When to start continuous kidney replacement therapy in critically ill children: a practical, PICU-focused, evidence-based review.

Acute kidney injury (AKI) and fluid overload (FO) are common in critically ill children and have been shown to be associated with adverse outcomes. Continuous kidney replacement therapy (CKRT) is the preferred renal support modality in paediatric intensive care to treat children with AKI and FO and may be necessary for non-renal indications like life-threatening toxin or electrolyte removal. However, the timing of CKRT initiation remains a contentious and highly variable clinical decision. Classic indications for dialysis are well established, yet modern paediatric intensive care practice increasingly emphasises earlier intervention for FO and evolving multi-organ dysfunction. Adult randomised trials have not demonstrated a survival benefit for early CKRT based on biochemical thresholds alone, mainly AKI stage. However, their applicability to paediatric populations is limited by distinct disease biology, developmental physiology, and fluid tolerance. This review synthesises current evidence and expert guidance to provide a pragmatic, physiology-driven framework for CKRT initiation in critically ill children. Emphasis is placed on dynamic assessment of kidney trajectory, fluid balance, and extra-renal organ impact rather than fixed biochemical thresholds or rigid timing paradigms. Integration of these factors balances the relative benefits and risks of early CKRT initiation and facilitates timely and individualised decisions that optimise outcomes in this vulnerable population.