**Abstract**

Acute kidney injury (AKI) represents one of the most frequent complications in critically ill patients. In recent years, mortality rates have exceeded 50%, and 10% of them require kidney replacement therapy (KRT). Since the 60's, the question of when to start KRT has been raised, classically the time of temporality when life-threatening (hyperkalemia, metabolic acidosis, uremia, and fluid overload); in the last decade, the possibility of early initiation was raised as a strategy to achieve better outcomes. Current evidence shows that the timing of late onset has the same results as the strategy of early onset. We will also review the considerations in relation to renal capacity and demand generated by the acute pathology in a critically ill patient and the set of variables to make better decisions.

**Keywords:** acute kidney injury, critically ill patients, kidney replacement therapy, uremic toxins, indications for hemodialysis
