Renal replacement therapy for AKI: When? How much? When to stop?

Severe acute kidney injury (AKI) requiring renal replacement therapy (RRT) is a serious clinical disorder in the intensive care unit (ICU), occurring in a significant proportion of critically ill patients. However, many questions remain about the optimal administration of RRT with regard to several important considerations, including treatment dose, timing of treatment initiation and cessation, therapy mode, type of anticoagulation, and management of fluid overload. While Level 1 evidence exists for RRT dosing in AKI, all the studies contributing to this evidence base employed fixed-dose regimens throughout a patient's continuous RRT (CRRT) course, without regard for the possibility of individualizing treatment dose according to the clinical status of a given patient at a specific time. As opposed to CRRT dose, no consensus about the timing of RRT in critically ill AKI patients exists currently. While numerous clinical trials over the past 40 years have attempted to assess "early" versus "late" initiation of RRT, they have been plagued by a myriad of methodological problems, including their largely observational nature and the widely varying definitions of early and late initiation. Although questions about the appropriate timing of CRRT discontinuation arise very frequently in clinical practice, even less information is available in the literature to guide this important decision. The aim of this review is to provide a comprehensive update on RRT delivery to critically ill AKI patients, with specific attention paid to treatment dose and timing and emphasis on addressing the practical questions that arise in daily clinical practice.