Peritonitis

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 pain & tenderness

The main manifestations of peritonitis are acute abdominal pain, tenderness, and 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 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 causing disease. Peritonitis is an example of acute abdomen.

Collateral manifestations

• Diffuse abdominal rigidity ("washboard abdomen") is often present, especially in generalised 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.

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.

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, IBD, intestinal infarction, intestinal strangulation, colorectal carcinoma, meconium peritonitis), or of the gallbladder (cholecystitis). Other possible reasons for perforation include trauma, ingestion of sharp foreign body (such as a fish bone), 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).
• 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. 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.