Chapter 160. Acute Lower Gastrointestinal Bleeding

1. What risk factors increase the severity of lower gastrointestinal (GI) bleeding?

2. What are the categories and individual causal factors for colonic ischemia?

3. What are the indications for tagged red blood cell scan and angiography in the setting of lower GI bleeding?

4. What are the indications for surgery in patients with diverticular bleeding and ischemic colitis?

Lower gastrointestinal (GI) bleeding is defined as bleeding that occurs from a source distal to the ligament of Treitz. This chapter will discuss only colonic sources of bleeding, as other chapters explore both upper gastrointestinal and small intestinal bleeding.

Lower GI bleeding accounts for about 20% of major gastrointestinal bleeding and is less common and generally less severe than upper GI bleeding. There are 20 to 27 hospitalizations per 100,000 adults in the United States due to lower GI bleeding. It generally occurs in the older population with a mean age between 63 and 77 years old. Nearly 80% of lower GI bleeding stops spontaneously, similar to upper GI bleeding. The overall mortality rate of lower GI bleeding is 2% to 4%. Similar to upper GI bleeding, patients who begin lower GI bleeding as an outpatient have a significantly lower mortality rate (3.6%) than inpatients who develop lower GI bleeding (23%).

Presentation

Definitions of Bleeding

Hematochezia is defined as bright red blood per rectum and usually implies a left colonic source, although it can be caused by a more brisk, proximal source of bleeding. Maroon stools are maroon-colored blood mixed with stool that is often associated with a right colonic source of bleeding; however, it can also result from a more brisk, proximal source of bleeding. Melena refers to black, tarry, foul smelling stool that results from the bacterial degradation of hemoglobin over a period of at least 14 hours. It usually implies an upper GI source of bleeding, although it may be associated with right colonic bleeding in cases of slow motility. Ingestion of iron, bismuth, charcoal, and licorice should be excluded as they all can turn stool black. Occult blood refers to the presence of small quantities of blood in the stool that does not change its color and can only be detected by performing a stool guaiac card test. Blood loss of at least 5–10 mL per day can be detected by stool guaiac card tests. The gastrointestinal tract normally loses about 0.5–1.5 mL of blood per day, which is not usually detected by guaiac tests.