RENAL RESEARCH INSTITUTE SYMPOSIUM: Effective Diffusion Volume Flow Rates (Qe) for Urea, Creatinine, and Inorganic Phosphorous (Qeu, Qecr, QeiP) During Hemodialysis

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Abstract
In vivo solute clearances can be estimated from dialyzer blood (Q b) and dialysate (Q d) flow rates and a solute‐ and dialyzer‐specific overall permeability membrane area product (KoA ). However, these calculations require knowledge of the flow rate of the effective solute distribution volume in the flowing bloodstream (Q e) in order to calculate in vivo clearances and KoA s. We have determined Q e for urea, creatinine, and inorganic phosphorus from changes in concentrations across the blood compartment and mass balance between the blood and dialysate streams. We made four serial measurements over one dialysis in 23 patients and found that Q eu equals the total blood water flow rate, Q ecr equals the plasma water flow rate plus 61% of red cell water flow rate, and Q eiP is limited to the plasma water flow rate. Equations are derived to calculate Q e for each of these solutes from Q b and hematocrit and in vivo KoA s for each solute were calculated.