The state of hyperhydration in critically ill patients with acute kidney injury (AKI) is associated with increased mortality. Bioelectrical impedance vector analysis (BIVA) appears to be a viable method to access the fluid status of critical patients but has never been evaluated in critical patients with AKI. The objective of this study is to evaluate the hydration status using BIVA in critical patients under intensive care at the time of AKI diagnosis and to correlate this measurement with mortality. A sample of 224 patients with AKI will be evaluated by BIVA and followed until they are discharged or death in intensive care unit and the BIVA vectors will be analysed to define differences in hydration characteristics from each group.