Ascites in Dogs
Dr. Douglas Brum
Abdominocentesis is the sampling of the ascites using a needle and syringe. The fluid obtained is then submitted to a laboratory for fluid analysis. This may be the single most important diagnostic test when evaluating an animal with ascites because specific diseases have specific fluid analysis characteristics. Ascitic fluid is divided into three different categories based on the fluid's cell count and protein concentration.
A complete history and physical examination is very important in determining the diagnostic aids of choice. Proper evaluation will determine the depth of the diagnostics needed.
Transudates are fluids of low cell count (under 1500cells/mcl) and low protein concentration (under 2.5g/dl). Examples of transudates include those caused by: hypoproteinemia, liver disease, some tumors and obstruction of lymphatic drainage.
Modified transudates are fluids with higher cell counts (1000 to 7000 cells/mcl) and protein concentration (2.5 to 7.5g/dl). Examples of modified transudates include ascites caused by: congestive heart failure, abdominal tumors, obstruction of the hepatic vein or thoracic caudal vena cava and some liver diseases.
Exudates are fluids with the highest cell counts (over 7,000 cells/mcl) and protein concentrations (usually over 3.0g/dl). Examples include: bleeding conditions, tumors, bacterial infections caused by bowel compromise, chyloabdomen (lymph fluid in the abdomen), urine and bile leakage and pancreatitis.
A pathologist also examines the cell types microscopically. Different types of cell populations represent different disease processes, and cytologic evaluation is a valuable aid in establishing a correct diagnosis.
CBC. The CBC evaluates the red and white blood cell lines. Elevations and morphology changes in the white blood cell line may indicate peritonitis. Decreases in the red cells are indicative of anemia. Acute blood loss or chronic debilitating diseases are potential causes of the anemia. Platelet (blood cells required for proper clotting) counts are assessed. Significant decreases may lead to intra-abdominal hemorrhage.
A biochemical profile evaluates several body systems. A decrease in serum albumin (hypoalbuminemia) would be noted. Decreased kidney function is assessed with increases in blood urea nitrogen (BUN) and creatinine. Liver disease is evaluated by elevations in ALT, AST and ALKP enzymes. Decreases in BUN, albumin, cholesterol and occasionally blood glucose might indicate decreased liver functional capability.
A urinalysis completes the assessment of kidney function. Urinary protein loss (proteinuria) may be noted, and a follow up urine protein creatinine ratio might be recommended to confirm and quantify significant urinary protein loss.
Chest x-rays evaluate the heart and lungs for evidence of cardiopulmonary disease. Cardiac enlargement or fluid in the chest may suggest right-sided heart failure. Masses near the diaphragm compressing the caudal vena cava may also be visualized. Abdominal x-rays may be useful in evaluating liver and kidney size as well as visualizing some abdominal masses. Unfortunately, if there is a significant amount of ascites, the abdominal structures are often obscured by the nature of the fluid.
A bile acid measurement is a specific test of liver function. If the ascites is due to liver disease the bile acids are generally highly elevated.
Serum lipase measurements test for pancreatic inflammation. Pancreatitis, pancreatic cancer and pancreatic abscesses may all cause elevations.
An abdominal ultrasound is an excellent test for evaluating abdominal organs when ascites is present. Generally, the fluid in the abdomen enhances the images, providing for greater detail. This allows for visualization of abdominal masses and evaluation of the liver, kidneys, spleen and pancreas. If indicated, abnormalities may be biopsied for definitive diagnosis.
If heart disease is suspected, an echocardiogram is indicated. The heart valves and heart muscle are visualized, and cardiac function may be assessed. Congestive heart failure has many causes, and an echocardiogram is the diagnostic test that provides the best information on the prognosis and treatment of the disease.
Endoscopy is a good, relatively noninvasive, method of assessing small bowel disease. The inner lining of the stomach and duodenum can be visualized and biopsied. Intestinal neoplasia, inflammatory bowel disease and intestinal lymphangiectasia may be a cause of a protein losing enteropathy (losing protein through the gastrointestinal system).
One or more of the diagnostic tests described above may be recommended by your veterinarian. In the meantime, treatment of the symptoms might be needed, especially if the problem is severe. The following nonspecific (symptomatic) treatments may be applicable to some, but not all, pets with ascites. These treatments may reduce severity of symptoms or provide relief for your pet. However, nonspecific therapy is not a substitute for definite treatment of the underlying disease responsible for your pet's condition.
The most important aspect of treating ascites is to determine how quickly the ascites has developed, and the clinical condition of your pet. If the ascites has developed slowly, and your pet is fairly strong, then emergency treatment is generally not required. If the ascitic fluid has developed rapidly, it is often associated with weakness and emergency care is indicated. Appropriate treatment pending a diagnosis of the primary cause of the ascites may include:
Therapeutic abdominocentesis. If there is a large amount of fluid in the abdomen it may be compressing the diaphragm, which leads to difficulty breathing. A needle is inserted into the abdominal wall and fluid drained to relieve the pressure, making breathing easier and your pet more comfortable. Once your pet is breathing more comfortably, the needle is withdrawn. All the fluid is not removed, however, because losing too much fluid from the body may lead to shifts in fluid homeostasis and shock.
Diuretics are medications given to promote the removal of fluid from the body. Fluid is excreted as urine production is increased. Diuretics are most effective in removing fluid from tissue rather than from a body cavity; thus they have limited effect on removing ascitic fluid from the abdomen. Furosemide (Lasix) is most commonly used.
Animals in respiratory distress often require oxygen for stabilization. Oxygen may be provided by an oxygen mask, nasal oxygen canola or an oxygen cage. Usually, once some fluid has been removed from the abdomen, the oxygen is no longer required.
A rapid onset of ascites might require intravenous fluid support to maintain tissue perfusion and treat an animal in shock. If the animal has a low total protein (due to a low blood albumin level), fluid support with colloids (fluids that increase the oncotic pressure of plasma) may be given to slow the production of the ascites.
Transfusions with blood, or blood products, might be required if the ascites is due to bleeding within the abdomen. If transfusions are needed, the animal is usually very weak and has a falling hematocrit (a blood test that measures anemia).
If infection is suspected, intravenous antibiotics are given pending definitive diagnosis. Ascites caused by infection is a situation requiring emergency surgery.