Biomedical Engineering Reference
In-Depth Information
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
a
b
c
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
β
/c
alb
α
c
alb
Figure 2. Strongly albumin-bound toxin partition between two albumin-containing solu-
tions. Data were collected at equilibrium in a double-compartment, closed loop dialysis
system, using different membrane modules and operating conditions. (a) Bilirubin partition
using a F40 module (Fresenius Medical Care, Bad Homburg, Germany); (b) Bilirubin par-
tition using a FX40 module (Fresenius Medical Care, Bad Homburg, Germany); (c) BSP
partition, data reported by Steiner et al. (2004)
A similar chemical approach can be used to describe partition of bilirubin between an
albumin-containing aqueous solution and an hydrophobic phase, like a polymeric mem-
brane, in which free bilirubin is soluble: this phenomenon can be represented by the fol-
lowing reaction
⇋
B
M
+
A
Α
(14)
where superscript
M
refers to the membrane phase. As a consequence, bilirubin solubility
is given by
AB
Α
!
Μ
0,Α
AB
−Μ
0,Α
A
−Μ
0,M
C
AB
C
A
C
AB
C
A
C
BIL
= exp
B
= S
BIL
(15)
RT
or, if conditions (7) and (8) hold, in the simplified form
C
BIL
C
ALB
−C
BIL
C
BIL
= S
BIL
(16)
3.
Dialysis Process
Although the bilirubin MW is far below the cut-off of standard dialysis membranes,
due to its extremely low water solubility at neutral pH, this toxin cannot be removed by
conventional dialysis against an aqueous buffer solution, but a binder is required in the
dialysate.
Albumin itself is used in the dialysate as binder for bilirubin, as well as other protein-
bound toxins, in the “albumin dialysis” process used in extracorporeal therapy, both in
