What are the signs of a small bowel obstruction (SBO)?

Signs and Symptoms of Small Bowel Obstruction (SBO)

Small bowel obstruction (SBO) is classically characterized by intermittent colicky abdominal pain, abdominal distention, nausea with or without vomiting, and constipation or obstipation. 1

Clinical Presentation

Cardinal Signs and Symptoms

• Abdominal pain
  • Typically colicky and intermittent
  • Often periumbilical or diffuse
• Abdominal distention
  • Highly specific physical finding
• Nausea and vomiting
  • More prominent with proximal obstructions
• Constipation or obstipation
  • May progress to complete absence of stool and flatus in complete obstruction

Important Clinical Pitfalls

• Watery diarrhea may be present in incomplete obstruction, leading to misdiagnosis as gastroenteritis 1
• Stool may still be present in early presentation, especially with high obstructions 1
• Pain may be less prominent in elderly patients, making diagnosis more challenging 1
• Signs of strangulation include fever, hypotension, diffuse abdominal pain, and peritonitis 2

Physical Examination Findings

• Abdominal distention - highly sensitive finding
• Abnormal bowel sounds - may be high-pitched, tinkling, or absent
• Tenderness - may be diffuse or localized
• Signs of dehydration - dry mucous membranes, tachycardia, orthostatic hypotension 3

Warning Signs of Strangulation/Ischemia

• Fever
• Tachycardia
• Localized or diffuse peritoneal signs
• Continuous (rather than colicky) abdominal pain
• Severe direct tenderness, involuntary guarding, abdominal rigidity, and rebound tenderness 3

Laboratory Findings

The minimum recommended laboratory tests include 1, 4:

• Complete blood count (WBC >10,000/mm³ may indicate peritonitis)
• Lactate (elevated in bowel ischemia)
• Electrolytes (often disturbed, particularly potassium)
• C-reactive protein (CRP >75 may indicate peritonitis)
• BUN/creatinine (to assess hydration status)

Imaging Findings

Plain X-rays

• Pathognomonic triad in high-grade obstruction 1:
  1. Multiple air-fluid levels
  2. Distention of small bowel loops
  3. Absence of gas in the colon
• Limited sensitivity (~70%) and specificity 1

CT Scan (Gold Standard)

• Sensitivity approaches 100% for complete obstruction 4
• Findings include:
  • Dilated small bowel loops (>2.5 cm)
  • Transition point
  • Collapsed distal bowel
  • Signs of ischemia (wall thickening, pneumatosis, portal venous gas) 4

Water-Soluble Contrast Studies

• Diagnostic and potentially therapeutic
• If contrast doesn't reach the colon within 24 hours, this indicates failure of non-operative management 1, 4

Ultrasound

• Increasingly recognized as useful, especially at bedside
• Findings include dilated fluid-filled loops and decreased peristalsis 5

Differential Diagnosis

• Postoperative ileus
• Narcotic bowel syndrome
• Colonic pseudo-obstruction
• Mesenteric ischemia
• Large bowel obstruction 3

Risk Factors

• Previous abdominal surgery (adhesions are the most common cause, ~65%) 3
• Hernias (10%)
• Neoplasms (5%)
• Crohn's disease (5%)
• Other causes (15%) including gallstone ileus, intussusception, volvulus, and foreign bodies 3

Early recognition of SBO signs and symptoms is crucial, as delayed diagnosis represents 70% of malpractice claims in SBO cases 1. Physical examination alone has only 48% sensitivity for detecting strangulation, even by experienced clinicians, highlighting the importance of appropriate imaging studies 1.