The goal of this observational study is to learn the epidemiology and outcomes of acute kidney injury in critically ill adult patients admited to the intensive care unit (ICU). The main questions it aims to answer are:To provide a contemporary update on the epidemiology (rates, severity, duration, and etiology) of acute kidney injury and associated outcomes in critically ill patients.

The co-primary outcomes are:

• occurrence rate of acute kidney injury within 7 days of ICU admission
• maximum severity of acute kidney injury within 7 days of ICU admission.

Secondary outcomes:

• Proportion of acute kidney injury in patients with and without known baseline serum creatinine
• Duration of acute kidney injury episodes (within first week of ICU admission)
• Proportion of episodes with rapid reversal (duration <48h) versus persistent acute kidney injury (duration ≥48h)
• Incidence of acute kidney disease at ICU discharge and hospital discharge, truncated at 90-d
• Use of Renal Replacement Therapy within 7 days of ICU admission
• Type and specifics of applied Renal Replacement Therapy (indications, timing, modality, method duration, anticoagulation, discontinuation)
• ICU lenght of stay (ICU LOS), Hospital lenght of stay (Hospital LOS)
• ICU readmission up to day 90
• Hospital readmission up to day 90
• Serum creatinine level at ICU and hospital discharge (truncated at day 90)
• RRT dependence at hospital discharge (any RRT applied within 72 hours of discharge)
• Mortality at hospital discharge (truncated at 90-d)
• Magnitude of acute kidney injury: area under the curve of acute kidney injury severity over time
• Incidence of acute kidney injury and maximum acute kidney injury severity stage defined by serum creatinine and/or urine output criteria only, within 7 days of ICU admission.

Additional endpoints for patients included in the "long term outcomes substudy":

• Serum creatinine level at day 90, and 1 y
• Renal Replacement Therapy dependence at day 90, and 1y
• Mortality at hospital discharge at day 90, and 1y
• Survival analysis up to day 90 and 1 y
• Health-related quality of life at day 90 and 1y
• Major Adverse Kidney Events (MAKE): a composite endpoint of death, use of Renal Replacement Therapy and decreased kidney function at day 90, and 1 year.

Inclusion Criteria:

• Age >=18 y
• Admitted to a participating ICU.
• Admitted to the ICU for more than 24-h, or anticipated length of stay in the ICU for 24-h or more.
• Informed Consent according to local ethical committee

Exclusion Criteria:

• End Stage Kidney Disease treated with maintenance renal replacement therapy
• Readmission to the ICU during same hospitalization episode
• Missing acute kidney injury defining data (no measured serum creatinine and <6 hours of documented urinary output)

adult ICU patients