Ascites

Ascites

Description

Ascites is defined as an excessive amount of fluid built up within the peritoneal cavity. Both the abdominal organs and the abdomen itself are lined with membranes called the peritoneum. Between these two linings is a space referred to as the peritoneal cavity. In pathological conditions that result in edema, or excessive fluid accumulation in bodily tissues, fluid can build up in the peritoneal cavity.

Smaller abdominal fluid amounts usually do not produce symptoms. However, larger accumulations can cause:

• rapid weight gain
• abdominal discomfort and distention
• shortness of breath and actual dyspnea, or difficulty breathing
• swollen ankles

Severe cases of ascites can result in the retention of literally gallons (each gallon equals nearly four liters) of liquid in the peritoneal cavity. If fluid retention is sufficiently severe, the abdomen becomes swollen and even painful. Breathing can be affected as the fluid-filled peritoneal cavity presses upon the diaphragm, a very necessary component of respiration. The diaphragm is made up of a dome-shaped sheet of muscles that separates the thoracic, or chest, cavity from the abdomen. When the muscle fibers of the diaphragm contract, the space in the chest cavity is enlarged, and air enters the lungs to fill the enlarged space. When pressure on the diaphragm from fluid build-up occurs, it lessens the ability of these diaphragm muscular fibers to expand and contract, and results in impaired breathing.

Ascites, in itself, is not a disease, but rather a symptom of several other pathological conditions. These include:

• Cirrhosis of the liver, which is responsible for 80% of all instances of ascites in the United States.
• Pancreatic ascites develops when a cyst that has thick, fibrous walls (pseudocyst) bursts and permits pancreatic juices to enter the abdominal cavity.
• Chylous ascites, which has a milky appearance caused by lymph that has leaked into the abdominal cavity. Although chylous ascites is sometimes caused by trauma, abdominal surgery, tuberculosis, or another peritoneal infection, it is usually a symptom of lymphoma or some other cancer.
• Cancer causes 10% of all occurrences of ascites in the United States. It is most commonly a consequence of disease that originates in the peritoneum (peritoneal carcinomatosis) or of cancer that spreads (metastasizes) from another part of the body. Tumors especially prone to malignant ascites formation include ovarian cancer and metastatic gastrointestinal tumors.
• Endocrine and renal ascites are rare disorders. Endocrine ascites, sometimes a symptom of an endocrine system disorder, also affects women who are taking fertility drugs. Renal ascites develops when blood levels of albumin dip below normal. Albumin is the major protein in blood plasma. It functions to keep fluid inside the blood vessels.

Causes

The two most important factors in the production of ascites due to chronic liver disease are low levels of albumin in the blood and an increase in the pressure within the branches of the portal vein that run through liver (portal hypertension). Low levels of albumin in the blood cause a change in the pressure necessary to prevent fluid exchange (osmotic pressure). This change in pressure allows fluid to seep out of the blood vessels. The scarring that occurs in cirrhosis causes portal hypertension. Blood that cannot flow through the liver because of the increased pressure leaks into the abdomen and causes ascites.

Other conditions that contribute to ascites development include:

• hepatitis
• heart or kidney failure
• inflammation and fibrous hardening of the sac that contains the heart (constrictive pericarditis)

Persons who have systemic lupus erythematosus but do not have liver disease or portal hypertension occasionally develop ascites. Depressed thyroid activity sometimes causes pronounced ascites, but inflammation of the pancreas (pancreatitis) rarely causes significant accumulations of fluid.

Treatments

Reclining minimizes the amount of salt the kidneys absorb, so treatment generally starts with bed rest and a low-salt diet. Urine-producing drugs (diuretics) may be prescribed if initial treatment is ineffective. The weight and urinary output of patients using diuretics is normally carefully monitored, often on a daily basis. This scrutiny involves watching for signs of:

• Hypovolemia (massive loss of blood or fluid) that can often result in drastic drops in blood pressure.
• Azotemia (abnormally high blood levels of nitrogen-bearing materials).
• Potassium imbalance that can result in cardiac arrhythmia.
• High sodium concentration. Sodium should be restricted from the diet as much as possible.

Because of the discomfort and respiratory difficulty moderate-to-severe accumulations of fluid can produce, fluid removal, or paracentesis , is often the treatment of choice. Paracentesis involves the extraction of fluid from the abdominal cavity via a needle that is usually inserted into the peritoneum under local anesthesia. This is a relatively safe and painless method of relieving fluid build-up. It is considered safer than diuretic therapy, resulting in fewer complications and requiring shorter hospital stays.

Large-volume paracentesis is also the preferred treatment for massive ascites. Diuretics are sometimes used to prevent new fluid accumulations, and the procedure may need to be repeated periodically.

In cases of ascites that do not respond appropriately to the treatments described above, a peritoneovenous shunt may be inserted. This device is equipped with a one-way valve that allows fluid from the peritoneal cavity to pass into the venous blood circulatory system. From there the fluid is eliminated by the kidneys. In cases of malignant ascites, there is a concern that the use of such a shunt could enhance the spread of the cancer. This relatively small risk must be balanced against the positive effect the shunt can have on the individual's quality of life as well as against his or her expected survival period.

Alternative and complementary therapies

Dietary alterations, focused on reducing salt intake, are an important facet of treatment. Potassium-rich foods like low-fat yogurt, mackerel, cantaloupe, and baked potatoes help balance excess sodium intake and help ensure proper heart function. Such complementary therapies should always be considered an adjunct to, not a substitute for, the conventional treatments described above.

Resources

BOOKS

Berkow, Robert, ed. The Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 1997.

PERIODICALS

Bieligk, S.C., B.F. Calvo, and D.G. Coit. "Peritoneovenous Shunting for Nongynecologic Malignant Ascites." Cancer 91, no. 7 (April 2001): 1247-9.

ORGANIZATIONS

National Cancer Institute, National Institute of Health. 31 Center Drive, MSC 2580, Bethesda, MD 20892-2580. (800) 4-CANCER. <http://www.nci.nih.gov>.

Joan Schonbeck