Small Bowel Obstruction

76yo female who has had previous bowel obstructions presented to ED again with vomitting and central abdominal pain. While awaiting an AXR, US was performed. 

Curvilinear probe in the epigastrium showing a dilated loop of bowel full of echogenic material and fluid with some back and forth peristalsis (above and below)

bowel loop dilated >2.5cm

3Abdominal XR revealed dilated loops of bowel and air fluid levels. The patient was managed conservatively with no further imaging given multiple presentations and previous CTs showing obstruction with no added pathology.

​This case begs the question: can and should abdominal US replace AXR as the first line imaging. It is radiation free, available immediately at the bedside and has been shown to be easier to interpret than the often ambiguous AXR.

Jang et al (1),  in a prospective study looking at ED abdominal US in patients presenting with Sx of SBO, showed that US has a sensitivity of 91% and a specificity of 84% for the diagnosis of SBO (CT abdomen gold standard). In comparison AXR had a sensitivity of 46% and a specificity of 67%. The EPs performing the US had had all completed an intro course in ED US, had performed at least 10 prior US scans and specific to SBO US, they had a 10 min teaching session and had performed 5 scans for SBO prior to the study. Thus, this is an easily learned skill. 

Similarly, Ünlüer et al (2) compared ED vs radiology US for SBO in patients presenting with suspected SBO Sx. THEY showed a sensitivity of 98% and a specificity of 93% for ED US. Ed vs radiology US had similar accuracy. EPs performing the US had 6 hours of dedicated teaching. The gold standard was surgical dx or a benign course at FU at 1/12. 

KEY FEATURES OF SBO ON US

DILATED BOWEL (most sensitive finding)
Commonly SI loops are considered dilated if >2.5cm. Dilated loops are often filled with fluid and hyper echoic particulate material.

ABNORMAL PERISTALSIS
Seen as back and forth movement of bowel contents or swirling like in a washing machine.

SINISTER FINDINGS suggesting infarction/ perforation

1. bowel wall thickening 
>3mm

2. intraperitoneal free fluid
The greater the amount of free fluid, the more likely surgical intervention will be required (3).

3. gas within bowel wall
hyperechoic locules of gas within the bowel wall​

4. absent peristalsis
no peristalsis over 5 mins

abnormal peristalsis

free fluid between dilated loops of bowel with inadequate peristalsis.

from UScases.info: intramural gas

US can also be used to detect the cause of obstruction. However, this is time consuming a requires meticulous scanning.
So in the next patient with sx and sn of SBO: consider US first and if positive, avoid the AXR and go straight to CT to look for cause. 


Further reading

Tips and Tricks: Clinical Ultrasound for Small Bowel Obstruction – A Better Diagnostic Tool?
Alice Chao, MD and Laleh Gharahbaghian, MD, FACEP 
https://www.acep.org/Content.aspx?id=100218

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REFERENCES
1. Timothy B Jang,1,2 Danielle Schindler,1 Amy H Kaji2​ Bedside ultrasonography for the detection of small bowel obstruction in the emergency department. Emerg Med J 2011;28:676-8.

2. Unlüer EE1, Yavaşi O, Eroğlu O, Yilmaz C, Akarca FK. Ultrasonography by emergency medicine and radiology residents for the diagnosis of small bowel obstruction. ​ Eur J Emerg Med. 2010 Oct;17(5):260-4. 

3. Ashraf F Hefny, Peter Corr,1 and Fikri M Abu-Zidan The role of ultrasound in the management of intestinal obstruction.  J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 84–86.