Small bowel obstruction

Background

• Mechanical obstruction of the small intestine preventing normal passage of intestinal contents
• Adhesions from prior surgery are the most common cause (60-75% of all SBO)
• Second most common cause: incarcerated hernia (~15%)
• Other causes: malignancy, Crohn's disease, intussusception, volvulus, gallstone ileus, foreign body, stricture
• Closed-loop obstruction: segment of bowel obstructed at two points → rapid progression to strangulation and ischemia
• SBO accounts for ~15% of ED visits for acute abdominal pain
• Mortality: <5% for simple SBO; up to 25% for strangulated SBO

Classification

• Partial: some gas/fluid passes through → flatus may be present
• Complete: no passage of gas or stool
• Simple: obstruction without vascular compromise
• Strangulated: obstruction with compromised blood supply → ischemia → necrosis → perforation

Clinical Features

• Crampy, intermittent abdominal pain (colicky; occurs in waves)
• Nausea and vomiting (the more proximal the obstruction, the earlier and more prominent the vomiting)
• Obstipation (absence of flatus and stool) — complete obstruction
• Abdominal distension (more prominent with distal obstruction)
• High-pitched, hyperactive bowel sounds → late: absent bowel sounds (ileus from ischemia)
• Prior surgical history — ask about ALL prior abdominal/pelvic operations
• Tachycardia, dehydration from third-spacing and vomiting

Signs of Strangulation (Surgical Emergency)

• Constant, severe pain (no longer colicky)
• Fever
• Peritoneal signs (rebound, guarding)
• Tachycardia, hypotension
• Leukocytosis with left shift
• Elevated lactate
• No single clinical or lab finding reliably rules out strangulation

Differential Diagnosis

• Large bowel obstruction
• Paralytic ileus (postoperative, metabolic, medication-related)
• Mesenteric ischemia
• Volvulus
• Incarcerated hernia
• Appendicitis
• Pancreatitis
• Pseudo-obstruction (Ogilvie syndrome — large bowel)
• Crohn's disease flare

Evaluation

Labs

• BMP: electrolytes (hypokalemia, metabolic alkalosis from vomiting), BUN/Cr (dehydration), bicarbonate
• CBC: leukocytosis (consider strangulation if WBC >15,000)
• Lactate: elevated suggests bowel ischemia (but normal lactate does NOT exclude strangulation)
• Lipase: rule out pancreatitis
• Type and screen if surgery likely

Imaging

Abdominal X-ray

• Sensitivity ~60-70% for SBO
• Findings: dilated small bowel loops (> 3 cm), air-fluid levels on upright, absence of colonic gas
• Three film series (supine, upright, CXR): may show free air if perforated
• Normal X-ray does NOT exclude SBO

CT Abdomen/Pelvis with IV Contrast (Test of Choice)

• Sensitivity 90-95% for SBO
• Identifies:
  • Transition point (dilated proximal → decompressed distal bowel)
  • Cause of obstruction (adhesion, hernia, mass, volvulus)
  • Signs of strangulation: bowel wall thickening, mesenteric haziness/fluid, decreased/absent bowel wall enhancement, pneumatosis intestinalis, portal venous gas
• Oral contrast NOT needed (pooled intraluminal fluid serves as natural contrast)
• Small bowel feces sign: particulate material in dilated SB (distal/complete obstruction)

Management

Initial Resuscitation

• NPO
• Aggressive IV fluid resuscitation (NS or LR) — patients are often significantly volume depleted
• Electrolyte correction (K, Mg replacement)
• NG tube decompression: for persistent vomiting, significant distension
• Pain control: IV opioids as needed; ketorolac
• Antiemetics: ondansetron 4 mg IV

Nonoperative Management (Adhesive SBO without Strangulation)

• Trial of nonoperative management for partial, adhesive SBO without signs of strangulation
• NG decompression + IV fluids + bowel rest
• Water-soluble contrast challenge (Gastrografin):
  • 100 mL PO/via NGT
  • If contrast reaches colon by 24 hours → predicts resolution with nonoperative management (sensitivity ~97%)
  • May also have therapeutic effect (osmotic — draws fluid into lumen, stimulates peristalsis)
• ~70-80% of adhesive SBO resolves with conservative management
• Failure of nonoperative trial: no improvement in 24-72 hours → surgery

Surgical Management

• Indications for emergent surgery:
  • Complete obstruction
  • Signs of strangulation/peritonitis
  • Incarcerated/strangulated hernia
  • Closed-loop obstruction on CT
  • Hemodynamic instability not responding to resuscitation
  • Failure of nonoperative management
• Surgical consult early for all cases (even if initially managed conservatively)

Disposition

• Admit all patients with SBO
• Surgical consultation in ED for all patients
• ICU if septic, hemodynamically unstable, or peritonitic
• Serial abdominal exams every 4-8 hours
• Repeat imaging if clinical deterioration

See Also

• Large bowel obstruction
• Ileus
• Volvulus
• Incarcerated hernia
• Mesenteric ischemia
• Abdominal pain

References

• Maung AA, et al. Evaluation and management of small-bowel obstruction: an Eastern Association for the Surgery of Trauma practice management guideline. J Trauma Acute Care Surg. 2012;73(5 Suppl 4):S362-369. PMID 23114494
• Defined by ten Broek RP, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction. World J Emerg Surg. 2018;13:24. PMID 29946347
• Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013;20(6):528-544. PMID 23758299