In the ICU, continuous forms of renal replacement therapy (CCRT) are superseding peritoneal dialysis and conventional forms of intermittent hemodialysis as the procedures of choice in the treatment of acute renal failure. More importantly, clinical observation has led to the expansion of CRRT's application beyond acute renal failure. CRRT now should be thought of as part of the integrated care of the critically ill patient. It is one of the many improvements in critical care that have made it possible to care for patients with ever more complex and catastrophic illnesses.

To date, no single advancement in therapy has reduced mortality in the ICU. Rather, such improvements prolonged the lives of patients who otherwise might have died. A reduction in mortality is not a satisfactory endpoint for deciding the worth of a single therapy. It is far more likely that a combination of technical advances and improvements in care cause a change in overall outcome.

The first clinical use of continuous hemofiltration was by Kramer et al<sup>38 Kramer P., Wigger W., Rielger J. , e al. Arteriovenous haemofiltration: A new and simple method for treatment of overhydrated patients resistant to diuretics Klin Wochenschr 1977 ;  55 : 1121  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> at the University of Gottingen in 1977. That publication described a simple extracorporeal arteriovenous circuit that used the heart or blood pressure to supply the hydrostatic pressure required to produce an ultrafiltrate of plasma eliminated through a relatively high flux (porous) semipermeable membrane filter. Since 1977, there have been rapid technologic advances. The ultrafiltration rate has gradually increased, replacement fluid has been added to accomplish solute and fluid removal, and roller pumps have replaced the heart.

The heart is an unreliable pump in critically ill patients and placement of large-bore catheters into the femoral artery presents significant risk in patients who are coagulopathic. Safety and efficiency have been improved with use of a temporary double-lumen hemodialysis catheter placed into a large vein (e.g., femoral, subclavian, internal jugular) and the introduction of a roller pump to generate a driving force for ultrafiltration. With a roller pump to generate the driving force, nephrologists can choose between two forms of continuous dialytic therapy: hemodialysis by convection or hemodialysis by diffusion. The first pump-driven machines were old hemodialysis machines laboriously rigged to adapt them for use in continuous high-volume renal replacement therapy.

Companies that were already producing conventional hemodialysis machines developed automated, computerized, user-friendly CRRT machines that could be run easily and safely by critical care nurses at the patient's bedside. Since 1997 the following excellent machines that provide various forms of slow, continuous renal replacement therapy and convenient adaptations that provide plasma exchange and plasma adsorption and perfusion, have arrived on the market:

There were associated technologic advances in the development of the following more highly porous and more highly biocompatible hemodialysis filters, which are able to filter the larger molecules that are thought to be responsible for the uremic state and its complications and less likely to activate complement: