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Small Bowel Obstruction (SBO)

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Small Bowel Obstruction (SBO)

Small bowel obstruction (SBO) is a blockage of the small intestine that prevents the normal passage of food, fluids, and gas through the bowel. It is a common surgical emergency that requires prompt diagnosis and treatment to prevent complications.

Also called

Small Intestinal Obstruction (SIO)

ICD-10

K56.609

Specialty

Gastroenterology

Onset

Chronic

Reviewed

July 2026

On This Page

Overview

  • Small bowel obstruction (SBO) is a type of mechanical bowel obstruction affecting the duodenum, jejunum, or ileum.
  • It may be partial (some bowel contents can pass) or complete (no passage of air or fluid).
  •  

Etiology & Risk Factors

-Etiology of Small Bowel Obstruction (SBO)

  • Postoperative adhesions – most common cause
  • Incarcerated hernias – second most common cause
  • Crohn disease (intestinal strictures)
  • Tumors (primary or metastatic)
  • Volvulus (twisting of the bowel)
  • Intussusception
  • Gallstone ileus
  • Foreign body or bezoar

-Risk Factors for Small Bowel Obstruction (SBO)

  • Previous abdominal surgery (adhesion formation)
  • History of abdominal tuberculosis (can lead to adhesions)
  • Abdominal or groin hernia
  • Crohn disease
  • Abdominal malignancy
  • Sudden, extreme weight loss (risk for superior mesenteric artery syndrome)

Pathophysiology

Obstruction → Stasis of intestinal contents & gas → ↑ Intraluminal pressure → Bowel distention → Third spacing of fluid → Dehydration & hypovolemia

↑ Intraluminal pressure → Vomiting → Loss of Na⁺, K⁺, H⁺, Cl⁻ → Hypokalemia + Metabolic alkalosis

↑ Intraluminal pressure → Compression of veins & lymphatics → Bowel wall edema → Reduced blood flow → Bowel ischemia → Necrosis & perforation → Peritonitis Bowel ischemia → Bacterial translocation → Sepsis

Clinical Presentation

  • Colicky, periumbilical abdominal pain
  • Nausea and early bilious vomiting
  • Abdominal distention (usually less severe than in large bowel obstruction)
  • Constipation or obstipation (complete inability to pass stool or gas in complete obstruction)
  • Red Flags (Suggest Complicated SBO)
  • Pain out of proportion to examination
  • Peritoneal signs (guarding, rebound tenderness)
  • Hemodynamic instability
  • Signs of systemic toxicity
  • Leukocytosis, metabolic acidosis, or elevated lactate

History Taking

  • Ask about:

    • When did the abdominal pain start?
    • Where is the pain? Is it colicky (comes and goes) or constant?
    • Have you had nausea or vomiting? Is the vomit green (bilious)?
    • Have you passed stool or gas today?
    • Is your abdomen swollen (distended)?
    • Have you had previous abdominal surgery?
    • Do you have a history of hernia?
    • Do you have Crohn disease or bowel cancer?
    • Have you had similar episodes before?
    • Do you have fever, severe continuous pain, or blood in the stool?
    •  

Physical Examination

  • Assess vital signs: Fever, tachycardia, hypotension
  • Inspect: Abdominal distention, previous surgical scars, hernias
  • Auscultate: High-pitched bowel sounds (early) → absent bowel sounds (late)
  • Percuss: Tympanic (drum-like) abdomen
  • Palpate: Diffuse abdominal tenderness, guarding or rebound tenderness (suggests peritonitis)
  • Digital rectal examination: Empty collapsed rectum (complete obstruction) or impacted stool
  • Assess hydration: Dry mucous membranes and signs of hypovolemia

Investigations

  • Laboratory Tests

    • CBC – leukocytosis (infection/ischemia)
    • BMP (electrolytes, urea, creatinine) – dehydration and electrolyte imbalance
    • Serum lactate – elevated suggests bowel ischemia
    • CRP – inflammation

    Imaging

    • CT abdomen and pelvis with IV contrast – gold standard (confirms SBO, site, cause, and complications)
    • Abdominal X-ray – dilated small bowel loops, multiple air-fluid levels, stepladder sign
    • Ultrasound – may show dilated fluid-filled bowel loops (especially if CT is not immediately available)

Diagnosis

  • Diagnosis of Small Bowel Obstruction (SBO)  is based on :

    • Clinical suspicion: Colicky abdominal pain + vomiting + abdominal distention + constipation/obstipation
    • Confirm with imaging: CT abdomen and pelvis with IV contrast (gold standard)
    • Supportive tests: CBC, electrolytes (BMP), CRP, serum lactate
    • Diagnosis is based on: Clinical findings + imaging + laboratory results
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Related Topics

Management

Initial Management

  • NPO (nothing by mouth)
  • IV fluids and electrolyte replacement
  • Nasogastric (NG) tube if persistent vomiting or significant abdominal distention
  • Pain relief and antiemetics
  • Early surgical consultation
  • Admit to the surgical service

Definitive Management

      • Conservative (nonoperative): Simple/partial SBO without signs of complications
      • Surgery: If there is:
        • Bowel ischemia or strangulation
        • Perforation or peritonitis
        • Closed-loop obstruction
        • Hemodynamic instability
        • Failure of conservative treatment (typically after up to 72 hours)
    •  

Complications

  • Bowel ischemia
  • Bowel perforation
  • Peritonitis
  • Sepsis (may occur if ischemia/perforation develope
  • A change from colicky pain to continuous pain, rebound tenderness, or signs of sepsis suggests complications and requires emergency surgery.
  •  

Prognosis

  • Good prognosis with early diagnosis and prompt treatment.
  • Delayed treatment increases the risk of bowel ischemia, perforation, sepsis, and death.
  • High risk of recurrence, especially in patients with adhesions or Crohn disease.
  • Untreated intestinal strangulation has a very high mortality rate.
  •  

Key Points / Clinical Pearls

  • Most common cause of Small bowel obstruction (SBO) : Postoperative adhesions.
  • Main symptoms: Colicky abdominal pain, vomiting, abdominal distention, constipation/obstipation.
  • Best diagnostic test: CT abdomen and pelvis with IV contrast.
  • Initial management: NPO + IV fluids + electrolyte correction + NG tube (if needed) + early surgical consultation.
  • Simple SBO: No bowel ischemia, strangulation, or perforation → may be treated conservatively.
  • Complicated SBO: Ischemia, strangulation, perforation, or closed-loop obstruction → emergency surgery.
  • Red flags: Continuous severe pain, rebound tenderness, fever, hypotension, elevated lactate, or signs of sepsis.
  • Major complications: Bowel ischemia → perforation → peritonitis → sepsis.
  •  
  • Schick MA, Kashyap S, Collier SA, Meseeha M. National Center for Biotechnology Information (NIH). Small Bowel Obstruction, StatPearls.
  • ten Broek RPG, Krielen P, Di Saverio S, et al. Bologna Guidelines for Diagnosis and Management of Adhesive Small Bowel Obstruction (ASBO): 2017 Update of the Evidence-Based Guidelines from the World Society of Emergency Surgery ASBO Working Group. World J Emerg Surg. 2018;13:24. PMID: 29946347.
  • Kaplan LJ, Martinez-Casas I, Mohseni S, et al; SnapSBO Collaborators. Small Bowel Obstruction Outcomes According to Compliance With the World Society of Emergency Surgery Bologna Guidelines. Br J Surg. 2025;112:znaf080. PMID: 40246692.
  • MedlinePlus, National Library of Medicine (NIH). Intestinal Obstruction: Medical Encyclopedia.
  • National Center for Biotechnology Information (NIH). Bowel Obstruction, StatPearls.