A prospective international, multi-centre, prevalence study on the epidemiology of the use of renal replacement therapy for ICU patients who have acute kidney injury and chronic end stage kidney disease.

Acute kidney injury (AKI) is a common finding in intensive care unit (ICU) patients. Approximately 30 to 65% of patients experience an episode of AKI, and 5% of ICU patients are treated with renal replacement therapy. AKI is associated withimportant short term and long-term morbidity as well as mortality, and therefore also with costs. Finally, there is a close link between chronic kidney disease (CKD) and AKI. CKD patients are at greater risk for developing AKI, and survivors of AKI treated with renal replacement therapy (AKI-RRT), may develop chronic kidney disease (CKD) and end stage kidney disease (ESKD).

Different aspects of RRT modality may impact on outcomes, and data that have emerged over the last decade have improved evidence and also rejected commonly accepted dogma. Initial data suggested a better outcome when a higher dose of treatment was applied [5,6]. However, one small and two large prospective randomised controlled trials failed to reproduce these earlier findings. Observational data seems to suggest that continuous RRT (CRRT) modalities are associated with better outcomes. However, relative small, randomized studies and meta-analyses do not demonstrate such a benefit. Observational data suggests that CRRT is associated with improved renal recovery, and also examining the data from the 2 large randomized studies on intensity of RRT suggest that CRRT confers a benefit. Also, despite RRT being available for over 50 years there are no clear consensus guidelines for the initiation of RRT. A recent survey found that up to 89 different combinations of indications are used. Recently, the Acute Kidney Injury Network and the Kidney Disease: Improving Global Outcomes (KDIGO) group, formulated recommendations for this. Recent observational studies indicated that commonly accepted cut offs such as serum urea concentration are probably not that important. Furthermore, timing of initiation may have an effect on outcome. Some studies suggest that early initiation is associated with better outcome, on the other hand others could not demonstrate a benefit and have even demonstrated inferior outcomes.

The most recent survey in Europe showed that CRRT is the preferred modality among intensivists, and that despite the recently published evidence treatment doses are similar to those of a decade ago.

Data on the use of renal replacement therapy (RRT) for AKI and for CKD in ICU patients are either on specific patient groups, such as cardiac surgery patients, based on surveys, or dates back for at least a decade. Furthermore, these studies suffered from exclusion bias, as patients who fulfilled criteria for initiation of RTT, but who were denied RRT, were not considered. That this may be an important consideration is illustrated by findings from a recent small single centre study that demonstrated similar mortality rate between RIFLE-F patients who were and who were not treated with RRT. Therefore, the Acute Kidney Injury Network (AKIN) recommended measuring the epidemiology of AKI.

The investigators anticipate that the evidence that has been generated on different topics of RRT for ICU patients may have influenced current practice. Also, the investigators anticipate regional differences in RRT practice.

Inclusion Criteria:

• Patients present in the ICU at time of the study data (date starting at 0:00 h, and ending at 23:59 h) (index ICU stay)
• ≥18 years of age
• When required by local EC regulations and EC approval, informed consent (written or oral) by the patient or relative.

Exclusion Criteria:

- none

Intensive Care Unit patients diagnosed with acute kidney injury and chronic end stage kidney disease.