SBOohhh no

Written by: Dr. Arrianna Mohammad

Edited by: Dr. Joann Hsu

HPI

73 year old female with a history of Afib on Eliquis and seizure disorder who presents for abdominal pain and vomiting x 1 week. Denies passing any gas for the past week as well and vomits about 6x a day, NBNB. Denies fever, cough, chest pain or SOB. Denies colonoscopy or any surgeries in the past. Also noted a mass in the right groin area during this time.


PE

ABDOMEN AND GI: Soft; (+) mild generalized tenderness, (-) guarding, (-) rebound, (+) distention, (+) firm mass noted in right groin, (-) reducible, (-) overlying skin changes


Bedside ultrasound of the abdomen shows:


Signs of SBO on US: Summary

  1. Bowel diameter >/= 2.5 cm

  2. Abnormal peristalsis:

    • To and fro movement

  3. Keyboard sign (plicae circulares) 

    • Confirms that you’re looking at small bowel (vs large bowel)

  4. Bowel wall thickness >/= 3 mm

  5. Extra-luminal fluid 




1)Bowel size

  • The upper limit of normal diameter of the bowel is generally accepted as 3cm for the small bowel, 6cm for the colon and 9cm for the cecum (3/6/9 rule)


2)Abnormal Peristalsis

  • Abnormal peristalsis in SBO is generally described as “to-and-fro” with a shuttling or swirling appearance to the luminal contents. 

Normal peristalsis

Abnormal to and fro peristalsis


3)Keyboard sign

  • Visualization of the plicae circularis which is only present in small bowel, not large bowel

  • More clearly visible when the loops are spread out by liquid and when there’s bowel wall edema

  • Large bowel has haustra which are much further apart than plicae

In this same clip, notice the the finger like projections into the lumen (the plicae) that mark the small intestine


4)Bowel wall thickness

  • Normal adult bowel wall thickness is typically </= 3mm

Measurement 3 shows the thickened bowel wall



5)Extra-luminal fluid 

  • Anechoic triangle between bowel loops = Collection of free fluid interspersed between bowel loops.

  • You can see in all the SBO clips above that there are triangles of fluid in between bowel loops.

  • Connotes high grade obstruction (and therefore worse prognosis)

    • High grade obstruction = complete obstruction, more likely to need surgical intervention


Extraluminal triangles of fluid

Here are some more clips from this patient:

Dilated small bowel loops see as soon as you place the probe on the patient

some more examples of extraluminal fluid, dilated bowel loops


Imaging for SBO

  • CT: Gold standard.

    • Sensitivities of 93%-96% and specificities of 93%-100% for the diagnosis of SBO

  • MRI: similar accuracy as CT, less accessible from the ED

  • Ultrasound: may be used as an adjunct to CT

    • Sensitivity 92.4% with 95% CI 89.0% to 94.7%) and specificity 96.6% with 95% CI 88.4% to 99.1% for SBO

    • Can be performed at bedside and interpreted immediately by the ED provider

    • No radiation

    • Accessible, fast













References:

Small bowel obstruction: Diagnosis by ultrasonography (aliem.com)

Booth EM