Acute kidney injury based on KDIGO (Kidney Disease Improving Global Outcomes) criteria in patients with elevated baseline serum creatinine undergoing cardiac surgery

INTRODUCTION Preoperatively elevated serum creatinine (SCr) is considered an independent risk factor for morbidity and mortality after cardiac surgery. The aim of this study was to apply the Kidney Disease Improving Global Outcomes classification for acute kidney injury in a population of patients with preoperatively elevated serum creatinine who underwent cardiac surgery (coronary artery bypass grafting or cardiac valve surgery) and to evaluate the acute worsening of renal function as a predictor of 30-day mortality. METHODS This was a single-center retrospective study that included patients from the Postoperative Cardiac Surgery Intensive Care Unit of the Hospital de Base, São José do Rio Preto Medical School. Demographics, type of surgery, laboratory data and pre, peri and postoperative data were obtained from a prospectively collected database. From January 2003 to June 2013, 2,878 patients underwent cardiac surgery, either coronary artery bypass grafting or cardiac valve surgery, at the Hospital de Base of São José do Rio Preto Medical School. Out of those, 918 showed elevated preoperative serum creatinine, with SCr > 1.30 mg/dL for men and > 1.00 mg/dL for women. Five hundred and forty nine patients (60%) undergoing coronary artery bypass grafting and 369 patients (40%) undergoing cardiac valve surgery. A Multivariate Cox Proportional Hazard Model (stepwise) was used to assess the relationship between AKI and mortality at 30 days. RESULTS Out of the 918 patients studied, 391 (43%) had postoperative AKI: 318 (35%) had Kidney Disease Improving Global Outcomes stage 1, 27 (2.9%) had Kidney Disease Improving Global Outcomes stage 2, and 46 (5.0%) had Kidney Disease Improving Global Outcomes stage 3. Patients in every stage of acute kidney injury showed progressive increase in EuroSCORE values, 30-day mortality rates, cardiopulmonary bypass duration, and intensive care length of stay. Among patients classified as Kidney Disease Improving Global Outcomes stage 3, 76% required dialysis with a 30-day mortality of 66%. The Cox proportional hazards model showed that the hazard ratio for 30-day mortality was 4.8 for Kidney Disease Improving Global Outcomes stage 1 patients, 13.5 for Kidney Disease Improving Global Outcomes stage 2 patients, and 20.8 for Kidney Disease Improving Global Outcomes stage 3 patients (P<0.001 for all). Subgroup analyses (coronary artery bypass grafting and cardiac valve surgery) had similar results. CONCLUSION In this population, acute kidney injury based on the Kidney Disease Improving Global Outcomes criteria was a powerful predictor of 30-day mortality in patients with elevated preoperative serum creatinine who underwent cardiac surgery (coronary artery bypass grafting or cardiac valve surgery).