Lethal six
Characteristics
Airway obstruction
Laryngeal trauma, foreign body aspiration, stridor, expanding neck hematoma, and gurgling
Tension pneumothorax
Hemodynamic instability, tracheal shift away from injury, one-way valve in injured lung
Open pneumothorax
Associated with open chest wall injury, air may enter pleural cavity through skin
Massive hemothorax
Lung parenchymal or intercostal artery injury, total whiteout of lung field
Flail chest
Two or more fracture sites in two or more consecutive ribs leading to paradoxical motion of chest wall, often have underlying lung contusion
Cardiac tamponade
Beck’s triad (hypotension, distended neck veins, muffled heart sounds)
Watch Out
The most common cause of airway obstruction occurs in patients with diminished airway reflexes in which a relaxed tongue falls back against the rear of the pharynx.
What are Considered the “Hidden” Six Injuries of Thoracic Trauma?
Hidden six | Characteristics |
|---|---|
Blunt aortic injury | High-energy rapid deceleration injury (e.g., fall from great height, high-speed MVC, aviation accident), widened mediastinum, deviation of the trachea to the right on CXR |
Esophageal injury | Penetrating trauma, subcutaneous air |
Tracheobronchial injury | Massive subcutaneous emphysema |
Diaphragmatic rupture | Due to sudden rise in intra-abdominal pressure, stomach and colon are the most frequently herniated structures; penetrating thoracoabdominal injuries; delayed diagnosis frequent (may be asymptomatic) |
Blunt cardiac injury | Spectrum from unexplained tachycardia, bundle branch block to cardiac rupture, associated with sternal fracture |
Pulmonary contusion | Develops within first 24 hours, often not seen on initial CXR |
Watch Out
The lethal six and hidden six make up the deadly dozen of thoracic trauma.
Watch Out
Do not assume that a combative trauma patient’s behavior is due to intoxication; the combative nature may represent an underlying physiologic derangement such as hypoxia or cardiac tamponade.
How Is the Diagnosis of Tension Pneumothorax Established?
This is a clinical diagnosis without a need for X-ray confirmation (will delay treatment). Suspect tension pneumothorax in patients with hypotension, dyspnea, tachypnea, jugular venous distention, unilaterally absent breath sounds, and a deviated trachea to the unaffected side.
How Is the Diagnosis of Traumatic Cardiac Tamponade Established?
This is also considered a clinical diagnosis and requires prompt intervention. Patients that present with Beck’s triad (hypotension, distended neck veins, and muffled heart sounds) should be suspected of having tamponade. The diagnosis can be supported with a FAST scan which demonstrates fluid in the pericardial sac. Patients may also exhibit pulsus paradoxus (decrease in systolic pressure ≥10 mmHg with inspiration).
What Is the Most Likely Diagnosis in This Patient?
Given that the patient has sustained a penetrating chest injury to the cardiac box in association with Beck’s triad, there is a high suspicion for cardiac tamponade. The cardiac box is defined as the area of the anterior chest wall bounded by the sternal notch and clavicles superiorly, the nipples laterally, and the subcostal margin inferiorly. Up to a third of patients with a penetrating wound in this area may have an associated cardiac injury. In addition, he has absent breath sounds on the left, in association with hypotension; thus he may have a concurrent tension pneumothorax.
History and Physical
What Is the Differential Diagnosis for a Combative Trauma Patient?
The clinician should be aware that combative behavior (as in the present patient) can be a sign of hypoxia (so-called air hunger), hypovolemic or cardiogenic shock, and hypoglycemia. Alcohol and other substance use are common behaviors among this patient population.
What Is the Differential Diagnosis of the Absent Breath Sounds on the Left?
Pneumothorax or massive hemothorax.
What Is the Implication of a Penetrating Injury to the Chest That Is Above Versus Below the Nipple?
The diaphragm is a dome-shaped muscle that peaks at an imaginary line between the nipples. A penetrating injury above the nipple line likely only involves injury to the thoracic structures. However, injuries below the nipple line may result in damage to either thoracic structures, abdominal contents, or the diaphragm itself, thus prompting investigation of all these areas.
Why Is It Important to Know the Type of Weapon Used in a Penetrating Injury?
Bullet injuries create unpredictable paths, and thus it is essential that the trajectory of the bullet is followed so as not to miss an injury. An entry and exit wound must be found. If there is no exit wound, the bullet must be located radiographically. Rarely, bullets may enter an artery and embolize.
What Is the Concern Given That the Systolic and Diastolic Pressures in the Patient Presented Are So Close to Each Other?
A pulse pressure less than 30 mmHg is considered narrow. This implies a compromised stroke volume. In the trauma setting, the differential diagnosis for a narrow pulse pressure includes pericardial tamponade, hypovolemic shock, and cardiogenic shock.
Why Is It Important to Roll the Patient Over?
In all patients with penetrating trauma, it is critical to check for wounds to the back that may otherwise be missed. The axilla and perineum are two other areas that should be examined in patients with penetrating mechanisms of injury. In general, cervical spine immobilization in patients with penetrating injuries is not required given the extremely low incidence of unstable cervical spine fractures.
What Is the Significance of Air Bubbling from a Penetrating Chest Wound?
This is also referred to as a sucking chest wound, a type of open pneumothorax (Table 45.1). An open pneumothorax indicates there is an injury to the lung or bronchial tree that connects directly to the atmosphere. With a sucking chest wound, the chest wall defect is so large (at least 2/3 the diameter of the trachea) that inspired air takes the path of least resistance and enters into the chest cavity through the wound instead of through the trachea.
Table 45.1
Types of pneumothorax
Type | Population | Mechanism |
|---|---|---|
Spontaneous | Young, tall, thin, male, smokers | Spontaneous rupture of apical alveolar blebs |
Open | All trauma patients | Free communication between the atmosphere and pleural space through an open chest wall wound |
Simple | All trauma patients | Jagged rib fracture punctures lung; stab or gun shot wound |
Tension | All trauma patients | Lung injury creates one-way valve |
Iatrogenic | Patients with central line or thoracentesis | Direct needle injury to the lung |
Watch Out
Always order a chest X-ray after putting in a central line to make sure you did not cause an iatrogenic pneumothorax.
What Is Subcutaneous Emphysema?
The word emphysema is derived from Greek emphusēma meaning trapped air. This condition occurs if air is trapped in the subcutaneous layer of the skin. The physical exam finding of subcutaneous emphysema on palpation is referred to as crepitus. In the trauma setting, subcutaneous emphysema is caused by a pneumothorax until proven otherwise.
Pathophysiology
Why Is a Tension Pneumothorax Dangerous?
Tension pneumothorax is considered the most dangerous type of pneumothorax because the injury creates a one-way valve effect. With each inspiration, air leaks out of the lung and into the pleural cavity. This leads to compression of the superior and inferior venae cavae, decreased preload, severe reduction in cardiac output, and hemodynamic instability.
Watch Out
A tension pneumothorax is rapidly exacerbated by positive pressure ventilation. Thus a tension pneumothorax should be decompressed with a chest tube as soon as it is suspected and prior to instituting positive pressure ventilation.
What Is the Implication of Distended Jugular Veins?
Distended jugular veins are suggestive of elevated jugular venous pressure (JVP), an indirect measure of central venous pressure. In the trauma patient, it should raise the suspicion of either cardiac tamponade or tension pneumothorax.
What Causes Hypotension in Cardiac Tamponade?
Although there are elevated pressures in all chambers of the heart, the primary reason why patients develop hypotension is because there is an exaggerated shift of the septum into the left ventricle and thus a compromised preload and cardiac output. As blood accumulates rapidly in the pericardial sac, the pericardial pressure exceeds the ventricular filling pressure, resulting in reduced cardiac output. Eventually, the pericardial and left ventricular filling pressures equilibrate, resulting in a further decrease in cardiac output.
What Is the Most Important Factor in the Development of Cardiac Tamponade?
The rapid accumulation of fluid is the most important factor. Traditionally, acute cardiac tamponade is associated with a sudden accumulation of 200 to 300 ml of intrapericardial fluid, whereas a chronic tamponade results from a slowly evolving accumulation of volumes between 1,000 and 2,000 ml.
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