Blog
About

7
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Volume Estimates in Chronic Hemodialysis Patients by the Watson Equation and Bioimpedance Spectroscopy and the Impact on the Kt/V urea calculation

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Background:

          Accurate assessment of total body water (TBW) is essential for the evaluation of dialysis adequacy (Kt/V urea). The Watson formula, which is recommended for the calculation of TBW, was derived in healthy volunteers thereby leading to potentially inaccurate TBW estimates in maintenance hemodialysis recipients. Bioimpedance spectroscopy (BIS) may be a robust alternative for the measurement of TBW in hemodialysis recipients.

          Objectives:

          The primary objective of this study was to evaluate the accuracy of Watson formula–derived TBW estimates as compared with TBW measured with BIS. Second, we aimed to identify the anthropometric characteristics that are most likely to generate inaccuracy when using the Watson formula to calculate TBW. Finally, we derived novel anthropometric equations for the more accurate estimation of TBW.

          Design and Setting:

          This was a cross-sectional study of prevalent in-center HD patients at St Michael’s Hospital.

          Patients:

          One hundred eighty-four hemodialysis patients (109 men and 75 women) were evaluated in this study.

          Measurements:

          Anthropometric measurements including weight, height, waist circumference, midarm circumference, and 4-site skinfold (biceps, triceps, subscapular, and suprailiac) thickness were measured; fat mass was measured using the formula by Durnin and Womersley. We measured TBW by BIS using the Body Composition Monitor (Fresenius Medical Care, Bad Homburg, Germany).

          Methods:

          We used the Bland-Altman method to calculate the difference between the TBW derived from the Watson method and the BIS. To derive new equations for TBW estimation, Pearson’s correlation coefficients between BIS-TBW (the reference test) and other variables were examined. We used the least squares regression analysis to develop parsimonious equations to predict TBW.

          Results:

          TBW values based on the Watson method had a high correlation with BIS-TBW (correlation coefficients = 0.87 and P < .001). Despite the high correlation, the Watson formula overestimated TBW by 5.1 (4.5-5.8) liters and 3.8 (3.0-4.5) liters, in men and women, respectively. Higher fat mass and waist circumference (general and abdominal obesity) were correlated with the greater TBW overestimation by the Watson formula. We created separate equations for men and women based on weight and waist circumference.

          Limitations:

          The main limitation of our study was the lack of an external validation for our novel estimating equation. Furthermore, though BIS has been validated against traditional reference standards, our assumption that it represents the “gold standard” for body compartment assessment may be flawed.

          Conclusions:

          The Watson formula generally overestimates TBW in chronic dialysis recipients, particularly in patients with the highest waist circumference. Widespread reliance on the Watson formula for derivation of TBW may lead to the underestimation of Kt/V urea..

          Abrégé

          Contexte:

          Une évaluation précise du volume d’eau total (VET) de l’organisme est essentielle pour valider l’efficacité de la dialyse (Kt/V urée). Recommandée pour le calcul du VET, la formule de Watson a pourtant été établie en fonction de volontaires sains. Conséquemment, elle fournit des estimations potentiellement inexactes chez les patients hémodialysés. La spectroscopie de bio-impédance (BIS – Bioimpedance Spectroscopy) pourrait s’avérer une alternative fiable pour mesurer le VET des patients hémodialysés.

          Objectifs de l’étude:

          Notre principal objectif consistait à comparer l’exactitude des valeurs de VET mesurées par la formule de Watson et par bio-impédance. Secondairement, nous cherchions à cerner les caractéristiques anthropométriques les plus susceptibles d’engendrer des valeurs imprécises avec la formule de Watson. Enfin, nous voulions dériver des équations anthropométriques fiables pour mesurer le VET des patients.

          TYPE et CADRE de l’étude:

          Nous avons mené une étude transversale auprès de patients hémodialysés à l’hôpital St Micheal’s de Toronto.

          Patients:

          Un total de 184 patients (109 hommes et 75 femmes) ont participé à l’étude.

          Mesures:

          Ont été effectuées une série de mesures anthropométriques : poids, grandeur, tour de taille, périmètre brachial et épaisseur de quatre plis cutanés (au biceps, au triceps, sous l’omoplate et au niveau de l’iliaque supérieur). Ces données ont servi à calculer la masse adipeuse avec l’équation de Durnin et Womersley. Pour les mesures du VET par bio-impédance (BIS), on a utilisé un Body Composition Monitor ou BCM (Fresenius Medical Care, à Bad Homburg, en Allemagne).

          Méthodologie:

          Nous avons utilisé la méthode de Bland-Altman pour calculer l’écart entre les mesures de VET obtenues par la formule de Watson et par BIS. Pour guider l’élaboration d’équations plus fiables, on a calculé les coefficients de corrélation de Pearson la bio-impédance (test de référence) et d’autres variables. On a développé des équations simplifiées et concises permettant de prédire le VET avec la régression par les moindres carrés.

          Résultats:

          Les valeurs de VET obtenues par la formule de Watson se sont avérées très étroitement corrélées avec les valeurs obtenues par bio-impédance (coefficient de corrélation : 0,87; p<0,001). Toutefois, la formule de Watson a surévalué le VET de 5,1 litres en moyenne (entre 4,5 et 5,8 litres) chez les hommes et de 3,8 litres en moyenne (entre 3,0 et 4,5 litres) chez les femmes. Une masse adipeuse élevée et un fort tour de taille (cas d’obésité générale et d’obésité abdominale) ont été associés aux plus importantes surestimations du VET données par la formule de Watson. Nous avons dérivé des équations distinctes pour les hommes et les femmes en tenant compte du poids du patient et de son tour de taille.

          Limites de l’étude:

          L’absence de validation externe des nouvelles équations élaborées pour l’estimation du VET constitue la principale limite de notre étude. Par ailleurs, bien que la spectroscopie de bio-impédance ait été validée contre les étalons de référence conventionnels, notre supposition selon laquelle cette méthode représenterait l’étalon par excellence pour mesurer la composition corporelle pourrait être erronée.

          Conclusion:

          La formule de Watson surestime généralement le VET des patients hémodialysés, particulièrement chez ceux qui présentent un fort tour de taille. Ainsi, le recours généralisé à cette formule pour la dérivation du VET des patients hémodialysés pourrait mener à une sous-évaluation du Kt/V urée.

          Related collections

          Most cited references 12

          • Record: found
          • Abstract: found
          • Article: not found

          Statistical methods for assessing agreement between two methods of clinical measurement.

          In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analysed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.
            Bookmark
            • Record: found
            • Abstract: not found
            • Article: not found

            Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years.

              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Malnutrition-inflammation complex syndrome in dialysis patients: causes and consequences.

              Protein-energy malnutrition (PEM) and inflammation are common and usually concurrent in maintenance dialysis patients. Many factors that appear to lead to these 2 conditions overlap, as do assessment tools and such criteria for detecting them as hypoalbuminemia. Both these conditions are related to poor dialysis outcome. Low appetite and a hypercatabolic state are among common features. PEM in dialysis patients has been suggested to be secondary to inflammation; however, the evidence is not conclusive, and an equicausal status or even opposite causal direction is possible. Hence, malnutrition-inflammation complex syndrome (MICS) is an appropriate term. Possible causes of MICS include comorbid illnesses, oxidative and carbonyl stress, nutrient loss through dialysis, anorexia and low nutrient intake, uremic toxins, decreased clearance of inflammatory cytokines, volume overload, and dialysis-related factors. MICS is believed to be the main cause of erythropoietin hyporesponsiveness, high rate of cardiovascular atherosclerotic disease, decreased quality of life, and increased mortality and hospitalization in dialysis patients. Because MICS leads to a low body mass index, hypocholesterolemia, hypocreatininemia, and hypohomocysteinemia, a "reverse epidemiology" of cardiovascular risks can occur in dialysis patients. Therefore, obesity, hypercholesterolemia, and increased blood levels of creatinine and homocysteine appear to be protective and paradoxically associated with a better outcome. There is no consensus about how to determine the degree of severity of MICS or how to manage it. Several diagnostic tools and treatment modalities are discussed. Successful management of MICS may ameliorate the cardiovascular epidemic and poor outcome in dialysis patients. Clinical trials focusing on MICS and its possible causes and consequences are urgently required to improve poor clinical outcome in dialysis patients.
                Bookmark

                Author and article information

                Journal
                Can J Kidney Health Dis
                Can J Kidney Health Dis
                CJK
                spcjk
                Canadian Journal of Kidney Health and Disease
                SAGE Publications (Sage CA: Los Angeles, CA )
                2054-3581
                10 January 2018
                2018
                : 5
                Affiliations
                [1 ]Division of Nephrology, St. Michael’s Hospital, Toronto, Ontario, Canada
                [2 ]Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Ontario, Canada
                Author notes
                Marc B. Goldstein, Division of Nephrology, St. Michael’s Hospital, 30 Bond Street, #3061, Toronto, Ontario, Canada M5B 1W8. Email: goldsteinma@ 123456smh.ca
                Article
                10.1177_2054358117750156
                10.1177/2054358117750156
                5768265
                © The Author(s) 2018

                This article is distributed under the terms of the Creative Commons Attribution 4.0 License ( http://www.creativecommons.org/licenses/by/4.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages ( https://us.sagepub.com/en-us/nam/open-access-at-sage).

                Categories
                Original Research Article
                Custom metadata
                January-December 2018

                Comments

                Comment on this article