Short, thrice-weekly hemodialysis is inadequate regardless of small molecule clearance.
Chronic hemodialysis sessions, as developed in Seattle in the 1960s, were long procedures with minimal intra- and interdialytic symptoms. Over the next three decades, financial and logistical pressures related to the overwhelming number of patients requiring hemodialysis created an incentive to shorten dialysis time to four, three, and even two hours per session in a thrice weekly schedule. This method spread rapidly, particularly in the United States, after the National Cooperative Dialysis Study suggested that time of dialysis is of minor importance as long as urea clearance multiplied by dialysis time and scaled to total body water (Kt/Vurea) equals 0.95-1.0. This number was later increased to 1.3, but the assumption that hemodialysis time is of minimal importance, as long as it is compensated by increased urea clearance, remained unchanged. Patients accepted short dialysis as a godsend, believing that it would not be detrimental to their well being and longevity. However, Kt/Vurea measures only removal of low molecular weight substances and does not consider removal of larger molecules. Nor does it correlate with the other important function of hemodialysis, namely ultrafiltration. Whereas patients with substantial residual renal function may tolerate short dialysis sessions, patients with little or no urine output tolerate short dialyses poorly because at a given interdialytic weight gain the ultrafiltration rate is inversely proportional to dialysis time. Rapid ultrafiltration is associated with cramps, nausea, vomiting, headache, fatigue, hypotensive episodes during dialysis, and hangover after dialysis; patients remain fluid overloaded with subsequent poor blood pressure control leading to left ventricular hypertrophy, diastolic dysfunction, and high cardiovascular mortality. Short, high-efficiency dialysis requires high blood flow, which increases demands on blood access. The classic, wrist arteriovenous fistula, the access with the best longevity and lowest complication rates, provides "insufficient" blood flow and is replaced with an arteriovenous graft fistula or an intravenous catheter. Moreover, to achieve high blood flows, large diameter intravenous catheters are used; these fit veins "too tightly" and so predispose to central-vein thrombosis. Longer hemodialysis sessions (5-8 hours, thrice weekly), as practiced in some centers, are associated with lower complication rates and better outcomes. Frequent dialyses (four or more sessions per week) with total weekly dialysis time sufficient to allow gentle ultrafiltration rates provide the best clinical results, but are associated with increased costs which are not properly reimbursed in the USA at present. Therefore, it is my strong belief that before a more appropriate reimbursement is available, a wide acceptance of longer, gentler dialysis sessions, in the current thrice weekly schedule, would improve overall hemodialysis results, decrease access complications, hospitalizations and mortality, particularly in anuric patients. Kt/Vurea should be abandoned as a measure of dialysis quality. The formula suggests that it is possible to decrease t as long as K is proportionately increased, but this is not true. The use of rigid, quantitative guidelines (e.g., spKt/Vurea of 1.3 per dialysis) assumes that all patients behave identically in response to therapeutic maneuvers, like the mean of the group, but this is also not true. The individual, clinical approach assumes that there are differences among patients, which require adjustment of dialysis schedule for each patient.
Division of Nephrology, Department of Medicine, University of Missouri, Columbia, Missouri, USA. Twardowskiz@health.missouri.edu
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D003404:Creatinine / Q000378:metabolism*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy; D008962:Models, Theoretical; D011187:Posture; D011788:Quality of Life; D006435:Renal Dialysis / Q000009:adverse effects* / Q000379:methods* / Q000401:mortality; D013997:Time Factors; D014508:Urea / Q000378:metabolism*
D014508:Urea; D003404:Creatinine