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The use of bioimpedance to aid volume assessment in dialysis patients

2014; Elsevier BV; Volume: 87; Issue: 1 Linguagem: Inglês

10.1038/ki.2014.310

1523-1755

Elizabeth Lindley, František Lopot,

Dialysis and Renal Disease Management

To the Editor: In their review of the role of bioimpedance in the assessment of volume in dialysis patients, Davies and Davenport1.Davies S.J. Davenport A. The role of bioimpedance and biomarkers in helping to aid clinical decision-making of volume assessments in dialysis patients.Kidney Int. 2014; 86: 489-496Abstract Full Text Full Text PDF PubMed Scopus (210) Google Scholar include the use of the ‘ECW/TBW ratio’ (extracellular to total body water ratio). As an example of this approach, the authors cite the paper presented by our group at the 2004 ISPD-EuroPD Congress.2.Lindley E. Devine Y. Hall L. et al.A ward-based procedure for assessment of fluid status in peritoneal dialysis patients using bioimpedance spectroscopy.Perit Dial Int. 2005; 25: S46-S48PubMed Google Scholar With fresh publicity of the newly named Lindley–Lopot formula, we would like to comment on its limitations and the subsequent OH index (overhydration index) approach. The Lindley–Lopot formula defines the mid-point of a normal range within which ECW/TBW depends on body composition. Water in adipose tissue is mainly extracellular and hence patients with a high proportion of adipose tissue, because of obesity or low muscle mass, will have a relatively high ECW/TBW. Trying to reach a population-based norm in these patients will lead to dehydration with the risk of accelerated loss of residual function, hypotension, and fatigue. Absolute overhydration (in liters), and the OH index (OH/ECW), for an individual subject can be obtained from the model published by Chamney et al.3.Chamney P.W. Wabel P. Moissl U.M. et al.A whole-body model to distinguish excess fluid from the hydration of major body tissues.Am J Clin Nutr. 2007; 85: 80-89PubMed Google Scholar in 2007, which gives OH (‘MExF’) as a function of ECW, ICW (intracellular water), and weight. In practice, the tissue hydration parameters on which this model is based must be optimized for specific devices. As with our formula (derived for the Xitron Hydra), this requires data for control subjects with a range of body compositions. For the Fresenius body composition monitor, optimization has led to modifications of the original parameters and a small age-related adjustment. However, although the constants in the Lindley–Lopot formula are expected to depend on typical body habitus for the population studied, no systematic effect of ethnic origin on tissue hydration has been identified to date. It should be emphasized that, although accurate measurements of hydration status can help in fluid management, especially where traditional indicators conflict, they will always be just one part of the clinical assessment.