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Acute mesenteric ischemia may develop on top of chronic mesenteric ischemia because of an underlying atherosclerotic lesion but also may occur de novo due to an embolic event. Typically, this is a result of cardiac dysfunction, including acute myocardial infarction, cardiac aneurysm, and dysrhythmia. The usual presentation is pain out of proportion to physical findings, where patients complain of the worst abdominal pain they have ever had, but physical examination elicits a soft abdomen with no discrete tender areas. Acute mesenteric ischemia is a surgical emergency where time is of the essence to avoid full-thickness bowel necrosis and even death.
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PREOPERATIVE PREPARATION
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Diagnosis is often made on computed tomographic angiography, where lack of contrast material is noted in one or more of the mesenteric vessels. The superior mesenteric artery is affected most commonly, and often the thrombus lodges at the site of the first branch. The arteries should be surveyed for any signs of atherosclerosis and the bowel examined for any thickening, implying early ischemia, or evidence of full-thickness necrosis. As soon as a diagnosis is made, an intravenous heparin bolus should be administered, and arrangements should be made for transfer to the operative suite made. Meanwhile, the patient should be hydrated, given prophylactic antibiotics, and hemodynamically monitored.
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General anesthesia is employed with meticulous attention to hemodynamic monitoring.
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Patients are positioned supine on the operating table, and the entire abdomen and anteromedial thighs should be prepared and draped in case saphenous vein is needed for mesenteric bypass. Some surgeons prefer to “frog leg” the patient so that the medial thigh is more accessible. A nasogastric tube is inserted and left in place at completion of the procedure. Then a time-out is performed.
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A vertical midline abdominal incision is made. The abdomen is explored, and note is made of any area of ischemia of the bowel or other organs. The small bowel is eviscerated to the right, and the root of the mesentery is palpated for the presence of a pulse (FIGURE 1A). The relevant anatomy is illustrated in FIGURE 1B. The superior mesenteric artery is exposed by dissecting parallel to it within the base of the mesentery. A self-retaining retractor is used for exposure purposes. Mesenteric venous branches and lymphatics are carefully ligated and divided. Silastic vessel loops are placed around the artery proximally, near the takeoff from the aorta, and distally, as well as on any side branches, which all should be preserved (FIGURE 2). Depending on the status of anticoagulation, additional intravenous heparin may be given.
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If the source of acute mesenteric ischemia is felt to be a more proximal embolic source, the artery may be opened transversely so that closure can be accomplished more ...