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Improving the “second generation Daugirdas equation” to estimate Kt/V on the once-weekly haemodialysis schedule

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Abstract

Introduction

The haemodialysis (HD) dose, as expressed by Kt/V urea, is currently routinely estimated with the second generation Daugirdas (D2) equation (Daugirdas in J Am Soc Nephrol 4:1205–1213, 1993). This equation, initially devised for a thrice-weekly schedule, was modified to be used for all dialysis schedules (Daugirdas et al. in Nephrol Dial Transplant 28:2156–2160, 2013), by adopting a variable factor that adjusts for the urea generation (GFAC) over the preceding inter-dialysis interval (PIDI, days). This factor was set at 0.008 for the mid-week session of the standard thrice-weekly HD schedule. In theory, by setting PIDI = 7, one could get GFAC = 0.0025, to be used in patients on the once-weekly (1HD/wk) schedule, but actually this has never been tested. Moreover, GFAC was derived not taking into account the residual kidney urea clearance (Kru). Aim of the present study was to provide a specific value of GFAC for patients on  a once-weekly hemodialysis schedule.

Subjects and methods

The equation to predict GFAC (GFAC-1) in the 1HD/wk schedule was established in a group of 80 historical Italian patients (group 1) and validated in a group of 100 historical Spanish patients (group 2), by comparing the Kt/V computed using GFAC-1 (Kt/VGFAC-1) with the reference Kt/V (Kt/VSS) values, as computed with the web-based Solute-Solver software (SS) (Daugirdas et al. in Am J Kidney Dis 54:798–809, 2009). Three more sets of Kt/V (Kt/V0.008, Kt/V0.0025 and Kt/V0.0035) values were computed using the GFAC of the original D2 equation (0.008), the GFAC predicted by PIDI/7 (0.0025) and the mean observed GFAC-1 (0.0035), respectively. They were compared with the reference Kt/VSS values.

Results

The predicting equation obtained from group 1 was: GFAC-1 = 0.0022 + 0.0105 × Kru/V (R2 = 0.93). Mean Kt/VSS in the group 2 was 1.54 ± 0.29 SD (N = 500 HD sessions). The mean percent differences for Kt/V0.008, Kt/V0.0025, Kt/VGFAC-1, and Kt/V0.0035 were 5.1 ± 1.0%, − 1.4 ± 0.7%, 0.0 ± 0.3%, − 0.3 ± 0.7%, respectively. No statistically significant difference was found between Kt/V values, except for Kt/V0.008.

Conclusion

A linear relationship was found between GFAC and Kru/V in patients on the 1HD/wk schedule. Such a relationship is able to improve the “second generation Daugirdas equation” for an accurate estimate of the single pool Kt/V in this setting. However, a simple replacement in the D2 equation of 0.008 with the mean observed GFAC (0.0035) could suffice in the clinical practice.

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Fig. 1
Fig. 2

Abbreviations

BUN:

Blood urea nitrogen, plasma concentration (mg/dL)

BWT:

Post-dialysis body weight (kg)

D2:

Second generation Daugirdas equation

G:

Urea generation rate (mg/min)

GFAC:

G-Factor, accounting for urea generation over the inter-dialysis interval prior to the studied HD session

GFAC-1:

GFAC obtained from the Eq. 3

HD:

Haemodialysis

HD/wk:

Number of HD sessions per week: 1HD/wk = once-weekly HD schedule; 3HD/wk = thrice-weekly HD schedule

Kru:

Residual kidney urea clearance (mL/min)

Kru/V ratio:

Ratio of Kru to V

Kt/V:

Fractional urea clearance = Kd × t/V (dimensionless),

Kt/V0.0025 :

Single pool Kt/V computed using the D2 equation with GFAC = 0.0025

Kt/V0.0035 :

Single pool Kt/V computed using the D2 equation with GFAC = 0.0035

Kt/V0.008 :

Single pool Kt/V computed using the D2 equation with GFAC = 0.008

Kt/VGFAC-1 :

Single pool Kt/V computed the D2 equation with GFAC = GFAC-1, as predicted by Eq. 3

RKF:

Residual kidney function

SS:

Solute Solver: web-based software (available at ureakinetics.org) that allows single pool and double pool urea kinetic modelling

T:

Duration of the dialysis session (in hours with the D2 equation)

UKM:

Urea kinetic model

V:

Post-dialysis urea distribution volume (L)

VVSP:

Variable-volume single pool

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Funding

No funding agency granted the present study.

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Authors and Affiliations

  1. Dialysis Centre SM2, Policoro, Italy

    Francesco Gaetano Casino

  2. Division of Nephrology, Miulli General Hospital, Strada Provinciale Santeramo, 70121, Acquaviva delle Fonti, Puglia, Italy

    Francesco Gaetano Casino & Carlo Basile

  3. Division of Nephrology, San Pedro de Alcantara Hospital, Cáceres, Spain

    Javier Deira & José Aguilar

  4. Division of Nephrology, Virgen del Puerto Hospital, Cáceres, Spain

    Miguel A. Suárez

  5. Division of Nephrology, Ospedale Madonna Delle Grazie, Matera, Italy

    Giovanni Santarsia

  6. Associazione Nefrologica Gabriella Sebastio, Martina Franca, Italy

    Carlo Basile

Authors
  1. Francesco Gaetano Casino
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  2. Javier Deira
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  3. Miguel A. Suárez
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  4. José Aguilar
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  5. Giovanni Santarsia
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  6. Carlo Basile
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Correspondence to Carlo Basile.

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Casino, F.G., Deira, J., Suárez, M.A. et al. Improving the “second generation Daugirdas equation” to estimate Kt/V on the once-weekly haemodialysis schedule. J Nephrol 34, 907–912 (2021). https://doi.org/10.1007/s40620-020-00936-5

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  • DOI: https://doi.org/10.1007/s40620-020-00936-5

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