• Clinical science



Peritonitis is an inflammation of the peritoneum that is often caused by a bacterial infection. Based on the etiology, peritonitis may be classified as primary or secondary. Primary peritonitis usually occurs in patients with underlying ascites, whereas secondary peritonitis affects those with a preexisting acute abdominal disease. Patients typically present with severe abdominal pain and guarding, as well as nausea and vomiting. In most cases, peritonitis constitutes a surgical emergency. Diagnosis is established based on the clinical presentation, laboratory tests, imaging, and peritoneal fluid analysis. Treatment includes administration of antibiotics as well as surgical interventions. Peritonitis may be further complicated by ileus, sepsis, or abdominal compartment syndrome.


Primary peritonitis (spontaneous bacterial peritonitis, or SBP)

Secondary peritonitis (more common)

Further causes

  • Peritonitis in immunosuppressed (mainly HIV-positive) patients
  • Chemical peritonitis; : nonbacterial, caused by irritants such as blood, bile, urine, or barium contrast in the peritoneal cavity


Clinical features

  • General symptoms
    • Diffuse abdominal pain with abdominal guarding and/or rebound tenderness
    • Nausea, and vomiting
    • Fever and chills (esp. in underlying infection, e.g., SBP)
    • Possibly shoulder pain
    • Ascites in SBP
  • Physical examination
    • Distressed patient, knees drawn up when supine , avoids movement
    • Abdominal pain and rigidity, rebound tenderness
    • Sparse peristaltic sounds (none in cases of ileus)

Peritonitis is considered a surgical emergency, as it may cause sepsis with shock and organ failure!



The diagnosis of peritonitis is based primarily on the physical manifestations. Peritoneal fluid analysis confirms the diagnosis, while imaging tests may detect help to identify the underlying disease and exclude differential diagnoses.

  • Laboratory tests
  • Imaging
    • Ultrasound may detect
    • Abdominal x-ray may detect:
      • Air-fluid levels (e.g., in ileus)
      • Free air secondary to organ perforation
    • CT scan of the abdomen and pelvis
      • Should not cause delay for surgical intervention if the diagnosis is clinically made
      • Test of choice for suspected visceral abscess
      • Indicated if diagnosis is unclear based on clinical or other imaging findings


Differential diagnoses

In certain conditions, patients show symptoms of peritonitis, although actual inflammation of the peritoneum is absent.

The differential diagnoses listed here are not exhaustive.


Primary peritonitis

Secondary peritonitis

  • Approach: remove the source of infection and treat the underlying cause via interventional procedures, eliminate bacteria via antibiotics, and maintain organ function via fluid resuscitation and supportive care
  • Interventional procedures
    • Surgery
    • Extensive laparoscopic irrigation (lavage), debridement, drainage
    • Ultrasound or CT-guided percutaneous drainage of abscesses
    • Scheduled revision surgery (second-look surgery) frequently necessary for extensive disease
  • General
  • Medical




We list the most important complications. The selection is not exhaustive.