Thoracic trauma (Proceedings)

Traumatic thoracic injuries are prevalent in small animals, particularly in dogs.

Etiology of thoracic trauma:

      - motor vehicular accidents (blunt trauma)

      - bite wounds (penetrating trauma)

      - less common mechanisms include

           o gunshot wounds

           o knife / stab wounds

           o other penetrating wounds (e.g. impaling)

           o being kicked by a larger animal (horse/cow); and

           o high-rise syndrome.

Injuries may range from mild to life threatening.

Approach to the trauma patient:

      - initial evaluation should concentrate on the major body systems (cardiovascular, lungs, brain) since a patient with significant thoracic trauma frequently has other serious and life-threatening injuries

      - all trauma patients should be immediately triaged to the treatment room

      - an IV catheter should be placed immediately and samples collected for determination of a packed cell volume, total solids, glucose and BUN (or a complete point of care profile such as a NOVA or i-STAT)

      - supplemental oxygen should be administered if any signs of respiratory distress are present

      - thoracocentesis may be performed if there is evidence of pneumothorax based on initial assessment

      - intravenous fluids should be given if shock is present

      - analgesia should be administered as needed

      - after the patient's condition has stabilized, further testing may be performed as indicated.

Specific sequelae of thoracic trauma include pneumothorax, pulmonary contusions, hemothorax, rib fractures, flail chest, diaphragmatic hernia and cardiac arrhythmias. These are briefly discussed below.

Pneumothorax refers to the development of free air within the pleural space. Air enters the pleural space either from the outside via penetrating injuries or secondary to leakage from damaged pulmonary parenchyma.

Diagnosis:

      - Auscultation and observation of respiratory pattern

           o Inappropriately quiet lung sounds for degree of respiratory distress

           o But can be misleading of respiratory sounds are louder than average associated with concurrent contusions etc.

           o Restrictive breathing pattern (short shallow breaths)

      - TFAST = thoracic focused assessment with sonography for trauma:

           o Absence of the glide sign suggests pneumothorax (i.e. lack of the normal dynamic interface between lung margins gliding along the thoracic wall)

           o Refer to Lisciandro et al. JVECC 18(3) 2008, p258-269 for complete description of the standard 4 point TFAST technique. These authors documented sensitivity = 78.1%, specificity = 93.4% and overall accuracy = 90% of TFAST relative to thoracic radiographs for the diagnosis of pneumothorax

      - Thoracic radiographs:

           o Considered the mainstay of diagnosis

      - Diagnostic thoracocentesis:

           o Often attempted based on clinical suspicion in animals with respiratory distress deemed too unstable for radiography, or following TFAST diagnosis of pneumothorax without radiographs

Treatment:

      - Therapeutic thoracocentesis:

           o ~ 25-30 ml/kg of air generally needs to be removed to provide significant improvement to respiratory status.

      - Thoracostomy tube placement with intermittent or continuous chest drainage

           o Occasionally required

           o Indicated if ≥ 3 needle thoracocentesis procedures are required in <12- 18 hours or if no end-point is reached during thoracocentesis

Prognosis:

      - usually resolves with time and medical management

Pulmonary contusion is another common traumatic thoracic injury. Pulmonary contusion occurs when blunt trauma to the chest causes pulmonary and alveolar interstitial and alveolar hemorrhage and edema; accompanied by parenchymal destruction. It is particularly associated with compression-decompression injury to the thorax.

Diagnosis:

      - clinical signs:

           o tachypnea/increased respiratory effort in dogs following trauma

           o hemoptysis

      - thoracic radiographs:

           o interstitial to alveolar infiltrates

Treatment:

      - supportive

      - oxygen therapy (cage vs. nasal vs. other)

      - mechanical ventilation in the most severe cases

      - careful fluid resuscitation (while it is vital to provide intravenous fluids to traumatized patients in shock, there is concern that rapid administration of large volumes of crystalloids may acutely exacerbate pulmonary contusions)

Prognosis:

      - clinical signs may worsen within first 24-48 hours, however most dogs improve significantly within 72 hours and lesions typically resolve within 3-10 days, unless complications such as pneumonia or ARDS develop

Hemothorax is another consequence of thoracic trauma. The impact of hemothorax is generally minimal in the contents of the patient's injuries as the volume of effusion is generally small. 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.

Rib fractures are often found on thoracic radiographs of trauma patients. Individual fractured ribs do not themselves typically affect lung function, but reflect a severe injury to the chest and can be very painful. Analgesia is the mainstay of treatment (opioids and/or local blocks). If multiple ribs are fractured at several sites, an unstable flail segment may be formed. This "flail" segment moves paradoxically with respiration. Various methods of stabilization have been described; however, frequently the underlying contusions is 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. Surgical repair should be undertaken as soon as possible after stabilizing the patient, generally within 12-24 hours of the injury. The presence of the stomach in the chest cavity should prompt emergency surgery due to the risk of gastric dilatation. Anesthesia and surgery is associated with significant risk in these patients. 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 is vital for a good outcome and involves standard attention to adequate intravascular volume, oxygen supplementation and pain relief (local and opoids). Most dogs with acute traumatic diaphragmatic hernias recover well with appropriate management.

Cardiac arrhythmias are common following trauma in dogs and are generally self-limiting. Severe tachycardias associated with cardiovascular instability may occasionally require therapy (such as lidocaine for malignant ventricular tachycardia).