What is the initial assessment and plan for a patient with a small bowel obstruction?

Initial Assessment and Plan for Small Bowel Obstruction

The priority in initial assessment is to immediately identify signs of peritonitis, strangulation, or ischemia that mandate emergent surgical exploration, while simultaneously initiating aggressive resuscitation with IV crystalloids, nasogastric decompression, and obtaining CT imaging to determine the cause and severity of obstruction. 1

Immediate Clinical Assessment

Identify Emergency Surgical Indications:

• Examine for peritoneal signs including rebound tenderness, involuntary guarding, and abdominal rigidity—these indicate bowel ischemia or perforation requiring immediate surgery. 1
• Assess vital signs for shock indicators: tachycardia, tachypnea, hypotension, cool extremities, and altered mental status suggest advanced obstruction or perforation. 1
• Fever combined with peritonitis strongly suggests strangulation or perforation. 2

Key History Elements:

• Document previous abdominal surgeries (85% sensitivity for adhesive SBO). 3
• Ask about last bowel movement and passage of flatus—complete obstipation suggests complete obstruction. 1, 3
• Inquire about constipation history, prior hernias, malignancy, inflammatory bowel disease, and radiation therapy. 1, 3

Physical Examination Priorities:

• Assess for abdominal distension (positive likelihood ratio 16.8 for SBO). 4, 3
• Auscultate for abnormal bowel sounds—high-pitched/hyperactive early, then absent with progression. 4, 5
• Examine ALL hernia orifices (inguinal, femoral, umbilical) and previous surgical scars. 1, 4
• Perform digital rectal examination to detect blood or masses. 4, 3
• Evaluate nutritional status and signs of dehydration. 1

Initial Laboratory Testing

Order immediately upon presentation:

• Complete blood count—marked leukocytosis >10,000/mm³ with left shift suggests peritonitis or ischemia. 1, 3
• Serum lactate—elevation indicates bowel ischemia (though normal values cannot exclude it). 1, 3
• Electrolytes including potassium (frequently low and requires correction). 1, 3
• BUN/creatinine to assess dehydration and pre-renal injury. 1, 3
• CRP (>75 mg/L suggests peritonitis). 1, 3
• Coagulation profile due to potential need for emergency surgery. 1, 3

Critical Pitfall: Normal laboratory values do NOT exclude ischemia—clinical judgment and imaging remain essential. 1

Immediate Management Interventions

Begin these simultaneously with assessment:

• IV fluid resuscitation with isotonic crystalloids (normal saline or lactated Ringer's) in volumes equivalent to estimated losses. 1, 3
• Insert nasogastric tube for gastric decompression—this prevents aspiration pneumonia and provides diagnostic information (feculent aspirate suggests distal SBO). 1, 4, 3
• Place Foley catheter to monitor urine output and assess adequacy of resuscitation. 1, 4
• Administer antiemetics for symptom control. 1, 3
• Provide appropriate analgesia (pain control does not mask surgical findings). 4
• Strict NPO status. 4, 3
• Consider IV antibiotics if signs of sepsis, peritonitis, or ischemia are present. 3, 6

Diagnostic Imaging Strategy

CT abdomen/pelvis with IV contrast is the primary diagnostic tool and should be obtained urgently in all patients without contraindications. 1, 3, 7

CT Imaging Protocol:

• Use IV contrast to evaluate bowel wall enhancement and identify ischemia. 3, 7
• Oral contrast is NOT needed for high-grade obstruction—non-opacified fluid provides adequate intrinsic contrast. 3
• CT has >90% diagnostic accuracy for SBO and identifies the cause, location, and severity. 3, 7, 5

CT Findings Requiring Emergency Surgery:

• Abnormal bowel wall enhancement (suggests ischemia). 3
• Bowel wall thickening with mesenteric edema. 3
• Pneumatosis intestinalis or mesenteric venous gas. 3
• Free air (pneumoperitoneum) indicating perforation. 8
• Closed-loop obstruction. 8
• Ascites in the setting of obstruction. 3

Alternative Imaging if CT Unavailable:

• Ultrasound has 91% sensitivity and 84% specificity for SBO (bedside US by emergency physicians: 95.5% positive LR). 4, 9, 5
• Look for dilated loops >2.5 cm with decreased peristalsis. 4, 9
• Plain radiographs have limited value (60-70% sensitivity) and cannot exclude SBO or determine need for surgery. 1, 3

Decision Algorithm for Operative vs. Non-Operative Management

IMMEDIATE SURGERY INDICATED IF:

• Signs of peritonitis on examination. 1, 8
• CT evidence of bowel ischemia (abnormal enhancement, pneumatosis, portal venous gas). 3, 8
• Free perforation with pneumoperitoneum. 8
• Closed-loop obstruction on imaging. 8
• Clinical deterioration despite resuscitation. 8, 6
• Hemodynamic instability unresponsive to fluids. 1

NON-OPERATIVE MANAGEMENT APPROPRIATE IF:

• Partial SBO without signs of ischemia or peritonitis. 8, 2
• Complete SBO in stable patient without concerning CT findings. 8
• Patient is hemodynamically stable after resuscitation. 8

Non-Operative Management Protocol:

• Continue NPO, NG decompression, IV fluids, and electrolyte correction. 8, 6
• Consider water-soluble contrast (Gastrografin 50-150 mL) via NG tube after adequate gastric decompression. 1
• Water-soluble contrast has 96% sensitivity and 98% specificity for predicting resolution with conservative therapy. 1
• If contrast reaches colon on X-ray within 4-24 hours, 90% will resolve without surgery. 1, 8
• If contrast does NOT reach colon by 24 hours, this predicts failure of non-operative management. 1

Timing for Surgical Consultation:

• Obtain immediate surgical consultation for ALL patients with SBO. 3, 2
• If non-operative management chosen, surgery is indicated if no improvement after 72 hours. 8, 6
• Delaying surgery when ischemia is present results in mortality up to 25%. 3

Admission and Monitoring

• All patients with SBO require hospital admission. 2
• Monitor vital signs, urine output, abdominal examination, and NG output every 4-6 hours. 6
• Repeat laboratory tests (CBC, lactate, electrolytes) every 12-24 hours or with clinical change. 6
• Serial abdominal examinations to detect development of peritonitis. 6

Common Pitfalls to Avoid

• Delaying NG tube placement increases aspiration pneumonia risk. 4
• Inadequate fluid resuscitation leads to pre-renal injury and worsens outcomes. 4
• Failing to correct electrolyte abnormalities (especially potassium) before surgery increases complications. 3
• Mistaking partial SBO with watery diarrhea for gastroenteritis delays diagnosis. 3
• Underestimating severity in elderly patients where pain may be less prominent. 3
• Relying on plain radiographs alone—they miss 30-40% of SBOs. 1
• Normal lactate and WBC do not exclude ischemia—maintain high clinical suspicion. 1