Ultrafiltration Control Research Articles

Influence of Ca and Na ions in backwash water on ultrafiltration fouling control

The effect of calcium and sodium in backwash water on the fouling control of ultrafiltration is investigated on a bench scale. Besides permeate of ultrafiltration and demineralized water, solutions with different calcium or sodium concentrations were used for backwash. The results show that backwashing with demineralized water is better than with permeate of ultrafiltration. The backwash efficiency decreases when calcium and sodium are added in demineralized water for backwash. That is probably because the presence of calcium and sodium in backwash water increases the Ca-bridging effect between the negatively charged membrane and the negatively charged NOM, and compresses the double layer of the membrane and the NOM, leading to a strong adhesion force on the membrane.

Fouling control in sugarcane juice ultrafiltration with surface modified polysulfone and polyethersulfone membranes

Commercial 50 and 100 kD polyethersulfone (PES) and polysulfone (PS) ultrafiltration membranes were surface modified by UV photografting of poly(ethylene glycol) methacrylate (PEGMA) monomer. The modified membranes were characterized by the degree of grafting, water flux and molecular weight cutoff (MWCO) rating. The flux and fouling of the modified and unmodified membranes were examined with sugarcane juice and its polysaccharide fraction. Under the conditions of this study, the modified membranes displayed a low degree of grafting (26–36 μg/cm 2), which was independent of the UV exposure duration; however, both membrane water flux and MWCO rating were affected by the irradiation time. In the best case, the modified membranes exhibited lower fouling with sugarcane juice; furthermore, the propensity to foul also decreased. More significantly, juice flux recovery was almost complete for successive UF-cleaning cycles.

Development of a multi-objective coagulation system for long-term fouling control in dead-end ultrafiltration

In this paper, a multi-objective control system has been developed and experimentally tested. The multi-objective control system can be effectively used to control short-term fouling as well as long-term fouling. In an earlier study it was found that coagulant dosing in ultrafiltration can be used effectively to control the short-term fouling resistance during several sequential filtration cycles. To control long-term resistance increase during sequential chemical cleaning cycles, usually, in open-loop setting of the cleaning frequency or variables which influence the cleaning efficiency, such as, the cleaning time and the chemical composition are adjusted. Additional introductory experiments showed that changes in the coagulant dosing have a more pronounced effect on long-term fouling than changes in the usual applied variables. For this reason, it was decided to develop a closed-loop multi-objective controller where the coagulant dosing is used as the manipulated variable to accomplish both control objectives namely the fouling resistance over multiple filtration cycles (the short-term objective), as well as the irreversible fouling resistance over multiple chemical cleaning cycles (long-term objective). However, the controller is too slow to deal with temperature changes influencing the effectiveness of the coagulant dosing. To handle these influences a kind of gain scheduler should be included in the control algorithm.

Is it time to revisit residual renal function in haemodialysis? (Review Article)

Residual renal function (RRF) is not currently emphasized for patients undergoing haemodialysis (HD). The role of RRF is well recognized in the peritoneal dialysis population as studies have clearly demonstrated a survival benefit with preservation of RRF. There is however, data to suggest that RRF is important in HD patients as well. Contemporary HD therapies using high flux biocompatible synthetic dialysers, bicarbonate buffered ultrapure dialysis fluids with ultrafiltration control appear to allow better preservation of RRF. The long held belief that peritoneal dialysis is better at preserving RRF than HD may no longer be true. More robust studies are required to determine the relative importance of RRF in HD and strategies to best preserve this vital asset.

Hemodialysis in children: general practical guidelines.

Over the past 20 years children have benefited from major improvements in both technology and clinical management of dialysis. Morbidity during dialysis sessions has decreased with seizures being exceptional and hypotensive episodes rare. Pain and discomfort have been reduced with the use of chronic internal jugular venous catheters and anesthetic creams for fistula puncture. Non-invasive technologies to assess patient target dry weight and access flow can significantly reduce patient morbidity and health care costs. The development of urea kinetic modeling enables calculation of the dialysis dose delivery, Kt/V, and an indirect assessment of the intake. Nutritional assessment and support are of major importance for the growing child. Even if the validity of these “urea only” data is questioned, their analysis provides information useful for follow-up. Newer machines provide more precise control of ultrafiltration by volumetric assessment and continuous blood volume monitoring during dialysis sessions. Buffered bicarbonate solutions are now standard and more biocompatible synthetic membranes and specific small size material dialyzers and tubing have been developed for young infants. More recently, the concept of “ultrapure” dialysate, i.e. free from microbiological contamination and endotoxins, has developed. This will enable the use of hemodiafiltration, especially with the on-line option, which has many theoretical advantages and should be considered in the case of maximum/optimum dialysis need. Although the optimum dialysis dose requirement for children remains uncertain, reports of longer duration and/or daily dialysis show they are more effective for phosphate control than conventional hemodialysis and should be considered at least for some high-risk patients with cardiovascular impairment. In children hemodialysis has to be individualized and viewed as an “integrated therapy” considering their long-term exposure to chronic renal failure treatment. Dialysis is seen only as a temporary measure for children compared with renal transplantation because this enables the best chance of rehabilitation in terms of educational and psychosocial functioning. In long term chronic dialysis, however, the highest standards should be applied to these children to preserve their future “cardiovascular life” which might include more dialysis time and on-line hemodiafiltration with synthetic high flux membranes if we are able to improve on the rather restricted concept of small-solute urea dialysis clearance.

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

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). 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. 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. 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.

Cell biology of the glomerular podocyte.

Glomerular podocytes are highly specialized cells with a complex cytoarchitecture. Their most prominent features are interdigitated foot processes with filtration slits in between. These are bridged by the slit diaphragm, which plays a major role in establishing the selective permeability of the glomerular filtration barrier. Injury to podocytes leads to proteinuria, a hallmark of most glomerular diseases. New technical approaches have led to a considerable increase in our understanding of podocyte biology including protein inventory, composition and arrangement of the cytoskeleton, receptor equipment, and signaling pathways involved in the control of ultrafiltration. Moreover, disturbances of podocyte architecture resulting in the retraction of foot processes and proteinuria appear to be a common theme in the progression of acquired glomerular disease. In hereditary nephrotic syndromes identified over the last 2 years, all mutated gene products were localized in podocytes. This review integrates our recent physiological and molecular understanding of the role of podocytes during the maintenance and failure of the glomerular filtration barrier.

PH adjustment for seasonal control of UF fouling by natural waters

Natural surface waters in Algarve, Portugal, have important seasonal variations in natural organic matter (NOM) content, that influences ultrafiltration (UF) performance. This paper addresses the evaluation of the pH adjustment for seasonal control of UF fouling at a laboratory scale, using a plate and frame polysulphone membrane of 47 kDa MWCO. Results of two types of natural water (clear water, 3–5 NTU, and turbid water, 33–34.6 NTU) and three different water pH values (acid, neutral and basic) demonstrated that the pH adjustment could be used for seasonal control of UF fouling: when the water has less NOM (in dry periods, clear water), the acid pH will improve the UF performance, while during and after intense rainfall periods (turbid water with high NOM concentration) basic pH will be advantageous, because it minimizes membrane fouling. This behaviour is explained for clear water in terms of charge effects on membrane size. For turbid water, the electrostatic repulsion between membrane surface and NOM and turbidity particles is reduced at pH 4.13 and protonation of the NOM functional groups decreases the hydrodynamic radii of humic substances while increasing their hydrophobicity and their tendency to adsorb. Therefore, a dense fouling layer develops and flux is lower at pH 4.13 than at pH 8.33. These results together with the observed raw water feed concentrations decline and rejection decrease with WRR confirm the extensive adsorption on the membrane enhanced by the moderate hardness cation of this water.

Experience with the GENIUS® Hemodialysis System

The late B. Tersteegen devised a clever way to combine the advantages of a closed tank hemodialysis system with the efficacy and bacteriological safety of a single-pass system. The Teerstegen equipment is now marketed as the GENIUS^® hemodialysis system. For each treatment, fresh dialysis fluid is prepared according to the physician’s prescription by mixing sterile ingredients (electrolytes and glucose) with preheated ultrapure water. The total amount of dialysis fluid is put into a thermally insulated glass tank (volume 75 l) of the hemodialysis machine. The filling and emptying process is completely automated. An UV radiator is used for desinfection. Due to a consequent hygienic concept, the system operates with an almost sterile and usually pyrogen-free dialysis fluid. During treatment, fresh dialysis fluid is taken from the top of the system, and the used dialysate is returned to the bottom. There is a sharp interface between the fresh and used dialysis fluids because of a small difference in temperature (1°C). True volumetric ultrafiltration control is simply achieved; ultrafiltration rates between 100 and 1,000 ml/h can be selected as considered appropriate by the physician. Microbiological examination: We cultured more than 2,000 dialysate specimens to examine bacterial contamination, and found either no bacterial growth at all (in the vast majority of the cases) or less than 1 CFU/ml dialysate. Clinical experience: We have utilized the GENIUS^® system since 1994. Meanwhile, more than 40,000 treatments have been performed in our center. Biochemical results of the first 19 stable hemodialysis patients (mean age 66 years, range 45–82), who had been treated with conventional hemodialysis systems for at least 6 months (range 6–157) before changing to GENIUS^®, were evaluated. We observed an increase of mean serum albumin concentration from 4.1 (±0.4 SD) g/dl to 4.8 (±0.3) g/dl (p < 0.01) within 6 months. Most patients reported improved well-being. Of these 19 patients, 18 preferred further treatment with the GENIUS^® system in comparison to conventional hemodialysis machines. Conclusion: The GENIUS^® hemodialysis system permits an individualized therapy of high quality; most patients prefer this system to conventional hemodialysis machines. Serum albumin levels increased significantly from normal to high normal values after change from conventional hemodialysis machines to GENIUS^®, probably due to less catabolic stress during the hemodialysis sessions.

Prospective Evaluation of an In-Center Daily Hemodialysis Program

Short duration daily hemodialysis (DHD) emerges as a well-tolerated alternative to standard hemodialysis (SHD). In this prospective study 5 patients in SHD were recruited to participate in an in-center DHD program. The SHD consisted of 3 sessions of 4 h each per week. Nonproportional mixture machines without an ultrafiltration control device and low flow dialyzers were used. For DHD, dialysis equipment and procedures were kept the same. Dialysis sessions, however, began at 6 p.m. (from Monday to Saturday) and lasted 2 h. Data from the last 6 months on SHD of the same patients were compared with the ones from each semester on DHD. Bone biopsy was performed at start and at the end of the 2-year study period. Hypotensive episodes, hypertensive crisis, cramps and headaches became 7–10 times less frequent in daily dialysis. A significant fractional increase (∼12%) was seen in mean values for hematocrit. Predialysis urea levels as well as predialysis creatinine levels declined significantly. Also lower during the daily dialysis period were the mean values for both phosphorus and Ca×P product. Significant increases were found in serum bicarbonate, albumin and in dry weight. The frequency of mean blood pressure ≧110 mm Hg on arrival for dialysis was significantly lower in every semester on daily hemodialysis. A significant twofold improvement in quality of life scoring was observed. Finally, daily hemodialysis also seemed to be beneficial to low turnover bone disease and bone aluminum deposition. These beneficial effects occurred despite of an increase in the frequency of missing days. Results from the present study which prospectively addressed the role of in-center short daily hemodialysis in the management of ESRD are encouraging.

Pediatric hemofiltration: Normocarb dialysate solution with citrate anticoagulation.

Fourteen children, newborn to 17 years of age, underwent continuous veno-venous hemofiltration with dialysis (CVVHD), using a new FDA-approved bicarbonate-based calcium-free dialysis solution (Normocarb) in combination with citrate anticoagulation. Dialysis prescription included use of the PRISMA system (Gambro, Lakewood, Colo., USA), with ACD-A (Baxter, Deerfield, Ill., USA) for anticoagulation and Normocarb (Dialysis Solution, Richmond Hills, Ontario, Canada) for dialysate. Diagnosis included 11 children with sepsis and 3 children with tumor lysis syndrome. Mean weight was 31.6+/-4.7 kg (range 3.7-62 kg) and average length of therapy was 11.4+/-3.7 days (range 6 h to 67 days). Length of circuit patency was 71.3+/-7.2 h (range 6 h to 127 h), which was influenced in part by a decision to change circuits at 72 h as per manufacturer's recommendation. No bleeding occurred. This protocol utilizes industry-manufactured CVVHD machinery with both thermic and ultrafiltration control, with an effective anticoagulation protocol, and industry-produced bicarbonate dialysate. The use of industry machinery and solutions allows for consistent industrial quality assurance standards. This potentially may decrease the cost of therapy and minimize the risk of pharmacy errors that can occur with pharmacy-made dialysis solutions.

Hemodialysis in children: principles and practice.

Hemodialysis has benefited from major progress over the last decade, improvements in technology and in clinical management. The morbidity over the sessions have decreased, seizures being exceptional, hypotensive episodes or headaches rare and pain related to the fistula puncture is effectively prevented by xylocaine ointment. The development of urea kinetic modeling allows the calculation of the dialysis dose Kt/V, and an indirect assessment of the protein intake. Even if the validity of these parameters are questioned their analyse provides an assessment and therefore is a "good thing." The patient also benefited from the technological revolution. The newer machines provide for precise control of ultrafiltration volumetrically assessed, buffered bicarbonate became a standard technique, biocompatible and highly efficient membranes and specific material available for infants have been developed. More recently the concept of ultrapure dialysate, ie, free of microbiological contamination, germs and endotoxins was developed, as was the availability of continuous blood volume monitoring during the session. The hemodiafiltration modality especially with the on line concept, because of all the advantages, should not be limited only to patients at risk.

Remote monitoring with automatic hemodialysis system for home hemodialysis

For safe hemodialysis therapy, we developed an automatic blood volume balanced ultrafiltration control system. This system controls the ultrafiltration rate automatically according to changes of blood volume to maintain an adequate blood volume level during hemodialysis. With the use of this system, hypovolemic events were significantly reduced. For the purpose of home hemodialysis, we applied this automatic ultrafiltration rate control system combined with remote monitoring. This system monitors blood pressure, pulse rate, blood volume, oxygen saturation, blood flow rate, ultrafiltration rate, intracircuit pressure, transmembrane pressure, dialysate conductivity, dialysate temperature, anticoagulant infusion, and so on. Furthermore, bidirectional audiovisual information between the patient's bedside console and our hospital was also obtained. All the monitoring data were transmitted with internet system by 64K ISDN cable. This is the first report to confirm the efficacy of an automatic hemodialysis system with remote monitoring in a hemodialysis session of a patient outside the hospital.

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

Alternative hemodialysis schedules have been proposed to improve the quality of the dialysis. Nonetheless, their influence upon mineral and bone disorders is unknown. To report the impact of a daily hemodialysis schedule upon the lesions of renal osteodystrophy. Prospective non-controlled study. Public University Hospital. Five patients treated by daily hemodialysis for at least 24 months. 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. 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. 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]. 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.

Application of automatic ultrafiltration controller with blood monitor for home hemodialysis patients

We have developed a new automatic ultrafiltration control system balanced with a blood volume (BV) monitor. This system has an algorithm that automatically controls the ultrafiltration rate (UFR), making a balance with blood volume during hemodialysis (HD). This system has been used in hospitalized chronic HD patients with some complications. The frequency of hypotension events during HD sessions was significantly reduced, demonstrating that this system controls UFR very safely. Furthermore, a personal computer connected with this system records trends in blood pressure, BV, UFR, and other values of the HD console. Records of several HD sessions are filed in a floppy disk. The electronic records are easily referred to monthly by HD staff in the clinic. The real-time data also can be sent to the HD center through a computer network system. This system could be used in patients undergoing home HD.

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

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

Continuous Blood Volume Monitoring and Ultrafiltration Control.

Continuous blood volume monitoring (CBVM) is believed to be a promising method for making the determination of patients' "dry weight" more objective, and ultrafiltration (UF) control more appropriate. Although blood volume response to UF and the interrelation between blood volume changes and changes in hemodynamic parameters are highly individual, certain principles of this response and interrelation can be identified and exploited for effective use of CBVM. The present work summarizes the authors' findings from practical CBVM application over the past 5 years and their opinions on the future development of this method. Four distinct types of blood volume response to constant UF rate were identified: Type 1, flat line throughout the whole session; Type 2, flat line during the first part of dialysis, followed by a linear decrease during the remaining time; Type 3, linear decrease right from dialysis start; and Type 4, linear decrease first, followed by a flat line during the remaining time. The possibility of a shift from one type to the other was verified. Blood volume reduction due to UF was found to have a static and a dynamic component. The most important factors affecting both components were found to be, by sensitivity analysis of a three-pool kinetic model, degree of overhydration, vascular system compliance, and UF volume (for the static component); and UF coefficient of the capillary wall and UF rate (for the dynamic component). Type 3 response, induced by more vigorous UF, was found to significantly decrease the volume of residual daily diuresis on the first postdialysis day. If confirmed, this finding may serve as a basis for the response type choice in patients with still significant residual renal function. Exploitation of the existence of dynamic blood volume reduction component for the first generation of automated biofeedback UF controllers may be complemented by automated identification of patient's plasma refilling capacity and/or position of his/her point on the Guytonian pressure/volume characteristics curves, and thus may more advanced "intelligent" UF controllers be constructed in the future.

Continuous Blood Volume Monitoring and Ultrafiltration Control

Continuous Blood Volume Monitoring and Ultrafiltration Control

Increasing the safety of volumetric ultrafiltration control

Deviations in ultrafiltration volume can cause various problems for patients undergoing a haemodialysis treatment. With the introduction of high flux dialysers, closed systems with volumetric fluid balancing became the systems of choice, because control of transmembrane pressure used previously is too inaccurate and unsafe to be used with such filters. In this article, a reliable and cost effective test method is described to increase the safety of a closed system. The test is carried out by simply analysing the dialysate pressure while the dialyser is isolated from the system for typically 7.2 seconds. No additional sensors and components other then a valve combination used to isolate the dialyser are required.

Adaptive control of ultrafiltration

An adaptive controller has been developed and implemented for the control of ultrafiltration in dialysis treatments of patients with renal problems. The reason for using adaptive control is the large difference in process dynamics when different dialysis filters are used. For several reasons, an adaptive pole-placement controller with least-squares identification was chosen. Due to the nature of the process, special attention was paid to the problem of having a smooth startup. This and other design considerations are discussed in a special section following the description of the process and the control design. A few registrations of signals from the real process are also shown.