Dogs have two lung divided into sections called lobes. Each lung lobe has microscopic sacs called alveoli that are connected to microscopic tubes called bronchioli. These are connected to larger and larger tubes called bronchi. The lungs, located in the chest cavity, are covered by a membrane called the pleura. The space between the lungs and chest wall is called the pleural space and normally only contains a small amount of liquid, which lubricates the lungs.
Pneumothorax can be caused by a number of causes; however, the end result is collapse of the lungs and air within the pleural space. Two main types of pneumothorax include traumatic and spontaneous. Traumatic is due to an injury or surgery that punctures the lungs, esophagus or chest cavity and results in leaking of air into the pleural space.
Spontaneous pneumothorax is typically caused by a disease of the lungs. The most common cause is a pulmonary bulla, which is an air blister that develops on the surface of the lung. This subsequently ruptures and leaks air into the pleural space. Other causes of spontaneous pneumothorax may include a foreign object within the lung, lung abscess, migrating parasites, and lung tumors.
Signs and diagnosis
The most common sign of pneumothorax is increased respiratory rate. As the lungs progressively collapse, marked breathing difficulty may be noted along with a grey to blue color of the gums and tongue. Weakness, caused by a lack of oxygen, may also be noted. Other nonspecific signs may include coughing, vomiting, lethargy and lack of appetite. Your veterinarian may detect decreased lung sounds with the aid of a stethoscope.
The diagnosis of pneumothorax is based on chest X-rays that demonstrate air within the pleural space and collapse of the lungs. In the absence of any traumatic event, a presumptive diagnosis of spontaneous pneumothorax is made. A CT scan is useful to further define the underlying cause of the pneumothorax. Tests done prior to surgery may include a complete blood count, blood chemistry profile, and urinalysis to check internal organ health.
Conservative treatment for spontaneous pneumothorax commonly fails and therefore is not usually recommended. If the pneumothorax is severe, the air may be aspirated from the pleural space with the use of a needle or in some cases with a chest tube. Surgery commonly requires exposure of both sides of the chest via an incision made through the breastbone. The offending lung lobe is identified and surgically removed. A chest tube is routinely placed in the patient and will be removed once fluid production within the chest is minimal. In some cases, oxygen therapy may be needed until the patient’s respiratory function has stabilized.
One study included 64 cases with spontaneous pneumothorax. Causes of pneumothorax (determined by surgery) from most frequent to least frequent included bullous emphysema, cancer and migrating plant foreign bodies. Of all cases, 28 were treated with surgery and 36 were treated conservatively (chest tap, chest tube, +/- cage rest). Of the surgical group 89% had failed conservative efforts. Mortality rate with surgery was 12%. Of those treated medically alone, without surgery in the acute phase, 50% had recurrent pneumothorax. Mortality rate with medical treatment alone was 53%.
For more information on this subject, speak to the veterinarian who is treating your pet.