 3. Power analysis The sample size of this trial was calculated based on the primary endpoint: the reduction of AKI incidence. Despite we do not have track incidence, AKI is very common in our MGH patients after open-heart surgery, and it is reasonable to assume that AKI incidence is similar to those recent reports from US and European studies at major academic centers CPB AKI incidence has been reported to be between 50 to 60. In our prior trial on NO in cardiac surgery, the sample size was calculated to find a 30 reduction in the incidence of AKI n212 in that trial. We estimate a greater 35 reduction in the incidence of AKI because we anticipate that this population with endothelial dysfunction will be more affected by the beneficial therapeutic properties of NO. Thus, in the NO group the incidence of AKI is expected to decrease from 55 to 35.75. The sample size needed to detect a difference, assuming an alpha error of 0.05 two-sided test and a study power of 0.8, is 114 patients per group. In order to account for possible dropouts, we increased our sample size by 10. We will enroll 250 patients, 125 in the NO group and 125 patients in the control N2 group. 