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Ionic Dialysance Measurement Is Urea Distribution Volume Dependent: A New Approach to Better Results
Author(s) -
Goldau Rainer,
Kuhlmann Uwe,
Samadi Nader,
Gross Malte,
Graf Thomas,
Orlandini Giancarlo,
Marcelli Daniele,
Lange Harald
Publication year - 2002
Publication title -
artificial organs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.684
H-Index - 76
eISSN - 1525-1594
pISSN - 0160-564X
DOI - 10.1046/j.1525-1594.2002.06817.x
Subject(s) - urea , chemistry , bolus (digestion) , chromatography , analytical chemistry (journal) , biomedical engineering , surgery , medicine , organic chemistry
Conductivity (CD)‐based dialysance measurements precisely match urea dialysance with <5% difference. For measurement, a CD step‐profile is applied by increasing dialysate inlet CD at time t 0 for 10% above baseline and lasting for 2–5 min until t 1 , followed by a decrease to –4% until t 2 and a final return to baseline, meanwhile recording dialysate CD at filter inlet ( cdi ) and outlet ( cdo ), dialysate flow ( Qd ), and ultrafiltration (UF)‐rate ( Qf ). Electrolytic dialysance ( KeCn ) is calculated by KeCn I,J = (1 −[ cdo I − cdo J ]/[ cdi I − cdi J ])( Qd + Qf ) with time index I≠J . The combinations in I,J are not equivalent: KeCn 0,1 < KeCn 1,2 < KeCn 0,2 . Each difference is 2% to 5%, and a difference versus urea clearance remains. An in vivo on‐line clearance study (10 patients, 100 dialysis sessions, 265 measurements) with automatic electrolytical dialysance measurements and permanent data recording was conducted. Two methods were applied: a CD step‐profile and a significantly smaller, dynamic CD bolus. Both were compared to laboratory reference of urea clearance. Reference Kt / V has been calculated using equilibrated single‐pool methods and direct quantification. Urea generation was ignored. The results are as follows. The reference blood‐side urea clearance was 164.0 ± 11.8 ml/min, n = 265. The mean errors of the ionic dialysance results are KeCn 0,1 : −9.1 ± 4.8%, n = 250; KeCn 1,2 : −5.6 ± 4.4%, n = 250; KeCn 0,2 : 6.8 ± 7.7%, n = 250; KeCn Bolus : 0.1 ± 4.8%, n = 162. The KeCn I,J error is urea distribution volume related. Kt / V comparison to equilibrated single pool is as follows: KeCn 1,2 t / V : 0.0 ± 5.0% (r = 0.96, n = 45); KeCn Bolus t / V : 5.3 ± 3.9% (r = 0.98, n = 44). The comparison to direct quantification is as follows: KeCn 1,2 t / V : −2 ± 6.4% (r = 0.95, n = 68); KeCn Bolus t / V : 3.2 ± 6.3% (r = 0.95, n = 66). V could roughly be measured. Dialysance measured by the step‐function method was dependent on sodium load and distribution volume while the CD‐bolus dialysance was not. Errors are generated by measurement‐induced sodium shift that is sufficient even to estimate urea distribution volume. For dialysance measurements, small dynamic CD boli are preferable to stable step functions.