Large bowel obstruction

1. History

• Onset and progression: Gradual vs. acute — malignant LBO typically has an insidious onset over days to weeks with progressive constipation and self-medication with OTC laxatives; volvulus may present more acutely [1][3]
• Cardinal symptoms: Obstipation (absence of flatus and stool — present in ~90%), abdominal pain (colicky → constant), abdominal distension, nausea/vomiting [5-6]
• Vomiting character: Late-onset and feculent vomiting suggests distal or long-standing obstruction; vomiting is less prominent in LBO than SBO [1]
• Timing: Duration of symptoms — hours (volvulus) vs. days to weeks (malignancy, stricture) [3]
• Bowel habit changes: Progressive narrowing of stool caliber, alternating constipation/diarrhea, hematochezia or melena (suggests malignancy) [7]
• Weight loss, anorexia: Suggests underlying malignancy or chronic process
• Prior episodes: Recurrent episodes of bloating/obstipation suggest volvulus or chronic stricture [3]
• Important negatives: Passage of flatus (argues against complete obstruction), bilious vs. feculent emesis, presence of diarrhea (overflow around partial obstruction)

2. Alarm Features

• Peritonitis: Guarding, rebound tenderness, rigidity — suggests perforation or ischemia → emergent surgery [1][5]
• Hemodynamic instability: Tachycardia, hypotension — suggests sepsis, perforation, or severe dehydration [1]
• Fever with leukocytosis: Concerning for bowel ischemia, necrosis, or perforation [6]
• Cecal diameter >9 cm on imaging: High risk of perforation per Laplace's law [1]
• Pneumatosis intestinalis or portal venous gas on CT: Signs of tissue ischemia with impending perforation [1]
• Closed-loop obstruction (competent ileocecal valve with distal obstruction): Rapid progression to ischemia and perforation [1]
• Feculent emesis: Indicates long-standing or complete distal obstruction [1]
• Rapidly worsening, constant pain replacing colicky pain: Suggests transition from simple obstruction to strangulation [1]

3. Medications

4. Diet

• NPO in acute setting — bowel rest is a cornerstone of initial management [1]
• Gradual reintroduction of clear liquids → low-residue diet after resolution
• Long-term: Low-residue diet in patients with strictures or partial obstruction; high-fiber diet may be beneficial for prevention of diverticular disease but should be avoided in acute obstruction
• Hydration: Aggressive IV hydration to correct dehydration from vomiting, third-spacing, and poor oral intake [1]

5. Review of Systems

• GI: Nausea, vomiting (character and timing), last bowel movement, last flatus, hematochezia, melena, change in stool caliber
• Constitutional: Fever, chills, weight loss, fatigue, anorexia
• GU: Urinary symptoms (pelvic mass effect), hematuria (fistula)
• Gynecologic: Pelvic masses, endometriosis (uncommon cause of LBO) [9]
• Neuropsychiatric: Cognitive impairment, psychiatric medications (risk factor for volvulus) [3]

6. Collateral History and Family History

• Collateral: Nursing home/institutional status (high risk for volvulus and pseudo-obstruction), baseline functional status, medication list, recent hospitalizations or surgeries [3]
• Family history: Colorectal cancer, Lynch syndrome, familial adenomatous polyposis, inflammatory bowel disease [7]
• Social context: Chronic constipation, laxative dependence, immobility, dietary habits

7. Risk Factors

• Colorectal cancer: Age >50, family history of CRC, personal history of polyps, IBD, obesity, smoking, processed meat consumption [7]
• Volvulus: Advanced age, neuropsychiatric disorders, institutionalization, chronic constipation, redundant sigmoid colon, diabetes, prior abdominal surgery [2-3]
• Diverticular stricture: History of recurrent diverticulitis, prior pelvic radiation [10-11]
• Pseudo-obstruction (Ogilvie syndrome): Recent surgery/trauma, hospitalization, electrolyte abnormalities, opioid/anticholinergic use, sepsis, cardiac disease [3]
• General: Prior abdominal/pelvic surgery (adhesions — rare cause of LBO), prior radiation therapy, inflammatory bowel disease [1]

8. Differential Diagnosis

• Colorectal carcinoma — most common cause of mechanical LBO in adults (~60%) [1][3]
• Sigmoid volvulus — "coffee bean" sign on AXR; more common in elderly, institutionalized patients [3]
• Cecal volvulus — younger patients, female predominance; requires surgical management [2]
• Diverticular stricture — history of recurrent diverticulitis; can be difficult to distinguish from malignancy [10-11]
• Acute colonic pseudo-obstruction (Ogilvie syndrome) — no mechanical cause on imaging; critical to differentiate as treatment is medical, not surgical [1][3]
• Fecal impaction — especially in elderly, immobile, or opioid-dependent patients
• Incarcerated hernia — inguinal, incisional, or internal; highest risk of strangulation [5]
• Inflammatory bowel disease (Crohn's stricture) — rare in colon; should prompt suspicion for malignancy [1]
• Extrinsic compression — pelvic tumors (ovarian, uterine), peritoneal carcinomatosis, endometriosis [9][12]
• Ischemic colitis with stricture — history of vascular disease, watershed distribution [9]

9. Past Medical History

• Prior colorectal cancer, polyps, or cancer screening history
• History of diverticulitis or diverticular disease
• Prior abdominal/pelvic surgery (adhesions, anastomotic stricture)
• Prior abdominal/pelvic radiation
• Inflammatory bowel disease
• Neuropsychiatric conditions (risk for volvulus)
• Chronic constipation and laxative use
• Hernia history

10. Physical Exam

11. Lab Studies

• CBC: Leukocytosis with neutrophil predominance — concerning for ischemia/sepsis [1][6]
• BMP/CMP: Electrolyte derangements (hypokalemia, hypochloremia from vomiting), prerenal azotemia (elevated BUN/Cr), metabolic alkalosis [1]
• Serum lactate: Elevated in bowel ischemia — though may be falsely normal in closed-loop obstruction [1]
• VBG: Acid-base status assessment [1]
• Coagulation profile [1]
• Type and screen if surgical intervention anticipated
• CEA: Low sensitivity for primary CRC diagnosis (~46%); not useful acutely but may be drawn for baseline if malignancy suspected [7]
• Blood cultures if sepsis suspected

12. Imaging

First-line: Abdominal radiograph (upright and supine) — often the initial study; may show dilated colon (>6 cm, cecum >9 cm), air-fluid levels, absence of rectal gas [14]

• [3]

Gold standard: CT abdomen/pelvis with IV contrast — imaging modality of choice [1][9][14]

• Sensitivity 90–96%, specificity ~91% for mechanical LBO [1][15-16]
• Identifies transition point, etiology (mass, volvulus, stricture), and complications
• Key findings: transition point ± mass, "whirl sign" (volvulus), pneumatosis intestinalis, portal venous gas, free fluid, pneumoperitoneum [1][3][9]
• Differentiates mechanical LBO from pseudo-obstruction [9][14]

13. Special Tests

• Colonoscopy: Diagnostic and potentially therapeutic — can localize lesions, obtain biopsies, place stents, and perform endoscopic detorsion of sigmoid volvulus; not recommended in unstable patients or those with peritonitis [1-2]
• Neostigmine challenge: For ACPO — 2 mg IV over 3–5 min with cardiac monitoring (risk of bradycardia); success rate ~80–90% [2]
• Water-soluble contrast enema: Therapeutic and diagnostic in partial obstruction

14. ECG

• Indications: Baseline ECG in elderly patients, pre-operative assessment, and before neostigmine administration (risk of symptomatic bradycardia) [2]
• Relevant findings: Electrolyte-related changes — peaked T waves or U waves (hypo/hyperkalemia), QT prolongation (hypomagnesemia, hypocalcemia)
• Pre-neostigmine: Must have cardiac monitoring; atropine at bedside

15. Assessment

Clinical summary: LBO is a surgical emergency until proven otherwise. The majority are caused by colorectal cancer (most common), volvulus, and diverticulitis. [1][3] Critical early decisions include distinguishing mechanical obstruction from pseudo-obstruction and identifying signs of ischemia, perforation, or closed-loop obstruction.

Complications

• Bowel ischemia (~14%), necrosis (~9%), perforation (~5%) [5]
• Sepsis, multiorgan failure
• Cecal perforation (highest risk when diameter >9–12 cm) [1-2]
• Aspiration from feculent vomiting

16. Treatment Plan

Initial stabilization ("suck and drip"): [1]

• NPO, nasogastric tube decompression
• Aggressive IV fluid resuscitation
• Electrolyte correction
• Foley catheter for urine output monitoring
• Broad-spectrum antibiotics if signs of infection/ischemia

17. Disposition

Admission criteria (all patients with confirmed LBO should be admitted): [1]

• Complete mechanical LBO — surgical admission
• Partial LBO with inability to tolerate oral intake
• Any signs of ischemia, perforation, or hemodynamic compromise — ICU consideration
• Pseudo-obstruction requiring monitoring and potential neostigmine

18. Follow Up / Return Precautions

Return precautions — instruct patients to return immediately for:

• Recurrence of abdominal distension, pain, or inability to pass gas/stool
• Fever, chills, or rigors
• Persistent vomiting
• Bloody stool
• Lightheadedness, dizziness, or fainting