Mixed predilution and postdilution online hemodiafiltration compared with the traditional infusion modes

Mixed versus predilution hemodiafiltration effects on convection volume and small and middle molecule clearance in hemodialysis patients: a prospective randomized controlled trial

Background

The use of newly developed mixed-dilution hemodiafiltration (HDF) can supplement the weaknesses of pre- and postdilution HDF. However, it is unclear whether mixed-HDF performs well compared to predilution HDF.

Methods

We conducted a prospective, open-labeled, randomized controlled trial from two hemodialysis centers in Korea. Between January 2017 and September 2019, 60 patients who underwent chronic hemodialysis were randomly assigned at a 1:1 ratio to receive either predilution HDF (n = 30) or mixed-HDF (n = 30) for 6 months. We compared convection volume, changes in small- and medium-sized molecule clearance, high-sensitive C-reactive protein (hs-CRP) level, and dialysis-related parameters between the two dialysis modalities.

Results

A mean effective convection volume of 41.0 ± 10.3 L/session in the predilution HDF group and 51.5 ± 9.0 L/session in the mixed-HDF group was obtained by averaging values of three time-points. The difference in effective convection volume between the groups was 10.5 ± 1.3 L/session. This met the preset noninferiority criteria, suggesting that mixed-HDF was noninferior to predilution HDF. Moreover, the β2-microglobulin reduction rate was greater in the mixed-HDF group than in the predilution HDF group, while mixed-HDF provided greater transmembrane pressure. There were no significant between-group differences in Kt/V urea levels, changes in predialysis hs-CRP levels, proportions of overhydration, or blood pressure values. Symptomatic intradialytic hypotension episodes and other adverse events occurred similarly in the two groups.

Conclusion

Use of mixed-HDF was comparable to predilution HDF in terms of delivered convection volume and clinical parameters. Moreover, mixed-HDF provided better β2-microglobulin clearance than predilution HDF.

Renal Replacement Modality Affects Uremic Toxins and Oxidative Stress

Nowadays, the high prevalence of kidney diseases and their related complications, including endothelial dysfunction and cardiovascular disease, represents one of the leading causes of death in patients with chronic kidney diseases. Renal failure leads to accumulation of uremic toxins, which are the main cause of oxidative stress development. The renal replacement therapy appears to be the best way to lower uremic toxin levels in patients with end-stage renal disease and reduce oxidative stress. At this moment, despite the increasing number of recognized toxins and their mechanisms of action, it is impossible to determine which of them are the most important and which cause the greatest complications. There are many different types of renal replacement therapy, but the best treatment has not been identified yet. Patients treated with diffusion methods have satisfactory clearance of small molecules, but the clearance of medium molecules appears to be insufficient, but treatment with convection methods cleans medium molecules better than small molecules. Hence, there is an urgent need of new more validated, appropriate, and reliable information not only on toxins and their role in metabolic disorders, including oxidative stress, but also on the best artificial renal replacement therapy to reduce complications and prolong the life of patients with chronic kidney disease.

Updates on hemodialysis techniques with a common denominator: The personalization of the dialytic therapy

Hemodialysis (HD) is a life-saving therapy for patients with end-stage renal disease. In dialyzed patients, the prevalence of multi-morbidity is rising driven by various factors, such as the population aging, the incomplete correction of uremia, and the side effects of the dialysis therapy itself. Each dialyzed patient has their own specific clinical and biochemical problems. It is therefore unthinkable that the same dialysis procedure can be able to meet the needs of every patient on chronic dialysis. We have very sophisticated dialysis machines and different dialysis techniques and procedures beyond conventional HD, such as hemodiafiltration (HDF) with pre- and post-dilution, acetate-free biofiltration (AFB), hemofiltration (HF), and expanded HD. Each of these techniques has its own specific characteristics. To solve some intradialytic clinical issues, such as arterial hypotension and arrhythmias, we have biofeedback systems with automatic regulation of the blood volume, body temperature, arterial pressure, as well as potassium profiling techniques in the dialysis bath. New technical innovations, such as citrate-containing dialysate or heparin-coated membranes, could reduce the risk of bleeding. To better address to patient needs, the strengths and weaknesses of each of these systems must be well-known, in order to have a personalized dialysis prescription for each patient.

Mixed hemodiafiltration reduces erythropoiesis stimulating agents requirement in dialysis patients: a prospective randomized study

BACKGROUND

Improved responsiveness to erythropoiesis stimulating agents (ESAs) in patients on on-line post-dilution hemodiafiltration (Post-HDF) compared with conventional hemodialysis (HD) was reported by some authors but challenged by others. This prospective, cross-over randomized study tested the hypothesis that an alternative infusion modality of HDF, mixed-dilution HDF (Mixed HDF), could further reduce ESAs requirement in dialysis patients compared to the traditional Post-HDF.

METHODS

One-hundred-twenty prevalent patients from 6 Dialysis Centers were randomly assigned to two six-months treatment sequences: A-B and B-A (A, Mixed HDF; B, Post-HDF). Primary outcome was comparative evaluation of ESA (darbepoetin alfa) requirement and ESA resistance. Treatments efficiency, iron and vitamins status, inflammation and nutrition parameters were monitored.

RESULTS

In sequence A, darbepoetin requirement decreased during Mixed HDF from 29.5 to 23.7 µg/month and increased significantly during Post-HDF (32.3 µg/month at 6th month) while, in sequence B, it increased during Post-HDF from 38.2 to 43.7 µg/month and decreased during Mixed HDF (23.9 µg/month at 6th month). Overall, EPO doses at 6 months on Mixed and Post-HDF were 23.8 and 38.4 µg/month, respectively, P < 0.01. A multiple linear model confirmed that Mixed HDF vs Post-HDF reduced significantly ESA requirement and ESA resistance (P < 0.0001), by a mean of 29% (CI 23-35%) in the last three months of the observation periods.

CONCLUSIONS

Mixed HDF decreased darbepoetin-alfa requirement in dialysis patients. This might help preventing the untoward side effects of high ESA doses, besides having a remarkable economic impact. Additional evidence is needed to confirm this potential benefit of Mixed-HDF.

Online Hemodiafiltration Inhibits Inflammation-Related Endothelial Dysfunction and Vascular Calcification of Uremic Patients Modulating miR-223 Expression in Plasma Extracellular Vesicles

Decreased inflammation and cardiovascular mortality are evident in patients with end-stage chronic kidney disease treated by online hemodiafiltration. Extracellular vesicles (EV) are mediators of cell-to-cell communication and contain different RNA types. This study investigated whether mixed online hemodiafiltration (mOL-HDF) beneficial effects associate with changes in the RNA content of plasma EV in chronic kidney disease patients. Thirty bicarbonate hemodialysis (BHD) patients were randomized 1:1 to continue BHD or switch to mOL-HDF. Concentration, size, and microRNA content of plasma EV were evaluated for 9 mo; we then studied EV effects on inflammation, angiogenesis, and apoptosis of endothelial cells (HUVEC) and on osteoblast mineralization of vascular smooth muscle cells (VSMC). mOL-HDF treatment reduced different inflammatory markers, including circulating CRP, IL-6, and NGAL. All hemodialysis patients showed higher plasma levels of endothelial-derived EV than healthy subjects, with no significant differences between BHD and mOL-HDF. However, BHD-derived EV had an increased expression of the proatherogenic miR-223 with respect to healthy subjects or mOL-HDF. Compared with EV from healthy subjects, those from hemodialysis patients reduced angiogenesis and increased HUVEC apoptosis and VSMC calcification; however, all these detrimental effects were reduced with mOL-HDF with respect to BHD. Cell transfection with miR-223 mimic or antagomiR proved the role of this microRNA in EV-induced HUVEC and VSMC dysfunction. The switch from BHD to mOL-HDF significantly reduced systemic inflammation and miR-223 expression in plasma EV, thus improving HUVEC angiogenesis and reducing VSMC calcification.

Effects of high-volume online mixed-hemodiafiltration on anemia management in dialysis patients

Background

Anemia is a major comorbidity of patients with end-stage renal disease and poses an enormous economic burden to health-care systems. High dose erythropoiesis-stimulating agents (ESAs) have been associated with unfavorable clinical outcomes. We explored whether mixed-dilution hemodiafiltration (Mixed-HDF), based on its innovative substitution modality, may improve anemia outcomes compared to the traditional post-dilution hemodiafiltration (Post-HDF).

Methods

We included 174 adult prevalent dialysis patients (87 on Mixed-HDF, 87 on Post-HDF) treated in 24 NephroCare dialysis centers between January 2010 and August 2016 into this retrospective cohort study. All patients were dialyzed three times per week and had fistula/graft as vascular access. Patients were matched at baseline and followed over a one-year period. The courses of hemoglobin levels (Hb) and monthly ESA consumption were compared between the two groups with linear mixed models.

Results

Mean baseline Hb was 11.9±1.3 and 11.8±1.1g/dl in patients on Mixed- and Post-HDF, respectively. While Hb remained stable in patients on Mixed-HDF, it decreased slightly in patients on Post-HDF (at month 12: 11.8±1.2 vs 11.1±1.2g/dl). This tendency was confirmed by our linear mixed model (p = 0.0514 for treatment x time interaction). Baseline median ESA consumption was 6000 [Q1:0;Q3:16000] IU/4 weeks in both groups. Throughout the observation period ESA doses tended to be lower in the Mixed-HDF group (4000 [Q1:0;Q3:16000] vs 8000 [Q1:0;Q3:20000] IU/4 weeks at month 12; p = 0.0791 for treatment x time interaction). Sensitivity analyses, adjusting for differences not covered by matching at baseline, strengthened our results (Hb: p = 0.0124; ESA: p = 0.0687).

Conclusions

Results of our explorative study suggest that patients on Mixed-HDF may have clinical benefits in terms of anemia management. This may also have a beneficial economic impact. Future studies are needed to confirm our hypothesis-generating results and to provide additional evidence on the potential beneficial effects of Mixed-HDF.

A reliable method to assess the water permeability of a dialysis system: the global ultrafiltration coefficient

Background

Recent randomized controlled trials suggest that sufficiently high convection post-dilutional haemodiafiltration (HC-HDF) improves survival in dialysis patients, consequently this technique is increasingly being adopted. However, when performing HC-HDF, rigorous control systems of the ultrafiltration setting are required. Assessing the global ultrafiltration coefficient of the dialysis system [GKD-UF; defined as ultrafiltration rate (QUF)/transmembrane pressure] or water permeability may be adapted to the present dialysis settings and be of value in clinics.

Methods

GKD-UF was determined and its reproducibility, variability and influencing factors were specifically assessed in 15 stable patients routinely treated by high-flux haemodialysis or HC-HDF in a single unit.

Results

GKD-UF invariably followed a parabolic function with increasing QUF in dialysis and both pre- and post-dilution HC-HDF (R2 constantly >0.96). The vertex of the parabola, GKD-UF-max and related QUF were very reproducible per patient (coefficient of variation 3.9 ± 0.6 and 3.3 ± 0.3%, respectively) and they greatly varied across patients (31–42 mL/h−1/mmHg and 82–100 mL/min, respectively). GKD-UF-max and its associated QUF decreased during dialysis treatment (P < 0.01). The GKD-UF-max decrease was related to weight loss (R2 = 0.66; P = 0.0015).

Conclusions

GKD-UF is a reliable and accurate method to assess the water permeability of a system in vivo. It varies according to dialysis setting and patient-related factors. It is an objective parameter evaluating the forces driving convection and identifies any diversion of the system during the treatment procedure. It is applicable to low- or high-flux dialysis as well as pre- or post-dilution HDF. Thus, it may be used to describe the characteristics of a dialysis system, is suitable for clinical use and may be of help for personalized prescription.

Optimization of the convection volume in online post-dilution haemodiafiltration: practical and technical issues

In post-dilution online haemodiafiltration (ol-HDF), a relationship has been demonstrated between the magnitude of the convection volume and survival. However, to achieve high convection volumes (>22 L per session) detailed notion of its determining factors is highly desirable. This manuscript summarizes practical problems and pitfalls that were encountered during the quest for high convection volumes. Specifically, it addresses issues such as type of vascular access, needles, blood flow rate, recirculation, filtration fraction, anticoagulation and dialysers. Finally, five of the main HDF systems in Europe are briefly described as far as HDF prescription and optimization of the convection volume is concerned.

Factors Associated with Albumin Loss in Post-Dilution Hemodiafiltration and Nutritional Consequences

Introduction

Hemodiafiltration is currently one of the most effective techniques of extra-renal purification but results in an increase of albumin loss in dialysate. We aimed to determine the factors associated with albumin loss during post-dilution hemodiafiltration, compare an “automatic” mode of infusate flow control versus a “manual” control, and assess the potential nutritional impact.

Methods

This prospective observational study included all hemodialysis patients in our institution who underwent post-dilution hemodiafiltration 3 times a week on a Fresenius 5008 for at least 2 months. At each session, albumin content was measured in a representative effluent dialysate volume. The automatic mode of the Fresenius 5008 was used for automatic infusate flow control.

Results

In all, 18 patients (mean age 60.7 ± 15 years) underwent 85 post-dilution hemodiafiltration sessions. The mean albumin loss was 3134 ± 2450 mg/session. Albumin loss was significantly affected by infusate flow, infusate volume, transmembrane pressure and ultrafiltration volume. The loss was greater with Toraysulfone and FX 1000 membranes rather than FX 80 or FX 100 membranes. With AutoSub rather than manual control, infusate flow was greater ( P<.001), transmembrane pressure was higher (P = .004), and the albumin loss was greater (P = .010). However, there was no correlation between albumin loss and nutritional variables.

Conclusions

Albumin loss during post-dilution hemodiafiltration was correlated with increased transmembrane pressure and infusate flow, especially AutoSub flow control, and type of membrane. However, this loss, when moderate, did not seem to affect nutritional aspects and should not limit the use of hemodiafiltration.

Arteriovenous fistulas and digital hypoperfusion ischemic syndrome in patients on hemodialysis

AIM: To determine survival parameters as well as characteristics of patients with this syndrome.

METHODS: The investigation was conducted over a period of eight years, as a prospective, non-randomized, clinical study which included 204 patients, treated by chronic hemodialysis. Most patients received hemodialysis 12 h per week. As vascular access for hemodialysis all subjects had an arteriovenous fistulae. Based on surveys the respondents were divided into groups of patients with and without digital hypoperfusion ischemic syndrome. Gender, demographic and anthropometric characteristics, together with comorbidity and certain habits, were recorded. During this period 34.8% patients died.

RESULTS: Patients with digital hypoperfusion ischemic syndrome were older than those without ischemia (P = 0.01). Hemodialysis treatment lasted significantly longer in the patients with digital hypoperfusion ischemic syndrome (P = 0.02). The incidence of cardiovascular disease (P < 0.001) and diabetes mellitus (P = 0.01), as well as blood flow through the arteriovenous fistula (P = 0.036), were higher in patients with digital hypoperfusion ischemic syndrome. Statistically significant differences also existed in relation to oxygen saturation (P = 0.04). Predictive parameters of survival for patients with digital hypoperfusion ischemic syndrome were: adequacy of hemodialysis (B = -3.604, P < 0.001), hypertension (B = -0.920, P = 0.018), smoking (B = -0.901, P = 0.049), diabetes mellitus (B = 1.227, P = 0.005), erythropoietin therapy (B = 1.274, P = 0.002) and hemodiafiltration (B = -1.242, P = 0.033). Kaplan-Meier survival analysis indicated that subjects with and without digital hypoperfusion ischemic syndrome differed regarding the length of survival (P < 0.001), i.e., patients with confirmed digital hypoperfusion ischemic syndrome died earlier.

CONCLUSION: Survival was significantly longer in the patients without digital hypoperfusion ischemic syndrome.

Comparison of the effects of predilution and postdilution hemodiafiltration on neutrophils, lymphocytes and platelets

Numerous studies have been carried out to investigate the solute removal efficiency of hemodiafiltration (HDF). However, the effect of the dilution mode on blood cell damage during HDF has not yet been examined in detail. Here, we compared predilution and postdilution HDF with respect to their effects on blood cells. Five patients were allocated to one session each of predilution HDF and postdilution HDF. Concentrations of interleukin (IL)-6, intercellular adhesion molecule (ICAM)-1, and platelet-derived microparticles (PDMP), and the phagocytotic and sterilizing functions of neutrophils before and after the HDF sessions were evaluated. Lymphocyte blastoid transformation induced by mitogens was also evaluated by measurement of the [(3)H]-thymidine uptake. The IL-6 and ICAM-1 concentrations decreased after predilution HDF, and increased after postdilution HDF. Lymphocyte blastoid transformation was more pronounced after predilution HDF than after postdilution HDF. There was no significant difference in PDMP between the dilution modes. We conclude that predilution HDF could be more favorable for dialysis patients than postdilution HDF from the point of view of the effects on the blood cells, especially neutrophils and lymphocytes.

Benefits of first-half intensive haemodiafiltration for the removal of uraemic solutes

AIM

Haemodiafiltration (HDF) is the most efficient blood purification method and can remove a wide spectrum of solutes of different molecular weights (MW). The purpose of this study was to investigate whether the removed amounts of solutes, especially the larger molecules, could be increased by changing the HDF filtration procedure.

METHODS

A new first-half intensive HDF treatment (F-HDF) was designed, whereby convective clearance is intensively forced during the first half of a HDF session. We compared the removed amounts of solutes in the same group of nine patients treated by F-HDF, constant rate-replacing HDF (C-HDF) and a high-flux haemodialysis (HD).

RESULTS

F-HDF can remove significantly larger amounts of α(1) -microglobulin (MG), molecular weight (MW) 33,000, compared with HD and C-HDF (30.1 ± 15.1 vs 12.4 ± 0.3, 15.0 ± 3.1 mg, P < 0.01). Regarding the removal amounts and clear space of β(2) MG, MW 11,800, there were no significant differences between the three treatment modalities. Regarding amounts of creatinine, urea nitrogen and phosphorus, there were no significant differences between the three treatment modalities.

CONCLUSION

In post-replacement HDF with a high-flux membrane dialyzer, the method used in the present study in which replacement is completed during the first half of the process, is associated with a greater rate of larger molecule removal than the conventional uniform replacement method.

[Technical advances in haemodialysis]

Survival improvement of our haemodialysis patients is partly due to technologic improvement of the dialysis therapy. High permeability membranes and bicarbonate dialysate were the most relevant of past decades. What are the present technologic innovations that will provide clinical benefit? Acetate-free biofiltration, biofeedback systems, better haemodiafiltration techniques and techniques with adsorption could be part of them.

Comparison of middle-molecule clearance between convective control double high-flux hemodiafiltration and on-line hemodiafiltration

Hemodiafiltration (HDF) is now a well-recognized treatment modality for end-stage renal disease (ESRD) patients. It provides superior characteristics over conventional hemodialysis in many respects. On-line HDF, however, which has been mainly used in clinical practice, requires a special machine. Interestingly, the recently innovated convective-control double high-flux hemodiafiltration (CC-DHF) machine can provide HDF treatment with an adjustable convection rate by using the conventional volume-controlled dialysate flow hemodialysis machine in a modified way. The present study was conducted to compare the efficacy of CC-DHF compared to on-line HDF in terms of middle and small solute clearances in 12 stable, chronic hemodialysis patients who underwent hemodialysis three times a week for at least 6 months. The results showed that the beta 2-microglobulin (beta 2M) removal represented by the beta 2M clearance in CC-DHF was comparable to that in on-line HDF (112.4+/-17.0 vs. 119.4+/-15.5 ml/min respectively, NS). Also, the beta 2M reduction ratio in the CC-DHF group did not differ from the on-line HDF group (85.5+/-4.2% vs. 86.1+/-6.7%, NS). With regard to small solute clearances, the values of single-pool Kt/V and phosphate clearance did not differ between CC-DHF and on-line HDF groups. In conclusion, CC-DHF provides removal of beta 2M and small molecule uremic toxins that is comparable to on-line HDF. An on-line HDF machine may not be available in all hemodialysis centers, whereas CC-DHF can be easily set up, with proper precautions regarding the fluid quality. Therefore, CC-DHF can provide the benefits of convective therapy to patients in situations where use of an on-line HDF machine is limited.

Quantitative analysis of convective dose in hemofiltration and hemodiafiltration: "Predilution" vs. "postdilution" reinfusion

In hemofiltration (HF) and hemodiafiltration (HDF), removal of medium and high-molecular-weight solutes is greatly enhanced by convective mechanisms as compared with simple diffusion; increasing convective flows may allow greater removal rates of these solutes. Use of "predilution" (pre-H[D]F) may allow higher ultrafiltration rates than the "postdilution" mode (post-H[D]F); yet, the dilution of plasma water may have unpredictable effects on "endogenous" water convection. We have applied a mathematical analysis to evaluate and compare endogenous water convective flow rates in pre-H(D)F vs. post-H(D)F. Endogenous plasma water recovered in ultrafiltrate was calculated according to patient (hematocrit, total protein level) and session parameters (blood flow, ultrafiltration rate, programmed weight loss), in absolute terms and as a fraction of endogenous plasma water delivery to the filter. Maximally efficient post-H(D)F was modelled according to a preset postfilter hematocrit or filtration fraction. Nomograms were constructed expressing endogenous water convective fluxes in relation to parameters of interest (ultrafiltration rate, blood flow, hematocrit) with both post-H(D)F and pre-H(D)F, and "efficiency" of pre-H(D)F vs. post-H(D)F (as the ratio of endogenous water convective flow rate with the 2 techniques) as a function of the ultrafiltration/reinfusion rate. In post-H(D)F, the model predicts maximal ultrafiltration rates within the limits of a preset hemoconcentration at the filter outlet; additionally, the model allows to calculate ultrafiltration/reinfusion quantities to be set in pre-H(D)F to equal and overcome maximal convective efficiency of post-H(D)F. This "equivalence" ultrafiltration rate may greatly vary according to patient's hematocrit and blood flow, so that the ultrafiltrate-reinfusate volume available in the system dictates, in any patient, which mode of reinfusion may attain higher "endogenous" convective flow rates. Pre-H(D)F may allow higher fractional and absolute "endogenous" convective flow rates as compared with post-H(D)F, provided that adequate amounts of reinfusate are available. For lower reinfusate volumes than "equivalence" values, post-H(D)F remains a better option.

Transmembrane pressure modulation in high-volume mixed hemodiafiltration to optimize efficiency and minimize protein loss

The aim of the present study was transmembrane pressure (TMP) modulation in high-volume mixed hemodiafiltration (HDF) to optimize efficiency and minimize protein loss. The optimal flow/pressure conditions in on-line mixed HDF assisted with a feedback control of TMP were defined in this prospective randomized study in order to obtain maximal efficiency in solute removal while minimizing potential side effects. Two different TMP profiles in mixed HDF were compared in 12 unselected patients who underwent two study periods of 2 weeks each in cross-over randomized sequence: (A) constant TMP at around 300 mmHg and (B) profiled TMP, in which TMP was slowly increased from a low initial value to the maximal value. In both procedures, the mean volume exchange was 10.6+/-1.4 l/h. Mean filtration fraction was 53%. Instantaneous beta2-microglobulin (beta2-m) clearance was higher at the start of the session with profiled TMP (207+/-35 vs 194+/-28 ml/min, P<0.005), whereas no differences were found at the end (135+/-19 vs 132+/-19 ml/min). Profiled TMP resulted in a higher mean beta2-m clearance of the session (97.0+/-15.4 vs 87.8+/-18.3 ml/min, P<0.01), in lower albumin loss in the first 30 min (0.62+/-0.14 vs 0.98+/-0.18 g, P<0.0001), and, in the whole session (3.98+/-1.19 vs 5.24+/-0.77 g, P<0.001), in higher dialyzer ultrafiltration coefficients and lower resistance indexes. This study showed that the TMP feedback modulation in mixed HDF was highly effective in maintaining very high ultrafiltration rates and filtration fractions, and minimized potential side effects as a result of the improved preservation of membrane permeability and more favorable dialyzer pressure regimen.

Convective and adsorptive removal of beta2-microglobulin during predilutional and postdilutional hemofiltration

BACKGROUND

Beta(2)-microglobulin (beta2-m) removal in patients with end-stage renal disease (ESRD) is maximal with convective techniques, such as hemofiltration (HF) or hemodiafiltration (HDF). Although the infusion mode of the replacement solution (predilution or postdilution) is expected to influence the efficiency of HF, experimental data in this respect are scanty. We therefore investigated the impact of the fluid reinfusion mode on the efficiency of HF in 11 ESRD patients who underwent both treatments.

METHODS

The dialyzer (AK 200 ULTRA) was equipped with a 3-layer polyamide membrane (Poliflux 21 S, surface 2.1 m(2)) and blood flow was kept between 300 and 400 mL/min. beta2-m concentrations were measured in plasma water and ultrafiltrate at appropriate times during a 240-minute treatment. The following dialytic parameters were calculated: total amount of beta2-m removed (A(tot)), beta2-m removed by convection (A(con)) and by adsorption (A(ads)), percent reduction in beta2-m plasma water concentration (% Cpw(in)), total plasma water clearance (CLpw(tot)), convective plasma water clearance (CLpw(con)), adsorptive plasma water clearance (CLpw(ads)), and sieving coefficient (SC).

RESULTS

CLpw(tot), CLpw(ads), and% Cpw(in) were similar in pre- and postdilutional conditions, whereas CLpw(con) and SC were higher and CLpw(ads) was lower in postdilution than in predilution HF. Since a significant inverse correlation was found between A(ads) and SC, predilution probably determines greater protein fouling than postdilution.

CONCLUSION

The 2 techniques appear to be equivalent in terms of total beta2-m removal, although this final result is obtained by different contributions of convective and adsorptive elimination.

Impact of Convective Flow on Phosphorus Removal in Maintenance Hemodialysis Patients

OBJECTIVE

Hyperphosphatemia leads to increased risk of death in maintenance hemodialysis patients (MHD). This study investigated phosphorus (P) removal, P reduction rate (PRR), and P rebound, comparing on-line, high-volume hemodiafiltration in postdilution (HDF) and high-flux hemodialysis (HD) in a setting of an equal amount of produced dialysate solution in both modalities.

METHODS

A total of 22 MHD patients, treated with regular 3 x 4 hours HDF weekly, were randomly dialyzed with one 4-hour session of HDF and of HD. In both modalities, an equal amount of produced dialysate solution of 800 mL/minute was used. The only variable was the fact that in HDF, 100 mL/min of this produced dialysate solution was used as replacement fluid. The other parameters were kept identical: blood flow rate, 350 mL/min; high-flux polysulfone F80 dialyzer; and 4800 E monitor, (Fresenius, Bad Homburg, Germany). The P removal was measured in total spent dialysate and ultrafiltrate volumes. Statistical analyses were done with the paired t-test.

RESULTS

The mean total P removed with HDF was 1159 +/- 296 mg, and 972 +/- 312 mg with HD (P < .001), ie, 19% higher in HDF; PRR was significantly higher in HDF (63.3%) versus HD (58.6%) (P = .014). The mean serum P did not differ: 5.3 mg/dL in HDF and 5.2 mg/dL in HD. There was a linear correlation between serum P and P removal. With a serum P level up to 5 to 5.5 mg/dL, HDF achieved a higher P removal compared with HD. The difference gradually decreased as the serum P value increased. Above 7 mg/dL, no difference in total P removal was observed. There was a high but equal rebound percentage at 60 minutes in HDF (42%) and HD (39%) (P = .42). With HDF, no predialysis metabolic acidosis was noted.

CONCLUSIONS

Treatment with on-line HDF in postdilution resulted in a higher P removal and higher PRR compared with HD. The long-term implementation of this modality may result in a more optimal serum P control, without an increase in the number of or lengthening of the dialysis sessions.

Beta2-microglobulin removal by extracorporeal renal replacement therapies

There is increasing evidence that end-stage renal disease patients with lower beta(2)-microglobulin plasma levels and patients on convective renal replacement therapy are at lower mortality risk. Therefore, an enhanced beta(2)-microglobulin removal by renal replacement procedures has to be regarded as a contribution to a more adequate dialysis therapy. In contrast to high-flux dialysis, low-flux hemodialysis is not qualified to eliminate substantial amounts of beta(2)-microglobulin. In hemodialysis using modern high-flux dialysis membranes, a beta(2)-microglobulin removal similar to that obtained in hemofiltration or hemodiafiltration can be achieved. Several of these high-flux membranes are protein-leaking, making them suitable only for hemodialysis due to a high albumin loss when used in more convective therapy procedures. On-line hemodiafiltration infusing large substitution fluid volumes represents the most efficient and innovative renal replacement therapy form. To maximize beta(2)-microglobulin removal, modifications of this procedure have been proposed. These modifications ensure safer operating conditions, such as mixed hemodiafiltration, or control albumin loss at maximum purification from beta(2)-microglobulin, such as mid-dilution hemodiafiltration, push/pull hemodiafiltration or programmed filtration. Whether these innovative hemodiafiltration options will become accepted in clinical routine use needs to be proven in future.

Uremic toxins: a new focus on an old subject

The uremic syndrome is characterized by an accumulation of uremic toxins due to inadequate kidney function. The European Uremic Toxin (EUTox) Work Group has listed 90 compounds considered to be uremic toxins. Sixty-eight have a molecular weight less than 500 Da, 12 exceed 12,000 Da, and 10 have a molecular weight between 500 and 12,000 Da. Twenty-five solutes (28%) are protein bound. The kinetics of urea removal is not representative of other molecules such as protein-bound solutes or the middle molecules, making Kt/V misleading. Clearances of urea, even in well-dialyzed patients, amount to only one-sixth of physiological clearance. In contrast to native kidney function, the removal of uremic toxins in dialysis is achieved by a one-step membrane-based process and is intermittent. The resulting sawtooth plasma concentrations of uremic toxins contrast with the continuous function of native kidneys, which provides constant solute clearances and mass removal rates. Our increasing knowledge of uremic toxins will help guide future treatment strategies to remove them.

Selection of Dilutional Method for On-Line HDF, Pre- or Post-Dilution

Post- and pre-dilution methods equally have advantages and disadvantages, therefore we should choose the more favorable one for clinical use. However, it still remains controversial which technique is better in on-line HDF. In post-dilution, the clearances of small molecular uremic toxins increase as well as low molecular proteins, however the risk of albumin leakage caused by high transmembranous pressure (TMP) also increases. We can avoid the risk of albumin leakage because there are several maneuvers which aid in avoiding an increase of TMP, such as glucose infusion and gradual control of Q(f). On the other hand, the pre-dilution method is rather safe in the risk of albumin leakage but has an obvious clearance loss of small molecular substances caused by a decreased dialysate flow rate. The influence of microbial contamination and acetate are rather severe in pre-dilution on-line HDF. These lines of evidence suggest that post-dilution on-line HDF is the best choice for treating chronic HD patients.

Clinical cross-over comparison of mid-dilution hemodiafiltration using a novel dialyzer concept and post-dilution hemodiafiltration

BACKGROUND

Several studies have indicated that the improved elimination of middle molecules by convective renal replacement procedures might be associated with a better outcome in end-stage renal disease (ESRD). On-line mid-dilution hemodiafiltration (HDF) with the Nephros OLpur MD 190 hemodiafilter represents a novel extracorporeal renal replacement therapy concept to increase the removal of middle molecules.

METHODS

In a prospective cross-over study in 10 ESRD patients, this technique was compared to on-line post-dilution HDF with a conventional synthetic high-flux dialyzer, operated at its technical limit, concerning small and middle molecular solute removal. Each patient was treated 3 times for 4.0 +/- 0.4 hours with both filters. Blood flow was 400 mL/min, substitution flow (Q(S)) during mid-dilution HDF 200 mL/min, and during post-dilution HDF 100 mL/min, and effective dialysate flow of 700 - Q(S) mL/min. Instantaneous clearances, reduction ratios (RR), and middle molecule mass transfer in continuously collected dialysate were determined.

RESULTS

While urea and creatinine clearances were significantly lower (6.4% and 3.9%, respectively), middle molecule removal was much more efficient in mid-dilution HDF over the whole range of investigated proteins: compared to post-dilution HDF, beta(2)-microglobulin (11.8 kD) clearance (165.8 +/- 26.59 vs. 201.9 +/- 20.63 mL/min; P < 0.001), RR (80.0 +/- 5.4% vs. 82.2 +/- 5.7%; P < 0.001), and dialysate mass transfer (53% higher; P < 0.001) were significantly higher. For the larger middle molecules, cystatin C (13.4 kD) and retinol-binding protein (21.2 kD), mid-dilution HDF resulted in an even more superior performance, indicated by significantly higher values of all investigated parameters.

CONCLUSION

On-line mid-dilution HDF with the Nephros OLpur MD 190 hemodiafilter appears to be a true technologic step ahead in terms of improved middle molecule removal. This efficient procedure gives hope to play a role in preventing or at least retarding dialysis-related long-term complications, such as beta(2)m amyloidosis, in ESRD patients, and may contribute to a more adequate dialysis therapy.

Beta-2 microglobulin in ESRD: an in-depth review

Beta-2 microglobulin is the most widely studied low-molecular-weight protein in end-stage renal disease. It is known to cause dialysis-related amyloidosis (DRA), by virtue of its retention when renal function fails, its deposition in tissues, its aggregation into fibrils, and its ability to become glycosylated. The onset of DRA may be protracted by the use of noncellulosic membranes, especially when high-volume hemodiafiltration is used in the treatment of renal failure. Adsorptive methods have been developed to improve the removal of beta-2 microglobulin. There seems to be a relative risk reduction in mortality when patients are treated with dialysis membranes that have a higher clearance of beta-2 microglobulin.

On-line mixed hemodiafiltration with a feedback for ultrafiltration control: effect on middle-molecule removal

BACKGROUND

Increased middle-molecular uremic toxin removal seems to favorably influence survival in dialysis patients. The aim of this study was to verify if, in on-line mixed hemodiafiltration, solute removal by convection may be enhanced by forcing the ultrafiltration rate (QUF) and optimizing the infusion technique in order to achieve the highest possible filtration fraction (FF).

METHODS

Removal of beta2-microglobulin (beta2-m), urea, creatinine, and phosphate were compared in 20 patients randomly submitted to one dialysis session (A), one postdilution hemodiafiltration session (B), and three sessions of mixed hemodiafiltration (C, D, and E) at different infusion rates (QS). In mixed hemodiafiltration, a newly developed feedback system automatically maintained the transmembrane pressure (TMP) within its highest range of safety (250 to 300 mm Hg) at constant QUF, while ensuring the maximum FF by splitting infusion between pre- and postdilution.

RESULTS

A mean QS of 134 +/- 20 mL/min (mean FF = 0.65) was attained in post-HDF, and up to 307 +/- 41 mL/min (mean FF = 0.69) in mixed hemodiafiltration. The mean dialysate clearances (KDQ) for all tested solutes and urea eKt/V were significantly higher in all hemodiafiltration sessions than in dialysis. Only in the case of urea did the infusion mode have no significant effect. KDQ for beta2-m was maximal in session D and significantly higher than in session B (90.2 +/- 11 mL/min vs. 77.5 +/- 11 mL/min; P = 0.02). KDQ for beta2-m significantly correlated with QS and the plasma water flow rate (QPW). The highest KDQ for beta2-m was found at values of QS approximately QPW. Beyond this value KDQ decreased.

CONCLUSION

The mixed infusion mode in hemodiafiltration, controlled by the TMP-ultrafiltration feedback, seems to improve the efficiency of hemodiafiltration by fully exploiting the convective mechanism of solute removal. The feedback automatically adjusted the infusion rate and site to the maximum FF taking into account flow conditions, internal pressures, and hydraulic permeability of the dialyzer and their complex interactions.

Effects of the infusion mode on bicarbonate balance in on-line hemodiafiltration

BACKGROUND

Electrolyte and acid-base balance may be differently affected by the infusion mode in on-line hemodiafiltration (HDF). We studied the effects of the different infusion modes on bicarbonate transport across the dialyzer membrane, and thus on the final bicarbonate balance of the HDF sessions.

METHODS

Instantaneous HCO3- transfer across the dialyzer membrane, blood bicarbonate profile and the total balance of the sessions were studied in six dialysis patients under the same operating conditions over 36 HDF sessions, in order to compare the effects of predilution HDF (pre-HDF), postdilution HDF (post-HDF), and mixed HDF on the final bicarbonate balance.

RESULTS

The final HCO3- balance was more positive in post-HDF vs pre-HDF (142 +/- 36 vs 99 +/- 41 mmol/session, p<0.05), with a final blood HCO3- concentration of 26.6 +/- 1.0 vs 25.4 +/- 1.1 mmol/L, (p<0.05). Mixed HDF yielded intermediate results (balance: 119 +/- 42 mmol/session, final HCO3- 26.2 (1.2 mmol/L). These differences were seen to result from the increased HCO3- concentration of blood entering the filter in predilution, due to the infused HCO3-, enhancing convective loss and reducing the driving force for diffusive HCO3- gain.

CONCLUSIONS

Bicarbonate concentration in dialysate-reinfusate is critical in order to obtain an adequate end of session HCO3- balance in on-line HDF. The predilution method produced the lowest cumulative net HCO3- gain between the three studied infusion modes. Our data suggest that, under the same operating conditions and excluding the effect of ultrafiltration, dialysate HCO3- should be increased by about 2 mmol/L in pre-HDF, and 1 mmol/L in mixed HDF, to yield the same final balance as in post-HDF.