- Clinical Suspicion
While risk factors, history, and corresponding symptoms are helpful to point us toward the right direction, appropriate imaging is necessary for definitive diagnosis.
If the patient is clinically found to have a profoundly dilated abdomen that is unusual for their baseline, nasogastric tube must be inserted to decompress the abdomen first by emptying the contents before proceeding with the imaging.
- Gold Standard: Abdominal X-Ray
Upright chest x-ray, upright and supine abdominal radiographs are all obtained. If patient cannot stand, they will lay on their side to visualize the air-fluid levels on x-ray. Findings on positive SBO include:
- Dilated bowel loops WITH air-fluid levels: when upright or lateral, the radiograph can visualize the interface between the air and fluid, as the content settles down and cannot move through.
- Average air-fluid level width of 2.5cm or more may indicated severe or complete obstruction.
- If air-fluid levels differ by more than 5mm in the same loop on upright film, this may indicate a mechanical cause.
- “A string of pearls” sign may be seen, if the loops are completely full with no air.
Pros: Available, inexpensive, involve little radiation, timely.
Cons: Less specific; may not be able to distinguish between SBO vs LBO vs ileus
Specificity: 67-83%
Sensitivity: 80-83%
- Abdominal CT
CT abdomen is taken with the IV contrast (unless allergic to contrast or kidney failure. For suspected COMPLETE obstruction, no oral contrast allowed), though the contrast is not compulsory. CT is better than radiographs for identifying the specific site of obstruction.
- Free air: “football sign” under diaphragm or air on retroperitoneal space