How to Diagnose Bowel Obstruction in a Simple Way
Start with a focused clinical assessment followed immediately by CT abdomen/pelvis with IV contrast, which achieves >90% diagnostic accuracy and supersedes all other imaging modalities. 1
Step 1: Rapid Clinical Assessment (5 minutes)
Key History Points
- Ask about previous abdominal surgeries – This single question has 85% sensitivity for adhesive small bowel obstruction, the most common cause (55-75% of cases). 1, 2
- Document the four cardinal symptoms: colicky abdominal pain, vomiting, abdominal distension, and inability to pass flatus or stool. 2, 3
- Inquire about last bowel movement and flatus passage – Absence of flatus occurs in 90% of cases and absence of bowel movements in 80.6%. 2
- Review medications – Opioids can cause narcotic bowel syndrome that mimics mechanical obstruction. 4, 1
Critical Physical Examination Findings
- Assess for abdominal distension – Present in 65.3% of cases with a positive likelihood ratio of 16.8, making it the single most powerful physical finding. 2, 5
- Auscultate bowel sounds – Hyperactive sounds with "rushes" indicate mechanical obstruction, while absent sounds suggest ischemia or ileus. 2, 6
- Check for peritoneal signs (guarding, rebound tenderness) – These indicate strangulation, ischemia, or perforation requiring immediate surgery. 2, 6
- Examine all hernia orifices and prior surgical scars – Hernias cause 10-15% of small bowel obstructions. 1, 2
Red Flags Requiring Immediate Surgical Consultation
- Fever, tachycardia, tachypnea, or confusion 2
- Intense pain unresponsive to analgesics 2
- Peritoneal signs (guarding, rebound, rigidity) 2, 6
- Hypotension or signs of shock 2
Step 2: Immediate Laboratory Tests
Order these while arranging imaging:
- Complete blood count – Leukocytosis >10,000/mm³ suggests peritonitis or strangulation. 1, 2
- Lactate level – Elevated lactate indicates bowel ischemia and mandates urgent surgery. 1, 2
- Electrolytes – Hypokalemia is common and must be corrected before any surgery. 1, 2
- BUN/creatinine – Assesses dehydration severity. 1, 2
- CRP – Values >75 mg/L may indicate peritonitis. 1
Step 3: Definitive Imaging – CT Abdomen/Pelvis with IV Contrast
This is the single most important diagnostic step. 1, 7
Why CT is Superior
- >90% diagnostic accuracy for detecting presence, location, and cause of obstruction 1, 7, 5
- Identifies life-threatening complications that plain X-rays cannot detect 1, 7
- Plain X-rays have only 50-60% sensitivity and are inconclusive in 20-52% of cases – they waste time and should be skipped. 1, 5
Key CT Findings to Report
Confirms obstruction:
- Dilated bowel loops >2.5-3 cm proximal to a clear transition point with collapsed bowel distally 8
Absolute indications for emergency surgery (report immediately):
- Reduced or absent bowel wall enhancement (ischemia) 1, 8, 7
- Closed-loop obstruction (C-shaped or U-shaped dilated loop) 1, 8
- Pneumatosis intestinalis or mesenteric venous gas 1, 8
- Pneumoperitoneum (free air = perforation) 8
- Mesenteric edema with ascites and absence of small-bowel feces sign 1, 8
Identifies the cause:
- Adhesions (cannot be directly visualized but diagnosed by exclusion) 4, 1
- Hernias, masses, volvulus, or strictures 1, 7
Important Technical Points
- No oral contrast is needed – Intrinsic bowel fluid provides excellent natural contrast. 1, 8
- IV contrast is essential – Required to assess bowel wall enhancement and detect ischemia. 1, 8
Step 4: Immediate Management While Awaiting Imaging
Begin these interventions simultaneously:
- IV crystalloid resuscitation – Patients are typically volume-depleted. 1, 8
- Nasogastric tube insertion – Decompresses stomach, prevents aspiration, reduces vomiting. 1, 8
- NPO status (nothing by mouth) 8
- Foley catheter – Monitor urine output to assess hydration. 1
Step 5: Decision Algorithm Based on CT Results
If High-Risk Features Present → Immediate Surgery
Any of these findings mandate urgent surgical consultation: 1, 8
- Signs of ischemia (abnormal enhancement, pneumatosis, venous gas)
- Closed-loop obstruction
- Pneumoperitoneum
- Clinical peritonitis
Mortality increases from 10% to 25-30% with bowel necrosis, making early recognition critical. 1
If No High-Risk Features → Trial of Conservative Management
- Continue NPO, NG decompression, IV fluids 1, 8
- Correct electrolytes (especially potassium and magnesium) 1, 8
- Safe observation window is 48-72 hours maximum – beyond this, complication rates rise sharply. 1, 8
Water-Soluble Contrast Protocol (After 48 Hours)
- Administer 50-150 mL Gastrografin via NG tube after adequate gastric decompression 1, 8
- Obtain abdominal X-ray 24 hours later 1, 8
- If contrast fails to reach colon at 24 hours → 96% sensitivity and 98% specificity for predicting need for surgery. 8
- This protocol reduces operative rates, shortens hospital stay, and accelerates resolution. 8
Common Pitfalls to Avoid
- Do NOT order plain X-rays when CT is available – They delay diagnosis without adding value and are inconclusive in 20-52% of cases. 1, 5
- Do NOT give water-soluble contrast before 48 hours or before adequate gastric decompression – Risk of aspiration pneumonia and hypovolemic shock. 8
- Do NOT extend conservative management beyond 72 hours without repeat CT – Mortality doubles when necrosis develops. 1, 8
- Do NOT miss incomplete obstruction presenting with watery diarrhea – Can be mistaken for gastroenteritis. 1, 2
- Do NOT underestimate obstruction in elderly patients – Pain may be less prominent while complications are more severe. 1
Alternative Imaging When CT is Contraindicated
Ultrasound
- 90% sensitivity and 96% specificity for small bowel obstruction 1, 5
- Useful in pregnancy, children, and when radiation exposure is a concern 1, 5
- Bedside ultrasound by emergency physicians has positive likelihood ratio of 9.55 5