• Clinical science

Bowel obstruction


Bowel obstruction is the interruption of the normal passage of bowel contents either due to a functional (e.g., ileus) or mechanical cause. Functional bowel obstruction, or paralytic ileus, is a disturbance of peristalsis of the gastrointestinal tract in the absence of mechanical obstruction. Postoperative ileus is the most common cause, which also include metabolic disturbances or drugs. Mechanical bowel obstruction is classified according to the location as either small bowel obstruction (SBO) or large bowel obstruction (LBO), and by the severity of obstruction as either partial or complete. The most common causes are postoperative bowel adhesions in SBO and tumors in LBO. Typical symptoms and signs are abdominal distention, pain, constipation, nausea, and vomiting, with partial obstructions leading to less severe symptoms. Severe cases are often accompanied by dehydration and electrolyte abnormalities. In patients with mechanical bowel obstruction, there may also be a history of partial obstructive symptoms such as worsening intermittent constipation. Bowel sounds on auscultation are typically absent in paralytic ileus, whereas mechanical obstructions present with a high-pitched tinkling sound. The diagnosis is confirmed primarily with x-ray and CT scan, although abdominal ultrasound has a growing role, particularly in emergency department settings. Findings include distended bowel loops, air-fluid levels in the bowel, and changes in peristalsis. Additional laboratory tests include a CBC and blood gas analysis for assessment of infection, electrolyte imbalances, and metabolic imbalances (e.g., alkalosis). Treatment is usually conservative, including fluid and electrolyte replacement, bowel rest, and nasogastric suction. Operative treatment is required for clinically deteriorating patients, those with signs of bowel ischemia/necrosis, or persistent obstructions. Surgery involves bowel decompression with resection of ischemic bowel and removal of detectable causes (e.g., adhesions).



Mechanical bowel obstruction

Paralytic ileus




Clinical features

  • Nausea, vomiting (may be projectile vomiting)
  • Dehydration (especially in SBO), possible fever
  • Constipation or obstipation with abdominal distention (tympanic abdomen)
    • SBO
      • Proximal: nausea and vomiting (worse with food intake, may be bilious) with early discontinuation of PO intake, late-onset obstipation
      • Distal: late-onset vomiting, possible fecal vomiting
      • Closed loop obstruction: lumen occluded at two points; can lead to ischemia requiring emergency surgery
    • LBO
      • Proximal: may mimic SBO
      • Distal: vomiting often absent; obstipation
  • Abdominal pain/discomfort: vague or periumbilical cramping, colicky pain (corresponding to peristalsis)
    • Persistent, focal pain usually implies bowel necrosis. Presence of back pain is usually not a favorable prognostic sign, as it often results from mesenteric ischemia.
    • Suddenly acute pain, followed by temporary pain relief (due to release of pressure) indicates bowel perforation.
  • Pathological auscultation
  • Possibly palpable mass on palpation (e.g., tumor); empty, tender rectum; possibly signs of peritonitis

Note: Patients with partial obstructions usually have milder symptoms (such as postprandial abdominal discomfort), a more gradual progression or chronic time course, and may still be able to pass gas and have bowel movements.



In the workup of suspected mechanical bowel obstruction, imaging offers quick confirmation of the diagnosis as well as detection of conditions requiring immediate surgery (e.g., perforation). Laboratory tests may further help to assess the severity of the condition (e.g., electrolyte imbalance due to vomiting).


  • First-line initial test: abdominal x-ray : complete survey includes erect and supine abdominal x-ray , as well as erect chest x-ray
    • SBO/LBO: dilated loops of small or large bowel (on upright x-ray), air-fluid levels proximal to the obstruction, distal bowel collapse, minimal or no gas in colon
    • LBO: air-fluid levels in the colon, bowel distention before obstruction, kidney bean appearance of bowel (e.g., volvulus)
    • Paralytic ileus: uniform distribution of gas in the small bowel, colon, and rectum
    • Bowel perforation: free air in the abdomen
  • CT abdomen with IV and oral contrast: indicated in stable patients who do not need immediate surgical intervention to confirm and further characterize the SBO or LBO
    • More sensitive than x-ray and allows determination of :
      • Location
      • Functional (ileus) vs. mechanical obstruction
      • Severity (partial vs. complete)
      • Presence of tumor
  • Abdominal ultrasound: used with increasing frequency in the ER to rule out SBO or diagnose abdominal pain of uncertain etiology. Also used in likely obstructed patients with a contraindication to CT (contrast allergy, pregnancy) or who are critically ill (easy bedside test)
  • Barium or gastrografin enema Useful to diagnose patients who have had prior intestinal surgery (ex. subtotal colectomy with anastomosis)
    • Differentiates between partial and complete obstruction
    • “Bird-beak” sign seen especially in LBO due to volvulus
    • “Apple core” sign seen in LBO due to colonic malignancy

When imaging with contrast (CT, enema) and a perforation is expected, use gastrografin contrast as it is water-soluble!

Laboratory tests


Differential diagnoses

The differential diagnoses listed here are not exhaustive.


Mechanical bowel obstruction


  • Treatment goals: resuscitation, intestinal decompression, restoration of normal peristaltic activity
  • Indications: partial obstruction, complete obstruction with no signs of ischemia/necrosis (leukocytosis, metabolic acidosis, persistent pain) or clinical deterioration (fever, tachycardia)
  • Measures
    • Nasogastric tube for intestinal decompression
    • Fluid resuscitation, electrolyte correction
    • Bowel rest (NPO) with diet advancement as tolerated while the patient regains bowel function
      • Patients with chronic or recurrent partial obstructions due to chronic diseases (e.g., strictures resulting from Crohn's or radiation enteritis) may be managed with oral fluid intake in an outpatient setting.
    • Antibiotics: not indicated for uncomplicated bowel obstructions; indicated in cases of suspected bowel perforation and as prophylaxis prior to surgery
  • Etiology-specific treatments:
    • Sigmoid volvulus: sigmoidoscopy is diagnostic and therapeutic
    • Fecal impaction: stool evacuation (manual disimpaction, distal softening/washout with enemas or suppositories, proximal softening/washout with oral solutions like polyethylene glycol or sodium phosphate)

Peristalsis-inducing medication is contraindicated in complete mechanical bowel obstruction!


  • Indications: complete obstruction with the above signs of ischemia/necrosis or clinical deterioration, persistent partial obstruction (>3-5 days), suspected intestinal strangulation
  • Surgical bowel decompression
    • Restoration of intestinal transit: operation depends on the findings (e.g., removal of adhesions, segmental bowel resection for intestinal ischemia, bowel resection and stenting for tumors, herniotomy)
      • If bowel resection is required, the intervention may be done in a single procedure with anastomosis or permanent ostomy creation, or in 2 or 3 stages with a temporary diverting ostomy.
    • Stoma construction if bowel passage cannot be restored

Bowel obstruction requires a swift workup to establish whether emergent surgery is necessary!

Paralytic ileus