Future Technology for Continuous Renal Replacement Therapies Claudio Ronco, MD, Rinaldo Bellomo, MD, Mary Lou Wratten, MD, and Ciro Tetta, MD 0 Critically ill patients are increasingly treated with continuous hemofiltration and derived techniques, now grouped under the term of continuous renal replacement therapy (CRRTj. CRRT can provide adequate blood purification and correction of electrolyte derangements. They also seem to prevent further injury to the patient by maintaining a stable level of homeostasis. Recently, newer indications have been proposed for CRRT, including the treatment of neonates, patients with heart disease, and septic patients. It has been hypothesized that continu- ous therapies might contribute to the removal of noxious substances in the middle molecular-weight range, such as cytokines or autocoids. According to these new indications, technical developments are making available new forms of treatment, new materials, and specially designed machines. 0 1996 by the National Kidney Foundation, Inc. INDEX WORDS: Hemofiltration; acute renal failure; sepsis; continuous therapies; hemodialysis. A CUTE renal failure (ARF) is a rapid de- cline in renal excretory function. It has re- cently become fairly rare to find isolated ARF after shock, bleeding, or trauma. Being able to prevent milder injuries, we are now faced with the more severely injured patients who suffer from failure of many organs simultaneously. They are in shock and have respiratory failure, signs of liver damage, a low cardiac output, and often disturbed states of consciousness. Every year, 172 adults per million inhabitants develop ARF. The causes of ARF are cardiovascular in- sufficiency, postsurgery, obstetrical, prostate obstruction, medical, including toxins, glomeru- lonephritis, hematological, dehydration or hem- orrhage, and miscellaneous.‘” In a recent retro- spective study of 118 patients with ARF admitted between 1980 and 1991, Alexopoulos et al” showed a change in the patterns and prognostic factors of ARE in a medical setting in comparison with an earlier series in the 1960s. The investiga- tors showed a marked decline in the hypotension- related cases and a concomitant increase in the nephrotoxic causes. The overall mortality rate was 27%, virtually unchanged in comparison to the study from the 1960s. Sepsis and cardiovas- cular complications are the leading causes of the death.4’5 Under such circumstances, an effective renal replacement therapy must provide adequate blood purification from uremic toxins, correction of fluid, electrolyte and acid-base derangements, maintenance of the highest level of homeostasis, protection of the kidneys from further injury, and acceleration of recovery of renal function after ARF. In 1977, Kramer et al6 described a new treat- ment named continuous arteriovenous hemofil- tration (CAVH). This treatment was based on a highly permeable hemofilter connected to an ar- tery and a vein by modified hemodialysis blood lines. The arteriovenous pressure gradient moved the blood through the extracorporeal circuit, and no pumps were used. Slow continuous produc- tion of ultrafiltrate was achieved, and substitution fluid was administered in postdilutional mode to maintain the patient’s fluid balance. The technique was subsequently modified and newer options were made available. The use of a blood pump with a venovenous blood access became popular (continuous venovenous hemo- filtration [CVVH]), and the arteriovenous treat- ments were partially abandoned. At the same time, the hemofilters were equipped with a sec- ond port in the ultrafiltrate compartment, thus permitting the countercurrent circulation of dial- ysate (continuous arteriovenous hemodiafiltra- tion [CAVHD]/continuous venovenous hemodia- filtration [CVVHD]). In such cases, the treatment was named continuous hemodialysis or continu- ous hemodiafiltration. All of these modifications are today available as routine treatments (Fig l), and sl;‘“3cial machines have also been designed to facilitate the clinical application of these tech- niques.‘** In modem equipment, continuous measure- ment of the pressure decrease inside the filter, obtained from adequate pressure measurements, From the Department of Nephrology, St Bortolo Hospital, Vicenza, Italy; and the Intensive Care Unit, Austin Hospital, Heidelberg, Australia. Address reprint requests to Claudio Ronco, MD, Depart- ment of Nephrology, St Bortolo Hospital, Via Rodolji, 36100 Vicenza, Italy. 0 1996 by the National Kidney Foundation, Inc. 0272-6386/96f2805-0319$3.00/O American Journal of Kidney Diseases, Vol28, No 5, SuppI (November), 1996: pp S121-S129 s121