Acute renal failure in critically ill patients is seldom an isolated problem but is more usually associated with multiple organ failure. When choosing an extracorporeal kidney replacement therapy, these other failing organs must be taken into account. Therefore the choice of an artificial kidney in patients requiring intensive care depends on both the efficacy of the technique and its possible adverse effects on cerebral, pulmonary and cardiovascular function. The most important pathogenic factors in the development of dysequilibrium syndromes, arterial hypoxemia and hypotension are treatment timing, diffusive solute transfer, bio-incompatible membranes and some specific dialysate components (buffer, electrolyte concentrations). It is important to understand the mechanisms by which these factors exert their adverse effects. Application of these pathophysiological mechanisms to the cardiopulmonary and neurologic status of the individual patient permits the prediction of their clinical outcome. This approach will lead to individualised treatment selection, thereby avoiding deleterious side-effects without loss of efficacy.