Managing thoracic trauma (Proceedings)
Traumatic thoracic injuries are prevalent in small animals, particularly in dogs. The most common causes of thoracic trauma are motor vehicular accidents and bite wounds. Other possible, although less common mechanisms include gunshot, knife wounds or being kicked by a larger animal (horse/cow). Injuries may range from mild to life threatening.
The initial evaluation of the patient with thoracic trauma should concentrate on the major body systems (heart, lungs, brain). A patient with significant thoracic trauma frequently has other injuries as well. The patient should be immediately taken to a treatment room for further therapy. An IV catheter should be rapidly placed and samples collected for determination of a packed cell volume, total solids, glucose and BUN. Supplemental oxygen should be administered if any signs of respiratory distress are present. Intravenous fluids should be given if shock is present. After the patient's condition has stabilized, further testing (such as radiographs) may be performed.
Pneumothorax refers to the development of free air within the pleural space. The air gets to the pleural space either from the outside or via air leakage from the pulmonary parenchyma. Radiography, thoracocentesis or auscultation may identify pneumothorax. Auscultation of dogs with pneumothorax may be misleading if respiratory sounds are louder than average. In many emergency practices, dogs showing respiratory distress may undergo thoracocentesis based upon trauma history and increased respiratory effort. Approximately 25-30 ml/kg of air generally needs to be removed to provide significant improvement to respiratory status. Occasionally, a thoracostomy tube is required to prevent either continuous or intermittent chest drainage. Generally, a dog is considered a candidate for a chest tube if it requires greater than three needle thoracocentesis in less than 12- 18 hours or if no end-point is reached during thoracocentesis. Animals will breathe with a restrictive pattern (short shallow breaths).Pulmonary contusion is another common traumatic thoracic injury. Pulmonary contusion occurs when blunt trauma to the chest causes alveoli to fill with blood and fluid (inflammation). Pulmonary contusion occurs in a large percentage of animals with thoracic trauma. Contusion may be identified radiographically as interstitial to alveolar infiltrates or clinically by tachypnea/increased respiratory effort in dogs following trauma. Therapy for pulmonary contusion is supportive and includes oxygen and fluid therapy as needed to maintain adequate circulating volume. Some clinicians vividly recall dogs with pulmonary contusion that appeared to rapidly deteriorate following a large volume of intravenous crystalloids. Most dogs with pulmonary contusion improve significantly in 2-3 days and recover completely in less than one week.
Hemothorax is another common sequalae of thoracic trauma. The impact of hemothorax is more likely from hypovolemia from the blood loss, than from the pleural effusion. Hemothorax is usually a presumptive diagnosis after identification of pleural effusion on chest radiographs from a trauma patient. Treatment is supportive. Thoracocentesis is avoided unless otherwise indicated. Surgical exploration is a last resort.
Rib fractures are also common in the patient with thoracic trauma. Rib fractures appear to be painful, particularly on inspiration. Individual fractured ribs do not themselves typically affect lung function, but reflect a severe injury to the chest. Therapy for rib fractures typically is conservative and includes pain management (opoids and local blocks). Some clinicians advocate loosely applied support bandages. If multiple ribs are fractured at several sites, an unstable piece or flail segment may be formed. This "flail" segment moves paradoxically with respiration. Various methods of stabilization have been described; however, frequently the underlying contusions may actually be more detrimental to lung function.
Diaphragmatic hernias may also occur in animals with significant chest injuries. The muscular portion of the diaphragm is the area most frequently torn. In general, animals with traumatic diaphragmatic hernias have other significant intrathoracic injuries try to better clarify the margins of the diaphragm. The timing of surgery may be equally important in successful patient outcome. Surgery should be undertaken when the patient is cardiovascularly stable. This should be within 12-24 hours of the injury. However, if the stomach is in the chest cavity, this is a surgical emergency because the stomach may distend with air and severely compromise ventilation. In general, in the patient with an acute diaphragmatic hernia, associated injuries may also play a significant role in deciding the time of surgery. Remember that surgery and anesthesia (and the recovery period) may be stressful to the critically injured dog. Safe anesthesia requires a rapid intubation and positive pressure ventilation from the time of entry into the abdominal cavity until the integrity of the diaphragm is restored. All efforts should be made to limit anesthesia and surgery time.
Post-operative care usually involves standard attention to adequate intravascular volume, oxygen supplementation and pain relief (local and opoids). Most dogs with acute traumatic diaphragmatic hernias recover well from surgery, but the adequate monitoring and support in the post-operative period is critical.
Cardiac arrhythmias are common following trauma in dogs and are generally self-limiting. However, severe tachycardias may occasionally require therapy (such as lidocaine). Animals having sustained severe trauma should be monitored for cardiac complicatons as well.
Most dogs with traumatic thoracic injuries recover uneventfully from their injuries with no lasting complications. The standard course is for the patient to look the worse for the first 24 hours after presentation and then to make relatively rapid recovery. Successful management includes appropriate identification of injuries and well-timed interventions.