Acute Lower Gastrointestinal Bleeding

Acute lower gastrointestinal bleeding is haemorrhage from a source distal to the ligament of Treitz, usually the colon.

• Diverticular bleeding causes 30 to 40 percent, followed by ischaemic colitis, haemorrhoids, colitis (inflammatory and infective), angiodysplasia, neoplasia and post-polypectomy bleeding.
• Most episodes stop spontaneously (about 80 percent).
• Risk factors: age above 65 years, NSAIDs, anticoagulants, antiplatelet drugs, hypertension, renal disease and atherosclerosis.

Presentation is haematochezia, ranging from streaks to maroon stool or frank blood.

• Painless bleeding favours diverticulosis, angiodysplasia and haemorrhoids; cramping pain with bloody diarrhoea favours ischaemic, infective or inflammatory colitis.
• Change in bowel habit and weight loss favour neoplasia.
• Tachycardia, hypotension and syncope indicate major bleeding. Rectal examination and proctoscopy find haemorrhoids, fissures and rectal tumours.
• Differential diagnosis: brisk upper gastrointestinal bleed (about 10 to 15 percent of haematochezia with shock), small bowel source, anorectal disease, radiation proctopathy, solitary rectal ulcer, Meckel diverticulum in the young.
• Complications: hypovolaemia, anaemia, recurrent bleeding (diverticular rebleeding about 15 to 20 percent), myocardial ischaemia and complications of therapy.

Resuscitate first, then localise.

• Full blood count, group and crossmatch, coagulation screen, urea, creatinine, lactate.
• Haemodynamically stable: colonoscopy within 24 hours after bowel preparation with 4 L polyethylene glycol solution (split over 4 to 6 hours); nasogastric lavage or upper endoscopy if an upper source is suspected.
• Unstable or ongoing brisk bleeding: CT angiography first (detects bleeding at 0.3 to 0.5 mL/min), then embolisation.
• Technetium-labelled red cell scan detects slower bleeding (0.1 mL/min) but localises poorly.
• Flexible sigmoidoscopy for suspected left-sided or anorectal disease; stool cultures and Clostridioides difficile testing if colitis is suspected.

Supportive

• Two large-bore cannulae, crystalloid 500 mL boluses, red cell transfusion for haemoglobin below 7 g/dL (below 8 g/dL with cardiovascular disease).
• Correct coagulopathy (prothrombin complex concentrate 25 to 50 IU/kg for warfarin plus vitamin K 5 to 10 mg IV).
• Hold anticoagulants and NSAIDs; reintroduce anticoagulation once bleeding settles, typically after 7 days.

Endoscopic:

• Adrenaline 1 in 10,000 injection plus through-the-scope clips or band ligation for diverticular bleeding with stigmata; thermal coagulation for angiodysplasia.
• Haemorrhoids: band ligation or sclerotherapy.

Radiological and surgical:

• Selective angiographic embolisation (success above 80 percent; bowel ischaemia 1 to 5 percent).
• Surgery (segmental colectomy guided by localisation; subtotal colectomy only if unlocalised and life threatening) for failure of other measures.

Special groups: patients on antiplatelet therapy for stents should keep aspirin; elderly patients need cautious fluid replacement and troponin monitoring.

Red flags: haemodynamic instability, ongoing bleeding after 24 hours, blood transfusion above 2 units, anaemia in an adult over 50 with change in bowel habit (exclude colorectal cancer).

Follow-up: complete colonoscopy for those not fully assessed, 6 to 8 weeks after the episode; fibre intake 25 to 30 g daily for diverticular disease.