THOMAS DEPNER

This session was well attended despite its timing as the last session of the Symposium on Home Hemodialysis. Each of the five seasoned nephrologists who participated in the roundtable discussion addressed either radically new methods or major changes in the way current therapy is administered. In contrast to the usual formal delivery of scientific information, the participants were asked to freely speculate about future developments.

The first speaker, Frank Gotch, MD, Davies Medical Center, San Francisco, California, revealed a theoretical argument for changing the way peritoneal dialysis is delivered. He showed that although tidal dialysis provides a slight increase in urea clearance, combining the tidal concept with continuous dialysate flow increased the clearance much further - to as much as twice that of tidal clearance. Gotch provided support for this theory by citing earlier work by Shinaberger, and by showing preliminary in vitro experiments that confirmed the increase in clearance. He speculated that this method of dialysis, which would be ideal for nighttime peritoneal dialysis, could be an alternative to nightly hemodialysis.

As a sequel to this concept, Martin Roberts, PhD, Sepulveda VA Medical Center, Los Angeles, California, presented a brief description of a 'wear-able artificial kidney.' Roberts’ model, which is in the development stage, extended the Gotch theory by adding a dialysate regeneration system to the continuous flow of peritoneal dialysate. His system consists of a sorbent cartridge that is part of the Redy hemodialysis system. This system is no longer marketed, but the cartridge continues to be provided by a new company that recently took charge of servicing the approximately 100 Redy systems remaining in use throughout the world. Roberts showed that his wearable device could provide a continuous Kt/V of 6.5 per week, over three times the current minimum amount recommended by the DOQI committee for continuous peritoneal dialysis. Dr. Roberts stated that the device also has potential for removing protein-bound uremic toxins.

Professor Franco Tesio, MD, Ospedale Provinciale, Pordenone, Italy, supported the concept of a wearable artificial kidney and briefly described a hemofilter/hemodialyzer that is enclosed in a 2-L plastic bag. The bag essentially functions as the dialysate compartment and is designed for periodic removal of filtrate or exchange of dialysate, much like peritoneal dialysis. The small hollow fiber filter/dialyzer prototype has been used in a limited number of patients. Continuous blood flow through the dialyzer was achieved by connection to the blood circulation through catheters inserted into an artery and a vein.

John Moran, MD, chief medical officer for VascA, Inc., Topsfield, Massachusetts, described a new blood access device that is implanted subcutaneously and includes a spring-loaded valve for puncturing. The patient is able to achieve high blood flow rates via 14-gauge needles inserted in the same location for each dialysis. After conditioning, a relatively blunt needle may be substituted for the standard sharp needle. The advantages of this access device include improved body image, elimination of postdialysis bleeding, quick on and off, freedom of the hands during dialysis, and the higher efficiency of venovenous dialysis. The device is sterilized between uses with chlorpactin, a hypochlorite-containing sterilant that is effective at physiologic pH.

John Daugirdas, MD, University of Illinois, Chicago, Illinois, gave a succinct and informative discussion of protein-bound uremic toxins and efforts to remove them by various techniques, including Roberts’ sorbent system described above. The loss of albumin via peritoneal dialysate has been speculated to account for the unexpected success of peritoneal dialysis. The cause of reduced binding of drugs to uremic albumin, a well-known consequence of chronic renal failure not reversed by dialysis, was demonstrated many years ago by Gulyassy. He showed that accumulation of organic acids that reversibly bound to serum albumin accounted for the binding defect in uremia, and that these bound acids could be removed at low pH, effectively restoring albumin-binding to its normal state. The eluate comprised over 100 separate compounds identified using high performance liquid chromatography. Whether any of these compounds can be removed by prolonged and more efficient dialysis is not currently known.

Richard Sherman, MD, Robert Wood Johnson Medical School, New Brunswick, New Jersey, gave a brief explanation for the success of more frequent dialysis. Continuous removal of solute is more efficient, especially for solutes that, unlike urea, have low intercompartmental mass-transfer coefficients. Although clearance may be high, removal is markedly reduced when blood concentrations of these solutes fall rapidly during intermittent hemodialysis. Therefore, attempts to explain the differences in weekly urea Kt/V for hemodialysis and peritoneal dialysis with similar outcomes may be analogous to putting 'square pegs into round holes.'

Discussions among panel members and the audience underlined the excitement generated by daily hemodialysis, especially when performed using modern technology at night in the patient’s home. Potential impediments such as lack of easy blood access suitable for home hemodialysis are gradually being cir-cumvented or removed. The audience extended the discussion of the future to include bioartificial kidneys that may add known or unknown functions ordinarily provided by native kidney tubules, and genetic engineering to regenerate new native kidneys and other organs in people with irreversible damage to their birthright organs.