II. Types

  1. Simple mechanical obstruction
    1. Bowel lumen is obstructed
    2. No vascular compromise
  2. 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
  3. Strangulated obstruction
    1. Bowel lumen and vascular supply is compromised

III. 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 results from Vomiting, minimal absorption, and bowel edema
  5. Metabolic Alkalosis and Hypokalemia
    1. Vomiting: Potassium, chloride and hydrogen ion loss
    2. Proximal renal tube resorbs bicarbonate (contraction alkalosis)
  6. Bacterial overgrowth from intestinal stasis results in foul Emesis and risk of bacteremia
  7. 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

IV. 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)
      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

V. Causes: By Type

  1. Obturation
    1. Colonic Polyp
    2. Intussusception
      1. Children: Usually idiopathic
      2. Adults: 95% have underlying mechanical cause
      3. AIDS may predispose to Intussusception
    3. Gallstones that have entered the bowel lumen
      1. More common in those over age 65 years
    4. Bezoar
    5. Barium
    6. Ascaris infection
    7. Tuberculosis
    8. Actinomycosis
    9. Diverticulitis
  2. Intrinsic bowel lesions
    1. Congenital anomalies (Pediatric)
      1. Atresia
      2. Stenosis
      3. Bowel duplication
    2. Strictures
      1. Inflammatory Bowel Disease (e.g. Crohn's Disease)
      2. Colon Cancer
  3. Extrinsic bowel lesions
    1. Adhesion
      1. Abdominal or pelvic surgery
        1. Appendectomy
        2. Colorectal Surgery
        3. Gynecologic procedures
        4. Hernia Repairs
      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
      2. More common in Africa, Middle East and India
      3. Occurs in Intestinal Malrotation or adhesions
  4. Idiopathic Intestinal Obstruction
    1. See Bowel Pseudoobstruction)

VI. Symptoms: Classic presentation

  1. Colicky Abdominal Pain
  2. Nausea and Vomiting
  3. Abdominal distention
  4. Cessation of flatus and Bowel Movements

VII. Symptoms

  1. Frequent and recurrent Generalized Abdominal Pain
    1. Duration: Seconds to minutes
    2. Character: Spasms of crampy Abdominal Pain
    3. Frequency
      1. Intermittent pain initially
      2. Every few minutes in proximal obstruction
      3. Constant pain suggests ischemia or perforation
  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

VIII. Signs

  1. Bowel sounds
    1. Initial: High pitched, hyperactive bowel sounds
    2. Later: hypoactive or absent bowel sounds
  2. Tender abdominal mass
    1. Closed loop Bowel Obstruction may be palpable
  3. Abdominal distention and tympany on percussion
    1. Indicates distal obstruction
  4. Rectal examination for blood

IX. 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

X. Labs

  1. Complete Blood Count
  2. Metabolic Panel
  3. Serum Lactic Acid

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

  1. Indications
    1. All cases of suspected Small Bowel Obstruction should undergo abdominal xray (first-line test)
  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
    3. Upright or decubitus view: Air-fluid levels
    4. 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. String of pearls sign (specific for obstruction)
    1. Series of small pockets of gas in a row
  5. Coffee-bean sign
    1. Bowel loops are distended and air filled
    2. U-Shaped bowel loop divided by edematous bowel wall
  6. Pseudotumor Sign
    1. Bowel loop filled with fluid (resembles mass)
  7. 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

XII. Imaging: CT Abdomen

  1. Test Sensitivity: 90% for high grade SBO
    1. However, much less sensitive in partial Small Bowel Obstruction
  2. Indications (second-line test after plain Abdominal XRay)
    1. Adjunct to plain Abdominal XRay to identify obstruction site and cause
    2. Definitive diagnosis of Bowel Obstruction is not clear from Abdominal XRay and clinical exam
    3. Identifies emergent Bowel Obstruction causes (e.g. Volvulus)
    4. Pre-surgical planning to identify obstruction site
    5. 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. Findings: Diagnosis
    1. Dilated bowel loops proximal to obstruction
    2. Decompressed bowel distal to obstruction
  4. 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

XIII. 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 is associated with a 97% chance of spontaneous resolution
    3. Rectal fluoroscopy
      1. Elucidates obstruction site in Large Bowel

XIV. Imaging: Other advanced imaging

  1. Ultrasound Abdomen
    1. Consider in pregnancy or in unstable patients
    2. Test Sensitivity approaches 85% (however CT is typically performed instead in most cases)
  2. MRI Abdomen (93% Test Sensitivity for SBO cause)
    1. CT Abdomen is typically preferred instead
    2. May be performed with enteroclysis (Nasogastric Tube instills contrast directly into duodenum)

XV. Differential Diagnosis (Abdominal Pain, distention, Nausea, cessation of flatus/stool)

  1. Adynamic Ileus (e.g. medication-induced such as Opioids)
  2. Ascites
  3. Bowel Pseudoobstruction (Ogilvie Syndrome)
    1. Acute Large Bowel dilation with risk of dysmotility (e.g. Diabetes Mellitus, Scleroderma)
  4. Bowel Perforation
  5. Ischemic bowel (superior mesenteric syndrome)
  6. Gastroenteritis
  7. Cholelithiasis
  8. Cholecystitis
  9. Pancreatitis
  10. Peptic Ulcer Disease
  11. Postoperative Paralytic Ileus
  12. Appendicitis
  13. Myocardial Infarction
  14. Pregnancy

XVI. Management: Conservative Therapy

  1. Fluid replacement
    1. Intravenous fluid replacement and maintenance
    2. Monitor fluid output with urine catheter
  2. Bowel decompression
    1. Nasogastric Tube
    2. Long intestinal tube (eg. Cantor) offers no advantage
  3. Surgical Consultation
  4. 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. Second-generation Cephalosporin
  5. 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] (or open in [QxMD Read])

XVII. 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 >48 hours despite treatment
    3. Acute management of surgically reversible cause (e.g. Strangulated Hernia, Volvulus)
    4. Signs of abdominal Sepsis, bowel ischemia or bowel perforation
      1. Peritonitis
      2. Clinical instability
      3. Unexplained Leukocytosis or Metabolic Acidosis

XVIII. 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

XIX. 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

XX. References

  1. Torrey in Marx (2002) Rosen's Emergency Med, p. 1283-7
  2. Townsend (2001) Sabiston Surgery, p. 883-8
  3. Turnage in Feldman (1998) Sleisenger GI, p. 1799-804
  4. Jackson (2011) Am Fam Physician 83(2): 159-5 [PubMed] (or open in [QxMD Read])
  5. Matsuoka (2002) Am J Surg 183:614-7 [PubMed] (or open in [QxMD Read])

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