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Medical management of respiratory distress following trauma (Proceedings)

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Aug 01, 2009

Initial triage evaluation of the post-trauma patient should include a careful evaluation of respiratory function. The patient is evaluated with particular emphasis on three major aspects of the respiratory system:

1) Is there a patent airway, or could it be obstructed by external compression, tracheal tears, foreign bodies or blood clots?

2) Is there normal mechanical function of the chest wall and pleural cavity, or could respiratory failure be caused by the presence of air, blood or abdominal contents (diaphragmatic hernia) in the pleural space; or a failure of effective motion of the chest wall due to the presence of a flail chest or a high cervical spinal cord lesion?

3) Is a failure of oxygenation occurring due to pulmonary parenchymal lesions such as pulmonary contusions, atelectasis, or aspiration pneumonia?

If the airway is not patent, immediate steps are required to establish a functional airway. Such steps might include (but are not limited to) endotracheal intubation and suctioning, emergency tracheostomy, or foreign body removal. Similarly, if there is an abnormality in the chest wall or pleural cavity, aggressive steps such as thoracocentesis or surgery for a diaphragmatic hernia may be required. In either of these situations, definitive therapy is usually accompanied by oxygen supplementation. It is important to remember that many trauma patients suffer from multiple possible causes of respiratory distress. For example, pneumothorax is commonly accompanied by pulmonary contusions.

The most common causes of respiratory distress following trauma in dogs are pneumothorax and pulmonary contusions.

Pneumothorax

Pneumothorax is a common complication of trauma, and is the most likely cause of dyspnea in such animals. It is most commonly caused by rupture of alveoli secondary to increase in intrathoracic pressure against a closed glottis. Less frequently, pneumothorax can also be caused by direct penetration of the thoracic wall by a sharp object, rib fractures, or rupture of major airways such as the trachea or bronchi. If a major airway has ruptured, pneumothorax will be accompanied or preceded by pneumomediastinum. The absence of pneumomediastinum on thoracic radiographs makes a tear in a major airway very unlikely.

When the trauma patient is presented in severe respiratory distress, diagnostic tests such as radiographs may be impossible to obtain, or may cause the unstable animal to decompensate. In such animals, the clinician must rely on a physical examination diagnosis of pneumothorax. Physical examination abnormalities that may be found in the animal with pneumothorax include:

  • tachypnea: rapid, shallow breathing
  • recruitment of the secondary muscles of respiration
  • nasal flare
  • unwillingness to lie down, especially in lateral recumbency
  • inward scalloping of the intercostal muscles on inspiration
  • barrel chest
  • muffled or quiet lung sounds, difficulty ausculting the heart
  • may be unilateral
  • percussion of the thorax may reveal excessive resonance suggestive of pneumothorax

If radiographs can be obtained, the classical signs of pneumothorax may be seen:

  • elevation of the cardiac silhouette off the sternum
  • collapse of the lung lobes, especially the caudal lobes
  • absence of lung markings in the periphery
  • pneumomediastinum may be diagnosed if the great vessels in the cranial mediastinum are outlined by air

If pneumothorax is suspected based on physical examination, diagnostic thoracocentesis should be performed immediately, and the pleural space evacuated until negative pressure is obtained. Radiographs should not be obtained prior to performing thoracocentesis, because the stress of positioning and restraint may precipitate decompensation. Furthermore, radiographs will have to be obtained after evacuation of air from the pleural space (to assess the severity of concurrent pulmonary contusions and to rule out diaphragmatic hernia), and therefore obtaining images prior to thoracocentesis will result in additional and unnecessary charges to the client.

Thoracocentesis may be repeated as often as necessary. In many cases, a single procedure is required. Some dogs or cats, however, may require multiple aspirations of air from the chest if an ongoing leak occurs. If large volumes of air are aspirated on multiple occasions, or if repeated thoracocentesis necessary, the clinician may choose to place a chest tube for intermittent aspiration or continuous negative pressure suction. Surgical aspects of chest tube placement are beyond the scope of this presentation. Supplementation of oxygen is recommended whenever a stressful procedure such as thoracocentesis or chest tube placement is undertaken. In near cardiac arrest cases, if a tension pneumothorax is suspected, the animal should be intubated and a mini thoracotomy should be performed immediately to allow evacuation of the pleural cavity. In such cases, regular thoracocentesis with syringe and stopcock will probably be too slow to be effective.