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.
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 approximately 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.
Kanagasundaram
Nigel S
NS
Section of Dialysis and Extracorporeal Therapy, Department of Hypertension/Nephrology, OH, USA. suren.kanagasundaram@nuth.nhs.uk
Greene
Tom
T
Larive
Armand B
AB
Daugirdas
John T
JT
Depner
Thomas A
TA
Paganini
Emil P
EP
D058186:Acute Kidney Injury / Q000628:therapy*; D000368:Aged; D001806:Blood Urea Nitrogen; D002302:Cardiac Output / Q000502:physiology; D016638:Critical Illness / Q000628:therapy; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D007668:Kidney / Q000098:blood supply* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011446:Prospective Studies; D012039:Regional Blood Flow / Q000502:physiology; D006435:Renal Dialysis / Q000379:methods*; D017582:Renal Replacement Therapy / Q000379:methods; D014508:Urea / Q000097:blood*; D014655:Vascular Resistance / Q000502:physiology
D014508:Urea