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Pleural Effusion in Dogs

Pleural effusion is the abnormal accumulation of fluid within the chest cavity (which is lined by a membrane, or pleural lining). This occurs either because too little fluid is being absorbed in the pleural cavity, or because too much fluid is being produced in the pleural cavity.

Alterations in the dog's blood pressure and protein content in the blood, or the penetrability of blood vessels and lymphatic function, may contribute to fluid accumulation.

Pleural effusion can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

  • Coughing
  • Difficulty breathing
  • Increased rate of breathing
  • Dog places itself in unusual positions to ease breathing
  • Open-mouth breathing
  • Bluish to purplish color of skin
  • Exercise intolerance
  • Lack of energy
  • Lack of appetite


  • High hydrostatic (fluid) pressure
  • Low Oncotic Pressure: inability of blood plasma proteins to pull water into the circulatory system, resulting in excess fluid build-up(edema)
  • Vascular or lymphatic abnormality: disorders of the vessels and/or ducts that convey fluids
  • Chest filled with lymph fluid mixed with lipids (fat particles)
  • Lymphangiectasia(dilation of the lymph vessels)
  • Diaphragmatic hernia: passage of a loop of intestine through an abnormal hole in the diaphragm muscle (which separates the chest cavity from the abdominal cavity)
  • Blockage of the vena cava (the major vein from the lower part of the body that feeds into the heart)
  • Congestive heart failure (CHF)
  • Cancer in the chest cavity
  • Blood in the chest cavity
  • Trauma to the chest
  • Lung lobe torsion (twisting)
  • Blood clot of the lungs
  • Infection: bacterial, viral, or fungal
  • Heartworms
  • Hypoalbuminemia: abnormally low levels of blood protein albumin
  • Protein-losing enteropathy (intestinal disease)
  • Protein-losing nephropathy (kidney disease)
  • Liver disease
  • Inflammation of the pancreas
  • Overhydration
  • Bleeding disorder


Your veterinarian will perform a complete physical exam, with a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. The bloodwork analysis is the primary diagnostic tool for finding the underlying cause for the pleural effusion.

You will need to give a thorough history of your dog's health, including a background history of symptoms, and possible incidents that might have predated this condition. The history you provide will give your veterinarian clues as to which organs may be involved in the fluid buildup.

A sample of pleural fluid obtained by piercing the dog's chest cavity with a needle will be sent to the laboratory for analysis. The type of pleural fluid withdrawn will enable your veterinarian to diagnose the cause of the pleural effusion. X-ray and ultrasound imaging of the chest cavity are also very helpful in analyzing the causative factors.


Primary treatment will be to relieve respiratory distress by drawing fluid out of the chest cavity with a needle. The treatment that will follow depends on the definitive cause your veterinarian is able to diagnose. Insertion of indwelling chest tubes, thoracic (chest) surgery, and pleuroperitoneal shunts (diversion of pleural fluids) are common treatments. A pleuroperitoneal shunt is when the veterinarian places a catheter in the chest cavity to transfer its fluid to the abdominal cavity.

Living and Management

Your veterinarian will schedule follow-up appointments with you as needed to treat your pet’s underlying disease, if one is present. The prognosis is usually guarded to poor, although some dogs will have a complete recovery of health.

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