referring now to fig1 - 2 , wherein similar components of the instant invention are referenced in like manner , a preferred apparatus for ionic enhanced dialysis / diafiltration , and accompanying methods for using the same , are disclosed . turning now to fig1 depicted therein is a first embodiment of a hemodialysis / diafiltration device which uses an internally supplied acid solution stream . a water source 102 supplies water or other base fluids , such as saline , to system 100 in order to create dialysate , substitution fluids and the like . the water , or other fluid is then provided to a water preparation device 104 which pre - treats the incoming fluid by heating , degassing and / or any other suitable method known to one of ordinary skill in the art . the pre - treated fluid is next transported via appropriate tubing or the like to a flow balance system 106 which has an inlet controller 106 a and outlet controller 106 b , which in turn may continuously monitor and adjust flow rates of fluids entering or exiting the internal components of system 100 . flow balance system 106 may contain one or more microprocessor controls and the like which are programmed to automatically accomplish this functionality within predefined parameters . the pre - treated fluid is transported first to internal components of system 100 through inlet controller 106 a . a portion of the pre - treated fluid equivalent to the net amount of fluid to be removed from the patient may be siphoned through an ultrafiltration pump 108 to a drain 134 . a remaining portion of pre - treatment fluid is next transported via appropriate tubing or the like to an auxiliary pump 110 . pump 110 transports a pre - determined portion of the pre - treated fluid to a closed vessel 112 which may contain concentrated acid , such as citric acid or the like , to form a secondary acidic solution for provision to dialyzer cartridge 122 , as described below . pump 110 may be controlled by , for example , a microprocessor controller which is programmed to accept a predetermined portion of pre - treated fluid for creating the secondary acidic solution . alternatively , the flow through pump 110 may be manually monitored and adjusted as needed . the secondary acidic solution flows from vessel 112 to an acid inlet valve 114 . the acid inlet valve may likewise be automatically or manually controlled to allow a predetermined rate of secondary acidic solution to flow therethrough . the secondary acidic solution then flows to a mixing chamber 116 . the mixing chamber 116 has a second inlet which receives dialysate solution from outlet port 148 of second dialyzer cartridge 138 , described further below . mixing chamber 116 may be automatically or manually monitored and adjusted to allow a predetermined amount of secondary acidic solution to flow to inlet port 120 of first dialyzer cartridge 122 via interdialysate pump 118 . a remaining portion of the pre - treated fluid which is not accepted through pump 110 is transported to inlet port 146 of second dialyzer cartridge 138 . the system 100 may be provided with monitoring means for determining the appropriate ph that is required to return blood treated in first dialyzer cartridge 122 to a normal level . once that level has been determined , the acid pump 154 and / or a bicarbonate pump 156 may be employed to pull additional acid concentrate 150 or bicarbonate concentrate 152 to adjust the ph of the remaining pre - treated fluid prior to providing the fluid to inlet 146 . blood to be cleaned is received from a patient and enters the first dialyzer cartridge 122 . the blood is carried by suitable tubing , as is known in the art , for example , bloodline tubing made from flexible polyvinylchloride ( pvc ). the flow rate of incoming blood is generally in the range of 100 to 600 ml / min , preferably 200 to 500 ml / min . first dialyzer cartridge 122 contains a semi - permeable membrane 124 that divides the dialyzer cartridge 122 into a bloodside compartment 126 and a dialysate compartment 128 . as blood passes through blood compartment 126 , plasma water containing blood substances is filtered across semi - permeable membrane 124 . at the same time , acidic dialysate received from dialysate port 120 flows through dialysate compartment 128 in a direction counter to the blood flow . blood substances and toxins are transferred across semi - permeable membrane 124 by diffusion due to a difference in concentration between the blood in blood compartment 126 and the acidic dialysate in dialysate compartment 128 . the acidic dialysate containing blood substances and toxins removed from the blood are transported to drain 134 via dialysate pump 132 and outlet controller 106 b . the partially dialyzed blood then exits first dialyzer cartridge 122 through conduit 136 . the blood then flows through conduit 136 and enters bloodside compartment 142 of second dialyzer cartridge 138 . the second dialyzer cartridge preferably contains a semi - permeable membrane 140 which divides the second dialyzer cartridge 138 into a bloodside compartment 142 and a dialysate compartment 144 . as the blood passes through bloodside compartment 142 , plasma water containing blood substances is filtered across the semi - permeable membrane 140 . the ph of the treated blood is returned to a desired concentration due to the difference in ph concentration between the low ph blood in bloodside compartment 142 and the higher ph dialysate in dialysate compartment 144 as received through inlet port 146 . cleansed blood then exits the second dialyzer cartridge 138 and is recycled to the patient ( not shown ) through suitable tubing , for example , bloodline pvc tubing , as is known in the art . the dialysate exits the dialysate compartment 144 of second dialyzer cartridge 138 through outlet port 148 and is provided to mixing chamber 116 , described above . the dialyzer cartridges 122 , 138 may be of any type suitable for hemodialysis , hemodiafiltration , hemofiltration , or hemoconcentration , for example , the fresenius f60 , available from fresenius medical care , lexington , mass ., the baxter conn . 110 , available from baxter health care , deerfield , ill ., the minntech hemocor hph 400 , available from minntech corporation , minneapolis , minn ., or the hospal filtral 16 , available from hospal a . g ., switzerland . membranes 124 , 140 are preferably medium or high flux membranes , for example , the polysulfone , cellulose triacetate or acrylonitrile membranes available from fresenius medical care , lexington , mass ., minntech corporation , minneapolis , minn ., baxter health care , deerfield , ill ., or hospal a . g ., switzerland . in an embodiment of the present invention in which diafiltration is desired , the blood may be mixed with sterile substitution fluid between the first and second dialyzer cartridges at inlet 180 of conduit 136 to form a blood / substitution fluid mixture . one way to accomplish this is disclosed in pct application no . pct / us99 / 17468 entitled “ method for efficient diafiltration ” filed in the name of collins et al ., the entirety of which is hereby incorporated by reference . collins et al . uses two cartridges connected in series to perform forward filtration of plasma water from the blood compartment to the dialysate compartment in both cartridges simultaneously . substitution fluid is added directly into the blood after it exits the first cartridge and before it enters the second cartridge . in the present invention , preparation of a sterile substitution fluid may be performed by filtration of a portion of pre - treated dialysate which is received from the inlet controller 106 a through substitution filter pump 158 . the pre - treated dialysate flows across at least two filter membranes 166 , 174 with a preferred molecular weight cut - off of not more than 40 , 000 daltons . to accomplish this , a portion of the fresh dialysate solution may be split off the dialysate fluid stream at some point prior to entering dialysate compartment 144 of the second dialyzer cartridge 138 . the split - off portion of the dialysate solution may flow through a conduit or the like which leads to a substitution pump 158 . substitution fluid pump 158 generates the needed pressure to force the fluid down a conduit into inlet ports 162 of first substitution fluid filter cartridge 160 . first substitution filter cartridge 160 contains a semi - permeable membrane 166 that separates the filter cartridge 160 into an upstream compartment 164 and a downstream compartment 166 . first upstream compartment 164 has inlet ports 162 . first downstream compartment 168 has one or more outlet ports connected to conduits 170 . the substitution fluid from first downstream compartment 168 then flows into second substitution fluid cartridge 171 containing a semi - permeable membrane 174 which separates the second cartridge 171 into a second upstream compartment 172 and a second downstream compartment 176 . the sterile substitution fluid exits second substitution fluid cartridge 171 through second outlet ports 178 and is mixed with blood exiting first cartridge 122 to form the blood / substitution fluid mixture described above . the pre - treated dialysate not used as substitution fluid enters the second dialyzer cartridge 138 through inlet port 146 of dialysate compartment 144 , and flows counter - parallel to the blood flow as it traverses through bloodside compartment 142 . during diafiltration , excess plasma water filters across semi - permeable membrane 140 and mixes with the dialysate fluid , so as to maintain a patient &# 39 ; s dry weight as the treated blood is infused . the dialysate fluid together with the filtered plasma water exits the second dialyzer cartridge 138 at outlet port 148 , through a tube or conduit which directs the fluid to the mixing chamber 116 , described previously above . referring now to fig2 therein is depicted second embodiment of a hemodialysis / diafiltration system 200 which uses an externally supplied acid solution stream . the system 200 functions in a similar manner to system 100 except that acid solution 112 a may be provided pre - mixed from an external source , and drawn into the mixing chamber 116 by an acid pump 113 , rather than being mixed within the machine as in system 100 . the dialysis / diafiltration methods and devices of present invention described above may be used as an add - on type system in conjunction with an existing ultrafiltration - controlled dialysis machine . however , it should be appreciated that the dialysis / diafiltration methods and devices of the present invention can also be embodied in a unitary , stand - alone dialysis / diafiltration machine . in one embodiment of the present invention , the dialysis / diafiltration device includes first and second dialyzer cartridges 122 , 138 . alternatively , a single cartridge having at first and second separate dialyzer sections may be used . the device may also include at least one sterility filter 160 , 171 , which may contain semi - permeable membranes . the sterility filter ( s ) 160 , 171 are operative to remove bacteria , endotoxins , and other particulate from the dialysate , thereby generating a suitable substitution fluid stream on - line . a sterile / non - pyrogenic substitution fluid for use in conjunction with the present invention may be prepared by drawing a portion of fresh dialysate solution from a dialysate inlet line and pumping it through one or more sterile filter cartridge 160 , 171 . in a preferred embodiment of the present invention , the sterile filter cartridges 160 , 171 perform at least a double filtration of the dialysate solution before the solution is introduced into the blood as a substitution fluid . this double filtration can be performed by two separate ultrafiltration filter cartridges or a single cartridge that has multiple sections to perform multiple filtration of the substitution fluid . the use of multiple filtration to generate the on - line substitution fluid makes the system of the present invention safer , should one of the filters fail during treatment . during operation of one embodiment of the present invention , blood enters a blood side compartment 126 of a first dialyzer cartridge 122 , whereby a portion of plasma water is filtered across the semi - permeable membrane 124 into the adjacent dialysate compartment 128 . as the blood leaves the first dialyzer cartridge 122 , substitution fluid may be added to the blood at a rate higher than the rate at which blood is filtered out of the first dialyzer cartridge . the diluted blood may then enter the bloodside compartment 142 of the second dialyzer cartridge 138 , whereby additional plasma water ( equal to the excess amount of substitution fluid ) is filtered across the semi - permeable membrane 140 and into the adjacent dialysate compartment 144 . in this manner , the substitution fluid acts as a post - dilution fluid relative to the first dialyzer cartridge as well as a pre - dilution fluid relative to the second dialyzer cartridge . the dialysate fluid may be generated by a dialysis machine , or by any other method known to one of ordinary skill in the art . in an embodiment of the present invention , the dialysate fluid enters the second dialyzer cartridge 138 and runs counter - parallel to the blood flow direction . the dialysate fluid acts to provide a concentration gradient against the bloodside fluid thereby facilitating the diffusion of solutes across the semi - permeable membrane 140 . as the dialysate traverses through the dialysate compartment , the dialysate flow rate increases due to plasma water filtering across into the dialysate compartment 144 , as mentioned above . upon exiting the second dialyzer cartridge 138 , the dialysate fluid may be pumped into the mixing chamber 116 . upon exiting the dialyzer cartridges 122 , 138 , the used dialysate may be transported back either to the dialysis machine or to the drain 134 . the dialysis machine ( riot shown ) used in conjunction with the present invention may perform all of its normal functions , such as preparing dialysate , metering dialysate flow rate , monitoring pressures , controlling net ultrafiltration , monitoring used dialysate for blood presence , etc . the diafiltration add - on system operates in conjunction with the dialysis machine , whereby the dialysate fluid from the dialysis machine is re - distributed by the hemodiafiltration add - on system to its respective dialyzer and sterile filter cartridges . the fluid handling components of the diafiltration add - on system may be integrated with a microprocessor unit for controlling and executing the diafiltration aspect of the treatment . the systems disclosed in the foregoing may contain further pumps , monitoring devices , valves , electronic components , controllers , connector fittings , tubing , etc ., as required in order to coordinate the operation of the system components . although the invention has been described in detail in the foregoing embodiments , it is to be understood that they have been provided for purposes of illustration only and that other variations both in form and detail can be made thereupon by those skilled in the art without departing from the spirit and scope of the invention , which is defined solely by the appended claims .
a dual - stage system and methods for using the same include first and second filtration cartridges is provided and is particularly suited for hemodiafiltration and / or hemodialysis . as fluid enters the first diafiltration cartridge , the hydrogenion concentration is reduced by exposing it to an acidic solution such as citric acid across a filter membrane . this stage allows for improved removal of certain toxins in the fluid , such as protein - bound substances that disassociate more readily from proteins at lower ph . as the filtered fluid enters the second filtration cartridge , the ph of the fluid is restored to normal levels prior to infusion to a patient .