A 78-year old man presents with abdominal pain and decreased oral intake. His vitals are normal but he looks uncomfortable. After you introduce yourself, you palpate his abdomen which is diffusely tender. Your immediate gestalt is “Small Bowel Obstruction” but you’re not sure why. Frankly, you think, “I can do better than gestalt.”
Can you?
1. What are the various positive and negative likelihood ratios for clinical and radiographic features of a small bowel obstruction? (recall +LR>10 is considered useful for genuinely increasing suspicion of disease, -LR <0.1 is considered useful for genuinely decreasing suspicion of disease).
1a. Previous surgery?
1b. Abdominal distension?
2. What is the sensitivity and specificity of imaging modalities for small bowel obstruction?
2a. A normal abdominal X-ray?
2b. Air fluid levels seen on abdominal X-ray
2c. CT findings.
3. In a trained EM provider, what are the likelihood ratios for small bowel obstruction using bedside ultrasound?
Your questions answered!
1. What are the various positive and negative likelihood ratios for clinical and radiographic features of a small bowel obstruction? (recall +LR>10 is considered useful for genuinely increasing suspicion of disease, -LR <0.1 is considered useful for genuinely decreasing suspicion of disease).
1a. Previous surgery? +LR 3.8 (surprisingly unhelpful), -LR 0.19 (pretty good)
1b. Abdominal distension? +LR 5-16 (not helpful or helpful, depending on study cited, and patient). -LR 0.4 (not that helpful).
2. What is the sensitivity and specificity of imaging modalities for small bowel obstruction?
2a. A normal abdominal X-ray? sensitivity 66-77% (many false negatives).
2b. Air fluid levels seen on abdominal X-ray? specificity 50-57% (many false positives).
2c. CT findings? 92% sensitive and 93% specific. This is the “gold standard.”
3. In an EM provider with “brief training”, what are the likelihood ratios for small bowel obstruction using bedside ultrasound? +LR 9.5 possibly truly useful), -LR 0.04 (impressive). Looking for dilated loops of bowel >2.5cm across and “fluid moving around” instead of a bunch of air.
Want to know how to do ultrasound for small bowel obstruction?
http://5minsono.com/sbo/
Other resources:
FOAMcast episode 23 on SBO and Acute Mesenteric Ischemia.
Rosen’s Chapter 92. Roline and Reardon. Disorders of the Small Intestine.
Tintinalli Chapter 45. Hess. Intestinal Obstruction and Volvulus.
