The changing pattern of severe acute renal failure

The pattern of severe acute renal failure has changed considerably over the past 2 decades. Severe acute renal failure is now most commonly seen in the intensive care unit and is just one of the manifestations of the multi-organ dysfunction syndrome. The pathogenesis of severe acute renal failure is complex involving decreased renal perfusion, humorally mediated renal vasoconstriction and local migration and activation of inflammatory cells. The initial final common pathway to renal injury seems to be outer medullary ischaemia. Protection from renal dysfunction in critically ill patients must therefore be directed toward sufficient haemodynamic resuscitation to avoid inadequate medullary perfusion. Such perfusion is highly dependent on the maintenance of optimal intravascular filling, adequate cardiac output and, importantly, adequate renal perfusion pressure. In these patients, such renal perfusion pressure can often only be maintained if vasopressor agents are used and titrated to keep the mean arterial pressure at the highest effective and safe level (mean arterial pressure of approximately 80-85 mmHg in most septic patients). If severe acute renal failure develops despite full medical support, renal replacement therapy becomes necessary. There is now a growing worldwide trend toward the use of continuous haemofiltration techniques as the preferred mode of renal replacement therapy. Such techniques provide important practical advantages and, in many cases, are the only form of renal replacement therapy that the patient is able to tolerate. Continuous haemofiltration also appears to provide not only outstanding haemodynamic stability but also some membrane adsorption and removal of the humoral mediators of sepsis. This makes continuous haemofiltration a particularly attractive approach to renal support and is responsible for this treatment now being the leading form of acute renal replacement therapy in Australia. After a relatively static period, the area of acute renal failure management is rapidly evolving and offering some promise of a level of support able to match the illness severity associated with it.