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Prescribing hemodialysis using a weekly urea mass balance model
J K Leypoldt1, C Kablitz, M C Gregory
1Research Service, Veterans Affairs Medical Center, Salt Lake City, Utah.
Blood Purification
|January 1, 1991
Summary
Monitoring predialysis BUN alone is insufficient for adequate hemodialysis. A new urea mass balance model simplifies assessing hemodialysis adequacy and protein catabolism, improving patient care.
Area of Science:
- Nephrology
- Biomedical Engineering
- Mathematical Modeling
Background:
- Prescribing hemodialysis solely based on predialysis Blood Urea Nitrogen (BUN) is inadequate for ensuring sufficient patient therapy.
- The National Cooperative Dialysis Study suggests adequate hemodialysis requires a protein catabolic rate (PCR) > 1 g/day/kg and either a time-averaged BUN concentration (TACurea) < 50 mg/dL or Kt/V > 1.
Purpose of the Study:
- To derive mathematical relationships from a weekly urea mass balance model to evaluate TACurea and protein catabolism (via urea generation rate, G).
- To simplify the assessment of hemodialysis adequacy without conventional urea kinetic modeling.
Main Methods:
- Developed a weekly urea mass balance model to calculate TACurea and G.
- Utilized midweek predialysis BUN concentration (BUNMW) for calculations: TACurea = 0.7 BUNMW and G = 0.7 BUNMW(Kr + Kd tau/T).
- Validated the model with clinical data from 139 sessions on 91 patients.
Main Results:
- The derived equations for TACurea and G showed high correlation with values obtained from conventional urea kinetic modeling (r = 0.96 and 0.94, respectively).
- The model effectively assesses protein catabolism and hemodialysis adequacy using simple calculations.
Conclusions:
- Individualized hemodialysis prescription can be optimized by using this urea mass balance model.
- Hemodialysis adequacy can be reliably assessed by monitoring TACurea and G calculated from the weekly urea mass balance model.