INTRODUCTION AND EPIDEMIOLOGY
Historically, lower GI bleeding is the loss of blood from the GI tract distal to the ligament of Treitz. However, management and outcomes differ if the bleeding originates from the small intestine compared with the colon.1 Nevertheless, lower GI bleeding is a common problem in emergency medicine and should be considered potentially life threatening until proven otherwise.
Lower GI bleeding occurs more often than upper GI bleeding, with an annual incidence of approximately 109 per 100,000 and a mortality of <1%.2 Because blood must travel through the upper GI tract down to the lower GI system, upper GI bleeds are the most common source for all causes of blood detected in the lower GI system. Among patients with an established lower GI source of bleeding, the most common cause is diverticular disease, followed by colitis, hemorrhoids, and adenomatous polyps/malignancies.3
About 80% of episodes of lower GI bleeding resolve spontaneously.4 However, one cannot predict which episodes will spontaneously resolve or which episodes will result in complications. This is partly due to the difficulty in establishing a pathophysiologic diagnosis. In one study, a cause for bleeding was found in <50% of the cases.5
Hematochezia is either bright red or maroon-colored rectal bleeding. If hematochezia originates from a upper GI source, it indicates brisk upper GI bleeding, which may be accompanied by hematemesis and hemodynamic instability. Approximately 10% of hematochezia episodes may be associated with upper GI bleeding.6 Melena is dark or black-colored stools and usually represents bleeding from a upper GI source (proximal to the ligament of Treitz) but may also represent slow bleeding from an lower GI source.
Diverticular bleeding is usually painless and results from erosion into the penetrating artery of the diverticulum. Diverticular bleeding may be massive, but up to 90% of episodes will resolve spontaneously. Bleeding can recur in up to half of patients.7,8 Although most diverticula are located on the left colon, right-sided diverticula are thought to be more likely to bleed.9 Elderly patients with underlying medical illnesses, those with increased needs for transfusion, and those taking anticoagulants or NSAIDs have increased morbidity and mortality.7
Vascular ectasia, which includes arteriovenous malformations and angiodysplasias of the colon, is a common cause of lower GI bleeding. Vascular ectasia can also be present in the small bowel and is difficult to diagnose. The development of vascular ectasia in the large bowel seems to be due to a chronic process and increases with aging. Inherited conditions can also give rise to arteriovenous malformations. There is also a suggestion that valvular heart disease is a risk factor for developing bleeding vascular ectasias, although this is an area of debate.4
ISCHEMIC COLITIS AND MESENTERIC ISCHEMIA