A peritoneovenous shunt refers to the surgical insertion of a shunting tube to achieve the continuous emptying of ascitic fluid into the venous system.
Ascites is a serious medical disorder characterized by the pathological accumulation of fluid in the peritoneal cavity, the smooth membrane that lines the cavity of the abdomen and surrounds the organs. Ascites is usually related to acute and chronic liver disease (cirrhosis) and to a lesser degree, to malignant tumors arising in the ovary, colon, or breast. Ascites may also be associated with chronic kidney disease and congestive heart failure. The formation of ascitic fluid results from the interplay of three factors: abnormally high pressure within the liver or the veins draining into the liver (portal hypertension); abnormally low amounts of albumin in the blood (hypoalbuminemia); and changes in sodium and water excretion by the kidneys.
When medical therapy fails, peritoneovenous shunts help manage chronic ascites.
Cirrhosis is the seventh leading cause of death by disease in the United States, killing over 25,000 people each year. Fifty percent of patients with cirrhosis will develop ascites over a period of 10 years. Cirrhosis—regardless of its cause—greatly increases the risk for liver cancer. Few studies have been conducted on the risk for liver cancer in patients with primary biliary cirrhosis; however, one study reported an incidence of 2.3%. Approximately 4% of patients with cirrhosis caused by hepatitis C develop liver cancer. In Asia, about 15% of people who have chronic hepatitis B develop liver cancer, but this high rate is not seen in other parts of the world. One Italian study that followed a group of hepatitis B patients for 11 years found no liver cancer over that period of time.
A variety of shunts have been designed for peritoneovenous shunting, including the Hyde shunt (1966-1974), LaVeen shunt (1974-1980), and Denver shunt. The latter predates the LaVeen shunt, but is more popular as of 2003. All designs work about equally well.
For the peritoneovenous shunt insertion procedure, the patient only requires a local anesthetic and a sedative. A long needle is inserted into the jugular vein in the neck, and is passed down through the superior vena cava, the large vein that delivers blood from the head, neck, and upper limbs back to the heart. This serves to widen the vein. The surgeon makes an incision and inserts a tube traversing the subcutaneous tissue of the chest wall. The tube connects the peritoneal cavity to the neck, where it enters the widened jugular vein. There the surgeon attaches a pressure-sensitive one-way valve to prevent backflow.
Ascites may go unnoticed for quite some time until the patient notices a slight increase in waistline. Severe ascites with marked abdominal distension becomes very disabling, especially when associated with swelling of the legs, pleural effusions (fluid around the lungs), and shortness of breath.
Diagnosis can be established by examination of the ascitic fluid, which allows the physician to differentiate between cirrhosis and tumor-induced ascites. The fluid is taken from the peritoneal cavity in a procedure called a paracentesis . Ascitic fluid analysis includes a total polymorph count, protein and albumin concentrations, and placement of at least 10 ml of ascitic fluid each into blood culture bottles for processing. If a measurement called the serum-ascitic fluid albumin gradient is greater than 11 g/L, cirrhosis, not cancer, is suspected.
After surgery, the patient's vital signs are monitored in a recovery room . Pain medication and antibiotics are administered as needed. Once released from the hospital, the patient is expected to abstain from alcohol, and follow a low-salt diet and medication regime designed to control ascites.
Patients also require training in shunt maintenance. To keep the fluid moving out of the abdomen, the shunt has to be properly pumped on a daily basis. Twice a day—once at bedtime and again prior to rising in the morning—the shunt is pumped about 20 times. This is essential to limit the accumulation of fibrin and other debris within the shunt, and to avoid the formation of an occlusive fibrin sheath at the venous tip.
Complications following peritoneovenous shunt insertion are common and include infection, leakage of ascitic fluid, accumulation of abnormally large amounts of fluid in the intercellular tissue spaces of the body (edema), deregulation of the blood clotting mechanism (coagulopathy), and shunt blockage. Clogging of the shunt with debris is the most common complication. Some patients develop further complications from the ascitic fluid entering directly into their bloodstream. Often, scar tissue develops, making future liver transplants difficult.
In spite of the complications associated with the procedure, many patients obtain useful relief from ascites following peritoneovenous shunt insertion.
The most recent guidelines from the American Association for the Study of Liver Diseases recommend peritoneovenous shunting only under these conditions:
Cirrhosis is irreversible, but the rate of progression can be very slow depending on its cause and other factors. Five-year survival rates are about 85% in the Unites States and can be lower or higher depending on severity.
Alternative treatments for ascites include:
There is no satisfactory treatment for refractory ascites in patients with cirrhosis. Both peritoneovenous shunts and paracentesis have been used, but there is uncertainty about their relative merits.
See also Portal vein bypass .
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American Gastroenterological Association. 4930 Del Ray Avenue, Bethesda, MD 20814. (301) 654-2055. http://www.gastro.org .
Society for Vascular Surgery. 900 Cummings Center, Beverly, MA 01915-1314. (978) 927-8330. http://svs.vasculaweb.org .
"Ascites." Family Practice Notebook. http://www.fpnotebook.com/GI35.htm .
Monique Laberge, Ph.D.
Peritoneovenous shunt insertion is performed in a hospital by a surgeon specialized in gastroenterology or hepatology.