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[peritoneum + -itis]
Inflammation of the serous membrane that lines the abdominal cavity and its viscera.
SEE: chemical peritonitis; SEE: primary peritonitis; SEE: secondary peritonitis

Peritonitis is caused by infection of the abdominal cavity without obvious organ rupture (primary peritonitis), by perforation (rupture) of one of the internal organs (secondary peritonitis), or by instillation of a chemical irritant into the abdominal cavity (chemical peritonitis).

Primary peritonitis occurs in patients with cirrhosis and ascites, in some patients with tuberculosis (esp. those with AIDS), and in patients who use the peritoneum for dialysis. Cirrhotic patients develop peritonitis from infection of the peritoneal contents by microorganisms such as Streptococcus pneumoniae, enterococci, or Escherichia coli. Patients who use the peritoneum for dialysis (chronic ambulatory peritoneal dialysis patients) sometimes contaminate their dialysate with hand-borne microbes such as staphylococci or streptococci. Dialysis patients may also develop peritonitis after the infusion of irritating substances (such as antibiotics like vancomycin) into the peritoneal cavity during treatment for these infections.

Common causes of secondary peritonitis are ruptured appendix, perforated ulcer, abdominal trauma, and Crohn disease. The gases, acids, fecal material, and bacteria in the ruptured organs spill into and inflame the peritoneum.

Primary peritonitis is marked by moderate to mild abdominal pain, fever, change in bowel habits, and malaise. Dialysis patients may notice clouding of their discharged dialysate. Fever, weight loss, inanition, and other systemic symptoms are common in tuberculous peritonitis.

Secondary peritonitis is marked by intense, constant abdominal pain that worsens on body movement. It is often associated with nausea, loss of appetite, and fever or hypothermia. On examination the abdomen is typically distended and quiet, and the patient holds very still in order to limit discomfort.

In patients with organ rupture, a plain x-ray examination of the abdomen may reveal air trapped beneath the diaphragm. Ultrasonography or abdominal computed tomography is used to visualize intraperitoneal fluid, abscesses, and diseased organs. Paracentesis or peritoneal lavage are also helpful in the diagnosis of some cases.

Primary peritonitis may respond to the administration of antibiotics or antitubercular drugs, but the prognosis is guarded. Secondary peritonitis is treated with surgical drainage, repair or removal of the ruptured viscus, fluid resuscitation, and antibiotics.

The prognosis depends on the patient's underlying condition, the rapidity of the diagnosis and of subsequent medical and/or surgical interventions.

The patient with peritonitis of uncertain cause is prepared for paracentesis. Paracentesis may be used for diagnostic or therapeutic purposes. In the latter instance large volumes of fluid (1 to 5 L) may be withdrawn or allowed to drain from the peritoneal cavity. Some patients are left with drains in place. The skin surrounding the drain should be inspected daily for evidence of inflammation, erosion, or infection. Vital signs, including blood pressure and pulse, should be obtained after the procedure to ensure the patient does not become hypotensive. Fevers may indicate unresolved infection. Antipyretic drugs and analgesics should be given as prescribed for fever, pain, and patient's comfort. When the underlying cause of the fluid accumulation is identified, the patient should be educated about the disease and its proposed treatment, adverse effects of any drugs or treatments recommended, and follow-up care.

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