Bowel Obstruction: SBO and LBO Diagnosis & Management
Bowel obstruction — mechanical blockage of the intestinal lumen — is divided into small bowel obstruction (SBO, 75% of cases, most commonly adhesions) and large bowel obstruction (LBO, 25%, most commonly colorectal cancer). Correct classification guides management: partial SBO can be managed non-operatively, but strangulation or complete obstruction requires urgent surgery.
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update Updated October 2026
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bolt The 60-second version
check_circleSBO: adhesions most common cause (60–70%); LBO: colorectal cancer most common cause (60%)
check_circleCT abdomen/pelvis is gold standard; strangulation signs (pneumatosis, portal venous gas) = emergency surgery
check_circlePartial SBO: trial of NPO + NG tube decompression for 48–72h; gastrografin challenge is both diagnostic and therapeutic
check_circleSigmoid volvulus: coffee bean sign on X-ray; treat with flexible sigmoidoscopy; cecal volvulus requires surgery
check_circleClosed-loop obstruction = highest ischemia risk; virgin abdomen with SBO = less likely adhesive, more likely to need surgery
Small Bowel Obstruction (SBO): Causes, Presentation, Imaging
**Most common causes (mnemonic AHHH)**: **A**dhesions (most common in adults, 60–70% — prior abdominal surgery), **H**ernia (inguinal, femoral, incisional — most common in patients with no prior surgery), **H**intussusception (most common in children <2, lead point in adults = malignancy/Meckel's), **H**arlington's tumor (neoplasm). Also: volvulus, Crohn's disease stricture, gallstone ileus (air in biliary tree on X-ray = Rigler's triad). **Presentation**: colicky periumbilical pain, nausea/vomiting (bilious early; feculent late = more distal), distension, obstipation (no flatus = complete). **X-ray**: dilated small bowel loops (>3 cm, central distribution, valvulae conniventes = complete plicae), air-fluid levels, paucity of colonic gas. **CT abdomen/pelvis with IV contrast** (gold standard): transition point, dilated proximal and decompressed distal bowel. Signs of strangulation (ischemia): free fluid, pneumatosis intestinalis, portal venous gas, mesenteric edema, decreased bowel wall enhancement — these mandate emergency surgery.
Large Bowel Obstruction (LBO): Causes and Volvulus
**Most common causes**: colorectal carcinoma (most common, 60%), volvulus (20%, most commonly sigmoid colon), diverticular stricture, Ogilvie syndrome (colonic pseudo-obstruction — no mechanical obstruction). **Sigmoid volvulus**: elderly, institutionalized, chronic constipation; X-ray shows 'coffee bean' sign (massively dilated sigmoid loops pointing to right upper quadrant); initial treatment = flexible sigmoidoscopy decompression (if no peritonitis) followed by elective sigmoid resection. **Cecal volvulus**: younger patients, CT with 'whirl sign'; requires surgery (right hemicolectomy) — endoscopic decompression unreliable. **Colorectal cancer obstruction**: CT identifies tumor + level; emergent surgical options: Hartmann procedure (sigmoid colectomy + colostomy — safest for unprepared bowel), or self-expanding metal stent as bridge to elective surgery (controversial). **Ogilvie syndrome**: IV neostigmine (anticholinesterase) is first-line after colonoscopic decompression failure; occurs in ICU/post-operative patients.
Management Principles: Operative vs Non-operative
**Initial management (all obstructions)**: NPO (nil per os), nasogastric tube (NG tube) for decompression and symptom relief, IV fluids (LR preferred) for resuscitation, serial abdominal exams, Foley catheter for urine output monitoring, correct electrolytes (hypokalemic hypochloremic metabolic alkalosis from vomiting). **Non-operative (partial SBO)**: 80% resolve with conservative management; trial for 48–72h; gastrografin challenge (water-soluble contrast study) both diagnostic and therapeutic for adhesive SBO. **Operative indications**: complete SBO not resolving after 48–72h, any signs of strangulation (ischemia), peritonitis, free air on imaging, virgin abdomen (no prior surgery — less likely adhesive), closed-loop obstruction (two points of obstruction → highest ischemia risk), volvulus not decompressible endoscopically, LBO from malignancy. **Post-operative care**: risk of short bowel syndrome if significant bowel resection, TPN if >100 cm small bowel removed.
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3 real questions on Bowel Obstruction
Straight from the Progress Note question bank, each with a cited explanation. No account needed.
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What is the most likely diagnosis?
Mont4nha, CC0, via Wikimedia Commons
Answer: C. Sigmoid volvulus occurs when a redundant, mobile sigmoid colon twists around its mesenteric axis, producing a closed-loop obstruction that appears radiographically as a massively dilated, inverted U-shaped loop with a central dividing wall — the classic 'coffee bean' or omega-loop sign — most common in elderly or chronically constipated patients. Cecal volvulus (A) also produces a single markedly dilated gas-filled loop, but it characteristically arises from the right lower quadrant and migrates toward the left upper quadrant or mid-abdomen, rather than forming the paired coffee-bean compartments seen here. Toxic megacolon (B) produces diffuse colonic dilation with mucosal thickening and thumbprinting in the setting of severe colitis, without the discrete twisted closed-loop appearance. Acute colonic pseudo-obstruction (D) causes diffuse colonic dilation without a mechanical transition point or twist, typically in critically ill or postoperative patients. Small bowel obstruction (E) produces multiple dilated, centrally located loops with valvulae conniventes rather than a single large colonic loop with the coffee-bean configuration.
Source: Alavi, K., et al. (2021). The American Society of Colon and Rectal Surgeons clinical practice guidelines for the management of colonic volvulus and acute colonic pseudo-obstruction. Diseases of the Colon & Rectum.
From our NCLEX bank
A nurse assesses a client who reports abdominal cramping and vomiting and has not passed stool or flatus for 2 days. Which finding would the nurse expect with a bowel obstruction?
Answer: B. In a bowel obstruction the intestine works harder to move contents past the blockage, producing abdominal distension with high-pitched tinkling bowel sounds above the obstruction (option B). A soft, flat abdomen with normal bowel sounds (A) would not explain the client's symptoms. Frequent large watery stools (C) describe diarrhea, which is the opposite of the obstipation this client reports. A rigid board-like abdomen with no pain (D) is contradictory, since rigidity indicates peritonitis and is intensely painful. The nurse keeps the client NPO and notifies the provider, anticipating decompression.
Source: Jackson, P., & Vigiola Cruz, M. (2018). Intestinal obstruction: Evaluation and management. American Family Physician, 98(6), 362–367.
From our NCLEX bank
A nurse is caring for a client who reports crampy abdominal pain, abdominal distension, and vomiting, and the nurse notes that bowel sounds are high-pitched and then absent. Which action by the nurse is most appropriate?
Answer: A. Crampy pain, distension, vomiting, and high-pitched then absent bowel sounds suggest a bowel obstruction, so the nurse recognizes it, keeps the client nothing by mouth, and notifies the provider (option A). Encouraging the client to eat (B) can worsen the obstruction and increase vomiting and aspiration risk. Giving a stimulant laxative (C) is dangerous with a possible obstruction. Applying a heating pad and waiting hours (D) delays care and could mask a worsening condition. Keeping the client nothing by mouth and escalating are the immediate priorities. The nurse anticipates nasogastric decompression, intravenous fluids, and imaging.
Source: Jackson, P., & Vigiola Cruz, M. (2018). Intestinal obstruction: Evaluation and management. American Family Physician, 98(6), 362–367.
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What are the signs of strangulation in bowel obstruction and why do they mandate surgery?expand_more
Strangulation (bowel ischemia) signs: fever, constant (not colicky) severe pain, peritoneal signs (rebound, guarding), leukocytosis with bandemia, lactic acidosis, CT findings of pneumatosis intestinalis (air in bowel wall), portal venous gas, decreased bowel wall enhancement, free fluid. Strangulation = compromised blood supply → bowel infarction, perforation, sepsis, death within hours. It cannot be managed non-operatively — immediate surgery is required.
Why is a 'virgin abdomen' (no prior surgery) important in evaluating SBO?expand_more
Adhesions (the most common SBO cause) only form after prior abdominal surgery or peritoneal inflammation. A patient with no prior surgery presenting with SBO is less likely to have adhesive disease and more likely to have a hernia, malignancy, volvulus, or Crohn's as the etiology. These causes are less responsive to conservative management, so a lower threshold for earlier surgical intervention is appropriate in virgin abdomen SBO.
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