What is the initial diagnostic approach for a patient with suspected lower gastrointestinal (GI) bleeding and no blood in the nasogastric tube (NGT)?

Management of Massive Lower GI Bleeding with Negative NGT

For a patient with massive lower GI bleeding and no blood in the nasogastric tube (NGT), upper GI endoscopy should be performed first, followed by colonoscopy if negative, and then CT angiography (CTA) if both are negative. 1, 2

Diagnostic Algorithm for Massive Lower GI Bleeding

Step 1: Initial Assessment and Upper GI Endoscopy

• Upper GI endoscopy should be the first diagnostic procedure, even with suspected lower GI bleeding, as 10-15% of severe hematochezia cases have upper GI sources 1
• A negative NGT aspirate does not reliably exclude an upper GI source, as this finding is not always accurate 3
• Upper endoscopy should be performed after adequate resuscitation if the patient has stabilized 3

Step 2: If Upper Endoscopy is Negative

• Proceed to colonoscopy after adequate bowel preparation
• Colonoscopy should be performed within 24 hours of presentation 2
• Endoscopic hemostasis therapy should be provided if high-risk stigmata are found (active bleeding, non-bleeding visible vessel, or adherent clot) 2

Step 3: If Colonoscopy is Negative or Not Feasible

• CT angiography (CTA) should be performed, which has high sensitivity (80-90%) for detecting active bleeding at rates as low as 0.3-1.0 mL/min 1
• CTA can localize the bleeding source and guide subsequent interventions 4

Step 4: If CTA is Negative

• Consider video capsule endoscopy (VCE), especially if small bowel bleeding is suspected
• VCE has highest diagnostic yield (87-91%) when performed within 48 hours of bleeding 3
• Nuclear medicine studies (tagged RBC scan) may be considered for intermittent or slow bleeding 3, 1
• Mesenteric angiography has limited value if CTA is negative 3

Special Considerations

Hemodynamic Instability

• If the patient is hemodynamically unstable with active bleeding, the sequence may be altered:
  • CTA may be performed first before endoscopy 1
  • Angiography with potential embolization may be needed urgently 5

Therapeutic Options Based on Diagnosis

• Diverticular bleeding: Endoscopic clips, thermal therapy, or angiographic embolization 1
• Angiodysplasia: Argon plasma coagulation or thermal therapy 1, 5
• Small bowel sources: Deep enteroscopy guided by VCE findings 6

Common Pitfalls to Avoid

1. Delaying upper endoscopy: Despite suspected lower GI bleeding, upper sources are common and should be ruled out first 1, 2
2. Blind colonic resection: If a source is not identified after thorough investigation, blind resection should not be performed 7
3. Delayed VCE: If small bowel bleeding is suspected, VCE should be performed within 48 hours for highest yield 3
4. Overlooking recurrent bleeding: Repeat colonoscopy should be considered for patients with evidence of recurrent bleeding 2

By following this systematic approach, the source of bleeding can be identified in the vast majority of patients, allowing for targeted therapeutic intervention and improved outcomes.