Small bowel obstruction

Background

• SBO without hx of surgery, no hernia is malignancy until proven otherwise
• "Never let the sun rise or set on a small bowel obstruction"

Causes

• Adhesions (Hx of previous abdominal surgeries +LR 3.86 and -LR 0.19)
• Hernia
• Malignancy
• Intraluminal strictures
  • Crohn's disease
  • Radiation therapy
  • Mesenteric ischemia
• Intussusception (due to lymphoma as lead point)
• Foreign body (bezoars)
• Trauma (duodenal hematoma)
• Gallstone ileus

Clinical Features

• Abdominal pain
  • Colicky
  • Periumbilical or diffuse
  • Paroxysms of pain occur q5min
• Vomiting
  • More common in proximal than distal obstruction
  • Bilious (proximal) or feculent (distal ileal)
    • Abdominal pain relieved with vomiting positively predictive +LR (4.50-2.82) -LR (0.78-0.35)
• Abdominal distention
  • Seen more in distal than proximal obstruction
  • +LR (16.8-5.64) -LR (0.43-0.34)
• Inability to pass flatus
  • Pts may pass flatus/stool initially
    • Takes 12-24hrs for colon to empty
    • History of constipation +LR 8.8 and -LR 0.59
• Dehydration
• Anorexia
• Ischemia (increased intraluminal pressure initially leads to venous obstruction, progresses to frank arterial ischemia)
  • Fever
  • Leukocytosis
• Abnormal Bowel sounds
  • Studies suggest that auscultating bowel sounds is not clinically useful to differentiate between normal and pathologic

Differential Diagnosis

Diffuse Abdominal pain

• Abdominal aortic aneurysm
  • Aortocaval fistula
• Acute gastroenteritis
• Aortoenteric fisulta
• Appendicitis (early)
• Bowel obstruction
  • Large bowel obstruction
    • Ogilvie's syndrome
  • Small bowel obstruction
  • Malignant bowel obstruction
• Bowel perforation
• Diabetic ketoacidosis
• Gastroparesis
• Hernia
• Hypercalcemia
• Inflammatory bowel disease
• Mesenteric ischemia
  • Mesenteric vein thrombosis
• Pancreatitis
• Peritonitis
• Sickle cell crisis
• Spontaneous bacterial peritonitis
• Volvulus

Diagnosis

Labs

• CBC
  • WBC >20K suggests bowel gangrene, abscess, or peritonitis
  • WBC >40K suggests mesenteric vascular occlusion
• Chemistry - degree of dehydration, evidence of ischemia (acidosis)
• Lactate - Sn (90-100%), though not Sp marker of strangulation

Imaging

• Xray
  • Acute Abdominal Series
  • Upright chest film: rule out free air
  • Upright abd film: air-fluid levels:
    

    Peds SBO
  • Supine abd film: width of bowel loops most visible (estimate of amount of distention)
  • String of pearls sign (small pockets of gas along the small bowel that are trapped between the valvulae conniventes) is virtually diagnostic
    • Sen 75% Spec 66% +LR 1.6 -LR 0.43
    • Air in colon or rectum makes complete obstruction less likely (esp if symptoms >24hr)
    • If pt does not tolerate upright position left lateral decub abd film can substitute
• CT A/P with IV contrast
  • Consider if plain films are non-diagnostic
  • Can show closed-loop obstruction, evidence of ischemia
  • Per American College of Radiology PO contrast is no longer indicated