University of Missouri, Columbia, MO, USA
Keywords: daily haemodialysis; haemodialysis machine; home haemodialysis
Introduction
Quotidian (daily) haemodialyses have been tried with excellent clinical results for more than three decades, but the attempts were short lived because of a lack of suitable equipment and adequate reimbursement. In recent years, groups in Europe and America established quotidian dialysis programs, either short, performed during the daytime or long, performed during the night. A brief history of the development of quotidian dialysis has been published [1,2].
All reports confirm beneficial effects of quotidian haemodialysis. These include improved blood pressure control, cardiac morphology and function, haematocrit, nutrition, sexual function, physical activity, vitality, energy, mental health, social functioning, patient survival, technique survival, endocrine function, mineral metabolism, bone disease and blood access function [213].
Moreover, the use of drugs, morbidity and hospitalization requirements are decreased. Therefore, despite the higher cost of dialyses, the global cost of treatment of ESRD patients is lower; however, the cost of dialysis alone is higher and is not fully reimbursed to dialysis providers in the USA [14].
Although haemodialysis technology has improved in recent decades, it was not specifically designed for frequent, home haemodialysis. Major problems with the existing technology and a history of the development of a machine designed specifically for quotidian, home haemodialysis have been described [15].
A device for daily haemodialysis should be simple and easy to use. In addition, it should perform most of the chores related to set up for dialysis and tear down after dialysis. Finally, it should be inexpensive to operate. Such a machine, called the personal haemodialysis (PHD®) system, has been recently manufactured by Aksys, Ltd (Lincolnshire, IL, USA) and tested in a clinical trial. Described here are the design of the machine, its operation and advantages for frequent haemodialysis, particularly performed by patients at home.
Outline of the machine design
The machine is composed of a dialyzer module, dialysis solution module, water treatment module, control module and graphic user interface (touch screen). The dialyzer module contains a dialyzer, an arterial line with blood pump and a venous line with air trap (Figure 1). The arterial and venous lines are provided with pressure gauges. Between dialyses, the arterial and venous lines are connected to the fluid lines of the dialysis solution module.
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The central feature of the dialysis solution module (Figure 1) is a 50 l main tank with two receptacles for bottles with chemicals necessary to produce dialysis solution. Bottle no. 1 (acid concentrate) contains an aqueous solution of sodium chloride, potassium chloride, calcium chloride, magnesium chloride, acetic acid and dextrose. Bottle no. 2 contains powdered sodium bicarbonate and sodium chloride. The machine prepares ultrapure dialysis solution from the dry chemicals, the concentrate, and RO water warmed to 30°C. Dialysis solution, taken from the bottom of the tank, is warmed to
37°C and delivered through the dialysis solution line to the dialysate compartment of the dialyzer via an inline ultrafilter 1. Dialysate is returned through the dialysate line to the top of the tank. The dialysis solution circuit is connected to the 4 l ultrafiltration (UF) tank and excess fluid is transferred to the UF tank and measured directly. Because of the temperature difference between fresh dialysis solution and spent dialysate, the mixing of the two in the main tank is limited (depicted in Figure 1
by shading between the dialysis solution and dialysate). Almost the whole tank volume may be used as a single pass dialysis solution delivery system for short dialysis. All operations are guided by a computer in the control module and by the commands from the graphic user interface module.
The PHD® system combines four machines in one: a dialysis machine, a reuse apparatus, a water treatment appliance, and a device manufacturing ultrapure, infusion quality solution. The machine is based on a tank dialysis solution system. Elimination of a proportioning system significantly simplifies machine design. The use of positive pressure UF eliminates the need for a deaeration pump. Finally, the closed system allows direct measurements of ultrafiltrate, which further simplifies the machine and reduces its cost. In place of these unnecessary components, the machine introduces several new elements, which improve safety and eliminate labour and disposables.
Brief description of machine operation
Heat disinfection and integrity of filters test prior to each dialysis
The UF tank, fluid lines, dialyzer, arterial and venous lines, and the main tank are filled with RO water heated to 85°C and recirculated for 1 h. Hot water also enters the RO membrane (path not shown in Figure 1), so the whole system, including the blood tubing set and the dialyzer, is disinfected. After 1 h, the water is drained; the system is rinsed with fresh RO water. Once rinsed, the integrity of the dialyzer and ultrafilters is checked using a pressure test.
Preparation of dialysis solution for each dialysis
The system is filled with RO water, including the blood compartment of the dialyzer and the bloodlines. The dialysis solution is prepared by dissolving the powdered chemicals and diluting the concentrate in water in the main tank. The temperature of the dialysis solution is regulated by a thermistor, and the proper dissolution of chemicals is checked by the first conductivity meter (CM 1). The dialysis solution fills the dialysate and blood compartments of the dialyzer.
Dialysis
Discard prime and start of dialysis. The patient changes the transducer protector, attaches the arterial and venous lines to the blood access, injects heparin to the arterial line and touches the start button to activate the system. The blood and UF pumps are activated. Negative pressure in the dialysate compartment pulls dialysis solution from the blood compartment and blood enters the blood compartment of the dialyzer through both the arterial and venous lines. Once the compartment is filled with blood, the blood pump speed increases and the UF pump speed automatically adjusts to create appropriate transmembrane pressure for the desired UF. The dialysis solution is heated to 37°C, flows through the dialysate compartment of the dialyzer and returns to the top of the main tank (Figure 1
).
Backflush and solute infusion. Every 15 min, if desired, the directions of blood and UF pumps are reversed to create negative pressure in the blood compartment and positive pressure in the dialysate compartment. The fluid from the UF tank flows to the dialysis solution line through the bypass. The reversed transmembrane pressure gradient filters dialysate through the membrane into the blood compartment dislodging proteins and other molecules embedded in the dialyzer membrane pores. After a bolus of fluid passes through the membrane, the direction of pumps is reversed and dialysis continues. Backflushes are intended to preserve the efficiency of dialyzers for up to 30 reuses.
If infusion of fluid is necessary, ultrapure dialysis solution may be infused during dialysis in the same way as during the backflush.
Rinseback. At the end of dialysis, the direction of the blood pump is reversed. Dialysate from the main tank flows through the heater and ultrafilter 1 to the dialysate compartment of the dialyzer, creating high pressure in the dialysate compartment. The blood is returned to the patient through both the arterial and venous lines, pushed by the dialysate transferred to the blood compartment due to the reversed transmembrane pressure gradient. This method allows for almost complete return of blood with minimal delivery of fluid to the patient. After the blood is returned, the patient disconnects lines from the blood access and attaches the lines to the connectors in the dialyzer module, changes bottles 1 and 2, tests the quality of pre-treated water and gives information through the touch screen that the machine may start preparation for the next dialysis.
Preparation of the machine for the next dialysis
The machine first determines the clearance of the dialyzer by measuring changes in conductivity. The blood pump pulls RO water to the blood compartment of the dialyzer through the ultrafilter 2 and the dialysis solution flows countercurrently through the dialysate compartment. Based on the changes in conductivity measured by the second conductivity meter (CM 2), the conductivity clearance is calculated by the machine's computer. If clearance is within an appropriate range, the dialyzer is accepted and the machine continues with the heat disinfection and dialysis solution preparation for the next dialysis, as described above.
Results of the clinical trial
For the machine approval, the Food and Drug Administration (FDA) requested an extensive daily dialysis study trial comparing new machines to the conventional ones. Twenty-three patients used the PHD® machine for 17.4 patient-years and performed more than 3700, five to six times weekly, dialysis sessions on the PHD®, including more than 3300 at home. The results with the PHD® system were compared to those on conventional machines used for 10.4 patient-years in over 2800, five to six times weekly, dialyses performed at home [16]. The machine proved to be safe, dialyzers and lines were cleaned well, and there was no significant decrease in dialyzer clearances with consecutive uses up to 28 times [17]. Heat sanitization of dialyzers and lines in situ resulted in exceptionally pure dialysis solution, many times cleaner than saline used in regular dialysis [18].
Subjectively, patients preferred the PHD® machine because they experienced fewer intradialytic symptoms than on haemodialyses performed with conventional machines. There was a decrease in the incidence of hypotension, headache, nausea, arrhythmias, cramps, backaches, chills and access problems. This phenomenon was attributed to the use of ultrapure dialysis solution [19]. Based on the submitted results, the FDA approved the machine for general use without restrictions on March 26, 2002. It will be used initially for short, hemeral (daytime) dialysis. A major obstacle for use in nocturnal dialysis is the time (18 h) necessary for the preparation of the machine for the next dialysis. Appropriate modifications are being made to shorten this time to 13 h so the machine may be used for nocturnal haemodialysis as well.
Advantages of PHD®
Saving of labour
The PHD® system does the work of dialysis technician and reuse technician between dialyses, and dialysis helper during dialysis.
The machine reuses in situ dialyzer and lines so they do not need to be changed for a month, checks dialyzer performance and prepares dialysis solution. The only thing the patient has to do is to change the two chemical bottles and the transducer protector for each dialysis, and to test the quality of pre-treated water.
The machine computer calculates dialysis solution flow based on the prescribed time of dialysis, and required rate and volume of fluid removal based on weight gain. In case of cramps or weakness during dialysis, the machine has ultrapure fluid immediately available for infusion by pressing a button.
Saving of money, storage space and volume of wastes
Reuse of dialyzers and lines saves cost and volume of supplies. The use of dry chemicals and low volume concentrates significantly reduces the volume of supplies, which must be transported, stored and disposed. Online production of injection quality dialysis solution eliminates the need for saline bags. Table 1 shows the comparison of approximate weight and volume of annual supplies for the PHD® system and conventional machines. The use of heat disinfection essentially eliminates the environmental hazards associated with chemicals.
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Saving of time
The time saving for preparation for dialysis and tear down after dialysis is particularly important in daily dialysis. The machine is easy to use, as the patient does not have much to do before or during dialysis; therefore, training time is shorter.
Conclusions
Daily dialysis programs are developing rapidly in many centres in the world, providing excellent clinical results. Any device designed for frequent, home haemodialysis should have similar components: a dialysis machine, a reuse apparatus and a water treatment appliance. An additional, desirable feature, practically eliminating the use of saline, is a device manufacturing ultrapure, infusion quality dialysis solution. Such a machine saves time for a patient (or helper) by setting up for dialysis and tearing down after dialysis, and saves money by reusing supplies and decreasing transportation costs. The PHD® system fulfils these requirements.
Acknowledgments
I thank Derek Wiebenson of Aksys, Ltd for information regarding details of machine operation in its final design. Information on possible conflict of interest: The author is a Member of the Aksys Scientific Advisory Board and is an author of five patents [2022], which were the basis of the machine design.
Notes
Correspondence and offprint requests to: Zbylut J. Twardowski, MD, PhD, FACP, University of Missouri, Dialysis Clinic, Inc., 3300 LeMone Boulevard, Columbia, MO 65201, USA. Email: twardowskiz{at}health.missouri.edu
References
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