INCIDENCE AND EPIDEMIOLOGY
Intestinal ischemia occurs when splanchnic perfusion fails to meet the metabolic demands of the intestines, resulting in ischemic tissue injury. Mesenteric ischemia affects 2–3 people per 100,000, with an increasing incidence in the aging population. Delay in diagnosis and management results in a high mortality, and prompt interventions may be lifesaving. Intestinal ischemia is further classified based on etiology, which dictates management: (1) arterioocclusive mesenteric ischemia, (2) nonocclusive mesenteric ischemia, and (3) mesenteric venous thrombosis.
Risk factors for arterioocclusive mesenteric ischemia are generally acute in onset that include atrial fibrillation, recent myocardial infarction, valvular heart disease, and recent cardiac or vascular catheterization, all of which result in embolic clots reaching the mesenteric circulation. Nonocclusive mesenteric ischemia, also known as “intestinal angina,” is generally more insidious and often seen in the aging population affected by atherosclerotic disease. Patients with chronic atherosclerotic disease could also suffer an acute insult from emboli leading to complete occlusion. Nonocclusive mesenteric ischemia is also seen in patients receiving high-dose vasopressor infusions, patients presenting with cardiogenic or septic shock, and cocaine overdose. It is 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. Mesenteric venous thrombosis is less common and 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
The blood supply to the intestines is depicted in Fig. 322-1. To prevent ischemic injury, extensive collateralization occurs between major mesenteric trunks and branches of the mesenteric arcades. 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. 322-1, 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.
Occlusive ischemia is a result of disruption of blood flow by an embolus or progressive thrombosis in a major artery supplying the intestine. In >75% of cases, emboli originate from the heart and preferentially lodge in the superior mesenteric ...