Int J Colorectal Dis (2009) 24:789–795 patients without AL (3.9%; p= 0.001). The incidence of urinary tract infections, pneumonia, ileus, and wound infections did not differ significantly. Abdominal wound dehiscence (AWD), however, occurred more often in the group of patients with AL (8% vs. 5%, p = 0.046). The mean hospital stay after operation and the stay at the ICU of patients with AL were 47 days and 7 days, respectively, whereas patients without AL stayed in the hospital 14 days and 1 days at the ICU, respectively (p=0.000). Discussion Leakage of a colorectal anastomosis still is a vast problem despite decades of research on this matter. This study was performed in order to improve understanding of this complication and to study new potential risk factors. Incidence of anastomotic leakage In this study, an overall incidence of 8.7% was found over a period of 10 years. In literature leakage rates between 3% and 6% are reported for colonic anastomosis [28, 29], while leakage rates between 16% and 19% for low colorectal anastomosis are reported [2, 30]. Therefore this finding can be considered “average” considering anastomoses in the colon as well as in the rectum were included. The trend that was found in our study, i.e., higher leakage rates with lower anastomosis, is well-known too [31]. The leakage rate after resection of the transverse colon (four of 27) is remarkably high, which is not confirmed in literature [6]. Possibly the involvement of the watershed area at the splenic flexure and Griffiths’ critical point (insufficient marginal artery at splenic flexure) contribute to this high leakage rate [32]. However, since this group is relatively small and the 95% confidence intervals for the leakage rate is wide (4–34%), this finding should be considered only as an indication for further research. Risk factor analysis The multivariate risk factor analysis showed BMI, time of operation and prophylactic drainage to be major factors, independently associated with anastomotic leakage. A BMI higher than 30, which is considered obese according to the Centers of Disease Control and Prevention (CDC) [33], increased the risk for developing leakage almost three-fold. As to the explanation of this correlation, it remains unclear whether obesity indicates a defect of tissue structure and healing, whether the increased intra- abdominal pressure plays a role or whether construction of an anastomosis simply is technically more demanding because of thick mesenteries and epiploic appendices. A 793 possible solution might be to lower the threshold for construction of a diverting stoma in this population [31]. However, since construction of a stoma is difficult in patients with high BMI, sensibilization and a higher alert for anastomotic leakage in these patients on the ward is a more logical consequence of this finding. Patients operated upon after-hours had more than a twofold increased risk of anastomotic leakage. This finding was independent of the urgency of the operation, which may be explained by the fact that urgent operations were also performed during-hours and elective operations were performed after-hours (Table 4). The latter occurs regularly due to incoming trauma- or transplantation patients that require immediate operation (Table 4). Possible explanations could be found in the fact that significantly more anastomoses were constructed by resi- dents after-hours (95%) than during-hours (81%; p< 0.001) and that after-hours, obviously, significantly more urgent operations were performed (86%) than during-hours (10%; p <0.001). However, these factors were no independent risk factors in multivariate analysis. Since many potential confounders have been accounted for and are not significant (Table 1), it is reasonable to assume a decreased technical performance of the operating team has contributed to a higher leakage rate at night. This assumption is supported by several studies that have shown medical errors to occur more often at night [24, 34]. In addition, physicians appear to be less proficient at night, which leads to more errors at night than during daytime [25–27]. Decreased non-technical skills of the operating team at night, like teamwork- and management skills and situational awareness, could have contributed to higher leakage rates as well. Situational awareness (SA), defined as the ability of the surgeon to observe, understand and predict events in the operating room (OR), appears to be closely related to technical error rates [35]. In addition, the situational awareness, teamwork- and management skills of the anesthetists and nurses may have an important impact on the outcome of surgical patients as well [27]. Based upon these results, it should be considered to construct a diverting stoma when after-hours construction of a colo- rectal anastomosis is required. Table 4 Distribution of urgent and elective operations Urgent vs. Elective Time of surgery During hours After-hours Urgent 64 (10%) 92 (87%) Elective 569 (90%) 14 (13%)