Small Bowel Obstruction

Aka: Small Bowel Obstruction, Mechanical Ileus, Mechanical Bowel Obstruction

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II. Epidemiology

  1. Small Bowel Obstruction accounts 2-4% of Acute Abdominal Pain presentations to the emergency department (and 20% of emergent abdominal surgeries)
  2. Average age of onset: 64 years old

III. Types

  1. Simple mechanical obstruction
    1. Bowel lumen is obstructed
    2. No vascular compromise
  2. Strangulated obstruction
    1. Bowel lumen and vascular supply is compromised
  3. Closed loop obstruction
    1. Both ends of a bowel loop are obstructed
    2. Results in strangulated obstruction if untreated
    3. Rapid rise in intraluminal pressure
      1. Contained fluids and gas are trapped without proximal or distal exit
    4. Causes
      1. Volvulus (most common)
      2. Incarcerated Hernia
      3. Internal Hernia (associated with prior Roux-en-Y Bypass)
      4. Congenital bands
      5. Intestinal Malrotation

IV. Pathophysiology: Process (Occurs quickly in closed loop obstruction)

  1. Obstruction forms in either Small Bowel (much more common) or Large Bowel
  2. Bowel dilates proximal to obstruction
  3. Flatus and Bowel Movements cease
  4. Dehydration and Acute Kidney Injury results from Vomiting, minimal absorption, and bowel edema
  5. Even without oral intake, gastric, biliary and pancreatic secretions continue to accumulate within the bowel lumen
  6. Metabolic Alkalosis and Hypokalemia
    1. Vomiting: Potassium, chloride and Hydrogen Ion loss
    2. Proximal renal tube resorbs bicarbonate (contraction alkalosis)
  7. Bacterial overgrowth from intestinal stasis
    1. Stool forms within the Small Bowel (fecalization)
    2. Foul Emesis (odor of feces)
    3. Risk of bacteremia from Bacterial translocation across the bowel wall
  8. Incomplete obstruction (partial Small Bowel Obstruction) may still allow some forward flow of stool
  9. Intestinal dilation with increased intraluminal pressure
    1. Luminal pressure greater than venous pressure results in bowel wall edema and hyperemia
    2. Arterial flow diminishes due to compression and results in bowel ischemia, necrosis and perforation

V. Causes: By Frequency

  1. Most Common Causes
    1. Postoperative Adhesions (accounts for 50-60% of cases)
    2. Hernia (10-25% of cases, especially younger patients)
    3. Neoplasms (10-20% of cases, esp. older patients)
      1. Colon Cancer (most common, typically large Bowel Obstruction)
      2. Ovarian Cancer
      3. Pancreatic Cancer
      4. Gastric Cancer
  2. Less Common Causes (each less than 5% of cases)
    1. Inflammatory Bowel Disease
    2. Intussusception
    3. Volvulus
    4. Intraabdominal abscess
    5. Gallstones in the bowel lumen
    6. Foreign Body Ingestion

VI. Causes: By Type

  1. Intrinsic bowel lesions
    1. Congenital anomalies (Pediatric)
      1. Atresia
      2. Stenosis
      3. Bowel duplication
    2. Strictures
      1. Colon Cancer
        1. Peritoneal metastases
        2. Abdominal Radiation Therapy
      2. Inflammatory Bowel Disease
        1. Crohn Disease
        2. Ulcerative Colitis (10% within 3 years of colectomy, or 25% after restorative proctocolectomy)
          1. Aberg (2007) Int J Colorectal Dis 22(6): 637-42 [PubMed]
          2. Parikh (2008) Am Surg 74(10): 1001-5 [PubMed]
  2. Extrinsic bowel lesions
    1. Adhesion
      1. Abdominal or pelvic surgery
        1. Appendectomy
        2. Colorectal Surgery
        3. Gynecologic procedures
        4. Hernia Repairs
        5. Roux-en-Y Bypass (Internal Hernia risk)
      2. Surgery in presence of peritonitis or Trauma
    2. Hernia (higher risk for Strangulation)
      1. Internal Hernias via mesenteric defects
      2. External Hernias abdominal wall
      3. Obturator hernia
        1. More common in emaciated elderly women
    3. Small Bowel Volvulus
      1. Rare compared to colon Volvulus (e.g. Sigmoid Volvulus)
      2. More common in Africa, Middle East and India
      3. Occurs in Intestinal Malrotation or adhesions
  3. Obturation (Uncommon to Rare)
    1. Colonic Polyp
    2. Intussusception
      1. Presents with Vomiting, Abdominal Pain and sausage-shaped abdominal mass (and a late finding, Currant Jelly Stool)
      2. Children: Usually idiopathic
      3. Adults: 95% have underlying mechanical cause
      4. AIDS may predispose to Intussusception
    3. GallstoneIleus
      1. Gallstones that have entered the bowel lumen
      2. More common in those over age 65 years
    4. Bezoar
    5. Barium
    6. Ascaris infection
    7. Tuberculosis
    8. Actinomycosis
    9. Diverticulitis
    10. Lumphoma
  4. Idiopathic Intestinal Obstruction
    1. See Bowel Pseudoobstruction)

VII. Symptoms: Classic presentation

  1. Colicky Abdominal Pain
  2. Nausea and Vomiting
  3. Abdominal Distention
  4. Cessation of Flatus and Bowel Movements

VIII. Symptoms: General

  1. Frequent and recurrent Generalized Abdominal Pain
    1. Duration: Seconds to minutes
    2. Character: Spasms of crampy Abdominal Pain (colicky pain)
    3. Frequency
      1. Intermittent pain initially
      2. Every few minutes in proximal obstruction
      3. Constant pain suggests ischemia or perforation
  2. Associated Symptoms
    1. Nausea and Vomiting
      1. Vomitus differs between proximal obstruction (bilious) and distal obstruction (feculent)
    2. Stool passage
      1. Initially may be present despite complete obstruction
      2. Later, obstipation (no stool) in complete obstruction
  3. Symptoms more severe in proximal obstruction
    1. Proximal obstruction
      1. Severe, Colicky Abdominal Pain
      2. Develops over hours and occurs every few minutes
      3. Bilious Emesis
      4. Mild Abdominal Distention
    2. Distal obstruction
      1. Develops over days and becomes progressively worse
      2. Emesis may occur and is brown and feculent
      3. Significant Abdominal Distention

IX. Signs

  1. Vital Signs: Dehydration vs SIRS Criteria (Sepsis with peritonitis)
    1. Sinus Tachycardia
    2. Hypotension
  2. Bowel sounds
    1. Initial, Early: High pitched, hyperactive bowel sounds
    2. Later (after several hours): Hypoactive or absent bowel sounds
  3. Tender abdominal mass
    1. Closed loop Bowel Obstruction may be palpable
  4. Abdominal Distention and tympany on percussion
    1. Indicates distal obstruction
    2. Abdominal Distention and tympany has greatest Positive Predictive Value for Small Bowel Obstruction
  5. Rectal Examination
    1. Blood
    2. Fecal Impaction or rectal mass
  6. Clues to underlying etiology
    1. Abdominal wall or Inguinal Hernias
    2. Surgical scars

X. Diagnosis: Factors predicting Bowel Obstruction

  1. History of prior surgery
  2. Constipation history
  3. Age over 50 years
  4. Vomiting
  5. Abdominal Distention
  6. Hyperactive bowel sounds

XI. Labs

  1. Complete Blood Count
    1. Leukocytosis may be significant (e.g. >20k) in bacteremia and intestinal perforation
  2. Comprehensive Metabolic Panel or Basic Metabolic Panel
    1. Hypokalemia
    2. Contraction Alkalosis (Dehydration)
    3. Acute Kidney Injury (increased Serum Creatinine)
  3. Serum Lactic Acid
    1. Increased with bowel ischemia, Sepsis and Dehydration

XII. Imaging: Flat and upright (or decubitus) abdominal XRay

  1. Indications
    1. CT Abdomen has largely replaced abdominal XRay when there are no delays (e.g. ED)
    2. Abdominal XRay has previously been a first-line test in suspected Small Bowel Obstruction
      1. However, it has poor accuracy (low Test Sensitivity and Test Specificity)
      2. Abdominal XRay is most useful in excluding abdominal free air (upright view)
  2. Efficacy
    1. Test Specificity: 50%
    2. Test Sensitivity: 60% (up to 80-90% in high grade obstruction)
      1. False Negative in early obstruction and high jejunal or duodenal obstruction
  3. Typical findings of Bowel Obstruction
    1. Bowel distention proximal to obstruction
    2. Bowel collapsed distal to obstruction (<6 cm colon, <9 cm cecum)
    3. Minimal colonic gas
    4. Upright or decubitus view
      1. Multiple air fluid levels
      2. Air-fluid levels >2.5 cm
    5. Supine view findings in Small Bowel Obstruction
      1. Sharply angulated distended bowel loops
      2. Step-ladder arrangement or parallel bowel loops
      3. Large Bowel with minimal air
      4. Stomach dilated
      5. Smal bowel dilated >2.5 cm
  4. Findings on upright or decubitus films
    1. String of pearls sign (specific for obstruction)
      1. Series of small pockets of gas in a row (gas trapped in the superior Small Bowel wall)
    2. Coffee-bean sign
      1. Bowel loops are distended and air filled
      2. U-Shaped bowel loop divided by edematous bowel wall
    3. Pseudotumor Sign
      1. Bowel loop filled with fluid (resembles mass)
    4. Signs of perforation
      1. Free air above the liver on upright or left lateral decubitus films
      2. Consider upright Chest XRay which may best demonstrate free air

XIII. Imaging: CT Abdomen and Pelvis

  1. Obtain with Intravenous Contrast
    1. Contrast identifies Small Bowel ischemia findings
  2. Indications
    1. First-line study for high suspicion of Small Bowel Obstruction
      1. Replaces plain Abdominal XRay as it identifies obstruction site and cause
      2. Identifies emergent Bowel Obstruction causes (e.g. Volvulus)
      3. Pre-surgical planning to identify obstruction site
    2. Definitive diagnosis of Bowel Obstruction is not clear from Abdominal XRay and clinical exam
    3. Distinguishes partial from complete obstruction
      1. No Contrast Material seen distal to obstruction site
      2. Avoid use of rectal contrast to allow differentiation of partial from complete obstruction
  3. Efficacy
    1. Test Sensitivity: 90-93% for high grade Small Bowel Obstruction
      1. However, much less sensitive in partial Small Bowel Obstruction
      2. Consider Oral Contrast in low grade, partial obstruction
    2. Test Specificity: 100%
  4. Findings: Diagnosis
    1. Dilated bowel loops proximal to obstruction
    2. Decompressed bowel distal to obstruction
  5. Findings: Causes and complications
    1. Intussusception
    2. Volvulus
      1. C loop of distended bowel with radial mesenteric vessels and medial conversion
    3. Ischemia
      1. Thickened bowel walls and poor flow of Contrast Material
    4. Bowel perforation
      1. Pneumatosis Intestinalis, peritoneal free-air, and mesenteric fat stranding
    5. Extraluminal mass (e.g. abscess, neoplasm)
    6. Closed loop obstruction
    7. Strangulated bowel

XIV. Imaging: Contrast Fluoroscopy

  1. Indications
    1. Partial Intestinal Obstruction
    2. Refractory but stable cases of Intestinal Obstruction
  2. Protocols
    1. Water-soluble Contrast Material such as gastrograffin (may also be therapeutic in up to 74% of SBO patients)
    2. Small-bowel follow through
      1. Serial XRays after Oral Contrast (or NG instilled contrast)
      2. Contrast Material passing to Rectum within 24 hours of oral intake
        1. Associated with a 97% chance of spontaneous resolution
    3. Rectal fluoroscopy
      1. Demonstrates obstruction site in Large Bowel

XV. Imaging: Other advanced imaging

  1. Ultrasound Abdomen
    1. Consider in pregnancy, Unstable Patients or when Bedside Ultrasound is available
    2. Unable to identify transition point
    3. Efficacy (operator dependent)
      1. Test Specificity: 100%
      2. Test Sensitivity: 85% (however CT is typically performed instead in most cases)
        1. However, intraluminal gas and increasing mean BMI/Body habitus results in decreasing efficacy
    4. References
      1. Suri (1999) Acta Radiol 40(4): 422-8 [PubMed]
  2. MRI Abdomen (93% Test Sensitivity for SBO cause)
    1. CT Abdomen is typically preferred due to its lower cost and more rapid imaging
    2. Consider in pregnancy and adolescents
    3. May be performed with enteroclysis (Nasogastric Tube instills contrast directly into duodenum)

XVI. Differential Diagnosis (Abdominal Pain, distention, Nausea, cessation of Flatus/stool)

  1. Adynamic Ileus or postoperative Paralytic Ileus
    1. Transient intestinal dysfunction and dysmotility without a physical blockage, anywhere along the Small Bowel or colon
    2. Similar presentation to SBO (Nausea, Vomiting, obstipation, crampy Abdominal Pain)
    3. Causes include recent surgery, medication-induced ileus (e.g. Opioids, Tricyclic Antidepressants)
  2. Bowel Pseudoobstruction (Ogilvie Syndrome)
    1. Acute Large Bowel dilation with risk of dysmotility (e.g. Diabetes Mellitus, Scleroderma)
  3. Constipation
  4. Ascites
  5. Bowel Perforation
  6. Ischemic Bowel (superior mesenteric syndrome or Mesenteric Ischemia)
  7. Gastroenteritis
  8. Cholecystitis or Biliary Colic
  9. Pancreatitis
  10. Peptic Ulcer Disease or Dyspepsia
  11. Appendicitis
  12. Myocardial Infarction
  13. Pregnancy

XVII. Management: Conservative Therapy

  1. Surgical Consultation
  2. Admit all patients with complete Small Bowel Obstruction
  3. Fluid Replacement
    1. Intravenous Fluid Replacement and maintenance
    2. Electrolyte replacement (e.g. Potassium Replacement)
    3. Consider monitoring fluid output with urine catheter
  4. Bowel decompression
    1. Keep patient NPO without food or drink
    2. Nasogastric Tube
      1. No evidence for routine use in Small Bowel Obstruction
      2. Typically recommended for refractory Vomiting and Stomach distention
      3. Paradis (2014) Emerg Med J 31(3): 248-9 +PMID:24532357 [PubMed]
      4. Witting (2007) J Emerg Med 33(1):61-4 +PMID: 17630077 [PubMed]
    3. Long intestinal tube (eg. Cantor) offers no advantage
  5. Water soluble contrast trial
    1. Indicated in adhesion related Small Bowel Obstruction
    2. Contraindicated in pregnancy and non-adhesion SBO
    3. Technique
      1. Give Diatrizoate (e.g. Gastrografin) water soluble undiluted contrast 100 ml
      2. Clamp Nasogastric Tube for 2 to 4 hours
      3. Obtain KUB XRay at 6-24 hours to evaluate progression of contrast
        1. Progression of contrast to colon is predictive of Small Bowel Obstruction spontaneous resolution
        2. Lack of contrast in colon at 24 hours may indicate need for surgical intervention
  6. Antibiotic
    1. Indications (Not for routine use)
      1. Surgery planned
      2. Bowel ischemia or infarction
      3. Bowel perforation
      4. Fever and Leukocytosis at presentation
    2. Cover Gram Negative Bacteria and Anaerobes
      1. Ciprofloxacin and Metronidazole OR
      2. Piperacillin-Tazobactam (Zosyn)
  7. Possible benefit: Magnesium, Acidophilus, Simethicone
    1. Avoid in complete Bowel Obstruction due to bowel ischemia and perforation risk
    2. Give orally, then clamp NG tube x1 hour; Repeat tid
      1. Magnesium Oxide 500 mg
      2. L. acidophilus 0.3 grams
      3. Simethicone 40 mg
    3. Studied in partial Small Bowel Obstruction
      1. Unblinded trial
      2. Reduced length of stay and number needing surgery
      3. Chen (2005) CMAJ 173:1165-9 [PubMed]

XVIII. Management: Surgical Intervention

  1. Spontaneous resolution often occurs without surgery within 48 hours
    1. Partial Small Bowel Obstruction: 75%
    2. Complete Small Bowel Obstruction: Up to 50%
  2. Predictors of resolution without surgery
    1. Early postoperative Bowel Obstruction
    2. Adhesive obstruction (prior laparotomy)
    3. Crohn's Disease
  3. Indications for Surgery
    1. Inadequate relief with Nasogastric Tube placement
    2. Persistant symptoms >3-5 days without resolution with conservative management
    3. Acute management of surgically reversible cause
      1. Strangulated Hernia
      2. Volvulus
      3. Intra-abdominal malignancy
    4. Signs of abdominal Sepsis, bowel ischemia or bowel perforation
      1. Peritonitis
      2. Clinical instability
      3. Unexplained Leukocytosis or Metabolic Acidosis

XIX. Complications

  1. Intestinal Ischemia or infarction
  2. Bowel necrosis, bowel perforation and Bacterial peritonitis
  3. Hypovolemia
  4. Complications of surgical intervention if needed
  5. Fluid and Electrolyte imbalance

XX. Prognosis: Recurrence of obstruction due to adhesions

  1. Risk after first episode: 53%
  2. Risk after more than one episode: 83%
  3. Surgical Consultation to review elective surgery for reversible causes (e.g. Hernia Repair)
    1. However risk of additional postoperative intestinal adhesions

XXI. References

  1. Han (2022) Crit Dec Emerg Med 36(12): 4-10
  2. Torrey in Marx (2002) Rosen's Emergency Med, p. 1283-7
  3. Townsend (2001) Sabiston Surgery, p. 883-8
  4. Turnage in Feldman (1998) Sleisenger GI, p. 1799-804
  5. Jackson (2018) Am Fam Physician 98(6): 362-7 [PubMed]
  6. Jackson (2011) Am Fam Physician 83(2): 159-5 [PubMed]
  7. Matsuoka (2002) Am J Surg 183:614-7 [PubMed]

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