Subclinical AKI and Clinical Outcomes in Elderly Patients Undergoing Cardiac Surgery: Diagnostic Utility of NGAL versus Standard Creatinine Increase Criteria

Abstract

<b><i>Background:</i></b> Acute kidney injury (AKI) is a common and serious postoperative complication in patients undergoing cardiac surgery and its incidence is particularly high among elderly patients. Cardiac surgery-associated AKI (CSA-AKI) represents the second most common cause of AKI in the intensive care unit but its true incidence could be underestimated, especially in elderly population. The current biomarkers of AKI are unreliable and delayed during acute changes in kidney function. In the setting of subclinical AKI (SAKI), biomarkers of tubular damage, such as NGAL, seem to be an early indicator of kidney damage. The aim of this study was to investigate NGAL utility in the SAKI diagnosis in the first 48 h after cardiac surgery and its helpfulness in predicting adverse clinical outcomes in comparison to current criteria for AKI. <b><i>Methods:</i></b> This is an observational study of 72 patients admitted to San Bortolo’s cardiac surgery department for elective cardiosurgical procedure enrolled over a 5-months period. All patients underwent peripheral venous sample 48 h after cardiac surgery to assess plasmatic creatinine (48Cr) and NGAL (48pNGAL) in addition to exams already foreseen by clinical practice. For each patient we studied renal, respiratory and cardiovascular outcome during hospitalization as well as 30 days and 6 months mortality. Creatinine Increase AKI (CrIAKI) was defined by 48CrI ≥0.3 mg/dL and SAKI was defined by 48pNGAL ≥100 pg/dL. We also assessed Respiratory (ArespO) as well as Cardiovascular (ACvO) outcome. <b><i>Results:</i></b> Thirty days mortality was 8.3% (6 patients) and 6 months mortality was 12.5% (9 patients). A total of 27 patients (37.5%) presented AKI according to KDIGO (4) and 4 (5.5%) needed renal replacement therapy (RRT). SAKI was significantly associated with 30 days mortality (<i>p</i> = 0.0238), 6 months mortality (<i>p</i> = 0.002), Adverse renal outcome (ARenO) (<i>p</i> = 0.004) and need for RRT (<i>p</i> = 0.005). CrIAKI was significantly associated with 30 days mortality (<i>p</i> = 0.009) and ARenO (<i>p</i> = 0.0001), but not with 6 months mortality nor need for RRT.