Abstract:
The invention provides a device for use in a cartridge for on-line preparation of a solution for a medical procedure. The device comprises a hollow body, the body having a first end and a second end and is provided with through holes in its wall. The second end is closed, while the first end is open and adapted for receiving fluid introduced into the cartridge. The fluid leaves the device through said holes. Furthermore, the invention relates to a cartridge provided with such a device, a method of manufacturing such a cartridge and the use of a charge of concentrate in such a cartridge.

Description:
This application is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/SE2004/000436, filed on Mar. 23, 2004, which claims priority from Swedish Application No. 0301044-4, filed on Apr. 7, 2003, and the benefit of U.S. Provisional Application No. 60/461,657, filed on Apr. 7, 2003. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to on-line preparation of a solution intended for a medical procedure, in particular of sodium chloride or bicarbonate solution for hemodialysis. The on-line preparation in view takes place in a cartridge containing a powdered or granular concentrate, such as sodium chloride or sodium bicarbonate. More particular, the invention relates to a device for use in a cartridge of the above-mentioned type, a cartridge provided with such a device, a method of manufacturing such a cartridge and the use of a charge of concentrate in such a cartridge. 
     To those skilled in the art, it will be apparent that the present invention can be used in connection with other medical procedures where a fluid suitable for the procedure is obtained from mixing of a solvent (e.g. water) with at least one concentrate in powder form, such as replacement fluids in connection with hemodiafiltration and hemofiltration operations. 
     BACKGROUND OF THE INVENTION 
     Dialysis is a well-known method for treatment of kidney insufficiency. In hemodialysis, the blood of a patient suffering from impaired kidney function is conducted from a patient blood vessel to a dialysis machine and is returned to the patient after the treatment. The blood is conducted along one side of a permeable membrane in a dialyzer or filter connected to the dialysis machine, at the same time as dialysis fluid or dialysate may be conducted along the opposite side of the same membrane. Waste substances or poisons that are to be removed from the blood pass potentially with the help of diffusion from the blood to the dialysis fluid through the membrane. Excess water is also removed from the blood. A hemodialysis treatment typically lasts 3-5 hours. Preferably, a treatment may be performed while the patient is sleeping during night and may in that case last for about 8 hours. 
     On-line preparation of dialysis fluid is known. For example, the on-line preparation of a saturated bicarbonate solution from powdered bicarbonate contained in a cartridge is disclosed in DE 198 01 107 A1. 
     For the preparation of a dialysis fluid, saturated sodium bicarbonate solution may be mixed with a solution comprising appropriate electrolytes, such as K + , Ca 2+  and Mg 2+ . 
     In EP 0 278 100 B1 a powder cartridge is shown. The cartridge comprises a closed vessel provided with penetrable membranes at its upper inlet end and its lower outlet end, respectively. Within the vessel, there is provided a supply of powder concentrate of sufficient quantity so as to be suitable for a dialysis treatment session. For instance, in connection with the preparation of dialysis fluid or solution, the concentrate may consist of powdered sodium chloride or sodium bicarbonate. 
     In use, a powder containing prior-art cartridge is first primed with fluid, such as water, either from the top or from the bottom. Enough fluid is introduced into the cartridge during priming so that the fluid level is above the powder level. The powder is dissolved in the fluid and a saturated solution can leave the cartridge through the outlet in the bottom of the cartridge. As the solution leaves the cartridge a corresponding amount of new fluid is introduced into the cartridge. To establish that the degree of saturation of the solution leaving the cartridge is satisfactory, the conductivity of the solution may be measured. An unsatisfactory conductivity (saturation) will trigger an alarm in the dialysis machine. 
     The above-mentioned way of on-line preparation of solutions for medical use by means of a powder cartridge has many advantages. There are, however, some disadvantages with prior-art cartridges. After a few hours of use, the mixture of the fluid and the powder in the cartridge may become inhomogeneous. In some instances, clods may be formed. The clods may prevent gas bubbles from rising to the liquid surface. When a bubble is “released”, a channel in the powder bed may be created, sometimes all the way down to the lower outlet of the cartridge. This may allow unsaturated solution to leave the cartridge causing a conductivity alarm. The alarm must be taken care of either by the patient or by a nurse or medical attendant. If these problems occur, they may be remedied by knocking on the cartridge wall or by shaking the cartridge. However, often the cartridge has to be discarded, while still containing a considerable amount of powder, and replaced by a new cartridge. 
     The formation of channels in the powder bed might have other causes. For example, the fluid may be introduced gradually through the top inlet and fall in drops down to and impact the liquid surface. This may give rise to pressure waves in the liquid bed which in turn create fluid currents perpendicular to the powder bed surface. These currents may work their way down in the powder bed, creating channels in the bed reaching the lower outlet, making it possible for unsaturated solution to leave the cartridge. 
     SUMMARY OF THE INVENTION 
     In these circumstances it is an object of the present invention to create opportunities for improved on-line preparation of a solution intended for a medical procedure, in particular of sodium chloride or bicarbonate solution for hemodialysis, by means of a powder or granular cartridge. This and other objects are achieved by a device for use in a cartridge, the device comprising the features of the enclosed independent device claim, a cartridge provided with such a device according to the enclosed independent cartridge claim, a method of manufacturing such a cartridge comprising the steps of the enclosed independent method claim, and/or a method of use comprising the features of the enclosed independent use claim. Preferred embodiments are set forth in the enclosed dependent claims and in the following description. 
     By arranging a device according to the invention in a powder cartridge for online preparation of a solution, the fluid continuously introduced in the cartridge may be distributed in a desired way so as to minimize the risk of formation of channels and inhomogeneities in the powder bed. In turn this minimizes the risk of unsaturated solution leaving the cartridge. Thus, the chance that the whole amount of powder in the cartridge can be used is increased. This is of course favorable, both as regards operating results and costs. 
     Furthermore, during the initial priming of a cartridge, the inventive device provides a more even distribution of the fluid. 
     By preferably letting the device being elongated and having the through holes vertically distributed over its elongated wall, it is possible to let the fluid be output below the liquid/air surface also when the liquid level is sinking gradually. Therefore, the fluid does not fall in drops down on the liquid surface. The generation of pressure waves is avoided. Consequently, the formation of channels in the powder bed is minimized. 
     The device is preferably conical, which means that it easily can be stuck into the dry powder bed when preparing a cartridge. 
     The inventive cartridge exhibits advantages corresponding to those mentioned above as regards the inventive device. 
     The manufacturing method according to the invention is simple and cost-effective. 
     The use of an inventive cartridge, wherein the solvent is entering the vessel via an inventive device, allows a more efficient use of the powder or granulate and longer periods without operating interruptions. This implies a cost-effective process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior-art cartridge for on-line preparation of a solution. 
         FIG. 2  shows a device according to a preferred embodiment of the invention for use in a cartridge. 
         FIG. 3  shows an inventive device attached to a cartridge lid. 
         FIG. 4  is an isometric cut-away view of an inventive cartridge. 
         FIG. 5 and 6  illustrate the principle of the use of an inventive cartridge. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In hemodialysis, the blood of a patient suffering from impaired kidney function is conducted from a patient blood-vessel (of for example the patient forearm) to a dialysis machine and is returned to the patient after the treatment. The blood is conducted along one side of a permeable membrane in a dialyser or filter working with and/or as a part of the dialysis machine. At the same time, a dialysis fluid may be conducted along the opposite side of the same membrane. A transfer of waste substances or poisons and excess water that are to be removed from the blood may take place by the help of diffusion through the membrane from the blood to the dialysis fluid. One dialysis treatment may typically last from about 3 to 8 about hours. 
     In  FIG. 1 , a prior-art cartridge  1  for on-line preparation of a saturated bicarbonate solution from powdered sodium bicarbonate is shown. For the preparation of a dialysis fluid, the saturated sodium bicarbonate solution may be mixed with a solution comprising appropriate electrolytes, such as K + , Ca 2+  and Mg 2+ . The cartridge  1  may include a closed vessel or container  2  with an upper inlet end  3  and a lower outlet end  4 . Within the vessel  2 , there is provided a supply of powder concentrate  5  of sufficient quantity so as to be suitable for one or more treatments. The quantity of the powder contained in the cartridge would be on the order of magnitude of 400-1500 grams. Sodium chloride is another typical example in dialysis procedures. 
     Hereinafter a preferred embodiment of the inventive device for use in a powder or granulate cartridge will be described. 
     A device  6  according to the invention is shown in  FIG. 2 . The device comprises an elongated, and in some embodiments substantially conical tube  6  made typically of a plastic such as polypropylene. The tube  6  isclosed at its lower end  7  and open at its upper end  8 . In the wall  9  of the tube  6  through holes  10  are provided. This particular embodiment has eight holes  10  arranged in pairs on opposite sides of the tube  6 . Furthermore, the device  6  is provided with a neck portion  11 , which may be provided with engagement means, such as flanges or threads  11 ′. In  FIG. 3 , a device  6  attached to a lid  12  of a cartridge is shown. Preferably, the neck portion  11  and the lid  12  are constructed so that the device  6  can be snapped onto the lid  12 . Alternatively, the device  6  and the lid  12  can be made as an integral unit. 
     It is appreciated that the inventive device  6  as well as the cartridge  13  (vessel  14  and lid  12 ) (see e.g.  FIG. 4 ) can be made of other materials than polypropylene. 
     In  FIG. 4 , an embodiment of the inventive cartridge is shown. The cartridge  13  may be made of a polypropylene (or other material) vessel or container  14  and a polypropylene (or other material) lid  12 . The lid  12  has a liquid permeable inlet  16 . A solvent, which is to be introduced into the cartridge  13 , may be supplied via a tube  17 . In the bottom end of the vessel  14  a liquid permeable outlet  18  is provided. A tube  19  for discharge of a solution may be connected to the outlet  18 . The tubes  17  and  19  may not necessarily form part of the inventive cartridge. Furthermore, the cartridge  13  has a conical tube  6  as disclosed above (cf.  FIG. 2 ) connected at its neck portion  11  to the lid  12 . The embodiment of the device  6  shown in  FIG. 4  comprises two elongated flanges or ridges  15   a ,  15   b . The ridges  15   a ,  15   b  are arranged longitudinally along and on the inside of the device  6 . These ridges  15   a ,  15   b  may act as “fluid guides”. The incoming fluid may then follow the inside wall of the tube  6  or flow along the ridges  15   a ,  15   b . The “fluid guides” may alternatively consist of plastic pellets. 
     An inventive cartridge may be manufactured according to the following. Reference is made to  FIGS. 4 and 5 . A vessel  14  is provided and a batch of powder or granulate  20  is poured into the vessel  14 . A tightly fitting lid  12  is attached to the vessel  14  so that the tube  6  is stuck into the powder bed  20 . The lid  12  may be threaded or may be welded to the vessel  14 . Alternatively, using a self-containing cartridge, the powder may be sucked into the vessel  14  through some kind of membrane. 
     In use (see  FIGS. 5 and 6 ), first air is sucked from the cartridge  13  for the purpose of creating a vacuum in the cartridge. Then the cartridge is primed with a solvent, such as water, by letting solvent flow into the cartridge at a relatively high flow rate of about 1000 mL/min. It should be noted that the air removal and water priming may occur substantially simultaneously. In  FIG. 5  a primed cartridge is shown. The solvent may be introduced either through the upper inlet  16  or the lower outlet  18 , then having dual purpose, i.e. inlet at priming and outlet of saturated solution. In this example, the powder  20  may be sodium bicarbonate, and then the solvent  21  should be present in a sufficient amount so that the liquid level  22  is above the surface  23  of the powder bed  20 . The powder  20  is dissolved in the solvent  21  and a saturated sodium bicarbonate solution may leave the cartridge  13  through the outlet  18 . New solvent  21  is gradually entering the cartridge  13 , at a relatively low flow rate which is less than or about the same as the rate of solution leaving the cartridge and may be of about 15 mL/min. The sodium bicarbonate solution may then be mixed outside the cartridge with a fluid containing electrolytes for yielding a dialysis fluid. 
     At least the lower holes of the tube  6  should be situated below the fluid level  22  and the fluid outlets  10  should be “directed” substantially towards the vessel wall so that the outflow of solvent  21  from the tube  6  is directed substantially horizontally, i.e. in parallel with the fluid level  22 , as shown in  FIG. 6 . 
     The incoming fluid may then be prevented from freely falling in drops down to the fluid surface. The pressure waves and the currents will then be directed towards the wall of the vessel and dampened out before they reach the powder bed  20 . The channeling effect is minimized. Tests have shown that the functioning time before an alarm is triggered can be prolonged as much as two hours compared to when using a prior-art cartridge intended for example for 8 h of use. 
     It should be noted that the cartridge  13  may also be formed without a lid, either as a closed vessel or an open vessel (not shown). 
     It is easily appreciated that the inventive device can be applied together with other types of cartridges, and the inventive idea for cartridges containing other substances than sodium bicarbonate. It is further appreciated that the inventive idea can be applied for other medical purposes than hemodialysis, such as for replacements fluids for hemodiafiltration and hemofiltration.