Bowel obstruction

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:
  • Large bowel obstruction (LBO): obstruction at the level of the cecum, colon, or rectum
  • Small bowel obstruction (SBO): obstruction at the level of the duodenum, jejunum, or ileum
  • Gastric outlet obstruction (GOO): obstruction at the level of the pyloric channel or duodenum

Reference:^[1]

Etiologic classification ^[2]

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

Common etiologies

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

• Bowel obstruction → stasis of luminal contents and gas proximal to the obstruction → ↑ intraluminal pressure, which leads to the following: ^[1][3]
  • Gaseous abdominal distention → sequestration of fluids within the distended bowel loops (third spacing) → 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

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.

Progression

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]

• 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) ^[1][2]
• Complicated bowel obstruction: bowel obstruction associated with strangulation, ischemic necrosis, or perforation ^[1][2]
• Red flags for complicated bowel obstruction ^[1][2]
  • Pain out of proportion
  • Peritoneal signs
  • Signs of systemic toxicity, e.g., SIRS
  • Hemodynamic instability
  • Laboratory abnormalities: e.g., significant leukocytosis, metabolic acidosis, ↑ lactate

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
  • NPO status
  • Obtain IV access with two large-bore peripheral IVs; simultaneously draw blood for urgent laboratory studies.
  • IV fluid resuscitation
  • Electrolyte repletion as needed
  • Insert a nasogastric tube in patients with recurrent vomiting and/or significant abdominal distention.
  • Supplemental oxygen as needed
• Administer supportive care as needed.
  • Parenteral analgesics
  • Parenteral antiemetics
  • Empiric antibiotics for intraabdominal infections (not routinely recommended for simple bowel obstruction) ^[8][9]
    • If fever and/or leukocytosis are present ^[3]
    • For strangulated or perforated bowel obstruction
    • As prophylaxis for operative malignant bowel obstruction ^[8]
• Obtain imaging: See “Diagnostics.”
• Disposition: Admit to the surgical service or transfer to the operating room (based on surgery consult). ^[3][6][10]
• 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. ^[3][6][10]

References ^{[1][3][11][12]}

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][13][14]}

• Initial imaging modality: depends on the type of bowel obstruction and hemodynamic stability of the patient
  • Acute bowel obstruction ^[3][14]
    • Stable patients: CT abdomen and pelvis with IV contrast
    • Unstable patients: Consider abdominal series x-ray or abdominal ultrasound first, along with urgent surgical consultation.
  • Subacute bowel obstruction
    • Preferred: CT abdomen and pelvis with IV contrast
    • Alternatives: MRI with and/or without IV contrast, water-soluble contrast challenge, and specialized dynamic contrast studies
• Findings: Radiological signs common to all imaging modalities are detailed in the table.

Abdominal series x-ray

• Indication: most appropriate initial test in hemodynamically unstable patients or in resource-poor centers ^[3][15]
• Findings
  • 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. ^[14]
  • Variable sensitivity (50–65%) ^[7][8][15]
  • 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

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! ^[17]

CT abdomen and pelvis (gold standard) ^{[6][8][9][12][18]}

• Indications
  • With IV contrast: most appropriate initial test in hemodynamically stable patients with acute bowel obstruction ^[7][19]
  • With water-soluble oral contrast: Consider in patients with subacute bowel obstruction and no evidence of complications. ^[14]
  • Without contrast: for patients with a contrast allergy
• Findings
  • 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
    • Single site of obstruction: e.g., in volvulus or incarcerated hernia
    • Multiple sites of obstruction: e.g., obstructing colorectal cancer with a competent ileocecal valve
    • Progresses rapidly and is associated with an increased risk of strangulation
• 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. ^[14]

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

Abdominal ultrasound ^{[8][10][20][21]}

POCUS or formal ultrasound can be performed.

• Indication: Hemodynamically unstable patients (may be preferred over abdominal x-ray) ^[20][22][23]
• Findings ^[20][24][25]
  • 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% ^[23]
  • Thickened bowel wall
  • Prominent plicae circulares of dilated small bowel loops (sometimes referred to as the keyboard sign) ^[24]
  • 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.

MRI abdomen and pelvis (with and/or without IV contrast) ^[14]

• 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 ^[8][15][26]

• Indication: suspected distal LBO if CT is unavailable ^[8]
• Findings ^[15]
  • Tapering of the bowel lumen at the site of obstruction
    • Complete bowel obstruction: contrast not visible beyond the obstruction
    • Partial bowel obstruction: small amount of contrast visible beyond the obstruction
  • Bird beak sign: in volvulus
  • Apple core sign: in colonic malignancy ^[26]

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][12]

• Indication: SBO, to differentiate partial SBO from complete SBO ^[7][14]
• 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][12]
• Findings ^[14]
  • Normal WSCc: contrast reaches the colon within 24 hours of administration
    • Indicates partial bowel obstruction
    • The patient may be a candidate for nonoperative management.
  • Intraluminal and intramural causes of bowel obstruction may be identified (see “Etiology”). ^[9]
• Additional considerations
  • WSCc is also used to evaluate response to nonoperative management.
  • See “Nonoperative management of mechanical bowel obstruction.” ^[9]

Laboratory studies ^{[6][12][13][27]}

• Routine studies: CBC, BMP, serum lactate, and CRP
• Additional studies: See “Approach to acute abdomen.”
• Supportive findings
  • In patients who are dehydrated
    • ↑ BUN and creatinine (prerenal acute kidney injury)
    • ↑ Hematocrit (due to hemoconcentration)
  • In patients with recurrent vomiting
    • Hypochloremic hypokalemic metabolic alkalosis
    • Hyponatremia
  • Suggestive of complicated bowel obstruction ; ^[6][13][27]
    • Hyperkalemia , elevated serum lactate, and metabolic acidosis: suggestive of bowel ischemia ; ; ; ^[5][7]
    • Leukocytosis (> 16,000 cells/mcL) ^[12]
    • Elevated nonspecific inflammatory markers (↑ CRP and serum creatine kinase) ^[6]
    • ↑ Amylase ^[1][5][7]
    • Altered coagulation panel (e.g., elevated INR in sepsis)

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

• Differential diagnoses of mechanical bowel obstruction
  • Paralytic ileus (see “Mechanical bowel obstruction vs. paralytic ileus”)
  • Bowel perforation (secondary peritonitis)
  • Mesenteric ischemia
  • Inflammatory bowel disease
  • Ovarian torsion
• Differential diagnoses of SBO
  • Acute appendicitis
  • Acute pancreatitis
  • Pelvic inflammatory disease
• Differential diagnoses of LBO
  • Diverticulitis
  • Toxic megacolon
  • Chronic megacolon
  • Acute colonic pseudo-obstruction (Ogilvie syndrome)
• See also: “Differential diagnoses of acute abdomen.”

References:^{[3][28][29][30]}

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”).

Surgery ^{[3][5][9][13][31]}

• Indications
  • 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) ^[9][13][32]
  • Underlying etiology necessitates surgical intervention (e.g., surgery for inguinal hernia; enterolithotomy fo gall stone ileus)
• Procedure: exploratory laparotomy
  • Management of the obstruction (e.g., adhesiolysis, hernia reduction, cecopexy, tumor resection)
  • Resection of gangrenous bowel with restoration of intestinal transit or creation of a stoma

Endoscopic intervention ^[6][33][34]

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 endoscopic decompression, detorsion, and reduction.
• 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 ^[35]

• Indication: simple bowel obstruction caused by fecal impaction
• Procedures
  • The specific procedure is chosen based on the site of fecal impaction, only after bowel perforation has been definitively ruled out.
    • Manual disimpaction
    • Distal softening or washout with enemas or suppositories
    • Proximal softening or washout with oral solutions such as polyethylene glycol or sodium phosphate
  • See “Treatment of fecal impaction” for details and dosages.
• Important consideration: Identify and manage the underlying cause of constipation that led to fecal impaction.

Indications ^{[5][6][9][13]}

• Early postoperative bowel obstruction (i.e., within 6 weeks of abdominal surgery) ^[12]
• Partial bowel obstruction with no evidence of complications
• Consider in patients with complete SBO and no evidence of complications. ^[5][9][13]

Contraindications ^[5]

• Complicated bowel obstruction (e.g, peritoneal signs, signs of strangulation)
• Refractory metabolic acidosis
• Significant leukocytosis (> 18,000/mm³)
• Significant cecal dilation

Initial measures

• Bowel rest (NPO)
• Supportive care
  • IV fluid therapy (initial fluid resuscitation followed by maintenance fluid therapy)
  • Electrolyte repletion
  • Parenteral analgesics (nonopioid analgesics are preferred) ^[36][37]
  • Parenteral antiemetics as needed

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. ^[38]

Nasogastric tube insertion (bowel decompression)

• Indications: not routinely required but should be considered in the following situations ^[39][40]
  • Persistent vomiting
  • Significant upper GI distention
  • Complete bowel obstruction
  • Volvulus
• Contraindications ^[41]
  • Absolute: midface trauma or recent nasal surgery
  • Relative: coagulopathy, esophageal injury, alkaline ingestion
• Procedure ^[42]
  • Position the patient in an upright or semirecumbent position, if possible.
  • Lubricate the tip of the nasogastric tube with a water-soluble lubricant.
  • Consider topical anesthesia if available.
  • Pass the tube through the most patent nostril, across the oropharynx, and into the stomach.
  • Insert the nasogastric tube parallel to the nasal floor, not angled upward.
  • Verify the placement of the tube clinically (e.g., by aspirating gastric contents and/or rapidly instilling 10 mL of air via a syringe and auscultating it in the epigastrium).
  • Obtain radiological confirmation of correct tube placement before using the tube as a conduit to administer medication or nutritional support.

On chest x-ray, a properly placed nasogastric tube will cross the diaphragm in the midline and terminate below the left hemidiaphragm.

Chilling the nasogastric tube by placing it in the refrigerator or under cold water stiffens the tube, preventing coiling in the oropharynx! ^[42]

Serial monitoring

• Symptom severity
• Bowel movements
• Serial abdominal examination every 4–8 hours ^[12][13]
• Fluid balance (input and output chart) including nasogastric tube output ^[3]

Duration of nonoperative management trial ^{[5][13][32][43]}

• 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

• Arrange urgent general surgery and gastroenterology consults.
• NPO
• IV fluid resuscitation
• Electrolyte repletion
• Consider nasogastric tube insertion with continuous suction
• Supplemental oxygen as needed
• Parenteral analgesics
• Parenteral antiemetics
• Consider IV empiric antibiotic therapy for intraabdominal infection in complicated bowel obstruction.
• Obtain imaging and laboratory studies.
• Transfer to the operating room or admit to the surgical service.

• Bowel ischemia
• Bowel perforation
• Peritonitis

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.

• Mortality rate in untreated intestinal strangulation: 100%
• High risk of recurrence , particularly with chronic or recurring etiologies
• 30-day readmission rate: 16%
• Mortality rate after delayed treatment of closed-loop obstruction: 35%

References:^[5]

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