Acute kidney injury (AKI) is common in hospitalized patients, and its incidence is rising sharply in intensive care units. It is associated with significant morbidity and mortality due to a profound change in its epidemiological profile - multifactorial in origin, often septic, and associated with other organ failures. The mortality rate reaches 30-50% in the most severe forms, particularly when AKI requires renal replacement therapy (RRT). Temporary RRT, when indicated, must be part of an overall therapeutic approach that also includes support for other vital functions, particularly cardio-circulatory, respiratory and nutritional. The current diversification of these methods means that they must be well mastered and the potential of each of them in terms of cost, efficacy, limitations and risks must be fully understood before a therapeutic decision can be taken. This narrative review was written by an expert panel and presented to the members of the jury of the French consensus conference to help in the development of guidelines for the use of RRT in critically ill adult and pediatric patients, excluding cases related to acute intoxication.