Magnitude and precision of absolute blood volume estimated during hemodialysis

<b>Background:</b> Management of body fluid volumes and adequate prescription of ultrafiltration (UF) remain key issues in the treatment of chronic kidney disease patients.<b>Objective:</b> This study aims to estimate the magnitude as well as the precision of absolute blood volume (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mi>b</mml:mi></mml:msub></mml:mrow></mml:mrow></mml:math>) modeled during regular hemodialysis (HD) using standard data available with modern dialysis machines.<b>Methods:</b> The estimation utilizes a two-compartment fluid model and a mathematical optimization technique to predict UF-induced changes in hematocrit measured by available on-line techniques. The method does not rely on a specific hematocrit sensor or a specific UF or volume infusion protocol and uses modeling and prediction tools to quantify the error in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mi>b</mml:mi></mml:msub></mml:mrow></mml:mrow></mml:math> estimation.<b>Results:</b> The method was applied to 21 treatments (pre-UF body mass: 65.57<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>±</mml:mo></mml:mrow></mml:math>13.44 kg, UF-volume: 3.99<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>±</mml:mo></mml:mrow></mml:math>1.14 L) obtained in ten patients (4 female). Pre-HD <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mi>b</mml:mi></mml:msub></mml:mrow></mml:mrow></mml:math> was 5.4<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>±</mml:mo></mml:mrow></mml:math>0.53 L with an average coefficient of variation of 9.8% (range 1 to 22%). A significant moderate correlation was obtained when <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mi>b</mml:mi></mml:msub></mml:mrow></mml:mrow></mml:math> was compared to a different method applied to the same data set (<i>r</i> = 0.5). Specific blood volumes remained above the critical level of 65 mL/kg in 17 treatments (80.9%).<b>Conclusion:</b> The method offers the opportunity to detect critical blood volumes during HD and to judge the quality and reliability of that information based on the precision of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>V</mml:mi></mml:mrow><mml:mi>b</mml:mi></mml:msub></mml:mrow></mml:mrow></mml:math> estimate.