Timing of renal replacement therapy in critically ill patients: where are the hands on the clock?

Renal replacement therapy (RRT) is a key component in the management of acute kidney injury (AKI) in the intensive care unit (ICU). Whilst most studies in critically ill patients have focused primarily on RRT methods and modalities, no consensus exists on optimal timing of RRT initiation. There is agreement to start up RRT as soon as possible in the presence of life-threatening fluid overload, hyperkalemia, uremia, or metabolic acidosis (1). However, the ideal timing of RRT to treat AKI that is not accompanied by urgent clinical or metabolic complications is still debated. Some experts promote early initiation to assure immediate adequate control of metabolic, fluid, and pro-inflammatory parameters. Adepts of a delayed initiation strategy adhere to more in-depth diagnostic and therapeutic “fine-tuning” which could even obviate the need for RRT. Benefits of each approach must, of course, be outweighed against potential risks such as “overshoot” dialysis and hemodynamic complications associated with an early initiation protocol or worsening metabolic and clinical status (when RRT is “postponed”). Earlier institution of RRT in critically ill patients with AKI is thought to have a beneficial impact on survival. However, this conclusion is mainly based on heterogeneous studies of variable quality (2).