- Bowel obstruction occurs when the normal flow of intraluminal contents is interrupted.
- Classification of bowel obstruction includes functional (due to abnormal intestinal physiology, ie. postoperative ileus) or mechanical, partial or complete, and acute or chronic.
- With respect to location, the distribution of small and large bowel obstructions is estimated to be 75% and 25% of cases, respectively.
- Acute mechanical small bowel obstruction accounts for 2-4% of emergency department visits, 15% of hospital admissions, and 20% of emergency surgical interventions for abdominal pain.
- In the United States and Western Europe, the most common causes of mechanical small bowel obstruction are intraperitoneal adhesions, tumors, and incarcerated hernias.
- Less frequent causes of obstruction include Crohn disease, gallstones, volvulus, and intussusception.
Clinical Presentations and Risk Factors
- Most patients with small bowel obstruction will present acutely with an abrupt onset of colicky abdominal pain, nausea, vomiting, and abdominal distention.
- One study found that the absence of passage of flatus (90%) and/or feces (80.6%) and abdominal distension (65.3%) were the most common symptoms and physical exam findings in bowel obstruction, respectively.
- Risk factors for obstruction include:
- Prior abdominopelvic surgery.
- Abdominal wall or groin hernia.
- Intestinal inflammation.
- Prior abdominopelvic irradiation.
- Foreign body ingestion.
Physical Examination and Laboratory Investigations
- Physical examination should include evaluation for systemic signs of dehydration or sepsis, abdominal inspection, auscultation, percussion, and palpation, as well as a digital rectal examination.
- Typical laboratory investigations for patients presenting with abdominal pain include complete blood count with differential, electrolytes, BUN, and creatinine.
- In patients presenting with systemic signs of illness (ie. fever, tachycardia, hypotension, altered mental status), additional laboratory investigation should include:
- Arterial blood gas.
- Serum lactate (specificity = 42-87%, sensitivity = 90-100% for ischemia in small bowel obstruction.)
- Blood cultures (metabolic acidosis can occur with bowel ischemia or severe hypovolemia causing hypoperfusion of other organs.)
- Abdominal imaging is required to confirm the diagnosis, identify the location of obstruction, judge whether the obstruction is partial or complete, identify complications related to obstruction, and determine the etiology.
- Plain abdominal radiography is the initial imaging modality of choice to rapidly confirm the diagnosis, followed by contrast-enhanced CT of the abdomen and pelvis to further characterize the obstruction (provided the plain films do not have findings that indicate the need for immediate intervention.)
- Plain films should include an upright chest film and upright and supine abdominal films to look for dilated bowel loops (> 2.5 cm), air-fluid levels (>3), and free air under the diaphragm on upright films suggesting perforation.
- Complications of bowel obstruction include bowel compromise (ischemia, necrosis, and perforation) and sepsis.
- CT findings suggestive of bowel ischemia include:
- Poor or absent bowel wall enhancement.
- Bowel wall thickening.
- Gas in the bowel wall (pneumatosis intestinalis.)
- Pneumoperitoneum is a sign of perforation and may be detected as:
- Free air under the diaphragm on upright chest or upright abdominal radiography.
- Free air over the spleen or liver on a lateral abdominal film or abdominal CT.
- Free air as a “football sign” on a supine abdominal film or abdominal CT.
- Bowel compromise, clinical signs of deterioration (fever, leukocytosis, tachycardia, peritonitis) or a surgically correctable cause of bowel obstruction (ie. incarcerated hernia, volvulus, NOT adhesions) require immediate surgical exploration, while other patients may be candidates for a trial of non-operative management.
- 60-85% of adhesion-related small bowel obstructions resolve without surgery.
- All patients with bowel obstruction require admission to the hospital and prompt surgical consultation to determine if immediate surgical intervention is needed.
- Initial management:
- Fluid resuscitation.
- Electrolyte repletion.
- NG tube decompression for patients with significant distension, nausea, or vomiting.
- Not indicated for most patients with uncomplicated small bowel obstruction.
- Indicated for patients with suspected bowel compromise or inflammatory/infectious causes of non-adhesive obstruction.
- For adhesive small bowel obstruction with no CT indications for immediate surgery, consider a Gastrografin challenge.
- Hypertonic water-soluble contrast agent administered via NG tube; may be therapeutic.
- Obtain abdominal radiographs 6-24 hours after administration → evidence of Gastrografin reaching the colon is predictive of resolution without surgical intervention.
- Note: Gastrografin is contraindicated in pregnancy.
Criteria For Hospital Admission
- All patients with bowel obstruction should be admitted to the hospital.
Criteria For Transfer To Another Facility
- Dependent on resource availability.
Criteria For Close Observation And/or Consult
- All patients with bowel obstruction need prompt surgical consultation to determine if immediate surgical intervention is needed.
Drożdż, W., & Budzyński, P. (2012). Change in mechanical bowel obstruction demographic and etiological patterns during the past century: observations from one health care institution. Archives of Surgery, 147(2):175-80.
UpToDate: Management of small bowel obstruction in adults.
The purpose of this document is to provide health care professionals with key facts and recommendations for the diagnosis and treatment of patients in the emergency department. This summary was produced by the BC Emergency Medicine Network and uses the best available knowledge at the time of publication. However, healthcare professionals should continue to use their own judgment and take into consideration context, resources and other relevant factors. The BC Emergency Medicine Network is not liable for any damages, claims, liabilities, costs or obligations arising from the use of this document including loss or damages arising from any claims made by a third party. The BC Emergency Medicine Network also assumes no responsibility or liability for changes made to this document without its consent.
Last Updated Feb 17, 2022
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