A broad spectrum of topics was covered
in the hemodialysis (HD)
kinetics session. William Clark, MD,
Baxter Healthcare, Indianapolis, Indiana,
set the stage by providing an overview of
dialyzer mass transfer. He emphasized the
engineering concept of treating overall diffusive
mass transfer resistance in a dialyzer
as the sum of three resistances in series
(blood compartment, membrane, and
dialysate compartment).
Claudio Ronco, MD, San Bortolo
Hospital, Vicenza, Italy, provided a comprehensive
overview of dialyzer membrane
structure and function. Dr. Ronco
discussed basic differences between cellulosic
and synthetic membranes and the
effects of such parameters as membrane
pore size, pore distribution, wall thickness,
and hydrophobicity on solute and water
removal characteristics.
Ken Leypoldt, PhD, University of
Utah, Salt Lake City, Utah, addressed the
issue of blood and dialysate compartment
resistance on small solute removal in HD.
He presented evidence from both in vitro
and clinical studies showing that low
dialysate flow rates significantly reduce
solute KoA values of high-efficiency dialyzers,
and discussed recent clinical data
suggesting that blood flow rate also may
have a significant effect.
John Daugirdas, MD, University of
Illinois, Chicago, Illinois, focused on
effects of compartmentalization on urea
removal during HD. He discussed the
development of a double-pool urea
Kt/V methodology (rate equation) and its
use in the multicenter Hemodialysis
(HEMO) Study.
Frank Gotch, MD, Medical Systems
Consultant, San Francisco, California,
addressed the issue of dialysate-side versus
blood-side quantification of HD. Although
dialysate-side measurements are considered
the “gold-stan-dard,” he cautioned that clinical
application of this approach might be fraught with
difficulty, resulting in inaccurate values.
Thomas Depner, MD, University of California–Davis,
Sacramento, California, addressed the general
issue of uremic toxicity by discussing
the effectiveness of dialytic
removal. He emphasized that
mass removal is influenced not
only by solute molecular weight
(i.e., diffusive removal by the dialyzer),
but also intercompartmental
(intracorporeal) mass transfer.
Consequently, mass removal is
not directly proportional to dialyzer
clearance during dialysis.
With increasing dialyzer clearances,
mass removal tapers off,
reaching a plateau.
Rod Kenley, Kenley
Consultants, Libertyville, Illinois,
provided information on mass
transfer in the recirculating batch
AKSYS Personal Hemodialysis System
(PHD™). In this system, fresh dialysis
solution, at 30°C, is drawn from the bottom
of a tank, heated to 37 or 38°C, delivered
to the dialysate compartment of the
dialyzer, and returned to the top of the
tank. Used dialysate is separated by a thermocline
from the fresh dialysis solution. In
such a system, low molecular weight
solute clearances decrease once the molecules
penetrate to the fresh dialysis solution.
High molecular weight solute
clearances do not decrease significantly,
even after the fresh dialysis solution is
mixed with the dialysate.
Naomi Dahl, PharmD, UMDNJ–
Robert Wood Johnson Medical School, New
Brunswick, New Jersey, discussed pharmacokinetic
issues in the HD patient.
Multiple drug interactions and the effect of
certain drugs on metabolic processes were
highlighted.
Finally, Frantiÿsek Lopot, PhD, Charles
University; Prague, Czech Republic,
focused on continuous blood volume monitoring
(CBVM) in HD, which is believed to
be a promising method of determining
patients’ “dry weight” more precisely and
controlling ultrafiltration (UF) more appropriately.
Four distinct types of blood volume
response to UF were identified, and
the possibility of a shift from one type to
the other over a period of time was verified.
Blood volume reduction in relation to
UF was found to have static and dynamic
components. The most important factors
affecting both components were found, by
a sensitivity analysis of a three-pool kinetic
model, to be degree of overhydration, vascular
system compliance, UF volume (for
the static component), and UF coefficient
of the capillary wall and UF rate (for the
dynamic component).
