Risk Index for Postoperative Acute Kidney Injury After Valvular Surgery Using Cardiopulmonary Bypass

Background: Acute kidney injury (AKI) after valvular surgical procedures with cardiopulmonary bypass carries potentially high mortality and morbidity rates. This study investigated the risk factors for AKI, and the study investigators developed a risk index to predict postoperative AKI.

Methods: A total of 1,484 consecutive non-dialysis-dependent patients who underwent valvular operations using cardiopulmonary bypass between 2008 and 2011 were retrospectively investigated. The definition of AKI is newly required temporary hemodialysis or a creatinine level greater than 2.0 mg/dL with more than twofold elevation compared with the preoperative value.

Results: Postoperative AKI occurred in 91 patients (6.1%), among whom new dialysis dependence occurred in 45 patients (3.1%), resulting in hospital death in 22 patients (48.9%), discharge with renal function recovery in 19 (42.2%), and permanent dialysis dependence in 4 (8.9%). The overall hospital mortality rate was 3.9%. The mortality rate in patients with postoperative AKI-related complications and those who required new hemodialysis was 35.2% (32 of 91) and 48.9% (22 of 45), respectively, which was higher than in patients without AKI (1.9%; 26 of 1,393). Independent risk factors of postoperative AKI were smoking (odds ratio [OR], 2.008; p = 0.0151), diabetes mellitus (OR, 2.730; p = 0.0014), arteriosclerosis obliterans (OR, 4.351; p = 0.0317), congestive heart failure (OR, 2.455; p = 0.0052), estimated glomerular filtration rate less than or equal to 30 mL/min (OR, 4.855; p < 0.0001), and operation time longer than 8 hours (OR, 4.068; p = 0.0005). The risk index based on these risk factors predicted postoperative AKI (area under the curve, 0.81) and new requirement of hemodialysis (area under the curve, 0.86).

Conclusions: Based on these risk factors, the study investigators were able to predict the postoperative incidence of renal dysfunction after valvular operations with cardiopulmonary bypass.