Peritonitis: definition, causes, classification, symptoms, diagnosis and treatment
DEFINITION AND CLASSIFICATION
Peritonitis is inflammation of the peritoneal lining, usually due to infection or chemical irritation. Primary (spontaneous) peritonitis occurs without an evident surgically treatable perforation, classically spontaneous bacterial peritonitis in cirrhosis. Secondary peritonitis follows contamination from perforation, leakage, trauma or infection of an intra-abdominal organ. Tertiary peritonitis is persistent/recurrent infection after apparently adequate treatment, often in critically ill patients. It may be localised or generalised, acute or chronic.
CAUSES AND PATHOGENESIS
Common secondary causes include perforated peptic ulcer, appendicitis, diverticulitis, bowel ischaemia/perforation, biliary leakage, anastomotic leak, trauma and pelvic infection. Gastric/duodenal contents initially cause chemical irritation, followed by bacterial contamination. Inflammation produces capillary leak, ileus, third-spacing, hypovolaemia and systemic inflammatory response; untreated disease progresses to sepsis, shock and multiorgan failure.
CLINICAL FEATURES
Severe abdominal pain, worse with movement or coughing, is typical. There may be involuntary guarding, rigidity, rebound tenderness, fever, tachycardia, tachypnoea, dehydration, reduced bowel sounds and abdominal distension. Late signs include hypotension, confusion, oliguria and shock. Elderly, immunosuppressed and steroid-treated patients may have muted signs.
DIAGNOSIS
Diagnosis is clinical supported by investigations. Obtain FBC, CRP, electrolytes, renal/liver function, blood gas/lactate, coagulation and blood cultures if septic. Contrast CT is highly useful in stable patients to identify source, free gas, fluid, abscess or leak. Ultrasound may identify biliary/pelvic causes. Diagnostic paracentesis is essential in new ascites or suspected spontaneous bacterial peritonitis; ascitic neutrophils ≥250 cells/mm³ support SBP. Do not delay source control for imaging when the patient is unstable with clear peritonitis.
MANAGEMENT
Resuscitate using ABCDE, IV fluids, oxygen as needed, analgesia, nil by mouth, urinary catheter and close monitoring. Start broad-spectrum IV antibiotics promptly, covering likely enteric Gram-negative and anaerobic organisms, then tailor to cultures and local policy. Source control is decisive: urgent surgery for perforation, necrotic bowel or uncontrolled contamination; percutaneous drainage for suitable abscesses; repair/resection/diversion depending on pathology and patient condition. In septic shock, critical care support and vasopressors may be required after fluid assessment. Reassess for ongoing sepsis, residual collection or leak.
COMPLICATIONS
Complications include septic shock, acute kidney injury, ARDS, DIC, intra-abdominal abscess, adhesions, bowel obstruction, fistula, wound dehiscence and death. Prevention depends on early diagnosis, timely antibiotics and effective source control.