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Article Review/Hyperlink
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Hakim RM, Held PJ, Stannard DC, Wolfe RA, et al
Effect of the dialysis membrane on mortality of chronic
hemodialysis patients
Kidney Int
(Aug) 50:566-570 1996

Hakim has proposed a hypothesis that use of a complement activating
membrane is detrimental to patients both in terms of morbidity and
ultimate survival. In this study, the USRDS data set was used to see
how type of dialysis membrane was related to mortality. Patients were
randomly chosen from dialysis units, and patients using acetate
dialysis were excluded. The strength of the analysis was, that the
analysis was restricted to patients in whom URRs were available,
controlling for the confounding effect of adequacy. Also, data on a
large array of comorbid conditions was collected and controlled for in
the analysis.
Membranes were divided into 3 groups: unsubstituted
cellulose, modified cellulose (which includes hemophan, cellulose
acetate, and cellulose triacetate), and synthetic (primarily
polysulfone and PAN). The principal finding was, that the relative
risk of death was about 0.75 for modified cellulose and synthetic
membranes vs. for unsubstituted cellulose.
Comment: On the surface, the data appear to be
support the hypothesis promulgated by Hakim, that complement
activation by unsubstituted cellulose membranes has measurable adverse
clinical effects. However, there are a number of confounding effects
present in the data which leave the question of causality in doubt.
1) Although the data were controlled for by geographic
region, a strong center effect may have been present. For example, an
abstract will be presented at ASN 96 by the USRDS, that units using
synthetic membranes spend more money per patient in terms of staffing
than those using unsubstituted cellulose membranes. Also, use of a
high flux membrane requires use of a volumetric dialysis machine, the
use of which per se may be associated with better volume control and
perhaps better survival.
2) There was a strong trend in the data favoring better outcome
with membranes having a higher UF rate. Hakim argues that UF rate and
complement activation are inversely related, which is true. However,
the trend for lower mortality with higher UF rates were also seen
within some membrane groups.
3) The great majority of patients in the study were reusing
dialyzers. If mortality was associated with complement activation,
one would expect the use of bleach to result in a higher mortality
rate. This trend was not seen in the data, although this finding was
not reported given the relatively small number of patients and the
large number of reuse methods employed.
4) Even if a membrane effect is present, it is not at all clear if
it is due to biocompatibility or to flux. Given the high percentage
of reuse without bleach of unsubstituted cellulose membranes, a flux
based explanation of lower mortality with synthetic membranes is
equally plausible. At least the flux question will be addressed by the
NIH HEMO trial, which compares low flux (cellulose acetate and low
flux polysulfone) with high flux (cellulose triacetate, high flux
polysulfone) membranes. Unsubstituted cellulose membranes were
excluded from the NIH HEMO trial, in an attempt to separate out flux
and biocompatibility issues.
Overall, the study emphasizes the difficulties of analyzing
data from cross-sectional studies. I don't believe that the case
against unsubstituted cellulose membranes is a strong one in 1996,
certainly not in terms of mortality. Nevertheless, the USRDS data remains to
be explained, and one of the explanations (not the only one) is, that the
dialyzer membrane does affect mortality. (John T. Daugirdas, M.D.,
University of Illinois at
Chicago)
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