Skip to content
Download PDF

Acute Intestinal Obstruction

Chapter 341 | Part 10: Disorders of the Gastrointestinal System · Part 10 – Gastrointestinal Disorders · Chapter 341

Key Clinical Points

  1. Cardinal signs of acute obstruction: colicky abdominal pain, abdominal distention, emesis, and obstipation.
  2. Closed-loop obstruction (e.g., volvulus, hernia) carries a significantly higher risk of strangulation and ischemia.
  3. CT sensitivity for high-grade bowel obstruction is ~95% with 96% specificity; however, accuracy for closed-loop obstruction is lower (~60%).
  4. Barium studies are strictly contraindicated in patients with suspected complete or high-grade obstruction due to risk of barium concretions.
  5. Cecal diameter >10–12 cm in distal colonic obstruction indicates a high risk of ischemic necrosis and perforation.
  6. Neostigmine is the primary treatment for Ogilvie's syndrome but must only be used after mechanical obstruction is excluded.
  7. Postoperative adhesions are the leading cause of small-bowel obstruction (>50% of cases).
  8. Ileus is distinguished from mechanical obstruction by the absence of colicky pain and the potential passage of flatus/stool.
  9. Late CT findings such as mesenteric venous gas, pneumatosis intestinalis, and pneumoperitoneum indicate bowel necrosis.
  10. Neostigmine is contraindicated in any patient with suspected mechanical obstruction.

DEFINITION & CLASSIFICATION

• General Definition: Acute intestinal obstruction occurs either mechanically from blockage or from intestinal dysmotility (functional). • Mechanical Obstruction: Caused by blockage from extrinsic, intrinsic, or intraluminal disease. • Functional Obstruction: Also known as ileus or pseudo-obstruction; present when dysmotility prevents movement without a mechanical blockage. • Severity Classifications: ◦ Simple obstruction: No vascular insufficiency or ischemia. ◦ Strangulated obstruction: Vascular insufficiency and intestinal ischemia are evident.

Classification of Obstruction

• Mechanical: ◦ Extrinsic: External to the bowel wall. ◦ Intrinsic: Within the bowel wall. ◦ Intraluminal: Inside the lumen.

EPIDEMIOLOGY

• Hospitalization Rate: Accounts for ~1–3% of all hospitalizations. • Surgical Volume: Represents 1/4 of all urgent or emergent general surgery admissions. • Small Bowel Involvement: Approximately 80% of cases involve the small bowel. • Ischemia Prevalence: About one-third of patients show evidence of significant ischemia. • Mortality (Strangulation): ◦ Surgery within 24–30 h of symptoms → ~8% mortality. ◦ Delay beyond 24–30 h → Mortality triples. • Trends: While incidence/prevalence have increased over the last two decades, morbidity and mortality appear to be decreasing.

ETIOLOGY & PATHOPHYSIOLOGY

• Etiologic Categories: ◦ Extrinsic: Most common cause of small intestine obstruction (e.g., adhesions, hernias). ◦ Intrinsic: Usually congenital, inflammatory, neoplastic, or traumatic. ◦ Intraluminal: Bezoars, feces, foreign bodies, gallstones, and enteroliths. ◦ Functional: Dysmotility without blockage.

Pathophysiologic Cascade

• Initial Response: Increased intestinal contractility proximally and distally to obstruction. ◦ Progression: Peristalsis slows → proximal dilation with gas/fluid accumulation → increased intraluminal pressure. ◦ Vascular Impact: Pressure exceeds venous pressure → impaired venous/lymphatic drainage → edema → hypoxemia. ◦ Tissue Damage: Epithelial necrosis can occur within 12 h of obstruction. ◦ Critical Failure: Arterial supply compromised → full-thickness ischemia, necrosis, and perforation. ◦ Bacterial Growth: Stasis increases counts of E. coli, S. faecalis, and Klebsiella. ◦ Systemic Impact: Inflammation leads to reactive oxygen species and neutrophil/macrophage activation; loss of absorption causes dehydration; emesis leads to loss of K^+, H^+, and Cl^-. ◦ High Pressure Effects: Intraperitoneal fluid → increased intraabdominal pressure → elevated diaphragm → inhibited respiration → impaired systemic venous return. • Closed-loop Obstruction: ◦ Definition: Both proximal and distal openings of a segment are occluded (e.g., volvulus, hernia). ◦ Risk: Most common precursor for strangulation; higher risk of rapid ischemia and systemic inflammation.

Incidence by Cause

• Table 341-1 & 341-2 Summary: ◦ Postoperative adhesions: >50% overall. ◦ Neoplasms: ~20%. ◦ Hernias (ventral/internal): ~10% (higher risk of strangulation). ◦ Inflammatory bowel disease/other inflammation: ~5% (may resolve if inflammation subsides). ◦ Intussusception, volvulus, others: <15%.

CLINICAL FEATURES

• Cardinal Signs: Colicky abdominal pain, abdominal distention, emesis, and obstipation. ◦ Distal Obstruction → More fluid accumulation → greater distention, more discomfort, delayed emesis (feculent if bacterial overgrowth present). ◦ Proximal Obstruction → Less distention, more pronounced vomiting. • Systemic Signs: Patients may be critically ill; often oliguric, hypotensive, and tachycardic due to volume depletion. Fever is a warning sign for strangulation or systemic inflammation. • Physical Examination: ◦ Bowel Sounds: ◦ Early Small-bowel Obstruction → high-pitched, 'musical' tinkling sounds; peristaltic 'rushes' (borborygmi). ◦ Late Stage/Ileus → absent or hypoactive. ◦ Masses: Tender abdominal/groin mass → suggests incarcerated hernia. ◦ Peritoneal Signs: Severe pain with localization or signs of irritation → suspicious for strangulation/necrosis. ◦ Distinction via Flatus: Ongoing, regular discharge of stool/flatus may indicate partial obstruction or ileus rather than complete mechanical obstruction.

DIFFERENTIAL DIAGNOSIS

• Ileus vs. Mechanical Obstruction: ◦ Ileus (Functional): No mechanical blockage; typically lacks colicky pain; may pass flatus/stool. ◦ Obstruction (Mechanical): Physical blockage exists; complete obstruction leads to obstipation. • Causes of Ileus (Table 341-3): ◦ Procedural: Intraabdominal procedures, lumbar spinal injuries/surgery. ◦ Metabolic: Hypokalemia, hypomagnesemia, hyponatremia, uremia, severe hyperglycemia. ◦ Drugs: Opiates, antihistamines, psychotropics (haloperodil, tricyclic antidepressants), anticholinergics. ◦ Other: Ischemia, inflammation/hemorrhage, lower lobe pneumonia, systemic sepsis, hyperparathyroidism, Ogilvie's syndrome, myopathies/neuropathies, collagen vascular diseases (lupus, scleroderma).

DIAGNOSTIC APPROACH

  1. Laboratory Assessment: • CBC and serum electrolytes/creatinine. • Findings: Mild hemoconcentration, elevated WBC (simple obstruction); Hypokalemia, hypochloremia, metabolic alkalosis (emesis/dehydration). • Malignancy Indicators: Guaiac-positive stools, iron-deficiency anemia. • Ischemia/Sepsis Indicators: High WBC with immature forms, metabolic acidosis. • Specific Markers: Serum d-lactate, creatine kinase BB isoenzymes, intestinal fatty acid binding protein (suggestive of strangulation).
  2. Imaging Studies: • Abdominal Radiography: ◦ Rapid assessment; identifies 'staircasing' (dilated loops >2.5 cm) and air-fluid levels. ◦ Distinguishes obstruction from ileus if air-fluid levels are present without significant colonic distension. ◦ Volvulus → 'coffee bean' shaped dilated shadow. • Computed Tomography (CT): ◦ High sensitivity (~95%) and specificity (96%) for high-grade obstruction. ◦ Lower accuracy for closed-loop obstruction (60%). ◦ Findings: Altered bowel wall enhancement (early ischemia), mesenteric venous gas, pneumoperitoneum, pneumatosis intestinalis (late/necrosis). ◦ Contrast Study: Water-soluble contrast in cecum within 4–24 h → high sensitivity/specificity (~95%) for improvement. ◦ Volvulus signs: 'bird's beak', 'c-loop', or 'whorl' deformity. • Ultrasound: Used primarily when x-ray is contraindicated (e.g., pregnancy). • Specialized Procedures: ◦ CT scan after water-soluble contrast enema → distinguish ileus/pseudo-obstruction from distal large-bowel obstruction. ◦ Contrast enemas or colonoscopies → required to identify causes of acute colonic obstruction.

MANAGEMENT & TREATMENT

  1. Initial Stabilization: • Fluid resuscitation and electrolyte repletion (address hypokalemia, etc.). • Nasogastric tube suction → decompresses stomach, reduces distention, improves comfort, reduces aspiration risk. • Foley catheter → monitor urine output. • Monitoring: Central venous pressures for patients with cardiac disease.
  2. Antibiotics: • Controversial; prophylactic use may be warranted if surgery is anticipated.
  3. Surgical Intervention: • Indicated for complete bowel obstruction or signs of strangulation/ischemia.
  4. Specific Management: • Ogilvie's Syndrome (Colonic Pseudo-obstruction): ◦ Treatment: Neostigmine. ◦ Requirement: Must have cardiac monitoring and atropine available; must exclude mechanical obstruction first. • Stenting: Consider for high-grade obstruction with unresectable stage IV malignancy or for pre-operative bowel preparation.

Barium Contraindications

• Rule: Barium studies are contraindicated in patients with evidence of complete or high-guard bowel obstruction. ◦ Reason: Risk of barium concretions and potential for required surgery; also renders cross-sectional imaging/angiography uninterpretable.

COMPLICATIONS & PROGNOSIS

• Ischemic Necrosis: Identified within 12 hours of obstruction. ◦ Risk Factors: Cecal diameter >10–12 cm in distal colonic obstruction → high risk of necrosis/perforation. ◦ Late CT Findings: Mesenteric venous gas, pneumatosis intestinalis, and pneumoperitoneum → indicate bowel necrosis. • Sepsis: Resulting from bacterial translocation (E. coli, S. faecalis, Klebsiella) into bloodstream or other sites. • Systemic Inflammatory Response: Triggered by severe hemodynamic compromise or tissue ischemia.

SPECIAL POPULATIONS

• Pregnancy: Ultrasound is the preferred modality when x-ray is contraindicated. ◦ Note: Risk of obstetric complications from large-bowel obstruction (e.g., if caused by malignancy or volvulus).

KEY PEARLS & HIGH-YIELD POINTS

• Clinical Trap: Do not use Neostigmine until mechanical obstruction is definitively excluded. ◦ Rule: Neostigmine → only for pseudo-obstruction (Ogilvie's). ◦ Contraindication: Mechanical obstruction. • Diagnostic Clue: 'Staircasing' on X-ray and dilated loops >2.5 cm are hallmarks of small-bowel obstruction. ◦ Distinction: If air-fluid levels exist without colonic distension, it is more likely to be mechanical obstruction than ileus. ◦ Volvulus: Look for 'coffee bean' (X-ray) or 'bird's beak' (CT). • Critical Threshold: Cecal diameter >10–12 cm → high risk of ischemia/perforation. ◦ Action: Requires urgent surgical evaluation.

Reference Tables

TABLE 341-1 Most Common Causes of Acute Intestinal Obstruction Extrinsic Disease Adhesions (especially due to previous…

Harrison's 22e, p.2590

  • Extrinsic Disease
  • Adhesions (especially due to previous abdominal surgery), internal or external
    hernias, neoplasms (including carcinomatosis and extraintestinal malignancies,
    mostly commonly ovarian), endometriosis or intraperitoneal abscesses, and
    idiopathic sclerosis
  • Intrinsic Disease
  • Congenital (e.g., malrotation, atresia, stenosis, intestinal duplication, cyst
    formation, and congenital bands—the latter rarely in adults)
  • Inflammation (e.g., inflammatory bowel disease, especially Crohn’s disease,
    but also diverticulitis, radiation, tuberculosis, lymphogranuloma venereum, and
    schistosomiasis)
  • Neoplasia (note: primary small-bowel cancer is rare; obstructive colon cancer
    may mimic small-bowel obstruction if the ileocecal valve is incompetent)
  • Traumatic (e.g., hematoma formation, anastomotic strictures)
  • Other, including intussusception (where the lead point is typically a polyp or
    tumor in adults), volvulus, obstruction of duodenum by superior mesenteric
    artery, radiation or ischemic injury, and aganglionosis, which is Hirschsprung’s
    disease
  • Intraluminal Abnormalities
  • Bezoars, feces, foreign bodies including inspissated barium, gallstones (entering
    the lumen via a cholecystoenteric fistula), enteroliths

TABLE 341-3 Most Common Causes of Ileus (Functional or Pseudo-Obstruction of the Intestine)

  • Intraabdominal procedures, lumbar spinal injuries, or surgical procedures on the
    lumbar spine and pelvis
  • Metabolic or electrolyte abnormalities, especially hypokalemia and
    hypomagnesemia, but also hyponatremia, uremia, and severe hyperglycemia
  • Drugs such as opiates, antihistamines, and some psychotropic (e.g., haloperidol,
    tricyclic antidepressants) and anticholinergic agents
  • Intestinal ischemia
  • Intraabdominal or retroperitoneal inflammation or hemorrhage
  • Lower lobe pneumonias
  • Intraoperative radiation (likely due to smooth muscle damage)
  • Systemic sepsis
  • Hyperparathyroidism
  • Pseudo-obstruction (Ogilvie’s syndrome)
  • Ileus secondary to hereditary or acquired visceral myopathies and neuropathies
    that disrupt myocellular neural coordination
  • Some collagen vascular diseases such as lupus erythematosus or scleroderma

TABLE 341-2 Acute Small-Intestinal and Colonic Obstruction Incidences CAUSE Postoperative adhesions Neoplasms Hernias…

Harrison's 22e, p.2590

CAUSE INCIDENCE
Postoperative adhesions >50% overall
Hernias (especially ventral or internal types, where the risk of
strangulation is increased)		 ~10%
Intussusception, volvulus, other miscellaneous diseases <15%