What are the signs of bowel obstruction?

Signs of Bowel Obstruction

Bowel obstruction presents with absence of flatus (90% of cases), absence of bowel movements (80.6%), colicky abdominal pain, and abdominal distension (65.3%), with distension being the strongest predictive sign (positive likelihood ratio 16.8). 1

Cardinal Clinical Features

Primary Symptoms

• Colicky abdominal pain that worsens as the bowel attempts to overcome the obstruction 1
• Absence of flatus occurs in 90% of cases 1
• Absence of bowel movements occurs in 80.6% of cases 1
• Nausea and vomiting are more prominent and occur earlier in small bowel obstruction 1
• Abdominal bloating is consistently present 1

Physical Examination Findings

• Abdominal distension occurs in 65.3% of cases and has the strongest predictive value (positive likelihood ratio 16.8, negative likelihood ratio 0.27) 1, 2
• Abdominal tenderness on palpation 1
• Hyperactive or absent bowel sounds depending on the stage of obstruction 1
• Visible peristalsis may be seen in thin patients 1
• Digital rectal examination may reveal blood or a rectal mass, particularly in colorectal cancer cases 1

Critical Warning Signs of Complications

These signs indicate strangulation, ischemia, or impending perforation and require immediate surgical consultation 2:

Systemic Signs

• Fever, tachypnea, tachycardia, and confusion suggest bowel ischemia or strangulation 1
• Hypotension, cool extremities, mottled skin, and oliguria indicate shock 1

Abdominal Examination Red Flags

• Intense pain unresponsive to analgesics 1
• Diffuse abdominal tenderness with guarding or rebound tenderness 1
• Absent bowel sounds (as opposed to hyperactive sounds in early obstruction) 1

Laboratory Findings Suggesting Complications

• Leukocytosis >10,000/mm³ and neutrophilia 1, 2
• Elevated lactic acid levels indicating intestinal ischemia 1, 2
• Low serum bicarbonate and arterial pH 1
• Elevated amylase levels 1
• Abnormal renal function tests indicating severe dehydration 1
• CRP >75 may indicate peritonitis 2

Distinguishing Small vs. Large Bowel Obstruction

Small Bowel Obstruction

• More frequent vomiting that occurs earlier in the clinical course 1
• Green/yellow vomit in proximal obstruction 1
• Most commonly caused by adhesions (55-75% of cases, particularly in patients with previous abdominal surgery) 1
• History of previous abdominal surgery has 85% sensitivity and 78% specificity for adhesive small bowel obstruction 2

Large Bowel Obstruction

• Less frequent vomiting 1
• Feculent vomiting in distal obstruction 1
• More gradual symptom development 1
• Recurrent left lower quadrant pain 1
• Most commonly caused by cancer (60% of cases) 1
• May have history of bloody stools, unexplained weight loss, or chronic constipation 1, 2

Common Pitfalls to Avoid

• Do not mistake incomplete obstruction with watery diarrhea for gastroenteritis—paradoxical diarrhea can occur with partial obstruction 1, 2
• Do not overlook bowel obstruction in elderly patients where pain may be less prominent or atypical 1, 2
• Do not delay surgical consultation when signs of ischemia are present—mortality can reach 25% with bowel ischemia 2
• Physical examination has only 48% sensitivity for detecting strangulation, so maintain high clinical suspicion and obtain imaging promptly 2

Essential Diagnostic Workup

History

• Previous abdominal surgeries (85% sensitivity for adhesive obstruction) 2
• Last passage of flatus or bowel movement 2
• Previous diverticulitis, chronic constipation, rectal bleeding, or weight loss 2
• Medications affecting peristalsis 2

Physical Examination

• Examine all hernia orifices and previous surgical incision sites 2
• Check vital signs for shock 2
• Perform digital rectal examination 2

Imaging

• CT scan with IV contrast is the gold standard with approximately 90% accuracy and superior ability to detect ischemia and determine need for urgent surgery 1, 2
• Ultrasound has 90% sensitivity and 96% specificity and is particularly useful in children and pregnant women 1, 2
• Plain abdominal X-rays have limited value with only 50-60% sensitivity and 20-30% inconclusive results 1, 2