Risk factors profile for acute kidney injury after cardiac surgery is different according to the level of baseline renal function

Acute kidney injury (AKI) occurs frequently after cardiac surgery. Although numerous variables were identified as predictors for AKI, there is a lack of information about possible differences in risk factors according to the level of preoperative renal function. Preoperative, intraoperative, and postoperative data from 4118 adult patients submitted to cardiac surgery from January 1, 2000, to December 31, 2005, were included in the study. AKI was defined by an increase in serum creatinine (S-Cr) >= 0.3 mg/dL after surgery. Patients were stratified into two groups: group 1, C-Cr >= 60 mL/min/1.73 m(2) BSA; group 2, C-Cr < 60 mL/min/1.73 m(2) BSA. Risk factors were assessed using a multiple logistic regression model. In all, 749 patients (42.5%) developed AKI. The mortality rate of the entire population was a 5.2%. In patients of group 1 (n = 2678), the variables independently associated with the onset of AKI were age, diabetes, preoperative use of diuretics, non-scheduled surgery, cardiopulmonary by-pass (CPB) time, CPB mean arterial pressure, hemodilution, and postoperative use of norepinephrine. Baseline S-Cr was associated with AKI only in patients of group 2 (n = 1440). Age, EuroSCORE, non-coronary surgery, hemodilution, and postoperative use of vasoactive drugs were also predictors of AKI in this group of patients. The mortality rate was significantly higher in group 2 than group 1 (8.5% vs. 3.6%, p = 0.000). In conclusion, the present study demonstrated a difference in variables associated with postoperative AKI, according to baseline renal function. The degree of preoperative renal function was a predictor of AKI only in patients with CKD stages 3-4, as well as other risk factors. In addition to other well known risk factors for AKI in this setting, the use of diuretics in patients of group 1 and the level of hemodilution during CPB in both groups should be emphasized, as they are potentially modifiable.