History and development of continuous renal replacement techniques.

In 1966 two research groups, one in the United States and the other in Germany, were independently evaluating new membranes for renal replacement techniques. These filters were characterized by high filtration rates, where solutes up to a certain molecular weight were filtered by convection. At the same time the understanding of the transport mechanisms through membranes was improving. In 1976 Burton created the term "hemofiltration" for this new convective technique, and the first multicenter trial was initiated to evaluate its effectiveness for treating chronic renal failure. In 1977 Kramer in Göttingen (Germany) developed the continuous arteriovenous hemofiltration (CAVH) technique, which used a systemic arteriovenous pressure difference in an extracorporeal circuit to continuously produce an ultrafiltrate. The advantages of this effective method for elimination of fluid and solutes were its technical simplicity and the hemodynamic stability of even critically ill patients. Therefore, it soon became a widely used method for treating acute renal failure in intensive care patients. However, its limited capacity to remove nephrotoxins in the presence of high catabolism and complications connected to the arterial access lead to the development of a venovenous pump-driven technique (CVVH) in order to become independent from the systemic circulation and the arterial access. Further progress to improve solute clearance was made by combining the convective principle of hemofiltration with the diffusive transport of dialysis (continuous arteriovenous hemodialysis or hemodiafiltration). Today this combination has become the most effective renal replacement technique for treating acute renal failure in critically ill patients.