Ultrasound for Small Bowel Obstruction


By Stephen Alerhand, MD
EM Resident Physician
Icahn School of Medicine at Mount Sinai

Edited by Alex Koyfman, MD (@EMHighAK)


Case History

67 year-old M PMH CAD, DM, CHF, rectal adenocarcinoma s/p partial colectomy p/w 2 days of increasing abdominal distention and pain, with minimal stool passage and flatus. He looks very uncomfortable on exam and has severe diffuse abdominal tenderness.

T 98.7, HR 105, BP 110/76, RR 16, O2 sat 100% RA

Given the patient’s history of abdominal surgery, current pain/distention/lack of stool passage, and severe tenderness on exam, you are concerned for a bowel obstruction. This patient carries several other co-morbidities and appears extremely uncomfortable, and your crowded urban hospital has been ED boarding all weekend. Your attending thus asks you to consult GenSurg to get them on board and hopefully admit to their service early.

You relay the story to the consultant. Unsurprisingly, he asks for the CT scan and says the dispo will be pending those results.

Over the next 30 minutes, this patient continues to require several doses of IV pain medicine and close attention from the already-overburdened nursing staff. It is essentially assumed that this patient is going up to the Surgical service anyway upon the CT result. Hearing this dilemma, the neighborhood friendly Ultrasound fellow strolls in carrying a set of papers in each hand.

He briefly summarizes the literature, brings the resident and Consult to the bedside, and demonstrates significant bowel loop distention by US (as explained further below). A discussion is held and the Surgical consult feels compelled to agree that the entire clinical picture and ultrasound demonstration together paint a clearer picture. His team admits the patient and will take him straight upstairs from the CT scan.

Both the nursing staff and ED administrators wandering around give the US fellow a nice pat on the back. Everyone benefits: ED flow, overburdened nurses, other patients requiring attention in the ED, and most of all, the patient himself.


Paper #1
Schmutz, G.R. et al. Small bowel obstruction: role and contribution of sonography. Eur Radiol 7, 1054-1058.


  • SBO diagnosed by plain films in 5-60% of cases, equivocal in 10-20%

Type of Study:

  • Prospective, n=123 patients suspected of SBO


  • Included: clinical signs and/or symptoms compatible with SBO, SB fluid levels on upright abdominal films w/o any non-obstructive cause
  • Excluded: abdominal surgery <30 days ago, abdominal trauma
  • US dx: >25 mm in jejunum, >15 mm in ileum, over more than three loops
  • Final dx: intra-operative, pathology, other imaging, clinical follow-up


  • Sensitivity 95%, specificity 82.1%
  • Cause predicted in 62.6% of mechanical obstruction (vs. 3% with plain films) and 40.6% of small bowel ileus
  • Accuracy of 89% with US versus 71% for plain abdominal films

US for SBO I


Paper #2
Jang, Timothy B. Schindler, Danielle. Kaji, Amy H. Bedside ultrasonography for the detection of small bowel obstruction in the emergency department. Emerg Med J 2011 28:676-678.

Type of Study:

  • Prospective, n=76


  • Included: treating MD ordered CT to eval for SBO
  • US dx: proximal SBO >25 associated with collapsed distal bowel loops or decreased or absent bowel peristalsis
  • X-ray dx: multiple gas- or fluid-filled loops of dilated bowel with a small or moderate amount of colonic gas, or dilated gas- or fluid-filled loops of bowel with a gasless colon consistent with prior descriptions in the literature
  • CT used as reference standard


  • Dilated bowel had 91% sensitivity and 84% specificity for SBO
  • Decreased bowel peristalsis had 27% and 98% respectively
  • Xray had 2% sensitivity and 66.7% specificity when diagnostic, was non-diagnostic 36% of time



ED Pearls
  • CT is more expensive, confers radiation, not available 24 hrs/day everywhere, takes longer (oral contrast, CT availability), can be dangerous to transport patient away from physicians/nurses
  • US is cheaper, no radiation, performed quickly at bedside, allows frequent re-exams, no transport from clinical area
  • Can reduce need for plain abdominal films
  • Can expedite surgical consultation/treatment (NG tube, pain meds, transfer to Surg floor) prior to CT scan
  • Can improve ED flow
  • Consider replacing abdominal x-ray with bedside US


POCUS to Evaluate for SBO1
  • Select highest frequency possible based on body habitus
    • 3-5 MHz in large adults
  • Probe marker towards patient’s R side
  • Sequential graded compression in transverse plane, from RLQ to LUQ
  • Then from LLQ to RUQ in longitudinal plane
  • Gentle downward pressure applied every few cm to assess bowel compressibility
  • Look for dilated (>25 mm), non-compressible small bowel proximal to collapsed, compressible bowel
  • Secondary signs: localized bowel wall edema (>3 mm thick), free fluid within abdomen, no change during peristalsis
  • To identify transition point, follow abnormal bowel until you see normal bowel
  • Lack of compressibility (on its own w/o transition point) cannot differentiate between obstruction and ileus



Additional References
  1. Dawson, Matthew. Mallin, Mike. Introduction to Bedside Ultrasound: Volumes 1 and 2. Chapter 29: Small Bowel Obstruction.
  2. Guttman, Joshua et al. Point-of-care ultrasonography for the diagnosis of small bowel obstruction in the emergency department. CJEM. 2014 Aug 1;16(0):30-3.

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