Page 700 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Hemodialysis and Extracorporeal Blood Purification 687

350 600 dialysance becomes an acceptable predictor of the urea
300 500 clearance of the dialyzer, K d-urea . Analogous to measure-
250 400 ment of blood-based dialyzer clearance, ionic dialysance
is computed from measurements of dialysate conductivity
200 300
(concentration of ionic solutes) at the inlet and outlet
200
Ionic dialysance (K d-ionic, mL/min) 350 600 Blood flow (Q b, mL/min) during the dialysis treatment, serial updates of the instan-
150
ports of the dialyzer in response to transient changes in
100
100
inlet dialysate conductivity and the instantaneous
3:00
5:00
When ionic dialysance is programmed sequentially
A 50 0:00 1:00 2:00 Time 4:00 h:min 0 dialysate and blood flow rates.*
taneous clearance (K d-ionic ) of the dialyzer can be
300
500
monitored, and the depurated volume for treatment
400
250
200
ionic Kt/V, as a surrogate for sp Kt/V, provided when the
150
200
ionic dialysance is indexed to urea distribution volume,
100 300 (K d-ionic t) is predicted at the end of the session. The
100
V. The availability and simplicity of ionic dialysance to
50 0 predict dialysis delivery at every treatment should
0:00 1:00 2:00 3:00 4:00 5:00 promote a better understanding of the kinetics of dialytic
B Time h:min therapy and the efficacy of dialysis prescriptions.
Figure 29-6 Screen shots of the ionic dialysance display of the Sudden or progressive decreases of K d-ionic during the
Gambro Phoenix illustrating the ionic dialysance (solid line, left axis) treatment can alert possible clotting in the dialyzer or
and blood flow (dashed line, right axis) throughout a dialysis session. development of access recirculation that may compromise
A, Demonstrates constant dialyzer performance and extraction the adequacy of the treatment. It is also possible to make
ratio during the treatment with a K d-ionic of approximately 195 mL/ interim projections of the ionic Kt/V for the session to
min at a Q b of 300 mL/min (extraction ratio, 0.65). B, Illustrates a
marked and progressive decrease in K d-ionic after 1.5 hours of ensure the treatment targets will be met by the end of
treatment associated with extensive clotting of the dialyzer the scheduled session time. If therapeutic targets will
necessitating termination of the treatment. not be met under current circumstances, adjustments
to treatment time, blood flow, and dialysate flow, access
repositioning, or dialyzer exchange can be initiated to
the monitoring of individual dialysis sessions and ensure modify the forecast treatment to ensure adequacy. 29
adequate dialysis delivery (Figure 29-6). Automated, Routine animal hemodialysis is provided intermit-
bloodless kinetic modeling systems using ionic clearance tently three times weekly based on human convention.
are available on many modern delivery systems and As for humans, this schedule represents a compromise
provide kinetic assessments for each dialysis treatment between clinical benefits, time constraints, and financial
as an alternative to blood-based modeling burden. However, recent experience in human patients
techniques. 24,67,108,114,118 Dialysance of a dialyzer is a with daily dialysis schedules has demonstrated marked
measure of solute mass transfer across the dialysis mem- theoretical and clinical benefits to the increased dialysis
{
brane when the solute is present in both the blood and frequency. Because diffusion is a first order process, dial-
dialysate. Ionic dialysance is a kinetic assessment of the ysis becomes more efficient as the frequency of dialysis
transfer characteristics of the ionic solutes in the blood increases. 28,46,66,99 Critical analysis of varying dialysis
and dialysate. The collective concentration ionic solutes schedules has shown the total weekly dose calculated as
in solution can be measured by the conductivity of the the sum of the individual treatments is not equivalent
solution, which is proportional to the electric current among dialysis schedules with differing frequencies. Daily
conducted through the solution. The conductivity of treatment schedules have equivalent clinical outcomes to
both plasma and the dialysate is influenced primarily by traditional three times a week hemodialysis schedules
the concentration of sodium and chloride and will change even when delivered at a lower total weekly dose. For
with perturbations of these solutes. 67,114 The clearance of example, six treatments per week at a sp Kt/V of 1.0 per
a solute by the dialyzer is equal to its dialysance when the treatment are more efficient than three conventional
solute is present only in the blood and is absent in the treatments per week with a sp Kt/V of 2.0 per treatment.
dialysate. The collective dialysance of small-molecular- To reconcile these differences, the concept of standard
weight ions (such as sodium) is considered equivalent Kt/V ( std Kt/V) has been proposed to compensate for
to the dialysance of urea, and consequently ionic the differences in efficiency when comparing schedules
dialysance can be used as a reasonable surrogate for the with different intermittence. 50,64–6699 Standard Kt/V is
dialysance of urea. In conventional single-pass hemodial-
ysis, circuits in which the dialysate contains no urea, urea *References 53, 54, 67, 92, 128, 130.
dialysance becomes equal to urea clearance, and ionic { References 28, 46, 63, 66, 72, 100, 171, 174.