Lower Gastrointestinal Bleeding Approach
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Direct answer
Lower gastrointestinal bleeding is haemorrhage from a source distal to the ligament of Treitz, usually presenting as fresh blood per rectum or, less often, melaena. Causes differ by age, with diverticular disease and angiodysplasia dominant in older adults and Meckel diverticulum and inflammatory colitis in younger patients. Management begins with haemodynamic stabilisation, followed by colonoscopy after bowel preparation once the patient is stable.
What you must remember
- Definition: bleeding from a source distal to the ligament of Treitz, with an upper source excluded first when melaena or haemodynamic instability is present.
- Diverticular bleeding: the commonest cause of significant lower bleeding in older adults, often painless, sudden and usually right-sided.
- Angiodysplasia: vascular ectasia of the caecum and right colon in the elderly, causing occult bleeding and iron deficiency anaemia.
- Meckel diverticulum: the classic cause in young people, sometimes containing ectopic gastric mucosa, which is detected by a technetium pertechnetate scan.
- Haemorrhoids: the commonest source of rectal bleeding overall, but they should not be assumed without examining the colon in an older patient.
- Colonoscopy: the first-line diagnostic and therapeutic test once the patient is stable and the colon is adequately prepared.
- Imaging: CT angiography for brisk bleeding, tagged red cell scintigraphy for slower bleeding, and angiography with embolisation when endoscopy fails.
- Surgery: subtotal colectomy is a last resort for life-threatening bleeding without a localised source.
A graded approach from resuscitation to imaging
A 68-year-old man on aspirin presents with two episodes of large, painless, bright red blood per rectum in the past six hours. His pulse is 110 per minute and his blood pressure is 96/60 mmHg.
- Resuscitate first: Two large-bore cannulas, crossmatched blood and crystalloid fluids restore circulation, with pulse and urine output tracked.
- Look for an upper source: A nasogastric aspirate, or upper endoscopy if melaena is present, excludes an upper bleed, because a brisk upper bleed can present as red blood per rectum.
- Review antithrombotic drugs: Antiplatelet and anticoagulant therapy is reviewed with the relevant specialist, and reversal is considered only for life-threatening bleeding.
- Prepare and scope: Colonoscopy after bowel preparation finds and treats many sources, such as clips or thermal coagulation for angiodysplasia, and is usually done within about 24 hours of stabilisation.
- Image if endoscopy fails: CT angiography detects active bleeding, and angiography with embolisation treats a localised source when colonoscopy is incomplete.
- Reserve surgery: Subtotal colectomy is kept for persistent haemorrhage without a localised source after embolisation has failed or is not possible.
Where the exam tries to catch you
Lower GI bleed questions test the age-based differential and the sequence of investigations.
- Trap: Attributing red blood per rectum in an elderly patient to haemorrhoids without examining the colon. Correct: Diverticular and angiodysplastic bleeds are common in older adults, so colonoscopy is needed before blaming haemorrhoids.
- Trap: Assuming a negative colonoscopy excludes bleeding. Correct: Small bowel sources, including Meckel diverticulum and small bowel angiodysplasia, need capsule endoscopy or enteroscopy.
- Trap: Attributing every bleed in a young patient to haemorrhoids. Correct: Meckel diverticulum and inflammatory bowel disease are the classic exam causes in younger patients.
- Trap: Insisting on a full bowel preparation during brisk, unstable bleeding. Correct: Preparation is modified or deferred in unstable patients, and urgent imaging is used to localise the source.
Frequently asked questions
What are the commonest causes of lower gastrointestinal bleeding in older adults?
Diverticular disease and angiodysplasia are the commonest causes of significant lower gastrointestinal bleeding in older adults. Colorectal cancer and ischaemic colitis are also considered, and colonoscopy is the usual investigation to identify the source.
Which investigation is first-line for lower GI bleeding in a stable patient?
Colonoscopy after adequate bowel preparation is the first-line investigation for a stable patient with lower gastrointestinal bleeding. It identifies the source and allows therapy such as clipping or thermal coagulation during the same procedure.
When is CT angiography used in lower GI bleeding?
CT angiography is used in lower gastrointestinal bleeding when bleeding is brisk or ongoing and colonoscopy has not localised the source. It can detect active extravasation, which then guides angiographic embolisation.
Which investigation identifies a Meckel diverticulum in a patient with rectal bleeding?
Technetium pertechnetate scintigraphy identifies ectopic gastric mucosa in a Meckel diverticulum, the classic cause of lower bleeding in young patients. Small bowel imaging or enteroscopy is used when the scan is negative but suspicion remains.