Acute kidney injury on normally functioning kidneys and long-term mortality after coronary bypass surgery.

Acute renal failure (ARF) can occur in up to 50% of patients after cardiac surgery, depending on the definition of ARF, which is based on changes in plasma creatinine. Dialysis-requiring ARF affects 1% of patients after cardiac surgery [1]. Therefore, most of the patients develop milder forms of ARF with a wide spectrum of severity. Acute kidney injury (AKI) is the new consensus term employed for ARF to highlight that the process is a continuum of kidney damage that starts well before any functional derange-ment in kidney excretory function is detectable by clinical standard methods, basically plasma creatinine [2]. Likewise, a consensus functional classification of AKI developed in 2004 (the RIFLE classification) categorizes patients in stages of severity that have been shown to be in stepwise direct association with morbidity and mortality [3]. It has been known for a long time that the short-term mortality of critically ill patients who develop dialysis-requiring AKI is very high and averages 60–70% [1]. AKI in the context of critical illness, surgery or any acute illness is clinically attributed to reversible acute tubular necrosis, either toxic or ischemic. However, even when most of the patients (around 85%) recover renal function, AKI has important consequences. AKI has been demonstrated to be an independent determinant of mortality in cardiac surgery patients [1]. In recent years, it has become clear that less severe and reversible AKI is also associated with mortality in several contexts. Lassnigg et al. [4] demonstrated that the 30-day mortality in cardiac surgery patients who developed a 0-to 0.5-mg/dl and >0.5-mg/dl rise in serum creatinine was 2.77-and 18.64-fold higher, respectively, than in patients without a change in serum creatinine. AKI in the context of cardiac surgery has also been shown to influence long-term mortality. A study found [5] that the hazard ratio for death at 100 months after hospital discharge was 1.63 in patients who developed a 25% or greater rise in serum creatinine after surgery. This increase in long-term mortality was independent of whether, at discharge from the hospital, renal function had recovered, even though not to normal, because mean preopera-tive renal function was below normal in these patients. In this issue, Chalmers et al. [6] have evaluated the effects of AKI on long-term mortality in 4029 patients with normal pre-operative plasma creatinine who underwent cardiac bypass surgery. The authors show that the development of AKI adversely affects mortality after a mean follow-up …