Pulmonary complications of trauma (Proceedings)
Each trauma patient should be evaluated in an orderly and systematic manner. It is the job of the triage team to evaluate and treat injuries interfering with vital physiological functions. While trauma by its very nature is a polysystemic disease, pulmonary complications present one of the most common, and life-threatening aspects of trauma triage. It is the purpose of this lecture not to review trauma triage, but to concentrate on the pathophysiology, diagnosis, and treatment of traumatic injury to the respiratory tract. These injuries require immediate recognition and treatment, as aggressive fluid therapy can make some of these injuries worse. It is important to assume some degree of thoracic and pulmonary injury in all trauma patients. In one study, thoracic injuries were present in 58% of the dogs presented for treatment of orthopedic injures. Pulmonary contusions, pneumothorax, and fractured ribs were most commonly observed.
Lung contusion is the most common acute pulmonary complication of blunt chest trauma. Such a contusion may occur under the site of a flail chest or independent of obvious external injury. A large bruise in a very bad place, the conutsed alveoli fill with blood, and fluid resulting in atelectasis. Hypoxemia will result from pulmonary shunt as blood flows through these non-ventilated portions of lung. With time, pulmonary contusions appear radiographically as a diffuse interstitial to alveolar lung pattern. The location varies with the injury. It is important to note that contusions may not be evident on radiographs for several hours after the injury so a radiograph taken on admission may not reveal the severity of the injury.Complicating trauma management is evidence that respiratory insufficiency following pulmonary contusion may be iatrogenic. The use of large volumes of rapidly administered crystalloid solutions can exacerbate the fluid loss into damaged tissues worsening the hypoxemia associated with the contusions. Maintaining plasma colloid oncotic pressure with the use of plasma or other colloid solutions may lessen the occurrence of respiratory insufficiency by preventing water loss into the injured lung. We use conservative fluid replacement in trauma patients with pulmonary contusions. Using a combination of crystalloid fluids (22-44 ml/kg, ¼ to ½ of a typical shock volume) and colloid solutions (plasma, whole blood, Oxyglobin®, or hydroxyethyl starch) we strive to maintain a minimally acceptable blood pressure (mean pressure of 60 mmHg) while avoiding iatrogenic pulmonary fluid overload. Patients with severe contusions may present with or develop hemoptysis. Blood from the mouth, agitation and respiratory distress are all indications that pulmonary parenchymal hemorrhage is ongoing and aggressive treatment is necessary. These patients are quickly restrained (fast acting anesthetic or a paralytic) and intubated. Ventilating with 100% oxygen and 5-10 cm H20 positive end-expiratory ventilation will help keep remaining alveoli open, and open atelectic lung units. Patient tidal volume should be monitored closely as positive pressure ventilation and damaged lungs can lead to a tension pneumothorax.
Simple pneumothorax occurs when gas accumulates in the pleural space but pleural pressure does not significantly exceed atmospheric pressure. Gas can enter the space either from outside the chest wall, as occurs with bite wounds, sharp objects, or weapons, or via the lung through a tear in the lung parenchyma. Small amounts of gas cause pleural pressure to increase slightly, but it remains sub atmospheric during inspiration because it is in equilibrium with the negative alveolar pressure. Although pleural and alveolar pressures become positive during forced expiration, slight separation of the pleural spaces does not compromise ventilation. If the pneumothorax is small and the pleural leak seals itself, the gas will be absorbed as a result of partial pressure differences between gas in the pleural space and in the blood. Tension pneumothorax is characterized by a progressive increase in pleural pressure sufficient to impair circulation. This occurs as gas enters the pleural space and remains there during expiration because tissue or fluid occludes the pulmonary parenchyma. While tension pneumothorax can occur during spontaneous negative pressure inspiration, it is more likely with intubated patients receiving positive pressure ventilation. The accumulating gas not only collapses the lungs but also interferes with venous return to the right atrium. Thoracocentesis is preferred in the initial evaluation of thoracic injury. With a 20-gauge needle attached to an intravenous extension set, 3-way stopcock, and 60 ml syringe, one will aspirate air, fluid, or both. It is advisable to aspirate from both right and left sides of the thorax.
A thoracostomy tube allows rapid, continuous evacuation of air or fluid from the pleural space. If it becomes necessary to use needle thoracocentesis more than twice to alleviate dyspnea, placement of the thoracostomy tube is necessary. Before placing the tube, a sterile preparation of the thorax is provided. Insertion is best accomplished with a stylet enclosed in the tube in order to avoid unnecessary dissection of subcutaneous tissues the thoracostomy tube can be either intermittently drained with a syringe, or continuously evacuated using controlled suction. Intermittent syringe evacuation is the only way to quantify the volume of air removed.
The thoracostomy tube is removed when the pleural leak has sealed and the lungs have re-expanded and/or when fluid drainage has decreased in blunt trauma this is usually one to three days. Physical examination and chest roentgenograms are used to determine suitability of drain removal. Additionally, daily cytological evaluation of the thoracic effluent should be monitored for incidence of infection.
Rib fractures are painful and limit diaphragmatic and chest wall motion. Failure to adequately expand the lungs results in atelectasis of the underlying lung and hypoxemia. Flail chest occurs when three or more ribs, or the junction of ribs and the sternum, are each fractured at two points. This results in paradoxical inward movement of the flail segment during inspiration when the rest of the thoracic cage expands. Because the hypoxemia associated with flail chest results from atelectasis due to pain and contusions of the lung underlying the flail segment, therapy is aimed at relieving pain through analgesics and local blocks, supplemental oxygen, and supportive measures while the contused lung heals.