Continuous renal replacement therapies for the treatment of acute renal failure in intensive care patients.

Continuous renal replacement therapies are extensively utilized for the treatment of acute renal failure in the critically ill patient. The arterio-venous circulation has been partially substituted by the veno-venous pump driven circulation. Diffusion has been added to convection in order to increase the small solutes clearance even though sometimes the pure convection is still advantageously utilized. Hemofilters have been changed in hemodiafilters with the possibility of countercurrent dialysate circulation. The blood path geometry has been specifically designed to operate under conditions of low pressure and flow. Therefore lower amounts of heparin are required to maintain the extracorporeal anticoagulation with a reduced risk of bleeding. New techniques and new materials permit us today to carry out continuous therapies with a low rate of complications and an increased percentage of survival among the treated patients. The improved understanding of the multiple organ failure syndrome and the pathophysiology of the septic syndrome, suggest today newer indications for continuous renal replacement therapies. The proposed mechanisms of action of the therapy should be the removal of chemical mediators such as platelet activating factor, interleukin-1 and tumor necrosing factor alfa, not only by a filtration process, but also by the adsorption on the surface and structure of the artificial membrane. These new mechanisms may in part be responsible for the beneficial effects of continuous therapies in the patients affected by acute renal failure and other organ dysfunctions.