Although there is limited research regarding the accuracy of ultrasound to evaluate SBO, initial study results are encouraging. The previously cited meta-analysis by Taylor et al3 identified six ultrasound studies, two of which were performed in the ED. In one of these two studies, Unlüer et al10 performed a prospective study that enrolled 174 patients in the ED, 90 of whom were subsequently found to have an SBO. In addition, Unlüer et al’s study found that relatively inexperienced emergency medicine (EM) residents were able to use bedside ultrasound in the diagnosis of SBO with a sensitivity of 97.7% and a specificity of 92.7%.
Another ED study by Jang et al15 enrolled 76 patients, 33 of whom were diagnosed with SBO using CT. In this study, the authors found ultrasound to have a 91% sensitivity and 84% specificity for dilated bowel, and a specificity of 98% and sensitivity of 27% for decreased peristalsis.15 Imaging in this study was performed by EM residents, who received only 10 minutes of didactic lecture.
The criteria used in the abovementioned studies varied slightly. The study by Jang et al15 used either fluid-filled dilated bowel >2.5 cm or decreased/absent forward bowel peristalsis, while the study by Unlüer et al10 defined sonographic SBO as two of the three following criteria: greater than 3 dilated loops of either jejunum (>25 mm), or of ileum (>15 mm), increased peristalsis or a collapsed colonic lumen. In cases of higher-grade obstruction, the Tanga sign, fluid seen outside of the dilated loops of bowel, has also been reported (Figure 2).16
Conclusion
There are several distinct advantages to using bedside ultrasound in cases of suspected SBO, including its lack of ionizing radiation, the ability to perform the scan rapidly, and the high accuracy rate in detecting this condition—even in the hands of providers with minimal training. In addition to its cost-effectiveness, ultrasound may be preferred in patients with relative contraindications to CT, such as pregnant patients and patients with contrast allergies. Even in patients in whom there is no contraindication to CT, ultrasound may be used to safely and quickly identify and risk-stratify those who require further imaging versus those who can be safely discharged home—or possibly even finding alternative diagnoses of acute abdominal pain (eg, acute cholecystitis, ureterolithiasis, abdominal aortic aneurysm).
Dr Avila is an attending physician and ultrasound fellow in the department of emergency medicine at the University of Kentucky, Lexington. Dr Smith is the director of emergency ultrasound in the department of emergency medicine at the University of Tennessee College of Medicine Chattanooga. Dr Whittle is the director of research in the department of emergency medicine at the University of Tennessee College of Medicine Chattanooga.