Abstract:
A medical pump or the like provides for a multi-function flow monitor that provides for capacitive plates positioned on opposite sides of the IV line to sense changes in the electrical environment within the IV line to deduce IV line pressure, the presence of IV fluid bubbles, the presence of the IV line within the pump, and/or correct pump operation. Each of these conditions may he determined by different analysis of the capacitance across the capacitive plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 14/104,371 filed Dec. 12, 2013 and hereby incorporated by reference, which claims the benefit of U.S. provisional application 61/736,778 filed Dec. 13, 2012 and hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to medical pumps for the delivery of medicines to patients under controlled rates and dosages and in particular to a pump sensor for characterizing this flow. 
         [0003]    Medical pumps, such as syringe pumps or peristaltic infusion pumps, are known for computer-controlled delivery of medication or contrast agents (henceforth drugs) to patients over a period of time. Typically the drug is delivered in a syringe (for a syringe pump) or a flexible bag (for peristaltic infusion pump) that may be connected to an IV line attached to a needle for insertion into the patient. When a nurse or other health care professional ministering to the patient receives the drug, the healthcare professional reviews the drug description for correctness and enters the desired dose and rate into the pump. The syringe or IV line must then be mechanically connected to the pump mechanism and the mechanism activated to begin pumping. Failure to properly install, set up or connect the drug container properly to the pump can raise safety issues. 
         [0004]    During the pumping operation, the drug flow may be automatically monitored by one or more sensors that detect proper operation of the medical pump. Different such sensors may detect, for example, flow rate, line pressure, the presence of bubbles in the drug and the like. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a sensor for medical pumps that may simultaneously detect combinations or sub combinations of: flow rate, IV line pressure, IV line bubbles, and/or proper seating of the IV line within the pump. In a principal embodiment, opposed capacitor plates are installed on opposite walls of the IV line. The distance between the two plates is greater than the outer diameter of the IV line. Pressure changes in the IV line are manifest in low amplitude capacitance changes as more fluid fills the space between the two plates with increased pressurization of the IV line. Bubbles are detected by the same sensor by more abrupt capacitance changes caused by fundamental changes in the permittivity of the dielectric between the plates (air vs. fluid). Proper seating of the IV line may be provided by detecting a fluid filled IV line between the plates such as abruptly affects the intervening permittivity before pumping. 
         [0006]    It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. Ali of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]      FIG. 1  is a simplified perspective representation of a medical pump employing the sensor of the present invention for an IV line that may be contained within a portion of the pump coverable by a pump door; 
           [0008]      FIG. 2  is a block diagram of the principal elements of the pump including a processor for monitoring the sensor of the present invention using a stored program; 
           [0009]      FIG. 3  is a fragmentary front elevational view of the sensor of the present invention showing two capacitor plates flanking an IV line inserted therebetween; 
           [0010]      FIGS. 4 a  and 4 b    are simplified front elevational views similar to that of  FIG. 3  showing passage of an air bubble between the capacitor plates; 
           [0011]      FIGS. 5 a  and 5 b    are simplified top cross-sectional views of the IV line and capacitor plates of  FIG. 3  showing increased, percentage of the cross section being filled with fluid with increased pressure of the IV line; 
           [0012]      FIGS. 6 a  and 6 b    are simplified top cross-sectional views similar to  FIGS. 5 a  and 5 b    showing displacement of the IV line between the capacitor plates prior to proper seating by closure of the door of  FIG. 1 ; 
           [0013]      FIG. 7  is a plot of capacitance change across the capacitor plates of  FIGS. 4-6  showing interpretation of those changes by the program of the processor of  FIG. 2  for identifying proper seating of the IV line, pressure in the IV line, and bubbles in the IV line; 
           [0014]      FIG. 8  is a plot similar to  FIG. 7  showing fluctuations caused by operation of the positive displacement pump that may be counted to deduce flow rate; and 
           [0015]      FIG. 9  is a process flow diagram of a program and circuitry executed by the medical pump of  FIG. 1  for the processing of the capacitive signal into various sensed conditions of pressure, bubble presence, IV line presence, and pump operation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Referring now to  FIG. 1 , a medical pump  10 , for example an infusion pump, may provide for a housing  12  having a front opening door  14  that may reveal a pump compartment  16 . An IV line  20  may be threaded through the pump compartment  16  for pumping and monitoring of an IV fluid from a sterile connector  23  to an IV bag  22  through the IV line  20  to be delivered to through a sterile connector  24  to a hypodermic needle  25  or similar connection to a patient (not shown). The IV line  20  may be a highly compliant material that may be sterilizable and is, preferably, non-Pyrogenic, non-DEHP and latex-free. One such material is silicone rubber which provides for high compliance as will be desired for pressure sensing to be described below. Another example is non-DEHP PVC material. 
         [0017]    The pump compartment  16  may hold peristaltic pump elements  26  through which the IV line  20  may be threaded for controllably pumping liquid therethrough according to techniques understood in the art. Generally such pumps operate with positive displacement to provide a precise flow amount with each pump cycling. A sensor element  28  per the present invention may be placed above and/or below the pump elements  26  to also receive the IV line therein. An inside of the door  14  covering the pump compartment  16  may provide for seating features  30  that will ensure proper seating of the IV line  20  within the peristaltic pump elements  26  and sensors  28  when the door  14  is closed, as will be described further below. 
         [0018]    Referring now to  FIG. 2 , the pump  10  may include a controller  32  (which may be a microprocessor based circuit) having a memory  34  for holding a stored operating program  36  controlling operation of the pump  10  according to a desired dose and rate of desired drug delivery through the IV line  20 . In particular, the controller  32  may use the data in the memory  34  to control the pump elements  26  in the pump compartment  16 , for example, by successively compressing the pump elements  26  about the IV line  20  for peristaltically moving fluid through the IV line  20 . 
         [0019]    The controller  32  may further communicate with the sensor element  28  of the present invention for receiving a signal therefrom. Generally, the controller  32  executing the stored program  36  may interpret the signal from the sensor element  28  to monitor pressure in the IV line  20  installed in the pump compartment  16  for detection of blockage or other pumping irregularities. In addition, the signal from the sensor element  28  may be monitored to detect bubbles in the IV line  18  and to detect proper seating of the IV line  20  in the sensor element  28 , as will he described below. 
         [0020]    The controller  32  may also communicate with a display screen  38  for displaying various programming and operating parameters of the medical pump  10  and a switch array  40  for inputting data, for example, for programming or initiating or stopping of the pumping action into the medical pump  10  for use by the controller  32 . 
         [0021]    The controller  32  may also communicate with an alarm  41 , for example an audio, display, or wireless transmitter system for communicating an alarm to a user. 
         [0022]    Referring now to  FIG. 3 , the sensor element  28  may provide a first set of opposed conductive plates  42   a  and  42   b  in parallel opposition across a diameter of a vertically extending IV line  20  inserted therebetween in the pump compartment  16 . Each of the conductive plates  42   a  and  42   b  may be connected by leads  44  to circuitry that may measure the capacitance between these plates  42   a  and  42   b  using conventional techniques, for example a frequency counting oscillator employing the capacitance between the plates  42   a  and  42   b  to control an electrically resonant circuit oscillator frequency, or an integrator using the capacitance between the plates  42   a  and  42   b  to affect an integrator time constant and measuring the value of the integration at a fixed time period after a reset signal. 
         [0023]    The conductive plates  42   a  and  42   b  are preferably mounted to the housing  12  in fixed opposition across the diameter of the IV line  20  with a separation slightly larger than the diameter of an unpressurized IV line  20 . It will be understood generally that the capacitance between the plates  42   a  and  42   b  will be a function of their area and their separation, which remains substantially fixed and the effective dielectric constant (permittivity) between the plates which will be determined by the material of the IV line  20  and predominantly by the liquid contained therein and the diameter of the IV line  20 . 
         [0024]    Referring now to  FIG. 4 a   , during normal operation of the pump  10 , the space within the tube  20  between the plates  42   a  and  42   b  will be occupied primarily with a drug whose principal component is water having a known and substantially constant permittivity. As a result, during normal operation, there will be a substantially constant dielectric between the plates  42   a  and  42   b . Referring to  FIG. 4 b   , however, a bubble  52  passing through the tube  20  between the plates  42   a  and  42   b  will substantially change the dielectric between the plates  42   a  and  42   b  based on the significant differences between the dielectric constant of water and air. This bubble  52  will cause an abrupt decrease in the capacitance between the plates  42   a  and  42   b.  Generally the permittivity of air is approximately 1 whereas the permittivity of water is approximately 80.4. 
         [0025]    Referring now to  FIG. 5   a,  when the drug within the IV line  20  between the plates  42   a  and  42   b  is at a low pressure, the walls of the IV line  20  may be contracted to a relatively smaller diameter under the natural elasticity of the material of the IV line  20 . In contrast, as shown in  FIG. 5 b   , an increase in pressure will expand the cross-section of the tubing  20  to a larger diameter decreasing the airspace between the plates  42   a  and  42   h  and supplanting it with a higher permittivity of water. Generally, this change in capacitance will be both slower and more subtle than the changing capacitance provided by the bubble  52  of  FIG. 4 b    as discussed above. This effect provides a measure of pressure in the IV line  20 . 
         [0026]    Referring now to  FIG. 6 a   , a rearward wall of the IV line  20  between the plates  42   a  and  42   b  may be spaced from a wall support  56  when the tube  20  is not fully inserted into the pump compartment  16  and therefore not fully inserted between the plates  42   a  and  42   b.  Proper location of the tube  20  between the plates  42   a  and  42   b,  as shown in  FIG. 6 b   , will move the tube  20  back against the wall support  56  to be centered between the plates  42   a  and  42   b . This centering will increase the capacitance between the plates  42   a  and  42   b  by increasing the high permittivity dielectric material centered between the plates  42   a  and  42   b  in contrast to the incomplete insertion of  FIG. 6 a    thereby allowing a determination of proper seating of the tube  20  between the plates  42   a  and  42   b  from the capacitance therebetween. Generally this change in capacitance between the states of  FIGS. 6 a  and 6 b    may be readily distinguished from a bubble  52  per the example of  FIGS. 4 a  and 4 b    by its significant increase in capacitance for an extended duration as opposed to decreasing capacitance significantly for a short period. In addition, the changing capacitance caused by the change in states shown in  FIGS. 6 a  and 6 b    will occur by design before actual pumping of liquid (proper closure of the door being a predicate for pump operation) further differentiating it from pressure changes or included bubbles. 
         [0027]    Referring now to  FIG. 7 , an example capacitance signal  60  as a function of time monitored by the controller  32  of  FIG. 2  may therefore detect three conditions, detecting at a time t 1  a closure of the door caused by an increase in capacitance more than the predetermined threshold before operation of the pump. At time t 2 , a bubble may be detected as distinguished by a rapid decrease and then rapid increase in capacitance over a short period of time (e.g., less than ten seconds). Changes in pressure within the IV line may be determined over time range t 3  (e.g., tens of seconds) after time t 1  by slowly changing values in the capacitance (with increased capacitance values indicating increased pressures). 
         [0028]    Referring now to  FIG. 8 , the capacitance signal  60  may be further analyzed to deduce the periodic pressure fluctuations caused by operation of pump elements  26  possibly augmented by frequency domain filtering at the pump cycle rate or synchronous filtering in phase with pump operation. Detecting these periodic pressure fluctuations of a predetermined amplitude can confirm operation of the pump elements  26  and counting the fluctuations can provide a measure of flow rate based on known volume displacement in each pump cycle of the pump elements  26 . It will be appreciated that pressure sensing techniques other than capacitive sensing may also be used to deduce this flow rate including for example techniques that measure IV line deformation by optical or mechanical means. 
         [0029]    A pressure range may be developed to indicate a desired pumping pressure and to sound the alarm in the event that the pressure exceeds or falls below this range. Likewise the presence of a bubble  52  may sound the alarm and stop the pump operation. Pump operation may be prevented from starting if the door has not been closed (indicated by not properly loaded tubing) as indicated by the detection at t 1 . 
         [0030]    Referring now to  FIG. 9 , the controller  32  may implement a capacitive sensing block  62  operating as described above to measure the capacitance between the capacitive sensor plates  42  as discussed. A measured capacitance signal  60  may then be processed in a number of different signal chains to reveal the desired information about IV fluid flow. The capacitance signal  60  may, for example, be received by a window averager  66  operating to take an average value of a predetermined time window of the measured capacitance signal  60 , for example 10 seconds, to provide a smoothing of the capacitance value that may indicate the average pressure of the IV liquid free from influence by short-term perturbations. Alternative methods of providing the smoothing may include, for example, a low pass filter. 
         [0031]    The output from the averager  66  may be provided to a calibration table  68  or the like converting capacitance values to internal pressure of the IV line  20  as may be empirically determined for particular types of IV tubing. The output of the calibration table  68  may then provide a pressure value  70  which may be received by an alarm logic matrix  72 , for example, monitoring the pressure value  70  to detect overpressure indicating, for example, blockage of the IV line  20 , or underpressure, for example, indicating an exhaustion of the liquid medicine from the IV bag  22 . Either of these conditions may result in the presentation of an alarm to the user and may deactivate pumping by the pump. 
         [0032]    The capacitance value  64  may alternatively or in addition be provided to a high pass filter  74  that accentuates the short-term perturbations in the capacitance signal  60  caused by a bubble. Adaptive filters or autocorrelation circuits or the like may be used alternatively as is understood in the art. The output of the high pass filter  74  is then provided to a threshold circuit  76  which determines whether any perturbation in the capacitance signal  60  is of the type such as would indicate a bubble has passed between the capacitive plates. It will be understood that the high pass filter removes the “DC” value of the capacitance signal  60  to permit this threshold circuit  76  to operate with a substantially constant threshold regardless of slowly changing overall pressure of the IV fluid. A bubble detection output  78  may also be provided to the alarm logic matrix  72  to provide an alarm or deactivate the pump. 
         [0033]    The capacitance signal  60  may alternatively or in addition be sent to threshold circuit  80  detecting a threshold that will be exceeded when an IV line  20 , even with low pressure, is in place in the pump housing between the plates  42 . An IV line presence signal output  82  may also be provided to the alarm logic matrix  72  to provide either an alarm or to disable portions of the pump when an IV line  20  is not in place. 
         [0034]    Capacitance signal  60  may finally be provided to a synchronous demodulator  84 , for example, receiving a signal from the pump elements  26  to detect perturbations in the pressure shown in  FIG. 8  caused by pump operation. Alternative demodulation systems may employ bandpass filtering and threshold detecting or the like. A pump confirmation signal  86  provided from the synchronous demodulator  84  is also received by the alarm logic matrix  72  to provide an alarm in the event of pump failure if the pump is not operating when otherwise indicated. 
         [0035]    It will be appreciated that this sensor may be used to provide measures of all of these conditions as has been described above or any subset of these conditions. Further it will be appreciated that the sensor may be incorporated into the pump elements  26 , for example, or that multiple such sensor elements  28  may be used. 
         [0036]    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”, and “below” 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. 
         [0037]    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. 
         [0038]    References to “a microprocessor” and “a processor” or “the microprocessor” and “the processor,” can be understood to include one or more microprocessors 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. Generally it will be appreciated that the microprocessor  32  may be accompanied with ancillary discrete circuitry as necessary and that the functions described above may be implemented wholly in discrete circuitry or in a combination of discrete circuitry and a microprocessor. 
         [0039]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.