Ischemic diseases of the large intestine.

The blood flow within the walls of the digestive tract must be sufficient to maintain its structural and functional integrity. All episodes of vascular insufficiency cause ischemic damage to the organ and carry the threat of diffuse or focal necrosis. Certain forms of ischemic colitis or proctitis arise from episodes of reduced peripheric or splanchnic blood flow; indeed, those which do not culminate in necrosis of the colonic wall are more frequently caused by hemodynamic disorders than by vascular occlusions. The crisis is often mitigated by the development of collateral circulation; this is, however, of rather poor quality so patients become very vulnerable to subsequent slight changes in cardiac output. Necrotic, gangrenous ischemic colitis arises from a combination of occlusive damage to the arteries and general hemodynamic disturbances. The vascular insufficiency may be slight or severe, temporary or long-lasting, localized or diffuse. In addition, the attack occurs in a septic medium in the presence of abundant microbial flora which may be highly pathologic. Thus infection complicates and aggravates the ischemic damage, resulting in the gangrenous aspect of the lesion tending to hide its ischemic origin. Indeed, the variability of the manifestations of the disease in one of its primary characteristics, and is a function of the different causative factors. A knowledge of the anatomy and pathophysiology of the splanchnic circulation and its hemodynamics is essential for a full appreciation of the diagnosis and treatment of the disorders, and for the adoption of the aggressive approach necessary to improve the poor prognosis of ischemic diseases of the colon and rectum. All treatment should be based on 1) constant, prolonged intensive care; 2) precise monitoring of any change in status; 3) rapid excision of any necrotic (often gangrenous) tissue. Ischemic colitis is most likely to occur in elderly patients with a history of cardiovascular disease, but can also affect younger individuals. It is a frequent, potentially lethal, entity. Although it can be classified as a separate disease on the basis of its clinical, radiological and anatomical characteristics, it is often confused with other disorders of the colon. Although the abdominal surgeon is most likely to be concerned with this disease, the vascular surgeon incising the lower aorta should always be on the look-out for segmentary ischemia of the distal colon which may occur following operation.