Chapter 166 Thoracic Trauma
Thoracic trauma in dogs and cats most often is the result of automobile accidents. The lack of apparent external injuries may be misleading; the diaphragm, thoracic wall, heart, or lungs may be severely damaged with little apparent damage to the overlying skin. Evaluate animals presented for treatment of thoracic trauma thoroughly but rapidly; if necessary, institute treatment prior to completing a full patient assessment. Animals with thoracic trauma may suffer concurrent abdominal or skeletal injuries.
This chapter discusses the major disorders caused by thoracic trauma: pulmonary and myocardial contusions, pneumothorax, rib fractures and flail chest, hemothorax, and diaphragmatic hernia; see Chapter 164 for discussion of chylothorax.
Injuries to abdominal viscera are discussed in respective organ-system chapters.
ETIOLOGY
Blunt Trauma
• Blunt trauma to the thoracic cavity usually is the result of automobile accidents. It may also be the result of being kicked by a human or farm animal (horse, cow), being struck by a heavy object, or falling from heights (e.g., falling from a window of a high-rise building).
• The severity of injury depends on the mass of the object delivering the blow, the velocity of the object, and the area to which the blow is delivered. It has been shown experimentally that when a blow equivalent to that delivered by a car is administered to the thorax of anesthetized dogs, the thoracic viscera may be compressed until the opposing parietal pleural surfaces underlying the ribs may almost be brought into contact. The ribs of young animals are pliable and tend to fracture less often than those of older animals.
Penetrating Trauma
• Penetrating trauma usually is the result of a gunshot. It may also result from a sharp instrument (e.g., a knife, screwdriver, stick, or arrow) or from deep bite wounds inflicted by a big dog on a smaller dog or cat.
• Consider the type of projectile, point of entry, and path of the penetrating object when attempting to diagnose thoracic trauma, even if wound entry is distant to the thoracic cavity. The path of a projectile may be altered if it strikes bony structures.
• It is often unclear whether thoracic injuries have resulted from penetrating wounds. Depending on the extent of injury, signs of cardiovascular collapse or respiratory distress may develop more slowly in patients suffering penetrating injuries of the thorax.
CLINICAL SIGNS
• Tachypnea or dyspnea (difficulty breathing) is a typical presenting sign in dogs and cats that suffer thoracic trauma. The animal may have an anxious or distressed appearance. The owner may or may not have observed the injury. Clinical signs of thoracic trauma may be delayed in onset, especially those associated with diaphragmatic hernia.
• Hypovolemic shock may result from internal or external hemorrhage or accumulation of fluid within tissue spaces. An animal suffering from hypovolemic shock has an increased heart rate, weak peripheral arterial pulses, cold extremities, and pale mucous membranes, and it often appears depressed or stuporous (see Chapter 156 for further discussion of shock).
DIAGNOSIS
Physical Examination
Observation
• Rapidly developing dyspnea usually is the result of pneumothorax, pulmonary contusion, or hypovolemia.
• Rapid, shallow, choppy breathing can result from restriction of the thoracic wall because of painful rib fracture.
• Paradoxical motion of the chest wall is caused by collapse of a portion of the rib cage on inspiration when multiple rib fractures create an unstable flail chest wall.
• Decreased hemithorax movement (fixation) can be seen on the side into which abdominal viscera have herniated through a ruptured diaphragm.
Palpation
• Palpate the thoracic wall for rib fractures, unstable (flail) segments, hematomas (usually adjacent to rib fractures), subcutaneous emphysema (crepitus), intercostal muscle tears (usually under intact skin), and abnormal location of the cardiac apex beat (displaced by herniation of abdominal viscera).
Auscultation
• Carefully auscultate the entire thoracic cavity to determine whether breath sounds can be identified throughout the thoracic cavity. The absence of respiratory sounds strongly suggests displacement of the lungs by air, fluid (e.g., blood), or abdominal viscera. Crackles suggest intrapulmonary fluid accumulation.
• Auscultate the heart as well. A change in the location or pitch of heart sounds suggests displacement of the heart by air, fluid, or viscera. Ventricular arrhythmias may occur as the result of traumatic myocarditis or myocardial ischemia; however, their onset is more frequently observed 24 to 48 hours after the traumatic episode.
Percussion
• Perform percussion of the thoracic wall to determine increased or decreased resonance. By placing one hand flat on the thoracic wall and tapping the knuckle of the middle finger with a percussion hammer or the tips of the fingers of the opposite hand, a sound of consistent frequency is produced in normal animals.
• In animals with air or air-filled viscera underlying the thoracic wall, the pitch is deeper and more resonant, whereas the sound produced in animals with fluid or solid viscera immediately under the thoracic wall is dull and less resonant.
• Percussion aids detection of pneumothorax, pleural effusion (e.g., hemothorax and chylothorax), diaphrag-matic hernia, and consolidation of lung lobes.
• Skilled use of this technique requires frequent practice on normal animals to allow a distinction between normal and abnormal sounds.
Fractures
• Examine the animal for the presence of fractures; do not be distracted by the obvious presence of broken bones but continue searching for evidence of more serious internal injuries.
• If spinal fractures are suspected, handle the animal with great care until these have been stabilized or it is determined radiographically that the spine is intact.
Surface Wounds and Abrasions
• Clip hair from the thoracic wall area as necessary to identify abrasions, bruises, or wounds that may point to likely sites of intrathoracic injury.
Thoracic Radiography
Take radiographs to evaluate the heart, lungs, pleural space, and thoracic wall (see Chapters 143 and 159 for a discussion of thoracic radiography).
• It is sometimes advisable to delay thoracic radiography of the injured animal until after higher priority conditions such as shock have been stabilized by emergency treatment. Pulmonary contusion, characterized by hemorrhage and fluid accumulation within the lungs, may not reach its greatest extent for 6 to 12 hours and then often may not appear radiographically to be improved for 7 to 10 days after injury.
• Evaluate the pleural space carefully for fluid, air, or abdominal viscera, and evaluate the integrity of the diaphragmatic outline.
• Look for radiographic evidence of fracture or dislocation of skeletal structures and subcutaneous emphysema, which indicates leakage of air into the subcutaneous space from the environment, the thoracic cavity, or a major airway.
• Pneumomediastinum is seen as air outlining the mediastinal contents and is indicative of tracheobronchial rupture.
• Often it is difficult to identify a diaphragmatic hernia on thoracic radiographs, particularly if obscured by accumulation of fluid within the pleural space. If a large quantity of pleural fluid is present, remove it and repeat the radiographs (see Chapter 159) or obtain an ultrasound examination, if readily available.
• Observations suggesting a diaphragmatic hernia include cranial displacement of the stomach, the loss of the caudal outline of the liver, and the presence of gas-filled viscous organs within the thoracic cavity.
Thoracocentesis
If indicated, perform thoracocentesis to obtain a sample of pleural fluid or to drain air from the pleural space (see Chapter 3 for technique).
• Analyze the fluid for the presence and concentration of red blood cells (RBCs) and plasma protein. The fluid may be whole blood, or it may be a combination of transudate, exudate, chyle, and blood, depending on the severity and duration of injury and the organs affected.
• Centrifuge an aliquot of the fluid and examine the cellular portion microscopically for degenerative neutrophils, bacteria, and organic matter (see Chapter 164). These findings may suggest a severe inflammatory process and possibly perforation of the esophagus or gastrointestinal tract.
Blood Samples
• Draw blood and store the sample in anticoagulant and serum tubes (preferably before initiating treatment), unless analyzed immediately.
• Although these samples may not be needed, it is often helpful to determine the biochemical status of the animal at the time of hospital admission when attempting to distinguish between preexistent disease and that which has developed acutely after injury. These same considerations apply to the collection and storage of urine samples.
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