Final answer:
Bowel ischemia following AAA repair arises due to disruptions in blood flow to the intestines caused by compromised collateral circulation, occlusion of intestinal arteries, or thromboembolic events.
Step-by-step explanation:
Bowel ischemia can arise from abdominal aortic aneurysm (AAA) repair due to a disruption in blood flow to the intestines. During AAA repair, especially when the aneurysm is located close to the origins of the intestinal arteries, collateral circulation may be compromised. Collateral circulation refers to alternate pathways of blood flow that become important when a primary vessel is obstructed or narrowed. If these collateral routes are disturbed during surgery, it can lead to ischemia, which is a deficiency of blood supply to a tissue. This occurs because the blood vessels supplying the bowel may get occluded or the blood flow may be inadvertently redirected away from the intestines.
Besides direct vessel manipulation, another cause of ischemia post-AAA repair can be thromboembolic events, where blood clots that form during the procedure break off and occlude the intestinal arteries. Moreover, prolonged operation time and clamping of the aorta can contribute to a decreased blood supply to the intestines, increasing the risk of ischemia.