Managing thoracic trauma (Proceedings)

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

Etiology of thoracic trauma

Motor vehicular accidents (blunt trauma) are the most common cause of thoracic trauma in dogs; bite wounds (penetrating trauma) are not uncommon. Less common mechanisms include gunshot wounds, knife / stab wounds, other penetrating wounds (e.g. impaling), being kicked by a larger animal (horse/cow); and 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 EC8+). Intravenous fluids should be given if shock is present, however hypotensive or low volume resuscitation should be considered in animals with respiratory distress (discussed further in the context of pulmonary contusions).

Supplemental oxygen should be administered if any signs of respiratory distress are present. During initial evaluation this is usually done by flow-by or with a face mask. Once the patient is stabilized and ready to be moved to a cage, oxygen can be administered via a nasal cannula or in an oxygen cage if it is still deemed necessary. Thoracocentesis may be performed if there is evidence of pneumothorax based on initial assessment (see below). Analgesia should be administered as needed. Opioids are the initial analgesic drug class of choice, however pure mu agonists (especially morphine and hydromorphone) can cause panting and confound assessment of respiratory status. After the patient's condition has stabilized, further testing may be performed as indicated.

Specific sequelae of thoracic trauma include (in order of most common to least common) pulmonary contusions, pneumothorax, hemothorax, rib fractures, flail chest, and diaphragmatic hernia.

Pulmonary contusions

Pulmonary contusions are a very common consequence of thoracic trauma, identified in 58% of dogs with chest trauma in a recent retrospective study. 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

Pulmonary contusions may be suspected based on clinical signs of tachypnea/increased respiratory effort in dogs following trauma. Breaths sounds are generally increased or harsh on thoracic auscultation, and crackles may be appreciated in severe cases. Hemoptysis may also be evident in severe cases. Thoracic radiographs are again the mainstay of diagnosis; the presence of generalized or multifocal interstitial to alveolar infiltrates is characteristic.

Treatment

Is generally supportive. Mild pulmonary contusions may not impair gas exchange and hence no specific treatment may be required. In hypoxemic patients, oxygen therapy is indicated (cage vs. nasal vs. other). Mechanical ventilation is indicated in the most severe cases, and may be necessary for days. In animals with a suspicion of pulmonary contusions, it is recommended to be careful with the volume of fluid administered during initial 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, by increasing hydrostatic pressure in the pulmonary vasculature and “blowing off” clots. Excessive fluid administration will also contribute to a dilutional coagulopathy that can cause ongoing pulmonary hemorrhage.

Prognosis

Depends on the severity of contusions and concurrent injuries. It is also important to be mindful that clinical signs may worsen within the 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.

Pneumothorax

Pneumothorax refers to the development of free air within the pleural space. Pneumothorax was documented in 47% of dogs sustaining chest trauma in a recent retrospective study. Air enters the pleural space either from the outside via penetrating injuries or secondary to leakage from damaged pulmonary parenchyma.

The diagnosis is often suspected on the basis of auscultation and observation of respiratory pattern. Dogs with a pneumothorax have inappropriately quiet lung sounds for the degree of respiratory distress. Lung sounds may be essentially absent in the most dorsal part of the chest. Note however that louder than average breath sounds may be ausculted associated with concurrent pulmonary contusions. Animals with pleural effusion usually have a restrictive breathing pattern (short shallow breaths).

TFAST = thoracic focused assessment with sonography for trauma can be incorporated into the initial physical examination of trauma patients and aid in the diagnosis of pneumothorax. Absence of the glide sign suggests pneumothorax (i.e. lack of the normal dynamic interface between lung margins gliding along the thoracic wall). 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 are still considered the mainstay of diagnosis, however thoracocentesis should be performed first in the unstable patient. Radiographs will reveal air in the pleural space, retracted lung lobes and the cardiac silhouette will be raised off the sternum. Diagnostic thoracocentesis is 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

Treatment involves therapeutic thoracocentesis. Generally ~ 25-30 ml/kg of air needs to be removed to provide significant improvement to respiratory status. If the pneumothorax recurs following repeated centesis, then thoracostomy tube placement with intermittent or continuous chest drainage is indicated (for example if >2-3 needle thoracocentesis procedures are required in <12- 18 hours or if no end-point is reached during thoracocentesis). There are a variety of options for thoracostomy tubes. The ideal tube should have multiple fenestrations, be easily placed and able to withdraw fluid as well as air. Photographs of the Mila chest tube, ArgyleÔ TurkelÔ and ArgyleÔ Trocar tubes will be shown.

Blood patching, also referred to as blood pleurodesis, has also been described for the management of persistent pneumothorax. In contrast to spontaneous pneumothorax, dogs with traumatic pneumothorax almost never require thoracotomy.

Prognosis

Prognosis is good since traumatic pneumothorax usually resolves with time and medical management. Prognosis often depends more on other injuries.

Hemothorax

Hemothorax is another consequence of thoracic trauma. The impact of hemothorax is generally minimal in the context 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 tFAST or chest radiographs from a trauma patient. Treatment is supportive. Thoracocentesis is avoided unless otherwise indicated (e.g. if pneumothorax). Damage to the great vessels and massive hemothorax is suspected to occur and result in immediate / rapid death, such that the affected animal would be dead on arrival.

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. Options for provision of analgesia include IV opioids (ideally as a CRI), local blocks, intercostal nerve blocks, placement of a wound soaker type catheter, intrapleural analgesia if a chest tube is in place, parenteral NSAIDS once the animal is hemodynamically stable, and/or an epidural (high).

Flail chest

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 are more detrimental to lung function. Medical management involves oxygen, mechanical ventilation, positioning (affected side down), ± chest wrap / bandage, analgesia (as for rib fractures) and treatment of concurrent problems.

Surgical management is indicated for any penetrating thoracic injuries, including flail chest. A median sternotomy is usually indicated to facilitate exploration of the chest. Lung lobectomy can be performed as indicated. In the setting of a concurrent flail chest the chest wall can be reconstructed as necessary.

Diaphragmatic hernias are uncommon but will occur in animals with significant chest injuries. The muscular portion of the diaphragm is the area most frequently torn.

Clinical signs

Consequences of diaphragmatic herniation depend on the extent of herniation of abdominal contents. Variable dyspnea, tachypnea and cyanosis maybe present. Breath sounds may be absent and heart sounds muffled. Additionally, thoracic borborygmus may be appreciated and the abdomen may appear empty (“tucked”).

Diagnosis

Is based on thoracic radiographs.

Treatment

Medical management includes oxygen supplementation, positioning, gastric decompression, pain management and treatment of concurrent problems. Depending on the location of herniation, the animal may breathe more easily in sternal recumbency vs. having the affected side down. Having the dog on an inclined plane (raised, angled board) may help to keep abdominal contents in the abdomen.

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 (decompression via NG or orogastric tube is indicated pre-operatively). Other indications for emergency surgery include fluid unresponsive shock (since it may be associated with hemorrhage from a herniated parenchymal organ) and unremitting abdominal pain (since it may be associated with strangulated, herniated bowel).

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.

Surgery involves a midline laparotomy. Occasionally the incision must be extended into a caudal sternotomy. The herniated viscera are reduced, and the entire diaphragm should be inspected. The diaphragm can usually be closed with a simple continuous appositional herniorrhaphy; involved reconstructive techniques are less commonly required for acute traumatic hernias. Following closure of the diaphragm, air should be evacuated from the pleural space and a careful exploratory celiotomy should be performed before closure. A thoracostomy tube is usually maintained in the immediate post-operative period.

Post-operative care is vital for a good outcome and involves standard attention to adequate intravascular volume, oxygen supplementation and pain relief (local and opioids).

Prognosis

Most dogs with acute traumatic diaphragmatic hernias recover well with appropriate management. Prognosis for survival is excellent if the patient survives the first 12-24 hours post-operatively, but the reported mortality rate is variable (54-90%). Recurrence is uncommon with proper surgical technique.