Peritonitis

Peritonitis is an inflammation of the peritoneum, the serous membrane that lines part of the abdominal cavity and viscera. Peritonitis may be localised or generalised, and may result from infection (often due to rupture of a hollow organ as may occur in abdominal trauma or appendicitis) or from a non-infectious process.

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 (forced cough may be used as a test), flexing one's 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. The localization of these manifestations depends on whether peritonitis is localized (e.g., appendicitis or diverticulitis before perforation), or generalized to the whole abdomen. In either case, pain typically starts as a generalized abdominal pain (with involvement of poorly localizing innervation of the visceral peritoneal layer), and may become localized 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 vomiting and bloating.

Complications

 * Sequestration of fluid and electrolytes, as revealed by decreased central venous pressure, may cause electrolyte disturbances, as well as significant hypovolemia, 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, causing splinting and subsequent breathing difficulties.

Infected peritonitis

 * Perforation of part of the gastrointestinal tract 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, and 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 in patients with ascites, in particular, in children. See the article on spontaneous bacterial peritonitis for more information.
 * Intra-peritoneal dialysis predisposes to peritoneal infection (sometimes named "primary peritonitis" in this context).
 * 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 to 48 hours.
 * Sterile abdominal surgery, under normal circumstances, causes localised or minimal generalised peritonitis, which may leave behind a foreign body reaction and/or fibrotic adhesions. However, peritonitis may also be caused by the rare 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.

Diagnosis
A diagnosis of peritonitis is based primarily on the clinical manifestations described above. If peritonitis is strongly suspected, then surgery is performed without further delay for other investigations. Leukocytosis, hypokalemia, hypernatremia, and acidosis may be present, but they are not specific findings. Abdominal X-rays may reveal dilated, edematous intestines, although such X-rays are mainly useful to look for pneumoperitoneum, an indicator of gastrointestinal perforation. The role of whole-abdomen ultrasound examination is under study and is likely to expand in the future. Computed tomography (CT or CAT scanning) may be useful in differentiating causes of abdominal pain. If reasonable doubt still persists, an exploratory peritoneal lavage or laparoscopy may be performed. In patients with ascites, a diagnosis of peritonitis is made via paracentesis (abdominal tap): More than 250 polymorphonucleate cells per μL is considered diagnostic. In addition, Gram stain and culture of the peritoneal fluid can determine the microorganism responsible and determine their sensibility to antimicrobial agents.

Pathology
In normal conditions, the peritoneum 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.

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 that may have caused peritonitis. The exception is spontaneous bacterial peritonitis, which does not always benefit from surgery and may be treated with antibiotics in the first instance.

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 48 hours). If untreated, generalised peritonitis is almost always fatal.