Abstract:
A blood treatment system has a housing formed of transparent plastic material configured so that substantially the entire blood flow path is visible. A generally planar blood filtration media assembly divides a blood treatment chamber within the housing into first and second interior spaces that are visible through the transparent housing, with a cardiotomy manifold in fluid communication with the first interior space and a venous blood inlet in fluid communication with the second interior space. A generally planar blood defoamer media assembly is provided generally parallel with and spaced apart from the blood filtration media assembly. The blood defoamer media assembly divides the second interior space from the blood storage chamber. The blood flow path along each side of the blood filtration media assembly and each side of the blood defoamer media assembly is visible.

Description:
This application is a continuation of U.S. patent application Ser. No. 08/659,808, filed Jun. 7, 1996, now U.S. Pat. No. 5,871,693. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a blood treatment system, such as a venous and cardioplegia blood reservoir, with a high degree of visibility. 
     BACKGROUND OF THE INVENTION 
     Various surgical procedures require interrupting the normal functioning of the heart and lungs of the patient. Some of the functions of these organs are temporarily replaced by an extracorporeal blood handling system. The main volume of the patient&#39;s blood, known as the venous return stream, is typically withdrawn from the patient through a venous cannula inserted into the right atrium. The blood handling system collects the volume of blood in a venous reservoir. The blood handling system serves to pump the blood, regulate the carbon dioxide and oxygen content, regulate the temperature, defoam and remove emboli and particulate matter using one or more filters. The blood is then returned to the patient through an aortic cannula inserted into the aorta distal to the heart. 
     Blood from the surgical field, known as cardiotomy blood, is typically drawn into a cardiotomy reservoir. The cardiotomy blood typically contains gas bubbles, fragments of tissue, bone chips, blood clots, surgical debris and other dangerous and undesirable contaminants. The cardiotomy reservoir defoams, filters and collects the cardiotomy blood prior to combining it with blood in the venous reservoir. The level of filtration required for cardiotomy blood is typically greater than that required for the relatively clean venous return stream. 
     The high level of filtration necessary for cardiotomy blood may cause damage to blood constituents, such as due to sheer stress. Consequently, cardiotomy blood filtration is preferably performed separately from filtration of the relatively clean venous return stream. Integrated cardiotomy reservoirs (ICR) combine the treatment of both cardiotomy and venous blood streams. 
     Turbulent flow may develop at various locations within the blood handling system. Turbulent flow can cause bubbles to form in the blood and can increase the blood-to-air contact. Blood to air contact causes hemolysis of red blood cells. Hemolysis refers to the lysis or destruction of erythrocytes with the release of hemoglobin, resulting in a reduction in the ability of the blood to carry oxygen. 
     Blood handling systems can also have locations of blood stasis that can cause blood clotting or separation of blood components. Medical care providers are increasingly interested in viewing the condition of the blood throughout the entire blood circuit. Current blood treatment systems typically have internal regions that are not visible to the medical staff, such as the interior of cylindrically shaped filter media. Areas within the blood handling system that cannot be viewed by the medical staff may result in undetected blood stasis or clots. 
     Typical blood handling systems have a large number of discrete parts, requiring manual assembly, increasing the risk of assembly errors and increasing manufacturing costs. Manufacturing a variety of distinct extracorporeal blood handling systems with different blood treatment elements increases manufacturing and inventory costs. Variability between products also raises the risk of errors in assembly or marketing of finished products, resulting in a potentially detrimental medical impact on the patient. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a modular blood treatment cartridge and a method of assembling the same. 
     The present modular blood treatment system utilizes a blood treatment cartridge with a two-dimensional assembly process that facilitates automated assembly and substitution of a variety of blood treatment media. 
     The present invention is also directed to a modular blood treatment cartridge with a high degree of biocompatibility and visibility. 
     The modular blood treatment system defines a blood flow path for facilitating automated assembly along a single build axis. A blood treatment cartridge has a blood treatment media receiving opening that defines an entrance to a first chamber. The first chamber includes a first interior space and a second interior space. At least one cardiotomy blood sucker port is in fluid communication with the first interior space via a cardiotomy manifold. A venous blood inlet is in fluid communication with the second interior space. A first blood treatment media is interengaged with the blood treatment cartridge along the build axis. The first blood treatment media is preferably interposed between the first interior space and the second interior space. A second blood treatment media is interengaged with the blood treatment cartridge along the build axis. The second blood treatment media is preferably interposed between the second interior space and the blood treatment media receiving opening. A blood storage section is interengaged with the blood treatment cartridge along the build axis and extends substantially across the blood treatment media receiving opening. The blood storage section includes an outlet port. 
     The modular blood treatment system is preferably a transparent plastic material configured so that substantially the entire blood flow path is visible. 
     The blood treatment cartridge has a first ledge for receiving the first blood treatment media and a second ledge for receiving the second blood treatment media. The first ledge preferably defines a perimeter larger than the second ledge. 
     The first blood treatment media is a cardiotomy blood treatment media. The second blood treatment media is a venous blood treatment media. In one embodiment, the cardiotomy blood treatment media includes both a defoamer mesh and a filter media. The cardiotomy blood treatment media is a filter media with an average pore size of about 20 to 40 microns. The venous blood treatment media is preferably a defoamer media. A first frame preferably extends around a perimeter of the first blood treatment media. A second frame preferably extends around a perimeter of the second blood treatment media. 
     The blood storage section includes a blood diverter forming a pair of funnel-shaped blood flow channel extending between the blood treatment media opening and the outlet port. The funnel-shaped blood flow channels define a first downward flow axis at an angle of about 20 to 24 degrees with respect to horizontal. The funnel-shaped blood flow channel also defines a second flow axis perpendicular from the first flow axis extending downward from the blood diverter at an angle of about 3 to 7 degrees. 
     The cardiotomy manifold defines a downward curving surface extending from the at least one cardiotomy blood sucker port to the first interior space having a radius of about 2.54 to 7.62 cm. The opening in a blood sucker port is tangent to the downward curving surface of the cardiotomy manifold. The venous blood inlet includes a directionalized, low-velocity prime bowl for directing a portion of the blood flow path toward edges of the first chamber. The venous blood inlet has a cross-section at least four times greater than a cross-section of the venous blood inlet. 
     In an alternate embodiment, the blood storage section is a flexible blood reservoir in fluid communication with the outlet port. 
     In an alternate embodiment, the modular blood treatment system includes a blood treatment cartridge having a blood treatment media receiving opening defining an entrance of a first chamber. The first chamber includes a first interior space and a second interior space. At least one cardiotomy blood sucker port is in fluid communication with the first interior space via a cardiotomy manifold. A venous blood inlet is in fluid communication with a second interior space within the interior space. At least one cardiotomy blood treatment media is interposed between the first interior space and the second interior space. At least one venous blood treatment media is interposed between the second interior space and the blood treatment media receiving opening. A blood storage section extends substantially across the blood treatment media receiving opening. The blood storage section includes an outlet port. At least one blood diverter is located in the blood storage section for forming at least one funnel-shaped blood flow channel between the blood treatment media opening and the outlet port. The funnel-shaped blood flow channel defines a first downward flow axis at an angle of about 20 to 24 with respect to horizontal. 
     In an alternate embodiment, the modular blood treatment system includes a cardiotomy manifold defining a downward curving surface extending from the cardiotomy blood sucker ports to the first interior space. The downward curving surface has a radius of about 2.54 to 7.62 cm. 
     In another embodiment, the modular blood treatment system has a visible blood flow path. The transparent blood treatment cartridge has a blood treatment media receiving opening defining an entrance of a first chamber. The first chamber defines a first interior space and a second interior space. At least one cardiotomy blood sucker port is in fluid communication with the first interior space via a cardiotomy manifold. The venous blood inlet is in fluid communication with a second interior space within the interior space. At least one discontinuous cardiotomy blood treatment media is interposed between the first interior space and the second interior space so that the first interior space is visible through the transparent blood treatment cartridge. At least one discontinuous venous blood treatment media is interposed between the second interior space and the blood treatment media receiving opening so that the second interior space is visible through the transparent blood treatment cartridge. The transparent blood storage section extends substantially across the blood treatment media receiving opening. 
     As used herein: 
     Biocompatibility refers to a low-turbulent flow path that minimizes hemolysis and blood-air contact. 
     Initial Break Through Volume refers to the volume of fluid required before the fluid penetrates the filter media and reaches the output port in the reservoir. Initial break through volume is typically most significant when priming the modular blood treatment system. 
     Sucker Bypass refers to a condition where both the venous return stream and the cardiotomy blood stream both pass through the cardiotomy filters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an exploded view of an exemplary modular blood treatment system; 
     FIG. 2 is a top view of the modular blood treatment cartridge system of FIG. 1; 
     FIG. 3 is a side sectional view of the modular blood treatment system of FIG. 1; 
     FIG. 4 is an alternate side sectional view of the modular blood treatment system of FIG. 1; 
     FIG. 5 is a front view of the modular blood treatment system of FIG. 1; 
     FIG. 6 is a back view of the modular blood treatment system of FIG. 1; 
     FIG. 7 is an exploded view of an alternate modular blood treatment system for cardiotomy blood; 
     FIG. 8 is a top view of an alternate cardiotomy blood treatment system; 
     FIG. 9 is side sectional view of the cardiotomy blood treatment system of FIG. 8; 
     FIG. 10 is side view of the cardiotomy blood treatment system of FIG. 8; and 
     FIG. 11 is a schematic view of a method of assembling the present modular blood treatment system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-6 illustrate one embodiment of the present modular blood treatment system  20 . Blood treatment cartridge  22  has a blood treatment media receiving opening  24  defining an entrance to a chamber  26 . A cartridge flange  28  extends around the perimeter of the blood treatment media opening  24  for engagement with a corresponding flange  30  on a front blood reservoir  32 , as will be discussed in detail below. 
     A series of sucker ports  34  are located along a top edge of the blood treatment cartridge  22 . The sucker ports  34  are preferably connected to one or more lines of tubing conducting cardiotomy blood from the surgical site to the modular blood treatment system  20  (not shown). As best seen in FIG. 4, the blood sucker ports  34  are in fluid communication with a cardiotomy manifold  36  that leads to a separation chamber  37 . The cardiotomy manifold  36  and sucker ports  34  define an arch  33  having a radius of curvature of about 3.8 cm (1.5 inches), and preferably in the range of 2.54 cm to 7.62 cm (1.0 inches to 3.0 inches). The bores for the sucker ports  34  are preferably tangent to the surface of the arch  33 . The arch  33  directs the cardiotomy blood vertically downward into a first interior space  90  with minimal disturbance. The gradual shape of the arch  33  causes bubbles in the cardiotomy blood stream to rise to the surface. The bubbles may be broken when they contact pre-filter defoamer material  64  as the cardiotomy blood flows along the arch  33 . Alternatively, the bubbles in the cardiotomy blood collect at the bottom of the separation chamber  37 , where they are broken or popped by the pre-filter defoamer material  64 . The cardiotomy blood preferably does not flow through the pre-filter defoamer material  64 . The present cardiotomy manifold  36  can process at least six liters/minute (such as for example during sucker bypass) for an indefinite period of time. 
     Cardiotomy blood enters the modular blood treatment system  20  through the sucker ports  34  and cardiotomy manifold  36 , and flows into the first interior space  90 . The portion of the chamber  26  between the first blood treatment media assembly  72  and the second blood treatment media assembly  82  defines a second interior space  92 . The venous blood stream and filtered cardiotomy blood stream are collected in the second interior space  92  prior to defoaming. 
     As best illustrated in FIG. 3, a swiveling venous inlet connector  40  on a venous drop tube  42  is fluidly connected to the cartridge  22 . A fluid line (not shown) carries the venous return stream from the patient to the inlet connector  40 . A 30-70 durometer, silicone O-ring  31  is preferably interposed between the venous inlet connector  40  and the venous drop tube  42 . The venous inlet connector  40  preferably is arranged at between 30 and 60 degrees with respect to the venous drop tube  42  and has an outside diameter of 12.6 mm. A venous sampling luer site  54  is located on the venous inlet connector  40 . The venous inlet connector  40  preferably includes a connector flange  44  that engages with a semicircular ledge  46  on the back of the blood treatment cartridge  22 . An opening  50  is provided in the venous drop tube  42  for receiving a temperature sensor  48 . The stainless steel thimble  49  is preferably hermetically sealed across the opening  50  in fluid communication with the venous return stream. The temperature sensor  48  is preferably located within the thimble  49 . 
     The venous drop tube  42  preferably includes a cuvette tube  52  with a sensor window  43  (see FIG.  6 ). The sensor window  43  typically interfaces with an infrared sensor for measuring oxygen content and hematocrit in the venous return stream. A suitable cuvette tube  52  is available from CDI, a division of Minnesota Mining and Manufacturing Company, located in Tustin, Calif., under product designation CDI 100. 
     Turning to FIG. 2, the blood treatment cartridge  22  preferably includes a series of ports along the top surface. A pair of filtered luer ports  55  provide access to the cardiotomy manifold  36 . A 6.35 mm (0.25 inch) diameter prime port  58  in fluid communication with the cardiotomy manifold  36  is provided for priming the modular blood treatment system  20 . A vent port  53  is provided for releasing excess pressure from the chamber  26  during usage. The vent port  53  is preferably in fluid communication with the second interior space  92 , although it will be understood that a series of vents may be provided for some applications. A recirculation port  63  allows priming fluid, such as saline, to be recirculated between the modular blood treatment system  20  and an oxygenator (not shown) during the prime cycle. Finally a drug inlet port  51  provides access to the interior space  92  containing the venous return stream and the filtered cardiotomy blood stream. An exemplary oxygenator is shown in U.S. Pat. No. 5,149,318 (Lindsay) and U.S. Pat. No. 5,514,335 (Leonard et al.). 
     An auxiliary cardiotomy inlet  56  provides direct access to the chamber  92 . In the event that the cardiotomy blood treatment media assembly  72  fails, a secondary filter assembly (not shown) for filtering the cardiotomy blood stream can be inserted into the blood circuit with minimal disruption to the surgery procedure. The filtered blood stream from the secondary filter assembly can then be directed to the chamber  92 , thereby bypassing the failed assembly  72 . An alternate system for handling medical fluids is shown in U.S. Pat. No. 5,254,080 (Lindsay). 
     As shown best in FIGS. 1 and 3, a prime bowl  60  is located at the bottom of the venous drop tube  42  in fluid communication with the interior space  92  through an elongated inlet  59 . Blood collects in the prime bowl  60  below chamber  26 . In the event that the blood pumps fail, allowing blood in the drop tube  42  to travel backwards through the blood circuit, the prime bowl  60  operates as a trap to prevent air in the blood treatment system  20  from entering the venous blood stream. A blood trap is shown in U.S. Pat. No. 5,282,783 (Lindsay) and U.S. Pat. No. 5,403,273 (Lindsay). 
     The prime bowl  60  also operates as a velocity reducer. The prime bowl  60  preferably has a cross-section about four to six times greater than the cross section of the drop tube  42 . Consequently, the velocity of the venous return stream in the drop tube  42  is reduced to about 15-20% of its original velocity. For example, if the modular blood treatment system is operating at seven liters/min, the velocity of the venous return stream is reduced from 55 meters/min. to about 8.3 meters/min. The reduced velocity minimizes splashing, foam-creating turbulent flow and contact with the air. The elongated shape of the elongated inlet  59  cause the venous return stream to exit the prime bowl  60  primarily laterally toward the edges  22 A,  22 B of the blood treatment cartridge  22  so that blood stasis in these regions is minimized. 
     A series of support veins  62  are formed along the chamber  26  proximate the cardiotomy manifold  36  for supporting the pre-filter defoamer material  64 . The pre-filter defoamer material  64  serves to dissipate bubbles on the surface of the cardiotomy blood stream without directly interrupting the flow. Although the pre-filter defoamer material  64  is generally a planar sheet folded as shown best in FIG. 4, it will be understood that a variety of shapes are possible, such as a triangular cross-section. A pre-filter ledge  68  is located on each of the support veins  62  for retaining the pre-filter defoamer material  64  proximate the sucker ports  34 . The pre-filter defoamer material  64  is preferably inserted into the chamber  26  along a build axis “A”. 
     A filter seal ledge  70  is located around the perimeter of the chamber  26  adjacent to the cardiotomy manifold  36 . The filter seal ledge  70  is configured to receive a first blood treatment media assembly  72 . The first blood treatment media assembly  72  is preferably a filtration media  74  supported by a media frame  76 . The media frame  76  is preferably inserted into the chamber  26  along the build axis “A” to engage with the filter seal ledge  70  adjacent to the cardiotomy manifold  36 . As discussed above, the first blood treatment media assembly  72  and cardiotomy manifold forms a first interior space  90  (see FIG.  3 ). 
     A defoamer seal ledge  80  is located along the perimeter of the interior space  26  for receiving a second blood treatment media assembly  82 . The second blood treatment media assembly  82  is preferably a defoamer media  84  retained in a media frame  86 . A support screen  85  may optionally be positioned on one or both sides of the defoamer media  84 . The media frame  86  is preferably configured to engage with the defoamer seal ledge  80 . The filter seal ledge  70  preferably defines a smaller perimeter than the defoamer seal ledge  80  so that the blood treatment media assemblies  72 ,  82  can be easily inserted into the blood treatment cartridge  22  along the build axis “A.” The media  74 ,  84  may be retained in the frames  76 ,  86  by a urethane potting resin, mechanical gasket, UV cured adhesive, or a variety of other methods. The first and second blood treatment media are preferably planar or some other discontinuous configuration that does not create enclosures that can not be viewed by the medical staff. Discontinuous configuration generally refers to media material that does not form a self-contained enclosure or pocket, such as a cylinder or pouch configuration. 
     It will be understood that additional seal ledges may be included along the perimeter of the chamber  26  for receiving additional blood treatment media. The perimeter of the seal ledges preferably increases in size closer to the cartridge flange  28  so that they can be automatically stacked in the chamber  26  along the build axis “A.” In an alternate embodiment, a single seal ledge is provided proximate the cardiotomy manifold  36 . Spacers may then provided along the perimeter of the chamber  26  to maintain the appropriate separation between the blood treatment media  72 ,  82 . 
     The front blood reservoir  32  preferably includes a blood storage section  100  and a drain port  102 . A handle  106  is preferably provided along the top of the front blood reservoir  32 . A series of alternate sampling ports  101  may be provided along the top of the reservoir  32 . It will be understood that the handle  106  may be located along any surface of the modular blood treatment system  20 . The handle  106  may be used for carrying the modular blood treatment system  20 , retaining sampling syringes or sampling lines during use. The blood storage section  100  preferably has a capacity of 2.0-4.0 liters. The treated blood exits the modular blood treatment system  20  via the drain port  102  prior to further handling and treatment, such as regulation of carbon dioxide content, oxygen content and temperature. The blood is ultimately returned to the patient through an aortic cannula inserted into the aorta distal to the heart. 
     A diverter dome  104  may optionally be included in the front blood reservoir  32 . The diverter dome  104  reduces the volume retained in the storage section  100  proximate the outlet port  102 . In the preferred embodiment, the volume of the storage section  100  below the level of the bottom of the second filter media assembly  82  is approximately 300 cc. The diverter dome  104  is configured to define funnel-shaped flow channels shown by arrows  105  on either side toward the outlet port  102  (see FIG.  6 ). The diverter dome  104  preferably has a radius of curvature along a leading edge  109  of about 9.53 mm (0.375 inches). The radius along the leading edge  109  blends into a radius of about 6.35 cm (2.5 inches) and then 7.62 cm (3.0 inches) along the sides toward the trailing edges  107 . The radius of curvature for the trailing edges  107  is about 23.9 mm (0.94 inches). The portion of the diverter dome  104  about 22.6 mm (0.89 inches) long between the two trailing edges  107  is straight. The diverter dome  104  has an overall length of about 12.6 cm (4.95 inches). The distance between the two trailing edges  107  is about 10.1 cm (4.0 inches). 
     As best seen in FIGS. 3 and 6, bottom surface  108  of the funnel-shaped flow channels  105  defines a first flow axis B extending downward at an angle α of about 20 to 24 degrees from horizontal toward the outlet port  102 . The bottom surface  108  preferably defines a second flow axis C having a downward taper of approximately 3 to 7 degrees extending away from the diverter dome  104  and generally perpendicular to the first flow axis B. The resulting flow is away from the diverter dome  104  toward the curved edges  111  on either side of the outlet port  102 . The compound curves along the bottom surface  108  results in a low-turbulent, sheet-flow of blood through the front blood reservoir  32 . 
     FIG. 7 is an exploded view of an alternate modular blood treatment system  120  for treating primarily cardiotomy blood. A front blood reservoir  122  seals the blood treatment media receiving opening  24 ′ on the blood treatment cartridge  22 ′. The cartridge  22 ′ is further discussed below in connection with FIGS. 8-10. It will be understood that the front blood reservoir  122  may be used with the cartridge  22  shown in FIGS. 1-6. The modular blood treatment system  120  is preferably assembled along the build axis A′, as discussed herein. 
     The front blood reservoir  122  preferably has minimal volume for retaining blood. An outlet port  124  diverts the treated blood through a tubing  126  to a secondary blood storage reservoir  128 , such as a flexible pouch or bag. The blood reservoir  128  preferably includes a pair of valves  130 ,  132  for venting air and adding drugs. The venous return stream is delivered directly to the blood reservoir  128  by a venous input line  134 , thereby bypassing the modular blood treatment system  120 . Check valves  131  may optionally be provided in the tubes  126 ,  134 . A cap  136  is preferably located in the venous inlet to seal the chamber  26 ′. In the configuration of FIG. 7, the modular blood treatment system  120  treats only the cardiotomy blood drawn in through the sucker ports  34 ′. 
     FIGS. 8-10 illustrate the cardiotomy blood treatment cartridge  22 ′ of FIG. 7 used with the front blood reservoir  32  of FIG.  1 . Since the venous return stream is not directed through the modular blood treatment system  20 ′, the chamber  92 ′ is significantly compressed as compared to the chamber  92  in FIG.  4 . The compressed chamber  90 ′ reduces the initial break through volume to prime the system  20 ′. The operation of the cardiotomy manifold  36 ′, the first and second blood treatment media assemblies  72 ′,  82 ′ and the front blood reservoir  32 ′ are substantially the same as discussed above. 
     The pre-filter defoamer material  64  is preferably constructed of an open cell, blood compatible, synthetic polymeric foam, such as a reticulated polyurethane foam, that collapses blood foam into liquid blood. The pre-filter defoamer material  64  preferably has 5-20 pores per inch (PPI) and most preferably  10  pores per inch. The pre-filters are preferably treated with an anti-foam compound such as silicone. 
     The filtration media may be constructed of fibrous polyester depth filter. Commercially available filtration media include Dacron polyester felt having a mean aperture size in the range of about 20 to 50 microns, and preferably 30 microns. The filtration media  74  is alternatively constructed of a pleated depth media with a pore size of about 20-40 microns and most preferably with pore size of 30 microns. 
     The defoamer media may be constructed from a woven screen of nylon, polyester or polypropylene. The defoamer media  84  is preferably a mesh with 10-40 pores per inch and most preferably 26 pores per inch. The defoamer media is preferably coated with silicone. The defoamer media  84  is preferably supported on the downstream side by a support screen  85  having pore sizes of about 300-400 microns. A suitable silicone coated, reticulated polyurethane foam with 26 PPI is available from Lydall Westex, located in Hamptonville, N.C. 
     The modular blood treatment systems  20 ,  20 ′,  120  are preferably molded from a clear thermoplastic such as polycarbonate or PET-G (glycol modified polyethylene terephthalate). In a preferred embodiment, the components have a nominal wall thickness of about 2.16 mm to 2.29 mm (0.085 inches to 0.090 inches). The components of the modular blood treatment systems  20 ,  20 ′,  120  are preferably treated with heparin. Heparin is an acid mucopolysaccharide that acts as an antithrombin, anti-thromboplastin, and an anti-platelet factor to prolong clotting time of whole blood. 
     The present modular blood treatment systems  20 ,  20 ′,  120  are designed so that the blood stream is easily visible to the medical staff at all times. Visibility of the blood stream is necessary to monitor for potential filter failure, blood stasis, debris, color and other factors. In particular, the drop tube  42 , the blood treatment cartridge  22  and the front blood reservoir  32  are preferably constructed of a clear plastic material. Consequently, all sides of the pre-filter defoamer material are visible from either the top, back, bottom or sides of the cartridge  22 . The chambers  90 ,  90 ′,  92 ,  92 ′ are visible around the perimeter of the cartridges  22 ,  22 ′ (see FIGS. 3,  4  and  9 ). The contents of the front blood reservoirs  32 ,  32 ′,  122  are visible from the front or sides thereof. 
     FIG. 11 is a schematic illustration of a preferred method  200  of assembling the present modular blood treatment systems  20 ,  20 ′,  120 . A pick and place robot  202  locates a blood treatment cartridge on an assembly carousel  204 . The carousel  204  rotates to a second station  205  where a pick and place robot  206  installs a pre-filter foam material in the blood treatment cartridge along the build axis “A.” A glue dispenser arm  208  applies a bead of glue along the filter seal ledge at station  207  in preparation for insertion of the first blood treatment media. The carousel moves the assembly to station  209  where pick and place robot  210  inserts the first blood treatment media into the chamber along the build axes A or A′. The glue is then cured at a UV curing station  212 . The carousel  204  then moves the partially assembled blood treatment system to an unload cart  213  where a pick and place robot  214  transfers the assembly to a second carousel  216 . 
     A glue dispenser arm  218  at station  217  applies a bead of glue along the defoamer seal ledge in preparation for insertion of the second blood treatment media. A pick and place robot  220  at station  219  installs the second blood treatment media along a build axes A or A′ into the chamber. The glue is cured at a UV curing station  222 . The carousel  216  then rotates to a second glue dispenser arm  224  at station  223  where glue is applied along the cartridge flange in preparation for installation of the front blood reservoir  32 . A pick and place robot  226  at station  225  installs the front blood reservoir along a build axis A or A′. The glue is cured by a UV cure robot arm  228 . The carousel  216  then rotates to station  230  where a pick and place robot  232  removes the modular blood treatment system  20 , where it is forwarded for inspection and packaging. 
     The structure of the modular blood treatment system permits each of the components to be inter-engaged along a single build axis, thus facilitating automated assembly. Additionally, the minimal number of components renders automated assembly a cost-effective alternative. Automated assembly provides a number of key advantages for medical devices of this type. First, assembly is extremely accurate and repeatable. Secondly, the modular nature of the blood treatment system permits a variety of blood treatment media to be substituted automatically during the assembly process. The automated assembly process permits the type of blood treatment media installed in a particular modular blood treatment system to be accurately tracked and recorded. 
     All patents and patent applications referred to above are hereby incorporated by reference. 
     The present invention has now been described with reference to several embodiments described herein. It will be apparent to those skilled in the art that many changes can be made in the embodiments without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but only to structures described by the language of the claims and the equivalents to those structures.