Simple Kt/V formulas based on urea mass balance theory.
The ratio Kt/V (K is patient clearance, t dialysis time, V urea space) has become the standard measure of dialysis adequacy. In this article simple Kt/V equations are developed theoretically from the urea mass balance equation. Two approximations lead to the most precise equation: [formula: see text] where R is the post to pre dialysis urea ratio, BW/V is the amount of fluid removed during dialysis (delta BW) expressed as a fraction of urea distribution space (V) at dry body weight (BW), and t is dialysis length in hours. A second equation arises with V approximated as 58% of BW. One further approximation leads to a simpler but slightly less precise Kt/V formula: [formula: see text] These and earlier published equations were tested with two sets of data: 1) 49 sessions involving 17 patients on maintenance dialysis and 2) 540 computer simulations spanning all likely values of Kt/V (0.6-1.6), protein catabolic rate (0.6-1.6), interdialytic weight gain (0-4% of BW per day) and dialysis session length (2-4 hr). The most precise formula (upper equation above) had a maximum error of 0.031 and 0.035 Kt/V units for the clinical and simulated data, respectively, whereas the lower equation was slightly less accurate with maximum Kt/V errors of 0.079 and 0.081, respectively. The proposed Kt/V equations are considerably more accurate than previously published formulas.
Department of Chemical Engineering, Lakehead University, Thunder Bay, Ontario, Canada.
L J
LJ
Garred
D L
DL
Barichello
B
B
DiGiuseppe
W G
WG
McCready
B C
BC
Canaud
D003198:Computer Simulation; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000628:therapy*; D007700:Kinetics; D008954:Models, Biological; D011237:Predictive Value of Tests; D011506:Proteins / Q000378:metabolism*; D006435:Renal Dialysis / Q000295:instrumentation; D014508:Urea / Q000378:metabolism*
D011506:Proteins; D014508:Urea