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Emergency and Acute Medicine – Bowel Obstruction (Small and Large)
Overview And Definitions
Bowel obstruction is interruption of normal intestinal transit from mechanical or functional (nonmechanical) causes. Small-bowel obstruction (SBO) accounts for about 20% of acute surgical admissions. Adhesions are the leading cause (≈60%), followed by neoplasms, hernias, strictures (e.g., inflammatory bowel disease), trauma-related bowel wall hematoma, and miscellaneous causes such as ascaris infection. Large-bowel obstruction (LBO) occurs primarily in older adults and is most commonly due to carcinoma (≈60%), diverticular disease (≈20%), volvulus (≈5%), colitis (ischemic or radiation), Crohn’s disease, foreign bodies, and functional obstruction. Functional, nonmechanical etiologies include paralytic ileus (e.g., electrolyte derangements, injury) and pseudo-obstruction (Ogilvie syndrome), which represents about 11%.
Etiology And Pathophysiology
Obstruction causes proximal intestinal dilation from swallowed air and accumulated GI secretions, increasing intraluminal pressure. Retrograde peristalsis produces vomiting. Progressive bowel edema and ongoing secretions worsen distention and lead to third spacing into the lumen. Strangulated obstruction can cause bowel wall ischemia, promoting aerobic and anaerobic bacterial overgrowth with methane and hydrogen production. This can progress to peritonitis, sepsis, and death. Mortality is essentially 100% for untreated strangulated obstruction, drops to ~8% with surgery within 36 hours, and rises to ~25% if surgery is delayed beyond 36 hours.
Clinical Presentation
Key historical clues include prior abdominal surgery, malignancy, hernias, prior colonoscopy, and significant family history. Pain is often intermittent early, but becomes constant with strangulation; symptoms may be vague in elderly or altered patients. Vomiting varies with level of obstruction—bilious emesis with proximal obstruction and feculent emesis with distal obstruction. Patients may report obstipation, constipation, diarrhea, stool caliber changes, and weight loss.
Vital signs may show tachycardia and hypotension from volume depletion, fever with strangulation or perforation, and hypothermia with sepsis. Abdominal examination often reveals distention and variable, frequently diffuse tenderness. Bowel sounds may be hyperactive and high-pitched early, becoming hypoactive late. Pain out of proportion to exam should raise concern for ischemic or gangrenous bowel. Peritoneal signs suggest strangulation or perforation. Evaluate for ventral, inguinal, and femoral hernias. Digital rectal exam may reveal a rectal mass or blood (gross or occult).
Geriatric Considerations
Abdominal pain in older adults may be vague. Nausea, vomiting, and abdominal pain can also occur with acute myocardial infarction; however, abdominal distention, obstipation, and colicky pain support a GI source.
Pediatric Considerations
Intussusception is the leading cause of obstruction in infants, most commonly between 3 and 12 months. Other causes include incarcerated inguinal or umbilical hernia and malrotation with volvulus, which can occur as early as 3–7 days of life. The “double bubble” sign on plain radiograph suggests partial duodenal obstruction (air in stomach and proximal duodenum). Pyloric stenosis presents with progressive, projectile, nonbilious postprandial vomiting, typically at 2–5 weeks of age, with a male predominance (≈5:1). Additional pediatric causes include duodenal atresia, Hirschsprung disease, and imperforate anus.
Essential Evaluation
A careful history and physical examination are central.
Diagnostic Tests And Interpretation
Laboratory studies commonly include CBC (leukocytosis is common), electrolytes/BUN/creatinine/glucose (hypokalemia, hypochloremic metabolic alkalosis, prerenal azotemia), lactate, amylase/lipase, liver enzymes/function tests to exclude hepatobiliary pathology, stool heme testing, urinalysis, type and crossmatch, PT/PTT, and ECG in patients at risk for coronary disease.
Imaging begins with upright chest radiograph to assess for pulmonary pathology and free air under the diaphragm. Abdominal radiographs (supine and upright) have ~75% sensitivity and ~53% specificity. Findings include dilated bowel loops (normal small bowel <3 cm), cecal dilation>13 cm suggesting perforation risk, air–fluid levels, and the “string of pearls” sign when small bowel is nearly fluid-filled. Plain films are less helpful for detecting strangulation. CT abdomen is highly sensitive (≈90% for SBO; ≈91% for LBO), identifies neoplasms and stages malignancy, localizes the transition point, and is more useful than plain films for early strangulation when IV contrast is used; CT has reduced the need for contrast enemas. MRI can approach CT sensitivity but availability varies. Ultrasound is more sensitive and specific than plain films for SBO but generally less accurate than CT. Upper GI studies, barium enemas, and endoscopy may be used when carcinoma or a mass is suspected, though their use has declined due to CT and they may be difficult in severely ill patients.
Differential Diagnosis
Paralytic ileus, pseudo-obstruction (Ogilvie), perforated ulcer, pancreatitis, cholecystitis, colitis, and mesenteric ischemia.
Prehospital Care
Establish IV access for patients with dehydration, vomiting, or significant abdominal pain.
Initial Stabilization And ED Management
Prioritize ABCs. Provide isotonic IV fluid resuscitation with 0.9% normal saline or lactated Ringer’s, especially for volume depletion and suspected strangulation or perforation (adults: 1 L bolus; pediatrics: 20 mL/kg bolus). Correct electrolyte abnormalities, particularly hypokalemia. Place a nasogastric tube for decompression, insert a Foley catheter for urine output monitoring, and obtain early surgical consultation. Administer antibiotics when strangulation or perforation is suspected, ensuring coverage for gram-negative aerobes and anaerobes. Provide analgesics and antiemetics. Address underlying causes when appropriate (e.g., steroids for inflammatory bowel disease or radiation enteritis).
Medications
For suspected ischemia/strangulation, options include combination therapy with metronidazole (1 g IV then 500 mg IV q6h; pediatrics 7.5-30 mg/kg/day divided q6-8h) plus ciprofloxacin 400 mg IV q12h or ceftriaxone 1-2 g IV q24h (pediatrics 25-75 mg/kg/day IV up to 2 g divided q12-24h). Single-agent broad-spectrum regimens include piperacillin-tazobactam 3.375 g IV q4-6h (pediatrics 150-400 mg/kg/day divided q6-8h), ampicillin-sulbactam 1.5-3 g IV q6h (pediatrics 100-400 mg/kg/day divided q6h), meropenem 1 g IV q8h (pediatrics 60-120 mg/kg/day divided q8h), or imipenem-cilastatin 250-1,000 mg IV q6-8h (pediatrics 50-100 mg/kg/day divided q6-12h). Analgesia may include morphine 2-10 mg per dose (pediatrics 0.1-0.2 mg/kg IV/IM/SC q2-4h) q2-6h PRN. Antiemetics include ondansetron 4 mg IV (pediatrics 0.1 mg/kg IV divided q8h) q4-8h PRN or promethazine 12.5-25 mg (pediatrics >2 years: 0.25–1 mg/kg/day IV/IM/PR divided q4–6h PRN) q4h.
Disposition
All suspected or confirmed bowel obstructions require admission with early surgical consultation. Discharge is appropriate only when labs and imaging are normal, symptoms resolve, and obstruction is no longer suspected.
Follow-Up Recommendations
Discharged patients should have normal laboratory and radiologic studies, a timely re-evaluation appointment, and clear return precautions outlining symptoms that require immediate ED return.
Clinical Insights And Common Errors
Patients with vomiting should be carefully examined for incarcerated hernias. Strangulated obstruction can be missed when symptoms are subtle, particularly in very young, very old, or altered patients. Another frequent error is inadequate correction of fluid deficits and electrolyte abnormalities.
Overview And Definitions
Bowel obstruction is interruption of normal intestinal transit from mechanical or functional (nonmechanical) causes. Small-bowel obstruction (SBO) accounts for about 20% of acute surgical admissions. Adhesions are the leading cause (≈60%), followed by neoplasms, hernias, strictures (e.g., inflammatory bowel disease), trauma-related bowel wall hematoma, and miscellaneous causes such as ascaris infection. Large-bowel obstruction (LBO) occurs primarily in older adults and is most commonly due to carcinoma (≈60%), diverticular disease (≈20%), volvulus (≈5%), colitis (ischemic or radiation), Crohn’s disease, foreign bodies, and functional obstruction. Functional, nonmechanical etiologies include paralytic ileus (e.g., electrolyte derangements, injury) and pseudo-obstruction (Ogilvie syndrome), which represents about 11%.
Etiology And Pathophysiology
Obstruction causes proximal intestinal dilation from swallowed air and accumulated GI secretions, increasing intraluminal pressure. Retrograde peristalsis produces vomiting. Progressive bowel edema and ongoing secretions worsen distention and lead to third spacing into the lumen. Strangulated obstruction can cause bowel wall ischemia, promoting aerobic and anaerobic bacterial overgrowth with methane and hydrogen production. This can progress to peritonitis, sepsis, and death. Mortality is essentially 100% for untreated strangulated obstruction, drops to ~8% with surgery within 36 hours, and rises to ~25% if surgery is delayed beyond 36 hours.
Clinical Presentation
Key historical clues include prior abdominal surgery, malignancy, hernias, prior colonoscopy, and significant family history. Pain is often intermittent early, but becomes constant with strangulation; symptoms may be vague in elderly or altered patients. Vomiting varies with level of obstruction—bilious emesis with proximal obstruction and feculent emesis with distal obstruction. Patients may report obstipation, constipation, diarrhea, stool caliber changes, and weight loss.
Vital signs may show tachycardia and hypotension from volume depletion, fever with strangulation or perforation, and hypothermia with sepsis. Abdominal examination often reveals distention and variable, frequently diffuse tenderness. Bowel sounds may be hyperactive and high-pitched early, becoming hypoactive late. Pain out of proportion to exam should raise concern for ischemic or gangrenous bowel. Peritoneal signs suggest strangulation or perforation. Evaluate for ventral, inguinal, and femoral hernias. Digital rectal exam may reveal a rectal mass or blood (gross or occult).
Geriatric Considerations
Abdominal pain in older adults may be vague. Nausea, vomiting, and abdominal pain can also occur with acute myocardial infarction; however, abdominal distention, obstipation, and colicky pain support a GI source.
Pediatric Considerations
Intussusception is the leading cause of obstruction in infants, most commonly between 3 and 12 months. Other causes include incarcerated inguinal or umbilical hernia and malrotation with volvulus, which can occur as early as 3–7 days of life. The “double bubble” sign on plain radiograph suggests partial duodenal obstruction (air in stomach and proximal duodenum). Pyloric stenosis presents with progressive, projectile, nonbilious postprandial vomiting, typically at 2–5 weeks of age, with a male predominance (≈5:1). Additional pediatric causes include duodenal atresia, Hirschsprung disease, and imperforate anus.
Essential Evaluation
A careful history and physical examination are central.
Diagnostic Tests And Interpretation
Laboratory studies commonly include CBC (leukocytosis is common), electrolytes/BUN/creatinine/glucose (hypokalemia, hypochloremic metabolic alkalosis, prerenal azotemia), lactate, amylase/lipase, liver enzymes/function tests to exclude hepatobiliary pathology, stool heme testing, urinalysis, type and crossmatch, PT/PTT, and ECG in patients at risk for coronary disease.
Imaging begins with upright chest radiograph to assess for pulmonary pathology and free air under the diaphragm. Abdominal radiographs (supine and upright) have ~75% sensitivity and ~53% specificity. Findings include dilated bowel loops (normal small bowel <3 cm), cecal dilation>13 cm suggesting perforation risk, air–fluid levels, and the “string of pearls” sign when small bowel is nearly fluid-filled. Plain films are less helpful for detecting strangulation. CT abdomen is highly sensitive (≈90% for SBO; ≈91% for LBO), identifies neoplasms and stages malignancy, localizes the transition point, and is more useful than plain films for early strangulation when IV contrast is used; CT has reduced the need for contrast enemas. MRI can approach CT sensitivity but availability varies. Ultrasound is more sensitive and specific than plain films for SBO but generally less accurate than CT. Upper GI studies, barium enemas, and endoscopy may be used when carcinoma or a mass is suspected, though their use has declined due to CT and they may be difficult in severely ill patients.
Differential Diagnosis
Paralytic ileus, pseudo-obstruction (Ogilvie), perforated ulcer, pancreatitis, cholecystitis, colitis, and mesenteric ischemia.
Prehospital Care
Establish IV access for patients with dehydration, vomiting, or significant abdominal pain.
Initial Stabilization And ED Management
Prioritize ABCs. Provide isotonic IV fluid resuscitation with 0.9% normal saline or lactated Ringer’s, especially for volume depletion and suspected strangulation or perforation (adults: 1 L bolus; pediatrics: 20 mL/kg bolus). Correct electrolyte abnormalities, particularly hypokalemia. Place a nasogastric tube for decompression, insert a Foley catheter for urine output monitoring, and obtain early surgical consultation. Administer antibiotics when strangulation or perforation is suspected, ensuring coverage for gram-negative aerobes and anaerobes. Provide analgesics and antiemetics. Address underlying causes when appropriate (e.g., steroids for inflammatory bowel disease or radiation enteritis).
Medications
For suspected ischemia/strangulation, options include combination therapy with metronidazole (1 g IV then 500 mg IV q6h; pediatrics 7.5-30 mg/kg/day divided q6-8h) plus ciprofloxacin 400 mg IV q12h or ceftriaxone 1-2 g IV q24h (pediatrics 25-75 mg/kg/day IV up to 2 g divided q12-24h). Single-agent broad-spectrum regimens include piperacillin-tazobactam 3.375 g IV q4-6h (pediatrics 150-400 mg/kg/day divided q6-8h), ampicillin-sulbactam 1.5-3 g IV q6h (pediatrics 100-400 mg/kg/day divided q6h), meropenem 1 g IV q8h (pediatrics 60-120 mg/kg/day divided q8h), or imipenem-cilastatin 250-1,000 mg IV q6-8h (pediatrics 50-100 mg/kg/day divided q6-12h). Analgesia may include morphine 2-10 mg per dose (pediatrics 0.1-0.2 mg/kg IV/IM/SC q2-4h) q2-6h PRN. Antiemetics include ondansetron 4 mg IV (pediatrics 0.1 mg/kg IV divided q8h) q4-8h PRN or promethazine 12.5-25 mg (pediatrics >2 years: 0.25–1 mg/kg/day IV/IM/PR divided q4–6h PRN) q4h.
Disposition
All suspected or confirmed bowel obstructions require admission with early surgical consultation. Discharge is appropriate only when labs and imaging are normal, symptoms resolve, and obstruction is no longer suspected.
Follow-Up Recommendations
Discharged patients should have normal laboratory and radiologic studies, a timely re-evaluation appointment, and clear return precautions outlining symptoms that require immediate ED return.
Clinical Insights And Common Errors
Patients with vomiting should be carefully examined for incarcerated hernias. Strangulated obstruction can be missed when symptoms are subtle, particularly in very young, very old, or altered patients. Another frequent error is inadequate correction of fluid deficits and electrolyte abnormalities.
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