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.
- Bowel obstruction: the interruption of normal passage through the bowel
- Mechanical bowel obstruction: the interruption of normal passage through the bowel due to a structural barrier (e.g., a tumor, adhesions)
- Paralytic ileus (functional bowel obstruction): temporary functional impairment of peristalsis in the absence of a mechanical obstruction (see “Mechanical bowel obstruction vs. paralytic ileus”)
- According to the site of obstruction, mechanical bowel obstruction can be classified as:
Etiologic classification 
Mechanical bowel obstruction can be classified into the following etiologic categories.
Extrinsic bowel obstruction
Intrinsic bowel obstruction
Intramural bowel obstruction
Intraluminal bowel obstruction
The causes of bowel obstruction vary according to the site of the obstruction and the age of the patient.
|Etiology of bowel obstruction |
|Most common causes|| |
|Other causes|| |
|Specific to infants and children|
Bowel obstruction → stasis of luminal contents and gas proximal to the obstruction → ↑ intraluminal pressure, which leads to the following: 
- Gaseous abdominal distention → sequestration of fluids within the distended bowel loops (dehydration and hypovolemia) →
- Vomiting → loss of fluid and Na+, K+, H+, and Cl- → hypokalemia, metabolic alkalosis, and hypovolemia
Compression of intestinal veins and lymphatics → bowel wall edema → compression of intestinal arterioles and capillaries → bowel ischemia, which leads to:
- ↑ Bowel wall permeability → translocation of intestinal microbes to the peritoneal cavity → sepsis
- Necrosis and perforation of the bowel wall → peritonitis
- Anaerobic metabolism and lysis of ischemic cells → accumulation of lactic acid and release of intracellular K+ → metabolic acidosis and hyperkalemia
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 
- 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 
|Clinical features associated with the site of bowel obstruction |
|Abdominal pain|| || |
|Vomiting and/or nausea|| |
|Constipation or obstipation|
|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. 
- Simple bowel obstruction: bowel obstruction with no evidence of complications (i.e., no features of bowel ischemia, bowel perforation, or red flags for complicated bowel obstruction) 
- Complicated bowel obstruction: bowel obstruction associated with strangulation, ischemic necrosis, or perforation 
- Red flags for complicated bowel obstruction 
|Clinical course of acute and subacute bowel obstruction|
|Acute bowel obstruction||Subacute 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.
- ABCDE approach: Evaluate vital signs, volume status, and the need for invasive monitoring.
- Urgent consults: general surgery, gastroenterology (also contact an intensivist as needed)
- Initial management
- Administer supportive care as needed.
- Obtain imaging: See “Diagnostics.”
- Disposition: Admit to the surgical service or transfer to the operating room (based on surgery consult). 
- Definitive management: See “Treatment.”
Admit patients with a bowel obstruction to a surgical service, even if conservative treatment is planned. Patients managed on a surgical service have better overall outcomes and lower health care expenditures than those managed on a medical service. 
- 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). 
Bowel obstruction requires a swift diagnostic workup to establish if emergency surgery is required.
Initial imaging modality: depends on the type of bowel obstruction and hemodynamic stability of the patient
- Acute bowel obstruction 
- Subacute bowel obstruction
- Findings: Radiological signs common to all imaging modalities are detailed in the table.
|Radiological signs of mechanical bowel obstruction common to all imaging modalities |
|Dilatation of bowel loops proximal to the obstruction|
|Intraluminal air beyond the site of obstruction|
|Evidence of complications|| |
|Evidence of the underlying etiology|
- Indication: most appropriate initial test in hemodynamically unstable patients or in resource-poor centers 
- Proximal bowel dilatation
- Minimal or no intraluminal air distal to the obstruction
- Stepladder sign (best seen on an upright view): multiple air-fluid levels and stacked dilated loops of small bowel
- Chest x-ray : Air under the diaphragm is an indicator of bowel perforation.
- See also “Radiological signs of mechanical bowel obstruction.”
- Important considerations : X-rays have a number of limitations. 
To detect pneumoperitoneum on a chest x-ray, patients must be sitting upright for at least 10 minutes to allow free air to move upward and collect under the diaphragm. Patients with severe abdominal pain often require preemptive analgesia to tolerate the procedure! 
CT abdomen and pelvis (gold standard) 
- With IV contrast: most appropriate initial test in hemodynamically stable patients with acute bowel obstruction 
- With water-soluble oral contrast: Consider in patients with subacute bowel obstruction and no evidence of complications. 
- Without contrast: for patients with a contrast allergy
- Similar to those seen on abdominal x-ray; see “Radiological signs of mechanical bowel obstruction.”
- Transition point: sudden narrowing of the bowel lumen at the site of obstruction
- Closed-loop bowel obstruction: a type of mechanical bowel obstruction in which the proximal and distal ends of the obstructed loop are closed
- Important consideration: In acute bowel obstruction, a CT scan is more accurate than an x-ray in the identification of the site of obstruction, complications, and underlying etiology, and, therefore, influences patient management to a greater extent. 
Closed-loop bowel obstructions are associated with an increased risk of bowel strangulation and perforation.
Abdominal ultrasound 
or can be performed.
- Indication: Hemodynamically unstable patients (may be preferred over abdominal x-ray) 
- Multiple fluid-filled dilated bowel loops > 2.5 cm in diameter adjacent to collapsed bowel loops (most specific finding) Sensitivity of 91% and specificity of 84% 
- Thickened bowel wall
- Prominent plicae circulares of dilated small bowel loops (sometimes referred to as the keyboard sign) 
- Altered peristalsis
- Increased (early finding) or decreased/absent (late finding)
- Pendular peristalsis: dysfunctional so-called “to-and-fro” peristalsis
- Intraperitoneal fluid accumulation may be present.
- Indication: hemodynamically stable patients with contraindications to radiation exposure
- Findings: similar to those identified with a CT scan; see “Radiological signs of mechanical bowel obstruction” for details.
Barium enema or water-soluble contrast enema 
- Indication: suspected distal LBO if CT is unavailable 
- Findings 
Water-soluble contrast challenge (WSCc) 
- Indication: SBO, to differentiate partial SBO from complete SBO 
- 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. 
- Findings 
- WSCc is also used to evaluate response to nonoperative management.
- See “Nonoperative management of mechanical bowel obstruction.” 
Laboratory studies 
- Routine studies: CBC, BMP, serum lactate, and CRP
- Additional studies: See “Approach to acute abdomen.”
- In patients who are dehydrated
- In patients with recurrent vomiting
Suggestive of complicated bowel obstruction ; 
- Hyperkalemia , elevated serum lactate, and metabolic acidosis: suggestive of bowel ischemia ; ; ; 
- Leukocytosis (> 16,000 cells/mcL) 
- Elevated nonspecific inflammatory markers (↑ CRP and serum creatine kinase) 
- ↑ Amylase 
- Altered coagulation panel (e.g., elevated INR in sepsis)
- Differential diagnoses of mechanical bowel obstruction
- Differential diagnoses of SBO
- Differential diagnoses of LBO
- See also: “.”
|Mechanical bowel obstruction vs. paralytic ileus|
|Definition|| || |
|Findings on imaging|
The differential diagnoses listed here are not exhaustive.
- See “Initial management of bowel obstruction” for first steps and supportive care.
- 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”).
- Interventional management
- Complicated bowel obstruction (i.e., signs of ischemia, perforation, or clinical deterioration)
- Closed-loop bowel obstruction
- Suspected bowel obstruction in patients presenting with hemodynamic instability refractory to initial fluid resuscitation
- Failure of nonoperative management (i.e., no improvement after 3 days of NOM; clinical deterioration/development of complications during NOM) 
- Underlying etiology necessitates surgical intervention (e.g., surgery for inguinal hernia; enterolithotomy fo gall stone ileus)
- Procedure: exploratory laparotomy
Endoscopic intervention 
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.
- Sigmoid volvulus: Attempt .
- Intraluminal bowel obstruction that is within reach of an endoscope: fragmentation or removal
- Inoperable malignant bowel obstruction: Consider placement of stents and decompression tubes.
Stool evacuation 
- Indication: caused by
- The specific procedure is chosen based on the site of fecal impaction, only after bowel perforation has been definitively ruled out.
- See “ and dosages. ” for details
- Important consideration: Identify and manage the underlying cause of constipation that led to fecal impaction.
- Early postoperative bowel obstruction (i.e., within 6 weeks of abdominal surgery) 
- Partial bowel obstruction with no evidence of complications
- Consider in patients with complete SBO and no evidence of complications. 
- Complicated bowel obstruction (e.g, peritoneal signs, signs of strangulation)
- Refractory metabolic acidosis
- Significant leukocytosis (> 18,000/mm3)
- Significant cecal dilation
- Bowel rest (NPO)
- Supportive care
Nasogastric tube insertion (bowel decompression)
- Indications: not routinely required but should be considered in the following situations 
- Procedure: See “Nasogastric tube placement.”
- Symptom severity
- Bowel movements
- Serial abdominal examination every 4–8 hours 
- Fluid balance (input and output chart) including nasogastric tube output 
Duration of nonoperative management trial 
- 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. 
Assessment of response and further management
|Assessment of response to NOM and further management|
|Clinical features||Supportive evidence||Further management|
|Clinical improvement|| || |
|Deterioration || |
|Lack of improvement (no evidence of complications)|| |
- Arrange urgent general surgery and gastroenterology consults.
- IV fluid resuscitation
- Consider nasogastric tube insertion with continuous suction
- Supplemental oxygen as needed
- Parenteral analgesics
- Parenteral antiemetics
- Consider complicated bowel obstruction. in
- Obtain imaging and laboratory studies.
- Transfer to the operating room or admit to the surgical service.
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.