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Complications of pulmonary and pleural injury
Chest trauma is the primary cause of death in up to 25% of fatalities following traumatic injury and a major contributing factor in another 25%. As few as 5% to 15% of these patients require acute operative intervention. Based on these generalizations, it is accepted that overall chest injury is common, acute operative intervention is uncommon, and a significant, although ill defined, number of thoracic operations are performed for delayed complications. The actual incidence of each of these varies based on the ratio of blunt to penetrating trauma admissions as well as overall volume. Pulmonary complications can result from direct injury to the lung secondary to the response to trauma outside the thorax. Significant injury-related changes in lung function can lead to interference in ventilation or pulmonary perfusion. Thus, contemporary management strategies include acute resuscitation approaches that mitigate lung injury, a high degree of suspicion for pulmonary injuries and delayed complications, and early and aggressive treatment of such complications.
Pulmonary complications
Pulmonary contusion
Pulmonary contusion, or lung bruising, is a generic term for a protean of manifestation of injury to the lung parenchyma. As many as 75% of patients who sustain blunt trauma to the chest will suffer a pulmonary contusion, with mortality rates of up to 40% documented in the literature. Bleeding into the lung parenchyma as a result of injury sets up a cascade of pathophysiologic changes that are typically worst in the first 48 hours after injury, and most commonly subside by 7 days. A high degree of suspicion is needed in the management of these injuries as radiologic findings lag time line of injury. Judicious use of resuscitation fluids is essential. Computed tomography (CT) is a more sensitive imaging modality as compared with plain chest radiographs. Factors that influence the degree of injury include mechanical forces such as the tearing of lung tissue by rib fractures or chest wall compression; bleeding into lung segments surrounding the direct impact area leading to bronchospasm; atelectasis adjacent to contused lungs; and pulmonary dysfunction as a result of increased mucus production and decreased production of surfactant by injured alveolar tissues. Alveolar ventilation is reduced in the contused lung. Ventilation-perfusion mismatch in the areas of lung contusion can lead to increase in intrapulmonary shunt from local vasoconstriction and subsequent loss of lung compliance. At the cellular level, impairment of the mucociliary function and pulmonary macrophage and lymphocytic activity make the patient susceptible to pneumonia.
In the acute phase, minimizing crystalloid resuscitation is associated with reduced respiratory failure. The current approach of using blood products rather than crystalloid resuscitation has been associated with a reduction in respiratory failure, ventilator days, and mortality. However, while the use of blood product-based resuscitation is associated with a reduction in parenchymal complications when compared with crystalloid, large-volume resuscitation is still associated with an increase in adult respiratory failure.
Management of patients with pulmonary contusions is primarily supportive. The objectives of pulmonary physiotherapy measures are to improve respiratory mechanics, help clear the bronchopulmonary tree from secretions, and decrease the areas of lung with atelectasis surrounding the contusion. Judicious fluid administration, control of pain associated with chest wall injuries, and careful hemodynamic monitoring are critical in the first few days after injury. The larger the area of pulmonary contusion, the higher the likelihood the patient will require mechanical ventilation. Severe unilateral pulmonary contusions may need the aid of independent mechanical ventilation via a double-lumen endotracheal tube to prevent barotrauma to the unaffected lung and undertreating the affected lung. While using mechanical ventilation, tidal volume and positive end-expiratory pressure (PEEP) should be adjusted by following serial measurements of intrapulmonary shunt (Qs/Qt).
Considerable controversy exists over the role of noninvasive ventilation (NIV) in the trauma patients. NIV includes noninvasive variable positive airway pressure (most commonly “bilevel”) devices consisting of a higher inspiratory positive airway pressure and a lower expiratory pressure as well as continuous positive airway pressure delivered using various nasal, oronasal and facial interfaces. Although the use of noninvasive positive-pressure ventilation has been described for nontrauma patients with acute hypoxic respiratory failure, as repeated from a series from Australia consisting of 75 patients, caution is needed for the use of such therapies in the acutely injured trauma patient. Intermittent positive-pressure breathing pushes a set volume of air to a preset pressure. Complications with such a modality include increased incidence of pneumothoraces in those with underlying lung disease, worsening of air leaks from parenchymal injuries, and associated abdominal distention and bloating as air can go down into the gastrointestinal tract. High-flow nasal oxygen (HFNO) administration is a relatively new technique that is used in the intensive care unit and increasingly in the operating room. HFNO has become popular in the intensive care unit for management of patients with acute hypoxemic respiratory failure when attempting to avoid intubation or to help after extubation. In some anesthesia contexts, HFNO has been referred to as THRIVE—an abbreviation for T ransnasal H umidified R apid- I nsufflation V entilatory E xchange. Active research is ongoing as to the wider applications of HFNO but its use in pulmonary contusion have not been validated. The Official European Respiratory Society / American Thoracic Society clinical practice guidelines on the use of NIV for acute respiratory failure do not address the use of NIV for pulmonary contusion, and given the uncertainty of the evidence they are unable to offer a recommendation for the use of NIV for de novo acute respiratory failure. Hence, trying to find the small category of trauma patients who may benefit from noninvasive positive-pressure ventilation is very difficult in the acute trauma setting, and largely unsubstantiated and investigated. Current Advanced Trauma Life Support protocols recommend that patients with significant hypoxia (Pao 2 < 70 mm Hg on room air, Sao 2 < 90%), hypoventilation (Paco 2 > 45 mm Hg), or altered mental status should be intubated within the first hour of injury. In patients with severe respiratory failure or adult respiratory distress syndrome (ARDS) several ventilatory strategies and advanced treatment modalities may be considered. Prone positioning leads to improved aeration of the posterior, dependent portions of the lung, leading to improved oxygenation and decreased ventilator-induced lung injury. Relative contraindications include intracranial pressure > 30 mm Hg, unstable pelvic and/or spine fractures, severe facial trauma, recent sternotomy, and/or anterior chest tube with active air leak.
Three main rescue modes of mechanical ventilation have been utilized. High-frequency oscillatory ventilation, while promising, has not been shown in randomized controlled studies to show a mortality benefit. Airway pressure release ventilation, utilizing constant continuous positive airway pressure with intermittent release to allow CO 2 removal, can be utilized on a patient who is spontaneously ventilating. Its efficacy is linked to the correct setting of release time; if too short, CO 2 removal is impeded; if too long, excessive exhalation can lead to volume loss and lung injury. Its efficacy or superiority has not been proven. Volume diffusive respirator uses percussive ventilation, which has the benefit of clearing airways and has been proven as a rescue ventilation mode in trauma patients. Patients do need to be sedated and often medically paralyzed with this mode. In practice, surgical critical care units use either airway pressure release ventilation or volume diffusive respirator based on their institutional experience.
Extracorporeal membrane oxygenation (ECMO) is a salvage therapy that is gaining increasing use in the trauma patient, including in the management of survivors of battlefield injury. In most trauma patients, cardiac function is sustained, allowing venovenous cannulation. While adequate oxygenation and ventilation are maintained by the circuit, ongoing ventilatory-induced lung injury may be reduced by minimizing ventilator settings or even extubating the patients. In the setting of persistent air leak, this reduction in airway pressures may help facilitate healing. Concerns for the use of ECMO in trauma patients are largely related to bleeding risk. Using heparin-bonded circuits, and in some cases no heparin strategies, bleeding risk can be mitigated albeit with an increased risk of thromboembolic complications. Understanding that heparin doses can be reduced means that traumatic brain injury is a relative, not absolute, contraindication. Retrospective reviews suggest that survival ranges from 44% to 70%, cerebrovascular complications range from as low as 14% to as high as 75% depending on heparin loads, and major bleeding complications range from 35% to 70%. The use of ECMO on trauma patients remains relatively limited to high-volume centers with established ECMO experience in other disease states.
Persistent air leak
Persistent air leaks may occur in one of three scenarios: after parenchyma injury, after anatomic lung resection, and in mechanically ventilated patients.
Persistent air leak after parenchymal injury
Injuries to the lung parenchyma can occur as a result of penetrating injury or blunt trauma with maceration or rib penetration or in patients with underlying predisposing parenchyma lesions such as bullous emphysema. Principles of management follow the algorithm for management of spontaneous pneumothorax. Simple tube thoracostomy with reexpansion of the collapsed lung is sufficient treatment in more than 80% of cases with the lung visceral pleura quickly sealing itself. Prospective studies have shown that placing the chest drain to water seal (i.e., off suction) after 48 hours will hasten resolution of the air leaks as the transpleural gradient is diminished. After ruling out technical factors (tube dislodgment or disconnection), air leaks lasting more than 3 days or associated with recurrent pneumothorax are indicative of a visceral pleural injury that needs adjuvants to seal. These persistent air leaks are most efficiently managed by thoracoscopic approaches rather than persistent chest drainage. Schermer reviewed the course of 39 trauma patients who, except for air leak, were ready for discharge (air leak > 3 days’ duration). Twenty-five agreed to video-assisted thoracoscopic surgery (VATS) with reduced chest tube duration (total 8 vs. 12 days) and length of stay (10 vs. 17 days).
CT scans can help define local lesions that may be amenable to thoracoscopic wedge resection or application of biologic sealants, which may also prompt earlier VATS. Carrillo reported a series of 11 patients who had persistent air leak (mean 6 days) following trauma (10 blunt). In 10 patients the source of the air leak was identified, and a segmental stapled resection was performed, and the last patient had a chemical pleurodesis. All chest tubes were removed within 48 hours, and nine patients were discharged home in 72 hours. In many instances, simply breaking down soft loculations and placing a chest drain under direct vision is the primary therapeutic benefit of thoracoscopy. We use pleural abrasion rather than chemical pleurodesis because it reduces the risk of parenchyma trapping and lacks the uncertain long-term impact of chemical agents in younger patients. Patients with underlying lung lesions should be managed as they would in nontrauma circumstances. A final option in patients with prohibitive operative risks or small leaks is to convert the patients to Heimlich valve and manage them as outpatients. As many as 80% will seal within 3 weeks using this approach.
Persistent air leak after pulmonary resection
As lobectomy and pneumonectomy are rarely performed for traumatic injury, it follows that the incidence of air leak (bronchopleural fistula, or BPF) is also small. However, the nature of acute lung resections is such that the risk is higher than after elective resection. Risk factors include long stumps, devascularization, and contaminated hemothorax. Ideally after lobectomy/pneumonectomy the stump should be reinforced at the time of original resection or during second-look exploration with pleural, intercostal, or another flap. A Brewter patch consisting of pericardial or pleural fat may also be applied. Once an air leak occurs, management is determined by timing (less than or more than 7 days postoperatively), degree or severity of air leak (ventilatory compromise and whether the defect can be visualized endoscopically), physiologic status, and whether or not the patient is mechanically ventilated. BPF may present in stable patients as a new productive cough, with a drop in pleural fluid levels (after pneumonectomy) of two or more rib spaces, or new air-fluid level. In ventilated patients, empyema and loss of tidal volume may predominate. The primary goal is to prevent aspiration. In nonintubated patients this is best accomplished by positioning upright or with affected side down. If there is not a drain in place, a new drain should be placed above the thoracotomy scar because the diaphragm tends to rise to the level of the scar and adhere. If the leak is small, and endoscopically the hole cannot be visualized clearly, it is reasonable to attempt bronchoscopic glue application.
Reoperation and stump closure are possible within 7 days, but the associated empyema increases the risk of failure. The longer the interval between the initial and second operations, the greater the technical difficulty. After pneumonectomy the mediastinum becomes inflamed and the stump is challenging to visualize, and mobilization is essentially impossible. Thus, after pneumonectomy the best option is probably to occlude the stump with omentum, pack the chest with packs, and plan serial washouts until the leak scarifies closed. An alternative approach, particularly after right-sided pneumonectomy, is to perform transcarinal right main bronchus resection. The residual stump cannot be removed as it tends to be fixed, but the mucosa should be cauterized and omentum or other viable tissue used to reinforce the new stump. The empyema cavity can then be treated by the drainage procedure of the surgeon’s choice. After lobectomy, similar options are possible, but further resection may be required (e.g., right middle lobectomy after right lower lobe stump leak). The management of the residual space may involve open chest drainage or a variety of space-filling options, as will be discussed in the section dealing with empyema.
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