Small bowel obstruction

1. History

• Prior abdominal surgery — single most important historical element; adhesions cause ~65% of SBO [1][3]
• Onset, character, and progression of abdominal pain: crampy/colicky → constant pain suggests ischemia [4-5]
• Nausea, vomiting (bilious early; feculent with distal obstruction), abdominal distension [1]
• Obstipation — cessation of flatus and stool; absence of flatus is a strong predictor of failed conservative management (OR 3.3) [6]
• Timing of symptom onset relative to presentation (1–2 days typical) [7]
• Prior episodes of SBO, prior radiation therapy, history of inflammatory bowel disease, known malignancy [3]
• Medication history: opioids and anticholinergics can cause ileus mimicking SBO [2]
• History of bariatric surgery (Roux-en-Y) — high risk for internal hernia/closed-loop obstruction [2]

Important negatives: passage of flatus, bowel movements, ability to tolerate PO, fever, bloody emesis/stool

2. Alarm Features

• Peritonitis — involuntary guarding, rigidity, rebound tenderness [1][3]
• Hemodynamic instability — tachycardia, hypotension, SBP <100 mmHg [3][8]
• Fever (OR 2.8 for failed conservative management) [6]
• Continuous, non-colicky pain (suggests transition from obstruction to ischemia) [3]
• Bloody emesis or stool, bloody peritoneal aspirate [9]
• Rapidly progressive clinical deterioration despite resuscitation
• Signs of sepsis/SIRS: tachycardia, fever, leukocytosis, metabolic acidosis [3]

Any of these features mandate timely surgical exploration (EAST Level 1 recommendation). [3]

3. Medications

• Contributors to ileus/pseudo-obstruction: opioids, anticholinergics, calcium channel blockers, phenothiazines [2]
• Treatment medications:
  • IV crystalloid (Lactated Ringer preferred over NS to avoid acidemia) [2]
  • Antiemetics (ondansetron)
  • Analgesics — IV acetaminophen, ketorolac preferred; minimize opioids as they worsen dysmotility
  • Antibiotics (gram-negative and anaerobic coverage) if fever/leukocytosis present [10]
  • Gastrografin (water-soluble contrast) — both diagnostic and therapeutic; can accelerate resolution and shorten LOS [3][11]
• Cautions: avoid oral contrast in emergent CT setting due to aspiration risk in supine patients; avoid normal saline for resuscitation [2]

4. Diet

• NPO is mandatory during acute obstruction [1-2]
• Progressive refeeding after resolution: clear liquids → liquid diet → low-residue diet → regular diet [11]
• Long-term: low-residue diet may reduce recurrence risk in patients with adhesive disease
• Adequate hydration is critical — significant third-spacing and dehydration are common

5. Review of Systems

• GI: nausea, vomiting (character/volume), last flatus, last bowel movement, diarrhea (watery diarrhea can occur with partial SBO and mimic gastroenteritis) [12]
• Constitutional: fever, chills, weight loss (malignancy concern)
• GU: decreased urine output (dehydration/AKI)
• Cardiovascular: lightheadedness, syncope (hypovolemia)
• Pulmonary: dyspnea (aspiration risk, abdominal distension limiting diaphragmatic excursion)

6. Collateral History and Family History

• Obtain operative reports from prior surgeries when possible
• Collateral from family regarding symptom timeline, medication use, functional status
• Family history: inflammatory bowel disease, familial adenomatous polyposis, hereditary cancer syndromes (Lynch syndrome) — relevant when malignancy is suspected as etiology
• Social context: functional status, nutritional baseline, ability to manage post-discharge care

7. Risk Factors

• Prior abdominal/pelvic surgery — most significant risk factor; appendectomy, colorectal, hernia, and gynecologic surgeries carry highest adhesion risk [1-2]
• Prior episodes of SBO (38.7% of adhesive SBO patients have prior SBO history) [7]
• Prior abdominal/pelvic radiation
• Inflammatory bowel disease (Crohn's disease ~5% of SBO) [1]
• Intra-abdominal malignancy (~5% of SBO; 12% in virgin abdomen SBO) [1][13]
• Hernias (inguinal, incisional, internal) — ~10% of SBO [1]
• History of bariatric surgery (internal hernia at Petersen defect) [2]

8. Differential Diagnosis

• Postoperative ileus — no transition point on imaging; diffuse bowel dilation; history of recent surgery [2]
• Large bowel obstruction — colonic dilation, mass or transition point in colon; incompetent ileocecal valve may cause concurrent small bowel dilation [2]
• Colonic pseudo-obstruction (Ogilvie syndrome) — massive colonic dilation without mechanical cause; post-surgical, critically ill patients [2]
• Acute mesenteric ischemia — primary vascular event; pain out of proportion to exam; atrial fibrillation risk factor [2]
• Narcotic bowel/opioid-induced dysmotility [1]
• Gallstone ileus — intraluminal cause; pneumobilia + ectopic gallstone on CT (Rigler triad) [14]
• Crohn's stricture — known IBD, terminal ileum involvement
• Intussusception — lead point mass in adults [14]
• Bezoar/foreign body — psychiatric history, prior gastric surgery [14]

9. Past Medical History

• Prior abdominal surgeries — type, number, and timing are critical [3]
• Prior SBO episodes and management (operative vs. nonoperative)
• Inflammatory bowel disease, diverticular disease
• Malignancy history (primary GI or metastatic)
• Hernia history (inguinal, ventral, incisional)
• Bariatric surgery (especially Roux-en-Y)
• Radiation therapy to abdomen/pelvis
• Chronic conditions affecting management: heart failure, CKD, coagulopathy

10. Physical Exam

• Vitals: tachycardia, hypotension, fever — signs of dehydration, sepsis, or strangulation [1][3]
• Abdomen:
  • Distension — hallmark finding (OR 2.43 for surgical intervention) [15]
  • Tympany to percussion [10]
  • Bowel sounds: high-pitched, tinkling (early/partial) → absent (late/complete) [1][5]
  • Tenderness: diffuse vs. focal; peritoneal signs (guarding, rigidity, rebound) suggest strangulation [1]
  • Asymmetric distension may suggest closed-loop obstruction [9]
• Hernia exam: thorough evaluation of all hernia sites — inguinal, femoral, umbilical, incisional, obturator [3][16]
• Rectal exam: empty rectal vault supports complete obstruction; occult blood (ischemia/malignancy)
• Dehydration signs: dry mucous membranes, poor skin turgor, orthostasis [1]

11. Lab Studies

Key pearl: Normal lactate and WBC do not exclude ischemia — sensitivity of clinical/lab indicators for strangulation is only ~40–50%. [3][16]

12. Imaging

First-line: CT abdomen/pelvis with IV contrast

• Sensitivity 91%, specificity 89% for SBO diagnosis; negative predictive value ~100% [2][19]
• Identifies transition point (93%), etiology (80–91%), and complications [3]
• IV contrast recommended to assess bowel wall perfusion; even with allergy, pretreat and administer if possible [2]
• Oral contrast generally not recommended in the emergent setting (aspiration risk) [2]

CT findings of SBO:

• Dilated small bowel >3 cm with transition point and decompressed distal bowel [2]
• Decompressed colon [3]
• Small bowel feces sign (particulate matter in dilated bowel — its absence predicts failure of conservative management, OR 5.23) [7][20]

CT findings suggesting ischemia/strangulation (mandate urgent surgical consultation): [21-22]

• Reduced bowel wall enhancement (specificity 92%, DOR 15.8) [21]
• Increased unenhanced bowel wall attenuation (specificity 98%, DOR 30.5) [21]
• Diffuse mesenteric haziness (specificity 89%, DOR 22.3) [21]
• Closed-loop configuration (specificity 85%, DOR 19.6) [21]
• Mesenteric venous congestion, free fluid, pneumatosis, portal venous gas [3][5]
• Whirl sign (mesenteric volvulus) [3]

Plain radiographs (AXR):

• Sensitivity 60–93%; cannot exclude SBO [2][4]
• Useful for: air-fluid levels, free air (perforation), serial monitoring
• Adequate as initial screen if CT unavailable; free air warrants immediate surgical exploration [2]

Ultrasound: Emerging role in ED; can identify dilated fluid-filled loops and peristalsis; operator-dependent [4]

13. Special Tests

• Gastrografin challenge: 100 mL undiluted via NGT → abdominal XR at 8–24 hours; contrast reaching colon/rectum predicts successful conservative management; both diagnostic and therapeutic (osmotic effect draws fluid into lumen, stimulates peristalsis) [3][11-12]
• Angers CT Score: Radiological scoring system incorporating beak sign, closed loop, intraperitoneal fluid, mesenteric haziness, mesenteric fluid, and bowel diameter >40 mm; score ≥5 predicts failure of conservative management (OR 2.39) [23]
• Point-of-care ultrasound (POCUS): Dilated, fluid-filled small bowel loops with back-and-forth peristalsis; can expedite ED diagnosis [4]

14. ECG

• ECG is not diagnostic for SBO but should be obtained in:
  • Patients with tachycardia or hemodynamic instability
  • Elderly patients to evaluate for atrial fibrillation (risk factor for mesenteric ischemia in the differential)
  • Preoperative assessment
• Electrolyte abnormalities (hypokalemia, hypomagnesemia) from vomiting/NG losses may cause QT prolongation, U waves, or arrhythmias
• Rule out acute coronary syndrome in elderly patients presenting with epigastric pain

15. Assessment

Severity stratification — the key clinical distinctions:

• Partial vs. complete obstruction: Complete obstruction has higher failure rate of conservative management (OR 4.1) and higher resection rates [3][6]
• Simple vs. complicated (strangulated/ischemic): Ischemia increases mortality from ~3% to 25–30% [1][5]
• Adhesive vs. non-adhesive etiology: Non-adhesive causes (hernia, malignancy, internal hernia) have higher strangulation rates (33% for hernia vs. 9% for adhesions) [2]

Predictors of failed conservative management: [6][17]

• Absence of flatus (OR 3.3), fever (OR 2.8), complete obstruction (OR 4.1), free fluid on CT (OR 3.7)
• Lack of small bowel feces sign, mesenteric haziness, transition point on CT [17][20]
• ≥3 risk factors predict failure with 84% sensitivity [6]

Typical vs. atypical presentations:

• Classic tetrad: colicky abdominal pain + nausea/vomiting + distension + obstipation [1]
• Atypical: watery diarrhea (partial SBO mimicking gastroenteritis); minimal pain in elderly; absence of classic signs in post-Roux-en-Y internal hernia [2][12]

16. Treatment Plan

Initial stabilization (all patients):

• IV fluid resuscitation: Lactated Ringer preferred; replace NG output (0.5 mL crystalloid per 1 mL output above 1000 mL) [2]
• NGT decompression: For significant distension and vomiting; low intermittent suction [4][12]
• NPO/bowel rest [1]
• Electrolyte correction: Monitor and replace K⁺, Mg²⁺, PO₄³⁻ daily (deficiencies worsen hypoperistalsis) [2]
• Foley catheter for I&O monitoring [2]
• Analgesia: IV acetaminophen, ketorolac; minimize opioids
• DVT prophylaxis

Nonoperative management (appropriate for hemodynamically stable patients without signs of ischemia/peritonitis):

• Successful in 65–85% of adhesive SBO [2-3]
• Most patients improve within 2–3 days [3][7]
• Gastrografin should be considered if partial SBO has not resolved in 48 hours — therapeutic and diagnostic [3]
• Serial abdominal exams and labs (q6–8h) to monitor for clinical deterioration [3]
• Conservative trial should not exceed 3 days — each day of delay increases odds of bowel resection by 20% [7]

Operative management — indications:

• Peritonitis, hemodynamic instability, clinical deterioration (EAST Level 1) [3]
• CT findings of ischemia, closed-loop obstruction, volvulus [3][5]
• Suspected internal hernia, irreducible hernia, neoplasm [2]
• Failure of nonoperative management by days 3–5 [3]
• Early surgery (<24 hours) in appropriately selected patients reduces mortality (RR 0.53), bowel resection rates (RR 0.56), and complications (RR 0.62) [6]
• Laparoscopic approach is viable in selected cases with decreased morbidity and shorter LOS [3]

Antibiotics: Gram-negative and anaerobic coverage (e.g., piperacillin-tazobactam or cefazolin + metronidazole) if fever, leukocytosis, or suspected ischemia [10]

17. Disposition

Admission (virtually all SBO patients):

• Admit to a surgical service — associated with shorter LOS, lower charges, and lower mortality compared to medical service admission (EAST Level 3) [3]
• ICU admission for hemodynamic instability, sepsis, or perioperative management

Observation indications:

Surgical consultation triggers:

• All confirmed SBO should have early surgical consultation [2][4]
• Emergent consultation: peritonitis, hemodynamic instability, CT evidence of ischemia/closed-loop/volvulus [3]
• Urgent consultation: complete obstruction, failure to improve with conservative management

Discharge criteria (rare from ED):

18. Follow Up / Return Precautions

Follow-up timing:

• Surgical follow-up within 1–2 weeks after discharge
• Earlier if managed nonoperatively (higher recurrence rate and shorter time to readmission vs. operative management) [2]

Return precautions — instruct patients to return immediately for:

• Recurrence of abdominal pain, vomiting, or distension
• Inability to pass gas or have bowel movements
• Fever or chills
• Bloody stool or vomit

Patient counseling:

• Adhesive SBO recurrence rate is ~20% at 5 years with nonoperative management, increasing with each subsequent episode; operative management reduces recurrence by ~50% [24]
• Advance diet slowly; avoid large meals initially
• Stay well hydrated
• Avoid constipation-promoting medications when possible

The following figure from Behman et al. illustrates the progressive increase in recurrence risk with nonoperative management versus the protective effect of surgical intervention across successive SBO episodes: