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Thursday, 13. February 2003 12:20 PM GMT
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).
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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