Definition: Obstruction of the intestines such that bowel contents are unable to pass through the small bowel into the large bowel

  • Mechanical Obstruction: presence of a physical barrier to the passage of bowel contents.
      • Examples: adhesions, neoplasms, inflammatory disease (i.e. Crohn’s), hernias, intussusception, parasitic infections and foreign bodies
      • Simple Obstruction: Obstruction occurs at a single point in the bowel
      • Closed-loop obstruction: Obstruction at two locations creating a segment of bowel with proximal and distal compromise of blood flow
  • Functional (neurogenic) Obstruction: Obstruction resulting from disruption of normal peristalsis in the GI tract in the absence of a mechanical obstruction (adynamic ileus). Examples include post-operative, hypokalemia and opiate use


  • Dilation of the bowel proximal to the obstruction
    • Results in accumulation of intestinal secretions and partially digested materials
    • Stimulates peristalsis resulting in early loose bowel movements as well as nausea and vomiting
  • Bowel wall becomes edematous
    • Decreased absorption capacity leading to further dilation
    • Decreased venous return and, ultimately, decreased arterial flow
  • Bacterial overgrowth occurs as a result of stasis
  • Translocation of bacteria (notably E.Coli) into the bloodstream can occur due to increased bowel wall permeability
  • Extensive fluid losses can result from transudative fluid loss into the bowel lumen
  • Recurrent vomiting can lead to metabolic alkalosis, electrolyte abnormalities and hypovolemia
  • Closed Loop Pathophysiology
    • Intraluminal pressure increases more rapidly due to inability of bowel contents to move in retrograde fashion
    • Venous and arterial compromise can occur more rapidly leading to intestinal ischemia and infarction
    • Infarction and necrosis of the bowel can lead to perforation with resulting peritonitis and sepsis

Presentation (Taylor 2013)

  • History
    • Abdominal pain
      • Often crampy in nature
      • Crescendo-decrescendo pattern
    • Abdominal distension
    • Nausea/Vomiting (more pronounced with proximal obstructions)
    • Constipation
    • Obstipation (inability to pass gas- typically a late finding)
    • Prior abdominal surgery or radiation treatments common
  • Physical Examination
    • Early findings
      • Generalized tenderness to palpation
      • Decreased bowel sounds or high pitched “tinkling”
        • (+) LR Abnormal Bowel Sounds: 6.33
        • (-) LR Abnormal Bowel Sounds: 0.27
    • Late findings
      • Fever
      • Abdominal distension
        • (+) LR: 5.64 – 16.8
        • (-) LR: 0.34 – 0.43
      • Absent bowel sounds
      • Peritoneal signs (i.e. rebound and guarding)

AXR with Air Fluid Levels: Case courtesy of Dr Aditya Shetty, From the case rID: 28737


  • Laboratory Tests
    • Commonly ordered lab tests (i.e. WBC) are non-sensitive and non-specific
    • Serum lactate
      • Elevated in cases of bowel ischemia or infarction
      • Elevation typically a late finding
  • Abdominal X-ray
    • Findings
      • Dilated loops of small bowel proximal to the obstruction
      • Visible valvulae conniventes (mucosal folds of the small intestine)
      • Air-fluid levels
      • String-of-beads sign (small pockets of gas within a fluid-filled small bowel)
    • Advantages: Rapidly performed, non-invasive, can be performed bedside in unstable patients
    • Disadvantages: Poor sensitivity and specificity
    • Test Characteristics (Taylor 2013)
      • (+) LR: 1.6 (1.1 – 2.5)
      • (-) LR: 0.43 (0.24 – 0.79)
  • CT SBO Case courtesy of Dr Jeremy Jones, From the case rID: 6135

    CT Scan

    • Findings
      • Dilated loops of small bowel > 2.5 – 3 cm (measure outer wall to outer wall)
      • Collapsed loops of bowel distal to the obstruction
      • Intestinal Ischemia/Infarction
        • Thickened bowel wall
        • Increased attenuation of the bowel wall
        • Pneumatosis intestinalis (non-specific)
        • Portal venous gas (non-specific)
    • Advantages
      • Increased sensitivity and specificity to plain radiographs
      • Often identifies cause of obstruction
      • Can identify alternate pathology or cause of symptoms
    • Disadvantages
      • Takes more time
      • Requires patient to leave department (may not be feasible if patient unstable)
    • Test Characteristics (5 – 10 mm slice) (Taylor 2013)
      • (+) LR: 3.6 (2.3 – 5.4)
      • (-) LR: 0.18 (0.09 – 0.35)
  • US SBO Case courtesy of Dr Maryam Saif AlAli, From the case rID: 43438


    • Findings
      • Dilated loops of bowel (diameter > 2.5 cm) – most sensitive and specific
      • Decreased peristalsis and retrograde peristalsis (to and fro sign or “whirling”)
      • Bowel Infarction/Ischemia
        • Fluid filled bowel with extra-luminal free air
        • Bowel wall thickening (> 3 mm)
        • Absence of peristalsis
    • Advantages
      • Non-invasive
      • Can be rapidly performed at the patient’s bedside
      • Excellent test characteristics
    • Disadvantages
      • Dependent on operator skill
      • Patient habitus may limit quality of images
      • Does not clearly delineate transition point
      • May not be accepted by consulting services for definitive diagnosis
    • Test Characteristics (Taylor 2013)
      • Formal US
        • (+) LR: 14.1 (3.6 – 55.6)
        • (-) LR: 0.13 (0.08 – 0.20)
      • ED US
        • (+) LR: 9.5 (2.1 – 42.2)
        • (-) LR: 0.04 (0.01 – 0.13)

US demonstrating a dilated loop of bowel with retrograde peristalsis (to and from sign or "whirling") (care of M. Vermeulen)

US demonstrating a dilated loop of bowel with retrograde peristalsis (to and from sign or "whirling") (care of M. Vermeulen)

Summary of Diagnostic Findings

Sensitivity Specificity (+) LR (-) LR
Decr Bowel Sounds (or high pitched “tinkling) 23 – 76% 88 – 93% 3.29 – 6.33 0.27 – 0.83
Abdominal Distension 62 – 67% 89 – 96% 5.64 – 16.8 0.34 – 0.43
Abdominal X-ray 75% 66% 1.6 0.43
CT Scan 87% 81% 3.6 0.18
Radiology US 90% 96% 14.1 0.13
ED US 97% 90% 9.5 0.04


  • Airway
    • It is uncommon for patients with SBO to have airway compromise
    • Patients with closed-loop obstruction can become septic and obtunded while having continued vomiting
  • Circulation
    • Advanced cases can develop septic shock
    • Most cases will have intravascular volume depletion secondary to transudation of fluids into the bowel and decreased PO intake
    • Volume expansion with isotonic fluids (Lactated ringers, 0.9% saline or balanced solutions) indicated
  • Electrolyte repletion as necessary (fluid loss will be accompanied by electrolyte loss)
  • Antiemetics: may be helpful in those with partial SBO and in those not actively vomiting

Directed Management

  • Surgical Consultation
    • Surgical exploration indicated (Maung 2012)
      • Patients with evidence of clinical deterioration
      • Patients with generalized peritonitis
      • CT findings with bowel ischemia or infarction
    • Non-operative patients will require serial abdominal examinations and consideration for operative management if the clinical picture changes
  • Nasogastric Tube (NGT) Placement
    • Traditional teaching argues for the use of NGT in all patients with SBO but literature to defend this approach is minimal (Paradis 2014)
    • Resolution of nausea/vomiting with antiemetics may obviate the need for an NGT
    • Indications for NGT placement
      • Intractable vomiting
      • Severe abdominal distension
      • Altered mental status or other aspiration risk
  • Antibiotics
    • Theory is that bacterial translocation from the gut will be increased due to bowel wall edema
    • Limited data to support administration in all cases (Maung 2012)
    • Broad-spectrum antibiotics should be administered in patients with signs of hypoperfusion and sepsis
  • Disposition
    • All patients should be admitted to a surgical service
      • Limited evidence demonstrates lower mortality and better outcomes in SBO admitted to surgical service (Oyasiji 2010)
      • Patients more likely to get operative intervention earlier upon decompensation
    • Patients with closed loop obstructions or signs of ischemia/infarction should be admitted to an ICU setting

Take Home Points

  1. SBO should be considered in all patients presenting with abdominal pain particularly if they have a prior abdominal surgical history
  2. Patients with SBO often have non-specific signs and symptoms. There is no history or physical exam feature that rules out the disease
  3. Lactate elevation is a late finding in SBO. A normal lactate does not rule out the diagnosis
  4. Plain X-rays perform poorly in making or ruling out the diagnosis. CT is the most widely accepted imaging modality but US (both formal and ED) has better performance characteristics
  5. Patients with SBO should have an emergent surgical consultation and treatment should start with good supportive care (IV fluids, electrolyte repletion, antiemetics)
  6. Patients with hypotension, hypoperfusion or frank sepsis from an SBO should be aggressively resuscitated and optimized for operative management

Read More

The Short Coat: Small Bowel Obstruction – A Likely Story?

Radiopaedia: Small Bowel Obstruction

5 Min Sono: SBO

Ultrasound Podcast: Episode 36 – Small Bowel Obstruction

LITFL: Small Bowel Obstruction

FOAMCast: Episode 23 – SBO and Mesenteric Ischemia

Roline CE, Reardon RF: Disorders of the small intestine, in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2010, (Ch) 92: p 1216-1227.


Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med 2013; 20(6): 528-44. PMID: 23758299

Maung AA et al. Evaluation and management of small-bowel obstruction: an eastern association for the surgery of trauma practice management guideline. J Trauma Acute Care Surg 2012; 73(5): S362-9. PMID: 23114494

Paradis M. Towards evidence-based Emergency Medicine: Best BETs From the Manchester Royal Infirmary. BET 1: Is Routine Nasogastric Decompression Indicated in Small Bowel Occlusion? Emery Med J 2014; 31(3): 248-9. PMID: 24532357

Oyasiji T et al. Small bowel obstruction: Outcome and cost implications of admitting service. Am Surg 2010; 76:687-691. PMID: 20698371