Pleural space disease is a common cause of respiratory distress in emergent and critical patients. Air, fluid, exudates, chyle, blood, and herniated abdominal organs may be present in the thoracic cavity. When any form of space occupying condition occurs, the lungs cannot expand normally and pulmonary function fails. These patients must be stabilized first with oxygen therapy and thoracocentesis (chest tap) to improve respiratory function before diagnostics such as radiography are performed.

Respiratory trauma and thoracic wounds

Chest wounds must be investigated to ensure the pleural lining of the thorax has not been breached. "Sucking chest wounds" are penetrating wounds that lead to pneumothorax, and the name is derived from the sound of air sucking in upon inspiration. A bandage of sterile lubricating gel and sterile gauze should be placed over the area to restore a seal. Palpation of the entire chest area is necessary to find any small penetrating injuries such as bite wounds or gunshot. The presence of subcutaneous emphysema indicates a penetrating injury, skin wound, or tracheal damage. Injuries to the trachea such as crushing, laceration, avulsion, or a migrating esophageal or tracheal foreign body may not exhibit obvious external trauma. However, air leakage at the site can dissect through tissue planes causing varying degrees of subcutaneous emphysema, pneumomediastinum, or pneumothorax. A chest tap is performed to remedy pneumothorax. Wounds are cleaned and evaluated for tissue trauma, dead space, or infection. Surgical exploration of the thorax is often recommended. Tracheal wounds should be cleaned and lightly bandaged with sterile materials to minimize accumulation of subcutaneous emphysema. Intrathoracic tracheal injury would require strict cage rest and possibly surgical correction. Radiographs of the chest are taken when the patient is stable and a culture from any penetrating wound to the chest.

Blunt trauma can lead to pleural space disease. Rib fractures and flail chest often cause pneumothorax and hemothorax by lacerating lung pleura and vessels. Rib fractures are often undiagnosed until radiographs are taken. Flail chest, is often observable because of the defect it produces, and is defined as a segment of two or more adjacent ribs fractured in both a dorsal and ventral location. Segments of flail chest will move freely and paradoxically with respiration. In addition to flail chest potentially lacerating lung tissue or vessels it also negatively affects ventilatory efficiency by decreasing the amount of negative pressure (tidal volume) generated during inspiration. Likewise respiratory function is decreased due to areas of pulmonary contusion in direct proximity with rib fractures and flail segments. Pneumothorax is one of the most common results of chest trauma and occurs in roughly one quarter to one half of patients exhibiting fractures from trauma. Pneumothorax is an accumulation of free air located outside the lungs but within the chest cavity. Pneumothorax can be classified as open when accompanied by a flesh wound that communicates to the chest or closed when the leak of air occurs from within the thorax. Closed pneumothorax can be relatively minor and self-limiting when the amount of air leakage is small. Tension pneumothorax is a term used to describe severe forms of closed pneumothorax where a defect in the lung leaks air into the pleural space during inspiration and then closes during the rest of the respiratory cycle. A one-way valve is formed letting air out into the pleural space and trapping it there. Large accumulations of air inhibit lung expansion and venous return to the heart. Alveolar collapse is progressive and will result in V/Q mismatch, intrapulmonary shunting, and lung lobe atelectasis. It has been reported that dogs can tolerate up to a full tidal volume of air accumulation before lung and cardiac function become severely affected. Treatment of pneumothorax is removal of air by chest tap or chest tube placement if air repeatedly or rapidly accumulates. Rib fractures generally do not require direct treatment but patients do benefit from treatment of pain. Flail chest may require external splinting or rarely surgical fixation to limit movement of the fractured segment. Radiographs, oxygen therapy, and pain relief are all staples of diagnosis and treatment plans.

Hemothorax

Accumulation of blood in the chest may occur as a result of trauma, coagulopathy, or neoplastic conditions. Removal of the accumulated blood is not necessary unless respiratory compromise is present. Treatment of hemothorax is supportive in nature and may include fluids and blood products if the patient is hypotensive. Diagnosis and treatment of underlying disease would be most appropriate before tapping the chest of patient with a concurrent coagulopathy, provided a chest tap is not immediately needed to relieve respiratory distress.