What is peritonitis?

What is Peritonitis

Peritonitis is an inflammatory process of the peritoneum that is most frequently infectious in nature, requiring prompt diagnosis and treatment with antibiotics and source control procedures to reduce mortality and morbidity. 1

Definition and Pathophysiology

Peritonitis represents inflammation of the peritoneum, functioning as a local equivalent of systemic inflammatory response syndrome (SIRS). 2 When caused by bacteria, it constitutes an intra-abdominal infection—essentially a local equivalent of systemic sepsis—where the outcome depends on the balance between the patient's systemic and peritoneal defenses versus the nature and duration of contamination. 2

Classification by Type

Peritonitis is categorized into three distinct types based on etiology and mechanism:

Primary Peritonitis (Spontaneous Bacterial Peritonitis)

• Occurs as a diffuse bacterial infection without loss of gastrointestinal tract integrity, typically in cirrhotic patients with ascites or those with peritoneal dialysis catheters. 1, 3
• Characteristically monomicrobial (caused by a single organism). 3, 4
• E. coli is the predominant pathogen (32-67% of culture-positive cases), followed by Klebsiella and Streptococcus species, which together account for nearly three-fourths of all cases. 3, 4
• Managed with antibiotics alone without surgical intervention. 3, 4

Secondary Peritonitis

• The most common form of peritonitis, resulting from loss of gastrointestinal tract integrity such as perforation. 1, 3
• Accounts for 1% of urgent or emergent hospital admissions and is the second leading cause of sepsis in intensive care units globally. 5
• Typically polymicrobial, involving both facultative/aerobic organisms and obligate anaerobes from colon-derived infections. 4
• Common causes include duodenal perforation (26.2%), typhoid ileal perforation (24.2%), and ruptured appendix (16.8%). 6
• Requires both source control (surgical intervention) and antibiotic therapy. 1, 3

Tertiary Peritonitis

• A recurrent infection of the peritoneal cavity occurring >48 hours after apparently successful surgical source control of secondary peritonitis. 1, 3
• Often associated with multidrug-resistant organisms. 1, 3
• Requires broader antimicrobial coverage for resistant organisms, possibly antifungals, and potentially additional surgical interventions. 3

Clinical Presentation

Common Signs and Symptoms

• Abdominal pain and tenderness occur in 74-95% of patients, often accompanied by rebound tenderness and guarding. 1
• Abdominal rigidity strongly suggests the presence of peritonitis. 1
• Tachycardia is observed in 62.5% of patients. 1
• Fever greater than 38.5°C is present in 38% of patients. 1
• Decreased bowel sounds are a common finding. 1
• Ileus symptoms such as vomiting and absence of defecation may be present. 1

Severe Presentations

• Hypotension and hypoperfusion signs (lactic acidosis, oliguria, altered mental status) indicate ongoing sepsis. 1
• Hemodynamic instability and shock can occur. 1
• When perforation occurs proximal to a tumor, it results in diffuse peritonitis and potentially septic shock. 1

Diagnostic Approach

Laboratory Findings

• Polymorphonuclear leukocyte (PMN) count >250/mm³ in ascitic fluid is diagnostic for spontaneous bacterial peritonitis. 1, 3, 7
• Leukocytosis with a left shift (band neutrophils >20%) is common. 1
• Elevated C-reactive protein (CRP) and serum lactate levels are common findings. 1
• Low ascitic fluid glucose (<50 mg/dL) and multiple organisms suggest secondary rather than primary peritonitis. 1, 4
• Elevated ascitic fluid total protein, lactate dehydrogenase (LDH), and low glucose levels indicate secondary peritonitis. 1

Imaging Findings

• CT scan has the highest sensitivity and specificity for detecting peritonitis compared to ultrasound and plain X-ray. 1
• Free air on plain abdominal radiograph indicates perforation, though sensitivity is lower. 1
• Ultrasound may show free fluid in the abdomen and is valuable in resource-limited settings. 1
• CT findings include free fluid and air, bowel wall thickening, pericolic fat inflammation, and ascites. 1

Prognosis and Complications

• Overall mortality is 6%, but rises to 35% in patients who develop severe sepsis. 5
• Delay in diagnosis and treatment significantly increases mortality rates, especially in diffuse peritonitis. 1
• Inadequate source control is associated with significantly elevated mortality rates. 1
• Common complications include dehydration (18.8%), septicemia (11.3%), paralytic ileus (6.4%), renal failure, hepatic encephalopathy, and multi-organ failure. 1, 6