Renal dysfunction is known to be frequently a component of multiple organ failure, a complex syndrome affecting the most severely ill critical patients. Bidirectional interaction between the kidneys and other organs has always been suspected; evidence suggests that severe kidney injury is an important protagonist in acute illness, even when managed by dialysis. In fact, if it seems that increasing the dose of renal replacement therapy does not reduce mortality, it could be inferred that acute kidney injury influences mortality through means that are not reversed by conventional renal support, either because the putative culprit toxins are not removed by renal replacement therapy or because renal replacement therapy is started too late to prevent these effects. It is known that the kidneys exert effects on other organs, such as the lung, liver, heart, and brain, in a process called 'crosstalk'. This effect means that the kidney is not only a victim, but also a culprit regarding the malfunction of other organs. This chapter will detail some traditional aspects of different renal replacement therapy modalities and prescription schedules, but it will also describe the most recent evidence on the management and support of the kidney during failure of other organs.