Pleural Effusion in Cats – Causes, Symptoms, and Treatment

Pleural Effusion in Cats - Causes, Symptoms, and Treatment, pets lover, best pets lover,

Pleural effusion is an accumulation of fluid of a different nature in the pleural space of cats. The pleural space is the gap between the two feline pleurae, which line the lung and aid in breathing. For this reason, an abnormal accumulation of fluid in this cavity causes cats to have respiratory distress, which causes them to become agitated and increase their respiratory rate.


Pleural effusion, more than a disease in itself, is a clinical sign of other feline diseases and pathological processes, so a good diagnosis is a key to knowing the origin of the effusion and the analysis of the liquid since, among other diagnostic tests, help find out.


If you want to know more about pleural effusion in cats, its causes, symptoms, and treatment, don’t hesitate to continue reading this best pets lover article.


What is pleural effusion?

Pleural effusion is an abnormal accumulation of fluid of various natures in the pleural space, which is the space between the visceral pleura (the membrane that covers the lungs) and the parietal pleura (the one that covers the walls of the chest, mediastinum, and diaphragm) and that naturally contains a minimal amount of fluid to lubricate the lungs during respiratory movements.


A disorder in the production or elimination of this fluid causes an excessive accumulation of it in the pleural space, which causes a restriction of lung movement during inspiration (lung expansion) that can cause the lobes of the lung to collapse.

In general, pleural effusion in cats can be caused by any of the following mechanisms:


  • Increased capillary permeability.
  • Reduction of the oncotic pressure of the capillaries.
  • Increased hydrostatic pressure in the capillaries.
  • Lymphatic obstruction.

Types of Pleural Effusion in Cats

Pleural effusion in cats can be of various types depending on the nature of the fluid accumulated in the pleural space. The liquid must be analyzed and, according to a series of characteristics and parameters, we can divide it into the following types:


  • Pleural effusion of pure transudate: the color of the liquid is clear or yellowish, with a little amount of protein (<2.5 gr/dl), without fibrin and little cellularity (<1,000 cells/microliter).
  • Pleural effusion of modified transudate: with a yellowish-pink color, somewhat cloudy, it has a protein quantity between 2.5 and 5 gr/dl, without fibrin, triglycerides, or bacteria and with a cell count of 1,000-15,000 cells/microliter (reaching to 100,000 if produced by lymphosarcoma) and with mesothelial cells, non-degenerate neutrophils and neoplastic cells in lymphosarcoma. You may also be interested in taking a look at this other AnimalWised post on Lymphoma in dogs, its treatment, and life expectancy.
  • Pleural effusion of inflammatory exudate: with the same color as the previous one, the amount of protein is 2.5-6 gr/dl, even reaching 8.5 gr/dl in the case of FIP and the presence of fibrin but without triglycerides or bacteria and cell content of 1,000-20,000 cells/microliter (reaching 100,000 if produced by lymphosarcoma) and with non-degenerate neutrophils, macrophages and neoplastic cells in tumors.
  • Pleural effusion of septic exudate: with a yellowish-brown color and cloudy or opaque, the total proteins are 3-7 gr/dl and it contains fibrin, bacteria but not triglycerides. The cell count is 5,000-300,000 cells/microliter and contains degenerated neutrophils, macrophages, and bacteria.
  • Pleural lymph effusion: the color, in this case, is milky-white (although sometimes it can be pinkish-reddish) with a protein quantity of 2.5-6 gr/dl and with fibrin, triglycerides, and no bacteria. The cell content is 500-20,000 cells/microliter and usually contains lymphocytes, neutrophils, and macrophages.
  • Pleural blood effusion: the color is red and opaque, with more than 3 gr/dl of protein and with fibrin but without triglycerides or bacteria, with a cell count similar to that of peripheral blood and with red blood cells and some bank cells.

Causes of Pleural Effusion in Cats

Many causes can produce an accumulation of fluid in the pleural space of cats. In general, any of the following diseases and disorders can cause feline pleural effusion:


  1. Liver disease: due to the development of hypoproteinemia that reduces oncotic pressure and allows fluid to leak out and accumulate in the pleural space.
  2. Kidney disease (glomerulonephritis): due to loss of protein in the urine. Discover here 4 symptoms of kidney disease in cats.
  3. Enteropathy: due to loss of proteins at the intestinal level.
  4. Congestive cardiomyopathy: due to congestive heart failure in diseases such as congenital heart defects, feline dirofilariasis, hypertrophic cardiomyopathy, or pericardial diseases. You can find more information about feline hypertrophic cardiomyopathy, its symptoms, and treatment in this other AnimalWised post.
  5. Wet feline infectious peritonitis (FIP): due to an immune vasculitis, causing damage to the endothelium of the blood vessels and egress of proteins and serum from the capillaries. The exudate is fibrinous nonseptic (nonbacterial). To learn more about Feline Infectious Peritonitis (FIP), its symptoms, and treatment, do not hesitate to consult this article.
  6. Bacterial infections: can cause accumulation of pus (pyothorax) due to the entry of bacteria through bites and
  7. wounds, perforation of the esophagus or trachea, an extension of pneumonia, penetration of spikes, serious periodontal infection, etc.
  8. Tumors in the mediastinum: such as lymphosarcoma, thymoma, hemangiosarcoma, or breast tumors.
  9. Lung tumor (adenocarcinoma): either primary or secondary due to metastasis from another location.
  10. Diaphragmatic hernia: due to the trauma or accident that caused it.
  11. Right or left middle pulmonary lobe torsion.
  12. Chest trauma: due to lung injury or rupture of blood vessels in the chest, it produces pleural blood effusion (hemothorax), as well as rodenticide poisoning (coagulopathy).

Symptoms of Pleural Effusion in Cats

The clinical signs of pleural effusion in the cat are generally as follows:


  • Dyspnea or respiratory distress.
  • Reduced lung sounds due to fluid.
  • Increased respiratory rate or tachypnea.
  • Cough: For more information about Cough in cats, symptoms, causes, and treatment, read this post that we suggest.
  • Exercise intolerance.
  • Anorexia and weight loss: do not hesitate to take a look at this article about Anorexia in cats, its causes, symptoms, and treatment.

In addition, depending on the disease or condition that caused it, the cat will present symptoms associated with the process. For example:


  • In disorders leading to congestive heart failure: Cats will also have hypothermia, weak pulse, and jugular vein distention, as well as an enlarged liver and ascites. You may be interested in this article that we recommend about Hypothermia in cats, its causes, symptoms, and treatment.
  • In cases of feline infectious peritonitis: they may present depression, fever, jaundice (yellowing of the mucous membranes), neurological and ocular signs. We suggest you consult this article to find out if My cat is depressed, the causes, symptoms, and treatments.
  • In the case of mediastinal tumors: regurgitation and dysphagia may also appear due to compression of the esophagus, Horner’s syndrome if the sympathetic chain is compressed, edema of the neck and head if the cranial vena cava is compressed, reduction of heart and lung sounds and distension of the jugular vein. If you did not know Horner’s Syndrome in cats, its causes, and treatment, we leave you this article so you can find out.
  • In the case of glomerulonephritis: cats will show signs of kidney disease such as increased urination and water intake, pale mucous membranes, vomiting, or uremic syndrome, among others.
  • In the case of liver disease: jaundice, increased liver enzymes, and ascites can be seen, and in protein-losing enteropathy, edema and ascites can also be seen, as well as a thromboembolic disease due to the loss of antithrombin at the intestinal level.

Diagnosis of Pleural Effusion in Cats

The first thing to do is a thorough history by questioning the sick cat’s caretaker and a physical examination of the cat to note clinical signs, body condition, respiration, auscultation, and mental status.


With symptoms such as respiratory distress, tachypnea, and reduced lung sounds, the diagnosis of pleural effusion is very likely. In an X-ray, the presence of fluid in the pleural space can be evidenced by preventing a normal visualization of the lungs and with the ultrasound it is possible to suspect or deduce what type of fluid it is (transudate, blood, lymph, pus), obtaining clear information with analysis of fluid after thoracentesis by cell count, cytology, and biochemistry. In case of suspected infection, the fluid should be cultured.


Other ways to diagnose pleural effusion in cats are:

  • Electrocardiogram– to evaluate heart function and detect arrhythmias and tests for FIP virus in suspected cases of this infectious disease.
  • Blood tests, biochemistry, and urinalysis: they are essential to rule out kidney, liver, or digestive causes and observe the general state of health of the cat.

Treatment of Pleural Effusion in Cats

Pleural effusion therapy will depend on the cause that originates it. Even so, emergency treatment includes oxygen therapy due to respiratory distress, thoracentesis or puncture of the pleural space to drain the fluid while taking samples for analysis, and diuretics such as furosemide or spironolactone to reduce the cat’s stress. Although it depends on the origin of the cause.


  • In tumors: chemotherapy should be used and, in some tumors, diaphragmatic hernias and torsion of the pulmonary lobe, the treatment will be surgical.
  • In the case of pyothorax: the infection that is causing the accumulation of pus in the pleural space should be treated with antibiotics. In chylothorax due to the accumulation of lymph in the pleural space, the chyle should be drained frequently by thoracocentesis or by placing a drainage tube in the cat. If this is not effective, surgical treatment should be considered with ligation of the thoracic duct after draining. the lymph from the pleural cavity.

If heart failure is evident, in addition to diuretics and oxygen, drugs such as nitroglycerin or digoxin can be used. In kidney, liver, and intestinal disease, effective therapy should be adapted to control these pathologies.


Sequelae of a pleural effusion in cats

Pleural effusion in cats can leave sequelae, although, generally, with proper therapy and diagnosis of the problem, cats maintain their health and quality of life as before the effusion. Among the main sequelae of pleural effusion in cats we find:


  • Lung damage such as pulmonary edema.
  • Poorly resolved infection that develops into a chronic abscess called an empyema.
  • Presence of air in the chest cavity or pneumothorax after thoracentesis.

This article is merely informative, at we do not have the authority to prescribe veterinary treatments or make any type of diagnosis. We welcome you to take your pet to the veterinarian if it presents any kind of condition or distress.