Epidemiology
Colonic ischemia frequently occurs in older people with comorbidities.[7] One systematic review identified 4 studies reporting incidence rates in general populations; three of the studies reported rates between 4.5 and 9 cases per 100,000 person-years and the fourth study reported a rate of 44 cases per 100,000 person-years.[8] These rates likely underestimate the true incidence as many patients with mild symptoms do not seek medical care.[8] Irritable bowel syndrome, recent cardiovascular surgery, constipation, chronic obstructive pulmonary disease, and other factors increase the risk of developing colonic ischemia between two- and fourfold.[8][9][10]
Acute mesenteric ischemia accounts for less than 0.2% of hospital admissions.[11] It occurs more commonly in those with comorbidities, most notably atrial fibrillation, myocardial infarction, and atherosclerosis. It has been estimated that acute arterial mesenteric ischemia is responsible for up to 1% of patients presenting with an acute abdomen.[12] One study in Sweden found that between 1970 and 1982, the overall incidence of acute thromboembolic occlusion of the superior mesenteric artery was 8.6 cases per 100,000 person-years, increasing to 216.5 cases per 100,000 person-years in those ages >85 years.[13] Nonocclusive mesenteric ischemia (NOMI) accounts for 20% to 30% of acute mesenteric ischemia.[11][14] The overall incidence of NOMI is 2 cases per 100,000 person-years, increasing to 40 per 100,000 in patients ages >80 years.[15] NOMI may also occur in patients receiving enteral nutrition in intensive care following surgery or trauma; in this context, it is associated with a very poor prognosis.[16]
Risk factors
A history of smoking, often in combination with peripheral vascular disease and hypertension, is also frequently present.[23]
A strong risk factor for mesenteric venous thrombosis (MVT). Diagnosis of MVT should be particularly suspected in patients who have sudden onset of severe abdominal pain and high risk of thromboembolism; approximately 50% of patients presenting with MVT have had a deep vein thrombosis or pulmonary embolus in the past.[18][23] Common causes of hypercoagulability include cirrhosis or portal hypertension; inheritable hypercoagulable states such as factor V Leiden, protein C deficiency, or prothrombin G20210A mutation; oral contraceptive use; malignancy; pancreatitis; and a history of recent surgery.[23]
Untreated, atrial fibrillation can result in the formation of thrombi within the heart, which then embolize to the mesenteric vasculature.[21]
Impaired wall motion secondary to myocardial infarction can act as a nidus for thrombus formation, which can then embolize to the mesenteric vessels.
Defects such as right-to-left shunts can increase the risk of emboli to mesenteric vessels.
Rheumatoid arthritis, polyarteritis nodosa, systemic lupus erythematosus, dermatomyositis, Takayasu arteritis, and thromboangiitis obliterans can all result in ischemia of the bowel. The exact clinical picture varies depending upon factors such as the size of the mesenteric vessel involved.
Chronic mesenteric ischemia most commonly occurs in patients with severe, occlusive atherosclerosis involving the celiac axis and mesenteric arteries.[17] Atherosclerosis may lead directly to intestinal hypoperfusion and ischemia due to partial or complete occlusion of vessels supplying the gut. When atherosclerosis occurs in more distant vessels, it can act as a source of emboli.
Severe atherosclerosis in vessels supplying the gut also makes individuals more vulnerable to bowel ischemia occurring from reductions in perfusion arising from congestive heart failure or shock.
Between 0.6% and 6.7% of patients who have recently undergone cardiac or major vascular procedures develop colonic ischemia; mortality may be as high as 80% in this population.[2][3] Surgical management of thoracic and abdominal aortic aneurysms (AAAs) is strongly associated with bowel ischemia; prevalence following repair of ruptured AAA is up to 10% and after elective endovascular repair incidence is up to 2.8%.[3][4] Factors that may underlie these figures include emboli arising from cross-clamping of the aorta, a risk of intestinal hypoperfusion in the postoperative period, and a relatively high incidence of heart failure in these patients. Significant risk factors for mesenteric ischemia post cardiac surgery include advanced age (>70 years), prolonged bypass time, emergency surgery, higher volume of blood loss, and other evidence of postoperative organ dysfunction, such as a rise in lactate, transaminases, and creatinine.[5][6]
Hypoperfusion due to shock may exacerbate to a critical level any underlying intestinal low-flow states that may be present due to atherosclerosis. Even in the absence of an existing low-flow state, severe shock can result in ischemia of the bowel.
Heart failure may exacerbate underlying intestinal low-flow states that may be present due to atherosclerosis. Even in the absence of an existing low-flow state, severe heart failure can lead directly to ischemia of the bowel.
Approximately 20% of older patients with colonic ischemia have a distal obstruction from carcinoma, stricture, fecal impaction, or diverticular disease. The proximal colonic distension leads to intraluminal dilation and increased pressure that may result in decreased mucosal perfusion.
Constipation and prolonged straining during defecation result in transient decreased colonic blood flow, which in patients with low-flow states can trigger ischemia.
Especially in the setting of severe atherosclerosis, use of vasopressors, digitalis, and cocaine have been shown to exacerbate nonocclusive mesenteric ischemia.[23]
Use of this content is subject to our disclaimer