Pleural Effusion in Dogs

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Overview of Canine Pleural Effusion

Pleural effusion is an abnormal accumulation of fluid in the pleural space, which is the cavity between the lungs and the thoracic wall. Normally, a small amount of fluid is present in the pleural space which serves to lubricate the surfaces and prevent friction as the lung expands and deflates. A disturbance in the production or removal of this fluid may cause excessive fluid to accumulate. This can interfere with the function of the lungs and lead to the restriction of lung expansion and ventilation. When this occurs the lung lobes may collapse. Severe accumulations are usually life-threatening.

Pleural effusion is a symptom of many diseases, but is rarely a disease itself. Diagnostic tests are needed to determine the underlying cause, and subsequent treatment recommendations are based on these findings. The type of abnormal fluid accumulated can help determine the underlying cause of the fluid. The fluid is usually categorized based on its protein level and the types and numbers of cells present.

Some of the diseases or conditions in which pleural fluid may accumulate include:

  • Heart failure
  • Infection (pyothorax)
  • Chylothorax
  • Cancer (hemangiosarcoma, mammary gland tumors, lymphosarcoma)
  • Liver disease or gastrointestinal disease if the blood protein levels become severely low
  • What to Watch For

    Signs of pleural effusion in dogs may include: 

  • Difficulty breathing (dyspnea)
  • Fast breathing (tachypnea)
  • Weight loss
  • Coughing
  • Lethargy
  • Decreased appetite
  • Exercise intolerance
  • Open-mouthed breathing
  • Diagnosis of Pleural Effusion in Dogs

    Diagnostic tests are needed to exclude other diseases that may cause similar signs and to determine the underlying cause of the effusion. Diagnostic tests that your veterinarian may wish to perform include:

  • A complete medical history and general physical examination, with emphasis on stethoscope examination (auscultation) of the heart and lungs
  • A chest radiograph (X-ray)
  • Measurement of blood pressure
  • An electrocardiogram (EKG)
  • Ultrasound examination of the heart (echocardiogram)
  • Laboratory tests
  • Treatment of Pleural Effusion in Dogs

    The treatment of pleural effusion ultimately will depend upon the underlying cause. Initial treatments may vary depending on the likelihood of the specific diseases based on your pet’s physical examination and history. Treatment may include:

  • Hospitalization with oxygen administration if your pet is having trouble breathing
  • The initial treatment for pleural effusion usually includes thoracentesis or removal of the fluid from the chest cavity to allow the lungs to re-expand. This is done by placing a small needle into the area of fluid accumulation and applying suction with a syringe to remove the fluid. Removing even a portion of the fluid will often improve your pet’s breathing.
  • Minimizing your pet’s stress level may be beneficial.
  • Depending on the cause of the fluid, a diuretic such as furosemide (Lasix®) or spironolactone may be given. If heart failure is suspected, treatment with oxygen and various drugs such as digoxin (Lanoxin®; Cardoxin®) or nitroglycerine ointment may also be initiated in some cases.
  • Home Care and Prevention

    Optimal treatment for a pet with pleural effusion requires a combination of home and professional veterinary care. Follow-up can be critical. Be aware of your pet’s general activity, exercise capacity and interest in the family activities.

    Keep a record of your pet’s appetite, ability to breathe comfortably (or not), and note the presence of any symptoms such as coughing or severe tiring.

    Never withhold water, even if your pet urinates more than normal, unless specifically instructed to do so. Difficult breathing is an emergency. See your veterinarian as soon as possible.

    Administer prescribed medication as directed and be certain to alert your veterinarian if you are experiencing problems treating your pet. Take your medications with you to your recheck examinations to show your veterinarian. Dosing is critical for heart medication.

    Regular examinations that include an interview about your pet’s clinical symptoms and quality of life should be scheduled. Be prepared to answer questions regarding your pet’s activity, appetite, ability to sleep comfortably, breathing rate and effort, presence or frequency of coughing, exercise tolerance and overall quality of life.

    During re-evaluations, a chest X-ray may be performed to evaluate the lungs for fluid. Measurement of arterial blood pressure may also be done periodically. Blood tests to examine kidney function and blood electrolytes are routinely recommended. A blood digoxin test should be done periodically if that drug is being administered and an electrocardiogram is recommended if there is a heart arrhythmia.

    In general, pleural effusion cannot be prevented. Once your pet has been diagnosed with pleural fluid you should prevent excessive physical activity or excitement, avoid high heat/humidity and avoid high salt (sodium) foods or treats.

    In-depth Information on Canine Pleural Effusions

    There are dozens of reasons for coughing, difficulty or labored breathing and fatigue. The conditions that are most likely to cause these signs are diseases of the airways and lung, abnormalities of the heart and blood vessels, and accumulation of air in the chest cavity (pleural space). Examples of such diseases include:

  • Heart failure
  • Lung cancer
  • Lung infection (fungal, bacterial, parasites)
  • Tumors in the airways
  • Obstruction of the airways (foreign bodies, tumors)
  • Deficiency of protein in the blood stream (hypoproteinemia)
  • Overhydration (such as when an excessive volume of fluid is given intravenously)
  • Trauma causing a diaphragmatic hernia
  • Trauma to the chest wall, lungs or heart
  • Diseases of the pancreas, such as pancreatitis (uncommon)
  • Liver disease
  • Blood clots in the large vessels
  • Abdominal surgery
  • Idiopathic (unknown cause)

    When severe, the accumulation of fluid around the lungs (pleural effusion) will cause your pet to have difficulty breathing. The condition can become life threatening. Though dramatic, the symptoms of difficulty breathing (dyspnea) are not specific for only one condition. There are numerous causes of pleural effusion and it is imperative that your veterinarian determine the cause in order to institute appropriate and specific therapy.

    However, initial treatment of pleural effusion in all cases where the animal is having difficulty breathing, is directed at removing the fluid in order to allow the lungs to re-expand and to improve ventilation (air intake).

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    In-depth Information on Diagnosis

    Diagnostic tests are needed to recognize pleural effusion and exclude other diseases that may cause similar symptoms. A complete medical history will be taken which will likely include the following questions:

  • Is there a history of illness?
  • What medications is your pet currently taking?
  • What medications has your pet taken in the past, and what was the response to therapy?
  • Has your pet been recently anesthesetized?
  • Has your pet been neutered?
  • Does your pet cough? If yes, how often? Is it worse during the day or at night, and does it worsen with exercise?
  • What circumstances make the breathing worse?
  • Has your pet ever had heartworm disease? Is he on heartworm prevention therapy now?
  • What is your pet’s environment and travel history?
  • Has your pet been exposed to any toxins (such as rat poison)?
  • Is there any possibility of trauma?
  • Is your pet vomiting or gagging?

    Your veterinarian will perform a thorough physical examination. The number of diagnostic tests that are necessary depends on the duration of signs, the extent of the illness, and what your veterinarian finds on the physical examination. The physical examination should include observation of respiration, auscultation of the heart and lungs, and determination of the color of mucous membranes. Your veterinarian will handle your pet with care during the examination so as to reduce stress. If your pet is having a great deal of difficulty breathing, emergency treatment will be necessary.

  • When your pet is stable, additional tests that may be performed include a complete blood count and other blood tests. These tests will help determine if anemia is a complicating factor and will allow your veterinarian to evaluate organ function (such as the kidney). A blood test to detect heartworm infection may be recommended in some patients.
  • X-rays (radiographs) are usually taken as soon as the patient is stable. The radiographs will be evaluated for heart enlargement, fluid, fractures, tumors and lung abnormalities. X-rays are often repeated after removing fluid for better visualization of structures.
  • Determination of the type of fluid that was in the chest involves evaluating the fluid for color, clarity, cell counts and protein levels. Fluids that are suspected of being chyle will have triglyceride concentrations done in serum (blood sample) and fluid for comparison.
  • Blood pressure will usually be measured. This is done with a special device that measures blood flow noninvasively through the vessels in the legs or tail. Both high and low blood pressure values need to be identified because either can occur in patients with pleural effusion.
  • An electrocardiogram (EKG) is often obtained to identify heart enlargement and determine the electrical activity of the heart. The electrocardiogram is a noninvasive test done by attaching small contact electrodes to the limbs and body.
  • Ultrasound examination of the heart (echocardiogram) may be needed for a definitive diagnosis. This noninvasive test requires sophisticated equipment that creates high frequency sound waves, much like the sonar of a submarine. An image of the heart is created. The echocardiogram is usually the test of choice to establish the cause of pleural effusion, but this examination may require referral to a specialist.

    Your veterinarian may recommend additional diagnostic tests to ensure optimal medical care. These are selected on a case-by-case basis if indicated from the examination, prior test results or lack of response. Examples may include:

  • An angiogram of the cranial vena cava (if not evaluated adequately by chest X-rays or ultrasound)
  • Blood cultures if signs of sepsis are noted
  • Bronchoscopy
  • A coagulation panel (tests ability of blood to clot normally) if there is blood in the chest
  • Contrast studies (radiographs taken after dye has been administered) of the esophagus, or endoscopy with a fiberoptic scope may be used to evaluate esophageal compression by tumors that arise near it.
  • Contrast lymphangiography to evaluate the thoracic duct in cases of chylothorax
  • CT scan to evaluate some tumors
  • Fine-needle lung aspiration/biopsy
  • Lymph node aspiration and cytology
  • MRI scan
  • Positive contrast peritoneography to rule out diaphragmatic hernia, although ultrasound is probably better
  • Taurine concentration to exclude taurine deficiency in cats with dilated cardiomyopathy
  • Evaluation of the urine (urinalysis) in cases of low blood protein (hypoproteinemia)

    Consultations with appropriate specialists may be recommended depending on the findings of these tests.

    In-depth Information on Treatment

    The principles of therapy for pleural effusion in dogs are dependent upon the underlying cause. Goals in therapy may include improving heart function, preventing fluid accumulation, preventing further deterioration of the heart muscle and antagonizing chemicals and hormones produced in excessive quantities in pleural effusion. Congenital heart defects should be referred to a specialist for management. The initial therapy should be aimed at the diagnosis and treatment of the underlying cause.

    Emergency management of animals with pleural effusion may include:

  • Placement in an oxygen cage or use of an oxygen mask or nasal tube
  • Placement of an intravenous catheter (if possible) to allow drugs to be given
  • Chest tap (thoracentesis)to remove some fluid and allow the lungs to expand more fully
  • Determination of red cell numbers and protein concentration in the blood (packed cell volume and total protein)

    Further therapy will be dependent upon the underlying cause.

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