Preoperative irradiation with 5x5 Gy in a murine isolated colon loop model does not cause anastomotic weakening after colon resection

Introduction There are conflicting studies on the influence of fractionated preoperative 5 days of 5 Gy irradiation on tissue oxygenation and subsequent colonic anastomotic strength. To elucidate the effect of preoperative irradiation on anastomotic strength, an isolated colon loop model was developed. Methods Male Wistar rats (n = 164) were randomly divided into three groups. One group remained untreated (control). In the other two groups, a loop of descending colon was exteriorized to create a hernia of the abdominal wall. After 4 weeks' recovery, this loop was locally irradiated with 5x5 Gy of gamma-rays or sham irradiated. One week after (sham-) irradiation, an anastomosis was performed in all groups. Tissue oxygenation (StO(2)) was determined with visible light spectroscopy. The animals were sacrificed 3 or 7 days after the operation and the anastomosis was tested for bursting pressure and breaking strength. Results Irradiated rats showed significantly more weight loss (90% SD 4.3 of initial body weight vs. 96% SD 2.8, p <= 0.05) and enteritis (18% vs. 5%, p = 0.013) compared to sham and control animals. StO(2) was not influenced by irradiation and was not predictive for anastomotic strength. The control group showed significantly lower bursting pressure and breaking strength compared to (sham-) irradiated animals. Conclusion We developed a new isolated loop model for intermittent irradiation of the colon. Preoperative irradiation of the distal part of a colon anastomosis was successfully administered with acceptable side effects and did not cause reduced tissue oxygenation nor clinical signs of anastomotic weakening, nor objective reduction in bursting pressure and breaking strength.