Biomedical Engineering Reference
In-Depth Information
4
3.5
3
c
β
alb
,
µ
M
2.5
50
300
600
1500
(*)1500
2
0
50
100
150
200
time, min
Figure 6. Simulated overall device clearances for bilirubin, as a function of time. The
operating conditions considered are reported in Tab. 3. The different lines refer to different
albumin concentration in the dialysate. The line marked with (*) was obtained setting to
zero the column adsorption capacity for bilirubin.
Superscripts
Α
and
Β
refer to blood (fiber-side of membrane module) and albumin dialysate,
respectively.
This result is clearly due to the two-fold effect of albumin in the dialysate on the overall
detoxification process: on one hand, an higher albumin concentration enhances bilirubin
transfer to the dialysate in the membrane module, but, on the other hand, impairs the regen-
eration of dialysate by adsorption. The first, positive effect is dominant at earlier operating
times, when the adsorption column is far from saturation and the overall performance is de-
termined by the dialysis process, while, at longer operating times, this condition is reversed
and adsorption becomes the controlling process.
Anyway, it must be pointed out that, with the operating conditions considered in the
simulations, a minor, if not negligible, initial improvement of the clearance is obtained in-
creasing the albumin concentration in the dialysate from 300
Μ
M to 1500
Μ
M. This is not
surprising, because such concentrations correspond to values of
1/Z
in the range 0.5
÷
2.5,
where the membrane clearance is quite insensitive to changes in
1/Z
(see Fig. 3). Further-
more, the overall clearances obtained are, in any case, as low as 3-4% and are limited by
the low performance of the dialysis module (the value of
Κ
calculated with the parameters
reported in Tab. 3 is as low as
2.3410
−2
). Bilirubin clearances of a few percent of the feed
flow-rate were also reported by Peszynski et al. (2002).
Finally, in order to highlight the importance of the regeneration efficiency for the pro-
longation of the treatment, Fig. 6 also shows a curve obtained by setting to zero the resin
adsorption capacity for bilirubin. It is clear that, in a system without dialysate regenera-
tion, the detoxification process becomes rapidly ineffective, due to the build-up of bilirubin
concentration in the dialysate.
