Journal Article

Dosing intermittent haemodialysis in the intensive care unit patient with acute renal failure—estimation of urea removal and evidence for the regional blood flow model

Nigel S. Kanagasundaram, Tom Greene, Armand B. Larive, John T. Daugirdas, Thomas A. Depner and Emil P. Paganini

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 23, issue 7, pages 2286-2298
Published in print July 2008 | ISSN: 0931-0509
Published online February 2008 | e-ISSN: 1460-2385 | DOI: http://dx.doi.org/10.1093/ndt/gfm938
Dosing intermittent haemodialysis in the intensive care unit patient with acute renal failure—estimation of urea removal and evidence for the regional blood flow model

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Background. Blood-side dosing methods may overestimate urea removal in comparison to dialysate-side measurements during intermittent HD (IHD) for acute renal failure (ARF). The present study sought to quantify this mass balance error (MBE) and explore potential explanatory factors.

Methods. Prospective, formal, blood-side urea kinetic modelling was performed in serial sessions (n = 42) in 18 intensive care unit ARF patients. Three blood-side estimates of urea removal were calculated and these were compared to urea removal derived from fractional dialysate sampling and use of an on-line urea monitor. We also examined urea rebound in these patients, as expressed by the intercompartmental urea clearance (Kc), and in a subset of patients examined the relation of Kc to cardiac output and systemic vascular resistance (SVR).

Results. The mean % MBE (MBE = blood − dialysate-estimated urea removal) was about 9% using conventional two-pool modelling based on a 60-min post-dialysis blood urea nitrogen (BUN) with or without the use of one or more intra-dialytic BUN values. The extent of MBE could not be explained by the clinical or dialytic variables that were measured. Part of the MBE error was due to overestimation of the intradialytic BUN profile, because model-independent profiling of intra-dialytic BUN values to compute urea removal reduced the MBE to ∼6%. The log Kc was correlated with cardiac output and showed trends towards an inverse correlation with SVR.

Conclusions. Classical, two-pool, blood-side UKM produces a modest overestimate of urea removal in IHD for critically ill ARF patients. The source of this small, residual MBE is unknown. The amount of urea rebound, as reflected by Kc, varied among patients and associated with cardiac output and SVR, as predicted by the regional blood flow model.

Keywords: mass balance error; multi-compartment modelling; renal replacement therapy; urea kinetic modelling; vasopressors

Journal Article.  8230 words.  Illustrated.

Subjects: Nephrology

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