Small bowel obstruction

(Redirected from Intestinal perforation)


Small bowel anatomy with surrounding structures.
  • Small bowel obstruction without history of surgery or hernia is malignancy until proven otherwise
  • "Never let the sun rise or set on a small bowel obstruction"


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
    • 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)
  • Abnormal bowel sounds
    • Studies suggest that auscultating bowel sounds is not clinically useful to differentiate between normal and pathologic[2]

Differential Diagnosis

Diffuse Abdominal pain



Upright abdominal X-ray demonstrating a small bowel obstruction. Note multiple air fluid levels.
Small bowel obstruction
Ultrasound shows dilated, non-compressible loops of bowel with characteristic to-and-fro motion of bowel contents[3]
Ultrasound shows dilated loops of bowel steep precipice and tumbling feces[4]
A small bowel obstruction as seen on CT.


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


  • Use the 3/6/9 rule for bowel imaging
    • Upper limit of 3cm for small bowel, 6cm for colon, and 9cm for cecum
  • Xray
    • Acute Abdominal Series
    • Upright chest film: rule out free air
    • Upright abdominal film: air-fluid levels:
    • Supine abdominal 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[5]
    • Small bowel diameter ≥3cm is associated with obstruction
      • 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 patient does not tolerate upright position left lateral decub abdominal 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
      • Modern CT Scanner (0.75mm slices): Sen 96%, Spec 100%, +LR infinity -LR 0.04
      • Historical CT scanner meta-analysis: Sen 87% Spec 81%, +LR 3.6 -LR 0.18
  • Ultrasound for SBO
    • Sen 97%, Spec 90%, +LR 9.5, -LR 0.04 (four studies, 2 done by EM residents and 2 by radiology residents)
  • MRI for SBO - Sen 92%, Spec 89% +LR 6.7 -LR 0.11


Volume resuscitation

  • IV fluid resuscitation with electrolyte repletion
  • Assessment of need for operative vs nonoperative management

Nasogastric tube

  • 14 French
    • Intermittent low wall suction
  • Nasogastric fluid losses can be replaced with NS + KCL (30-40 meq)
  • There is some evidence to suggest nasogastric tube decompression was not associated with decreased bowel ischemia or need for surgery[6]

Oral Contrast

  • Both diagnostic and therapeutic (draws water into the bowel stimulating peristalsis)
  • Associated with decreased hospital stay, more rapid resolution of symptoms
  • Repeat CT scan may be helpful to detect early signs of bowel ischemia
    • Repeat plain films are not helpful (only detect perforation)

Gastrografin PO

  • Alternative to operative management if early obstructive process
  • Gastrografin through NG or OG decreases bowel wall edema and increases bowel motility[7]
    • Diagnostic and therapeutic[8]
    • 100 cc of gastrografin through NG tube
    • Transit may be observed through serial radiographs
      • Contrast within the large bowel within 24 hrs suggest partial SBO
      • Contrast failing to reach large bowel within 24-48 hrs suggests complete obstruction, requiring laparotomy
    • Therapeutic, may reduce necessary operative rate by ~75%[9]
  • Avoid barium as it becomes inspissated in bowel, causing complete obstruction[10]
    • Gastrografin is water-soluble and relatively safer if perforation occurs

Non-operative Management vs. Operative

  • 75% of patients are amenable to non-operative management

Operative Management

  • 25% of patients admitted for SBO require surgery
  • Surgery is indicated for patients with:
    • Increasing pain, distention, or peristent high NGT output
    • Necrotic bowel
    • Closed-loop obstruction (incarcerated hernia, small bowel volvulus, cecal volvulus)
    • Fever, leukocytosis, peritonitis



  • Admit


  • In the context of advancing malignancy with widespread peritoneal metastases, bowel obstruction is common and often indicates a poor prognosis
  • A less interventional and more comfort based approach to treatment may be appropriate
  • See Malignant bowel obstruction for details

See Also


  1. Roline CE and Reardon RF. Disorders of the Small Intestine. Rosen's. Edition 8. Chapter 92. 2014. 1216-1224.
  2. Felder S, Margel D, Murrell Z, et al. Usefulness of Bowel Sound Auscultation: A Prospective Evaluation. J Surg. 2014; 71(5):768–773.
  5. Maglinte DDT, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR 1996; 167:1451-1455
  6. Berman, DJ et al. Nasogastric decompression not associated with a reduction in surgery or bowel ischemia for acute small bowel obstruction. Am J Emerg Med. 2017 Dec;35(12):1919-1921.PMID: 28912083
  7. Assalia A, Schein M, Kopelman D, et al. Therapeutic effect of oral Gastrografin in adhesive, partial small-bowel obstruction: A prospective randomized trial. Surgery 1994; 115: 433-437.
  8. Chen SC, Lin FY, Lee PH, et al. Water-soluble contrast study predicts the need for early surgery in adhesive small bowel obstruction. Br J Surg 1998; 85: 1692-1694.
  9. Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).
  10. Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).