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 organ as may occur in abdominal trauma) or on a non-infectious process. Peritonitis generally represents a surgical emergency.

Mechanisms and manifestations

Abdominal pain and tenderness

The main manifestations of peritonitis are acute abdominal pain, abdominal tenderness, and abdominal guarding, which are exacerbated by moving the peritoneum, e.g. coughing, flexing the hips, or eliciting the Blumberg sign (a.k.a. rebound tenderness, meaning that pressing a hand on the abdomen elicits less pain than releasing the hand abruptly, which will aggravate the pain, as the peritoneum snaps back into place). The presence of these signs in a patient is sometimes referred to as peritonism.^[1] The localization of these manifestations depends on whether peritonitis is localised (e.g. appendicitis or diverticulitis before perforation), or generalised to the whole abdomen. In either case pain typically starts as a generalised abdominal pain (with involvement of poorly localising innervation of the visceral peritoneal layer), and may become localised later (with the involvement of the somatically innervated parietal peritoneal layer). Peritonitis is an example of an acute abdomen.

Collateral manifestations

• Diffuse abdominal rigidity ("washboard abdomen") is often present, especially in generalized peritonitis
• Fever
• Sinus tachycardia
• Development of ileus paralyticus (i.e. intestinal paralysis), which also causes nausea and vomiting

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).
• Sepsis may develop, so blood cultures should be obtained.
• The fluid may push on the diaphragm and cause breathing difficulties.

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, surgery is performed without further delay from other investigations. Leukocytosis and acidosis may be present, but they are not specific findings. 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 chest X-rays. If reasonable doubt still persists, an exploratory peritoneal lavage may be performed (e.g. in cases of trauma, in order to look for white blood cells, red blood cells, or bacteria).

Causes

Infected peritonitis

• Perforation of a hollow viscus is the most common cause of peritonitis. Examples include perforation of the distal oesophagus (Boerhaave syndrome), of the stomach (peptic ulcer, gastric carcinoma), of the duodenum (peptic ulcer), of the remaining intestine (e.g. appendicitis, diverticulitis, Meckel diverticulum, inflammatory bowel disease (IBD), intestinal infarction, intestinal strangulation, colorectal carcinoma, meconium peritonitis), or of the gallbladder (cholecystitis). Other possible reasons for perforation include abdominal trauma, ingestion of a sharp foreign body (such as a fish bone, toothpick or glass shard), perforation by an endoscope or catheter, and anastomotic leakage. The latter occurrence is particularly difficult to diagnose early, as abdominal pain and ileus paralyticus are considered normal in patients who just underwent abdominal surgery. In most cases of perforation of a hollow viscus, mixed bacteria are isolated; the most common agents include Gram-negative bacilli (e.g. Escherichia coli) and anaerobic bacteria (e.g. Bacteroides fragilis). Fecal peritonitis results from the presence of faeces in the peritoneal cavity. It can result from abdominal trauma and occurs if the large bowel is perforated during surgery.
• Disruption of the peritoneum, even in the absence of perforation of a hollow viscus, may also cause infection simply by letting micro-organisms into the peritoneal cavity. Examples include trauma, surgical wound, continuous ambulatory peritoneal dialysis, intra-peritoneal chemotherapy. Again, in most cases mixed bacteria are isolated; the most common agents include cutaneous species such as Staphylococcus aureus, and coagulase-negative staphylococci, but many others are possible, including fungi such as Candida.
• Spontaneous bacterial peritonitis (SBP) is a peculiar form of peritonitis occurring in the absence of an obvious source of contamination. It occurs either in children, or in patients with ascites. See the article on spontaneous bacterial peritonitis for more information.
• Systemic infections (such as tuberculosis) may rarely have a peritoneal localisation.

Non-infected peritonitis

• Leakage of sterile body fluids into the peritoneum, such as blood (e.g. endometriosis, blunt abdominal trauma), gastric juice (e.g. peptic ulcer, gastric carcinoma), bile (e.g. liver biopsy), urine (pelvic trauma), menstruum (e.g. salpingitis), pancreatic juice (pancreatitis), or even the contents of a ruptured dermoid cyst. It is important to note that, while these body fluids are sterile at first, they frequently become infected once they leak out of their organ, leading to infectious peritonitis within 24-48h.
• Sterile abdominal surgery normally causes localised or minimal generalised peritonitis, which may leave behind a foreign body reaction and/or fibrotic adhesions. Obviously, peritonitis may also be caused by the rare, unfortunate case of a sterile foreign body inadvertently left in the abdomen after surgery (e.g. gauze, sponge).
• Much rarer non-infectious causes may include familial Mediterranean fever, porphyria, and systemic lupus erythematosus.

Treatment

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

• General supportive measures such as vigorous intravenous rehydration and correction of electrolyte disturbances.
• Antibiotics are usually administered intravenously, but they may also be infused directly into the peritoneum. The empiric choice of broad-spectrum antibiotics often consist of multiple drugs, and should be targeted against the most likely agents, depending on the cause of peritonitis (see above); once one or more agents are actually isolated, therapy will of course be targeted on them.
• Surgery (laparotomy) is needed to perform a full exploration and lavage of the peritoneum, as well as to correct any gross anatomical damage which may have caused peritonitis.^[2] The exception is spontaneous bacterial peritonitis, which does not benefit from surgery.

Prognosis

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.

Pathology

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.

References

1. ↑
2. ↑

• Peritonitis disease causes, treatment ...
• All Refer Health article on peritonitis
• Genuit T and Napolitano L. 2004. Peritonitis and Abdominal Sepsis. Emedicine.com
• Health square. 2004. Peritonitis.

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