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Article Review/Hyperlink
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Held PJ, Port Fk, Wolfe RA, Stannard DC, et al
The dose of hemodialysis and mortality
Kidney Int
(Aug) 50:550-551 1996

Owen et al (N Engl J Med 320:1001-1006, 1993), in a retrospective
cross-sectional study of about 15,000 NMC dialysis patients, showed
that mortality was linked to the urea reduction ratio. The mortality
risk decreased exponentially as the URR was increased, leveling off at
a URR of about 65%, corresponding to a Kt/V single pool value of about
1.2. The question as to whether further increases in URR are
beneficial has led to the NIH-funded HEMO trial, where a URR of about
65% is being compared to a URR of about 75% in a randomized,
prospective trial.
In this paper from the United States Renal
Data Systems, the effects of URR and Kt/V are assessed in a randomly
chosen sample of US dialysis patients. Although the sample size here
is much smaller than that of the Owen/Lowrie study, the strenghts of
the analysis are the random selection of study population, and the
control for a panoply of comorbid factors. The analysis was limited
to patients undergoing 3x/week dialysis using bicarbonate dialysate.
The data are quite similar to the Owen/Lowrie NEJM paper.
The mortality risk appears to decrease until a URR of about 65-70% or
a Kt/V of 1.2-1.3 is attained, and then appears to flatten, although
there is difficulty in assessing from this data whether or not further
increases in the URR are beneficial. The Kt/V and URR are tightly
linked, the only real difference between them being the extra Kt/V
afforded by ultrafiltration. Hence it was not surprising that either
measure was a good measure of adequacy. Interestingly, when dose of
dialysis was controlled for, treatment time was not a significant
predictor of mortality (although treatment times longer than 4 hours
are rarely given in the US, and this finding does not necessarily
conflict with the observation of excellent survivals in places like
Japan or Tassin, France, where dialysis times longer than 4 hours are
common or even the rule).
Comment: The data appear to confirm the wisdom of the
NIH Consensus Development Conference, which suggests that the target
URR for dialysis patients should be at least 65% or the Kt/V at least
1.2. Interestingly, in this data set, the concept advanced by Alan
Collins, that diabetics may need even higher doses of dialysis, was
not confirmed. Cross-sectional studies such as these (and this
applies to the USRDS, the Collins study, and the Owen/Lowrie analysis)
are fraught with error, as one never knows whether the effect one is
measuring is due to the variable in question, or to some associated,
but uncontrolled for factor. For example, it may be that in the
Collins paper, diabetics with less macrovascular disease were able to
achieve higher levels of Kt/V, and diabetics with less macrovascular
disease may intrinsically have a higher survival rate. So in
conclusion, the dialysis community awaits with great interest the
results of the NIH Hemo trial, which should definitively tell us if
even higher URR or Kt/V levels than those presently recommended by the
NIH Consensus Development Conference are beneficial. (John T.
Daugirdas, M.D., University of Illinois at Chicago)
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