Dose of Hemodialysis and Survival

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Abstract
BECAUSE the uremic toxin(s) has not been identified, the quantity of urea removed during hemodialysis is a clinically accepted surrogate to define the patient's risk profile. Numerous studies have demonstrated an association between the dose of hemodialysis and mortality among patients with end-stage renal disease (ESRD), when all demographic groups of patients are evaluated together.1-11 The 2 commonly accepted measures of hemodialysis dose are based on the fractional reduction of blood urea nitrogen concentration during a single hemodialysis treatment.12,13 The most frequently used measure of hemodialysis dose is the urea reduction ratio (URR), calculated by dividing the decrease in blood urea nitrogen (predialysis minus postdialysis blood urea nitrogen) by the predialysis concentration, expressed as a percentage.1,13,14 Another measure of hemodialysis dose is based on the pharmacokinetic theory that the fractional decrease in urea during a dialysis treatment is a mathematical function of the artificial kidney's clearance of urea (K) times the length of the treatment (t), divided by the urea distribution volume (V), approximated by the total body water (TBW).15,16 This ratio, Kt/V,12-14 can be calculated from the URR and they are conceptually and mathematically similar.14-16 Patient mortality is higher when the amount of urea removed (hemodialysis "dose") is low, and vice versa. Retrospective studies of mortality outcome for patients with ESRD suggest that the odds of death progressively increase when URR falls lower than 60% to 65%.1-5 Such findings, and an evidence-based professional consensus, have led 3 national organizations, including the principal payer of dialysis services, the Health Care Financing Administration, to advocate a URR of 65% or Kt/V of 1.2 as thresholds for adequate hemodialysis. These thresholds have recently been used to profile dialysis providers.12,13,17-19