This may be caused by haemorrhage from the colon, anal canal or small bowel. It is useful to distinguish those patients who present with profuse, acute bleeding from those who present with chronic or subacute bleeding of lesser severity .Severe acute lower gastrointestinal bleeding .This presents with profuse red or maroon diarrhoea and with shock. Diveicular disease is the most common cause and is often due to erosion of an aery within the mouth of a diveiculum. Bleeding almost always stops spontaneously, but if it does not, the diseased segment of colon should be resected after confirmation of the site by angiography or colonoscopy. Angiodysplasia is a disease of the elderly, in which vascular malformations develop in the proximal colon. Bleeding can be acute and profuse; it usually stops spontaneously but commonly recurs. Diagnosis is often difficult. Colonoscopy may reveal characteristic vascular spots and, in the acute phase, visceral angiography can show bleeding into the intestinal lumen and an abnormal large, draining vein. In some patients, diagnosis is achieved only by laparotomy with on-table colonoscopy. The treatment of choice is endoscopic thermal ablation but resection of the affected bowel may be required if bleeding continues. Bowel ischaemia due to occlusion of the inferior mesenteric aery can present with abdominal colic and rectal bleeding. It should be considered in patients (paicularly the elderly) who have evidence of generalised atherosclerosis. The diagnosis is made at colonoscopy. Resection is required only in the presence of peritonitis. Meckel's diveiculum with ectopic gastric epithelium may ulcerate and erode into a major aery. The diagnosis should be considered in children or adolescents who present with profuse or recurrent lower gastrointestinal bleeding. A Meckel's 99mTc-peechnetate scan is sometimes positive but the diagnosis is commonly made only by laparotomy, at which time the diveiculum is excised Primary prevention of variceal bleeding If non-bleeding varices are identified at endoscopy, b-adrenoceptor antagonist (b-blocker) therapy with propranolol (80-160 mg/day) or nadolol (40-240 mg/day) is effective in reducing poal venous pressure. Administration of these drugs at doses that reduce the hea rate by 25% has been shown to be effective in the primary prevention of variceal bleeding. In patients with cirrhosis, treatment with propranolol reduces variceal bleeding by 47% (number needed to treat for benefit (NNTB) 10), death from bleeding by 45% (NNTB 25) and overall moality by 22% (NNTB 16). The efficacy of b-blockers in primary prevention is similar to that of prophylactic banding, which may also be considered, paicularly in patients who are unable to tolerate or adhere to b-blocker therapy. Carvedilol, a non-cardioselective vasodilating b-blocker, is also effective and may be better tolerated at doses of 6.25-12.5 mg/day). For these, dose should be titrated, as tolerated, to achieve a hea rate of 50-55 beats/min, if possible.metrandazole can be given sigmoidal ulcer Ref Davidson edition23rd pg 869