Treatment Time and Ultrafiltration Rate Are More Important in Dialysis Prescription than Small Molecule Clearance

Abstract

Chronic hemodialysis sessions, as developed in Seattle in the 1960s, were long procedures with minimal intra- and interdialytic 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/V_urea) 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/V_urea 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/V_urea 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.

Association of Ultrafiltration Rate with Mortality in Incident Hemodialysis Patients

“…Though this group was a small proportion of our total cohort (<1%), they also had a relatively long treatment time with a median of 4.0 h per session, further adding to the notion that long treatment time may improve patient outcomes. Twardowski [26] stressed the importance of treatment time and UFR rather than small molecular clearance (Kt/V urea ) in assessing dialysis quality. In our study, associations between UFR and mortality were similar across strata of single-pool Kt/V.…”

Assessment and Management of Hypertension in Patients on Dialysis

“…Shortening the procedure to tailor dialysis to a minimum Kt/V may provoke intradialytic symptoms, postdialysis fatigue, and nonadherence to therapy; thus, this is not recommended. 124 Normotension can be achieved independently of the duration of dialysis if the control of volume is adequate. 125 In fact, left ventricular mass index was also improved to a comparable degree in DRIP trial participants, in which the duration of dialysis was not altered but the dry weight was challenged.…”

No Difference in Nitrogen Balance between Standard Prescriptions of Hemodialysis and Peritoneal Dialysis

“…Indeed, patient survival is often better in Asian PD patients, despite a Kt/V of only 1.7 [24] . It is also argued that Kt/V is a poor measure of dialysis quality [25] . We have shown that a dietary intake of less than 1.2 g/kg/day of protein does not necessarily lead to malnutrition in Asian dialysis patients [26] .…”

“…There are many factors affecting HD and PD efficiency [28] . Kt/V remains the most accepted index used to assess small-solute clearance in HD and CAPD even though it is believed that smallmolecule clearance is not so important in dialysis prescription [25] . Urea kinetic modeling provides a way to quantitatively examine the relationship between dialysis dose and accumulation as well as removal of uremic toxins.…”