiratory failure. Flail chest with paradoxical chest movement was once considered an absolute indication for positive pressure ventilation. However, many cases of flail chest are now managed effectively without intubation and mechanical ventilation. ARDS is a common complication of chest trauma, and may occur without associated chest contusion. When ARDS occurs in association with chest trauma, its management is similar to that with other causes of ARDS. Pain control is an issue in many patients with chest trauma. If large doses of narcotic pain control are required, respiratory depression may occur and mechanical ventilation may be necessary. Epidural narcotics, patient-controlled analgesia, and intercostal nerve blocks are used to control pain without associated respiratory depression.

Mask CPAP and Noninvasive Ventilation

The use of NIV has become increasingly common in the patient with chest trauma. The early use of NIV in patients with chest trauma facilitates stabilization of the chest, promotes recruitment of collapsed lung regions, and significantly reduces mortality and intubation rate without increasing complications. Some of these patients are managed with 8 to 12 cm H₂O CPAP and Fio₂ adjusted to maintain the Pao₂ more than 60 mm Hg. In some patients, NIV is indicated due to increased work-of-breathing. However, the patient who is requiring increasing levels of CPAP, Fio₂, or ventilatory support should be considered for invasive ventilation. Intubation is usually required if the patient is also hemodynamically unstable.

Ventilator Settings

Recommendations for initial ventilator settings in patients with chest trauma are listed in Table 19-2. Initially, full ventilatory support using volume control or pressure control is frequently used (Figure 19-1). However, some patients who are well managed for pain and are hemodynamically stable do well on pressure support.

Oxygenation is dependent on Fio₂, PEEP, the extent of pulmonary dysfunction, and hemodynamic stability. The initial Fio₂ should be set at 1, and then titrated to the desired level of arterial oxygenation using pulse oximetry. Generally, the initial PEEP level should be set at 5 cm H₂O. If the patient has significant barotrauma (eg, subcutaneous emphysema, pneumothorax, air leaks from chest tubes), then it may be desirable to set the initial PEEP at 0 cm H₂O. If the patient has significant pulmonary shunt, a trial of higher PEEP is appropriate. In patients with chest trauma, however, caution must be exercised when increasing airway pressure because barotrauma is common. As the result of blood loss, hemodynamic instability may result when PEEP is increased, and increasing PEEP may increase intracranial pressure in patients with associated head trauma. If a unilateral pulmonary contusion is present, care must also be exercised when increasing PEEP. With unilateral lung disease, PEEP may result in shunting of blood from higher compliance lung units to low-compliance nonventilated areas, which will result in increasing shunt and hypoxemia. With unilateral pulmonary contusion, lateral positioning with the contused lung up may be more beneficial than increasing PEEP.

With either volume ventilation or pressure ventilation, the plateau pressure should be kept below 30 cm H₂O. In trauma patients with satisfactory lung compliance (eg, postoperative thoracotomy), tidal volumes of 6 to 8 mL/kg of ideal body weight can be used with plateau pressure of less than 30 cm H₂O. Patients with pulmonary contusion and ARDS may require tidal volumes of 4 to 8 mL/kg to keep plateau pressure less than 30 cm H₂O. An initial respiratory rate of 15 to 25/min is often adequate. Respiratory rate is increased if required to establish a desired Paco₂. Permissive hypercapnia is generally well tolerated in chest trauma patients, provided that there is no accompanying head trauma with increased intracranial pressure. An inspiratory time less than or equal to 1 second is usually adequate in patients with chest trauma.

Monitoring

Monitoring the mechanically ventilated chest trauma patient is similar in many aspects to that with any mechanically ventilated patient (Table 19-3). Air leak is more likely in patients with chest trauma, and signs of air leak must be assessed frequently. Pneumothorax should be considered following any rapid deterioration of the mechanically ventilated chest trauma patient. Chest trauma patients should be ventilated at the lowest peak alveolar pressure and PEEP level that produces adequate arterial oxygenation. Auto-PEEP must be avoided. Pulmonary embolism is also common in these patients, and should be considered if clinical status rapidly deteriorates. As is the case with many surgical patients, fluid overload frequently occurs and is associated with shunting and decreased lung compliance. With prolonged mechanical ventilation, nutritional support is necessary to facilitate healing and weaning from mechanical ventilation.

Liberation

Discontinuation of mechanical ventilation can occur early and quickly in many chest trauma patients, such as those ventilated postoperatively following repair of a penetrating chest injury. Many of these patients have no previous cardiopulmonary disease and recover rapidly if there are no associated problems (eg, head trauma, ARDS). Those who have severe pulmonary contusion and ARDS may have a long mechanical ventilation course that may be complicated with pulmonary infection, empyema, sepsis, and pulmonary embolism. Ventilator liberation may be difficult in some of these patients, particularly if they develop multisystem failure. These patients may require prolonged weaning with periodic spontaneous breathing trials. Weaning may also be difficult in patients with severe chest wall injury or diaphragmatic injury. For patients who are difficult to wean, the goals should be treatment of injuries and preexisting medical conditions, bronchial hygiene (eg, secretion removal), nutritional support, and strengthening and conditioning of respiratory muscles (ie, periods of spontaneous breathing at subfatiguing loads).