Acute kidney injury Acute kidney injury (AKI) is a new term for acute renal failure (ARF) recently developed by an international group of nephrologists and critical care specialists. The introduction of this terminology will not only change the long-standing lack of a uniform and concise definition of the ARF group of diseases, but will also provide a more comprehensive coverage of the various causes of ARF. AKI refers to structural or functional abnormalities of the kidney that occur within 48 hours, as confirmed by blood and urine tests, histology and imaging. The diagnostic indicator is hyperalgesia, which is a 0.3 mg/dL increase in serum creatinine concentration or a 50% increase in serum creatinine level compared to the previous one. Another diagnostic indicator is decreased urine output, i.e., oliguria – urine output below 0.5 mL/kg/h for more than 6 hours. Epidemiology Most AKI occurs in hospitals, where the incidence ranges from 5% to 7%. In contrast, recent studies have shown that the incidence of community-acquired AKI is only 1 percent. In either case, AKI is extremely life-threatening, with a mortality rate of 36% to 86%. The mortality rate depends on the age of the patient, the cause of the AKI and its acuteness. Elderly patients with hospital-acquired AKI in the intensive care unit have a higher mortality rate. Furthermore, there has been a gradual increase in mortality in patients with AKI in recent years. Patients with seemingly mildly elevated serum creatinine levels can often lead to a significant increase in mortality. In several studies, an increase in serum creatinine concentration of only 0.3 mg/dL has been shown to significantly increase mortality. Pathology AKI has numerous etiologies, many of which are physiologic in nature. Decreased renal perfusion with or without cellular injury, tubular toxicity, ischemia or obstruction, inflammation and edema of the tubular interstitium, and progression of primary glomerular disease can all cause renal damage resulting in decreased glomerular filtration rate (GFR). From a conceptual and diagnostic point of view, the different causes of AKI can be summarized into three categories according to their anatomical location, namely, prerenal, renal and postrenal (see Figure 121 – 1). Each type has its own specific pathophysiological process, as well as different diagnostic indicators and prognosis.