Small Bowel Obstruction (SBO)

Risk factors

• Prior abdominal/pelvic surgery (adhesions — 60-75% of adult SBO)
• Hernia (incarcerated inguinal, femoral, ventral, internal — 2nd most common cause)
• Malignancy (primary or metastatic; carcinomatosis)
• Inflammatory bowel disease (Crohn strictures)
• Intussusception (rare in adults — exclude lead point such as polyp or tumor)
• Volvulus
• Radiation enteritis
• Foreign body, bezoar, gallstone ileus
• Congenital (Meckel diverticulum, Ladd bands, intestinal atresia)

Pathophysiology

Mechanical obstruction causes proximal dilation with accumulation of fluid, gas, and swallowed air. Initial increase in peristalsis (high-pitched bowel sounds) gives way to ileus and quiet abdomen. Bowel wall edema and increased intraluminal pressure compromise venous outflow first, then arterial supply → ischemia, necrosis, perforation. Third-spacing causes hypovolemia and electrolyte derangement (hypokalemic, hypochloremic metabolic alkalosis from emesis).

Clinical presentation

Differential diagnosis

• Paralytic ileus (post-operative, post-laparotomy, opioids, electrolytes) — No mechanical obstruction; diffuse gas distribution including colon; treat underlying cause; supportive
• Large bowel obstruction (volvulus, mass, fecal impaction) — Distension dominant; haustral markings; coffee-bean sign in sigmoid volvulus
• Acute mesenteric ischemia — Pain out of proportion, atrial fibrillation, elevated lactate; CT angiography
• Acute pancreatitis — Lipase >3× ULN; epigastric pain to back
• Acute cholecystitis / appendicitis — Focal tenderness, fever, leukocytosis
• Diabetic gastroparesis — Chronic vomiting, early satiety, diabetic history; gastric emptying study
• Ogilvie syndrome (colonic pseudo-obstruction) — Massive colonic dilation in elderly/hospitalized without mechanical obstruction; neostigmine treatment
• Constipation / fecal impaction — Older patient, opioid use; rectal exam

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A["Suspected SBO<br/>crampy pain, vomiting,<br/>distension, obstipation"] --> B["Resuscitate: NPO, NG tube,<br/>IV fluids, correct K+/electrolytes"]
  B --> C["CT abdomen/pelvis<br/>with IV contrast"]
  C --> D{"Peritonitis, strangulation,<br/>closed loop, or ischemia on CT?"}
  D -->|Yes| E["Emergent surgery"]
  D -->|No| F["Non-operative trial (partial or complete SBO)<br/>NG decompression + Gastrografin challenge<br/>serial exams up to 48-72 h"]
  F --> G{"Contrast in colon by 24 h<br/>and resolving by 48-72 h?"}
  G -->|Yes| J["Diet advancement<br/>+ discharge"]
  G -->|No| K["Surgical exploration"]

Treatment

Complications

• Strangulation, ischemia, perforation
• Sepsis, septic shock
• Bowel necrosis requiring resection
• Short bowel syndrome (extensive resection)
• Aspiration pneumonia (from vomiting)
• Volume depletion, electrolyte derangement, AKI
• Recurrent SBO
• Postoperative ileus, adhesions
• Mortality: 2-10% simple obstruction; up to 30% with strangulation/delayed surgery

PANCE pearls

• Always examine ALL hernia orifices in a patient with SBO — incarcerated hernia is the 2nd most common cause and the most easily missed.
• Hypokalemic, hypochloremic metabolic alkalosis is the classic acid-base disturbance from upper GI fluid losses.
• CT is the modality of choice — identifies transition point, cause, closed loop, and signs of ischemia.
• Gastrografin (water-soluble contrast) challenge is both diagnostic and therapeutic — passage to colon within 24 h predicts successful non-operative management of adhesive SBO.
• STRANGULATION signs: severe constant pain (not crampy), fever, leukocytosis, lactate elevation, peritonitis, hemodynamic instability — immediate operation.
• Closed-loop obstruction (bowel obstructed at two adjacent points) → high risk of strangulation; surgical emergency.
• Virgin abdomen (no prior surgery) with SBO — strongly consider alternative cause (hernia, malignancy, Crohn, intussusception); use CT to find the cause; mandatory exploration is no longer the rule, and stable patients without closed loop, hernia, or mass may have a non-operative trial.
• Bilious vomiting suggests proximal obstruction; feculent vomiting suggests distal/long-standing obstruction.
• Adhesive SBO: 65-80% resolve without surgery; failure to resolve by 48-72 h warrants operation.
• Gallstone ileus (Rigler triad): pneumobilia + SBO + ectopic gallstone — treat with enterolithotomy; cholecystectomy ± fistula repair often staged.
• Bezoars (phytobezoars from fiber, trichobezoars from hair) — endoscopic disruption ± enzymatic dissolution (Coca-Cola for phytobezoar).

References

• EAST 2012 — Maung AA, Johnson DC, Piper GL, 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-S369
• WSES 2017 — Ten Broek RPG et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO). World J Emerg Surg 2018;13:24
• Gastrografin Trial — Branco BC et al. Systematic review and meta-analysis of the diagnostic and therapeutic role of water-soluble contrast agent in adhesive SBO. Br J Surg 2010;97:470-478