Techniques for determining intraoperative compromise in colonic blood flow during aortic reconstruction are inadequate. We investigated the use of transanally recorded oxygen saturation in a porcine model. A Nellcor RS-10 reflectance pulse oximeter probe was attached to the balloon of a Foley catheter and passed transanally to record the oxygen saturation of the sigmoid colonic mucosa. The blood flow rate of the caudal mesenteric artery (CMA) was recorded with a Transonic ultrasonic flowmeter. CMA flow and transanal O2 saturation were recorded simultaneously as CMA flow was progressively decreased by compression of the infrarenal aorta. With unimpeded blood flow the mean O2 saturation in the distal colonic mucosa was 92.9% +/- 2.8. As CMA flow was progressively decreased to 20% of baseline flow, there was a linear decrease in colonic O2 saturation (r = 0.91 P < 0.01). At 20% of basal CMA flow, colonic O2 saturation was 54.0% +/- 4.1. Below 20% of basal CMA flow there was an abrupt loss of signal from the pulse oximeter. This study suggests that transanal pulse oximetry would provide a simple means of continuously monitoring the adequacy of distal colonic blood flow intraoperatively and may prove to be useful during aortic reconstruction when there is concern about the adequacy of blood flow to the distal colon.