Sandbox 2

Lower GI bleeding is defined as any bleed that occurs distal to the ligament of Treitz.

Incidence

• In the United States the incidence of LGIB ranges from 20.5 to 27 per 100,000 persons per year.

Age

• There is a greater than 200 fold increase from the third to the ninth decade of life.

Classification

• Lower GI bleeding can be classified into 3 groups based on the severity of bleeding:
  • Occult lower GI bleeding
  • Moderate lower GI bleeding
  • Severe lower GI bleeding

Blood supply

• The SMA and IMA are connected by the marginal artery of Drummond.
• This vascular arcade runs in the mesentery close to the bowel.
• As patients age, there is increased incidence of occlusion of the IMA.
• The left colon stays perfused, primarily because of the marginal artery.

Lower GI Tract		Arterial Supply	Venous Drainage
Midgut	Distal duodenum jejunum Ileum Appendix Cecum Ascending colon Hepatic flexure Proximal transverse colon.	Superior mesenteric artery (SMA)	Portal system.
Hindgut	Distal one-third of the transverse colon Splenic flexure Descending colon, Sigmoid colon Rectum	Inferior mesenteric artery (IMA)	Portal system ɸ
ɸ -Except lower rectum, which drains into the systemic circulation.