Pneumatic system solution simplifies dialysis treatment using single-needle haemodialysis
From development partner to series supplier – Cooperation with Fresenius Medical Care
Fluidic components play a key role in medical technology wherever liquids need to be precisely dosed or processes need to be pneumatically controlled. This is very much the case in dialysis, for example, which is a vital blood purification procedure that replaces the function of the kidneys for those with kidney failure. The treatment methods are continuously evolving, resulting in increasingly complex treatment devices.
Pneumatic system solution for dialysis machines
Dialysis machines consist of around 8,000 components. The fluidic assemblies, consisting of solenoid valves, pumps and sensors, must ensure precise and reliable processes. The demand is not so much for the individual components, but rather for application-specific system solutions whose individual components must be harmonised to work together perfectly. In addition, there is often a requirement for high precision, durability and compact dimensions. In such cases, manufacturers of medical devices are well advised to engage a fluidics expert who, based on an extensive solution portfolio and industry-specific knowledge, serves as a competent development and system partner, from the initial consultation through complete engineering to series production. Through their collaborative work on a fluid control solution for a pneumatic system in a dialysis machine, Fresenius Medical Care and Bürkert have together demonstrated just how successful a cooperative partnership can be when it comes to the development of fluidic system solutions.
Making life easier for nursing staff
The innovative 6008 CAREsystem dialysis machine was developed to make dialysis treatment in hospital easier for nursing staff. To this end, work processes have been simplified and the number of steps required has been reduced. The pressure on staff is reduced, leaving more time for individual patient care. Nevertheless, the dialysis system also offers a high degree of flexibility for haemodialysis, high-volume HDF and double-needle or single-needle treatments. This is because a universal blood tubing cartridge system is used for the application, which must be disposed of as a disposable item afterwards.
Replacement for a hose reel pump
The basis for the fluidic control in the single-needle haemodialysis process is a pneumatic system solution for flow reversal, which Bürkert developed for Fresenius in close cooperation with the company. It replaces the solution previously used for the single-needle haemodialysis, whereby the extracorporeal blood circuit was based on a hose reel pump and the associated disposable accessory, required additionally for single-needle treatment. The blood pump and the expansion chamber were located upstream of the dialyser on the arterial side of the extracorporeal circuit. The set-up with the alternating pump has proven successful in patient use and has delivered good treatment results. However, the manufacturer wanted to make handling easier for the operating staff, who are often under a lot of pressure in everyday hospital life. Above all, the aim was to reduce the work involved in connecting the tubes to the pumps, thus shortening the setup time.
Initial considerations focused on using proportional valves to regulate the necessary pressure or keep it constant. However, such a solution would have been comparatively costly. After the fluidics experts had studied the task and analysed the various specifications, they proposed a more efficient solution: a pneumatic control unit that works with solenoid valves. It impressed the developers of the 6008 CAREsystem right from the concept phase because it met almost all requirements straight away.
The compact assembly consists of three valves, a pressure sensor, a condensate trap and a diaphragm pump that generates overpressure in one chamber and negative pressure in the second chamber. A valve then switches dynamically between the two chambers, making a hose reel pump superfluous.
Only the cassette needs to be connected.
In principle, the compact assembly consists of three valves, a pressure sensor, a condensate trap and a diaphragm pump that generates overpressure in one chamber and negative pressure in the second chamber. A valve then switches dynamically between the two chambers, making a hose reel pump superfluous. The other two valves serve as bleed valves in the event of a fault. The operating personnel only need to connect the cassette, and no longer need to hose the pump. This is much faster and less prone to errors. In addition, the same cassette is suitable not only for single-needle applications, but also for double-needle applications. If necessary, the system can simply be switched over without having to make any changes to the bloodline system.
High demands were placed on the components for the process. The valves not only have to switch quickly, they also have to be durable. The valves used have already proven themselves in this regard in many other applications. Type 6144 is a direct-acting 3/2-way flipper solenoid valve. It is suitable for pressures up to 10 bar and has impressively low power consumption. The flipper principle produces only low switching noises and operates with low power consumption. The other two solenoid valves (type 127), which work in the pneumatic flow unit, have also demonstrated their value in many medical, laboratory and analytical technology applications. They enable precise switching with very low temperature input through the coil. In addition, the valves are very easy to flush thanks to the lack of dead space.
Biocompatibility proven in toxicity test
One of the key requirements that the fluidic system solution for the dialysis system had to fulfil was the biocompatibility of the materials used. Although there is no direct blood contact, there must be no outgassing. Successful toxicity tests have proven that there is no issue in this regard.
In the meantime, the pneumatic system solution has proven itself in clinical use. The housing, which was originally produced as a milled part, is now manufactured using injection moulding due to the large quantities now being produced, and Fresenius sees Bürkert as a reliable partner all the way from development through to series production. The collaboration is therefore continuing and new fluidic system solutions are currently under development.
“During the development phase, we worked closely with Bürkert and received excellent support from the fluidics specialists, so that after a short time we had an assembly available as a functional model. We were then able to use it for the start of series production with minor adjustments. I particularly appreciated the fact that not only products but also complete solutions were offered, from functional models to cost-optimised series parts.”