Cardiac Surgery Associated Kidney Injury: Predictors, Biomarkers and Prevention Associated Cost Reduction

Abstract

Background: Cardiac surgery associated acute kidney injury (CS-AKI) at any stage complicates 22-36% of procedures. It is independently associated with morbidity and total hospital costs. Existing risk prediction scores poorly discriminate high-risk patients. Functional markers, such as serum creatinine and urine output, reflect kidney function but do not indicate early stress. Therefore, it has been suggested that routine clinical assessment should be combined with damage biomarkers and functional markers for risk stratification, severity assessment and management planning. Objective: To determine the incidence and the main predictors of postoperative AKI in patients submitted to cardiac surgery, as well as to evaluate hospital and intensive care unit (ICU) length of stay (LOS) in these patients. A secondary analysis was made to estimate the potential benefit of including damage biomarkers evaluation in our clinical practice. Methods: In a retrospective single-center cohort study, we analyzed a consecutive sample of adult patients who underwent elective cardiac surgery between January and March 2015, at the Department of Cardiothoracic Surgery of São João Universitary Hospital Center. Preoperative and intraoperative data was collected. Data from all patients was analyzed until hospital discharge or death. A logistic regression was performed to evaluate independent predictors of CS-AKI. An economic analysis was performed from the hospitals' costs perspective. Costs reduction was calculated considering the absolute risk reduction (ARR) regarding the combined use of damage biomarkers - tissue inhibitor of metalloproteinases-2 and insulin-like growth factor-binding protein7 ([TIMP-2]x[IGFBP7]) - followed by the application of Kidney Disease: Improving Global Outcomes (KDIGO) bundle of care in high-risk patients. Results: We included 274 patients admitted for elective cardiac surgery, all Caucasian. CS-AKI occurred in 86 patients (31%). After adjustment, higher preoperative serum creatinine (mg/L, ORadj =1.10; CI95%: 1.01-1.19), lower preoperative hemoglobin (g/dL, ORadj =0.80; CI95%: 0.70-0.98) and preoperative hypertension (ORadj=2.91; CI95%: 1.24-6.84) remained significantly associated with CS-AKI. An increase in cardiopulmonary bypass time (CPB) (min, ORadj=1.01; CI95%: 1.00-1.01) and perioperative use of sodium nitroprusside (ORadj=5.31; CI95%: 1.51-18.72) were also significantly associated with the risk of CS-AKI. Male gender was marginally associated with CS-AKI (ORadj=2.02; CI95%: 0.99-4.11). Regarding the economic analysis, the expected cumulative surplus cost for the hospital, associated with CS-AKI (86 patients), was 120,695.84 EUR. Estimated cumulative costs for all 276 patients was 1,476,418.88 EUR. Based on an ARR of 16.6% (5.5-27.9%), the average reduction of cumulative costs, associated with the use of [TIMP-2]x[IGFBP7], would be of 31,190.12 (314.44-60,662.36) EUR. Conclusions: At our center, incidence of CS-AKI was 31%. Preoperative hemoglobin, serum creatinine, systemic hypertension, CPB time and nitroprusside were settled as AKI independent predictors. Costs associated with CS-AKI were increased, related to the overall increase in LOS. The use of damage biomarkers combined with early treatment strategy could be associated to a potential cost saving.