What are the signs and symptoms of peritonitis?

Signs of Peritonitis

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

Local Abdominal Findings

The hallmark physical examination findings include:

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

Systemic Signs of Inflammation

Peritonitis triggers a systemic inflammatory response with the following vital sign changes:

• Tachycardia is observed in 62.5% of patients (note: bradycardia is NOT an expected finding) 1, 2, 3
• Fever greater than 38.5°C is present in 38% of cases 1, 2, 3
• Hypotension indicates progression to septic shock 2, 3
• Tachypnea as part of the systemic inflammatory response 2, 3

Gastrointestinal Symptoms

Associated GI manifestations include:

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

Laboratory Abnormalities

Key laboratory findings that support the diagnosis:

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

For spontaneous bacterial peritonitis (SBP) specifically, ascitic fluid neutrophil count >250/mm³ is diagnostic, and low ascitic fluid glucose (<50 mg/dL) suggests secondary peritonitis 1, 2

Signs of Organ Dysfunction and Complications

As peritonitis progresses, watch for:

• Oliguria and decreased urinary output indicating hypoperfusion and developing renal failure 1, 3
• Altered mental status from lactic acidosis and shock 1, 2
• Hepatic encephalopathy particularly in cirrhotic patients 1, 2, 3
• Hemodynamic instability progressing to multi-organ failure 1, 2

Imaging Findings

When peritonitis is suspected based on clinical signs:

• CT scan has the highest sensitivity and specificity (>90% accuracy) for detecting peritonitis and should be performed in stable patients 2
• Free air on plain abdominal radiograph indicates perforation, though sensitivity is lower than CT 1, 2
• Ultrasonography may show free fluid in the abdomen and can be valuable in resource-limited settings 1, 2
• Multi-detector CT (MDCT) is 86% accurate in predicting the site of perforation 4

Critical Clinical Pitfalls

The classic presentation of "pain out of proportion to physical examination findings" may be present in early peritonitis, making diagnosis challenging. 2, 3 Physical signs may be subtle or masked by distracting injuries, head injuries, spinal cord injuries, or abdominal wall trauma 2. Peritoneal signs may take several hours to develop, particularly in small bowel injury, and serial examinations significantly improve diagnostic accuracy 2.

Delayed diagnosis beyond 24 hours significantly increases mortality rates and the need for more invasive treatments 2, 3. After diagnostic or therapeutic colonoscopies, all patients who present with abdominal pain, tenderness, abdominal distension, fever, or rectal bleeding should be investigated for perforation by laboratory tests and imaging exams 4.