Abstract:
A lightweight, easy-to-assemble, and portable cart for the performance of peritoneal dialysis is disclosed. The cart includes a top shelf, bottom shelf, and at least four adjustable connecting members or legs. The top shelf has a top surface designed to receive a PD cycler, and at least one hook to hang bags of solution. Various components of the cart include a plastic and foaming agent additive.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Application Ser. No. 61/232,931, filed on Aug. 11, 2009, which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates peritoneal dialysis carts and related systems. 
     BACKGROUND 
     Dialysis to support a patient whose renal function has decreased to the point where the kidneys can no longer sufficiently function is well known. Generally, two principal dialysis methods are utilized: hemodialysis; and peritoneal dialysis. 
     In hemodialysis, the patient&#39;s blood is passed through an artificial kidney dialysis machine. A membrane in the machine acts as an artificial kidney for cleansing the blood. Because the treatment is extracorporeal, it requires special machinery and generally, a visit to a center or hospital that performs the treatment. 
     Peritoneal dialysis (hereafter “PD”) was developed to provide an alternative therapy to hemodialysis. PD utilizes the patient&#39;s own peritoneum (a membranous lining of the abdominal cavity) as a semi-permeable membrane. With its good perfusion, the peritoneum is capable of acting as a natural semi-permeable membrane. 
     PD periodically infuses sterile aqueous solution into the peritoneal cavity. This aqueous solution is called PD solution or dialysate. Diffusion and osmosis exchanges take place between the solution and the blood stream across the peritoneum. These exchanges remove the waste products that the kidneys normally excrete. The waste products typically consist of solutes like urea and creatinine. The kidneys also function to maintain proper levels of other substances, such as sodium and water, which also need to be regulated by dialysis. The diffusion of water and solutes across the peritoneal membrane during dialysis is called ultrafiltration. 
     In continuous ambulatory PD, a dialysis solution is introduced into the peritoneal cavity utilizing a catheter, normally placed by a doctor. An exchange of solutes between the dialysate and the blood is achieved by diffusion. 
     Certain PD machines are automated. These machines are called cyclers. Cyclers are generally designed to automatically infuse, dwell, and drain PD solution to and from the patient&#39;s peritoneal cavity. A cycler is particularly attractive to a PD patient because it can be used at night while the patient is asleep. This frees the patient from the day-to-day demands of continuous ambulatory PD during his/her waking and working hours. 
     The treatment typically lasts for several hours. It often begins with an initial drain cycle to empty the peritoneal cavity of spent dialysate. The sequence then proceeds through a succession of fill, dwell, and drain phases that follow one after the other. Each phase is called a cycle. 
     Unlike hemodialysis machines, which are typically operated by doctors or trained technicians, PD machines may be operated by the patient. Many PD patients travel which require those patients to take their PD apparatus with them in a car, train, or plane. 
     SUMMARY 
     In general, the invention relates to portable peritoneal dialysis carts and related systems. 
     In some aspects of the invention, a cart includes a top shelf, a bottom shelf, and at least four connecting members which attach to the top and bottom shelves. 
     The top shelf has a top surface designed for a cycler to sit on top. The top shelf may include indentations that correspond with the feet or bottom surface of the cycler, so that the cycler cannot easily slip off of the surface of the top shelf. The top shelf may additionally comprise one or more tapered hooks or fingers for loading and hanging dialysis solution bags therefrom. The hooks may hold and support bags that hold between approximately 1 liter and 6 liters of solution. 
     In some embodiments, at least four connecting members connect to the bottom surface of the top shelf and the top surface of the bottom shelf. The connecting members are approximately parallel to each other, and the top shelf is approximately parallel to the bottom shelf. The connecting members may be adjustable so that the height of the top shelf may be raised or lowered to optimize treatment for the patient. 
     Wheels or casters may be connected to the bottom surface of the bottom shelf so that the cart may be easily wheeled on a variety of floor surfaces. 
     In certain embodiments, the shelves and connecting members are manufactured by injection molding of plastic with a foaming agent additive. This method reduces the cost of manufacturing significantly and allows that cost-savings to be passed along to the patient. Furthermore, the cart and its components made of injection-molded plastic with a foaming agent additive are significantly more lightweight than many counterparts made by standard injection molding. However, the cart remains sturdy and able to withstand the weight of the cycler and solution bags without undue stress or loss of balance. 
     The cart is easy to assemble and disassemble, and may be assembled and disassembled without any tools. Color in the plastic and foaming agent eliminates the need for painting the cart, thereby increasing the sterility and cost savings of the cart. Furthermore, the fully-assembled cart weighs less than approximately 20 pounds. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an apparatus and portable cart for performing peritoneal dialysis; 
         FIG. 2  is a perspective view of the portable cart of  FIG. 1 ; 
         FIG. 3  is a perspective view of a molded dialysis solution bag hook of the portable cart of  FIG. 1 ; 
         FIG. 4  is a perspective view of a connecting member of the portable cart of  FIG. 1 ; 
         FIG. 5  is a perspective view of a tube end of the connecting member of  FIG. 4 ; 
         FIG. 6  is a perspective view of another tube end of the connecting member of  FIG. 4 ; 
         FIG. 7  is a perspective view of a washer or caster nut that is used between a caster and a bottom shelf of the portable cart of  FIG. 1 ; 
         FIG. 8  is an exploded view of the portable cart of  FIG. 1 ; and 
         FIG. 9  is a perspective view of an adjustable connecting member that can be used in the portable cart of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a portable PD cart  10  includes a top shelf  2  that has a top surface designed to accommodate seating a PD cycler  4 . The top shelf  2  may include one or more indentations  12  that correspond with the feet or bottom surface of the cycler  4 . The one or more indentations  12  secure the cycler  4  to the top shelf  2  so that the cycler  4  does not slip around on, or off of, the surface of the top shelf  2  as the cart  10  is rolled along a floor surface. Other non-slip materials may be adhered to or included in the top surface of the top shelf  2  to accomplish the same goal. For example, non-slip tracking may be laid down on the top surface, the top surface may further comprise a course material that inhibits slipping, or guard rails may line the edges of the top surface. 
     The top shelf  2  may additionally comprise one or more tapered hooks  16  for loading and hanging dialysis solution bags therefrom. Further referring to  FIG. 3 , the hooks  16  are formed by a cut-out of the top shelf  2 , and have a tapered portion  26  that facilitates hanging at least one solution bag  24  therefrom. The at least one hook  16  is of a width and material strength sufficient to support a solution bag  24  that holds between approximately 1 liter and 6 liters of solution. In certain embodiments, the length of the hook is approximately between 1 and 2 inches. In one aspect, the length of the hook is approximately 1.5 inches. In other embodiments, the width of the hook is approximately between 0.5 and 1.5 inches. In one aspect, the width of the hook is approximately 1 inch. In certain embodiments, the depth of the hook is approximately between 0.2 and 1 inch. In one aspect, the depth of the hook is approximately 0.5 inches. The top shelf  2  may further include a handle  14  cut out for the user to easily grasp and move the cart. 
     Referring to  FIG. 2 , at least four connecting members  6  connect to the bottom surface of the top shelf  2  and to the top surface of the bottom shelf  8 . When the cart  10  is assembled, the connecting members  6  are approximately parallel to each other and perpendicular to the top and bottom shelves  2 ,  8 , and the top shelf  2  is approximately parallel to the bottom shelf  8 . The connecting members  6  may be adjustable in length so that the height of the top shelf  2  may be raised or lowered to optimize treatment for the patient. For example, a cart may come with several sets of connecting members  6 , each set of a different length that may be used depending upon the height of the patient&#39;s bed. In other embodiments, the connecting members  6  themselves may be adjustable. Referring to  FIG. 9 , for example, the connecting members  6  may comprise two separate pieces meeting at interface  11 , one that slides into the other, and can lock to each other at various different lengths. One of ordinary skill in the art can readily apply various extension and retraction technologies to the connecting members to achieve adjustable components. 
     Referring to  FIGS. 4 ,  5 , and  6 , the connecting member  6  has two ends  20 ,  22 . The two ends  20 ,  22  press fit, or are otherwise secured, into the connecting member  6 . In the embodiment shown, the two ends  20 ,  22  are different. However, for manufacturing and user simplicity, the two ends  20 ,  22  can also be the same as one another. In the embodiment shown, however, the end  20  is designed to attach to the bottom surface of the top shelf  2 , and the end  22  is designed to attach to the top surface of the bottom shelf  8 . To facilitate the connections to the shelves, end  20  is molded with threading on the inside  28 , and end  22  is molded to have threading on the outside  24 . As shown in  FIG. 7 , the bottom shelf  8  has recessed portions  30  on the top surface of the shelf  8  into which end  22  is designed to thread. Similarly and as shown in  FIG. 8 , the top shelf  2  has recessed portions  32  on the bottom surface of the shelf  2  into which end  20  is designed to thread. The connecting members  6  are therefore press fitted together and screwed into the shelves  2 ,  8  without necessitating any tools, complex mechanisms, or excessive physical strength. 
     As seen in  FIGS. 2 and 8 , casters  18  are attached to the bottom surface of the bottom shelf  8 . These casters  18  allow the cart  10  to roll across a floor surface and may further include a braking mechanism (not shown) to lock the casters  18  into place and prevent the cart from rolling. Different size wheels and/or casters  18  can be used to facilitate or inhibit the portability of the cart. For example, larger wheels or casters may be used for deeper threaded carpet and smaller wheels or casters for hardwood, tile or marble surfaces. Washers or caster nuts  34  may be used between the bottom surface of the bottom shelf  8  and the casters  18  to facilitate caster  18  (and cart  10 ) movement. 
     As discussed above, the various embodiments of the present application are designed to hold and support a PD cycler and solution bags. PD cyclers generally weigh between approximately 20 and 50 pounds. For example, the Liberty® cycler weighs approximately 32 pounds. As different size or weight solution bags are used (described above), as solution bags fill and empty throughout a treatment cycle, and as bags are loaded or unloaded from the cart, the cart remains properly weighted so that the cart does not become unstable or tip. 
     The various components of the cart, including but not limited to, the top shelf  2 , bottom shelf  8 , connecting members  6 , hooks  16 , handle  14 , connecting member ends  20 ,  22 , and washer or caster nuts  34  may all be made via injection molding using plastic and a foaming agent. In some embodiments, the plastic is a thermoplastic. In other embodiments, plastics that may be used include but are not limited to: polyphenylene oxide, polystyrene, polycarbonate, acrylonitrile butadiene styrene, and/or equivalents thereof. The plastic is self-extinguishing, or “VO Rated” plastic. In one aspect, the plastic used is Noyrl plastic (e.g., 215X). Foaming Agents, also known as Blowing or Nucleating Agents, eliminate sink marks, reduce density, shorten cycle time and reduce total production costs. In extrusion and injection molding, foaming agents save on material weight and lower total cost. They also improve extrusion rates by increasing the volume that can be processed per extruder in a given period of time, and endothermic foaming agents absorb heat and improve injection molding cycle time. Foaming agents that may be used comprise a concentration suitable for the plastics resins mentioned above. In one aspect, the foaming agent is Cel-Span® 899PS by Phoenix Plastic. In certain embodiments, the foaming agent is between approximately 1-10% of the total material mix. In one aspect, the foaming agent is between approximately 2-2.5% of the additive-plastic material mix. This method of manufacture allows the assembled cart to be both sturdy and lightweight. In various embodiments, the assembled cart (or all of the pieces of the disassembled cart taken together) weighs less than 20 pounds. 
     This method further allows the mold cavities to be filled with foaming plastic without the necessary high pressures of injection molding with other materials. The lower pressures of this method of manufacture also eliminate hardened steel molds or other high pressure molds (which are more costly) necessary for high pressure injection molding materials. Lower tooling costs and shorter run times are just a few examples of cost savings associated with this method. Color in the plastic and foaming agent eliminates the need for painting the cart, thereby increasing the sterility and cost savings of the cart. 
     The foregoing description is to be understood as being representative only and is not intended to be limiting. Alternative systems and techniques for making and using the compositions and devices of the invention and for practicing the inventive methods will be apparent to one of ordinary skill in the art and are intended to be included with the accompanied claims.