Why thrice weekly dialysis?

Why we settled on thrice weekly treatment during the early years of chronic hemodialysis has become a very important question now that the advantages of more frequent dialysis are becoming increasingly evident. We will try to explain the reasoning behind this in a historical format. Thrice weekly treatments were the result of an incremental process, not an intuitive one. Paul Teschan’s brilliant idea of prophylactic hemodialysis for the treatment of acute renal failure was the foundation for the decision on selecting the length of dialysis in our first patient with chronic renal failure, Clyde Shields. Teschan had proposed that the best way to treat acute renal failure was to use dialysis to prevent uremia rather than to wait until after uremic toxins had further damaged an already critically ill patient. We devised the continuousflow hemodialysis system as one way to implement Teschan’s idea. The dialysis continued for 24 hr without a dialysate bath change and used a 300-L tank made from a large Sears and Roebuck Company commercial chest-type freezer that contained enough dialysate for the entire 24-hr period. Dialysate temperature was maintained at 0 to 4 C to slow bacterial growth and to reduce clotting and platelet consumption. Dialysate outflow was returned to the tank and so the solute gradient between blood and dialysate became less favorable as treatment progressed. The blood lines were 20 feet long so the arterial line could pass through the dialysate tank to cool the blood entering the dialyzer and so the venous line could pass through a warming bath and rewarm the blood before returning it to the patient. These long lines also allowed patient mobility. With development of the Teflon shunt, this system was used to treat the first patients with chronic renal failure (Figure 1). The system originally used a six-layer Skeggs-Leonards hemodialyzer, but to reduce channeling, increase surface area, and reduce resistance to blood flow, this was changed to 2 four-layer Skeggs-Leonards dialyzers connected in parallel with a total surface area of 1.55 m. In 1961, these were replaced by a two-layer Kiil dialyzer with a surface area of 0.9 m or occasionally with a four-layer Kill dialyzer with a surface area of 1.8 m. Using these dialyzers, the low resistance to blood flow and near-arterial pressure from the arterial cannula eliminated the need for a blood pump, and blood flows of 150 to 200mL/min were readily achieved. With this setup it was relatively easy to perform a continuous 24-hr dialysis because very little professional supervision and few interventions were required. This was referred to as a ‘‘nursetechnician procedure’’ and was the precursor of the way in-center hemodialysis is practiced today. The fact that creation of our continuous flow hemodialysis system preceded development of the arteriovenous Teflon shunt for chronic dialysis unknowingly provided a great advantage over other dialysis programs that were using the Kolff rotating drum dialyzer or the twin-coil system. These dialyzers were very useful in the treatment of acute renal failure but unsuited to the treatment of chronic renal failure. Both required a dialysate bath change every 2 hr for a 6-hr dialysis and the twin-coil system also required a blood pump, adding complexity to the treatment. Furthermore, these dialyzers needed to be primed with 1 unit or more of blood, most of which could not be returned to the patient at the end of the dialysis. Although both had urea clearances more than three times that of the Skeggs-Leonards and the Kiil dialyzers, the total urea clearance per treatment was very similar Although we did not realize it at the time, our continuousflow system also allowed a slight but perhaps crucial increase in the removal of toxic middle molecules as a result of Correspondence to: Christopher R. Blagg, MD, Northwest Kidney Centers, Seattle, WA 98101, U.S.A. E-mail: blaggc@hotmail.com