Low Dialysate Flow Rate Research Articles

Haemodialysis with low dialysate flow rates: A comparison of high performance membranes and conventional membranes

Summary: We performed experimental studies to examine the effects of low dialysate flow rates on the clearance of small molecular weight substances, a middle molecular weight substance and a low molecular weight protein using a high performance membrane (HPM) and a conventional membrane (CVM). the blood flow rate was 200 mL/min and the diasylate flow rate varied between 300 and 500 mL/min. Clearance of urea and creatinine, representing small molecular weight substances, clearance of vitamin B12 representing a middle molecular weight substance, and clearance of myoglobin, representing a middle molecular weight substance, and clearance of myoglobin, representing a low molecular weight protein were measured. Lowering the dialysate flow rate from 500 to 300 mL/min in the HPM decreased the clearance of urea, creatinine, vitamin B12 and myoglobin by 7.2%, 8.6%, 8.4%, and 2.4%, respectively. Lowering the dialysate flow rate from 500 to 300 mL/min in the CVM decreased the clearance of urea, creatinine, and vitamin B12 by 8.7%, 10.9%, and 10.4%, respectively. Changes in the clearance of creatinine with reduced dialysate flow rate in the HPM were significantly lower than those in the CVM (P<0.05). Clearance of urea, creatinine, and vitamin B12 in the HPM at a dialysate flow rate of 300 mL/min were higher than those of in the CVM at a dialysate flow rate of 500 mL/min. These results suggest that dialysate flow rates can be reduced and water can be effectively saved by combining a dialysate flow rate of 300 mL/min with a HPM during water shortages due to natural disasters or climate changes.

Assessment of the effects of low dialysate flow rates on removal rates and clearance using high flux membranes.

The effects of the low dialysate flow rates on the removal rate and clearance of urea nitrogen, creatinine, uric acid, beta 2-microglobulin and myoglobin, using high flux membranes were studied. The removal rates for all substances were not significantly decreased. Although clearance of urea nitrogen, creatinine and uric acid was significantly decreased (p < 0.05), clearance of inorganic phosphate, beta 2-microglobulin and myoglobin was not significantly decreased. These results suggest that hemodialysis at low dialysate flow rates for a short term during water shortages due to natural disasters and drier climates can be performed with an insignificant reduction in removal rates and a minimum reduction in clearance.

Net Ultrafiltration May Not Eliminate Backfiltration During Hemodialysis with Highly Permeable Membranes

Backfiltration of dialysis solution can occur during hemodialysis with highly permeable membranes. A method has recently been developed for determining backfiltration rates in vitro at low dialysate flow rates by measuring changes in the local dialysate concentration of a marker macromolecule via sampling ports added to the hemodialyzer housing. In the present study, the influence of net ultrafiltration on backfiltration rates was determined for five commercial dialyzers containing membranes with different water permeabilities. In vitro experiments were performed (n = 3) using freshly donated whole blood at blood flow rates of 200 and 340 ml/min and at a dialysate flow rate of 100 ml/min. At zero net ultrafiltration, backfiltration rates increased with increasing membrane water permeability and ranged from 0.9 to 6.9 ml/min. At a net ultrafiltration rate of 10 ml/min, backfiltration was eliminated for dialyzers containing membranes with water permeabilities of less than 30 ml/h/mm Hg but remained significant for dialyzers with higher membrane water permeabilities. Therefore, despite a significant net ultrafiltration rate, backfiltration may still occur during hemodialysis with highly permeable membranes.

Measurement of Backfiltration Rates during Hemodialysis with Highly Permeable Membranes

A method for determining local transmembrane fluid movement in a commercial hemodialyzer at low dialysate flow rates by measuring changes along the dialyzer length in the local concentration of a marker macromolecule added to the dialysis solution has been developed. The method was evaluated in vitro at zero net ultrafiltration using dialyzers containing polysulfone (n = 4) and cuprophane (n = 3) membranes. The local concentration of the marker macromolecule along the dialyzer length was higher than the input dialysate concentration only during experiments with dialyzers containing polysulfone membranes. These observations provide direct empirical evidence that fluid movement in the dialysate to blood direction, i.e., backfiltration, occurs during hemodialysis with this highly permeable membrane. Net rates of backfiltration for the dialyzer containing polysulfone membrane were also calculated from changes in the local concentration of the marker macromolecule and mass balance considerations. The calculated backfiltration rates increased with increasing blood flow rate and trended upward with increasing dialysate flow rate. The described methodology provides a novel approach for the further characterization of fluid and solute transport during hemodialysis with highly permeable membranes.

A mathematical model of continuous arterio-venous hemodiafiltration (CAVHD)

Continuous arterio-venous hemodiafiltration (CAVHD) differs from conventional hemofiltration and dialysis by the interaction of convection and diffusion, the use of very low dialysate flow rates and by the deterioration of membrane conditions during the treatment. In order to study the impact of these phenomena on diffusive transport, we developed a mathematical model of the kinetics of CAVHD solute transport from plasma water to dialysate. The model yields an expression of the diffusive mass transfer coefficient, K d, as a function of blood, filtrate and dialysate flow rates and solute concentrations, which can be measured in the clinical setting. This paper gives a description of the model derivation. K d is demonstrated to vary depending on dialysate flow and duration of treatment.

In Vitro Study of Combined Convection- Diffusion Mass Transfer in Hemodialysers

Clearance measurements have been obtained for urea, Vit B12 and myoglobin by simultaneous hemodialysis and ultrafiltration (UF) techniques, using various commercially available hemodialysers. The experimental results confirm that the overall clearance is less than the clearance of each process occurring separately due to interaction between convection and diffusion. Adequate urea clearance (100 ml/min) can be obtained either by using high ultrafiltration (60 ml/min) with low dialysate flow rate (70 ml/min) or moderate ultrafiltration (less than 30 ml/min) with higher dialysate flow rate (120 ml/min). The comparison of experimental clearance with the predictions of theoretical model (1) for urea are found to be in good agreement for dialysate flow rates of more than 300 ml/min and for smaller dialysate flow rates the predicted clearances are higher than measured ones. An approximate correlation for the overall clearance is CL = CLD + QF/2 where CLD is the dialytic clearance and QF the UF flow rate.