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Ask a Vet: What Causes Fluid Buildup in a Dog's Legs?

Fluid Buildup in a Dog’s Legs

The causes of fluid buildup in a dog's legs are various and warrant investigation by a veterinarian considering that several causes can be serious and even life threatening at times. If you notice fluid buildup in your dog's legs it is therefore fundamentally important that you seek out assistance so to get to the root of the problem. Veterinarian Dr. Joanne Fernandez-Lopez shares some possible causes of fluid buildup in a dog's legs.


What Causes Fluid Buildup in a Dog's Legs?

Edema or fluid buildup is a common result from excessive filtration of fluid out of the capillaries, from depressed lymphatic function, physical injury or allergic reaction to antigen challenges. Following are several causes of fluid buildup in a dog's legs.

One common cause we see in our dogs is an increase in venous pressure which could come from applying a dressing too tight on the extremity of the pet. This makes blood back up in the veins and fluid starts to accumulate. This backup increases the pressure in the vein making fluid accumulate in the capillaries as well.

A common disease that causes increase in venous pressure and therefore edema is heart failure. If for example, the right ventricle of the heart fails, meaning it decreases its contractility, this results is in the pooling of blood in the right atrium and vena cava.

The consequence of this event happening too often is excessive capillary filtration and edema in the systemic organs. This is known as systemic edema and is a common complication of right-sided heart failure. In humans, you may notice that edema occurs in the distal limbs. However in pets, the systemic edema with right-sided heart failure is more often seen or noticeable in a distended abdomen with fluid or better known as ascites.

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You may also see this happening in pets with heartworm disease. The worms lodge on the right side of the heart (right atrium and right ventricle) causing a traffic jam of blood supply. The fluid accumulates and may cause enlargement of the belly or ascites. This end stage of heartworm disease is called caval syndrome. When left-sided heart failure occurs, fluid ends to accumulate in the lungs.

Left-sided heart conditions are severe myxomatous mitral valve degeneration, hypertrophic cardiomyopathy, dilated cardiomyopathy, and certain congenital cardiac diseases (e.g. patent ductus arteriosus).

Another common cause is a decrease in plasma protein concentration due to loss through the kidney, gut or a lack of production. In the kidney, the increase rate of loss is through the filtration unit called the nephrons which become more permeable to plasma proteins. This condition is called nephrotic syndrome. Proteins like albumin instead of staying in the bloodstream, get lost through the urine.

If there is a continuous loss of proteins in the urine it will reduce the concentration of proteins in the bloodstream.
As a consequence, the fluid in the bloodstream can move towards other areas of the body causing edema or water retention.

Now, in the gastrointestinal tract, there is a condition called inflammatory bowel disease or IBD in which the gut wall gets swollen and there is malabsorption of nutritional protein which then is lost through the stool. Pets tend to have weight loss, vomiting and diarrhea. An inflammatory disease like IBD or even cancer (example: lymphoma) can cause infiltration of inflammatory or cancerous cells in the gut wall and eventually an obstruction in the lymphatic vessels or lymphedema.

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Other condition is a decrease in production of protein by the liver due to malnutrition or liver failure. Victims of these two conditions tend to develop fluid within the abdomen. This is since concentrations of protein like albumin when they decrease in the blood vessels (a decrease in oncotic pressure) the fluid goes from the least to an area of more protein concentration. This third spacing of fluid can accumulate in any area. However, the abdomen is the most common location.

Other cause is physical trauma, like a scratch or a cut on the skin, results in a local bump or swelling. This is a normal response as the immune system is trying to deal with the wound. A similar swelling is observed when the skin reacts to some irritant agent or antigen challenge. This is very common in Boxers and Pitbulls. Allergens that could cause this are certain plants, foods, bee stings and other insect bites the pet is reacting to.

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How is Fluid Buildup in a Dog's Legs Diagnosed and Treated?

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Depending on the history, physical examination and the suspicion, your veterinarian will run full blood work CBC, Chemistry Panel, heartworm test, blood pressure, urinalysis and x-rays (radiographs) as a baseline.

If this is an allergic reaction, your veterinarian will immediately implement treatments like injectable steroids and antihistamines to decrease the swelling. With other suspected conditions and depending on the results from the baseline diagnostics, more tests will be recommended.

In the case of inflammatory bowel conditions, a full abdominal ultrasound with cobalamin and folate testing is the norm.

For urine lost of the protein (protein losing nephropathy) a urine protein to creatinine ratio is the test of choice to rule in or rule out this condition.

For liver disease, the chemistry panel could reveal elevated values or lower than normal values in liver enzymes, high bilirubin, high or low cholesterol and total protein. What proceeds is an ultrasound-guided liver biopsy that is sent to a veterinary pathologist for diagnosis.

Treatment is highly depend on suspicion at that moment and results from diagnostics. For congestive heart failure, oxygen therapy and diuretics (furosemide and/or spironolactone) will be given to relieve breathing effort and abdominal fluid buildup. If severe, we proceed with a thoracentesis or abdominocentesis. This means placing a needle in the pleural cavity (the space between lungs and ribs) or the abdomen/peritoneal space (between organs and abdominal wall) to be able to remove the fluid.

All these procedures can be done at your emergency clinic overnight or your regular veterinarian. Now, when
we are dealing with heartworm disease is a different story. The worms are lodged in the right chambers of the heart causing fluid obstruction and build up in the abdomen. Treatment is strict rest, oxygen therapy, steroids injections and doxycycline.

However, caval syndrome is the end stage of heartworm disease and prognosis is very guarded. The worms have already caused damage to the myocardium (heart muscle) and heart valves. To prevent this situation, please talk to your veterinarian about heartworm disease and preventive medication options for your pet.

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When albumin is dangerously low and edema is severe, your pet stays hospitalized with the goal of improving oncotic pressure (help improve amount of protein within blood vessels and prevent fluid from leaving). Your veterinarian may recommend albumin-containing products to add as fluid therapy. However, these can be unavailable at certain clinics due to cost.

As an alternative, Hetastarch or plasma blood products are used. They do not contain albumin, but helps improve oncotic pressure while treatment for the disease is done. If albumin is low due to protein loosing enteropathy (gut-wall disease like IBD or lymphoma), injectable steroids and antibiotics like metronidazole or tylosin are instituted.

When we are dealing with protein losing nephropathy (ex: glomerulonephritis), part of the treatment is
the use of Angiotensin-converting enzyme (ACE) inhibitors (ex: benazepril or enalapril), diuretics, antithrombotic medications antihypertensive medication and fluid therapy. Once your pet starts to improve, oral medications, specific diet management and long term therapy options are offered.

Remember symptoms to recognize involving edema are swollen limbs, eyelids, lips or abdomen. At times, your pet
may develop exercise intolerance, cough, difficulty breathing, enlarged abdomen, weight loss, vomiting or diarrhea. If one or all of these symptoms do occur, please visit your veterinarian as soon as possible for a full physical exam, diagnostics and a treatment plan tailored for your pet.

About the Author

Dr. Joanne Fernandez-Lopez is an emergency veterinarian on staff in the Emergency and Critical Care Department at Florida veterinary Referral Center (FVRC). Originally from Puerto Rico, Dr. Joanne Fernandez-Lopez graduated from North Carolina State University – College of Veterinary Medicine in Raleigh, NC.

joanne fernandez

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