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Bowel obstruction

Last updated: June 9, 2021

Summarytoggle arrow icon

Bowel obstruction refers to the interruption of the normal passage of bowel contents through the bowel, either due to a functional or mechanical obstruction. Functional bowel obstruction, or paralytic ileus, is a temporary disturbance of peristalsis in the absence of mechanical obstruction (see “Paralytic ileus”). Mechanical bowel obstruction is the interruption of normal passage through the bowel due to a structural barrier. Mechanical bowel obstruction can be classified as either a small bowel obstruction (SBO) or large bowel obstruction (LBO) according to its location, and, depending on the extent of the obstruction, as either partial or complete. Postoperative bowel adhesion is the most common cause of SBO and malignancy is the most common cause of LBO. Regardless of the cause, bowel obstruction typically manifests with nausea, vomiting, abdominal pain, abdominal distention, and constipation or obstipation. Bowel sounds are increased and high-pitched in the early phases of bowel obstruction and decreased or absent in the later stages. Bowel distention leads to third-space volume loss, resulting in dehydration and electrolyte abnormalities. The symptoms of bowel obstruction are typically less severe in partial bowel obstruction than in total bowel obstruction. A diagnosis of bowel obstruction should be confirmed on imaging (e.g., CT abdomen and pelvis). Typical findings include dilated bowel loops proximal to the obstruction, collapse of bowel loops distal to the obstruction, and multiple air-fluid levels. Laboratory tests are needed to assess severity (e.g., metabolic acidosis and elevated serum lactate suggest bowel ischemia) and identify acid-base and electrolyte imbalances. A trial of nonoperative management (NOM), which includes bowel rest and supportive care (such as IV fluids, analgesics, antiemetics, and, if needed, antibiotics) can be considered in patients with simple bowel obstruction with no evidence of complications. Surgery is indicated for complicated bowel obstruction, closed-loop bowel obstruction, or if there is no clinical improvement following NOM for simple bowel obstruction. The underlying cause of bowel obstruction should be sought for and managed appropriately.


Etiologic classification [2]

Mechanical bowel obstruction can be classified into the following etiologic categories.

Extrinsic bowel obstruction

Intrinsic bowel obstruction

Intramural bowel obstruction

Intraluminal bowel obstruction


Common etiologies

The causes of bowel obstruction vary according to the site of the obstruction and the age of the patient.

Etiology of bowel obstruction [1][3][4]
Most common causes
Other causes
Specific to infants and children

Cardinal signs

The cardinal signs of mechanical bowel obstruction are abdominal pain, vomiting, constipation, abdominal distention, and decreased bowel sounds, regardless of the underlying etiology. The severity and progression of clinical features differ according to the site and severity of the obstruction.

  • Complete bowel obstruction [5]
    • Total obstruction of the intestinal lumen, preventing the passage of air and fluid
    • Rapid progression of clinical features
    • Can be associated with obstipation (complete inability to pass stool or gas)
  • Partial bowel obstruction [6]
    • Partial obstruction of the intestinal lumen, allowing a small amount of air and fluid to pass through
    • Clinical features may be less severe than in complete bowel obstruction
    • Can be associated with the intermittent passage of flatus and overflow diarrhea

Partial bowel obstruction causes gradually progressive symptoms that are typically milder than those caused by complete obstruction. Obstipation is only present in complete bowel obstruction.

Clinical features associated with the site of bowel obstruction [1][3]
Clinical feature SBO LBO
Abdominal pain
  • Colicky, periumbilical
  • Colicky or constant
Vomiting and/or nausea
  • Early onset
  • Larger volume of vomitus than in LBO
  • Bilious
  • Late onset
  • Initially bilious
  • Progresses to fecal vomiting (presence of feces in vomitus)
Constipation or obstipation
Abdominal distention
  • Typically less severe than in LBO
  • Early and significant abdominal distention
Examination findings


Depending on the onset and progression of clinical features, mechanical bowel obstruction can be classified as simple or complicated and acute or subacute. [6][7]

Clinical course of acute and subacute bowel obstruction
Acute bowel obstruction Subacute bowel obstruction
Clinical course
  • Abrupt onset of typical symptoms
  • Fulminant course
  • Signs of systemic toxicity or hemodynamic instability may be present.
  • Can progress to complicated bowel obstruction
  • Clinical features are typically mild and progress slowly.
  • Signs of systemic toxicity or hemodynamic instability are rare.
  • Typically uncomplicated (simple bowel obstruction)
Typical causes

Bowel obstruction is an emergency and should be detected and managed early to minimize the risk of bowel perforation and strangulation, and the subsequent development of sepsis. The initial management of bowel obstruction is similar to that of undifferentiated acute abdomen.

References [1][3][10][11]

General principles

  • Imaging is required to:
    • Confirm mechanical bowel obstruction
    • Identify the site and assess the severity of the obstruction
    • Identify complications and the underlying etiology of the obstruction
    • Guide treatment planning
  • Laboratory studies provide supportive evidence to help assess the severity of the obstruction.

Do not wait for imaging before initiating definitive management if there is an emergent critical finding (e.g., peritonitis). [8]

Bowel obstruction requires a swift diagnostic workup to establish if emergency surgery is required.

Imaging [3][5][12][13]

Radiological signs of mechanical bowel obstruction common to all imaging modalities [2][13][14]
Pathology Findings
Dilatation of bowel loops proximal to the obstruction
  • 3-6-9 rule [14]
    • To help guide the identification of bowel dilatation on imaging
    • Transverse diameter greater than the following indicates dilation:
  • SBO: Dilated loops are predominantly central.
  • LBO : Dilated loops are predominantly peripheral.
Air-fluid level
Intraluminal air beyond the site of obstruction
Evidence of complications
Evidence of the underlying etiology

Abdominal series x-ray

  • Indication: most appropriate initial test in hemodynamically unstable patients or in resource-poor centers [3][14]
  • Findings
  • Important considerations : X-rays have a number of limitations. [13]
    • Variable sensitivity (50–65%) [7][8][14]
    • Cannot reliably identify the site of obstruction, underlying etiology, or extent of complications
    • Do not influence the management of acute bowel obstruction to the same extent as CT abdomen

CT abdomen and pelvis (gold standard) [6][8][9][11][17]

Closed-loop bowel obstructions are associated with an increased risk of bowel strangulation and perforation.

MRI abdomen and pelvis (with and/or without IV contrast) [13]

Abdominal ultrasound [8][16][19][20]

  • Indication: Consider in hemodynamically unstable patients with contraindications to radiation exposure (e.g., pregnant patients) if an ultrasonographer is available. [3]
  • Findings [19][21]
    • Multiple fluid-filled dilated bowel loops > 2.5 cm in diameter adjacent to collapsed bowel loops (most specific finding).
    • Altered peristalsis [19][21]
      • Can be increased (early), or decreased or absent (late)
      • Pendular peristalsis: dysfunctional so-called “to-and-fro” peristalsis
    • Prominent plicae circulares of dilated small bowel loops (sometimes referred to as the keyboard sign) [21]

Barium enema or water-soluble contrast enema [8][14][22]

Contrast enema helps differentiate complete bowel obstruction from partial bowel obstruction.

Barium enema is contraindicated if bowel perforation is suspected (water-soluble contrast enema can be used instead).

Water-soluble contrast challenge (WSCc) [8][11]

  • Indication: SBO, to differentiate partial SBO from complete SBO [7][13]
  • Procedure: A water-soluble contrast medium is administered orally or via an enteric tube, followed by abdominal x-ray 8 and 24 hours after ingestion. [7][11]
  • Findings [13]
    • Normal WSCc: contrast reaches the colon within 24 hours of administration
    • Intraluminal and intramural causes of bowel obstruction may be identified (see “Etiology”). [9]
  • Additional considerations

Laboratory studies [6][11][12][23]

Leukocytosis, metabolic acidosis, and elevated serum lactate in a patient with suspected bowel obstruction are suggestive of bowel ischemia.

Mechanical bowel obstruction vs. paralytic ileus
Mechanical bowel obstruction [1][3][24][25] Paralytic ileus
  • Interruption in the normal passage due to a structural barrier
  • Temporary impairment of peristalsis in the absence of a mechanical obstruction
  • Recent abdominal surgery
  • Atherosclerotic disease
  • Abdominal infections or inflammatory conditions
  • Certain medications (opioids, anticholinergics, antiparkinsonian agents)
Clinical features
  • Diffuse, continuous abdominal pain
  • Vomiting
  • Obstipation or constipation
  • Marked abdominal distention
  • Tympany on percussion
  • Absent bowel sounds
Findings on imaging
  • Diffusely dilated small and large bowel loops (i.e., uniform distribution of gas in the small bowel, colon, and rectum)
  • Air within rectum
  • No evidence of mechanical obstruction
  • Absent peristalsis


The differential diagnoses listed here are not exhaustive.

  • Initial management and supportive care: See “Management” section above.
  • Definitive management: depends on the severity and etiology of the obstruction and clinical presentation of the patient
    • Interventional management
      • Surgery: Transfer the patient to the operating room or admit to a surgical ward depending on the urgency of surgical intervention.
      • Endoscopic intervention: e.g., for the removal or fragmentation of foreign objects that are within reach of an endoscope
      • Stool evacuation
    • Nonoperative management: simple bowel obstruction with no evidence of complications (e.g., partial bowel obstruction or postoperative ileus)
    • Identify and treat the underlying cause (see “Etiology”).

Surgery [3][5][9][12][27]

Endoscopic intervention [6][29][30]

Endoscopic interventions can be considered for bowel obstruction with no signs of strangulation or perforation. Rigid or flexible sigmoidoscopy, upper GI endoscopy, or colonoscopy under procedural sedation can be used for endoscopic investigation for the following indications.

Stool evacuation [31]

Indications [5][6][9][12]

  • Early postoperative bowel obstruction (i.e., within 6 weeks of abdominal surgery) [11]
  • Partial bowel obstruction with no evidence of complications
  • Consider in patients with complete SBO and no evidence of complications. [5][9][12]

Contraindications [5]


Initial measures

Peristalsis-inducing medications (i.e., prokinetic agents such as metoclopramide) are contraindicated in complete mechanical bowel obstruction.

Prophylactic antibiotic therapy is not routinely indicated for simple bowel obstruction that is being managed nonoperatively. [36]

Serial monitoring

Duration of nonoperative management trial [5][12][28][37]

  • No longer than 72 hours
  • Some authors suggest trialing NOM for a maximum of 5 days.
  • Continuing nonoperative management for > 72 hours does not decrease the need for surgery but does increase surgical morbidity. [3]

Assessment of response and further management

Assessment of response to NOM and further management


Clinical features Supportive evidence Further management
Clinical improvement
  • Symptomatic improvement
  • Passage of flatus and feces
  • No fever
  • Soft abdomen, return of bowel sounds
  • Initiate dietary advancement gradually (i.e., start with clear fluids and advance as tolerated).
Deterioration [12]
  • Exploratory surgery [12]
Lack of improvement (no evidence of complications)
  • Status quo 48–72 hours after initiating nonoperative management
  • Consider therapeutic WSCc (especially in patients < 65 years of age without a previous abdominal surgery). [5][9]

A change in the character of pain (colicky pain becoming continuous), rebound tenderness on examination, and/or signs of sepsis in a patient with bowel obstruction indicate the onset of complications and necessitate emergency surgical intervention.

We list the most important complications. The selection is not exhaustive.


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