Acute mesenteric fischemia may develop on top on chronic mesenteric ischemia due to an underlying atherosclerotic lesion, but may also occur de novo due to an embolic event. Typically this is a result of cardiac dysfunction, including acute MI, cardiac aneurysm, and dysrhythmia. The usual presentation is “pain out of proportion to physical findings,” where the patient complains 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.
Diagnosis is often made on computed tomographic angiography (CTA) where lack of contrast is noted in one or more of the mesenteric vessels. The superior mesenteric artery is the most commonly affected, 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, intravenous heparin bolus should be administered and arrangements are made for transfer to the operative suite made. Meanwhile, the patient should be hydrated, given prophylactic antibiotics, and hemodynamically monitored.
General anesthesia is employed with meticulous attention to hemodynamic monitoring.
The patient is positioned supine on the operating table and the entire abdomen and anteromedial thighs should be prepared and draped, in case saphenous vein be needed for mesenteric bypass. Some prefer to “frog leg” the patient so that the medial thigh is more accessible. A nasogastric tube is inserted and left in place at the completion of the procedure.
A vertical midline abdominal incision is made. The abdomen is explored and note 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 palpated for the presence of a pulse (figure 1a). In figure 1b the relevant anatomy is illustrated. 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 should all be preserved (figure 2). Depending on the status of anticoagulation, additional IV heparin may be given.
If the source of acute mesenteric ischemia is felt to be a more proximal, embolic source, then the artery may be opened transversely, so that closure is accomplished more rapidly and patch angioplasty closure avoided (figure ...