Several life-threatening thoracic injuries should be recognized and treated during the initial survey. These are airway obstruction (noted above), tension pneumothorax, cardiac tamponade, massive hemothorax, open pneumothorax, and flail chest.
TENSION PNEUMOTHORAX The diagnosis of tension pneumothorax should be suspected based on clinical grounds alone. The presentation includes dyspnea, hypoperfusion, distended neck veins, diminished or absent breath sounds on the affected side, a hyperresonant percussion note on the affected side, and tracheal deviation to the opposite side. Not all elements of the presentation need be present to suspect the diagnosis. For example, the noise in the resuscitation area makes the percussion note difficult to hear. Also, distention of the neck veins may be absent in the face of hypovolemia.
If a tension pneumothorax is suspected, the next intervention must be the insertion of a small cannula (typically a 14-gauge intravenous catheter) through the chest wall into the pleural space. The purpose of this intervention is to convert the tension pneumothorax into an open pneumothorax. Although the classic description of this maneuver places the insertion point at the second interspace in the midclavicular line, any point in the superior, anterior, or lateral chest wall may be selected. Once the tension pneumothorax is decompressed (a hiss of gas exiting the pleural space may be audible) the patient's perfusion often improves within seconds. The initial survey should be completed and a chest tube (tube thoracostomy) inserted on the side of the tension pneumothorax as soon as practicable. Lack of improvement following decompression means that another cause of hypoperfusion should be sought immediately. If the neck veins remain distended, cardiac tamponade from pericardial blood (pericardial tamponade) must be suspected and treated immediately.
An x-ray of the chest should not be obtained in the patient with a suspected tension pneumothorax until after tube thoracostomy has been performed and the patient's perfusion improved.
PERICARDIAL TAMPONADE (CARDIAC TAMPONADE) Both blunt and penetrating thoracic injuries have the potential to cause blood to accumulate in the pericardium. Although stab wounds to the midchest are the most common cause, blunt compressive forces to the anterior heart can rupture the right atrium or its appendage while maintaining enough filling of the right ventricle to sustain life for a short interval. In either case, blood fills the poorly compliant pericardial sac, with pressure increasing sharply as each small increment of fluid accumulates.
The presentation of tamponade is similar to that of tension pneumothorax: both lesions cause obstruction of venous return to the heart. In addition to hypoperfusion and distended neck veins, the patient with tamponade may have "muffled" heart tones—muffling that is hard to hear in the busy environment of a trauma resuscitation. However, breath sounds should be audible bilaterally and the trachea should lie in the midline.
While the initial treatment of tamponade is emergency pericardiocentesis (described further on), immediate surgical intervention is required to control the bleeding. An intravenous bolus of fluid to transiently increase the pressure filling the right atrium may be helpful to increase cardiac output for a minute or two while preparations are being made for the pericardiocentesis and/or immediate surgical intervention.
Again, radiographs are conspicuous by their absence from this discussion. The poorly compliant pericardium, although full and under pressure from the blood within, casts a rather ordinary shadow on the chest x-ray. As little as 150 to 200 mL of blood may result in cardiac tamponade. Therefore, chest radiographs cannot be used to exclude this life-threatening diagnosis.
If surgery cannot be performed immediately, it may be wise to leave a cannula within the pericardial sac for serial aspirations as surgical preparations are being made. Aspiration of only 5 to 10 mL of fluid can substantially improve cardiac performance—again a consequence of the rigidity of the pericardium.
MASSIVE HEMOTHORAX Each hemithorax can potentially hold about 40 to 50 percent of the human circulating blood volume. While the hemithorax is ordinarily filled with air, a small amount of blood, and the tissues of the lung, blood can accumulate rapidly in the pleural space. A massive hemothorax in an adult is defined as 1500 mL or more—that is, about two-thirds of the available space in the hemithorax is occupied by blood.
Massive hemothorax is life-threatening by three mechanisms. First, the acute hypovolemia renders preload inadequate to sustain effective left ventricular function. Second, the collapsed lung induces hypoxia by disturbing ventilation-perfusion matching. Third, the pressure of the hemothorax compresses the vena cava (further impairing preload) and the pulmonary parenchyma, raising pulmonary vascular resistance.
If a radiograph of the chest has been obtained, the diagnosis of a massive hemothorax can be made if the aerated lung is completely surrounded by fluid (blood).
Immediate tube thoracostomy is required to initially manage the massive hemothorax. Surgical repair must be performed emergently. Common causes of massive hemothorax include injury to the lung parenchyma, to an intercostal artery, and to the internal mammary artery.
Patients with "ordinary" hemothorax will occasionally drain a moderate amount of blood but then rebleed or continue to bleed. If there is evidence of ongoing hemorrhage after initial drainage exceeding 600 mL/6 h (i.e., 100 mL/h for 6 h, 300 mL/h for 2 h, or 600 mL/h for 1 h), a "massive hemothorax equivalent" is diagnosed. In such cases of rebleeding/ongoing bleeding, conservative management requires thoracotomy, although occasional patients may be managed nonoperatively.
Since massive hemothorax is, by definition, associated with accumulation and subsequent drainage of large volumes of potentially "clean" blood, it is desirable to collect the effluent into an autotransfusion-prepared device. The decision to proceed with autotransfusion must be based on the patient's condition and the probability that the blood is free from contamination by enteral pathogens from an occult injury to the gastrointestinal tract.
OPEN PNEUMOTHORAX Open pneumothorax (discussed in detail further on) is an open communication between the outer chest wall and the pleural space. Respiratory distress is due to inability to ventilate the affected side. The injury is sometimes referred to as a "sucking chest wound" because of the sound produced as air moves through the wound. On examination, this injury is usually obvious. However, it may be obscured by the patient's position or clothing. Air entry is diminished on the affected side, and chest wall motion is less dynamic. The injury is very often associated with a hemothorax. The initial maneuver in the ED is to cover the wound with a three-sided dressing so that air can escape but not enter through the wound. Complete occlusion may convert the injury into a tension pneumothorax.
FLAIL CHEST The term flail chest refers to a free-floating segment of ribs that are no longer connected to the rest of the thorax. This entity is also described in detail further on. During the initial survey, the examiner must search for segmental paradoxical chest wall motion, which is easy to miss if not specifically sought. Air entry will be diminished on the affected side. Jugular venous pressure may be intermittently increased in rhythm with respirations due to pendelluft, as explained later in this chapter.
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