Pneumothorax in Cats
Dr. Anne Marie Manning
Chest radiographs are taken to visualize the lungs and the chest cavity. Normally, two X-rays are taken to allow complete assessment. Radiographs are evaluated for the presence of air within the chest cavity, fluid in or around the lungs, or space-occupying lesions in the lungs or chest cavity. The radiographs are also analyzed for the presence of rib fractures, bullae, and chest wall defects, which often accompany pneumothorax resulting from trauma. With pneumothorax, typical X-ray findings include elevation of the heart off the sternum (normally they touch), collapse of the lungs, and inability to follow the edges of the lungs out to the rib cage.
Your veterinarian may recommend any of the following in order to make a definitive diagnosis:
Thoracocentesis is both a diagnostic and therapeutic technique and is performed to remove air from the chest cavity. During this procedure, a local anesthetic is carefully injected into the muscles of the chest wall where the needle will be inserted. A needle is then passed through the chest wall into the chest cavity, and air is removed manually by aspiration with a syringe. In pets that do not have a pneumothorax, no air will be aspirated and negative pressure will be present. In other words, no air can be pulled into the syringe except with great effort and if released, the syringe will spring back to empty.
An arterial blood gas is a test performed to determine the pet's ability to oxygenate the blood by measuring the amount of arterial blood that is oxygenated. Normally, 95 to 100 percent of arterial blood is oxygenated. In pets with a pneumothorax, the amount of oxygenated blood is much lower. The most common artery for sampling blood is the femoral artery located on the inside of the thigh.
Pulse oximetry is another means to measure a pet's ability to oxygenate without having to draw blood. A probe is clipped onto the pet's lip, ear, tongue or skin fold or is inserted into the rectum and, using an infrared light source, detects the level of oxygenated blood. This test is an easier, less stressful means of measuring oxygenated blood in a pet that is having difficulty breathing but, under some circumstances, is not as accurate as an arterial blood gas.
A complete blood count (CBC), is a test that is performed to aid in the overall assessment of a pet's health when a pneumothorax is present. A CBC helps to identify anemia (low red blood cell count) that may occur due to blood loss following traumatic injuries, and helps to identify high or low white blood cell counts that occur with infection or inflammation.
A biochemistry profile is a blood test that allows evaluation of the internal organs such as the liver or kidneys. In pets that have a pneumothorax from cancer or trauma, this test is particularly important to determine whether the internal organs are affected.
Supplemental oxygen administration is given to all cats that are showing signs of difficulty breathing. In cases of mild pneumothorax, oxygen administration and cage rest may be the only treatments required while the body heals itself.
Thoracocentesis is indicated to remove moderate to large volumes of air from the chest cavity when the cat is exhibiting signs of difficulty breathing. By removing air from the chest cavity, the lungs are able to inflate normally and the cat breathes more easily.
A chest tube is placed when the volume of air removed via thoracocentesis is excessive. Chest tubes allow larger volumes of air to be removed more quickly or continuously. Tubes may be aspirated by hand, every few hours, or aspirated continuously by attaching the chest tube to a suction unit. The circumstances that dictate chest tube placement include the following:
- No endpoint is reached during thoracocentesis indicating a large continuous leak in the airways
- An endpoint was reached during thoracocentesis but thoracocentesis must be repeated more than two to three times, indicating a slow but continuous leak in the airways
- The volume of air removed during thoracocentesis was excessive for the patient's size.
Chest tubes are also placed following chest surgery to allow removal of residual air for the first 24 to 48 hours post surgery. Chest tubes are placed using sterile techniques, and require that the cat be heavily sedated or anesthetized. The tubes are held in place by sutures in the skin where the tube exits the chest, and with a bandage placed around the chest. Tubes are removed when minimal volumes of air or negative pressure are obtained during aspiration over a 6 to 12 hour period, indicating the leaky airway has sealed.
Surgery is indicated when the pneumothorax does not resolve over a period of 48 hours or longer despite the use of a chest tube and continuous suction. Surgery is also indicated to repair damage to the chest wall following traumatic injuries. If the pneumothorax involves only one side of the chest, a lateral thoracotomy is performed, which involves approach to the chest between the ribs on the affected side. If the source of the airway leak is unknown or the pneumothorax is evident on both sides of the chest in X-rays, a median sternotomy is performed, which is an approach to the chest through the sternum or midline of the chest. Pneumothorax caused by trauma rarely requires surgery whereas spontaneous pneumothorax often requires surgery.