Mid-Dilution: The Perfect Balance between Convection and Diffusion

Abstract

Although hemodiafiltration (HDF) offers the advantage of increased convective clearance for middle molecules, there is still controversy as to whether reinfusion should occur pre- or post-filter. Mid-dilution hemodiafiltration (MD HDF) is a new HDF technique that uses a special dialyzer, MD190, which allows both pre- and post-reinfusion. While externally the dialyzer looks similar to conventional hemodialyzers, the internal fibers are divided into two bundles by a special annular header that first lets the blood pass through the peripheral bundle in post-dilution, mix with the reinfusion fluid at the opposite end of the dialyzer and then proceed (after pre-dilution) to the dialyzer blood exit. The dialyzer is able to support substantially higher reinfusion rates (10-12 l/h). We have compared the removal characteristics of several small solutes and larger middle-molecular-weight toxins by examining instantaneous clearance at 45 min, the dialysis reduction ratio and total mass removal (by spilling) in a three-center prospective cross-over study. Twenty patients were randomized to a treatment sequence of one-week high-flux bicarbonate hemodialysis (HD) followed by MD HDF, or vice versa. The parameters evaluated included urea, creatinine, beta2-microglobulin, angiogenin, leptin, retinol-binding protein, and the effects on sodium, potassium, bicarbonate and calcium. Blood flow rates ranged between 300-450 ml/min (mean 359 +/- 44 HD, 367 +/- 35 MD HDF). The mean reinfusion for MD HDF was 166 +/-17 ml/min. MD HDF had a significantly better instantaneous clearance for urea (328 +/- 28 vs 277 +/- 40); creatinine (292 +/- 32 vs. 212 +/- 66); phosphate (324 +/- 38 vs. 242 +/- 63); beta2-microglobulin (249 +/- 27 vs. 100 +/- 24); angiogenin (173 +/- 27 vs. 28 +/- 32); and leptin (202 +/- 29 vs. 63 +/- 43). Treatments were well tolerated with no adverse reactions occurring during any of the treatments. The MD HDF filter's unique configuration is designed to deliver high-efficiency HDF with a significant improvement in small and middle molecule removal. MD HDF supports substantially higher ultrafiltration rates, and as such, results in a higher removal of middle-molecular-weight toxins.

Evaluation of a New Online Hemodiafiltration Mode with Automated Pressure Control of Convection

“…The percentage reductions of low- molecular-weight toxins in each treatment are consistent with the literature [21,22,23,24,25,26]. In particular, the reductions in plasma uremic toxin recorded in VOLc and TMPc are comparable to the postdilution HDF standard (VOLc mode) [22], whereas the removal rate recorded in ULTRAc mode is comparable to the mix-dilution HDF, where the convective volumes are extremely high also for high Q B (around 400 ml/min) [18,27].…”

Mid-Dilution: An Innovative High-Quality and Safe Haemodiafiltration Approach

“…Some data give an indication of a better per dialysis purifi cation of cystatin C (CyC), retinol-binding protein (RBP) or leptin compared to PostD [9,10] or angiogenin and RBP compared to high-fl ux haemodialysis [12].…”

Calcium Balance during Hemodialysis

“…Convective calcium loss is of particular importance in predilution hemodiafiltration (with the largest fluid exchange volumes); it has been recommended that such therapy should prompt the use of 0.25 mmol/l higher dialysate calcium concentration than would usually be utilized, to compensate for these potential increased losses (15). It has also been suggested that the use of mid‐dilution hemodiafiltration may allow higher exchange volumes while not inadvertently increasing this enhanced negative calcium balance (16).…”