Perioperative Free Hemoglobin Levels and Acute Kidney Injury Following Cardiac Surgery: A Cohort Study

Introduction Cardiac surgery-associated acute kidney injury (CS-AKI) is a common and lethal complication of cardiac surgery. The cardiopulmonary bypass (CPB) machine breaks erythrocytes and releases free hemoglobin (FHb) into plasma, leading to acute kidney injury (AKI). The ratio of free hemoglobin before and after cardiac surgery (post/pre-CPB FHb ratio) is a promising parameter for detecting hemolysis and predicting CS-AKI. Objectives The study aims to determine the relationship between the post/pre-CPB FHb ratio and CS-AKI and evaluate risk factors for CS-AKI. Methods A prospective cohort study was conducted on patients undergoing open heart surgery at Dr. Sardjito Hospital, Yogyakarta, Indonesia. Serial perioperative free hemoglobin levels were obtained, and all subjects were followed through to identify whether they developed CS-AKI. The appropriate statistical analyses were executed. A p-value of <0.05 was considered significant. Results A total of 21 of subjects experienced CS-AKI. The post/pre-CPB FHb ratio of 1.86 predicted CS-AKI with moderate discrimination (AUC 0.751; p=0.016). Notably, the CPB duration and mean arterial pressure were identified as independent risk factors for CS-AKI, underscoring the importance of these factors in predicting and managing CS-AKI. Conclusion When considered alongside other risk factors, the post/pre-CPB FHb ratio 1.86 emerges as a potent predictor for CS-AKI. This finding underscores the potential of measuring perioperative free hemoglobin levels, monitoring blood pressure, and optimizing the duration of CPB as valuable strategies to mitigate CS-AKI and improve patient outcomes.