What bowel sound findings are expected in a perforated viscus?

Bowel Sounds in Perforated Viscus

Bowel sounds are usually absent in patients with perforated viscus, particularly when diffuse peritonitis has developed. 1

Expected Physical Examination Findings

Bowel Sound Characteristics

• Absent bowel sounds are the typical finding in perforation with peritonitis 1
• This contrasts sharply with bowel obstruction, where bowel sounds are typically hyperactive or absent depending on the stage 1

Associated Clinical Presentation

The World Journal of Emergency Surgery describes the classic presentation of perforated viscus as: 1

• Acutely ill appearance with fever, tachypnea, tachycardia, and confusion
• Diffuse or localized abdominal tenderness with guarding and rebound tenderness
• Absent bowel sounds on auscultation
• Toxic symptoms of peritonitis (considered an ominous sign)

Important Clinical Caveats

Variable Presentation Patterns

Physical examination findings may be equivocal, and peritonitis may be present in only two-thirds of patients with perforated peptic ulcer. 2, 3

• Peritonitis may be minimal or absent, particularly with contained or sealed perforations 2
• Localized peritonitis is typical but not universal 2
• Up to one-third of patients may not demonstrate classic peritoneal signs 2, 3

Location-Dependent Findings

The type of perforation affects clinical presentation: 1

• Perforation at tumor site: Usually produces localized peritoneal contamination
• Perforation proximal to obstruction: Results in diffuse peritonitis with fecal spread and septic shock
• Both scenarios typically present with absent bowel sounds once peritonitis develops 1

Diagnostic Algorithm When Perforation is Suspected

Do Not Rely on Physical Examination Alone

Because bowel sounds and other physical findings can be equivocal, imaging confirmation is mandatory whenever perforation is suspected. 1

Recommended Diagnostic Approach

1. CT scan with IV contrast is the first-line diagnostic test (Strong recommendation, 1C) 1, 2, 3

   • Sensitivity and specificity superior to all other modalities
   • Can detect small amounts of free air and fluid
   • Identifies perforation site and extent of contamination

2. Plain radiographs (chest/abdominal X-ray) only when CT unavailable (Strong recommendation, 1C) 2, 3

   • Free air detected in only 30-85% of perforations 3
   • Positive predictive value of 92% for iatrogenic colonoscopy perforation 1

3. Ultrasound can detect pneumoperitoneum in experienced hands 1, 4, 5

   • Shows echogenic line with ring-down artifact
   • Useful when radiation should be limited (children, pregnancy)
   • Should not be considered definitive for excluding perforation 1

Laboratory Markers

Obtain these tests immediately, though findings are non-specific: 1, 2, 3

• White blood cell count (leukocytosis expected)
• Metabolic panel (metabolic acidosis common)
• Arterial blood gas
• Serum amylase (may be elevated)
• C-reactive protein and procalcitonin if delayed presentation 1

Common Pitfalls to Avoid

• Never dismiss perforation based on normal bowel sounds alone - up to 12% of perforations may have normal initial CT, and physical findings are unreliable 3
• Do not wait for classic peritonitis signs - only two-thirds of patients demonstrate full peritoneal findings 2, 3
• Avoid relying on plain radiographs when CT is available - they miss 15-70% of perforations 3
• Remember that absent bowel sounds can occur in both obstruction and perforation - differentiation requires imaging 1