Abstract:
Infusion systems according to the present invention provide a medical fluid infusion system operable at a relatively wide range of flow rates while simultaneously maintaining a high degree of accuracy and predictability through employing specific flow path architecture, flow path dimensional ranges, and pump control parameters, such as voltage, frequency, voltage rise time, pump size and quantity, and controlled restriction of the fluid flow path. Automatic recognition of restrictive elements is employed to facilitate the ease of use of different restrictive elements with a single infusion system and improve patient safety.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/611,452 filed Mar. 15, 2012, entitled Infusion System; U.S. Provisional Application Ser. No. 61/566,542 filed Dec. 2, 2011, entitled Infusion Pump; and U.S. Provisional Application Ser. No. 61/453,909 filed Mar. 17, 2011, entitled Infusion Pump, each of which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to medical infusion systems and related methods and, more particularly, to infusion systems employing a piezoelectric effect for medical and healthcare related applications. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fluid pumps can be driven based on various design principles including the piezoelectric effect. The piezoelectric effect can be employed to indirectly cause fluid flow, for example a piezoelectric driven motor or actuator can be used to linearly displace a plunger to push fluid from a reservoir or to rotate a rotor in a peristaltic-type pump. For example, U.S. Publication Nos. 2009/0124994 to Roe and 2009/0105650 to Wiegel et al., and U.S. Pat. Nos. 7,592,740 to Roe, and 6,102,678 to Perclat teach the application of such technologies to infusion pumps used in the medical and health care industries. 
         [0004]    Alternatively, the piezoelectric effect can be employed to cause fluid flow through the direct manipulation of a fluid chamber or flow path, for example through vibration of an internal surface of a fluid chamber. Such microelectromechanical system, or MEMS, micropumps can be fabricated using known integrated circuit fabrication methods and technologies. For example, using integrated circuit manufacturing fabrication techniques, small channels can be formed on the surface of silicon wafers. By attaching a thin piece of material, such as glass, on the surface of the processed silicon wafer, flow paths and fluid chambers can be formed from the channels and chambers. A layer of piezoelectric material, or a piezoelectric body such as quartz, is then attached to the glass on the side opposite the silicon wafer. When a voltage is applied to the piezoelectric body, a reverse piezoelectric effect, or vibration, is generated by the piezoelectric body and transmitted through the glass to the fluid in the chambers. In turn, a resonance is produced in the fluid in the chambers of the silicon wafer. Through the inclusions of valves and other design features in the fluid flow paths, a net directional flow of fluid through the chambers formed by the silicon wafer and the glass covering can be achieved. 
         [0005]    MEMS micropumps have become an established technology in the inkjet printer industry. Technological developments relating to increased definition and ink throughput for piezoelectric micropumps, or MEMS micropumps, for inkjet printers have achieved more precise printing with smaller ink throughputs. For example, it has become possible to control the ink throughput of inkjet printers employing MEMS micropumps at the picoliter level. Furthermore, in order to address the problems associated with uneven printing in inkjet printers due to the vaporization of gas dissolved in the ink, considerable development has also been directed to providing inkjet printers with structures for degassing the ink. 
         [0006]    MEMS micropumps employing the piezoelectric effect have also been contemplated for use in small and large-volume infusion pumps, i.e. pump systems that are typically employed to infuse fluids, medications, and nutrients into a patient&#39;s circulatory system. For example, with respect to small-volume infusion systems, U.S. Pat. Nos. 3,963,380 to Thomas, Jr. et al.; 4,596,575 to Rosenberg; 4,938,742 to Smits; 4,944,659 to Labbe et al.; 5,984,894 to Poulsen et al.; and 7,601,148 to Keller all describe various micropumps intended for implantation into a patient in order to administer small amounts of pharmaceuticals, such as insulin. Similarly, U.S. Publication No. 2007/0270748 to Dacquay et al. describes a piezoelectric micropump integrated into the tip of a syringe for very low volume delivery of ophthalmic pharmaceuticals to a patient&#39;s eye. 
         [0007]    In contrast to inkjet printers and small-volume infusion micropumps, typical medical infusion pumps must be operable to provide significantly increased fluid throughput. However, as fluid throughput, or fluid flow rates are increased, the potential for the vaporization of dissolved gas correspondingly increases. The vaporization of dissolved gas within the fluid flow paths of infusion pump systems presents a significant health hazard to patients receiving infusions. While the problems associated with the vaporizations of dissolved gas in inkjet printer micropumps, systems in which fluid throughputs are relatively low, has largely been addressed through the development of degassing technologies, satisfactory solutions have not been presented for high-throughput micropumps, such as infusion pumps, used in the health and medical industry. U.S. Publication No. 2006/0264829 to Donaldson and U.S. Pat. No. 5,205,819 to Ross et al. described large-volume infusion systems employing piezoelectric micropumps; however, neither of these systems provides solutions directed to overcoming the problems associated with vaporization of dissolved gas at high fluid throughputs. 
         [0008]    What is needed in the field is a highly accurate infusion pump system that provides a relatively wide range of fluid throughput while reducing or eliminating the risks to patients and increasing medical staff efficiency. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0009]    Infusion systems according to the present invention provide a medical fluid infusion system that achieves a relatively wide range of flow rates while maintaining a high degree of accuracy and predictability. Infusion systems according to the present invention achieve these advances by employing specific flow path architecture, flow path dimensional ranges, and pump control parameters, such as voltage, frequency, voltage rise time, pump size and quantity, and controlled restriction of the fluid flow path for generation of back pressure and controlling such characteristics and parameters relative to one another. 
         [0010]    In certain embodiments, infusion systems according to the present invention achieve automatic recognition of restrictive elements, thereby facilitating the ease of use of different restrictive elements with a single infusion system and improving patient safety. 
         [0011]    In another embodiment of the present invention, the infusion system is incorporated into a fluid bag thereby streamlining the infusion system for bed-side or mobile usage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which 
           [0013]      FIG. 1  is a diagram of an infusion system according to one embodiment of the present invention. 
           [0014]      FIG. 2  is a partial cross-sectional view of a pump core according to one embodiment of the present invention. 
           [0015]      FIG. 3A  is a partial cross-sectional view of a pump core and pump stay according to one embodiment of the present invention. 
           [0016]      FIG. 3B  is a plan view of a pump stay according to one embodiment of the present invention. 
           [0017]      FIGS. 4A and 4B  are graphs of a control voltage applied to an infusion system according to one embodiment of the present invention. 
           [0018]      FIG. 5  is a graph of a control voltage applied to an infusion system according to one embodiment of the present invention. 
           [0019]      FIGS. 6A ,  6 B, and  6 C are graphs of a control voltage applied to an infusion system according to one embodiment of the present invention. 
           [0020]      FIG. 7  is a diagram of a portion of an infusion system according to one embodiment of the present invention. 
           [0021]      FIG. 8  is a diagram of a portion of an infusion system according to one embodiment of the present invention. 
           [0022]      FIG. 9  is a cross-sectional view of a pump according to one embodiment of the present invention. 
           [0023]      FIG. 10  is a partial cross-sectional view of a flow restriction according to one embodiment of the present invention. 
           [0024]      FIG. 11  is a partial cross-sectional view of a restrictive patient line according to one embodiment of the present invention. 
           [0025]      FIG. 12  is a partial cross-sectional view of a flow restriction according to one embodiment of the present invention. 
           [0026]      FIG. 13  is a side elevation view of a portion of a patient line according to one embodiment of the present invention. 
           [0027]      FIG. 14  is a side elevation view of a portion of an outlet connection according to one embodiment of the present invention. 
           [0028]      FIGS. 15A and 15B  are partial cross-sectional views of auto-recognition features according to one embodiment of the present invention. 
           [0029]      FIG. 16  is a side elevation view of alignment features according to one embodiment of the present invention. 
           [0030]      FIG. 17  is a side elevation view of an infusion system incorporating a fluid bag according to one embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
         [0032]    As shown in  FIG. 1 , a generalized overview of an infusion systems or micro-infusion system  10  according to the present invention includes a patient fluid flow path  11  comprising an administrative set or tube set  14 , a pump core  18 , a patient line  20 , and a connector  24 . The administrative set  14  provides fluid communication between an infusion bag  12  and the pump core  18 . The administrative set  14  may include a drop cylinder  16  located between the infusion bag  12  and the pump core  18 . The patient line  20  provides fluid communication between the pump core  18  and the connector  24 . The connector  24  functions as a fluid access point with a patient circulatory system  22 . According to one embodiment of the present invention, all of the components of the fluid flow path  11  of the infusion system  10 , for example, the administrative set  14 , pump core  18 , patient line  20 , and connector  24  are disposable components of the system  10 . The infusion system  10  may also employ a bracket or support structure  13  that functions to secure the system  10  to, for example, a pole or stand. 
         [0033]    As shown in  FIG. 2 , the fluid flow path  11  enters the disposable pump core  18  at the pump core inlet  38  which is in communication with fluid passes  42 . For the sake of clarity, arrows  21  indicate the direction of fluid flow through the pump core  18 . The fluid passes  42  direct fluid through a filter  44 , a pump  36 , a valve  46 , an air trap  48 , a flow meter  50 , and out a pump core outlet  40 . While  FIG. 2  shows the filter  44 , pump  36 , valve  46 , air trap  48 , and flow meter  50  arranged along the flow path  11  in the order herein described, it is contemplated that these components may be arranged in a variety of other sequences along the flow path  11 . 
         [0034]    As shown in  FIG. 2 , the filter  44 , pump  36 , valve  46 , air trap  48 , and flow meter  50  are attached to a surface of a pump core base  52 . In an alternative embodiment, the filter  44 , pump  36 , valve  46 , air trap  48 , and flow meter  50  are located within or partially within the pump core base  52 . The fluid passes  42  are formed through or on a pump core base  52  and provide fluid communication between the components of the pump core  18 . In certain embodiments, the pump core base  52  is formed of a layered structure of, for example, stainless steel such as SUS 304, or other similarly suitable rigid material. In certain embodiments, the fluid passes  42  are formed between the layers of material forming the pump core base  52 . 
         [0035]    With respect to the pump  36 , it is contemplated that a variety of types of pumps, including peristaltic pumps, syringe pumps, and elastomeric pumps, can be employed as the pump  36 . However, in order to achieve the greatest accuracy, compact size, and convenience, the pump core  18  is a microelectromechanical, or MEMS, micropump driven by a piezoelectric effect. In brief, small channels and chambers are formed in a multilayer structure, such as stainless steel, silicon wafer or other similarly rigid material. By attaching a thin piece of material, such as glass, on the surface of the layered structure, flow paths and fluid chambers are formed. A layer of piezoelectric material, or a piezoelectric body such as quartz, is attached to the glass on the side opposite the layered structure. When a voltage is applied to the piezoelectric body, a reverse piezoelectric effect, or vibration, is generated by the piezoelectric body and transmitted through the glass to the fluid in the chamber formed in the layered structure. In turn, a resonance is produced in the fluid in the chamber. Through the inclusions of valves, flow restrictions, and/or other design features in the fluid flow paths, a net directional flow of fluid through the chamber formed by the layered structure and the glass covering can be achieved. Examples of such pumps and related control systems are described in greater detail in the Assignee&#39;s copending U.S. patent application Ser. No. 12/972,348 entitled Infusion Pump and U.S. patent application Ser. No. 12/972,374 entitled Patient Fluid Management System, the contents of which are each herein incorporated in their entirety. 
         [0036]    The filter  44  may be formed of, for example, a 20 micrometer stainless steel mesh and functions, in part, to prevent foreign particles from entering the pump  36  and flow meter  50 . The valve  46  functions to prevent the free flow of fluid through the pump and thereby through the fluid flow path  11 . The valve  46  may be formed of the same material or a different material as the pump core base  52  and may be formed separately or integrally with the pump core base  52 . The valve  46  is configured, for example, to close or otherwise prevent flow of fluid when the pump  36  is not active or otherwise in operation. The air trap  48  is formed of a membrane filter such as, a Durapore membrane filter and is configured to trap bubbles of approximately 1 millimeter and larger. 
         [0037]    The flow meter  50  may comprise a variety of known flow meters. For example, the flow meter  50  may be configured to determine fluid flow rates by employing a heater that heats the fluid being monitored and senses the flow of the heated fluid downstream of the heater. Such flow meters are available from Sensirion AG of Switzerland and Siargo Incorporated of the United States of America and are described in greater detail in at least U.S. Pat. No. 6,813,944 to Mayer et al. and U.S. Publication No. 2009/0164163, which are herein incorporated by reference. Alternatively, the flow meter  50  may be configured to employ two pressure sensors positioned on each side of a constriction within the fluid flow path  11 . Fluid flow rates are determined by the relative difference between the pressure sensors and changes thereof. Alternatively, the flow meter  50  may function based on the principles of distortion. For example, flow rates may be determined by measuring the distortion of a membrane having an orifice that is interposed in a fluid flow path. In certain embodiments, compensation for temperature and viscosity for the fluid for which a flow rate is being determined will be performed with the assistance of databases and the controller  28 . 
         [0038]    The pump stay  26  of the infusion system  10  houses the circuitry for providing power to the pump  36 , for providing power to the flow meter  50 , and for providing electrical communication of data from the flow meter  50  back to the controller  28 . Hence, as shown in  FIGS. 3A and 3B , in one embodiment of the present invention, the pump stay  26  employs a plurality of electrodes  30  for establishing electrical communication with the pump core  18 . A first electrode  30  is associated with an electrical circuit configured to provide power with, for example 1 to 180 volts, to the pump  36  of the pump core  18  from the controller  28 . A second and third electrode  30  are associated with an electrical circuit configured to provide power with, for example, a reference voltage of one to five volts to the flow meter  50  and to return a analogue or digital data signal from the flow meter  50  to the controller  28 . In certain embodiments an amplifier is employed to amplify the data signal from the flow meter. 
         [0039]    In certain embodiments of the present invention, the pump stay  26  incorporates memory and display features. In such a hybrid pump stay embodiment, the pump stay  26  need not be permanently networked or otherwise in continuous electrical communication with the controller  28 . The pump stay  26  is operable to store and execute the infusion protocol. The hybrid pump stay is further operable to display certain information, for example, current operational data such as flow rates and system pressure, as well as data relating to the infusion protocol. 
         [0040]    In operation, medical staff may carry a compact, mobile, control unit that employs an operator interface such as a touch screen or key pad. In order to program or prepare the hybrid pump stay  26  for execution of an infusion protocol, medical staff temporarily establishes electrical communication between the mobile controller and the hybrid pump stay  26  by, for example, connecting a wired coupling between the mobile controller and the hybrid pump stay  26  or by establishing wireless communication between the mobile controller and the hybrid pump stay  26 . Medical staff may then manually enter or download a preconfigured infusion protocol to the hybrid pump stay  26 , confirm the entry or download accuracy; start the infusion protocol, and then disconnect the mobile controller from the hybrid pump stay  26 . 
         [0041]    In this manner a hospital or other facility may utilize fewer control units to operate a greater number of infusion systems  10 . Furthermore, in accordance with current trends in healthcare safety, while the hybrid pump stay allows for observation of certain real-time and infusion protocol data, the hybrid pump stay  26  does not allow for infusion protocol adjustment without the mobile controller being present. In other words, the hybrid pump stay  26  does not allow for the patient or other non-authorized person to adjust the infusion system  10  at the bed-side unless a mobile controller is also present. 
         [0042]    As shown in  FIGS. 3A and 3B , the pump core  18  and the pump stay  26  are formed such that the components can be physically attached to one another by employing elements such as recesses and deflectable binders that are complementary to one another. Such mating systems are described in further detail in the Assignee&#39;s copending U.S. patent application Ser. No. 12/972,348 entitled Infusion Pump and U.S. patent application Ser. No. 12/972,374 entitled Patient Fluid Management System, the contents of which are each herein incorporated in their entirety. Electrical communication is established between pump core  18  and the pump stay  26  through complementary electrodes  30  formed on a surface  32  of the pump core  18  and a surface  34  of the pump stay  26 . In order that the pump core  18  and the pump stay  26  are mated in the proper orientation relative to one another, i.e. that the corresponding electrodes are properly mated to each other, the electrodes  30  on the pump core  18  are positioned in an asymmetric orientation that correspond to the asymmetric positioning of the electrodes  30  of the pump stay  26 , as shown in  FIG. 3B . In such a configuration, if the pump core  18  and the pump stay  26  are mated improperly, no electrical connection is established between the pump core  18  and the pump stay  26  and the infusion system  10  will be inoperable and/or provide the user with a notification or alert. In an alternative embodiment, asymmetric structural or visual features may be employed in the pump core  18  and the pump stay  26  such that it is obvious to a user that there is only one possible orientation for mating the pump core  18  and the pump stay  26 . For example, the pump core  18  and the pump stay  26  may both be asymmetrically shaped or may employ correspondingly colored indicators making obvious the proper orientation of the components. 
         [0043]    As shown in  FIG. 1 , in certain embodiments of the present invention, the controller  28  employs a power receiver  54  for receiving a universal 100-250 volt, alternating current. The current is, in turn, converted to, for example, a 2 to 7 volt, direct current by a power converter  56 , such as those well known in the art for use in mobile personal computers. The controller  28  further employs a battery  58  for providing power to the infusion system  10  when power is not received through the power receiver  54 , for example during transport of the system  10  while in use or during a power outage at a healthcare facility. 
         [0044]    The controller  28  also employs a user interface  60  having a screen for user viewing and a user input portion for entering the desired infusion information and/or adjusting infusion parameters. The user interface  60  may be in the form of a touch operable screen and/or may employ data entry buttons or keyboards. For example the user interface  60  may be a liquid crystal touch panel display and may employ a reset or reboot button. Additionally, the controller  28  may employ one or more communications ports  64  in the form of local area network or universal serial, or other similar communication connection ports. Exemplary controllers  28  are further described in the Assignee&#39;s copending U.S. patent application Ser. No. 12/972,348 entitled Infusion Pump and U.S. patent application Ser. No. 12/972,374 entitled Patient Fluid Management System. 
         [0045]    The controller  28  further employs a central processing unit, CPU, or other similar computing device operable to store and run software and/or firmware for operation of the infusion system  10 . Broadly speaking such software may employ a first component configured to analyze a real-time or present infusion state or situation, and a second component configured to realize data inputs or instructions enter by medical staff through the user interface  60 , determine needed adjustments, and provide the necessary signals to the system to realize the adjustments. In operation, a flow rate is input through the user interface  60  or is provided through the communication ports  64  of by medical staff. The software will break down or adopt the input flow rate relative to the specification of the infusion system  10  and then select the proper pump  36  or pumps  36  that match the demand. For example, in certain embodiments of the present invention, the software first recognizes the maximum potential flow rate of the infusion system  10 . Then the software calculates if the demand is within the specifications of the system  10 . If it is within the specification of the system  10 , the software calculates which pump and/or fluid chambers will be activated and how the same will be operated in order to achieve such flow rate(s). 
         [0046]    Once an infusion therapy is initiated, the software will monitor the information from flow meter  50  and calculate the amount of real-time fluid infused or accumulated fluid. If the ideal infusion schedule and the amount of real-time fluid infused or accumulated fluid is dissociated or not within a previously specified range of deviation, the software will calculates the new flow rate to required carry on the therapy and/or finish the therapy in order to achieve the ideal infusion schedule. For example, if (ideal infusion schedule)-(real-time infused or accumulated fluid) is negative, the flow rate is increased. If the difference is positive, the flow rate is decreased. 
         [0047]    In certain embodiments of the infusion system  10  of the present invention, the infusion system  10  is operable to provide infusion flow rates that range of, for example, 0.1 to 1000 milliliters per hour. In order to provide such a relatively broad range of flow rates, some or all of the following parameters of the infusion system  10  are manipulated: (1) the frequency of the current provided to the pump  36 ; (2) the voltage of the current provided to the pump  36 ; (3) the manner in which the voltage is applied to the pump  36 , i.e. the shape of the voltage curve applied to the pump  36 ; (4) the size and number of the pumps  36  or the size and number of the fluid chambers employed within a single pump  36 ; and (5) the back pressure applied downstream of the pump  36  in the fluid flow path  11 . Generally speaking, the frequency of the current provided to the pump  36  is in the range of, for example, 0 to 300 Hertz or 0 to 200 Hertz, and the voltage provided to the pump  36  is in the range of, for example, 50 to 200 volts or 80 to 140 volts. 
         [0048]    As shown in  FIG. 4A , the shape of the voltage curve, i.e. the shape of the curve showing the voltage applied to the pump  36  relative to the time in which the voltage is applied to the pump  36  approximates a rectangular wave form  70 . However, in certain circumstances when the voltage is applied as indicated in  FIG. 4A , a leading edge  66  of the rectangular wave form  70  over shoots or progresses beyond the desired maximum voltage desired thereby resulting in a leading edge  55  having a voltage spike  68 , as shown in  FIG. 4B .  FIG. 4B  is an enlarge view of area  65  of the leading edge  66  shown in  FIG. 4A . In certain circumstances, the voltage spike  68  may adversely affect the fluid flow rate and/or damage the pump  36 . For example, the voltage spike  68  may cause a fracture or breakage of the piezoelectric body of the pump  36 . 
         [0049]    Hence, in order to address this potential problem, in certain embodiments of the present invention, a sloping, curved or otherwise softened leading edge  66  of the rectangular wave form  70  may be employed, as shown in FIGS.  5  and  6 A- 6 C. In other words, the leading edge  66  is changed from a vertical line indicating an approximately single, instantaneous step up in voltage to an alternatively shaped line indicating a more gradual increase in voltage over a time “t”. The time t representing the time period from when voltage is initially increased to when the desired maximum voltage is achieved. The time t may, for example, range from 0.325 to 0.925 milliseconds, 0.425 to 0.825 milliseconds, or may be 0.625 milliseconds. 
         [0050]    For example, if all other control parameters are maintained consistent and the rectangular wave form  70 , shown in  FIG. 6B , is considered as generating a reference flow rate, increasing the time t such as shown in  FIG. 6A  results in a relative decrease in the flow rate. Conversely, decreasing the time t such as shown in  FIG. 6A  results in a relative increase in the flow rate. 
         [0051]    With respect to the size and number of the pumps  36 , it is noted that the larger the pump  36 , typically the lower the accuracy of the fluid flow rate of the pump  36 . Accordingly, in order to achieve both relatively high and low flow rates from the infusion system  10 , it may be desirable to employ multiple pumps  36  of varying sizes. In such a multi-pump  36  infusion system  10 , each individual pump  36  will be associated with a separate piezoelectric body. Alternatively stated, each pump  36  is independently activated by the controller  28 . As shown in  FIG. 7 , in certain embodiments of the present invention, the various pumps  36  are in fluid communication with one another in a parallel manner. Alternatively, as shown in  FIG. 8  the infusion system  10  may be configured to locate the pump  36  having the same specification, for example the same size, shown as boxes of the same size in  FIG. 8 , in series and locate the pump  36  having different specifications in parallel. 
         [0052]    An infusion system  10  according to the instant embodiment employ pumps  36   a ,  36   b ,  36   c  . . .  36   n  having different specifications, e.g. sizes. The system  10  may further employ n number of each of the pumps  36   a ,  36   b ,  36   c  . . .  36   n . Each of the pumps  36   a ,  36   b ,  36   c  . . .  36   n  operable to achieve a maximum flow rate of max( 36   a ), max( 36   b ), max( 36   c ) . . . max( 36   n ), respectively. Accordingly, the maximum flow rate of the system  10  is calculated according to the formula: 
         [0000]      Maximum Flow Rate=(Max(36 a )( n ))+(Max(36 b )( n ))+ . . . (Max(36 n )( n )) 
         [0053]    The minimum flow rate for such an infusion system  10  would be the lowest possible flow rate achieved by activating only the smallest pump  36 . For example, an infusion system composed of (1) two pumps  36  having maximum flow rates of 300 ml/h; and (2) two pumps  36  having maximum flow rates of 100 ml/h; and (3) two pumps  36  having maximum flow rates of 50 ml/h would be operable to generate flow rates ranging from a maximum flow rate of 1000 ml/h to the minimum flow rate of one of the 50 ml/h flow rate pump  36 , for example 0.1 ml/h. 
         [0054]    The pump  36  has a dimension, for example, a length and/or width, in the range of, for example, 4 to 18 millimeters; 7 to 15 millimeters; or 7 millimeters; or 15 millimeters. 
         [0055]    With respect to the control of the back pressure applied downstream of the fluid chamber(s) of the pump  36  in the fluid flow path  11 , back pressure may be generated in one or a combination of various manners. Broadly speaking, the smaller the diameter of the fluid flow path  11  and the greater the length of the reduced diameter, the greater the resulting resistance and back pressure generated. For example, in certain embodiments of the present invention, as shown in  FIG. 9 , fluid flow resistance and thus back pressure is increased by forming a pump  36  with a narrow outlet channel  72  relative to the pump  36  inlet channel  74 . 
         [0056]    In another embodiment, shown in  FIG. 10 , the resistance is provided in all or a portion of the patient line  20 . Wherein a distance L 1  is representative of the distance from a rigid coupling  74  of the pump core  18  to the beginning of the reduced diameter portion  76  of the patient line  20 . In embodiments employing an elastic patient line  20  formed of a material such as vinyl chloride, it is desirable to minimize the distance L 1 . A distance L 2  is representative of the length of the reduced diameter portion  76 , and a diameter L 3  is representative of the diameter of the reduced diameter portion  76 . The formula (L 2 /L 3 ) 2  is representative of the relationship between a fluid flow rate and the distance L 2  and the diameter L 3 . 
         [0057]    In yet another embodiment of the present invention, increased back pressure is achieved by increasing the surface area of the lumen of all or a portion of the patient line  20 . For example, the patient line  20  may employ an irregular shaped lumen  78 . Stated alternatively, tubing may be employed that has a lumen that is not circular in cross-section, as shown in  FIG. 11 . As the surface area of the lumen  78  increases relative to the volume of the lumen, the resistance and back pressure provided by the tubing increases. 
         [0058]    In another embodiment of the present invention, increased back pressure is achieved through employing restrictive couplings within or at either end of the patient line  20 . For example, as shown in  FIG. 12 , a restrictive coupling  80  having a lumen  82  reduced diameter or other restrictive feature is employed as the connector or interface between patient line  20  and the connector  24  leading into the patient&#39;s circulatory system 22 . 
         [0059]    In view of the above-described flow control parameters, one embodiment of the present invention may achieve a minimum flow rate of, for example, 0.01-0.1 milliliters per hour, by employing, for example, the patient line  20  having an irregularly shaped lumen  82 ; a single 7 millimeter pump  36  to which approximately 80 volts is applied with a time t of approximately 0.825 and approximately 5-25 Hertz. A maximum flow rate of, for example, 100-1000 milliliters per hour, may be achieved by employing, for example, a standard patient line  20  not having an irregularly shaped lumen  82 ; a single 15 millimeter pump  36  to which approximately 140 volts is applied with a time t of approximately 0.425 and approximately 200 Hertz. 
         [0060]    In view of the above-described embodiments in which the patient line  20  provides back pressure, it is further contemplated that a single infusion system  10  may be operable to function with different flow rate ranges by employing different restrictive patient lines  20  having different restrictive characteristics. Hence, in order to provide enhanced patient safety and ease of use, in certain embodiments of the present invention, infusion system  10  automatically recognizes and compensates for different restrictive or non-restrictive patient lines  20 . For example, in operation, medical staff may set up an infusion system  10  by, in part, connecting an administrative set  14  to the inlet  38  of the pump core  18  and a patient line  20  to the outlet  40  of the pump core  18 . According to one embodiment of the present invention, an interface between the outlet  40  of the pump core  18  and the patient line  20  allows for the infusion system  10  to identify the exact patient line  20  that is connected to the pump core  18  and to thereby use stored information regarding the specific patient line  20  that is connected in order to determine the implementation of the infusion protocol. 
         [0061]    As shown below in  FIG. 13 , an end portion  86  of the patient line  20  employs one or more protrusions  88 . The protrusions  88  are arranged so as to be complementary to receivers  90  employed in an outlet connector  92 , shown in  FIG. 14 . The outlet connector  92  is attached to or incorporated into the pump core  18  and functions as one side of the interface between the patient line  20  and the pump core  18 . The complementary side of the interface between the patient line  20  and the pump core  18  is the end portion  86  of the patient line  20 . When the end portion  86  of the patient line  20  is connected to the outlet connector  92  of the pump core  18 , the protrusions  88  are inserted into complementary receivers  90  located in the outlet connector  92  of the pump core  18 . The protrusions  88  and receivers  90  are arranged so that the patient line  18  can be connected to the pump core  18  in only one rotational alignment. Once inserted into the receivers  90  of the pump core  18 , the protrusions  88  actuate one or more switches. 
         [0062]    In one embodiment, actuation of the switches by the protrusions  88  results in establishing, disrupting, or manipulating the resistance of one or more electrical circuits and thereby allows for a change in an electrical state of the one or more circuits. The specific change in electrical state of the circuit or circuits resulting from the connection of a specific patient line  20  is recognized by the controller  28  as being an indication that the specific patient line  20  is being employed in the infusion system  10 . 
         [0063]    In order for a single pump core  18  to receive and automatically recognize a variety of different patient lines  20 , the outlet connector  92  employs receivers  90  that receive any of the combinations of protrusions that are present in the compatible patient lines  20 . Alternatively stated, there may be more receivers  90  present on the outlet connector  92  than there are protrusions  88  present on any single patient line  20 . The different patient lines  20  are distinguishable from one another by the different combinations; characteristics, such as length, width, and cross-sectional shape; and locations of the protrusions  88  employed on the end portion  86  of the patient line  20 . 
         [0064]    In one embodiment, the protrusions  88  activate dual in-line packaged, DIP, switches located within the receivers  90  of the outlet connector  92 . In another embodiment, as shown below in  FIGS. 15A and 15B , the switches are in the form of reversibly transposable elements  96  located within the receivers  90  of the outlet connector  92  that are displaced by insertion of the protrusion  88  into receivers  90 . 
         [0065]    In another embodiment, a portion of the protrusion  88 , for example a tip of the protrusion  88  or one or more circumferences around the protrusion  88  are coated or otherwise made of a conductive material, such as metal. Insertion of the protrusion  88  into the receiver  90  functions to establish, disrupt, or manipulate the resistance of an electrical circuit, a portion of which is located within the outlet connector  92 . In yet another embodiment of the present invention, upon insertion into the receivers  92 , the protrusions  88  break or otherwise manipulate conductive elements, such as thin wires, that form an electrical circuit, a portion of which is located within the outlet connector  92 . The breaking of the conductive elements establishes, disrupts, or manipulates the resistance of an electrical circuit, thereby providing a signal to controller  28  that allows the system to identify the specification of the attached tube set. 
         [0066]    In order to assist the medical staff in connecting the patient line  20  and the pump core  18  which, in certain embodiments is operable to be connected in only one rotational orientation, one or more alignment elements  98  may be employed on the patient line  20  and the pump core  18 . For example, as shown in  FIG. 16 , the alignment element  98  may be in the form of axial markings or coloration along a length of the patient line  20  and the outlet connector  92  and/or the pump core  18 . Alternatively, the alignment element  98  may be a physical feature of the patient line  20  and the outlet connector  92 , for example, the size and shape of one or more of the protrusions  88  and receivers  90  may function as an alignment element  98 . 
         [0067]    While the interface of the patient line  20  and pump core  18  has been described above as a longitudinally, insertion-based connection, in certain embodiments of the present invention, a threaded or rotational-based connection is employed alone or in combination with any of the above described features. 
         [0068]    According to one embodiment of the present invention, as shown in  FIG. 17 , certain components of the infusion system  10 , for example the pump core  18  or, alternatively, the pump core  18  and pump stay  26 , are incorporated into a fluid bag  102 . In certain embodiments, the fluid bag further incorporates an input port  134  for the augmentation of fluids into the interior of the bag  102 . The input port  134  may be formed of, for example a non-inflectional injector, such as a sure plug or a clave connector. 
         [0069]    Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.