Introduction

There is a wide spectrum of severity of acute renal dysfunction after cardiac surgery, ranging from subclinical renal injury to acute renal failure (ARF) requiring renal replacement therapy. The incidence of ARF following cardiac surgery varies depending on the definition, but approximately 5% of cardiac surgical patients require renal replacement for ARF. Acute renal failure is a serious complication; it is associated with increased mortality and prolonged critical care unit and hospital stays.

Measurement of renal function

Although serum creatinine and urine output lack sensitivity and specificity in renal dysfunction, these indices are the most easily measured in clinical practice. Measurement of glomerular filtration rate by creatinine clearance is less straightforward and is of limited value in the absence of steady-state conditions. Other tests of renal function are of questionable clinical use; newer biomarkers are under evaluation and may have greater sensitivity for detecting renal dysfunction.

Definition of acute renal failure

Until recently, there has been no consensus on the optimal measurement of renal function or the definition of ARF. An international interdisciplinary collaborative group, the Acute Dialysis Quality Initiative, has formulated a standard definition of acute renal dysfunction, a term that encompasses the range of abnormalities of renal function. The acronym RIFLE defines three grades of increasing severity of acute renal dysfunction (risk; injury; failure) and two outcome variables (loss; end stage).