What history, physical examination findings, and investigations are indicated for intestinal obstruction, and what typical results are expected?

Diagnosis of Intestinal Obstruction: History, Physical Examination, and Investigations

For suspected intestinal obstruction, obtain CT abdomen/pelvis without oral contrast as the primary diagnostic test, as it has >90% diagnostic accuracy and provides critical information about site, cause, and complications that directly guide management 1.

History: Key Clinical Features to Elicit

The most reliable historical findings that predict intestinal obstruction include 2, 3:

• Prior abdominal surgery (most predictive - adhesions cause 65-70% of cases)
• History of constipation/obstipation
• Intermittent crampy central abdominal pain
• Nausea and vomiting (particularly bilious)
• Failure to pass flatus or stool
• Age over 50 years

For strangulation risk assessment, specifically ask about 2:

• Fever
• Severe, constant pain (vs. intermittent crampy pain)
• Pain out of proportion to examination findings

Timing matters: Most patients present 3-7 days after symptom onset, though malignant obstructions often present after >14 days with gradual progression 4.

Physical Examination: Critical Findings

The most reliable physical examination findings include 2, 5, 3:

• Abdominal distension (highly sensitive)
• Abnormal bowel sounds (either high-pitched/hyperactive early, or absent later)
• Tympany to percussion
• Previous surgical scars (suggests adhesive etiology)

Signs suggesting strangulation/ischemia requiring emergency surgery 2, 6:

• Peritoneal signs (guarding, rebound tenderness)
• Hypotension
• Fever
• Diffuse severe abdominal pain
• Palpable mass (more common in strangulated cases, though not reliable)

Important caveat: History and physical examination alone cannot reliably exclude bowel obstruction or detect strangulation - imaging is essential 5, 6.

Investigations: Algorithmic Approach

Laboratory Tests

Order the following to assess for complications 2, 5:

• Complete blood count (elevated WBC suggests ischemia/perforation)
• Serum lactate (elevated in ischemia)
• Serum amylase (may be elevated)
• Basic metabolic panel (assess electrolyte derangements from vomiting)

Critical limitation: These labs are neither sensitive nor specific for strangulation, but abnormalities increase suspicion 1, 6.

Imaging Strategy

Primary recommendation: CT abdomen/pelvis without oral contrast 1

Why CT is preferred:

• Diagnostic accuracy >90% for high-grade obstruction
• Identifies site and cause of obstruction
• Detects complications (ischemia, closed-loop, volvulus, perforation)
• Distinguishes complete vs. partial obstruction
• No oral contrast needed - intrinsic bowel fluid provides adequate contrast

CT findings suggesting ischemia/need for emergency surgery 1:

• Abnormal bowel wall enhancement (decreased or increased)
• Bowel wall thickening
• Mesenteric edema
• Ascites
• Pneumatosis or mesenteric venous gas
• Intramural hyperdensity on non-contrast images

Plain abdominal radiographs: While often ordered initially, they have significant limitations 1:

• Sensitivity only 30-70%
• Cannot exclude obstruction
• Misleading in 20-40% of cases
• May prolong evaluation time
• Use only if CT unavailable or to avoid unnecessary imaging in low-risk patients

When to skip radiographs entirely: If any two of these are present, proceed directly to CT 3:

• Distended abdomen
• Increased bowel sounds
• History of constipation
• Previous abdominal surgery
• Age >50 years
• Vomiting

Special Scenarios

For intermittent/low-grade obstruction 1:

• Standard CT has lower sensitivity (48-50%)
• Consider water-soluble contrast challenge: Give 100 mL hyperosmolar contrast (diatrizoate) via NG tube or orally
• Obtain radiographs at 8 and 24 hours
• If contrast reaches colon by 24 hours = partial obstruction, rarely needs surgery
• If no passage = complete obstruction, likely needs surgery

Ultrasound 1:

• Sensitivity 91%, specificity 84% in adults
• Limited role in U.S. practice due to CT superiority
• Useful in pediatrics (intussusception, midgut volvulus)
• Consider for bedside evaluation if CT unavailable

Expected Findings Summary

Complete (High-Grade) Obstruction

• Dilated small bowel loops (>3 cm)
• Air-fluid levels
• Collapsed distal bowel
• Transition point visible on CT
• No passage of oral contrast distally

Partial (Low-Grade) Obstruction

• Some bowel dilation
• Contrast passes transition point (may take 24 hours)
• Gas/stool in colon

Adhesive Obstruction (Most Common - 65-70% of cases) 7, 8

• History of prior surgery
• CT shows transition point without mass, hernia, or other cause
• Small bowel feces sign
• May resolve with conservative management in 70-90% of cases

Strangulation/Ischemia (Requires Emergency Surgery)

• Clinical: fever, hypotension, peritonitis, severe pain
• Labs: elevated lactate, WBC
• CT: abnormal enhancement, wall thickening, mesenteric edema, pneumatosis

The key distinction driving management is complete vs. partial obstruction and simple vs. complicated (ischemic) obstruction 2, 8. CT provides this information reliably, making it the investigation of choice over plain films.