Kidney diseases beyond nephrology: intensive care

Acute kidney injury (AKI) is a complex disorder that occurs in a variety of settings with clinical manifestations ranging from a minimal elevation in serum creatinine to anuric renal failure [1]. It is often under-recognized and associated with severe consequences. Recent epidemiological studies demonstrate the wide variation in aetiologies and risk factors and describe the increased mortality associated with this disease (particularly when dialysis is required) [1–2]. AKI is currently recognized as the preferred nomenclature for the clinical disorder formerly called acute renal failure (ARF). This transition in terminology served to emphasize that the spectrum of disease is much broader than the subset of patients who experience kidney failure requiring dialysis support [3]. This new nomenclature underscores the fact that AKI exists along a continuum, recognizing that an acute decline in kidney function is often secondary to an injury that causes functional and/or structural changes in the kidneys and that the more severe the injury, the more likely the overall outcome will be unfavourable. The Acute Kidney Injury Network (AKIN), formed by members representing key societies in critical care and nephrology along with additional experts in adult and paediatric AKI, participated in a 2-day conference in Amsterdam, the Netherlands, in September 2005. The AKIN defined AKI as ‘an abrupt (within 48 h) reduction in kidney function currently defined as an absolute increase in serum creatinine of ≥0.3 mg/dl, a percentage increase in serum creatinine of ≥50% (1.5-fold from baseline) or a reduction in urine output (documented oliguria of <0.5 ml/kg/h for more than 6 h)’. Several specifications were provided by the workgroup to this updated definition and were followed by a new staged classification of AKI severity (Table 1); in synthesis, the time constraint of 48 h for diagnosis was selected based on the evidence that adverse outcomes with small changes in creatinine were observed when the creatinine elevation occurred within 24 to 48 h [4] and to ensure that the process was acute and representative of events within a clinically relevant time period. In the study by Chertow and