Summary![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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.
Definition![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
- 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:
Reference:[1]
Etiology![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
Etiologic classification [2]
Mechanical bowel obstruction can be classified into the following etiologic categories.
Extrinsic bowel obstruction | Intrinsic bowel obstruction | ||
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Intramural bowel obstruction | Intraluminal bowel obstruction | ||
Etiology |
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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] | ||
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SBO | LBO | |
Most common causes |
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Other causes |
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Specific to infants and children |
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Pathophysiology![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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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
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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
Clinical features![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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.
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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)
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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] | ||
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Clinical feature | SBO | LBO |
Abdominal pain |
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Vomiting and/or nausea |
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Constipation or obstipation | ||
Abdominal distention |
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Examination findings |
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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]
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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
Clinical course of acute and subacute bowel obstruction | ||
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Acute bowel obstruction | Subacute bowel obstruction | |
Clinical course |
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Typical causes |
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Management![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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)
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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
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Administer supportive care as needed.
- Parenteral analgesics
- Parenteral antiemetics
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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]
Diagnostics![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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]
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Initial imaging modality: depends on the type of bowel obstruction and hemodynamic stability of the patient
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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.
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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
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Acute bowel obstruction [3][14]
- Findings: Radiological signs common to all imaging modalities are detailed in the table.
Radiological signs of mechanical bowel obstruction common to all imaging modalities [2][14][15] | |
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Pathology | Findings |
Dilatation of bowel loops proximal to the obstruction |
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Air-fluid level |
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Intraluminal air beyond the site of obstruction |
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Evidence of complications |
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Evidence of the underlying etiology |
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Abdominal series x-ray
- Indication: most appropriate initial test in hemodynamically unstable patients or in resource-poor centers [3][15]
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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.”
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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]
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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
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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
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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]
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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]
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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]
- Tapering of the bowel lumen at the site of obstruction
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]
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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]
- Normal WSCc: contrast reaches the colon within 24 hours of administration
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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.”
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Supportive findings
- In patients who are dehydrated
- ↑ BUN and creatinine (prerenal acute kidney injury)
- ↑ Hematocrit (due to hemoconcentration)
- In patients with recurrent vomiting
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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)
- In patients who are dehydrated
Leukocytosis, metabolic acidosis, and elevated serum lactate in a patient with suspected bowel obstruction are suggestive of bowel ischemia.
Differential diagnoses![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
- Differential diagnoses of mechanical bowel obstruction
- Differential diagnoses of SBO
- Differential diagnoses of LBO
- See also: “Differential diagnoses of acute abdomen.”
Mechanical bowel obstruction vs. paralytic ileus | |||
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Mechanical bowel obstruction [1][3][28][29] | Paralytic ileus | ||
Definition |
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Etiology |
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Clinical features |
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Findings on imaging |
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References:[3][28][29][30]
The differential diagnoses listed here are not exhaustive.
Treatment![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
- 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
Interventional management![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
Surgery [3][5][9][13][31]
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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
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
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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.
- The specific procedure is chosen based on the site of fecal impaction, only after bowel perforation has been definitively ruled out.
- Important consideration: Identify and manage the underlying cause of constipation that led to fecal impaction.
Nonoperative management![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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)
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Indications: not routinely required but should be considered in the following situations [39][40]
- Persistent vomiting
- Significant upper GI distention
- Complete bowel obstruction
- Volvulus
- Procedure: See “Nasogastric tube placement.”
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][41]
- 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 | |||
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Response | Clinical features | Supportive evidence | Further management |
Clinical improvement |
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Deterioration [13] |
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Lack of improvement (no evidence of complications) |
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Acute management checklist![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
- 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.
Complications![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
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.
Prognosis![toggle arrow icon](https://manus-media.amboss.com/icons/chevron_up.svg)
- 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]