<b><i>Purpose:</i></b> The study aimed to investigate patients' characteristics, fluid and hemodynamic management, and outcomes according to the severity of cardiac surgery-associated acute kidney injury (CSA-AKI). <b><i>Methods:</i></b> In a single-center, prospective cohort study, we enrolled 282 adult cardiac surgical patients. In a secondary analysis, we assessed preoperative patients' characteristics, physiological variables, and medication for intra- and postoperative fluid and hemodynamic management and outcomes according to CSA-AKI stages by the Renal risk, Injury, Failure, Loss, End-stage renal disease (RIFLE) classification. Variables of fluid and hemodynamic management were further assessed with regard to the need for postoperative renal replacement therapy (RRT) and in-hospital mortality by the area under the curve for the receiver operating characteristic (AUC-ROC) and multivariate regression analysis. <b><i>Results:</i></b> Patients with worsening RIFLE stage, were significantly older, had lower estimated glomerular filtration rate and higher body mass index, more peripheral vascular and chronic obstructive pulmonary disease, atrial fibrillation, and prolonged duration of cardiopulmonary bypass (all <i>p</i> < 0.01). Patients with more severe AKI stage stayed longer in the intensive care and hospital, had higher in-hospital mortality, and requirement for RRT (all <i>p</i> < 0.001). Also, with worsening RIFLE stage, patients had lower intraoperative mean arterial pressure (MAP); <i>p</i> = 0.047, despite higher doses of norepinephrine (<i>p</i> < 0.001). The intraoperative MAP showed the best discriminatory ability (AUC-ROC: >0.8) for and was independently associated with RRT and in-hospital mortality. Moreover, with increasing AKI severity, patients received significantly more fluid infusion, and required higher dose of furosemide; nonetheless, they had increased postoperative fluid balance. <b><i>Conclusions:</i></b> In this cohort, reduced MAP and increased fluid balance were independently associated with increased mortality and need for RRT after cardiac surgery.