Initial Approach to Suspected Bowel Obstruction
Order a CT scan of the abdomen and pelvis with IV contrast immediately—do not start with a KUB X-ray, as it has poor diagnostic accuracy and will delay definitive diagnosis and management.
Why CT is Superior to KUB
CT scan is the imaging modality of choice for evaluating suspected bowel obstruction, as it provides critical information about the presence, location, and cause of obstruction, as well as complications like perforation or ischemia 1.
KUB has limited diagnostic value: Plain abdominal radiography is of limited utility unless free perforation (pneumoperitoneum) or obvious obstruction is suspected 1. In bowel obstruction, plain films are diagnostic in only 50-60% of cases, inconclusive in 20-30%, and misleading in 10-20% 1.
CT provides comprehensive assessment: CT with IV contrast is the key study in the emergency setting for detecting bowel obstruction, perforation, ischemia, abscesses, and identifying the underlying cause 1. When severe complications like perforation are suspected, CT is preferable to abdominal X-ray 1.
Clinical guidelines do not recommend KUB for constipation: The American College of Radiology does not recommend KUB as a primary diagnostic tool for constipation, and the American Gastroenterological Association only mentions it as part of an algorithm for bloating, not for primary constipation diagnosis 2, 3.
Clinical Assessment While Arranging Imaging
Look for red flags that indicate complicated obstruction requiring urgent intervention 1:
- Signs of peritonitis: Severe abdominal pain, guarding, rebound tenderness, or rigid abdomen suggest perforation or ischemia 1
- Systemic toxicity: Fever >37.8°C, tachycardia >90 bpm, hypotension, or altered mental status indicate potential sepsis 1
- Severe distension with absent bowel sounds: Suggests complete obstruction or ileus 4, 5
- History of previous abdominal surgery: Increases likelihood of adhesive small bowel obstruction 5
Immediate Management Before Imaging
Initiate supportive care without delay 1:
- IV crystalloid resuscitation: Isotonic dextrose-saline with supplemental potassium to replace losses 1
- Nasogastric tube decompression: Prevents aspiration and decompresses proximal bowel 1
- NPO status: Complete bowel rest 1
- Foley catheter: Monitor urine output 1
- Laboratory tests: Complete blood count, electrolytes, renal function, liver function, lactate, and coagulation profile 1
Key Laboratory Red Flags
Obtain labs urgently to assess for ischemia or perforation 1:
- Low serum bicarbonate, low arterial pH, or elevated lactate suggest intestinal ischemia 1
- Marked leukocytosis indicates possible perforation or necrosis 1
- Elevated amylase may indicate perforation 1
Differential Diagnosis for Left Lower Quadrant Pain
Your patient's presentation (LLQ pain, distension, vomiting, no bowel movement × 2 days) could represent 1, 6:
- Sigmoid diverticulitis: Most common cause of LLQ pain in adults, can cause obstruction 1
- Sigmoid volvulus: Sudden onset distension with LLQ pain 1
- Colorectal cancer: Can present with progressive obstruction and LLQ pain 1
- Adhesive small bowel obstruction: If history of prior surgery 5
When Surgery May Be Needed
Surgical consultation should be obtained early if 1:
- Signs of peritonitis or perforation are present 1
- Severe abdominal pain persists despite decompression 1
- CT shows complete obstruction, closed-loop obstruction, or ischemia 1
- Patient develops systemic toxicity or hemodynamic instability 1
Common Pitfalls to Avoid
- Do not delay CT imaging by ordering KUB first: This wastes time and provides limited diagnostic information 1, 2, 3
- Do not withhold analgesia: Early analgesia reduces patient discomfort without impairing diagnostic accuracy 7
- Do not miss elderly patients with atypical presentations: Elderly patients may present with minimal symptoms despite serious pathology 6
- Do not assume simple constipation: Two days without bowel movement plus distension, vomiting, and pain suggests mechanical obstruction, not simple constipation 5