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Peritonitis is defined as inflammation of the peritoneum (the serous membrane which lines part of the abdominal cavity and some of the viscera it contains). It may be localised or generalised, generally has an acute course, and may depend on either infection (often due to rupture of a hollow viscus) or on a non-infectious process. Peritonitis generally represents a surgical emergency.

Mechanisms & manifestations

Abdominal manifestations

Peritonitis generally presents as acute abdomen. The main clinical manifestations include acute pain, tenderness, and guarding, which are exacerbated by moving the peritoneum, e.g. by coughing, flexing the hips, or eliciting the Blumberg sign (also known as rebound tenderness, meaning that pressing a hand on the abdomen elicits pain, but releasing the hand abruptly will aggravate the pain, as the peritoneum snaps back into place). The localisation of these manifestations depends on whether peritonitis is localised (e.g. appendicitis or diverticulitis before perforation), or generalised to the whole abdomen; even in the latter case, pain typically starts at the site of the underlying cause. Diffuse abdominal rigidity ("washboard abdomen") is also often present, especially in generalised peritonitis

Other manifestations

Peritonitis may also present with aspecific manifestations such as fever and sinus tachycardia, and often causes paralysis of the intestine ("ileus paralyticus"), which in turn will cause nausea and vomiting.


Peritonitis may lead to a variety of complications. Sequestration of fluid and electrolytes, as revealed by decreased central venous pressure, may cause electrolyte disturbances, as well as significant hypovolaemia, possibly leading to shock and acute renal failure. A peritoneal abscess may form (e.g. above or below the liver, or in the lesser omentum); this is especially likely in the elderly, who tend to present late due to blunted pain perception. Also, sepsis may develop, so blood cultures should be obtained.

Diagnosis and investigations

A diagnosis of peritonitis is based primarily on clinical grounds, that is on the clinical manifestations described above; if they support a strong suspicion of peritonitis, no further investigation should delay surgery. Leukocytosis and acidosis may be present, but they are not specific findings. A plain abdominal X-rays may reveal dilated, oedematous intestines, although it is mainly useful to look for pneumoperitoneum (free air in the peritoneal cavity), which may also be visible on a chest X-rays. If reasonable doubt still persists, an exploratory peritoneal lavage may be performed (e.g. in cause of trauma, in order to look for white blood cells, red blood cells, or bacteria.


Infected peritonitis

Non-infected peritonitis


Depending on the severity of the patient's state, the management of peritonitis may include:


If properly treated, typical cases of surgically correctable peritonitis (e.g. perforated peptic ulcer, appendicitis, and diverticulitis) have a mortality rate of about <10% in otherwise healthy patients, which rises to about 40% in the elderly, and/or in those with significant underlying illness, as well as in cases that present late (after 48h). If untreated, generalised peritonitis is almost always fatal.


The peritoneum normally appears greyish and glistening; it becomes dull 2-4 hours after the onset of peritonitis, initially with scarce serous or slightly turbid fluid. Later on, the exudate becomes creamy and evidently suppurative; in dehydrated patients, it also becomes very inspissated. The quantity of accumulated exudate varies widely. It may be spread to the whole peritoneum, or be walled off by the omentum and viscera. Inflammation features infiltration by neutrophils with fibrino-purulent exudation.


  • Kasper et al, Harrison's Principles of Internal Medicine, 16th edition, McGraw-Hill 2005
  • Boon et al, Davidson's Principles & Practice of Medicine, 20th edition, Churchill Livingstone 2006
  • Garden et al, Principles & Practice of Surgery, 5th edition, Churchill Livingstone 2007
  • Carli et al, Urgences Medico-Chirurgicales de l'Adulte, 2nd edition, Arnette 2004