CHAPTER 68 Pneumothorax
Pneumothorax develops when air enters the pleural cavity as a result of pulmonary or thoracic wall injury. Pneumothorax has been reported as a rare condition in horses and is often the result of thoracic trauma, pleuropneumonia, or complications of upper airway surgery. Pneumothorax is classified according to its origin as primary or secondary (i.e., spontaneous versus traumatic or iatrogenic) and according to its physiologic nature as open (secondary to penetrating thoracic wall wounds) or closed (secondary to a tear in the airway or pulmonary surface). Penetrating wounds involving the thoracic wall are the most common cause of pneumothorax in horses. Severe pleuropneumonia, with slow leak of air from necrotic pulmonary tissue or from formation of bronchopleural fistulas, can also lead to accumulation of air in the pleural space and pneumothorax. With tension pneumothorax, a site of air leakage acts as a one-way valve, allowing air to enter the pleural cavity but not permitting its escape. Air continues to accumulate inside the pleural cavity during successive respiratory cycles, progressively increasing intrathoracic pressure to a point where it exceeds atmospheric pressure (i.e., positive pressure develops in pleural cavity), a life-threatening complication.
