Incidence and Epidemiology
Intestinal ischemia is an uncommon vascular disease associated with a high mortality. It is categorized according to etiology: (1) arterioocclusive mesenteric ischemia (AOMI), (2) nonocclusive mesenteric ischemia (NOMI), and (3) mesenteric venous thrombosis (MVT). Acute intestinal ischemia is more common than its counterpart, chronic arterial ischemia. Risk factors for acute arterial ischemia include atrial fibrillation, recent myocardial infarction, valvular heart disease, and recent cardiac or vascular catheterization. The increased incidence of intestinal ischemia seen in Western countries parallels the incidence of atherosclerosis and the aging population. With the exception of strangulated small-bowel obstruction, ischemic colitis is the most common form of acute ischemia and the most prevalent gastrointestinal disease complicating cardiovascular surgery. The incidence of ischemic colitis following elective aortic repair is 5–9%, and the incidence triples in patients following emergent repair. Other less common forms of intestinal ischemia include chronic mesenteric angina associated with atherosclerotic disease and MVT. The latter is associated with the presence of a hypercoagulable state including protein C or S deficiency, antithrombin III deficiency, polycythemia vera, and carcinoma.
Anatomy and Pathophysiology
Intestinal ischemia occurs when insufficient perfusion to intestinal tissue produces ischemic tissue injury. The blood supply to the intestines is depicted in Fig. 298-1. To prevent ischemic injury, extensive collateralization occurs between major mesenteric trunks and branches of the mesenteric arcades (Table 298-1). Collateral vessels within the small bowel are numerous and meet within the duodenum and the bed of the pancreas. Collateral vessels within the colon meet at the splenic flexure and descending/sigmoid colon. These areas, which are inherently at risk for decreased blood flow, are known as Griffiths' point and Sudeck's point, respectively, and are the most common locations for colonic ischemia (Fig. 298-1, shaded areas). The splanchnic circulation can receive up to 30% of the cardiac output. Protective responses to prevent intestinal ischemia include abundant collateralization, autoregulation of blood flow, and the ability to increase oxygen extraction from the blood.
Blood supply to the intestines includes the celiac artery, superior mesenteric artery (SMA), inferior mesenteric artery (IMA), and branches of the internal iliac artery (IIA). Griffiths' and Sudeck's points, indicated by shaded areas, are watershed areas within the colonic blood supply and common locations for ischemia.
Table 298-1 Collateral Arterial Intestinal Blood Flow |Favorite Table|Download (.pdf)
Table 298-1 Collateral Arterial Intestinal Blood Flow
|Involved Circulation||Mesenteric Artery||Adjoining Artery||Collateral Artery|
|Mesenteric||SMA||IMA||Arch of Riolan|
Occlusive ischemia is a result of disruption of blood flow by an embolus or progressive thrombosis in ...