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Thursday, 13. February 2003 12:20 PM GMT
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Adequacy of dialysis refers to the compromise between therapeutic outcome &
cost & inconvenience.
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Dialysis supports life despite complete cessation of renal function. This is
achieved at considerable cost to the community and inconvenience to the patient,
yet it fails to restore the patient to full functional normality and longevity.
It is not possible to reproduce renal function in its entirety. In general, the
greater the proportion of renal function replaced, the more expensive and
inconvenient the treatment.
Clearly, there is a minimum threshold quantity of dialysis needed to support
life, a maximum quantity, which might approach normal renal function, which
restores the patient to full health and an intermediate area in which the
patient is alive but functionally impaired. The concept of adequacy refers to
the compromise between acceptable outcome for the patient and acceptable cost
and inconvenience. Since adequacy depends on subjective assessment of what
constitutes an acceptable degree of impaired health, cost and inconvenience, it
is not a static quantity. Whether a treatment is considered adequate will depend
on patient expectations, on differing emphases on the part of the physician and
on the resource society is prepared to allocate. These issues are under constant
debate and vary widely even between institutions in the same region (Tattersal
et al., 1998).
Adequacy is derived from the Latin adaequare : to equalize. The question is:,
equal to what ?. The only acceptable gold standard is to clean blood and
biological fluids to a degree comparable with normal renal function . The
correct definition and realization of adequate dialysis is hampered by : (1) The
use of markers that are non toxic, or non-representative for large groups of
toxins ; (2) The technical limitations of dialysis; (3) The limited accuracy of
the usual parameters of dialysis performance; (4) The changing concepts and
definitions of adequate dialysis (Vanholder and Ringoir,1992).
Some may define adequacy of dialysis as a determination made by clinical
assessment of patient well being. Experience has taught, however, how inadequate
dialysis may be over-looked by strictly adhering to clinical criteria. Although
the inverse is equally true. The problem cannot be detached from economic
consideration, nor from the complex interaction between the dialysis procedure
and material on the one hand, and the patient on the other (Lazarus and Hakim,
1991).
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The ideal is to fully restore all of the functions of the failed kidney.
These functions include, water, sodium, potassium, calcium, phosphate, blood
pressure and acid/base homeostasis. The kidney also has hormonal function and
clears solutes from the blood. The molecular weight of the solutes to be cleared
range over two orders of magnitude from small (water, urea) to large
(beta-2-microglobulin). In practice, most aspects of normal renal function are
technically very difficult to reproduce. The art of prescribing dialysis is to
use the available technology and resource to provide sub-optimal treatment in a
controlled way so that, while normal renal function is not fully restored, the
patients are as fit as possible (Tattersal et al., 1998).
The adequacy debate requires objective measurements of patient outcome,
function, treatment side-effects, treatment cost and the degree of inconvenience
to the patient. Improvements to treatment require to be assessed with reference
to these factors in the light of increasing knowledge of human physiology and
kidney function. It is also necessary to measure the effect of dialysis on the
patient. Some markers respond rapidly to changes in dialysis treatment. These
include serum bicarbonate, hemoglobin, calcium, phosphate and blood pressure.
Others are relatively long term and, once detected, may be irreversible (Beta-2
microglobulin and amyloidosis) or difficult to treat (malnutrition, ventricular
hypertrophy, bone disease). It is therefore mandatory to have a working
definition of adequate dialysis and some way of ensuring that all patients
receive this, thereby preventing or delaying long-term complications. This
working definition requires constant refinement (Tattersal et al., 1998).
An alternative analysis relates toxicity to the rate at which the mass of
toxin can be cleared rather than its concentration. In this analysis, the toxin
inhibits metabolic or dietary processes leading to its generation. The greater
the mass of toxin removed, the greater its generation rate. Hence concentration
does not change, but the dietary and metabolic health of the patient will
improve as clearance increases (Lindasy and Spanner, 1989).
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