In adults, hematological ratios which can be calculated from a routinely ordered complete blood count with differential, such as the neutrophil/lymphocyte ratio, have been demonstrated to be correlated with acute kidney injury (AKI) and other clinical outcomes after cardiovascular surgery. In this retrospective observational study, the association between hematological ratios (neutrophil/lymphocyte ratio, platelet/lymphocyte ratio, neutrophil/lymphocyte\*platelet ratio, monocyte/lymphocyte ratio, and plateletcrit) and postoperative AKI, morbidity (length of ICU stay, hospital stay, mechanical ventilation, vasoactive infusion-free days, etc.) and mortality will be evaluated in neonates who underwent cardiac surgery with cardiopulmonary bypass.