Ionic dialysance allows an adequate estimate of urea distribution volume in hemodialysis patients.
BACKGROUND
An adequate estimation of urea distribution volume (V) in hemodialysis patients is useful to monitor protein nutrition. Direct dialysis quantification (DDQ) is the gold standard for determining V, but it is impractical for routine use because it requires equilibrated postdialysis plasma water urea concentration. The single pool variable volume urea kinetic model (SPVV-UKM), recommended as a standard by Kidney Disease Outcomes Quality Initiative (K/DOQI), does not need a delayed postdialysis blood sample but it requires a correct estimate of dialyser urea clearance.


METHODS
Ionic dialysance (ID) may accurately estimate dialyzer urea clearance corrected for total recirculation. Using ID as input to SPVV-UKM, correct V values are expected when end-dialysis plasma water urea concentrations are determined in the end-of-session blood sample taken with the blood pump speed reduced to 50 mL/min for two minutes (U(pwt2')). The aim of this study was to determine whether the V values determined by means of SPVV-UKM, ID, and U(pwt2') (V(ID)) are similar to those determined by the "gold standard" DDQ method (V(DDQ)). Eighty-two anuric hemodialysis patients were studied.


RESULTS
V(DDQ) was 26.3 +/- 5.2 L; V(ID) was 26.5 +/- 4.8 L. The (V(ID)-V(DDQ)) difference was 0.2 +/- 1.6 L, which is not statistically significant (P= 0.242). Anthropometric volume (V(A)) calculated using Watson equations was 33.6 +/- 6.0 L. The (V(A)-V(DDQ)) difference was 7.3 +/- 3.3 L, which is statistically significant (P < 0.001).


CONCLUSIONS
Anthropometric-based V values overestimate urea distribution volume calculated by DDQ and SPVV-UKM. ID allows adequate V values to be determined, and circumvents the problem of delayed postdialysis blood samples.
Di Filippo
Salvatore
S
Department of Nephrology and Dialysis, A. Manzoni Hospital, Lecco, Italy. s.difilippo@ospedale.lecco.it
Manzoni
Celestina
C
Andrulli
Simeone
S
Pontoriero
Giuseppe
G
Dell'Oro
Cesare
C
La Milia
Vincenzo
V
Tentori
Flavia
F
Crepaldi
Monica
M
Bigi
Maria Carla
MC
Locatelli
Francesco
F
D015312:Hemodialysis Solutions / Q000378:metabolism; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy*; D008954:Models, Biological; D012015:Reference Standards; D006435:Renal Dialysis / Q000379:methods* / Q000592:standards*; D014508:Urea / Q000378:metabolism
D015312:Hemodialysis Solutions; D014508:Urea