An abdominal ultrasound to assess for small bowel obstruction (SBO) is performed with the curvilinear low-frequency probe, scanning the most dependent portions of the abdomen as fluid-filled loops will be most easily identified in these areas. The exact pattern is not important as long as one ensures that the entire dependant portions of the abdomen are examined.
There are several signs to look for on ultrasound to make the diagnosis of SBO, the first of which is dilated loops of bowel >25 mm (Figure 1). Another sign is the “to and fro” peristalsis of bowel contents, also called dysfunctional peristalsis. In addition, clinicians should look for fingerlike projections from the inner wall of the intestine also referred to as the “keyboard” sign (Figure 2). These projections, the plicae circulares, become apparent in cases of SBO.
Ultrasound, readily available in many EDs, can help emergency physicians (EPs) to rapidly diagnosis SBO, as well as herniated bowel and fascial defects (Figure 3). This imaging modality should be used in a similar diagnostic manner as abdominal X-ray.
A recent study by Jang et al1 evaluating a sample of symptomatic ED patients showed 81% to 97% specificity of ultrasound in detecting obstruction (depending upon the ultrasound finding employed) compared to abdominal X-ray at 66%.1 This study further reported that dilated loops of bowel on ultrasound had a sensitivity of 91% and a specificity of 84%. In addition, a meta-analysis by Taylor and Lalani2 looking at bedside ultrasound in the ED showed a positive likelihood ratio of 9.55.
Even though computed tomography remains the gold standard for the diagnosis for SBO, the studies summarized above demonstrate the benefits of using bedside ultrasound in the ED setting. In addition to improving diagnostic capabilities, this modality assists the EP in quickly diagnosing this condition.
Dr Taylor is an assistant professor and director of postgraduate medical education, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia. Dr Meer is an assistant professor and director of emergency ultrasound, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia. Dr Beck is an assistant professor, department of emergency medicine, Emory University School of Medicine, Atlanta, Georgia.