Tips and Tricks: Clinical Ultrasound for Small Bowel Obstruction – A Better Diagnostic Tool?
Alice Chao, MD and Laleh Gharahbaghian, MD, FACEP
Small bowel obstruction (SBO) is a common challenge for the emergency physician (EP). It is estimated that approximately 300,000 annual hospitalizations in the United States are due to SBO. These patients comprise approximately 2% of all abdominal pain visits to the emergency department (ED). The history and physical exam are important to aid in the diagnosis of SBO. Abdominal pain, abdominal distension, nausea, vomiting, and past history of intra-abdominal surgeries causing adhesions should raise the EP’s suspicion.
Diagnostic imaging for SBO currently includes plain radiographs to assess for air-fluid levels and dilated loops of bowel, as well as computed tomography (CT) to detect the location of the transition point and potential causes. Magnetic resonance imaging (MRI) is considered by some radiology experts to be the best imaging tool, but requires significant time out of the ED, is not readily available, and has a significantly increased cost.
The use of ultrasound (US) for the diagnosis of SBO is a relatively new concept in the United States. However, US has already received quite a bit of attention due to its superiority in diagnosing SBO. In a recent meta-analysis, Taylor reported that US had better test characteristics than radiographs, CT or MRI. The LR + for was 14.1 for radiology US and 9.55 for clinical US, compared to 1.6 for radiographs, 3.6 for CT, and 6.8 for MRI. The ability to perform at the bedside, visualize abnormal peristalsis, low cost, and the lack of contrast or radiation exposure, makes ultrasound an invaluable adjunct.
Bedside US for the diagnosis of SBO can be learned and successfully performed by EPs after limited training. The sonographer may use either the curvilinear or phased-array probe for detection of SBO. High-frequency linear probes have also been used to successfully diagnose intestinal obstructions. Multiple regions of the abdomen should be assessed, including the epigastrium, bilateral colic gutters, and suprapubic regions.
There are several abnormalities to look for on ultrasound when evaluating for intestinal obstruction. Fluid-filled small bowel loops may be dilated to > 2.5-3cm.
Distinguishing between the jejunum and ileum is possible, as the jejunum will have prominent and numerous valvulae conniventes, whereas the ileum will lack valvulae conniventes.
There may also be increased intestinal contents (fluid and echogenic material within the lumen of the bowel), or increased peristalsis of the dilated segment, as evidenced by the to-and-fro or whirling motion of the bowel contents (Video). The most sensitive and specific sonographic finding is the presence of dilated small bowel loops. Click Here for Video.
The severity of the obstruction may also be assessed with US. Fluid-filled distended bowel with extraluminal free fluid between bowel loops, no peristalsis, and/or bowel wall thickening > 3mm may suggest bowel ischemia/infarction requiring even more urgent surgical evaluation and intervention.
There are some limitations to diagnosing SBO with ultrasonography. Partial SBOs may be more difficult to identify on US. Though possible, it is more challenging to identify the location of obstruction and the transition point. Finally, the specific cause of the SBO may not be adequately evaluated. Rapid identification of SBO on bedside ED US can expedite treatment such as nasogastric tube placement, which will aid in symptomatic relief and progression of disease, as well as notifying the appropriate consultation service. US for SBO may be the most exciting new application of ultrasound coming to the bedside!
- Irvine TT. Abdominal pain: a surgical audit of 1190 emergency admissions. Br J Surg. 1989;76:1121-5.
- Hastings TS, Powers RD. Abdominal pain in the ED: a 35 year retrospective. Am J Emerg Med. 2011;29:711-6.
- Jang TB, Chandler D, Kaji AH. Bedside ultrasonography for the detection of small bowel obstruction in the emergency department. Emerg Med J. 2011;28:676-8.
- Taylor MR, Lalani N. Adult Small Bowel Obstruction. Acad Emerg Med. 2013;20:528-44.
- Carpenter CR, Pines JM. The End of X-rays for Suspected Small Bowel Obstruction? Using Evidence-based Diagnostics to Inform Best Practices in Emergency Medicine. Acad Emerg Med. 2013;20:618-20.
- Unluer EE, et al. Ultrasonography by emergency medicine and radiology residents for the diagnosis of small bowel obstruction. Eur J of Emerg Med. 2010;17:260-4.
- Silva AC, Pimenta M, Guimaraes LS. Small Bowel Obstruction: What to Look For. RadioGraphics. 2009;29:423-39.
Back to Newsletter