Pneumothorax in dogs and cats

Pneumothorax in dogs and cats is the accumulation of air in the pleural space. The diagnosis is confirmed by means of thoracic radiography. The pleural cavity is normally under negative pressure, which helps to keep the lungs expanded in health. However, if an opening forms between the pleural cavity and the atmosphere or the airways of the lungs, air is transferred into the pleural space because of this negative pressure. A tension pneumothorax occurs if a one-way valve is created by tissue at the site of leakage, such that air can escape into the pleural space during inspiration but cannot reenter the airways or atmosphere during expiration. Increased intrapleural pressure and resultant respiratory distress occur quickly.

Leaks through the thoracic wall can occur after a traumatic injury or as a result of a faulty pleural drainage system. Air can also enter the thorax during abdominal surgery through a previously undetected diaphragmatic hernia. Pneumothorax from pulmonary air can occur after blunt trauma to the chest (traumatic pneumothorax) or as a result of existing pulmonary lesions (spontaneous pneumothorax). Traumatic pneumothorax in dogs and cats occurs frequently, and the history and physical examination findings allow this to be diagnosed. Pulmonary contusions are often present in these dogs and cats.

Spontaneous pneumothorax in dogs and cats occurs when preexisting pulmonary lesions rupture. Cavitary lung diseases include blebs, bullae, and cysts, which can be congenital or idiopathic or result from prior trauma, chronic airway disease, or Paragonimus infection. Necrotic centers can develop in neoplasms, thromboembolized regions, abscesses, and ganulomas involving the airways, and these can rupture, allowing air to escape into the pleural space. Thoracic radiography should be performed to identify cavitary lesions in dogs and cats with spontaneous pneumothorax, although lesions are not always apparent.

Dogs and cats with pneumothorax and a recent history of trauma are managed conservatively. Cage rest, the removal of accumulating air by periodic thoracocentesis or by chest tube, and radiographic monitoring are indicated. If abnormal radiographic opacities persist without improvement for more than several days in trauma patients, further diagnostic tests should be performed.

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