Pyothorax in Dogs

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Pyothorax is an infection of the chest cavity generally caused by bacteria, although less commonly it may be due to other organisms, such as viruses or fungi. The infection causes fluid to accumulate in the chest cavity – the space between the lungs and the body wall – which causes difficulty breathing. This is a serious condition and is often fatal if not treated promptly and aggressively.

The route by which the thoracic cavity becomes infected is often not apparent and there are numerous ways that infection can occur in the chest cavity.

Causes

  • Spread of infection from the blood stream
  • Migration of foreign objects, such as plant material or thorns, through the chest cavity or lungs
  • Penetrating wounds, particularly bite wounds
  • Extension of infection from the vertebrae
  • Extension from pneumonia
  • Lung tumors or abscesses that rupture
  • Lung or chest wall trauma
  • Perforation of the esophagus
  • Complication of surgery

    There is usually a fairly long gap between the incident that caused the infection and the development of clinical signs. When the infection is caused by an animal bite, the wound has often healed and the owner has forgotten about it by the time that the pet becomes ill.

    Pyothorax is particularly common in hunting dogs where the infection is related to the entrance of a foreign body, such as a piece of plant material, into the chest cavity through the body wall. Alternately, the plant material may be inhaled and migrate through the lung.

    What to Watch For

  • Difficulty breathing
  • Fever
  • Lethargy/listlessness
  • Decreased appetite
  • Cyanosis (gums appear blue)

    In some cases, despite aggressive treatment, pyothorax can be fatal.

    • Radiograph of a cat with chest fluid. The normal structures that are usually visualized on a chest radiograph (such as the heart and lungs) are difficult to visualize here because of the amount of fluid that is present.

    • Photograph of fluid that was removed from an animal with pyothorax. This fluid has granules and is typical of fluid infected with certain types of bacteria, but not all infected fluids show these types of granules.

    • Cytology or microscopic examination of a fluid from a dog with pyothorax. Bacteria can be seen within the cell that is in the center of the slide.

    • Chest radiograph of a cat with a chest tube in place. The chest tube is positioned between the lungs and the body and is used to drain the chest of fluid or air.

    Diagnosis

    Diagnostic tests are needed to determine why your pet is having difficulty breathing and to determine if there is an underlying cause. If your pet is diagnosed with pyothorax, he will require veterinary care. Your veterinarian's efforts will be directed at three things:

  • Making your pet more comfortable by removing as much of the fluid from the chest cavity as possible

  • Performing tests to determine whether there is an identifiable cause for the pyothorax

  • Treating the infection so that it does not recur

    Diagnostic tests that your veterinarian may wish to perform include:

  • Blood work. Animals with pyothorax often have an increased number of white cells in their blood stream.

  • Chest radiograph. Chest radiographs or X-rays are done to confirm the presence of fluid in the chest cavity and to help determine how much fluid is present.

  • Chest tap. A chest tap (needle thoracentesis) is done to remove some fluid to allow your pet to breathe easier and also to obtain some fluid for analysis.

    Most animals tolerate chest taps and the procedure can be done without any sedation, but occasionally your veterinarian may need to give your pet some sedation or even general anesthesia in order to remove the fluid.

  • Fluid analysis. The fluid is typically opaque or turbid looking and may be somewhat smelly. It can range from amber to red or white in color and may appear bloody.

  • Cytology. Your veterinarian will examine the fluid under a microscope to determine what type of cells are present and whether bacteria can be seen.

  • Culture and sensitivity. Your veterinarian will likely culture the fluid to determine which bacteria are present. Often they will test various antibiotics to see which ones are most effective against the invading bacteria.

    Treatment

  • If your pet is very ill and having difficulty breathing, your veterinarian will initially remove some of the fluid to allow him to breathe more easily and will likely place your pet on intravenous (IV) fluids. They will also initiate antibiotic treatment.

  • Once it has been determined that your pet has pyothorax, your veterinarian may wish to place a chest tube to facilitate removal of the fluid and to help treat the infection. The chest tube can be used to lavage (wash) the chest cavity. This is done by placing sterile fluid into the chest cavity through the tube and then removing the fluid.

  • If a cause for the infection is found, your pet may require surgery.

  • Long-term antibiotic therapy is an important part of treating pyothorax. Initially, antibiotics may be given intravenously, but you will need to continue oral antibiotics for 4 to 8 weeks.

    Home Care and Prevention

    Administer all medications that your veterinarian prescribes until they are gone. Observe your pet closely for evidence of difficulty breathing. If he becomes lethargic or stops eating, contact your veterinarian immediately.

    Do not allow your pet to fight with other animals. If you notice a wound on the chest wall, have your veterinarian examine it. Take note of any wounds so that if your pet develops a problem later you can point it out to your veterinarian.

    Do not feed your pet bones or other hard objects that might become lodged in the esophagus and cause perforation.

    There is very little else that you can do to prevent your animal from developing pyothorax, but being alert to the signs will allow the condition to be diagnosed earlier and may allow treatment to be more effective.

  • Pyothorax is a general term that denotes infection of the pleural cavity, which is the space between the lungs and the body wall. There are multiple different types of organisms that can cause pyothorax including bacteria, viruses and fungi.

  • The infection can be associated with foreign bodies (plant materials, sticks, even toothpicks), pneumonia, tumors, abscesses in the lungs or it may be iatrogenic, which means it was caused by the veterinarian doing procedures such as chest taps or as a complication of surgery.

  • Bacteria may enter the chest cavity when a foreign body penetrates the rib cage or is inhaled into the lungs. In many cases, after the foreign body initiates the infection, it migrates out of the chest cavity into another site of the body or even out of the body entirely. Thus, finding the initiating culprit is often a daunting (if not impossible) task.

  • Extension from pneumonia may also cause an infection in the pleural cavity, although this is a less common route for the infection to occur in dogs than in people. People with pneumonia often complain of pain associated with infection of the pleura, which is the lining of the lung. With time, the pleurisy may cause fluid to develop in the chest cavity, resulting in a pyothorax.

  • Rarely, the esophagus may perforate (develop a leak) and infect the thoracic cavity by leaking food and bacteria. The perforation may occur when a bone or other hard tissue becomes lodged in the esophagus. With time the pressure from the object may interfere with the blood supply to the esophageal wall and eventually cause the adjacent tissue to die. When this occurs, food and fluid may spill into the chest cavity. Pyothorax of this nature is very serious and often results in death fairly quickly after the perforation occurs. Sharp objects swallowed by the animal may also perforate the esophagus and cause leakage.

  • Spread of infection from surrounding tissues such as the vertebrae (diskospondylitis) is a relatively rare cause of pyothorax, but it can occur. Animals with diskospondylitis often have evidence of neurologic dysfunction such as weakness, ataxia or a wobbly gate that precede the development of the pyothorax.

  • Tumors that grow in the lung tissue can reach such a large size that the blood supply to the tumor is no longer adequate. When this happens, a portion of the tumor may become necrotic and infected. Such a tumor may rupture and leak bacteria into the chest cavity, causing a pyothorax. Although the animal may seek a veterinarian because of breathing difficulties associated with the pyothorax, the underlying problem in these animals is actually the tumor.

  • Abscesses can occur in the lungs. These abscesses may be a result of a foreign body that has penetrated the lungs and is lodged there. However, the inciting foreign body frequently causes the infection and then migrates out of the lung so that it can no longer be found. Grass awns on the West Coast of the United States are notorious for causing lung abscesses in dogs, with resultant pyothorax. As pet owners know who live in areas where grass awns are common, these pieces of plant material are also frequently found under the third eyelid, in the ear canal or in the tissues of the legs or other sites of the body.

  • Pyothorax associated with fungal infections is relatively uncommon. Although fungal infections are frequently noted in the lungs of dogs that live in endemic areas, they are less commonly associated with chest fluid.

  • Whenever a needle or a chest tube is placed into the chest cavity to drain fluid or air, there is a risk that the animal will develop an infection. Thus, it is important that these procedures be done carefully and with appropriate technique to minimize this risk.

  • Infection of the chest cavity can be a complication of chest surgery, although this is a rare development if proper technique is used. However, to further minimize this risk, your veterinarian may ask that you give your pet antibiotics after surgery. It is important that you follow your veterinarian's instructions regarding administration of any medications before or after your pet has surgery.

  • Diagnosis In-depth

    Diagnostic tests will be performed to:

  • Determine that fluid is present in the chest cavity
  • Verify that the fluid is infected
  • Determine if there is an underlying disease, such as abscess, lung tumor or foreign body, that might have caused the infection.

    To determine is fluid is present

  • Your veterinarian will take a complete medical history and will perform a thorough physical examination.

  • Careful auscultation of the chest (using a stethoscope) will help determine whether the heart and lung sounds are normal. When fluid is present, the heart sounds may be muffled. Additionally, lung sounds may be difficult to hear in certain parts of the chest if fluid is present.

  • Thoracic radiographs (chest X-rays) will be taken to identify fluid in the chest and determine how much is present and where it is located. The radiographs will also be evaluated to determine whether other causes of difficult breathing such as pneumonia, asthma or tumor or fluid formation (lung lobe torsion) might be present.

    To confirm that the fluid is infected

  • Fluid removed from the chest by needle thoracentesis (chest tap) is analyzed for physical characteristics (color, clarity), the type and number of cells, amount of protein and the presence of bacteria or other infective organisms.

  • Most infected fluids contain bacteria that are present within cells that have phagocytized (eaten) them as well as bacteria that are present outside of cells. The type of bacteria, whether they are round or oblong and how they stain, will be used to help identify the type of infection that is present.

  • Fluid will be submitted for a culture, during which the bacteria type is determined by growing it on certain medias, and for sensitivity in which different antibiotics are tested on the bacteria to see which ones are most effective in killing them.

    To determine if there is an underlying disease

  • After removing the fluid, your veterinarian may wish to repeat the radiographs to see if there is evidence of a tumor or abscess in the lung tissue or to look for the presence of a foreign body or diskospondylitis. The chest cavity will be checked to identify any evidence of a bone or other material in the esophagus that might have caused a perforation. The lungs will also be inspected to determine whether they are able to inflate normally once the fluid is removed.

  • An echocardiogram may be performed if there is any concern of heart dysfunction.

  • Routine blood work (complete blood count and serum biochemical panel) will often be done to help assess organ function and overall health of your pet.

  • Your veterinarian may recommend other tests to help further identify potential diseases that may have caused the pyothorax or to identify concurrent diseases that might be present.

    Treatment In-depth

    Treatment of pyothorax may require medical management alone or in combination with surgery, depending on the underlying cause.

    Medical Management

  • The initial concern in treating your animal is to improve his ability to breathe. Your veterinarian will generally remove the fluid in your pet's chest cavity using a needle. Occasionally, sedation or anesthesia are required but a chest tap can often be performed with the animal awake. Depending on the degree of difficulty that your animal is experiencing when breathing, oxygen therapy may be required.

  • Further treatment will depend on whether or not an underlying disease was identified. If an underlying lesion is found, your veterinarian will need to treat it and the infection.

  • Medical management of pyothorax usually involves placing the animal on fluids to correct dehydration and other blood abnormalities and initiating antibiotics. Generally, broad-spectrum antibiotics, which are those effective against a wide variety of bacteria, are initiated until the results of the culture and sensitivity are obtained. Antibiotic therapy is generally continued for a total of 6 to 8 weeks.

  • Many times antibiotic therapy alone is not enough to rid the chest of the infection completely. In such animals, chest tubes are often inserted so that fluid can be placed into the chest via the tube and then removed. This helps to wash the bacteria and clots out of the chest cavity and may decrease the likelihood of the infection recurring. This procedure of thoracic lavage is generally done two to three times a day for 5 to 7 days or until there is clinical improvement.

  • If an underlying cause for the infection is identified, such as a lung tumor, abscess or a foreign body, then surgery is necessary. The foreign body or mass must be removed in order to clear the infection. Additionally, if there is no response to the medical management, surgery is often recommended despite a definitive mass or lesion not being readily identified on the radiographs.

    Surgical Management

  • Several surgical approaches can be used for pyothorax depending on the lesion that has been identified. An incision may be made between the ribs if a lung mass has been identified, or the sternum may be opened so that both sides of the chest cavity can be evaluated. Many times it is not possible to find the foreign body that caused the infection, despite evidence that one was present previously.

  • The surgeon will remove as much of the infected tissues as possible and will submit it for histologic examination (under a microscope) and for culture.

  • Often a chest tube will be placed to allow lavage of the chest cavity to be continued after surgery.

    Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not rapidly improve.

  • Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your pet. Do not discontinue the antibiotics until they are all gone. Although it may seem that the antibiotics are being given for a long time, it is essential that they be continued in order to clear the infection and help prevent recurrence.

  • The frequency and nature of follow-up evaluations of your pet will be determined in part by the nature of any underlying diseases found. Your veterinarian will likely wish to re-evaluate your pet to make sure that the incision site is healing if surgery was done. Your veterinarian may want to see your pet frequently thereafter to make sure that the infection has resolved.

  • If you notice that your pet is having difficulty breathing, is less active than normal or has a decreased appetite, do not wait until your next scheduled visit to see your veterinarian. Take your pet in immediately. Pyothorax can be life-threatening so discuss with your veterinarian how to tell if your pet is in distress so that you will be better able to judge when you need to have your pet evaluated.

  • If surgery is performed, you will be asked to return for periodic evaluations. These evaluations may include taking thoracic radiographs to determine whether the fluid is present or to check for tumors if cancer was found initially.

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