Upright X-ray for Free Air Evaluation in Suspected SBO/Strangulated Hernia
Yes, order an upright abdominal X-ray as the initial imaging study, but recognize that CT abdomen/pelvis with IV contrast is the definitive study you will likely need to differentiate between simple obstruction and strangulated hernia, and should not be delayed if clinical suspicion for strangulation is high.
Initial Imaging Approach
Plain abdominal radiographs (including upright view) are the appropriate first-line imaging study for suspected bowel obstruction, as they can demonstrate dilated bowel loops, air-fluid levels, and the critical finding of free intraperitoneal air if perforation has occurred 1.
The upright view specifically helps detect free air under the diaphragm, which would indicate bowel perforation—a surgical emergency 1.
However, radiographs will frequently be inconclusive and additional imaging will be needed, particularly when trying to distinguish between simple obstruction and strangulated hernia 1.
Why CT is Likely Necessary
Hernias are the most common cause of strangulation in patients presenting with small bowel obstruction, with strangulation occurring in approximately 9.3% of SBO cases, and hernias accounting for 80% of strangulated cases 2.
Umbilical hernias can be "invisible" in obese patients without obvious bulging, making clinical examination unreliable 3.
CT abdomen/pelvis with IV contrast is superior to plain radiographs for detecting bowel ischemia, strangulation, and the specific etiology of obstruction 1.
CT findings that indicate strangulation and need for emergency surgery include: absence of post-contrast bowel wall enhancement (indicating necrosis), closed-loop obstruction, mesenteric edema, and pneumatosis 1.
Clinical Decision Algorithm
Proceed directly to CT if:
- Peritoneal signs are present on examination (indicates peritonitis or bowel compromise) 1
- Signs of strangulation: severe continuous pain, fever, tachycardia, leukocytosis, metabolic acidosis 1
- High clinical suspicion for strangulated hernia given the umbilical hernia and 4-day obstruction 2
Start with plain films only if:
- Patient is hemodynamically stable
- No peritoneal signs
- Mild symptoms
- You need to confirm obstruction before proceeding to CT
Critical Management Points
Bilious vomiting is a surgical emergency requiring urgent evaluation, with 20% of cases having serious underlying pathology requiring surgery 4, 5.
Time is critical: strangulated bowel has a 10-fold increase in mortality compared to simple obstruction 2.
Do not delay surgical consultation for imaging if there are peritoneal signs, hemodynamic instability, or high suspicion for strangulation 4.
Laboratory abnormalities suggesting strangulation include: severe acidosis, elevated lactate, leukocytosis, elevated CRP, and deranged liver function tests 1.
Common Pitfalls
Assuming adhesions are the cause without imaging: while adhesions are the most common cause of SBO overall (60%), hernias cause the majority of strangulations 2.
Missing occult hernias in obese patients: umbilical hernias may not be palpable or visible, requiring CT for diagnosis 3.
Waiting too long for imaging: if clinical suspicion for strangulation is high based on duration (4 days), bilious vomiting, and presence of hernia, proceed directly to CT rather than stopping at plain films 1, 2.
Relying on normal initial labs: laboratory values become progressively more accurate over time, and initial normal values do not rule out bowel ischemia 1.