The early years of on-line HDF: how did it all start? How did we get here?

In the mid-1980s, limits and side effects of contemporary hemodialysis were basically due to short treatment time, use of low-flux membranes and employment of acetate-buffered dialysate. These were already associated with a relatively high morbidity and cardiovascular mortality as part of diaysis-related pathology. Based on these considerations, the concept of on-line hemodiafiltration (HDF) was proposed as an innovative solution. By combining diffusive and convective clearances, HDF offered the most efficient modality to clear small and middle-sized uremic toxins. Furthermore, by using ultrapure dialysis fluid and high-flux synthetic membranes, HDF also offered the most biocompatible dialysis system, thereby going a long way towards preventing inflammation. Through provision of virtually unlimited amounts of sterile dialysis fluid by cold sterilization of fresh dialysate, on-line HDF offered an economical and viable method of conducting high-efficiency HDF (high volume exchange) therapy. By keeping the hemodialysis machine with all built-in technical options (e.g. adjustable blood pump, fluid-balancing system, conductivity meter, flow and pressure monitoring, bicarbonate-buffered dialysate), HDF benefited from being associated with the use of dialysis machines with excellent technology as well as highest safety standards. Use of ultrapure water made it then possible to produce dialysis fluid of intravenous grade quality with these machines. The first on-line HDF clinical trial was performed with a modified A2008C dialysis machine in 1984-85. This confirmed the feasibility and potential of the on-line HDF method. Some 25 years later, on-line HDF has proven to be safe, efficacious and with clinical benefits that justify it becoming a new standard for high-quality care of chronic kidney patients.