What is the initial workup for bowel obstruction?

Initial Workup for Bowel Obstruction

The initial workup for bowel obstruction should include a complete history, physical examination, laboratory tests, and imaging studies, with CT scan being the most accurate diagnostic tool for confirming obstruction and identifying complications requiring urgent intervention. 1, 2

Clinical Assessment

History

• Ask about previous abdominal surgeries (85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction) 1
• Inquire about last defecation/bowel gas passage 1
• Document history of previous diverticulitis episodes (suggesting diverticular stenosis) or chronic constipation (suggesting volvulus) 1
• Note any previous rectal bleeding or unexplained weight loss (suggestive of colorectal cancer) 1
• Review medication history, especially those affecting peristalsis (associated with pseudo-obstruction and adynamic ileus) 1

Physical Examination

• Assess for abdominal distension (positive likelihood ratio of 16.8, negative likelihood ratio of 0.27) 1
• Evaluate for signs of peritonitis that might indicate strangulation or ischemia (sensitivity of physical examination for strangulation is only 48%) 1
• Examine all hernia orifices (umbilical, inguinal, femoral) and previous surgical incision sites 1
• Perform digital rectal examination to detect blood or rectal masses 1
• Check vital signs for signs of shock (tachycardia, tachypnea, cool extremities, mottled skin) which may indicate severe obstruction, perforation, or ischemia 1

Laboratory Tests

• Complete blood count (marked leukocytosis >10,000/mm³ may indicate peritonitis) 1
• Electrolytes (low potassium values are frequently found and need correction) 1
• Renal function tests (BUN/creatinine to assess dehydration) 1
• Lactate levels (elevated in intestinal ischemia) 1
• CRP (values >75 may indicate peritonitis) 1
• Liver function tests 1
• Coagulation profile (due to potential need for emergency surgery) 1

Initial Management

• Begin supportive treatment immediately with intravenous crystalloids 1
• Insert nasogastric tube for decompression and to prevent aspiration pneumonia 1
• Place Foley catheter to monitor urine output 1
• Administer anti-emetics and maintain bowel rest 1

Imaging Studies

Plain Abdominal X-ray

• First-level radiologic study but has limited diagnostic value 1, 2
• Sensitivity of 50-60%, with 20-30% inconclusive and 10-20% misleading results 1
• Classic findings in high-grade obstruction: multiple air-fluid levels, distended small bowel loops, and absence of gas in the colon 1
• Can detect large volume pneumoperitoneum but not early signs of peritonitis or strangulation 1

Water-Soluble Contrast Studies

• Small bowel follow-through with water-soluble contrast is useful for adhesive small bowel obstruction management 1, 2
• If contrast hasn't reached the colon on X-ray after 24 hours, this indicates non-operative management failure 1, 2
• Can reduce hospital stay and may reduce need for surgery 2
• Contrast medium can be administered at 50-150 ml, either orally or via nasogastric tube 2

CT Scan with IV Contrast

• Superior diagnostic accuracy compared to plain radiography and ultrasound 2
• Approximately 90% accuracy in predicting strangulation and need for urgent surgery 2
• Should focus on four key points: confirming obstruction, determining transition point, establishing cause, and identifying complications 3
• Most important for identifying signs of ischemia, which indicates higher risk patients who need early surgical intervention 3

Ultrasound

• Can diagnose small bowel obstruction with 90% sensitivity and 96% specificity when dilated loops >2.5 cm are visualized 2
• Valid alternative to CT, especially in children and pregnant women 2

Pitfalls to Avoid

• Mistaking incomplete obstruction with watery diarrhea for gastroenteritis 1
• Overlooking bowel obstruction in elderly patients where pain may be less prominent 1
• Relying solely on plain X-rays to exclude the diagnosis of bowel obstruction 4
• Delaying surgical consultation when signs of strangulation or ischemia are present 3
• Failing to correct electrolyte abnormalities before surgical intervention 1