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Paracentesis

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 appendixall 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 tapparacentesis. 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

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Paracentesis

Paracentesis

Definition

Paracentesis is a procedure during which fluid from the abdomen is removed through a needle.

Purpose

There are two reasons to take fluid out of the abdomen. One is to analyze it. 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 the blood flow. Such scarring of the liver is called cirrhosis. Pressure builds up in the intestinal circulation, slowing flow and pushing fluid into the tissues. Slowly the fluid accumulates in areas with the lowest pressure and greatest capacity. The free space around abdominal organs receives most of it. 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. Infection changes the dynamics of body fluids, causing them to seep into tissues and spaces. Peritonitis can develop in several ways. Many abdominal organs contain germs that do not belong elsewhere in the body. If they spill their contents into the peritoneum, infection is the result. The gall bladder, the stomach, any part of the intestine, and most especially the appendixall 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. The pancreas 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, the resulting presentation of the disease, is 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 provoke its movement into body tissues and spaces.

Heart failure

The ultimate source of fluid pressure in the body is the heart, which 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 back pressure upstream, particularly below the heart where gravity is also pulling blood away from the heart. The extra fluid from heart failure is first noticed in the feet and ankles, where gravitational effects are most potent. In the abdomen, the liver swells first, then it and other abdominal organs start to leak.

Pleural fluid

The other major body cavity 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 compromises breathing. The kidneys function poorly in the presence of such external pressures and may even fail with tense, massive ascites.

Description

During paracentesis, special needles puncture the abdominal wall, being careful not to hit internal organs. If fluid is needed only for analysis, just a bit is 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 circulation 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 mostly to diagnose female genital disorders like ectopic pregnancy that 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 hole. 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.

Abnormal results

Fluid will continue to accumulate until the cause is corrected. Repeat procedures may be needed.

Resources

BOOKS

Glickman, Robert M. "Abdominal Swelling and Ascites." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

KEY TERMS

Ectopic pregnancy A pregnancy occurring outside the womb that often ruptures and requires surgical removal.

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Paracentesis

Paracentesis

Definition

Also known as peritoneal tap or abdominal tap, paracentesis consists of drawing fluid from the abdomen through a needle.

Purpose

Although little or no fluid is present in the abdominal (peritoneal) cavity of a healthy man, more than half an ounce may accumulate at certain times during a woman's menstrual cycle. Any cancer that originates in or spreads to the abdomen can result in fluid accumulation (malignant ascites ).

Doctors remove fluid (ascites) from the abdomen to analyze its composition and determine its origin, to relieve the pressure and discomfort it causes, and to check for signs of internal bleeding This procedure should be performed whenever an individual experiences sudden or worsening abdominal swelling or when ascites is accompanied by fever , abdominal pain, confusion, or coma.

Paracentesis in cancer patients

When performed on a patient who has been diagnosed with cancer, paracentesis helps doctors determine the extent (stage) of the disease and whether conservative or radical treatment approaches would most effectively relieve symptoms or lengthen survival.

Precautions

Before undergoing paracentesis, a patient must make the doctor aware of any allergies, bleeding problems or use of anticoagulants, pregnancy, or possibility of pregnancy.

Description

Paracentesis is performed in a doctor's office or a hospital. The puncture site is cleansed and, if necessary, shaved. The patient may feel some stinging as a local anesthetic is administered, and pressure as the doctor inserts a special needle (tap needle) into the abdomen. Occasionally, guidance with CT or ultrasound may be used.

When paracentesis is performed for diagnostic purposes, less than an ounce of fluid is drawn from the patient's abdomen into a syringe. As much as 15 ounces may be needed to determine whether ascites contains cancer cells. When the purpose of the procedure is to relieve pressure or other symptoms, many quarts of ascites may be drained from the abdomen. Because removing large amounts of fluid in a short time can cause dizziness, lightheadedness, and a sudden drop in blood pressure, the doctor may drain fluid slowly enough that the patient's circulatory system has time to adapt.

Laboratory analysis of abdominal fluid can detect blood, cancer cells, infection, and elevated protein levels often associated with malignant ascites. Results of these tests can help doctors determine the most appropriate course of treatment for a particular patient.

Preparation

No special preparations are required before this procedure. Patients should ask their doctor about special preparation requirements, but usually may eat, drink and take medications normally prior to paracentesis.

Aftercare

After removing the tap needle, the doctor may use a stitch or two to close any incision made (to ease the needle's entry into the abdomen) and applies an adhesive dressing to the puncture site.

Risks

Paracentesis occasionally causes infection. There is also a slight chance of the tap needle puncturing the bladder, bowel, or blood vessels in the abdomen. If large amounts of ascites are removed, the patient may need to be hospitalized and given intravenous (IV) fluids to prevent or correct severe fluid, protein, or electrolyte imbalances. A patient who has undergone extensive paracentesis should be warned about the possibility of fainting (syncope) episodes.

Normal results

Paracentesis is designed to establish the cause of, or to relieve symptoms associated with, an abnormal accumulation of fluid in the abdomen.

Abnormal results

Laboratory tests of ascites may indicate the presence of:

  • appendicitis
  • cancer
  • cirrhosis
  • damaged bowel
  • disease of the heart, kidneys, or pancreas
  • infection

Ascites that contains cancer cells is usually bloody. Cloudy abdominal fluid has been found in patients with extensive intraabdominal lymphomas. Ascites will continue to accumulate until its cause is identified and eliminated. Some patients need to undergo paracentesis repeatedly.

Resources

BOOKS

DeVita, Vincent T., et al., eds. Cancer: Principles & Practice of Oncology, vol. 2, 5th ed. Philadelphia: Lippincott-Raven, 1997.

Tierney, Lawrence J., et al., eds. Current Medical Diagnosis & Treatment 2000. New York: Lange Medical Books/McGraw-Hill, 2000.

OTHER

Dr. Koop Medical Encyclopedia Abdominal Tap. 3 May 2001. 20 July 2001 <http://aol.drkoop.com/conditions/ency/article/003896.htm>

Maureen Haggerty

KEY TERMS

Appendicitis

Inflammation of the appendix.

Cirrhosis

Scarring of the liver (from infection or tumor) resulting in liver dysfunction

Lymphoma

Cancer of the lymph system.

QUESTIONS TO ASK THE DOCTOR

  • How will paracentesis benefit me?
  • Will I have to have this procedure more than once?
  • How soon after this procedure can I resume my normal activities?
  • Will paracentesis cure my problem?
  • Will I require hospitalization?

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paracentesis

paracentesis (pa-ră-sen-tee-sis) n. tapping: the process of drawing off fluid from a part of the body through a hollow needle or cannula. In ophthalmology it involves an incision into the anterior chamber of the eye.

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Paracentesis

Paracentesis

Definition

Paracentesis is a procedure in which excess fluid in the abdomen is sampled by aspiration through a needle. The fluid may be called ascites fluid, abdominal fluid, or peritoneal fluid.

Purpose

Paracentesis is commonly performed to identify the cause of newly diagnosed ascites (excess fluid in the abdominal cavity); to diagnose changes in the condition of a patient already known to have ascites; and to relieve pressure from severe distention due to increased fluid in the abdomen. A sample of the fluid withdrawn from the abdominal cavity is nearly always sent for laboratory analysis to determine the presence or absence of infection, and/or to learn more about the cause of ascites if necessary. Ascites forms for a variety of reasons, including infection, diseases of various organs, and conditions that result in abnormal blood flow. The most common cause in the United States is alcoholic cirrhosis.

Precautions

Ascites is difficult to diagnose by physical exam, although with experience health care practitioners can note "shifting dullness" by percussion. Generally at least 500 mL (17 oz) of fluid must accumulate before the effusion is detected by x ray, and 1500 mL (3.2 pt) before ascites is easily detected on physical exam. Ultrasound may be necessary to differentiate ascites from obesity and other reasons for abdominal distention. Ultrasound may even be used to guide the needle for paracentesis. When performing this procedure, the physician should observe universal precautions for the prevention of transmission of bloodborne pathogens.

Description

Consent should be obtained for the procedure after discussion of the possible complications. The area beneath the umbilicus is cleansed with betadine or other antibacterial solution, and local anesthetic administered. A long thin needle or trochar with a stylet is inserted about 2 in (5 cm) below the umbilicus, and the appropriate amount of fluid withdrawn. Usually a syringe is used, but for large amounts of ascites, polyethylene tubing may be attached to vacuum bottles and the excess fluid aspirated. A minimum of 30 mL (1 oz) of fluid should be collected by sterile technique in two or three sterile syringes. One portion should be transferred to a tube containing EDTA for cell counts and the last syringe should be used to inoculate blood culture media. These samples and the remaining fluid should be sent to the laboratory for analysis. If cytologic exam is requested, 100 mL (3.4 oz) of fluid should be submitted to the laboratory.

Cirrhosis of the liver and malignant abdominal masses are the two most common causes of ascites. Cirrhosis is usually associated with a transudative fluid, a fluid of low cellularity and protein, while malignancy causes an exudative (inflammatory) fluid of high cellularity and protein. Transudative fluids result from changes in blood flow, and are typically seen in persons with cirrhosis, congestive heart failure, and a few other conditions that disrupt normal hemodyndamics. An explanation of ascites formation in cirrhosis serves well to explain some principles common to transudative fluid formation. Blood entering the portal vein from 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 compresses the hepatic sinusoids and vessels and restricts the blood flow. The blood bypasses the liver and enters the splenic, gastric, and esophageal veins, causing very high hydrostatic pressure. This pressure causes fluid to escape the vessels and enter the abdominal cavity. Slowly the fluid accumulates in the areas with the lowest pressure and the greatest capacity. The free space around abdominal organs receives most of it. 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, and lines the entire abdominal cavity, providing many folds and spaces in which fluid can gather. Normally, only 30-50 mL (1-1.7 oz) of fluid is found in the peritoneal cavity. The fluid itself is essentially an ultrafiltrate of plasma. Any condition that causes an increase in peritoneal fluid is called an effusion or ascites. Kidney disease can contribute to this process, since the kidneys have a critical role in fluid balance. Nephrotic syndrome in particular is associated with ascites formation. In this condition the kidneys lose large amounts of protein into the urine causing a drop in plasma oncotic pressure. Since proteins hold fluid in the vascular bed, loss of protein (albumin) causes fluid to enter the tissue spaces. Heart failure also can cause ascites, because decreased cardiac output causes blood to accumulate in the return circulation. The increased venous pressure results in fluid leaking from the circulatory system. First edema is noticed in the legs, due to the effect of gravity, then in ascites formation in the abdomen.

Malignancy, infection, pancreatitis, bowel obstruction, and several other conditions produce an exudative effusion. These conditions cause inflammation that results in increased blood vessel permeability. The fluid that accumulates typically contains white blood cells and if cancer is the cause, malignant cells from the tissue of origin. Malignancy may result from cancerous transformation of the cells that line the peritoneum, called mesothelial cells. Mesotheliomas may be difficult to distinguish from reactive mesothelial cells that occur whenever the lining of the abdomen is traumatized. The two most common metastatic cancers invading the abdomen are ovarian and breast cancer, but lymphoma, leukemia, lung, and many other cancers can also infiltrate the abdomen. Bacterial peritonitis is an infection of the peritoneum, and is a life-threatening cause of exudative ascites. It can result from intestinal perforation, leakage through a diseased bowel wall, ruptured appendix or gall bladder, or septicemia (infection in the blood). Inflammation of the abdominal wall can also result from blunt trauma, pancreatitis, intestinal obstruction, and other conditions.

Physical characteristics of ascites fluid

Normal ascites fluid is clear and straw colored. Turbid fluid occurs in bacterial peritonitis, malignancy, and pancreatitis. Green fluid occurs when bile is present. This can be caused by a ruptured bowel or perforated bile duct. Bloody fluid occurs in trauma, malignancy, and pancreatitis. Milky fluid contains chyle from the intestinal lymphatics and occurs when lymphatic vessels rupture.

Microscopic analysis

The WBC count is performed using a hemacytometer. Normal fluid has a very low WBC count (less than 300 per microliter) and does not have to be diluted. Counts above 1,000 indicate an exudative process. The differential is performed on a cytocentrifuged sample to concentrate the cells. Macrophages predominate in normal fluid and together with mesothelial cells account for about 70% of the nucleated cell population. Lymphocytes are normally less than 20% and neutrophils less than 10% of nucleated cells. Neutrophils accounting for 50% or 500 per microliter are most often associated with bacterial peritonitis. Lymphocytes will predominate in lymphoma, nephrotic syndrome, and congestive heart failure and may be abundant along with macrophages in tuberculosis. Red cell counts are also performed manually. Red cells often enter the fluid during sample collection, a process referred to as a traumatic tap. In this case, the red count will be low, the supernatant fluid will be pale yellow (normal), and the fluid will clear as more is collected. In the absence of a traumatic tap, red blood cells are most often encountered in malignancy and trauma. It is especially important to examine the fluid for the presence of malignant cells. As mentioned, metastatic cancer cells from ovarian and breast cancer are the most commonly seen infiltrates. Malignant mesothelial cells are difficult to distinguish from reactive mesothelial cells. Cytology should be evaluated with both Wright and Papanicilaou stains. Cytochemical tests and flow cytometry may be needed to identify malignant mesothelial cells, leukemic blasts (immature white cells), and lymphoma cells.

Biochemical tests

Chemical tests are performed on ascites fluid by the same methods used for plasma. Total protein, lactate dehydrogenase (LD), and glucose levels should be measured and compared to blood levels. Fluid to serum total protein and LD ratios are used to help distinguish exudative from transudative fluids. The serum albumin minus the fluid albumin is now considered the most sensitive single test to distinguish cirrhosis from malignancy as causes of ascites. Most transudative fluids are associated with cirrhosis and have a difference above 1.1. Most exudative fluids result from malignancy and have a difference less than 1.1. The fluid glucose is normally the same as the plasma glucose. Distinctly lower levels are seen in bacterial peritonitis, peritoneal tuberculosis, and malignancy. Lactate dehydrogenase is increased in bacterial peritonitis and malignant diseases. A fluid:-serum ratio of 0.6 or higher has a sensitivity of about 80% in identifying exudative fluids. Amylase is very useful in diagnosing exudates caused by pancreatitis. Levels are usually in excess of three times the upper limit of normal. Fluid amylase testing can detect pancreatitis in approximately 90% of cases, and is also positive in the majority of people with bowel obstruction, proliferation and intestinal cancer. Alkaline phosphatase is elevated in exudates associated with bowel injury, obstruction, and some malignancies such as hepatoma.

Tumor markers may be useful to help distinguish the tissue of origin and to increase the sensitivity of cancer detection. Both carcinoembryonic antigen levels and CA125 levels in abdominal fluid have been found elevated in some persons with malignant infiltration of the abdomen but negative initial cytology. Creatinine may be measured when it is suspected that inadvertent puncture of the urinary bladder occurred during paracentesis. Creatinine in urine is about 100 times higher than in ascites fluid.

Microbiology

Bacterial cultures are usually performed on ascites fluid, but recovery of organisms is low when the fluid is frankly transudative. Gram stain detects about 25% of cases of bacterial peritonitis. The sensitivity can be increased by fluorescent microscopy using acridine orange stain. Cultures are positive in about 75% of cases that are eventually documented as infections. Detection of bacterial peritonitis is more sensitive when blood culture bottles containing tryptic soy broth are inoculated immediately after collection of the fluid rather than plating the fluid after transport to the lab. Regardless of the media used, cultures should be performed under both aerobic and anaerobic conditions. Spontaneous bacterial peritonitis that usually occurs in cirrhosis following sepsis typically grows a single organism, usually E. coli or Streptococcus pneumoniae. Peritonitis resulting from bowel sources usually grows several different intestinal organisms.

Preparation

A hematocrit, prothrombin time, and platelet count should be obtained within 48 hours of paracentesis. This will identify which patients may be at risk for bleeding complications, and provide a baseline hematocrit to estimate blood loss should bleeding occur. In addition, blood should be collected for glucose, total protein, lactate dehydrogenase, and albumin at the time of paracentesis. These results are compared to those of ascites fluid as a diagnostic aid. Abdominal girth and vital signs should be documented. The patient should be asked to empty his or her bladder, and should be warned about very brief discomfort as the needle goes through the peritoneum, in spite of local anesthesia. If very large amounts of peritoneal fluid are to be removed, it may need to be done very slowly to avoid large fluid shifts and a rapid fall in blood pressure. In extreme cases, a central venous pressure (CVP) line may need to be placed in order to monitor the patient's fluid status.

Aftercare

Vital signs are documented several times, perhaps even hourly for several hours if a large volume has been removed. The site of needle puncture is covered with a simple sterile dressing, or closed with a stitch if a trochar was used, and the dressing observed for possible continued leakage or bleeding.

Complications

Serious intra-abdominal bleeding is possible, although not very frequent. Puncture of the bladder or bowel are also possible. If good sterile technique is not used, infection could be introduced into the abdomen, resulting in peritonitis.

Results

Results of laboratory tests on ascites fluid are dependent upon the method of analysis used. Most studies are performed with very small sample sizes, and cell counts are performed manually. This results in greater interlaboratory variation in normal ranges than usually is seen for measurements performed on blood. Representative values for commonly measured analytes are shown below:

  • Volume: 30-50 mL (1-1.7 oz).
  • Color: pale yellow.
  • Transparency: clear.
  • WBC count: <200 per microliter.
  • Total protein: <3.0 g/dL.
  • Amylase: 0-130 U/L (similar to plasma for the method used).
  • Serum to ascites albumin gradient (serum minus fluid albumin): greater than 1.1 g/dL.
  • Fluid: serum LD ratio <0.6.
  • Lactic acid: <40 mg/dL.
  • Bilirubin: <6.0 mg/dL and serum/fluid ratio below 1.0.

Health care team roles

A physician normally collects the ascites fluid using sterile technique. The physician is usually assisted by a nurse. Nursing staff are responsible for documenting the patient's status before and after the procedure; educating and preparing the patient for the procedure; and observing for complications. Samples must be clearly labeled and sent to the laboratory. Clinical laboratory scientists/medical technologists perform blood counts, biochemical, and microbiological tests. A histologic technician prepares and stains slides for cytological review by a pathologist.

A study in 2004 showed that large-volume paracentesis could be performed safely as an outpatient procedure by gastrointestinal endoscopy assistants, usually licensed practical nurses with special training. The study reported that paracentesis performed in an outpatients setting by these assistants was safe, efficient, and usually completed in two hours. They demonstrated no added risk to patients and said that a major benefit would be significant savings in physician time.

KEY TERMS

Ascites— Abnormal quantity of peritoneal fluid, an ultrafiltrate of plasma.

Edema— Fluids that have shifted outside of the circulatory system and are temporarily trapped in soft tissues.

Gram stain— A common laboratory test in which a specimen on a glass slide is subjected to a series of stains and rinses to visualize micro-organisms.

Lymphocyte— A specific type of white blood cell (leukocyte) involved in fighting atypical, fungal and viral infections.

Neutrophil— A specific type of white blood cell (leukocyte) involved in fighting bacterial infections. Also called a polymorphonuclear leukocyte.

Resources

BOOKS

Glickman, Robert M. "Abdominal Swelling and Ascites." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci. McGraw-Hill, 1998: 256-257.

Malarkey, Louise M., and Mary Ellen McMorrow. Nurse's Manual of Laboratory Tests and Diagnostic Procedures, 2nd ed. W.B. Saunders Company, 2000: 457-461.

Tierney, Lawrence M., Stephen J. McPhee and Maxine A. Papadakis. Current Medical Diagnosis and Treatment 2001. Lange Medical Books/McGraw-Hill, 2001: 578-580.

PERIODICALS

"Large-volume Paracentesis Can Be Performed Safely as an Outpatient Procedure." Obesity, Fitness & Wellness Week (Sept. 11, 2004): 448.

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Paracentesis

Paracentesis

Definition
Purpose
Description
Aftercare
Risks
Normal results

Definition

Paracentesis is a minimally invasive procedure that uses 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 surrounding tissues. Slowly the

KEY TERMS

Ascites— Fluid in the abdomen.

Ectopic pregnancy— A pregnancy occurring outside the womb that often ruptures and requires surgical removal.

Hepatitis— An inflammation of the liver.

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 the 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. Repeated 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

Paralytic ileus seeIntestinal obstruction repair

Parathyroid gland removal seeParathyroidectomy

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Paracentesis

Paracentesis

Definition

Paracentesis is a procedure in which excess fluid in the abdomen is sampled by aspiration through a needle. The fluid may be called ascites fluid, abdominal fluid, or peritoneal fluid.

Purpose

Paracentesis is commonly performed to identify the cause of newly diagnosed ascites (excess fluid in the abdominal cavity); to diagnose changes in the condition of a patient already known to have ascites; and to relieve pressure from severe distention due to increased fluid in the abdomen. A sample of the fluid withdrawn from the abdominal cavity is nearly always sent for laboratory analysis to determine the presence or absence of infection , and/or to learn more about the cause of ascites if necessary. Ascites forms for a variety of reasons, including infection, diseases of various organs, and conditions which result in abnormal blood flow. The most common cause in the United States is alcoholic cirrhosis.

Precautions

Ascites is difficult to diagnose by physical exam, although with experience health care practitioners can note "shifting dullness" by percussion. Generally at least 17 oz (500 mL) of fluid must accumulate before the effusion is detected by x ray, and 3.2 pt (1500 mL) before ascites is easily detected on physical exam. Ultrasound may be necessary to differentiate ascites from obesity and other reasons for abdominal distention. Ultrasound may even be used to guide the needle for paracentesis. When performing this procedure, the physician should observe universal precautions for the prevention of transmission of bloodborne pathogens.

Description

Consent should be obtained for the procedure after discussion of the possible complications (discussed below). The area beneath the umbilicus is cleansed with betadine or other antibacterial solution, and local anesthetic administered. A long thin needle or trochar with a stylet is inserted about 2 in (5 cm) below the umbilicus, and the appropriate amount of fluid withdrawn. Usually a syringe is used, but for very large amounts of ascites, polyethylene tubing may be attached to vacuum bottles and the excess fluid aspirated. A minimum of 1 oz (30 mL) of fluid should be collected by sterile technique in two or three sterile syringes. One portion should be transferred to a tube containing EDTA for cell counts and the last syringe should be used to inoculate blood culture media. These samples and the remaining fluid should be sent to the laboratory for analysis. If cytologic exam is requested, 3.4 oz (100 mL) of fluid should be submitted to the laboratory.

Cirrhosis of the liver and malignant abdominal masses are the two most common causes of ascites. Cirrhosis is usually associated with a transudative fluid, a fluid of low cellularity and protein, while malignancy causes an exudative (inflammatory) fluid of high cellularity and protein. Transudative fluids result from changes in blood flow, and are typically seen in persons with cirrhosis, congestive heart failure , and a few other conditions that disrupt normal hemodyndamics. An explanation of ascites formation in cirrhosis serves well to explain some principles common to transudative fluid formation. Blood entering the portal vein from 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 which results compresses the hepatic sinusoids and vessels and restricts the blood flow. The blood bypasses the liver and enters the splenic, gastric, and esophageal veins causing very high hydrostatic pressure. This pressure causes fluid to escape the vessels and enter the abdominal cavity. Slowly the fluid accumulates in the areas with the lowest pressure and the greatest capacity. The free space around abdominal organs receives most of it. This space is called the peritoneal space because it is enclosed by a thin membrance called the peritoneum. The peritoneum wraps around nearly every organ in the abdomen, and lines the entire abdominal cavity, providing many folds and spaces in which fluid can gather. Normally, only 1–1.7 oz (30–50 mL) of fluid is found in the peritoneal cavity. The fluid itself is essentially an ultrafiltrate of plasma. Any condition that causes an increase in peritoneal fluid is called an effusion or ascites. Kidney disease can contribute to this process, since the kidneys have a critical role in fluid balance . Nephrotic syndrome in particular is associated with ascites formation. In this condition the kidneys lose large amounts of protein into the urine causing a drop in plasma oncotic pressure. Since proteins hold fluid in the vascular bed, loss of protein (albumin) causes fluid to enter the tissue spaces. Heart failure also can cause ascites, because decreased cardiac output causes blood to accumulate in the return circulation. The increased venous pressure results in fluid leaking from the circulatory system. First edema is noticed in the legs, due to the effect of gravity, then in ascites formation in the abdomen.

Malignancy, infection, pancreatitis , bowel obstruction, and several other conditions produce an exudative effusion. These conditions cause inflammation that results in increased blood vessel permeability. The fluid that accumulates typically contains white blood cells and if cancer is the cause, malignant cells from the tissue of origin. Malignancy may result from cancerous transformation of the cells that line the peritoneum, called mesothelial cells. Mesotheliomas may difficult to distinguish from reactive mesothelial cells that occur whenever the lining of the abdomen is traumatized. The two most common metastatic cancers invading the abdomen are ovarian and breast cancer , but lymphoma, leukemia, lung, and many other cancers can also infiltrate the abdomen. Bacterial peritonitis is an infection of the peritoneum, and is a life-threatening cause of exudative ascites. It can result from intestinal perforation, leakage through a deseased bowel wall, ruptured appendix or gall bladder, or septicemia (infection in the blood). Inflammation of the abdominal wall can also result from blunt trauma, pancreatitis, intestinal obstruction, and other conditions.

Physical characteristics of ascites fluid

Normal ascites fluid is clear and straw colored. Turbid fluid occurs in bacterial peritonitis, malignancy, and pancreatitis. Green fluid occurs when bile is present. This can be caused by a ruptured bowel or perforated bile duct. Bloody fluid occurs in trauma, malignancy, and pancreatitis. Milky fluid contains chyle from the intestinal lymphatics and occurs when lymphatic vessels rupture.

Microscopic analysis

The WBC count is performed using a hemacytometer. Normal fluid has a very low WBC count (less than 300 per microliter) and does not have to be diluted. Counts above 1000 indicate an exudative process. The differential is performed on a cytocentrifuged sample to concentrate the cells. Macrophages predominate in normal fluid and together with mesothelial cells account for about 70% of the nucleated cell population. Lymphocytes are normally less than 20% and neutrophils less than 10% of nucleated cells. Neutrophils accounting for 50% or 500 per microliter are most often associated with bacterial peritonitis. Lymphocytes will predominate in lymphoma, nephrotic syndrome, and congestive heart failure and may be abundant along with macrophages in tuberculosis . Red cell counts are also performed manually. Red cells often enter the fluid during sample collection, a process referred to as a traumatic tap. In this case, the red count will be low, the supernatant fluid will be pale yellow (normal), and the fluid will clear as more is collected. In the absence of a traumatic tap, red blood cells are most often encountered in malignancy and trauma. It is especially important to examine the fluid for the presence


KEY TERMS


Ascites —Abnormal quantity of peritoneal fluid, which is basically an ultrafiltrate of plasma.

Edema —Fluids that have shifted outside of the circulatory system and are temporarily trapped in soft tissues.

Gram stain —A common laboratory test in which a specimen on a glass slide is subjected to a series of stains and rinses to visualize micro-organisms.

Lymphocyte —A specific type of white blood cell (leukocyte) involved in fighting atypical, fungal and viral infections.

Neutrophil —A specific type of white blood cell (leukocyte) involved in fighting bacterial infections. Also called a polymorphonuclear leukocyte.


of malignant cells. As mentioned, metastatic cancer cells from ovarian and breast cancer are the most commonly seen infiltrates. Malignant mesothelial cells are difficult to distinguish from reactive mesothelial cells. Cytology should be evaluated with both Wright and Papanicilaou stains. Cytochemical tests and flow cytometry may be needed to identify malignant mesothelial cells, leukemic blasts (immature white cells), and lymphoma cells.

Biochemical tests

Chemical tests are performed on ascites fluid by the same methods used for plasma. Total protein, lactate dehydrogenase (LD), and glucose levels should be measured and compared to blood levels. Fluid to serum total protein and LD ratios are used to help distinguish exudative from transudative fluids. The serum albumin minus the fluid albumin is now considered the most sensitive single test to distinguish cirrhosis from malignancy as causes of ascites. Most transudative fluids are associated with cirrhosis and have a difference above 1.1. Most exudative fluids result from malignancy and have a difference less than 1.1. The fluid glucose is normally the same as the plasma glucose. Distinctly lower levels are seen in bacterial peritonitis, peritoneal tuberculosis, and malignancy. Lactate dehydrogenase is increased in bacterial peritonitis and malignant diseases. A fluid:serum ratio of 0.6 or higher has a sensitivity of about 80% in identifying exudative fluids. Amylase is very useful in diagnosing exudates caused by pancreatitis. Levels are usually in excess of three times the upper limit of normal. Fluid amylase testing can detect pancreatitis in approximately 90% of cases, and is also positive in the majority of persons with bowel obstruction, proliferation and intestinal cancer. Alkaline phosphatase is elevated in exudates associated with bowel injury, obstruction, and some malignancies such as hepatoma.

Tumor markers may be useful to help distinguish the tissue of origin and to increase the sensitivity of cancer detection. Both carcinoembryonic antigen levels and CA 125 levels in abdominal fluid have been found elevated in some persons with malignant infiltration of the abdomen but negative initial cytology. Creatinine may be measured when it is suspected that inadvertent puncture of the urinary bladder occurred during paracentesis. Creatinine in urine is about 100 times higher than in ascites fluid.

Microbiology

Bacterial cultures are usually performed on ascites fluid, but recovery of organisms is low when the fluid is frankly transudative. Gram stain detects about 25% of cases of bacterial peritonitis. The sensitivity can be increased by fluorescent microscopy using acridine orange stain. Cultures are positive in about 75% of cases that are eventually documented as infections. Detection of bacterial peritonitis is more sensitive when blood culture bottles containing tryptic soy broth are inoculated immediately after collection of the fluid rather than plating the fluid after transport to the lab. Regardless of the media used, cultures should be performed under both aerobic and anaerobic conditions. Spontaneous bacterial peritonitis which usually occurs in cirrhosis following sepsis typically grows a single organism, usually E. coli or Streptococcus pneumoniae. Peritonitis resulting from bowel sources usually grows several different intestinal organisms.

Preparation

A hematocrit , prothrombin time, and platelet count should be obtained within 48 hours of paracentesis. This will identify which patients may be at risk for bleeding complications, and provide a baseline hematocrit to estimate blood loss should bleeding occur. In addition, blood should be collected for glucose, total protein, lactate dehydrogenase, and albumin at the time of paracentesis. These results are compared to those of ascites fluid as a diagnostic aid. Abdominal girth and vital signs should be documented. The patient should be asked to empty his or her bladder, and should be warned about very brief discomfort as the needle goes through the peritoneum, in spite of local anesthesia . If very large amounts of peritoneal fluid are to be removed, it may need to be done very slowly to avoid large fluid shifts and a rapid fall in blood pressure . In extreme cases, a central venous pressure (CVP) line may need to be placed in order to monitor the patient's fluid status.

Aftercare

Vital signs are documented several times, perhaps even hourly for several hours if a large volume has been removed. The site of needle puncture is covered with a simple sterile dressing, or closed with a stitch if a trochar was used, and the dressing observed for possible continued leakage or bleeding.

Complications

Serious intra-abdominal bleeding is possible, although not very frequent. Puncture of the bladder or bowel are also possible. If good sterile technique is not used, infection could be introduced into the abdomen, resulting in peritonitis.

Results

Results of laboratory tests on ascites fluid are dependent upon the method of analysis used. Most studies of normal persons are performed with very small sample sizes, and cell counts are performed manually. This results in greater interlaboratory variation in normal ranges than usually is seen for measurements performed on blood. Representative values for commonly measured analytes are shown below:

  • Volume: 1–1.7 oz (30–50 mL).
  • Color: pale yellow.
  • Transparency: clear.
  • WBC count: < 200 per microliter.
  • Total protein: < 3.0 g/dL.
  • Amylase: 0–130 U/L (similar to plasma for the method used).
  • Serum to ascites albumin gradient (serum minus fluid albumin): greater than 1.1 g/dL.
  • Fluid: serum LD ratio < 0.6.
  • Lactic acid: < 40 mg/dL.
  • Bilirubin: < 6.0 mg/dL and serum fluid ratio below 1.0.

Health care team roles

A physician collects the ascites fluid using sterile technique. The physician is usually assisted by a nurse. Nursing staff are responsible for documenting the patient's status before and after the procedure; educating and preparing the patient for the procedure; and observing for complications. Samples must be clearly labeled and sent to the laboratory. Clinical laboratory scientists/medical technologists perform blood counts, biochemical, and microbiological tests. A histologic technician prepares and stains slides for cytological review by a pathologist.

Resources

BOOKS

Glickman, Robert M. "Abdominal Swelling and Ascites." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci. New York: McGraw-Hill, 1998, pp.256-257.

Malarkey, Louise M., and Mary Ellen McMorrow. Nurse's Manual of Laboratory Tests and Diagnostic Procedures, 2nd ed. Philadelphia: W. B. Saunders Company, 2000, pp.457-461.

Tierney, Lawrence M., Stephen J. McPhee, and Maxine A. Papadakis. Current Medical Diagnosis and Treatment 2001. New York: Lange Medical Books/McGraw-Hill, 2001, pp. 578-580.

Erika J. Norris

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