What are the signs and symptoms of peritonitis?

Signs of Peritonitis

Peritonitis presents with abdominal pain and tenderness in 74-95% of patients, accompanied by rebound tenderness, guarding, and abdominal rigidity—the latter being a key clinical feature that strongly suggests the diagnosis. 1, 2

Local Abdominal Findings

The hallmark physical examination findings include:

• Abdominal rigidity is the most specific sign strongly suggesting peritonitis 1, 2
• Rebound tenderness and guarding are present in 82.5% of patients 1
• Abdominal pain and tenderness occur in 74-95% of cases 1, 2, 3
• Decreased or absent bowel sounds develop due to ileus 1, 2, 3
• Abdominal distension is seen in 6.6% as an isolated finding, though more commonly as part of the overall presentation 1, 2, 3

A critical pitfall is that peritoneal signs may take several hours to develop, particularly in small bowel injury where luminal contents have neutral pH and relatively low bacterial load 4. Serial examinations significantly improve diagnostic accuracy 4.

Systemic Signs of Inflammation

Vital sign abnormalities reflect the systemic inflammatory response:

• Tachycardia (not bradycardia) is observed in 62.5% of patients 1, 2, 3
• Fever greater than 38.5°C is present in 38% of cases 1, 2, 3
• Tachypnea occurs as part of the systemic inflammatory response 1, 2
• Hypotension indicates progression to septic shock and requires immediate intervention 1, 2

Gastrointestinal Symptoms

Associated GI manifestations include:

• Nausea and vomiting are reported in 35% of patients 1, 2
• Absence of defecation and other ileus symptoms 1, 2, 3
• Diarrhea may occur 1
• Rectal bleeding is observed in 15% of cases 1, 3

Laboratory Abnormalities

Key laboratory findings that support the diagnosis:

• Leukocytosis is present in 40% of patients, often with left shift (band neutrophils >20%) 1, 3
• Elevated C-reactive protein (CRP) levels 1, 2, 3
• Increased serum lactate indicates tissue hypoperfusion and ongoing sepsis 1, 2, 3
• Elevated serum creatinine (>50% above baseline) suggests renal dysfunction 1, 2, 3
• Elevated procalcitonin (PCT) is particularly significant in delayed presentations beyond 12 hours 1

For spontaneous bacterial peritonitis (SBP), ascitic fluid neutrophil count >250/mm³ is diagnostic 1, 3, while low ascitic fluid glucose (<50 mg/dL) suggests secondary peritonitis 1, 3.

Signs of Organ Dysfunction and Complications

Progressive peritonitis leads to multi-organ involvement:

• Oliguria and decreased urinary output indicate renal hypoperfusion 1, 2
• Altered mental status with lactic acidosis signals shock 1, 2
• Hepatic encephalopathy may develop, particularly in cirrhotic patients 1, 2, 3
• Hemodynamic instability progressing to multi-organ failure 1, 2
• Worsening liver function is especially concerning in patients with underlying cirrhosis 1, 2

Critical Clinical Pitfalls

The classic presentation of "pain out of proportion to physical examination findings" may be present in early peritonitis, making diagnosis challenging 1, 2. This is particularly problematic because:

• Delayed diagnosis beyond 24 hours significantly increases mortality rates and the need for more invasive treatments 1, 3
• Physical signs may be subtle or masked by distracting injuries, head injuries, spinal cord injuries, or abdominal wall trauma 4, 2
• In trauma patients, peritoneal signs may take many hours to develop due to delayed bowel perforation from vascular injury causing ischemia and necrosis 4

Imaging Findings

When the patient is hemodynamically stable:

• CT scan has the highest sensitivity and specificity (>90% accuracy) for detecting peritonitis and should be performed in stable patients with suspected diagnosis 1, 3
• Free air on plain abdominal radiograph indicates perforation, though sensitivity is lower than CT 1, 3
• Ultrasonography may show free fluid in the abdomen and can be valuable in resource-limited settings 1, 3
• FAST scan requires on average 620 mL of fluid to be detected, though highly skilled operators can detect as little as 400 mL 4

The overall mortality from peritonitis is 6%, but rises dramatically to 35% in patients who develop severe sepsis 5, with hospital mortality reaching 58% in severe cases with Mannheim Peritonitis Index >29 6. Time is critical—every 3 minutes spent in the emergency department equates to a 1% increased death probability in trauma patients 4.