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Ascites

From Academic Kids

In medicine (gastroenterology), ascites is a accumulation of fluid in the peritoneal cavity. Although unpleasant, it is not intrinsically harmful. Nevertheless, its causes and complications are both significant medical problems.

Contents

Signs and symptoms

Mild ascites is hard to notice, but severe ascites leads to abdominal distension. In patients with ascites, a doctor will attempt to identify causes, such as a history of liver disease, other signs of portal hypertension or signs of tuberculosis or nephrotic syndrome.

A proportion of chronic ascites patients also develop hepatic hydrothrorax, e.g. unilateral pleural effusion (mainly right-sided) due to liver disease, and many have para-umbilical herniations of the abdominal wall.

Diagnosis

Several blood tests are commonly performed for ascites, including full blood count, electrolytes and renal function, liver enzymes, and glucose. If the cause is not apparent, serology for viruses known to cause hepatitis and ferritin may contribute to the analysis.

Ultrasound investigation with doppler studies can be an important help, and may identify such problems as Budd-Chiari syndrome, portal vein thrombosis and cirrhosis. Additionally, the sonographer can make an estimation of the amount of ascitic fluid.

Studies of the fluid removed by paracentesis (see below) may aid in the diagnosis. It can also help diagnose spontaneous bacterial peritonitis, a serious complication of ascites.

Classification

Ascites exists in three grades:

  • Grade 1: mild, only visible on ultrasound
  • Grade 2: detectable with shifting dullness on physical examination
  • Grade 3: directly visible, confirmed with fluid thrill

Pathophysiology

Ascitic fluid can accumulate as a transudate or an exudate. Amounts of up to 25 litres are fully possible.

Roughly, transudates are a result of increased pressure on the portal vein (>8 mmHg), e.g. due to cirrhosis, while exudates are actively secreted fluid due to inflammation or malignancy. As a result, exudates are high in protein, high in lactate dehydrogenase, have a low pH (<7.30), a low glucose level, and more white blood cells. Transudates have low protein (<30g/L), low LDH, high pH, normal glucose, and fewer than 1 white cell per 1000 mm3. Clinically, the most useful measure is the difference between ascitic and serum albumin concentrations. A difference of less than 1 mg/dl implies an exudate.

Regardless of the cause, sequestration of fluid within the abdomen leads to additional fluid retention by the kidneys due to stimulatory effect on blood pressure hormones, notably aldosterone. The sympathetic nervous system is also activated, and renin production is increased due to decreased perfusion of the kidney. Extreme disruption of the renal blood flow can lead to the feared hepatorenal syndrome.

Other complications of ascites include spontaneous bacterial peritonitis (SBP), due to decreased antibacterial factors in the ascitic fluid such as complement. Many acutely ill ascitic patients have SBP and require antibiotic treatment.

If portal hypertension is the cause, complications can be fulminant, such as bleeding esophageal varices.

Causes

Causes for transsudates are:

  • Cirrhosis - 81%
    • alcoholic - 65%
    • viral - 10%
    • cryptogenic - 6%
  • Heart failure - 3%
  • Budd-Chiari syndrome or veno-occlusive disease
  • Constrictive pericarditis

Exudates are caused by:

Treatment

Primary treatment for ascites is with diuretics, which is safer than ascite drainage. If it remains refractory on diuretics, paracentesis may be necessary. The ascites thus gained should be analysed in the medical laboratory for the abovementioned causes.

Source

  • Oxford textbook of medicine
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