Dialytic Performance Evaluation of Rexeed™: a New Polysulfone-based Dialyzer with Improved Flow Distributions

New dialyzers are designed to optimize the convective and diffusive components of solute transport. Asahi Kasei Medical Co., Ltd. has developed a new high flux dialyzer series called Rexeed™ with improved flow distributions. We evaluated the in vivo dialytic performance of two dialyzers of the Rexeed™ series: Rexeed-18A and Rexeed-25A (1.8 m2 and 2.5 m2).

We calculated the clearance for urea, creatinine, phosphate and b2-microglobulin both in high flux dialysis (HFD) and in 15 liter postidiluitional on-line hemodiafiltration (HDF) mode.

With n=3 patients in high flux HD at blood flow 450, 400, 350 and 250 ml/min we found remarkably high clearance for urea (347±4%,305±0%,288±5%,230±3%, for Rexeed-18A and 361±3%,329±0%,313±1%,234±3% for Rexeed-25A), creatinine (282±10%,234±0%, 221±8%, 174±8%, for Rexeed-18A and 276±6%,245±0%,226±9%,172±13% for Rexeed-25A), phosphate (347±0%,316±0%,275±4%,202±16%, for Rexeed-18A and 364±3%,365±0%,286±3%,224±2% for Rexeed-25A) and b2-microglobulin (133±21%,124±0%,118±12%,98±11%, for Rexeed-18A and 159±8%,169±0%,157±8%,129±7% for Rexeed-25A)

With n=2 patients in HDF at blood flow 300 ml/min we found remarkably high clearance for urea (268±2%, for Rexeed-18A and 283±2% for Rexeed-25A), creatinine (183±6% for Rexeed-18A and 205±9% for Rexeed-25A), phosphate (245±3%, for Rexeed-18A and 270±2% for Rexeed-25A) and b2-microglobulin (166±12%, for Rexeed-18A and 192±4% for Rexeed-25A).

Our preliminary evaluation describes the characteristics and the performances of a new polysulfone-based hemodialyzer series called Rexeed™. Several innovative features have been implemented by the manufacturer. These constructive approaches seem to have produced a positive effect on the dialyzer performance at the bedside.

Noninvasive techniques for prevention of intradialytic hypotension

Episodes of hypotension during hemodialysis treatment constitutes an important clinical problem which has received considerable attention in recent years. Despite the fact that numerous approaches to reducing the frequency of intradialytic hypotension (IDH) have been proposed and evaluated, the problem has not yet found a definitive solution--an observation which, in particular, applies to episodes of acute, symptomatic hypotension. This overview covers recent advances in methodology for predicting and preventing IDH. Following a brief overview of well-established hypotension-related variables, including blood pressure, blood temperature, relative blood volume, and bioimpedance, special attention is given to electrocardiographic and photoplethysmographic (PPG) variables and their significance for IDH prediction. It is concluded that cardiovascular variables which reflect heart rate variability, heart rate turbulence, and baroreflex sensitivity are important to explore in feedback control hemodialysis systems so as to improve their performance. The analysis of hemodialysis-related changes in PPG pulse wave properties hold considerable promise for improving prediction.

FHD: an index to evaluate drug elimination by hemodialysis

BACKGROUND

In hemodialyzed patients, physicians have to (1) adjust drug dosage for a creatinine clearance lower than 10-15 ml/min and (2) know whether or not the drug will be removed by the dialysis session to decide whether it may be administered before or after the session on dialysis days. However, of several indices being used to evaluate drug removal by dialysis none is appropriate and we suggest a novel index named F(HD), which reflects the role of hemodialysis clearance of a drug in its overall clearance during the session.

METHODS

Pharmacokinetic simulations were performed to test the influence of dialysis on the pharmacokinetics of some drugs, whether F(HD) was considered or not, to determine when to administer the drug. F(HD) was then calculated for several drugs and its value compared with other indices. Five hemodialysis patients from our department for whom the time of drug administration was determined according to F(HD) were included in a small study and their drugs' trough concentrations were monitored.

RESULTS

F(HD) emphasized that considering hemodialysis clearance alone may lead to false interpretations of the potential dialyzability of some drugs. In our patients, who received their treatment according to the 'F(HD) rule', monitoring of trough levels gave satisfactory results.

CONCLUSION

The use of the 'F(HD) rule' should be tested on a long-term administration basis to confirm our conclusion. F(HD )could be the index of choice to determine when to administer a drug, before or after the session, in hemodialysis patients.

Hemodialyzer: from macro-design to membrane nanostructure; the case of the FX-class of hemodialyzers

Very few innovations have characterized the different components of the hemodialyzers in the past 20 years. Most improvements have concerned membrane biocompatibility. In this article, we focus our attention on the most recent advances in hemodialyzer components from the macro design of the unit to the nanostructure of the membrane. For this purpose, we took as an example the FX class of hemodialyzers (FMC, Bad Homburg, Germany). The studied devices were chosen as an example representing some of the most recent hemodialyzers and are well suited to describe technical innovations occurring in the field of dialyzer technology. In vitro and in vivo studies were performed to characterize hemodynamic parameters of three models (1.4-1, 8, and 2.2 m2) and to determine membrane permeability, sieving coefficients, and solute clearances. The units were characterized by a relatively high resistance of the blood and dialysate compartments, leading to an increased internal filtration if compared with similar hemodialyzers of other series. Nevertheless, the flow distribution in both compartments was homogeneous and well balanced. This effect was obtained by the improved blood and dialysate ports design, the increased packing density of the fibers and a reduction of the inner diameter of the fibers from 200 to 180 microm. At the same time, the sieving coefficients for middle-large solutes such as beta2 microglobulin and insulin were higher than those observed in standard high flux dialysers. The same effect was noted for the clearance values of these solutes. This was observed in the absence of significant albumin leakage. These results were obtained thanks to a new nano-controlled spinning technology applied to the fiber. The innermost layer of the membrane is in fact characterized by a homogeneous porosity, with increased number of pores of large dimension but a sharp cutoff of the membrane excluding albumin losses. In conclusion, new technologies and new diagnostic tools today allow for improvement in hemodialyzer design from its macro-components to its nano-structure. The application of nanotechnology to hemodialysis will probably contribute to further developments in hemodialyzer manufacturing.

Effects of in-center daily hemodialysis upon mineral metabolism and bone disease in end-stage renal disease patients

CONTEXT

Alternative hemodialysis schedules have been proposed to improve the quality of the dialysis. Nonetheless, their influence upon mineral and bone disorders is unknown.

OBJECTIVE

To report the impact of a daily hemodialysis schedule upon the lesions of renal osteodystrophy.

TYPE OF STUDY

Prospective non-controlled study.

SETTING

Public University Hospital.

PARTICIPANTS

Five patients treated by daily hemodialysis for at least 24 months.

INTERVENTION

Daily dialysis sessions were accomplished with non-proportional dialysis machines without an ultrafiltration control device, with blood flow of 300 ml/min, bicarbonate dialysate ([Ca]=3.5 mEq/L) at 500 ml/min, and low-flux membrane dialyzers. Sessions were started at 6:00 p.m. (except Sundays) and lasted 2 hours.

MAIN MEASUREMENTS

Serum levels of Ca and P from the last 6 months on conventional hemodialysis for the same patients were used for comparison with each semester of daily hemodialysis. Bone biopsies and PTH levels were obtained at the end of the conventional hemodialysis period and then again after 2 years of daily hemodialysis.

RESULTS

Mean serum calcium was significantly higher during the second and third semesters of daily dialysis [10.0 mg% (SD 0.6), and 10.0 mg% (SD 0.8), respectively] compared to standard dialysis [9.4 mg% (SD 0.8)], p < 0.05. Mean values for phosphorus were significantly lower during every semester of daily hemodialysis [6.3 mg% (SD 1.8), 5.8 mg% (SD 1.7), 6.0 mg% (SD 1.7), and 6.0 mg% (SD 1.8)] compared to standard dialysis [7.2 mg% (SD 2.7)], P < 0.05. Variations in mean Ca x P product followed the same pattern as for phosphorus [59.5 (SD 16.0), 57.1 (SD 16.3), 59.8 (SD 17.7), and 58.31 (SD 20.9) vs. 68.6 (SD 27.3), P < 0.05]. After 2 years on daily hemodialysis, 2 patients who had aplastic lesion were found to have mild bone disorder. In addition, one patient with mixed bone lesion and moderate bone aluminum accumulation had osteitis fibrosa with no aluminum. Intact PTH values at the beginning of study and after 2 years on daily hemodialysis did not differ [134 pg/ml (SD 66) vs. 109 pg/ml (SD 26), P = 0.60, respectively].

CONCLUSIONS

Patients treated using daily hemodialysis had better control of serum phosphorus and perhaps a lower risk of metastatic calcifications. Daily hemodialysis also seemed to be beneficial to low turnover bone disease and bone aluminum deposition.

Impact of biofeedback-induced cardiovascular stability on hemodialysis tolerance and efficiency

BACKGROUND

Hypotension is caused by a drop in blood volume during ultrafiltration, followed by vasoconstriction and reduced perfusion in some regions of the body.

METHODS

We carried out a prospective controlled crossover study on 12 hypotension-prone patients with two different modalities: (A) acetate-free hemodiafiltration with standard ultrafiltration control, and (B) acetate-free hemodiafiltration with monitoring of blood volume and automatic biofeedback with machine-driven adjustments on ultrafiltration and dialysate conductivity. We measured urea Kt/V and equilibrated Kt/V (eKt/V), urea rebound, and urea removal. Hypotensive episodes and interventions were recorded.

RESULTS

In group B, fewer hypotensive episodes were recorded (24 out of 72 in group B vs. 59 out of 72 in group A). Saline infusion was required in 57 cases in group A and 15 cases in group B. Urea Kt/V was 1.34 +/- 0.08 in group A and was 1.26 +/- 0.06 in group B; eKt/V was much higher in group B (1.12 +/- 0.05) than in group A (1.03 +/- 008). A significantly higher rebound was observed in group A (14.2 +/- 2.7%) compared with group B (6.4 +/- 2.3%). Discussion. A greater solute sequestration seems to occur during hemodialysis with hypotension. This results in lower eKt/V, enhanced postdialytic rebound, and lower solute removal. Higher efficiency can be observed when dialysis is carried out smoothly and cardiovascular stability is maintained. We conclude that new systems for blood volume monitoring and automatic biofeedback may not only reduce the number of hypotensive episodes during dialysis, but may also contribute to significantly increase the efficacy of the treatment.

Ultrafiltration profiling and measurement of relative blood volume as strategies to reduce hemodialysis-related side effects

Hemodialysis (HD) side effects, such as hypotension and muscle cramps, may be related to excessive ultrafiltration (UF) in relation to refilling of fluids from the extravascular space, resulting in hemoconcentration and reduction of relative blood volume (RBV). This study examines the suitability of RBV measurements and UF modeling to reduce the incidence of dialysis side effects. We followed up 188 dialysis sessions in 53 patients. RBV and incidence of side effects were evaluated. Six treatment regimens were examined: UF profile 0, with a constant UF rate; UF profile 1, with a linear decreasing UF rate; UF profile 2, with a stepwise decreasing UF rate; and UF profiles 3 through 5, with intermittent high UF rates interrupted by UF pauses. During dialyses with a constant UF rate (UF profile 0), 10.6% of the treatments were associated with symptomatic hypotension. UF profiles 2 through 5, intermittently using high UF rates, caused a marked increase in hypotensive episodes (18.4%). In contrast, UF profile 1, providing a continuously decreasing UF rate, showed a reduced incidence of hypotension at only 5.7%. Symptomatic hypotension occurred in 13 of 53 patients during one or more dialysis sessions. With the help of RBV measurements, a subgroup of 8 patients with hypovolemia-induced hypotension could be identified. In these patients, an individual threshold of RBV could be defined, below which 92.3% of all hypotensive episodes occurred. In the remaining 5 hypotension-prone patients, there was no correlation between the occurrence of symptomatic hypotension and low RBV during HD treatments. In conclusion, UF profiles intermittently using high UF pulses cannot be recommended. RBV measurements help define a subgroup of patients at risk for hypovolemia-induced hypotension. Only these patients may benefit from blood volume-controlled UF. The incidence of symptomatic hypotension can likely be reduced if an individual threshold of RBV is avoided during HD treatments, eg, using lower UF rates in these patients.

Strategies for improving hemodynamic stability in cardiac-compromised dialysis patients

In hemodialysis patients, structural changes at all levels of the cardiovascular system are common. The presence of these cardiovascular changes is a risk factor for the development of intradialytic hypotension. This explains the clinical observation that the incidence of symptomatic hypotension is high in elderly hemodialysis patients, who often have a history of long-standing hypertension and atherosclerosis, and in hemodialysis patients with cardiovascular disease. With an increasing number of cardiovascular compromised dialysis patients, special attention should be given to this group of patients. As the age of patients on hemodialysis increases steadily, it is a challenge to provide comfortable treatment in these patients by reducing the incidence of symptomatic hypotensive periods. This article describes the use of relatively new and simple clinical maneuvers to reduce the incidence of symptomatic hypotension.

Principles and practice of hemofiltration and hemodiafiltration

There is growing interest in the convective dialysis therapies, hemofiltration (HF) and hemodiafiltration (HDF). Both require dialysis membranes which are highly permeable to solutes as well as fluid, and in both cases large volumes of ultrafiltration are the condition for convective transport. In HDF the convection is combined with diffusion, and as a consequence, maximum clearance over the entire molecular weight spectrum is achieved. Optimal forms of HDF provide urea clearance 10-15% higher than the corresponding diffusive mode. The larger the solute, the greater is the impact of convection, and beta2-microglobulin (beta2m) levels may be up to 70% reduced. Traditional postdilution HF provides high clearance of medium sized and large molecules. Satisfactory clearance of small solutes requires blood flows in excess of 500 ml/min. With access to practically unlimited volumes of substitution solution through on-line ultrafiltration, predilution HF can now be used. This increases the clearance of small solutes to an acceptable range. For HDF as well as HF, large patient populations consistently treated for longer periods of time are needed to make valid outcome comparisons with other therapies.

Is high-flux dialysis cost-effective?

High-flux dialysis is a new method for providing routine-maintenance hemodialysis to patients with end-stage renal disease. It promises to shorten the duration of the dialysis session, but poses potential clinical risks to patients and financial risks to dialysis centers because of the high unit cost of purchasing new dialysis equipment. We retrospectively evaluated the cost-effectiveness of high-flux dialysis compared to conventional dialysis in a hospital-based center. The center provided only conventional dialysis until March 1989, when it initiated high-flux dialysis. The estimated annual costs of treatment were US $31,249 (high-flux) and $32,562 (conventional). The rate of hospital admissions was almost identical in both groups (conventional, 1.29 admissions per year; high-flux, 1.24 admissions per year; p = 0.23). Predicted prolongation of life expectancy with high-flux dialysis was significantly higher after statistical adjustment for observable patient characteristics (1.8 to 4.5 years; p < 0.01). The cost-effectiveness ratio was $28,188 per life-year saved for high-flux compared to conventional dialysis. These findings suggest that the added capital expense of purchasing high-flux equipment can be justified from the perspective of its societal cost-effectiveness.