Chronic hemodialysis sessions, as developed in Seattle in the 1960s, were long procedures with minimal intra- and inter-dialytic symptoms. Over the next three decades, dialysis duration was shorten to 4, 3, even 2 h in thrice weekly schedules. This method spread rapidly, particularly in the United States, after the National Cooperative Dialysis Study suggested that the 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 remained unchanged. However, Kt/Vurea measures only the removal of low molecular weight substances and does not consider the removal of larger molecules. Nor does it correlate with the other important function of hemodialysis, namely ultrafiltration. 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. 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. Time of dialysis should be adjusted in such a way that patients would not suffer from symptoms related to rapid ultrafiltration, would not have other uremic symptoms and most patients would have blood pressure controlled without antihypertensive drugs.

Copyright © 2007 S. Karger AG, Basel

The evolution of hemodialysis duration and various measures of dialysis adequacy has recently been reviewed [1-3]. This article will provide a synopsis of these reviews, updated with recent Dialysis Outcomes and Practice Patterns Study (DOPPS) data, strengthening the notion that longer hemodialysis duration and slower ultrafiltration is associated with reduced mortality and better treatment tolerance of hemodialysis patients [4]. A short discussion of volume-dependent hypertension and the 'lag phenomenon' will be also included.

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