<qa>  What is the primary aim of this study?2. Statistical methods The primary aim of this study is to determine whether supplementation with NO decreases the incidence of AKI in patients with endothelial dysfunction. A total of 250 cardiac-surgery patients will be enrolled, requiring more than 90 minutes of CPB. The two arms will be compared for homogeneity of baseline characteristics age, weight, sex, and GFR, intraoperative course cardiac-surgeonanesthesiologist, CPB time, amount of blood transfusions and postoperative data post-operative transfusions, adverse events directly related to surgery procedures. To examine differences between the two groups, we will use an unpaired Students t-test for continuous variables with a normal distribution, a Mann-Whitney U test for continuous variables that are not normally distributed and a Fishers exact test for dichotomous variables. Continuous variables will be described as meanstandard deviation SD when normally distributed, median with interquartiles IQR when not normally distributed, or count if a dichotomous variable. The change in the laboratory markers over time and between the two groups will be tested with a repeated measures ANOVA. The incidence of AKI and postoperative adverse events after prolonged CPB will be described in terms of relative risk with significance level and confidence intervals for the two groups. Based on the occurrence of missing data, the strategy to manage them will be decided. However, our aim would be not to use any kind of imputation. 