Abstract:
A warming system for large volume dialysis bags provides a basin configured to position the bags in a low thickness, wrinkle free configuration for maximum heat transfer. A centrally positioned thermal sensing element may provide accurate temperature measurement of interior bag temperature by a correction process and a weight sensor may automatically control the heater when the bag is in place.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to warming systems for medical fluids and in particular to a warming system adapted to large fluid volumes used in peritoneal dialysis. 
         [0002]    Peritoneal dialysis is often used in the treatment of patients with severe kidney disease as an alternative to hemodialysis. While hemodialysis removes waste and excess water from the blood using an external semipermeable membrane as a substitute for the kidney, peritoneal dialysis uses for this purpose the patient&#39;s peritoneum membrane that lines the abdominal cavity. Generally, a large quantity of sterile fluid is introduced into the abdomen (approximately 5 liters) where it resides to collect waste products from the proximate blood vessels. The water is then withdrawn bringing with it waste products. This process is repeated on a regular basis. 
         [0003]    Infusing the large amount of dialysate needed for this procedure can uncomfortably change the core temperature of the patient, particularly when the dialysate is at room temperature, substantially below normal body core temperatures. Properly warming the dialysate is complicated by the fact that it is normally maintained within a sterile plastic bag having relatively low thermal conductivity and low resistance to elevated temperatures and by the large volume of liquid which requires significant heat input to effect the necessary temperature change and which can be subject to thermal stratification. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a warming device for dialysate or similar fluids having a basin shape to flatten the dialysate bag and maximize an interface surface between the bag and the heated walls of the basin. By reducing the length of the thermal path through the dialysate and providing a large heating area contacting a broad surface of the bag, effective, fast and uniform warming of the dialysate can be obtained with gentle heat. 
         [0005]    Specifically the invention provides, in one embodiment, a warming system for infusible liquids having an upwardly open basin sized to receive a flexible polymer bag holding the infusible liquid. The basin provides a substantially horizontal floor having upwardly sloped opposed ends and sides adapted to support the flexible polymer bag in contact with the floor, end, and sides so as to reduce a vertical thickness of the bag while maintaining a substantially wrinkle free contact between the bag and the basin. A heater element is attached to the basin to conduct heat through the basin and bag into the contained infusible liquid when the bag is held within the basin. 
         [0006]    It is thus one feature of at least one embodiment of the invention to provide a warming system that can rapidly warm large volumes of dialysate to a uniform temperature by providing a heating surface that promotes a high surface to volume configuration of the dialysis bag. 
         [0007]    The heater element may contact each of the floor, ends, and sides to heat each of these surfaces and to conduct heat through each of these surfaces into the infusible liquid. 
         [0008]    It is thus a feature of at least one embodiment of the invention to make use of the ends and sides of the basin both for shaping of the bag and heating of the liquid. 
         [0009]    The area of the floor, ends, and sides together may be an area of greater than 100 square inches. 
         [0010]    It is thus a feature of at least one embodiment of the invention to allow rapid heating of a dialysate with relatively low temperature heaters by increasing the heat transmission interface. 
         [0011]    The basin may include a conductive metal heat spreader and the heater is attached to an outer surface of the basin. 
         [0012]    It is thus a feature of at least one embodiment of the invention to eliminate hot spots at the heater interface that would promote temperature variations within the dialysate and reduce the efficiency of the heat transfer. 
         [0013]    The basin may be mounted within a housing open at a top to expose an upper surface of the basin. 
         [0014]    It is thus a feature of at least one embodiment of the invention to provide a unit that may be conveniently placed on a tabletop for home healthcare use or other setting including a clinic or hospital. 
         [0015]    The invention may provide a dialysate sensor controlling the heater to be on only when a predetermined amount of dialysate is in the basin. 
         [0016]    It is thus a feature of at least one embodiment of the invention to provide for automatic liquid heating without the need to manipulate controls. 
         [0017]    The basin may be attached to the housing by spring elements allowing the basin to move under the weight of a contained bag and may further include an electrical switch sensing this movement to control the heater. 
         [0018]    It is thus a feature of at least one embodiment of the invention to provide for a highly reliable sensor for the presence of the dialysis bag within the warming unit to provide for one or both of automatic heating of an inserted bag and automatic shutoff of the unit when the bag is removed without additional action by the user. 
         [0019]    The system may further include a thermal sensor protruding upward from a floor of the basin to contact a bag placed within the basin. 
         [0020]    It is thus a feature of at least one embodiment of the invention to provide for a temperature sensor for automatic control of the heating element that may be closely coupled to the interior dialysate temperature. Upward projection of the temperature sensor ensures good contact between the bag and the sensor. 
         [0021]    The thermal sensor may be substantially centered within the basin. 
         [0022]    It is thus a feature of at least one embodiment of the invention to provide a sensor that closely couples to average dialysate temperature as represented by a center volume of the dialysate. 
         [0023]    The thermal sensor may include a thermal isolation element separating the thermal sensor from the basin. 
         [0024]    It is thus an object of at least one embodiment of the invention to permit juxtaposition of the heating element and sensor in close proximity without interference. 
         [0025]    The thermal isolation element may be a thermally insulating ring supporting the thermal sensor in a hole through the basin. 
         [0026]    It is thus a feature of at least one embodiment of the invention to provide a simple mechanism for integrating a thermal sensor for the dialysate into the basin. 
         [0027]    The temperature sensor may include a pair of temperature sensing elements that may be independently read and combined to deduce temperature. 
         [0028]    It is thus a feature of at least one embodiment of the invention to provide for greater precision in temperature measurement by obtaining different temperature samples of the dialysate and further to provide an ability to detect temperature sensor failure when the different temperature measurements deviate beyond a predetermined threshold. 
         [0029]    The warming system may further include user controls for providing a temperature display of a temperature of the infusible liquid and a correction circuit communicating with the display and the temperature sensor to add a temperature offset to a reading of the temperature sensor for display on the display, the temperature offset based on an empirically determined thermal resistance between the heater element and the infusible liquid. 
         [0030]    It is thus a feature of at least one embodiment of the invention to provide an accurate indication of the dialysate temperature using an external temperature probe preserving the sterility of the dialysis bag system. By modeling the thermal circuit of the dialysis bag and thermal sensor interface, accurate dialysate temperatures may be deduced from outside the bag. 
         [0031]    The control system may communicate between the heater and the thermal sensor for controlling the heater according to a reading of the thermal sensor and a desired temperature set point. 
         [0032]    It is thus a feature of at least one embodiment of the invention to permit user adjustment within a narrow range of the dialysate temperature using feedback control. 
         [0033]    The control system may control the heater to match a temperature from the temperature sensor plus the temperature offset determined by the correction circuit to the desired temperature setpoint. 
         [0034]    It is thus a feature of at least one embodiment of the invention to employ the same thermal modeling for accurate control of the dialysate temperature. 
         [0035]    The basin may include cut out portions exposing an under surface of the bag when the bag is supported in the basin, the cut out portions positioned to receive a user&#39;s hands for grasping the bag for placement or removal of the bag into or from the basin. 
         [0036]    It is thus a feature of at least one embodiment of the invention to provide a highly ergonomic warming system allowing an individual to easily manage large dialysis bags. 
         [0037]    The edges of the basin may provide for a downwardly extending rim providing a drip edge preventing water overflowing from the basin from traveling along and under surface of the basin. 
         [0038]    It is thus a feature of at least one embodiment of the invention to anticipate and manage possibly large dialysate spills and to divert any such spills from the heater system. 
         [0039]    The heater may be a flexible silicone heater pad adhered to an under surface of a metallic basin. 
         [0040]    It is thus a feature of at least one embodiment of the invention to provide a heater that may closely conform to a curved basin surface used in the present invention. 
         [0041]    These particular features and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0042]      FIG. 1  is a front perspective view of the warming system of the present invention showing an upwardly open basin for receiving a bag of sterile dialysate as may be grasped at the ends by a user and placed in the basin with a user&#39;s hands insertable into cutouts in the basin for ease of handling the bag; 
           [0043]      FIG. 2  is a fragmentary cross-section along line  2 - 2  of  FIG. 1  showing attachment of the heater pad to an outer surface of the basin, a spring mounting of the basin within a housing for sensing of placement of the bag, and a centrally mounted, thermally-isolated external temperature sensor for deducing liquid temperature within the bag; 
           [0044]      FIG. 3  is a top plan view of the basin of  FIG. 1  showing positioning of a silicone heating pad to provide a gentle heat through a basin floor, end walls and sidewalls; 
           [0045]      FIG. 4  is a fragmentary cross-section similar to  FIG. 2  taken along line  4 - 4  of  FIG. 3  showing cutouts in the basin exposing an under surface of the bag for simplified bag placement and removal; 
           [0046]      FIG. 5  is a flowchart of a program that may be executed by a controller board of the warming system; and 
           [0047]      FIG. 6  is a front elevational view of a control panel provided by the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0048]    Referring now to  FIG. 1 , a warming system  10  of the present invention may provide for an upwardly open, concave basin  12  having a generally horizontal floor  14  surrounded by upwardly sloping and opposed sidewalls  16  and upwardly sloping and opposed end walls  18 . The end walls  18  join with the sidewalls  16  to provide a continuous watertight surface terminating at an upper rim  20 . Generally the basin  12  will be fabricated from a ductile conductive metal such as aluminum to provide a heat spreading feature as will be described below. 
         [0049]    Referring now also to  FIG. 2 , basin  12  is sized to receive and substantially fully support a dialysis bag  22  holding, for example, five liters of infusion liquid  23 . The infusion liquid  23  may, for example, be a saline solution for peritoneal dialysis. 
         [0050]    As is understood in the art, the dialysis bag  22  may be constructed of a flexible transparent plastic material, such as a vinyl, and fabricated by joining two sheets  24  of the material at a peripheral seam  26  to provide within the seam  26  an enclosed pocket into which sterile infusion liquid  23  may be held. 
         [0051]    The flexible material of the dialysis bag  22  permits the dialysis bag  22  to adopt a variety of different volumetric configurations and the shape of the basin  12  is designed to promote a particular configuration maximizing heat transfer to the contained infusion liquid  23 . In particular, the basin  12  is shaped to support the dialysis bag  22  with one lower sheet  24  of the dialysis bag  22  lying in close abutment to the floor  14 , sidewalls  16 , and end walls  18  of the basin  12  and so that the seams  26  between the sheets  24  lie generally along a horizontal plane displaced to be approximately symmetrically located between the sheets  24  of the dialysis bag  22  to substantially eliminate buckling or wrinkling of the lower sheet  24  and minimizing a vertical thickness of the infusion liquid  23  within this constraint. In this way, contact between the dialysis bag  22  and the heater  28  may be substantially maximized and the thermal path to any volume element of the infusion liquid  23  from the basin  12  reduced. 
         [0052]    Referring momentarily to  FIGS. 2 and 3 , a heater  28  may be attached to an underside of the basin  12  to attach in the regions of the floor  14 , the sidewalls  16 , and the end walls  18  so that each may conduct heat directly into the supported dialysis bag  22 . The heater  28  may be substantially continuous over the surfaces except for sections near the area of the corners of the basin  12  at the joining of end walls  18  and sidewalls  16  to facilitate manufacturing and except for small openings for basin supporting structure, thermal sensors and the like as will be described below. Generally heater  28  contacts the basin  12  over a large area so that a low temperature (gentle) heat implemented over the portions of the basin  12  contacting the dialysis bag  22   10  rapidly heat the contained infusion liquid  23  without large temperature differences. For this purpose, the area of the heater  28  will typically be greater than 50 square inches and preferably greater than 100 square inches or more. 
         [0053]    A suitable heater  28  may be a silicone rubber electric heater. As is understood in the art, a silicone rubber electric heater provides a resistive conductive element, for example an etched foil or wire, embedded in a silicone rubber mat and is broadly commercially available from multiple vendors. 
         [0054]    Referring now to  FIG. 2 , the basin  12  may be held within a housing  30  as supported on one or more spring elements  32 , for example helical compression springs. The housing  30  maybe fabricated of an injection molded thermoplastic or the like and may include a lower surface having downwardly extending feet  31  for support on a table or the like. The housing  30  may have vertically extending sidewalls  33  above a horizontally extending base wall  35  and may be open at its upper surface to expose the upper surface of the basin  12  for receipt of the dialysis bag  22  within the basin  12 . The weight of the dialysis bag  22  on the basin  12  compresses the basin downward against the spring elements  32  and into the housing  30  activating a switch  34  indicating a presence of a dialysis bag  22  that may require heating. The switch  34  may be a simple mechanical microswitch, an optical switch, a strain gauge, a magnetic switch or the like providing an electrical signal that may communicate with the controller board  36  held within the housing  30 . 
         [0055]    The controller board  36  may also communicate with the heater  28  so that the heater  28  may be activated only when a dialysis bag  22  is in place in the basin  12 . This weight-based sensing system provides for robust and positive identification of the placement of a dialysis bag  22  in the basin  12  in contrast, for example, to optical bag sensors which may require more sophisticated processing to detect the dialysis bag  22  and overcome the transparent nature of the dialysis bag  22  and the contained infusion liquid  23 . 
         [0056]    Referring still to  FIG. 2 , controller board  36  may also communicate with a temperature sensor pair  38  positioned approximately in the center of the floor  14  to be near a center region of the liquid  23  contained in the dialysis bag  22 . This location provides a good measure of the average temperature of the liquid  23  in the dialysis bag  22 . 
         [0057]    The temperature sensor pair  38  may be mounted on a heat collector plate  40  that projects upward from a plane of the floor  14  of the basin  12  to provide a mesa-form pushing upward slightly on the lower sheet  24  into the dialysis bag  22  to ensure good contact therewith without substantially decreasing the thermal contact between the dialysis bag  22  and the floor  14  of the basin  12 . The heat collector plate  40  and temperature sensor pair  38  are thermally isolated from the heater  28  and the floor  14  by means of this offset and an aperture cut in the heater  28  and floor  14  and separated from the heat collector plate  40  by a thermally insulating spacer ring  42 . 
         [0058]    By promoting thermal contact between the temperature sensor pair  38  and the dialysis bag  22  through sheet  24  and distancing thermal proximity of the temperature sensor pair  38  and the heater  28 , a localized sensing region  44  projecting into the infusion liquid  23  may be created allowing better assessment and control of the liquid temperature. T 
         [0059]    A rear surface of the temperature sensor pair  38  may be embedded in a thermally insulating material  46  reducing the temperature drop between the liquid  23  and the sensor pair  38  promoting the ability to detect internal liquid temperature with an external temperature sensor pair  38  as will be discussed below. 
         [0060]    Referring to  FIGS. 1 ,  3 , and  4 , the end walls  18  of the basin  12  and corresponding regions of the housing  30  may include cutout  50  sized to receive hands  52  of a user when the hands  52  are positioned to grasp the dialysis bag  22  at its ends along its greater length as a user places the dialysis bag  22  down into the basin  12  or lifts it there from. The cutouts  50  expose a portion of an under surface of the dialysis bag  22  in the basin  12  simplifying its gripping by the hands  52  during removal or insertion. 
         [0061]    Referring to  FIGS. 1 and 4 , the rim  20  of the basin  12  and regions around the cutout  50  may have drip edges  56  formed therein, the drip edges  56  being downwardly extending edges that prevent water overflowing out of the basin  12  from traveling downward along the lower surface of the basin  12 , as adhered thereto by surface tension, into the region of the controller board  36 . 
         [0062]    Referring now to  FIGS. 1 and 6 , an outer front surface of the housing  30  may provide for a control panel  60  having an alphanumeric display  62 , for example, displaying a current temperature of the infusion liquid  23  or desired setpoint of the infusion liquid  23 , setting switches  64  allowing changing of the setpoint of temperature control of the liquid  23 , a mode switch  66  changing a mode of display  62 , and a ready indicator  68  indicating that the temperature of the liquid  23  is at its proper setpoint, as will be described. The switches  64  and  66  may, for example, be membrane switches of a type known in the art and the ready indicator a light emitting diode. 
         [0063]    Referring now to  FIGS. 2 and 5 , the controller board  36  may include a microcontroller  70  or similar processor of a type well known in the art and including generally a processor, memory and various I/O circuits. The microcontroller  70  may receive signals from the thermal sensor pair  38  the switch  34  and the switches  64  and  66  and may provide control signals to the display  62  and the ready indicator  68  and the heater  28 . An internal program  72  executed by the microcontroller  70 , as indicated by decision block  74 , may first detect whether a dialysis bag  22  is in place in the basin  12  (as shown in  FIG. 2 ) using the signal from the switch  34 . If not, an internal timer used for determining the age of the dialysis bag  22  (with respect to how long it has been heated) is reset, and the ready light  68  and the heater  28  are turned off (if they are on) as indicated by process block  76 . 
         [0064]    If a dialysis bag  22  is in place, the heater  28  may be turned on as indicated by process block  78 , for example, by means of solid-state switches such as an SCR on the controller board  36  as controlled by the microcontroller  70 . At this time a bag age timer is started as indicated by process block  80  that will keep track of how long the dialysis bag  22  has been in place and heated. 
         [0065]    At process block  82 , the temperature of the temperature sensor pair  38  is read and the separate temperature readings compared to see if they are beyond the predetermined range indicating an error at process block  84 . If an error is indicated the heater may be turned off and in error indicated on the display  60 , otherwise the temperature values are averaged and this temperature is corrected for an empirically determined temperature offset representing a difference between the temperature of the contained liquid  23  and the temperature at the sensor pair  38  caused by the thermal resistance therebetween. This temperature difference will generally be added to the temperature read at the temperature sensor pair  38  at process block  84 . 
         [0066]    At decision block  86 , a determination is made to see whether the temperature of the contained liquid  23  within the dialysis bag  22  is at a desired setpoint, the latter which may be entered by the user through the control panel  60  by conventional data entry routines not shown. This comparison considers the temperature at the temperature sensor pair  38  as corrected by the temperature offset described above. The range of set points entered by the user may be limited to those representing a safe range for the infusion liquid  23 . 
         [0067]    If at decision block  86  the deduced temperature of the infusion liquid  23  is below a predetermined range with respect to the desired setpoint, the program  72  loops back to decision block  74 , otherwise the program proceeds to process block  87  and the heater is turned off and the ready indicator  68  illuminated indicating that proper temperature has been obtained per process block  88 . 
         [0068]    At any time during this process, the mode switch  66  may be activated to allow the user to switch display  62  between the temperature of the contained liquid  23 , the desired setpoint and the bag age. The temperature of the contained liquid  23  is corrected with the temperature offset as described above. 
         [0069]    Referring to  FIGS. 1 and 2 , the controller board  36  may receive power from a line cord  100  passing into the housing  30  and having an associated line switch as is understood in the art. Multiple temperature switches  102  may be placed against the under surface of the basin  12  to monitor over temperature of the basin  12  independent of the operation of the controller board  36  to disconnect the heater  28  when over temperature conditions exist. 
         [0070]    Ideally the upper surface of the basin  12  will be substantially bare to provide improved thermal conductivity; however, it will be understood that a thin protective layer of plastic materials and/or anodization may be provided on the surface without unduly decreasing the effectiveness of the device. By providing a broad area, low-temperature heating of a substantially flattened dialysis bag  22 , rapid and accurate temperature control of the contained liquid  23  may be effected. 
         [0071]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, “below”, “clockwise”, and “counterclockwise” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0072]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0073]    References to a controller, computer or processor or its equivalent can be understood to include one or more computational devices including microprocessors, field programmable gate arrays, and application specific integrated circuits that can implement state aware logic and that can communicate in a stand-alone and/or a distributed environment(s), and can thus be configured to communicate via wired or wireless communications with other processors, where such one or more processor can be configured to operate on one or more processor-controlled devices that can be similar or different devices. Furthermore, references to memory, unless otherwise specified, can include one or more processor-readable and accessible memory elements and/or components that can be internal to the processor-controlled device, external to the processor-controlled device, and can be accessed via a wired or wireless network.