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Paracentesis

Definition

Paracentesis is a minimally invasive procedure using a needle to remove fluid from the abdomen.

Purpose

There are two reasons to take fluid out of the abdomen. One is to analyze it for diagnostic purposes; the other is to relieve pressure. Liquid that accumulates in the abdomen is called ascites. Ascites seeps out of organs for several reasons related either to disease in the organ or fluid pressures that are changing.

Liver disease

All the blood flowing through the intestines passes through the liver on its way back to the heart. When progressive disease such as alcohol damage or hepatitis destroys enough liver tissue, the scarring that results shrinks the liver and constricts blood flow. Such scarring of the liver is called cirrhosis. Pressure builds in the intestinal blood circulation, slowing flow and pushing fluid into the surrounding tissues. Slowly the fluid accumulates in areas with the lowest pressure and greatest capacity. The free space around abdominal organs receives the greatest amount. This space is called the peritoneal space because it is enclosed by a thin membrane called the peritoneum. The peritoneum wraps around nearly every organ in the abdomen, providing many folds and spaces for the fluid to gather.

Infections

Peritonitis is an infection of the peritoneum that can develop in several ways. Many abdominal organs contain germs that do not occur elsewhere in the body. If they spill their contents into the peritoneum, infection is the result. Infection changes the dynamics of body fluids, causing them to seep into tissues and spaces. The gall bladder, the stomach, any part of the intestine, and most especially the appendix—all cause peritonitis when they leak or rupture. Tuberculosis can infect many organs in the body; it is not confined to the lungs. Tuberculous peritonitis causes ascites.

Other inflammations

Peritoneal fluid is not just produced by infections. An inflamed pancreas, called pancreatitis, can cause a massive sterile peritonitis when it leaks its digestive enzymes into the abdomen.

Cancer

Any cancer that begins in or spreads to the abdomen can leak fluid. One particular tumor of the ovary that leaks fluid and results in fluid accumulation is called
Meigs' syndrome.

Kidney disease

Since the kidneys are intimately involved with the body's fluid balance, diseases of the kidney often cause excessive fluid to accumulate. Nephrosis and nephrotic syndrome are the general terms for diseases that cause the kidneys to retain water and promote its movement into body tissues and spaces.

Heart failure

The ultimate source of fluid pressure in the body is the heart, whose pumping generates blood pressure. All other pressures in the body are related to blood pressure. As the heart starts to fail, blood backs up, waiting to be pumped. This increases pressure in the veins leading to the heart, particularly below it where gravity is also pulling blood down. The extra fluid from heart failure is first noticed in the feet and ankles, where gravitational effects are most evident. In the abdomen, the liver swells first, then it and other abdominal organs start to leak.

Pleural fluid

The other major body cavity (besides the abdomen) is the chest. The tissue in the chest corresponding to the peritoneum is called the pleura, and the space contained within the pleura, between the ribs and the lungs, is called the pleural space. Fluid is often found in both cavities, and fluid from one cavity can find its way into the other.

Fluid that accumulates in the abdomen creates abnormal pressures on organs in the abdomen. Digestion is hindered; blood flow is slowed. Pressure upward on the chest from fluid-filled organs compromises breathing. The kidneys function poorly in the presence of such external pressures and may even fail.

Description

During paracentesis, special needles puncture the abdominal wall, being careful not to hit internal organs. If fluid is needed only for analysis, less than 7 oz (200 ml) are removed. If pressure relief is an additional goal, many quarts may be removed. Rapid removal of large amounts of fluid can cause blood pressure to drop suddenly. For this reason, the physician will often leave a tube in place so that fluid can be removed slowly, giving the system time to adapt.

A related procedure called culpocentesis removes ascitic fluid from the very bottom of the abdominal cavity through the back of the vagina. This is used most often to diagnose female genital disorders like ectopic pregnancy, which may bleed or exude fluid into the peritoneal space.

Fluid is sent to the laboratory for testing, where cancer and blood cells can be detected, infections identified, and chemical analysis can direct further investigations.

Aftercare

An adhesive bandage and perhaps a single stitch close the insertion site. Nothing more is required.

Risks

Risks are negligible. It is remotely possible that an organ could be punctured and bleed or that an infection could be introduced.

Normal results

A diagnosis of the cause and/or relief from accumulated fluid pressure are the expected results. Fluid will continue to accumulate until the cause is corrected. Repeat procedures may be needed.

Resources

BOOKS

Chung, Raymond T. and Daniel K. Podolsky. "Cirrhosis and its Complications." In Harrison's Principles of Internal Medicine, edited by Eugene Braunwald, et al. New York: McGraw-Hill, 2001.

Henry, J. B. Clinical Diagnosis and Management by Laboratory Methods. 20th ed. Philadelphia, PA: W. B. Saunders Company, 2001.

OTHER

Lehrer, Jennifer K. Abdominal tap—paracentesis. National Institutes of Health. January 1, 2003 [cited April 4, 2003]. <http://www.nlm.nih.gov/medlineplus/encyclopedia.html>.

"Paracentesis." American Thoracic Society. April, 2003 [cited April 4, 2003]. <http://www.thoracic.org/assemblies/cc/ccprimer/infosheet10.html>.

J. Ricker Polsdorfer, MD Mark A. Best, MD