What are the management options for flail chest and pulmonary contusion?
The presence of a flail segment obviously suggests an underlying pulmonary contusion, but if the patient is breathing rapidly and shallowly, this sign may not be evident. It should be emphasized, however, that neither the extent of the flail nor the number of ribs fractured accurately predicts respiratory failure. Chest wall bruising, rib cage deformities, and crepitus and/or pain during palpation of the thorax should suggest the presence of rib fractures or dislocation even in the presence of a normal chest radiograph. Cartilaginous injuries and fractures of poorly calcified ribs may not be detected by chest radio-graph. The initial film often does not show an underlying lung injury since pulmonary edema appears late. If present, a focal infiltrate beneath an area of multiple rib fractures makes the diagnosis of pulmonary contusion. Clinical signs such as dyspnea, tachypnea, intercostal muscle retrac-tion, and the use of accessory muscles of respiration should suggest underlying lung pathology. Monitoring with pulse oximetry in the initial stage is useful only if the patient is breathing room air; supplemental oxygen administration may mask inadequate ventilation, delaying the diagnosis and maneuvers that restore FRC and lung compliance toward normal. Likewise, arterial blood gases measured with the patient breathing room air may be useful. Of course, managing these patients without supplemental oxygen necessitates direct observation by a physician or qualified person. The usual pattern is a progressive decrease in arte-rial oxygen (PaO2) and increase in carbon dioxide (PaCO2) tensions resulting in a decrease in pH (respiratory acidosis). Although arterial hypoxemia may precede radiographic abnormalities, it may not reflect the size of the contusion because of restriction of blood flow to the injured lung by hypoxic pulmonary vasoconstriction. A PaO2/FIO2 <300 after the initial resuscitation phase is considered a risk factor for the development of subsequent acute respiratory failure. Quantifying the contusion volume with a chest radiograph, and preferably with a CT scan, may have a prognostic value for identifying the patient who will develop acute respira-tory distress syndrome (ARDS). Patients with contusion volumes greater than 20% of total lung volume are more likely to develop ARDS and pneumonia.
Early treatment is of utmost importance. A delay of even a few hours may result in progression of underlying lung pathology, with increasing morbidity and mortality. The goal is to decrease elastic recoil and the work of breathing, and to improve arterial blood gases without adverse hemodynamic effects. In patients without acute respiratory failure or associated injuries requiring tracheal intubation this can best be accomplished by continuous positive airway pressure (CPAP) of 10–15 cm H2O applied by face mask. The routine use of early tracheal intubation and mechanical ventilation with alveolar recruitment maneuvers, the usual practice before 1975, has fallen into disfavor because of an unacceptably high incidence of tracheobronchitis and pneumonia leading to sepsis, multiorgan failure, and death. At present, except in instances when tracheal intubation and mechanical ventilation are necessary (PaO2 <60 mmHg in room air, or <80 mmHg with supplemental oxygen, and conditions other than thoracic injury), the vast majority of patients do well with CPAP. When impending respiratory failure indicates tracheal intu-bation, airway pressure release ventilation (APRV) may be a reasonable choice. With this mode of ventilation in the spon-taneously breathing patient, CPAP is intermittently decreased for short periods with the device shown in Figure 79.1. In other words, spontaneous breathing is superimposed on mechanical ventilation. In addition to decreased work of breathing, the advantages of this technique over controlled mechanical ventilation are improved ventilation/perfusion (V/Q) matching, increased systemic blood flow, lower sedation requirement, greater oxygen delivery, and shorter periods of intubation.
In patients with severe life-threatening unilateral pul-monary contusion unresponsive to mechanical ventilation or APRV, differential lung ventilation via a double-lumen endobronchial tube should be considered. In bilateral severe contusions with life-threatening hypoxemia, high-frequency jet ventilation has been shown to improve systemic oxygenation effectively (Figure 79.2). This mode of ventilation may also improve depressed cardiac function caused by concomitant myocardial contusion or ischemia.
Irrespective of the mode of ventilation, effective removal of tracheobronchial secretions has a significant effect on outcome. Likewise, monitoring with pulse oximetry, an arterial line and, when indicated, a pulmonary artery catheter is important. The pulmonary artery catheter not only guides fluid management, which should be adjusted to the mini-mum consistent with adequate end-organ perfusion, but it also helps in ventilatory management, as it permits calcula-tion of oxygen delivery and intrapulmonary shunt fraction and thus helps to adjust the optimal level of CPAP.
Supplemental oxygen should be administered judiciously in order to permit the acquisition of maximal information from the initial oxyhemoglobin saturation with pulse oximetry or arterial blood analysis, as well as to avoid its detrimental effects, such as absorption atelectasis, interfer-ence with hypoxic pulmonary vasoconstriction in damaged lung regions, decreased mucociliary clearance, free radical formation, and decreased surfactant production.
Overzealous fluid infusion may result in an increase in the size of the lung contusion and a decrease in PaO2. Although it is possible to remove excess fluid with diuret-ics, their use is associated with electrolyte abnormalities, cardiac dysrhythmias, and hypovolemia. At least during initial resuscitation, the type of fluid used does not seem to affect outcome. Crystalloid solutions are favored because they are less expensive. In the presence of concomitant blunt cardiac injury, the complications of pulmonary contusion can easily confuse the clinical picture. In this situation, transesophageal echocardiography (TEE) or, if TEE is not available, pulmonary artery and wedge pressures are the best guides to fluid management.
Continuous epidural analgesia is the best pain manage-ment technique available for blunt chest trauma. It improves lung function and thus decreases overall morbidity. Other modalities, such as parenteral opioids, are not nearly as effec-tive, while multiple intercostal blocks are labor-intensive and short-lasting, and thus must be repeated at least twice a day. Continuous thoracic paravertebral block has been described but awaits further clinical evaluation.