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Fluid Around a Dog’s Lungs (Pleural Effusion)

 

Fluid around a dog’s lungs may form because of several underlying conditions that require veterinary attention. In a normal, healthy dog, only a minimal amount of fluid is found around a dog’s lungs for the purpose of allowing the lungs to glide smoothly within the chest cavity every time the dog breathes. Problems start when fluid around a dog’s lungs are in excessive quantity leading to symptoms and complications that will need addressed. If you suspect your dog has fluid around the lungs, please have your dog see the vet at your earliest convenience.

Build up of fluid in the lining of the lungs (pleural effusion) Cancer Research UK / Wikimedia

Pleural Effusion in Dogs 

The pleura is a thin membrane that is visible to the naked eye (macroscopic) and covers the dog’s rib cage, mediastinum (a membranous partition between the lungs) and lungs. To be more specific, the mediastinum, chest wall and diaphragm are covered by parietal pleura (attached to the wall), while the lungs are covered by visceral pleura (covering the organs).

The space found between the visceral and parietal pleura is medically referred to as pleural space or pleural cavity. Within this space are just a few milliliters of fluid, which, as mentioned, is meant to provide lubrication as the dog breathes.

When more fluid than normal is present, the condition is referred to as pleural effusion. The word “effusion” in medical terminology is used to depict an accumulation of fluid within an anatomic space, in this case, the space between the layers of the pleura.




Pleural effusion in dogs may be caused by several underlying medical conditions that warrant investigation by a vet. In order to address fluid around a dog’s lungs, it is therefore important to find the potential underlying cause and have it addressed.

Signs of Fluid Around a Dog’s Lungs 

The clinical signs associated with fluid around a dog’s lungs may develop acutely (all of a sudden) or insidiously over the course of several days or weeks.  Owners usually become aware of them as they witness their dogs developing various degrees of discomfort.

One of the main signs of pleural effusion in dogs is shortness of breath (dyspnea). The shortness of breath, consisting of rapid/shallow breathing, is due to the fluid impairing the expansion of the lungs. The degree of shortness of breath often doesn’t directly correlate with the amount of fluid present. Dogs who have accumulated substantial amounts of fluid chronically, may tolerate them with little shortness of breath.

Other symptoms may vary based on the underlying cause and may include coughing (often due to bronchial compression in presence of large amounts of fluids), presence of a fever (often seen in substantial effusions due to non-effective ventilation and heat exchange) and pleural pain which may be evoked by firmly palpating the space in between two ribs (intercostal space).

At the Vet’s Office 

Veterinarians will take a dog’s medical history and perform a physical exam paying particular attention to the dog’s gums and chest area. The vet will palpate and use percussion to detect potential signs of pleural effusion.

Upon palpation, vets may detect some changes in a dog’s anatomical structures when in presence of significant effusion. For fluid building up in one lung,  palpation may reveal a bulge in one side of the thorax causing an asymmetric appearance. The muscle between the ribs may feel as flat or convex and there may be difficulty in detecting heart and lung sounds.

Percussion over the intercostal space may be abnormal. Normal, healthy lungs, upon percussion provide a low frequency vibration; whereas, in lungs surrounded by fluid, there is a characteristic dulling of the vibration.

Next, chest x-rays may be taken to detect signs of pleural effusion in dogs which often manifests as an area of whiteness. Bloodwork including complete blood count, chemistry profile and blood gas analysis may be helpful. Further diagnostic tests such as an ultrasound may be carried out to rule out or confirm several conditions. Other more invasive diagnostic tests may include CT scan, MRI, thoracocentesis, biopsy etc.

Once the presence of pleural effusion in dogs is confirmed, a thoracocentesis may help determine the underlying cause. Not all dogs are suitable candidates for this procedure. In this procedure (usually done without sedation in collaborative dogs), pleural fluid is drawn from the intercoastal space (between the seventh and ninth rib) using a needle. This is often done during an ultrasound. The removal of extra fluid may too provide relief when there is a large amount of it causing lung compression. Once the fluid is removed, it is then analyzed.

Did you know? A potential complication of dogs with a history of chronic pleural effusion undergoing thoracocentesis is a thickening of the pleura and consequential pneumothorax, which is a collapsed lung due to presence of air in the pleural space.




Causes/Treatment for Fluid Around a Dog’s Lungs

Treatment for fluid around a dog’s lungs varies based on the underlying cause. Following are several potential causes of pleural effusion in dogs.

  • Heart failure. When dogs are affected by right-side heart failure, pleural fluid may accumulate. In these cases, often the vet detects signs of heart issues such as abnormal heart sounds, enlarged heart on x-rays, pericardial effusion (excess fluid between the heart and the sac surrounding the heart), distended neck veins and increased heart rate. Typically, cytological findings involve non-degenerate neutrophils, macrophages and reactive mesothelial cells. Treatment often consists of diuretics and vasodilators.
  • Cancer. Several types of metastatic cancer are prone to causing pleural effusion in dogs and these include lymphomas and carcinomas. With some forms of cancer, the fluid consists of blood that accumulates in the pleural cavity. Cytological findings include neoplastic cells. Treatment involves periodic thoracocentesis to remove excess fluids and chemotherapy.
  • Infections. In some cases, fluids around a dog’s lungs may be due to infections often derived as a result of bite wounds and penetrating foreign bodies in the chest wall such as sticks. Affected dogs may display lethargy, loss of appetite and fever. Cytologicial findings include degenerative neutrophils and bacteria. Treatment involves drainage  and antibiotics.
  • Other causes. Several other possible causes of fluid around a dog’s lungs include exposure to rat poison, trauma, lymphangiectasia, pancreatitis, auto-immune diseases, pulmonary thromboembolism and history of recent abdominal or thoracic surgery.


References:
  • Textbook of Veterinary Internal Medicine, Stephen J. Ettinger, Edward C. Feldman
  • DVM360: Managing pleural effusion (Proceedings)
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