Most dialysis apparatus currently in use must be very rigorously cleaned between uses to prevent contamination, either cross-contamination from one fluid to another or contamination, with for example bacteria, due to poor sanitation. This is particularly important in haemodialysis, which comprises removing blood from the body, processing it by means of diffusion exchange through a membrane with a dialysis solution, and then returning it to the body. In attempt to reduce the amount of cleaning required, various methods and apparatus have been developed which utilize disposable single-use processing systems.
In these, and in other medical procedures employing disposable fluid processing systems, it is typical for the operator, who may be a trained medical professional, to first select and locate an appropriate filter or membrane element and one or more flow sets. These items must then be removed from their sterile packaging and be connected together to form a fluid circuit, which is then installed on the particular processing apparatus with which the procedure is to be performed. Typically, the processing apparatus includes multiple pump, valve, detection and clamping elements which interact with various parts of the disposable circuit and which are operable to perform the process.
Previous designs to simplify the set up of such processes have proposed that some of the fluid circuit elements be contained in a disposable “cartridge” which can be interfaced with a re-usable machine. Often these systems have been complex requiring either a disposable flexible bag-like circuit to be placed in a non-disposable rigid supporting structure prior to inserting into the machine or requiring tubes to be connected to various elements of a non-disposable component prior to interfacing with the machine. While these designs go some way to providing a solution to the cleaning problem, they are complex and there is scope for error in their use. In haemodialysis in particular, there are two fluid circuits, namely the blood circuit and the processing fluid (i.e. dialysis solution) circuit and while, in the prior proposals, the disposable component includes the full circuit for the blood, the processing fluid is supplied from a re-usable machine. The processing fluid is typically supplied to the cartridge in one of two ways. The first is that large volumes of the sterile process fluid, namely water, containing various additional components, for example sodium bicarbonate, is supplied to the machine. These volumes must be kept under specific conditions and can only be stored for a finite amount of time before bacterial growth begins. In addition, if different patients require the use of different processing fluids this does not provide a universal system. The alternative solution is that the machine is provided with a supply of de-ionised water (commonly in a medical establishment this will be produced centrally and then piped to applications requiring it). The water is then heated in the machine to a temperature at which bacteria are killed and then cooled down to substantially the same temperature as the bodily fluid and then various additives are added to provide the required process fluid. When the machine is dormant between uses with this system it is necessary to sterilize all of the internal fluid lines within the apparatus between uses and consequently, although the system hygiene is improved by the use of disposable parts and the set up is partially simplified for the operator, the down-time between treatments is not reduced because of the cleaning process that is still required. Further, the machine complexity has remained high because of the need to provide the chemical and circulatory fluid paths required for the cleaning process.