How to diagnose peritonitis in a patient with ASUC (Acute Severe Ulcerative Colitis) and fulminant colitis, who has fever and tachycardia?

Diagnosing Peritonitis in ASUC/Fulminant Colitis

In a patient with ASUC or fulminant colitis presenting with fever and tachycardia, diagnose peritonitis through immediate clinical assessment for abdominal rigidity and rebound tenderness, followed by urgent CT scanning if the patient is hemodynamically stable, as CT has >90% accuracy and is superior to plain radiography or ultrasound. 1, 2

Critical Clinical Findings to Assess Immediately

Physical Examination Signs (Highest Priority)

• Abdominal rigidity is the single most important clinical finding that strongly suggests peritonitis and should be actively sought 1, 2
• Rebound tenderness and guarding occur in 82.5% of peritonitis cases and are present alongside abdominal pain/tenderness in 74-95% of patients 2, 3
• Decreased or absent bowel sounds indicate developing ileus and are commonly found 1, 2, 3
• Abdominal distension may be present, though isolated distension occurs in only 6.6% 2, 3
• Consider the "pinch-an-inch" test over McBurney's point as an alternative to rebound testing—grasp and elevate a skin fold, then allow it to recoil briskly; increased pain when skin strikes peritoneum indicates peritonitis 4

Systemic Signs Already Present

• Your patient's tachycardia (present in 62.5% of peritonitis) and fever (>38.5°C in 38% of cases) are consistent with but not diagnostic of peritonitis 1, 2, 3
• Assess for hypotension, which indicates progression to septic shock 2, 3
• Look for signs of hypoperfusion: altered mental status, oliguria, and lactic acidosis 1, 2

Additional Clinical Features

• Nausea/vomiting occur in 35% of peritonitis cases 2, 3
• Absence of defecation and other ileus symptoms may be present 1, 2
• Rectal bleeding occurs in 15% but is less specific in the context of underlying colitis 1, 2

Laboratory Evaluation

Essential Laboratory Tests

• Leukocytosis with left shift (band neutrophils >20%) occurs in only 40% of peritonitis cases, so normal white count does not exclude the diagnosis 1, 2, 3
• Elevated serum lactate indicates tissue hypoperfusion and ongoing sepsis 1, 2, 3
• Elevated C-reactive protein (CRP) is typically present 1, 2, 3
• Increased serum creatinine (>50% above baseline) suggests developing renal dysfunction 1, 2, 3
• Elevated procalcitonin is particularly significant if symptoms have been present >12 hours 2

Imaging Strategy

CT Scan is the Gold Standard

• CT scan has the highest sensitivity and specificity (>90% accuracy) for detecting peritonitis and should be performed in all hemodynamically stable patients with suspected diagnosis 2
• CT findings include: free fluid and air in the abdomen, bowel wall thickening, pericolic fat inflammation, and ascites 1
• CT is superior to both plain radiography and ultrasound for this indication 1, 2

Alternative Imaging if CT Unavailable

• Plain abdominal radiograph may show free air indicating perforation, but has lower sensitivity than CT 1, 2
• Ultrasonography may show free fluid but requires significant volume (400-620 mL) to be detected and is less reliable 2

Critical Pitfalls in ASUC/Fulminant Colitis

Diagnostic Challenges Specific to This Population

• Physical signs may be subtle or masked in critically ill patients, and peritoneal signs may take several hours to develop 2
• The classic presentation of "pain out of proportion to physical examination findings" may be present in early peritonitis, making diagnosis challenging 2, 3
• Postoperative or hospital-acquired peritonitis (relevant if patient has had recent procedures) shows particularly high mortality due to nonspecific symptoms 5, 6

Time-Critical Considerations

• Delayed diagnosis beyond 24 hours significantly increases mortality rates 1, 2
• In fulminant colitis, surgical intervention is indicated for hemorrhage, perforation, or peritonitis, and failure to recognize these complications promptly worsens outcomes 7
• Operating room latency ≥60 hours is an independent predictor of need for relaparotomy and death 1

When Peritonitis is Confirmed

Immediate Actions Required

• Obtain blood cultures before initiating antibiotics 1
• Initiate broad-spectrum antibiotics within the first hour covering E. coli, Klebsiella, Streptococcus species, and anaerobes 1
• Immediate surgical consultation is mandatory—delays beyond 24 hours significantly increase mortality 1
• Hemodynamically unstable patients or those with diffuse peritonitis require immediate surgical exploration 1

Source Control Strategy

• Source control includes resection or suture of perforated viscus, removal of infected organs, debridement of necrotic tissue, and drainage of collections 1
• In unstable patients with diffuse peritonitis, damage control surgery principles apply, potentially requiring Hartmann's procedure or resection with diverting stoma 1
• Mortality from peritonitis secondary to bowel perforation ranges from 4-10% even with appropriate management 1