### Abstract

Introduction: Urea distribution volume (V) can be assessed in different ways, among them the anthropometric Watson Volume (V_{W}). However, many studies have shown that V_{W} does not coincide with V and that the latter can be more accurately estimated with other methods. The present multicentre study was designed to answer the question: what V to choose to assess online Kt/V? Materials and methods: Pre- and postdialysis blood urea nitrogen concentrations and the usual input data set for urea kinetic modelling were obtained for a single dialysis session in 201 Caucasian patients treated in 9 Italian dialysis units. Only dialysis machines measuring ionic dialysance (ID) were utilized. ID reflects very accurately the mean effective dialyser urea clearance (Kd). Six different V values were obtained: the first one was V_{W}; the second one was computed from the equation established by the HEMO Study to predict the single pool-adjusted modelled V from V_{W} (V_{H}) (Daugirdas JT et al. KI 64: 1108, 2003); the others were estimated kinetically as: 1. V_ID, in which ID is direct input in the in the double pool variable volume (dpVV) calculation by means of the Solute-solver software; 2. V_Kd, in which the estimated Kd is direct input in the dpVV calculation by means of the Solute-solver software; 3. V_KTV, in which V is calculated by means of the second generation Daugirdas equation; 4. V_SPEEDY, in which ID is direct input in the dpVV calculation by means of the SPEEDY software able to provide results quite similar to those provided by Solute-solver. Results: Mean± SD of the main data are reported: measured ID was 190.6 ± 29.6 mL/min, estimated Kd was 211.6 ± 29.0 mL/min. The relationship between paired data was poor (R^{2} = 0.34) and their difference at the Bland–Altman plot was large (21 ± 27 mL/min). V_{W} was 35.3 ± 6.3 L, V_{H} 29.5 ± 5.5, V_{_}ID 28.99 ± 7.6 L, V_{_}SPEEDY 29.4 ± 7.6 L, V_KTV 29.7 ± 7.0 L. The mean ratio V_{W}/V_ID was 1.22, (i.e. V_{W} overestimated V_ID by about 22%). The mean ratio V_{H}/V_ID was 1.02 (i.e. V_{H} overestimated V_ID by only 2%). The relationship between paired data of V_ID and V_{W} was poor (R^{2} = 0.48) and their mean difference at the Bland–Altman plot was very large (− 6.39 ± 5.59 L). The relationship between paired data of V_ID and V_{H} was poor (R^{2} = 47) and their mean difference was small but with a large SD (− 0.59 ± 5.53 L). The relationship between paired data of V_ID and V_SPEEDY was excellent (R^{2} = 0.993) and their mean difference at the Bland–Altman plot was very small (− 0.54 ± 0.64 L). The relationship between paired data of V_ID and V_KTV was excellent (R^{2} = 0.985) and their mean difference at the Bland–Altman plot was small (− 0.85 ± 1.06 L). Conclusions: V_ID can be considered the reference method to estimate the modelled V and then the first choice to assess Kt/V. V_SPEEDY is a valuable alternative to V_ID. V_KTV can be utilized in the daily practice, taking also into account its simple way of calculation. V_{W} is not advisable because it leads to underestimation of Kt/V by about 20%.

Original language | English |
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Journal | Journal of Nephrology |

DOIs | |

Publication status | Published - Jan 1 2019 |

### Keywords

- Double pool urea kinetic model
- Hemodialysis
- Ionic dialysance
- Kt/V
- Urea distribution volume
- Watson

### ASJC Scopus subject areas

- Nephrology

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## Cite this

*Journal of Nephrology*. https://doi.org/10.1007/s40620-019-00636-9