Abstract:
A syringe pump provides a controlled metering of the medicament from a syringe by movement of the syringe plunger while also measuring flow from the syringe with a flow sensor. Simultaneous monitoring of flow command implicit in control of the syringe plunger and an actual flow provides additional safety and detection of irregularities in the delivery of the medicament.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional application 61/552,300 filed Oct. 27, 2011 and hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to syringe pumps as used for medical purposes and in particular to a syringe pump that provides improved monitoring of its operation. 
     Syringe pumps are known for use to administer certain amounts of fluid, for example medication or contrast agents (henceforth medicaments), to a patient over a period of time. Such pumps use a syringe comprised of a plunger sliding in a syringe tube. The plunger includes a piston-like seal that fits tightly against the inner surface of the syringe tube. Movement of the plunger decreases the volume contained in the syringe tube between the plunger seal and an outlet of the syringe tube to provide a positive displacement pumping action. 
     The syringe pump includes a syringe driver which provides movement of the plunger with respect to the tube via an electric motor. The motor can provide precise and slow movement of the plunger to deliver intravenous medications over several minutes without the need for a human operator. Flow rate may be controlled by knowing the geometry of the syringe and accurately controlling movement of the plunger. 
     The syringe pump may be connected to the patient by a standard intravenous (IV) line terminated with a hypodermic needle or the like. 
     SUMMARY OF THE INVENTION 
     The present invention provides a syringe pump with improved flow rate monitoring that may be used to detect problems with the IV line or its connection to the patient downstream from the syringe. Monitoring the flow rate deduced independently of known motion of the syringe, allows problems with obstructed flow or disconnection of the IV line to be determined. Monitoring the flow rate as well as other flow conditions such as air bubble in flow and pressure is made practical by use of sensors on the downstream tubing. Flow monitoring can be performed from outside the IV line to preserve the sterile environment of the IV line or may be integrated into the IV line in a pre-sterilized unit. 
     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. All 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 
         FIG. 1  is a block diagram of a syringe pump according to the present invention and showing a syringe and a syringe driver, the latter communicating with a control computer also receiving signals from downstream IV line sensors; 
         FIG. 2  is a simplified perspective view of one embodiment of the syringe driver of the present invention showing lateral engagement of the IV line with the downstream sensors by pressing the IV line into a channel; 
         FIG. 3  is a simplified cross-sectional representation of a through-tubing pressure sensor suitable for use with the present invention; 
         FIG. 4  is a simplified cross-sectional representation of a through-tubing air bubble sensor suitable for use with the present invention; 
         FIG. 5  is a simplified cross-sectional representation of a through-tubing flow rate monitor employing two pressure sensors of the type shown in  FIG. 3 ; 
         FIG. 6  is a simplified cross-sectional representation of a through-tube flow rate monitor employing ultrasound; 
         FIG. 7  is a simplified cross-sectional view of an integrated in-tube flow sensor employing a rotating mechanical element; 
         FIG. 8  is a simplified cross-sectional view of an integrated in-tube flow sensor employing heating and thermal sensing elements; 
         FIG. 9  is a simplified cross-sectional representation of a through-tube flow rate monitor employing optical sensing elements; 
         FIG. 10  is a fragmentary view of the needle-end of the IV tubing showing an alternative embodiment employing a remotely located pressure sensor; and 
         FIG. 11  is a flow chart of a program executable by the controller of  FIG. 1  for monitoring the operation of the syringe pump. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a syringe pump  10  of the present invention may employ a syringe  12  similar to a typical hypodermic syringe and having a syringe tube  14  with a first open end  16  receiving a plunger  18 . One end of the plunger  18  within the syringe tube  14  is connected to a piston seal  20  (for example of an elastomeric material) fitting snugly within the volume of the syringe tube  14 . 
     A second end  22  of the syringe tube  14 , opposite the open end  16 , connects to an IV tubing  24 , for example by a luer connector  26  or the like, to provide a continuous passageway between a hypodermic volume  28  contained between the piston seal  20  and the luer connector  26  of the IV tubing  24 . 
     The IV tubing  24  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. The IV tubing  24  passes from the syringe  12  through a bubble sensor  32 , a pressure sensor  30  and a flow sensor  33  and may be installed in bubble sensor  32 , the pressure sensor  30  and flow sensor  33  by being pressed into a gap between opposing walls of each of the bubble sensor  32  and flow sensor  33  and pressed against the pressure sensor  30  by a backstop  79  on a cover  68  to be described below. The IV tubing  24  may then proceed to a patient-end  34  where it attaches to a hypodermic needle  36 , catheter or other patient connection. 
     A portion of the plunger  18  extending away from the piston seal  20  and out of the syringe tube may be connected to a syringe driver  38 . The syringe driver  38  includes a plunger block  40  constrained for linear movement along an axis of the syringe tube  14  as driven by a motor  42 . The motor  42  may be, for example, a stepper motor or servomotor or the like and include an appropriate mechanism for speed reduction and conversion of rotary to linear motion, such as may be implemented by a linear screw, rack and pinion, belt drive or the like. The motor  42  receives power from a motor controller  48  to provide movement of the plunger block  40  to move the piston seal  20  through the volume of the syringe tube  14  at a controlled rate and controlled distance. Various position or velocity sensors such as encoders, tachometers, limit switches, and the like may be used to communicate with the motor controller  48  as is understood in the art to provide such controlled motion. In addition, the sensors can provide a first estimate of a flow of medicament from the syringe based on known dimensions of the syringe tube  14 . 
     An electronic controller  44  may coordinate operation of the syringe pump  10  through interface circuitry  46  of a type known in the art communicating with motor controller  48 , the pressure sensor  30 , the air bubble sensor  32 , and flow sensor  33 . In addition, the interface circuitry  46  may receive signals from a keypad  50  allowing for user entry of data or commands. In addition, the interface circuitry  46  may output data to a display  52  (for example a liquid crystal type alphanumeric and/or graphic display) and/or speaker  54 . 
     Generally, the interface circuitry  46  will communicate via an internal bus structure  56  with a processor  58 . The processor  58  may read data  60 , for example, entered by the user through the keypad  50  or stored in an electronic memory  59  and may execute a stored program  62  (also stored in the electronic memory  59 ) to provide data to the display  52  according to conventionally known techniques. 
     Referring now to  FIG. 2 , the syringe pump  10  may provide, for example, a housing supporting the various components described above and including a cradle  61  receiving the body of the syringe tube  14 . The cradle  61  provides a generally upwardly open channel to receive the syringe tube  14  in a direction perpendicular to an axis  63  of the syringe tube  14  to allow a newly charged syringe tube  14  to be easily installed in the syringe pump  10 . 
     The plunger block  40  may similarly provide an upwardly open slot  64  engaging an external portion of the plunger  18  to hold the plunger  18  to the plunger block  40 , so that the plunger  18  moves with the plunger block  40 . The IV tubing  24  may be pre-attached to the syringe tube  14  and pass through a notch in the cradle  61  to be received by upstanding flanking walls of the bubble sensor  32  and flow sensor  33  and over the pressure sensor  30  before exiting from the housing to pass to the patient. A cover  68  may fit over the bubble sensor  32 , the pressure sensor  30  and the flow sensor  33  to shield them from an external interference and to locate and properly retain the IV tubing  24  in the bubble sensor  32 , pressure sensor  30 , and flow sensor  33  and to provide a backstop  79  for the pressure sensor  30  described below. 
     Referring now to  FIG. 3 , the pressure sensor  30  may measure pressure of medicament  70  passing through the IV tubing  24  through the walls  74  of the IV tubing  24  so as to avoid the need for separate connections to the fluid-contacting pressure sensor and to avoid problems of sterilization of a fluid-contacting pressure sensor. In such a through-tubing sensing system, a spring-loaded plunger  72  may deform a portion of a wall  74  of the IV tubing  24  as held against a backstop  79 , for example, under a known spring biasing force from a spring  76 . An amount of deflection of the wall  74  may be measured, for example, by a Hall Effect sensor  78  positioned at the opposite end of the spring  76  from the plunger  72 , the latter which have an attached magnet  77 . The Hall Effect sensor can be positioned at other positions as well. This deflection may be corrected for known characteristics of the IV tubing  24 . Increased deflection of the wall  74  for a known material of the IV tubing  24  and the known spring biasing force of spring  76  may be converted to a pressure reading based on the proximity of the plunger  72  and magnet  77  with a Hall Effect sensor  78 . Generally, lower pressures of the medicament  70  will allow greater deflection of the wall  74  and higher pressures of medicament  70  will allow less deflection of the wall  74 . Alternative pressure sensing systems may be used and in this system other sensors other than a Hall effect sensor may be used for position monitoring including photo optic sensors. 
     Referring now to  FIG. 4 , the bubble sensor  32  may employ opposed ultrasonic transducers  80  and  82  transmitting an ultrasonic signal  84  through the medicament  70  in the IV tubing  24 . The occurrence of a bubble  85  between the transducers  80  and  82  will attenuate the ultrasonic signal passing between the transducers  80  and  82  resulting in a decrease in signal strength at receiving transducer  82  which may be compared to a threshold adjustably set to detect bubbles  85  of a given size. 
     The flow sensor  33  may employ, for example, the following techniques:
         (1) Ultrasonic, for example, through-tubing ultrasonic Doppler or ultrasonic transit time measurement and the supporting circuits.   (2) Infrared, for example, an Infrared (IR) emitter/emitters emitting IR light, IR detector(s), and the supporting circuits.   (3) Turbine and paddle wheel or alike   (4) Laser based flow sensor and the supporting circuits.   (5) Thermal time of flight based flow sensor and the supporting circuits.   (6) Differential pressure based techniques, such as two pressure sensors, or one differential pressure sensor, such as a piezoresistive monolithic silicon pressure sensor.       

     Referring now to  FIG. 5 , in one embodiment, the flow sensor  33  may measure the flow of medicament  70  passing through IV tubing  24  by measurements made through two pressure measurements made outside of the walls  74  of the IV tubing (again to avoid the need for separate connections to a fluid-contacting flow sensor and to avoid problems of sterilization of that fluid-contacting pressure sensor). In the manner described above with respect to  FIG. 3 , an upstream spring-loaded plunger  72   a  and a downstream spring-loaded plunger  72   b  may deform axially in separated portions of the wall  74  of the IV tubing  24  as held against a backstop  79  under a known spring biasing force of springs  76 . As described before, a deflection of the wall  74  may be measured, for example, by corresponding Hall effect sensors  78   a  and  78   b  positioned at opposite ends of the spring  76  from their respective plungers  72  which each may have an attached magnet  77 . Signals from Hall effect sensors  78   a  and  78   b  are transmitted to the electronic controller  44  and corrected for known characteristics of the IV tubing  24  and difference in pressure between the measurements made by the Hall effect sensor  78   a  and  78   b  determined. This pressure difference indicates pressure drop through the IV tubing  24 , a parameter that will change as a function of flow and thus may be used to deduce flow. Generally, lower pressure differences will indicate lower flow rates. This effect may be accentuated by a slight constriction in the IV tubing  24  between the pressure sensors, the latter provided, for example, by a protrusion  101  from the backstop  79  constricting the flow in between the pressure sensors. It will be understood that other methods of determining flexure of the IV tubing may be used including capacitive or optical sensing. 
     Referring now to  FIG. 6 , in an alternative flow sensing arrangement that does not breach the sterile envelope of the IV tubing  24 , an ultrasonic transmitter  102  may be positioned across the IV tubing  24  from an ultrasonic receiver  104  to provide a path of ultrasonic transmission  106  through the medicament  70  extending at least partly along the axis of the IV tubing  24 . Changes in the ultrasonic transmission between the ultrasonic transmitter  102  and ultrasonic receiver  104 , such as transmission delay or Doppler shift in frequency can then be processed by the electronic controller  44  and used to deduce flow rate of the medicament  70 . 
     Referring now to  FIG. 7 , an alternative flow sensor  33  may be integrated into an IV tubing  24 , for example by ultrasonic welding of the tubing  24  and components of the flow sensor  33  together, and sterilized before use to address the problems of direct contact between the medicament  70  and the sensor structure. In particular, the sensor structure may include axially aligned inlet and outlet flow formers  110   a  and  110   b , respectively, which generate a controlled axial swirl in the medicament  70 . In between the flow formers  110  may be free-turning vane assembly  112  (wheel turbine) whose speed of rotation will depend on the flow of the medicament through the IV tubing  24 . This speed may be deduced externally by a sensor  114  such as an optical sensor, a variable reluctance sensor, a Hall effect sensor (assuming a magnet on the vane assembly  112 ) or a capacitive sensor or the like, sensing changes in these parameters with rotation of the vane assembly  112 . This design may alternatively eliminate the flow formers in favor of a helix shaped vane assembly  112 . 
     Referring now to  FIG. 8 , an alternative flow sensor  33  may also be built into the IV tubing  24  to be sterilized with the IV tubing  24  as a unit and provides axially separated first and second thermal sensors  116   a  and  116   b  having electrical leads passing hermetically through a wall of the IV tubing  24  to be received by one half of a connector shell that allows releasable electrical connection to the electronic controller  44 . One of the thermal sensors, for example thermal sensor  116   a , may be heated by a slight electrical current and a difference between temperatures of the thermal sensors  116   a  and  116   b  used to deduce flow rate according to known techniques. 
     Referring now to  FIG. 9 , an optical flow sensor  33  may provide an optical sensor array  120  that can optically interrogate the medicament  70  as it passes by the optical flow sensor  33 . This optical sensor array  120  may detect a moving pattern of minor optical inclusions in the medicament  70  in the manner of an optical mouse to deduce linear speed of the medicament and hence volume flow based on the known diameter of the IV tubing  24 . LED or laser technologies may be used for this purpose together with an array of photo detectors or CCD linear camera. This particular sensor may work through the wall  74  of the IV tubing  24  or, for improved accuracy, may be integrated into the IV tubing  24 , or may interface with an optical window  122  integrated into the IV tube  24  as shown. Example circuitry for implementing this optical array is taught generally in U.S. Pat. No. 6,664,948 hereby incorporated by reference as may be modified to the use of a backlight or front lighting system for this purpose. 
     Referring now to  FIG. 10 , in one embodiment, the patient-end  34  of the IV tubing  24  may alternatively or also provide a sensor positioned on the IV tubing  24  close to the patient. In this implementation, the sensor  86  may measure not only the changing pressure of the medicament  70  but may also measure, or alternatively measure, fluctuations in IV tubing or its connector caused by coupling of the medicament  70  to the vascular system as transmits pressure fluctuations caused by beating of the patient&#39;s heart through the liquid  75  to the sensor  86 . The sensor  86  may be similar to the pressure sensor  30  using a plunger technique, or may use a piezoelectric transducer or MEMS-type accelerometer or the like. Other pressure sensing techniques may also be used. Signals from the sensor  86  may be transmitted through thin wires  88  running along the outside of the IV tubing  24 , or embedded in the IV set tubing wall, or may be transmitted wirelessly or the like. 
     Referring now to  FIGS. 1 and 11 , program  62  may make use of information from the pressure sensors  30  and/or  86  to detect problems with the delivery of medicament  70  to a patient by the syringe pump  10  that would normally be difficult to detect based on the slow flow rates of the delivery of liquid  75  by the syringe pump  10 . Generally, problems with flow are deduced by changes in IV line pressure. For example, pressure increases above a certain amount detected by pressure sensor  30  may indicate an occlusion of the IV tubing  24  that requires attention. Conversely, pressure drops below a certain amount may indicate that the IV tubing  24  has become disconnected or broken. With respect to pressure sensor  86 , alternative information that may indicate disconnection of the IV tubing  24  can be derived from a loss of the dynamic heartbeat pressure signal that may be detected by the sensor  86 . 
     Generally, the operation of the program  62  will allow data entry through the keypad  50  by a user as confirmed through display  52 . This data may include a desired flow rate and volume of medicament  70  for delivery from the syringe tube  14 . This data entry process is indicated by process block  90 . At succeeding process block  92 , typically after an activation command by a user at process block  90 , the motor  42  will be activated to produce the desired flow rate and volume per process block  92 . 
     At decision block  100 , the air bubble sensor  32  may be interrogated to see whether there is an air bubble in the IV tubing  24 . If so, the program proceeds to process block  98  to provide the alarm and disabling of further delivery of medicament  70 . 
     If there is no air bubble, at decision block  94 , pressure sensor  30  and/or  86  are checked to determine whether there has been a pressure deviation indicating either disconnection, breakage or obstruction of the IV tubing  24 . If such problems are detected, the program  62  proceeds to process block  95  to correct the motor drive in a closed loop fashion to bring the pressure into proper range. If that correction is not successful as indicated by decision block  96  program proceeds to process block  98  to deactivate the pump and set an alarm. Generally the alarm may be, for example, a tone or spoken warning provided through speaker  54 , the latter provided by speech synthesis techniques well known in the art. The alarm may be accompanied or followed immediately by deactivation of the syringe pump  10  per process block  98 , ceasing delivery of medicament  70 . 
     If there is no pressure deviation detected at decision block  94 , then the program proceeds to decision block  103  where the flow sensor  33  is interrogated to see whether proper flow rates are being provided. A determination of proper flow rates may compare the deduced flow rate from the flow sensor  33  against a range normalized to operation of the motor controller  48 . Generally the range is a small band around zero flow when the motor controller  48  is not operating and changes to a small band around a calculated flow based on operation of the motor controller  48  and a geometry of the syringe tube  14  when the motor controller  48  is activated to move the motor  42 . A flow higher than this range may indicate that the IV tube has become disconnected from the patient. In this situation, the motor  48  will be running at a faster rate than it should but an internal calculation from the motor speed may have error (for example, because a smaller syringe diameter may have been used in the calculation than the actual syringe diameter); etc. A flow lower than this rate may indicate an obstruction downstream from the syringe tube  14 . In this situation, the motor will be running at a slower rate than it should and again the internal calculation from the motor speed alone may have error (for example, because it uses a larger syringe diameter in the calculation than the actual size of the syringe); etc. If the flow rate is within range, the program returns to process block  92  to complete movement of the syringe to the desired volume. Otherwise, the program  62  proceeds to process blocks  95  and  96  as described above for closed loop control to adjust the flow rate by adjusting motor speed, and if this is not successful, possibly to process block  98  to provide the alarm and disabling of further delivery of medicament  70 . 
     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. 
     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. 
     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. 
     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.