Paracentesis is a surgical procedure in which a needle is inserted into the peritoneal cavity – the space between the two membranes that separate the organs in the abdominal cavity from the abdominal wall – in order to remove excess peritoneal fluid, also known as ascitic fluid. This procedure, which is sometimes called an abdominal or ascites tap, may be used for diagnostic or therapeutic purposes.
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While the body normally maintains a sufficient supply of ascitic fluid as a lubricant and anti-inflammatory agent, a buildup of surplus fluid, called ascites, is a disorder that can be the result of infection, injury or a serious condition like cirrhosis of the liver or cancer. A paracentesis, and subsequent analysis of the withdrawn ascitic fluid, can help determine the underlying cause of the ascites. Peritoneal mesothelioma, a rare form of cancer caused primarily by the ingestion of asbestos fibers, is often accompanied by ascites in the peritoneal cavity.
Patients with peritoneal mesothelioma-induced ascites might undergo a paracentesis to help verify the diagnosis, or more often, to alleviate stomach pain or difficulty breathing because of increased abdominal pressure caused by excessive fluid buildup (ascites).
Ascites develop in people with this disease because the peritoneal tumors cause a condition known as peritoneal carcinomatosis. This condition occurs when tumors are widespread throughout the abdomen. These tumors block the lymphatic system that normally regulates the flow of fluid in and out of the abdomen. Peritoneal mesothelioma tumors also weaken the endothelial cells in the abdominal wall. Endothelial cells normally function as barriers against various fluids in the walls of blood vessels. When these cells are weakened, fluids that contain protein and lipids (fat cells) leak out from blood vessels and accumulate in the peritoneal cavity.
Paracentesis is effective in helping patients manage the symptoms of ascites. However, over time, the fluid may become loculated, meaning it builds up in smaller spaces in the abdomen and does not flow freely in the peritoneal cavity, making it more difficult to drain. When this occurs, the procedure loses some of its effectiveness in draining fluid, and doctors may develop an alternative method for controlling fluid buildup.
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When performing a diagnosis using this procedure, a smaller amount of fluid may be obtained in a syringe. Pathologists study the cells found in the drained ascitic fluid. As a diagnostic tool for peritoneal cancer, paracentesis is less reliable than a biopsy because the cells in the ascetic fluid can sometimes appear benign. Doctors may try to diagnose the disease through with this procedure before performing a laparoscopy to obtain a tissue sample (because biopsies help to make a more definitive diagnosis).
Unlike a peritonectomy, which is a major surgery used to remove cancerous tumors from the abdominal cavity, a paracentesis is a minor surgery and first-line treatment option that can improve the quality of life for a person with peritoneal mesothelioma. Since ascites often reoccur with peritoneal mesothelioma, repeated therapeutic paracenteses can be administered as palliative care in patients with advanced stages of this disease.
Fast fact: When performing a paracentesis for diagnosis, 50 ml of fluid is taken from the peritoneal cavity. During a therapeutic paracentesis, no more than 1 L can be taken at a time.
This procedure is often performed as an out-patient procedure, taking approximately 20 to 30 minutes. Sometimes, an ultrasound is first administered to better visualize the size and scope of the ascitic fluid buildup.
After the bladder is emptied, patients are placed in bed with their head elevated at a 45 degree angle to allow fluid to accumulate in the lower abdomen. The insertion site is then cleaned with antiseptic and numbed before a large-bore needle is inserted to reach the peritoneal cavity.
Once the fluid begins to flow, the needle is removed and the cavity is drained via an intravenous catheter, either by gravity, a syringe, or by connection to a vacuum bottle. After the desired level of drainage is complete (no more than 500 ml in 10 minutes, and only one liter at a time, so that the body can equilibrate fluids and electrolytes), the catheter is withdrawn and the insertion site is covered with a sterile dressing and a small suture, if necessary. Alternatively, if the procedure is going to be repeated, a catheter with a flow control valve and protective dressing can be left in place.
If more than 5 liters of fluid is drained during the procedure, the patient may receive serum albumin to replace lost fluids, prevent a drop in blood pressure, or reduce the risk of shock. The patient is usually discharged within a few hours, provided that blood pressure is normal and there is no feeling of dizziness.
A paracentesis is a fairly simple procedure that presents very few risks.
If peritoneal mesothelioma cells are present, there is a chance they could spread (called "seeding") to the site where the needle was inserted. To make sure this doesn't occur, radiation therapy may be used along the site of the incision.
One documented complication that occurred in a patient with peritoneal mesothelioma was the repeated occurrence of a pneumothorax after a paracentesis procedure. A pneumothorax occurs when air builds up in the space around the lungs and doesn't allow the lung to expand fully. This is a rare complication, but doctors feel it should be considered in patients with pre-existing pulmonary disease.
Fast fact: The administration of albumin helps reduce morbidity and mortality in cirrhotic patients undergoing large-volume paracentesis caused by severe ascites.
Because peritoneal mesothelioma is rare, few studies have been done on the effectiveness of this procedure for this disease. While it is accepted as an effective method to control ascites, patients with the disease have a high rate of ascites recurrence. A disadvantage to paracentesis is that the patient must go to a hospital to have this procedure done. This can become costly and uncomfortable. If the patient necessitates frequent procedures, doctors may recommend the placement of a catheter instead.
In one study, a person who developed peritoneal mesothelioma was surgically fitted with a Tenckhoff catheter when his ascites did not respond to conservative management. The doctors were not in favor of frequent paracentesis as a primary treatment for the removal of excess fluid. The patient's symptoms were well controlled, and the catheter drained approximately 1 liter of fluid a day without the need for a hospital visit.
Some studies involving the use of paracentesis as a diagnostic tool show that the procedure is not always effective. In one case report, the procedure proved insufficient for an accurate diagnosis. Ascites were monitored for malignant cells, and multiple therapeutic paracentesis procedures routinely showed benign cytology. It wasn't until doctors conducted a PET scan and immunohistochemistry staining with cells obtained through fine needle aspiration that the diagnosis was made.
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