(1776) Acute Kidney Injury After Cardiac Surgery Is Associated With Perioperative Hemolysis

Introduction: AKI occurs in 3-40% of cases after cardiac surgery with cardiopulmonary bypass. Various factors have been associated with the risk of developing AKI, but free hemoglobin produced by hemolysis has also been reported to be involved (Ann Thorac Surg 2011;92:1539- 47). However, few studies have examined hemolysis in terms of free hemoglobin measurement and the development of AKI after cardiac surgery.

Methods: Adults cardiac surgery with cardiopulmonary bypass performed at Kawasaki Medical School Hospital from September 2023 to July 2024 was included. The study was approved by the Ethics Committee of the hospital. Management of patients including cardiopulmonary bypass were performed according to our general protocol. Blood and urine samples were collected at three time points: at anesthesia induction(T1), on admission to the intensive care unit(T2), and the day after surgery(T3) to measure neutrophil gelatinase-associated lipocalin (NGAL) and urinary cystatin C and free hemoglobin as an indicator of hemolysis, Stage 1 or higher was defined as AKI. Patients were divided into two groups: group A with AKI and group N without AKI.

Results: Twenty-eight patients were enrolled during the study period. Five of these patients (17.9%) developed AKI of stage 1 or higher by KDIGO classification. comparing group A (n=5) and group N (n=23), urinary NGAL at T2 and serum NGAL at T3 were significantly higher in group A [urinary NGAL 268. 5 ng/mL (95% CI: 111.7 - 425. 4) vs. 82.5 (10.6 - 154.5), P = 0.036, and serum NGAL 346.9 ng/mL (95% CI: 230.4 - 463.3) vs. 147.2 (95.1 - 199.2), P = 0.037 ]. Urinary cystatin C at T3 was also significantly higher in group A [1.3 mg/L (95% CI: 0.94 - 1.7) vs. 0.8 (0.66 - 1.0), P=0.024]. On the other hand, free hemoglobin concentration, an indicator of hemolysis, was higher in serum and urine at T2 and T3, and serum free hemoglobin was significantly higher in group A at T3 [0.056 g/dL (95% CI: 0.031 - 0.081) vs 0.007 (0.004 - 0.019), P=0.001].
Patients who developed kidney injury may have hemolysis, and this association should be investigated in the future.

Conclusions: Patients who developed AKI after cardiac surgery with cardiopulmonary bypass had elevated renal biomarkers in blood and urine. The degree of hemolysis was higher in patients with AKI than in those without AKI.