NDT Advance Access originally published online on November 26, 2007
Nephrology Dialysis Transplantation 2008 23(3):1075; doi:10.1093/ndt/gfm746
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Prescription of an intermittent haemodialysis dose using urea kinetic modelling is feasible in the critically ill patient
E-mail: suren.kanagasundaram{at}nuth.nhs.ukSir,
Helmut Schiffl's study, published in this journal [1], provides further confirmation of the difficulties of prescribing and delivering a urea-based dose of intermittent haemodialysis (IHD) in the critically ill patient. Using an anthropometric (Watson) estimate of body water [2] to help define the prescription, and the simplified Daugirdas II formula [3] to define dose delivery, significant prescription–delivery shortfalls were apparent in this population of critically ill maintenance HD patients.
The findings of this study are of interest but the approach and conclusions invite some comment.
Firstly, the distinction between ESRD and Acute Kidney Injury (AKI) is probably artificial—critical illness, rather than the cause of dialysis dependence, is likely to be the relevant factor. A prescription–delivery shortfall should thus not be unexpected, as shown by others [4] as well as by us [5]. The use of the Watson estimate of body water (developed from a non-uraemic population) may compound under-prescription of HD—and thus overestimate the prescription–delivery shortfall—in these patients who are often significantly fluid-loaded.
Secondly, the suggestion that critical illness violates the fundamental assumptions of urea kinetic modelling (UKM) warrants examination. Steady-state assumptions, with regard to urea generation and urea distribution volume, allow delivered dose to be assessed at relatively infrequent intervals in stable, chronic HD patients. In the only published evaluation of formal UKM in the critically ill AKI patient undergoing IHD [5], we have demonstrated wide inter- and intra-individual variability in these key factors. Despite this, we were able to derive an equilibrated Kt/V using formal, iterative double-pool UKM (rather than short-cut formulae) and were able to demonstrate that a target eKt/V could be prescribed to within a median absolute error of <0.14 Kt/V using practical prescription algorithms. Rather than violating urea kinetic assumptions, the presence of critical illness actually required the application of such dosing techniques on a frequent (i.e. sessional) basis, to account for the non-steady state.
Although low-molecular weight toxin clearance (using urea as a surrogate) is only one aspect of ‘dose’ in renal replacement therapy for the critically ill [6], a urea kinetic approach is entirely possible, if applied with the appropriate frequency and technique.
Conflict of interest statement. None declared.
Department of Renal Medicine, Newcastle-upon-Tyne Hospitals Trust, UK
References
- Schiffl H. Utility of urea kinetic modelling for prescription of adequate intermittent dialysis in critically ill maintenance dialysis patients. Nephrol Dial Transplant (2007) 22:2096.
[Free Full Text] - Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr (1980) 33:27–39.
[Abstract/Free Full Text] - Daugirdas JT. Second generation logarithmic estimates of single-pool variable volume Kt/V: an analysis of error. J Am Soc Nephrol (1993) 4:1205–1213.[Abstract]
- Evanson JA, Himmelfarb J, Wingard R, et al. Prescribed versus delivered dialysis in acute renal failure patients. Am J Kidney Dis (1998) 32:731–738.[Web of Science][Medline]
- Kanagasundaram NS, Greene T, Larive AB, et al. Prescribing an equilibrated intermittent hemodialysis dose in intensive care unit acute renal failure. Kidney Int (2003) 64:2298–2310.[CrossRef][Web of Science][Medline]
- Schiffl H, Lang SM, Fischer R. Daily hemodialysis and the outcome of acute renal failure. N Engl J Med (2002) 346:305–310.
[Abstract/Free Full Text]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||