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Ascites is
free fluid in the peritoneal cavity. The most common cause is portal
hypertension. Symptoms usually result from abdominal distention.
Diagnosis is based on physical examination and often ultrasonography
or CT. Treatments include bed rest, dietary Na restriction, diuretics,
and therapeutic paracentesis. Ascitic fluid can become infected
(spontaneous bacterial peritonitis), often with pain and fever. Diagnosis
of infection involves analysis and culture of ascitic fluid. Infection
is treated with antibiotics.
Etiology
Ascites can result from chronic, but not acute, liver diseases.
Hepatic causes include the following:
Portal vein thrombosis does not usually cause ascites unless hepatocellular damage is also present.
Nonhepatic causes include the following:
Pathophysiology
Mechanisms are complex and incompletely understood. Factors include altered Starling's forces in the portal vessels (low oncotic pressure due to hypoalbuminemia plus increased portal venous pressure), avid renal Na retention (urinary Na concentration is typically < 5 mEq/L), and possibly increased hepatic lymph formation.
Mechanisms that seem to contribute to renal Na retention include activation of the renin-angiotensin-aldosterone system; increased sympathetic tone; intrarenal shunting of blood away from the cortex; increased formation of nitric oxide; and altered formation or metabolism of ADH, kinins, prostaglandins, and atrial natriuretic factor. Vasodilation in the splanchnic arterial circulation may be a trigger, but the specific roles and interrelationships of these abnormalities remain uncertain.
Symptoms and Signs
Small amounts of ascitic fluid cause no symptoms. Moderate amounts cause increased abdominal girth and weight gain. Massive amounts may cause nonspecific diffuse abdominal pressure, but actual pain is uncommon and suggests another cause of acute abdominal pain (see Acute Abdomen and Surgical Gastroenterology: Etiology). If ascites results in elevation of the diaphragm, dyspnea may occur. Symptoms of spontaneous bacterial peritonitis (SBP) may include new abdominal discomfort and fever.
Signs include shifting dullness on abdominal percussion and a fluid wave. Volumes <1500 mL may not cause physical findings. Massive ascites causes tautness of the abdominal wall and flattening of the umbilicus. In liver diseases or peritoneal disorders, ascites is usually isolated or disproportionate to peripheral edema; in systemic diseases (eg, heart failure), the reverse is usually true.
Diagnosis
Diagnosis may be based on physical examination if there is a large amount of fluid, but imaging tests are more sensitive. Ultrasonography and CT reveal much smaller volumes of fluid (100 to 200 mL) than does physical examination. SBP is suspected in a patient with ascites who also has abdominal pain, fever, or unexplained deterioration.
Diagnostic paracentesis (see Diagnostic and Therapeutic GI Procedures: Abdominal Paracentesis) should be done if any of the following occur:
About 50 to 100 mL of fluid is removed and analyzed for gross appearance, protein content, cell count and differential, cytology, culture, and, as clinically indicated, acid-fast stain, amylase, or both. In contrast to ascites due to inflammation or infection, ascites due to portal hypertension produces fluid that is clear and straw-colored, has a low protein concentration, a low PMN count (< 250 cells/μL), and, most reliably, a high serum-to-ascites albumin concentration gradient, which is the serum albumin concentration minus the ascitic albumin concentration. Gradients > 1.1 g/dL are relatively specific for ascites due to portal hypertension. In ascitic fluid, turbidity and a PMN count > 250 cells/μL indicate SBP, whereas bloody fluid can suggest a tumor or TB. The rare milky (chylous) ascites is most common with lymphoma.
Treatment
(See also the American Association for the Study of Liver Disease's practice guideline Management
of Adult Patients with Ascites Due to Cirrhosis.) Bed rest and dietary Na restriction (2000 mg/day) are the first, and least risky, treatments for ascites due to portal hypertension. Diuretics should be used if rigid Na restriction fails to initiate diuresis within a few days. Spironolactone is usually effective (in oral doses ranging from 50 mg once/day to 200 mg bid). A loop diuretic (eg, furosemide 20 to 160 mg po usually once/day, or 20 to 80 mg po bid) should be added if spironolactone is insufficient. Because spironolactone can cause K retention and furosemide K depletion, the combination of these drugs often provides optimal diuresis with a lower risk of K abnormalities. Fluid restriction is indicated only for treatment of hyponatremia (serum Na < 120 mEq/L). Changes in body weight and urinary Na determinations reflect response to treatment. Weight loss of about 0.5 kg/day is optimal, because the ascitic compartment cannot be mobilized much more rapidly. More aggressive diuresis depletes fluid from the intravascular compartment, especially when peripheral edema is absent; this may cause renal failure or electrolyte imbalance (eg, hypokalemia) that may precipitate portal-systemic encephalopathy. Inadequate dietary Na restriction is the usual cause of persistent ascites.
Therapeutic paracentesis is an alternative. Removal of 4 L/day is safe; many clinicians infuse IV salt-poor albumin (about 40 g/paracentesis) at about the same time to prevent intravascular volume depletion. Even single total paracentesis may be safe. Therapeutic paracentesis shortens the hospital stay with relatively little risk of electrolyte imbalance or renal failure; nevertheless, patients require ongoing diuretics and tend to reaccumulate fluid more rapidly than those treated without paracentesis.
Techniques for the autologous infusion of ascitic fluid (eg, the LeVeen peritoneovenous shunt) often cause complications and are generally no longer used. Transjugular intrahepatic portal-systemic shunting (TIPS) can lower portal pressure and successfully treat ascites resistant to other treatments, but TIPS is invasive and may cause complications, including portal-systemic encephalopathy and worsening hepatocellular function. (See also the American Association for the Study of Liver Disease's practice guideline The
Role of TIPS in the Management of Portal Hypertension.)
Spontaneous
Bacterial Peritonitis (SBP)
Spontaneous
bacterial peritonitis is infection of ascitic fluid without an apparent
source. Manifestations may include fever, malaise, and symptoms
of ascites and worsening hepatic failure. Diagnosis is by examination
of ascitic fluid. Treatment is with cefotaxime or another antibiotic.
Spontaneous bacterial peritonitis (SBP) is particularly common in cirrhotic ascites, especially among alcoholics. This infection can cause serious sequelae or death. The most common bacteria causing SBP are the gram-negative Escherichia
coli and Klebsiella pneumoniae and the gram-positive Streptococcus pneumoniae; usually only a single organism is involved.
Symptoms and Signs
Patients have symptoms and signs of ascites. Discomfort is usually present; it typically is diffuse, constant, and mild to moderate in severity.
Signs of SBP may include fever, malaise, encephalopathy, worsening hepatic failure, and unexplained clinical deterioration. Peritoneal signs (eg, abdominal tenderness and rebound) are present but may be somewhat diminished by the presence of ascitic fluid.
Diagnosis
Clinical diagnosis of SBP can be difficult; diagnosis requires a high index of suspicion and liberal use of diagnostic paracentesis, including culture. Transferring ascitic fluid to blood culture media before incubation increases the sensitivity of culture to almost 70%. PMN count of > 250 cells/μL is diagnostic of SBP. Blood cultures are also indicated. Because SBP usually results from a single organism, finding mixed flora on culture suggests a perforated abdominal viscus or contaminated specimen.
Treatment
If SBP is diagnosed, an antibiotic such as cefotaxime 2 g IV q 4 to 8 h (pending Gram stain and culture results) is given for at least 5 days and until ascitic fluid shows < 250 PMNs/μL. Antibiotics increase the chance of survival. Because SBP recurs within a year in up to 70% of patients, prophylactic antibiotics are indicated; quinolones (eg, norfloxacin 400 mg po once/day) are most widely used. Antibiotic prophylaxis in ascitic patients with variceal hemorrhage decreases the risk of SBP.
Last full review/revision July 2009 by Steven K. Herrine, MD
Content last modified July 2009
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