The spectrum of ischemic bowel disease comprises acute and chronic mesenteric ischemia and colon ischemia and includes arterial as well as venous disorders. Each form of intestinal ischemia requires its own plan of diagnosis and management. In the absence of randomized controlled trials or similar forms of scientific inquiry, the diagnostic and therapeutic algorithms presented here are based on descriptive series and clinical experience.
Acute Mesenteric Ischemia
Acute mesenteric ischemia (AMI) can result from emboli, arterial and venous thrombi, or vasoconstriction secondary to low flow. Mortality rates reported over the last 15 years remain as high as they did more than 70 years ago and average 71%, with a range of 59%-93%. Diagnosis before intestinal infarction is the single most important factor to improve these poor results. Relief of persistent vasoconstriction, which is the cause of nonocclusive mesenteric ischemia and occurs in association with occlusive forms of ischemia, is another important factor. The objectives of this guideline for the management of acute mesenteric ischemia are early identification of patients who require prompt and aggressive evaluation in addition to delineation of the optimal form of therapy for each patient.
Patients at risk for acute mesenteric ischemia, as defined in the technical review, who have abdominal pain severe enough to call to the attention of a physician, whose pain persists for more than 2 or 3 hours, and whose clinical picture does not suggest some other abdominal problem, e.g., cholecystitis or diverticulitis, should be evaluated and treated for acute mesenteric ischemia according to algorithm 1 in the original guideline document.
Chronic Mesenteric Ischemia
Chronic mesenteric ischemia (CMI; "intestinal angina") is characterized by postprandial abdominal pain and marked weight loss and is caused by repeated transient episodes of inadequate intestinal blood flow, usually provoked by the increased metabolic demands associated with digestion. Because angiographic evidence of partial or complete occlusions of one or more of the major splanchnic vessels is common in the absence of chronic mesenteric ischemia, such abnormalities alone are not sufficient to diagnose chronic mesenteric ischemia. Many tests have been proposed for use in diagnosing chronic mesenteric ischemia, but none has proven sufficiently sensitive or specific. The objectives of this guideline are to help the physician identify patients with chronic mesenteric ischemia and determine the best means of re-establishing adequate intestinal blood flow (see Algorithm 2 in the original guideline document).
Colon Ischemia
Colon ischemia (CI) is the most common form of intestinal ischemia and comprises a spectrum of disorders: (1) reversible colopathy, (2) transient colitis, (3) chronic colitis, (4) stricture, (5) gangrene, and (6) fulminant universal colitis. Most cases of colon ischemia do not have a recognizable cause; however, colon ischemia is seen in a number of predisposing conditions. Any patient who develops mild-to-moderate abdominal pain, diarrhea, or lower intestinal bleeding with minimal-to-moderate abdominal tenderness, especially one who has one of the predisposing conditions, should be investigated for colon ischemia. Diagnosis is by colonoscopy or barium enema, and mesenteric angiography plays little role in diagnosis unless only the right side of the colon is affected or the individual has more pain than is customarily seen with colon ischemia. Most cases of colon ischemia resolve spontaneously, but surgery may be required acutely, subacutely, or in chronic cases as described in the technical review (see Algorithm 3 in the original guideline document).
Conclusion
The spectrum of ischemic bowel disease is broad, and each type of ischemic injury requires its own unique plan of management. In general, such plans have been developed on the basis of descriptive studies and clinical experience, not on randomized controlled trials or other highly reliable forms of scientific inquiry. However, certain fundamentals seem evident.
First, patients with acute mesenteric ischemia must be identified early in the clinical course of the disease and treated aggressively if the chance of survival is to be improved. The diagnosis should be suspected when individuals, especially those at high risk for acute mesenteric ischemia, develop severe and persisting abdominal pain that is disproportionate to their abdominal findings. Such persons should undergo mesenteric angiography if another cause for the pain cannot be found on plain x-ray film studies of the abdomen or computed tomography scan, followed by surgery if angiography shows a vascular cause for the pain. The role of vasodilators is clear for nonocclusive mesenteric ischemia and is strongly suggested but not as definite for occlusive disease of the superior mesenteric artery. The role of anticoagulants and thrombolytics is evolving.
Second, chronic mesenteric ischemia should be considered in any patient who develops chronic postprandial abdominal pain and weight loss in whom no diagnosis can be made from the usual diagnostic studies. Mesenteric angiography should demonstrate severe occlusion of at least two of the three splanchnic vessels, although by itself, i.e., in the absence of symptoms, an abnormal angiography result is not sufficient for diagnosis of chronic mesenteric ischemia. Treatment is either surgical or by percutaneous transluminal mesenteric angioplasty with or without stenting. Experience with angiographic treatment modalities is limited, and at present these modalities probably are best reserved for patients at high risk for surgical revascularization.
Third, colonic ischemia is the most common form of intestinal ischemia and usually has an excellent prognosis; most cases resolve spontaneously. Diagnosis is by colonoscopy or barium enema in an individual with a typical history. Mesenteric angiography plays little role in diagnosing colonic ischemia, unless only the right side of the colon is affected or the individual has more severe pain than is customarily seen with colonic ischemia, and hence acute mesenteric ischemia is suspected. Antibiotics are often used, despite an absence of good clinical evidence for their benefit. In patients who develop acute ischemic colitis, systemic corticosteroids are best avoided, and there is no evidence supporting the use of conventional agents used to treat inflammatory bowel disease. Surgery is indicated acutely for those with peritoneal signs, massive bleeding, or fulminant colitis; subacutely for those who do not improve after 2-3 weeks or who develop recurrent sepsis; and electively in cases of symptomatic ischemic stricture or chronic colitis.
