B37. Peritonitis: Causes, therapy, complications

Page created on September 23, 2021. Not updated since.


Peritonitis is the inflammation of the peritoneum, which lines the abdominal wall and most abdominal organs. We distinguish primary peritonitis (spontaneous bacterial peritonitis) and secondary peritonitis. Secondary peritonitis is peritonitis caused by bacterial infection from a surgically treatable intraabdominal source, like GI perforation, appendicitis, trauma, etc. Spontaneous bacterial peritonitis is peritonitis caused by bacterial infection of ascitic fluid which occurs in the absence of any surgically treatable intraabdominal source. The secondary form is much more common.

Spontaneous bacterial peritonitis is usually a monomicrobial infection, while secondary peritonitis is usually a polymicrobial infection. Secondary peritonitis may be generalised or local, while primary peritonitis is always generalised.

Peritonitis is a severe condition as it has a high risk of progressing to sepsis with high mortality. The underlying cause must be sought and treated.


Spontaneous bacterial peritonitis is a disease of cirrhotic patients, as it almost exclusively occurs in patients with ascites due to cirrhosis, and not ascites due to other causes. The pathomechanism is not well known but involves bacterial translocation from the intestinal lumen to lymph nodes, from which the bacteria spread to the circulation, eventually colonising the ascitic fluid.

Secondary peritonitis occurs due to:

  • Perforation of an abdominal organ
    • Perforated duodenal ulcer
    • Perforated appendicitis
    • Perforated diverticulitis
    • Mesenteric ischaemia
  • Abdominal organ inflammation with spread to adjacent peritoneum
    • Appendicitis
    • Diverticulitis
    • Pancreatitis
  • Penetrating wounds to the abdomen
  • Surgery
  • Leakage of intestinal anastomosis

Clinical features

Peritonitis causes abdominal pain. Movement usually worsens the pain, causing the patient to lie completely still, usually with the knees bent. Even gentle percussion over the affected area of the abdomen causes pain. “Guarding” on palpation, as well as rebound tenderness, are typical signs of peritonitis. The heel-drop test may be positive. See also topic A25 for the physical signs of peritonitis.

If generalised, peritonitis also causes signs of infection like fever.

Peritonitic signs in only one quadrant means local peritonitis is probable, while diffuse peritonitic signs is suspicious for generalised peritonitis.

Diagnosis and evaluation

The presence of peritonitis is usually established by physical examination, but the underlying cause must be sought. Stable patients should undergo imaging (x-ray, CT, ultrasonography) to identify the underlying cause. However, unstable or very ill-appearing patients may skip imaging to avoid delaying surgery.

Spontaneous bacterial peritonitis is diagnosed if the patient has cirrhosis and no surgically treatable intraabdominal source. Neutrophil count of > 250/µL in the ascitic fluid supports the diagnosis.


The treatment of secondary peritonitis involves supportive therapy, empiric wide-spectrum antibiotics, and treatment of the underlying cause, which almost always requires surgery. Local peritonitis does not invariably require antibiotics, for example when caused by appendicitis.

The treatment of spontaneous bacterial peritonitis involves fluid resuscitation and empiric antibiotics, without surgery.


  • Sepsis

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Surgery – Traumatology

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