Comparison of ischemic and reperfusion injury in canine bowel viability assessment.

The purpose of these experiments was to evaluate two methods of bowel viability assessment in two distinct models of intestinal ischemia. Bowel viability was assessed in 32 dogs by means of three methods: (1) a probe that quantified the intestinal electromyographic (EMG) measurements in millivolts (mV), (2) Doppler ultrasonography, and (3) perfusion fluorometry, which quantified serosal blood flow in indexed dye fluorescence units (dfi). Ischemia was created using one of two methods: (1) a chronic model in which the blood supply to 40 cm of ileum was ligated and viability assessed 24 hours later, or (2) an acute model in which the main superior mesenteric artery was occluded for 3 1/2 hours and then released. Viability parameters were assessed every 5 minutes for 30 minutes after release. After viability assessment was completed, the ischemic bowel was resected and anastomosed at the site where the EMG measurements approximated 50% of the values obtained in normal bowel. In the chronic group 3 of 20 dogs died of necrosis in contrast to none of 12 dogs in the acute reperfusion group. In the acute model EMG values steadily increased after reperfusion, stabilizing by 15 minutes after release. Mean EMG values at 15 through 30 minutes after release were significantly greater than the 5- and 10-minute postrelease and prerelease values, suggesting that the electromyogram is affected by reperfusion. Conversely, postrelease fluorometry measurements rapidly increased to levels that exceeded measurements obtained in normal bowel. There was a significant difference in the number of audible Doppler signals in the marginal artery of survivors of the acute vs. the chronic model. Fluorometry measurements in survivors of the acute model (99+/-9 dfi) were significantly greater than measurements in the chronic model (54+/-4 dfi, P<or=0.004). Conversely, intermodel differences in the EMG measurements were not significant. These results show significant differences in the magnitude of ischemic damage induced by reperfusion vs. mesenteric ligation, which had a significant impact on the objective blood flow measurements that were used to predict bowel viability. The results also suggest that intestinal reperfusion injury in dogs has a negligible impact on bowel survival.