Infrarenal aortic occlusion, colonic blood flow, and the effect of nitroglycerin afterload reduction.

Colonic ischemia has been reported to occur in 1% to 13% of all cases of aortic reconstruction. To examine intestinal blood flow in aortic occlusion, three groups of dogs were subjected to measurement of hemodynamic parameters and mesenteric blood flow. Group I served as a control group, while group II underwent balloon catheter occlusion of the infrarenal aorta. Group III received intravenous nitroglycerin infusion during and after aortic occlusion. There was no statistically significant change in intestinal blood flow in group I. Small bowel mucosal blood flow fell in group II. Small bowel serosal blood flow was preserved but total small bowel and small bowel mucosal values fell sharply in group III. Ascending and descending colonic blood flow was unaltered in group I but fell significantly in groups II and III. After restoration of normal aortic circulation, small bowel mucosal flow remained significantly below baseline in groups II and III. Ascending and descending colonic blood flow also remained depressed in groups II and III. Both mucosal and serosal blood flow fell and serosal values remained constant in group III. Both groups exhibited decreased total, mucosal, and serosal blood flow in the descending colon after release of the aortic occlusion. These data show that temporary infrarenal aortic occlusion causes significant changes in intestinal blood flow. The mechanism is due to persistent autoregulatory vasoconstriction. Nitroglycerin used for afterload reduction in aortic reconstruction does not ameliorate decreases in intestinal blood flow and may actually shunt blood away from the distal colon and the distal intestinal mucosa during aortic occlusion.