Abstract:
A system for controlled delivery of medicinal fluid includes a fluid pathway assembly defining a fluid pathway and including means for calculating a first calculated fluid flow rate using gas laws. The fluid pathway assembly has an inline flow sensor element received within the fluid pathway movable in response to fluid flowing in the fluid pathway. A flow control device is removably attached to the fluid pathway assembly and has a sensor for sensing a position of the inline flow sensor element in the fluid pathway, the position of the inline flow sensor element being representative of a second calculated fluid flow rate. The fluid pathway assembly includes a variable flow resistor adjustable to regulate a rate of fluid flow in the fluid pathway assembly. A drive mechanism attached to the flow control device is operably coupled to the variable flow resistor when the flow control device is attached to the fluid pathway assembly. The variable flow resistor is adjustable by the drive mechanism to achieve a target flow rate when the first calculated flow rate and/or the second calculated flow rate differs from the target flow rate.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority, as a continuation-in-part type application, under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/280,894, filed Aug. 27, 2008, now pending, which is a 371 of application No. PCT/US07/04945, filed Feb. 27, 2007, which claims priority to U.S. provisional patent application Ser. No. 60/777,193, filed on Feb. 27, 2006. 
         [0002]    This application also claims priority, as a continuation-in-part type application, under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/280,869, filed Aug. 27, 2008, now pending, which is a 371 of application No. PCT/US07/02039, filed Jan. 23, 2007, which claims priority to U.S. provisional patent application Ser. No. 60/777,193, filed on Feb. 27, 2006. 
         [0003]    Each of the aforementioned applications is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0004]    The present disclosure relates to intravenous infusion therapy. More specifically, the disclosure relates to a system, components of the system, and methods associated with the system for organizing the fluid flow for applications which require an accommodation of a broad flow rate range, a wide range of input and output pressures, and a wide range of delivered fluid viscosities, such as those seen with Intravenous (IV) infusion therapy. 
         [0005]    Conventionally, healthcare providers have had three technical options for intravenous infusions. Many intravenous infusions are controlled by manually adjusting a resistance in the flow path between a fluid source and the patient, based on the operator&#39;s observation of the rate of drips formed within a chamber in line with the fluid flow. The flow rate range that can be controlled with this method is limited by the relatively large and fixed size of the drops and the relatively low reliability of the human operator to accurately compute the flow rate. This method is critically flawed by virtue of the fact that it requires a human observer to maintain an accurate and consistent flow rate. In many circumstances, a trained human observer is not available. This manual method also lacks an important ability to electronically record and communicate the results of the infusion. 
         [0006]    A relatively small number of infusions are controlled with the use of a fixed volume of liquid under a fixed amount of pressure and a fixed resistance, providing a fixed flow rate. Unfortunately, the fixed rate and fixed fluid volume do not provide the flexibility required for most infusions. Similar to a manual infusion, this method does not provide the opportunity to electronically record the results of the infusion. 
         [0007]    Because of the strong requirement for more precise control of flow rate, flexibility of fluid volumes, and the desire to keep track of the flow information, many infusions are controlled using a positive displacement fluid pump. These large volume positive displacement devices are generally of the peristaltic or reciprocating piston type. Both types come at a price of complexity, size, weight, limited battery life, and significant financial cost. Early versions of positive displacement pumps created a new hazard for patients in what was known as “runaway infusion,” where the highly controlled fluid flow was suddenly uncontrolled when a door or other containment mechanism on the pump was released. In response to this undesirable feature, pumps were later required to incorporate “flow stop” mechanisms, so that the flow rate would stop entirely if the fluid tubing were removed from the flow control device. Unfortunately, the cessation of flow is sometimes as hazardous to patients as a sudden increase. Another unintended consequence of positive pumping systems is the possibility of infusing lethal amounts of air into a patient. This possibility did not exist with low pressure gravity infusions. As a result, positive displacement pumps have incorporated air detection systems to prevent this hazard, yet these alarm systems are the source of very significant nuisance alarms, resulting in operator inefficiency and patient anxiety. 
         [0008]    The present disclosure recognizes the safety advantages inherent in a low pressure infusion, the need to accurately control flow, and the necessity of modern healthcare environments to have infusion data electronically available. 
       SUMMARY 
       [0009]    The disclosure is directed to an medicinal fluid administration apparatus and method for using this apparatus, comprising a fluid pathway assembly and a flow control device wherein fluid flowing through the fluid flow system is controlled via closed loop quasi-static adjustment of in-line pressure based resistance in combination with a low pressure pneumatic pump element. This sensor-based infusion platform (SIP) utilizes wireless communication to a network to maintain device software and dataset integrity, broadcast alarms, and record infusion status information. 
         [0010]    These and other features of the disclosure, including various novel details of construction and combinations of parts, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular device embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this disclosure may be employed in various and numerous embodiments without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0012]      FIG. 1   a  is a rear view of the preferred embodiment of the Flow Control Device (controller) with the Fluid Path (disposable) installed as would be to deliver an infusion; 
           [0013]      FIG. 1   b  shows the two major assemblies of the embodiment herein—the Flow Control Device or controller with a Fluid Path (disposable administration set) installed in the pocket in the rear of the of the device; 
           [0014]      FIG. 2  is a rear perspective view of the flow control device showing the interface to the cassette; 
           [0015]      FIG. 3  shows an exploded view of the controller; 
           [0016]      FIG. 4  shows an assembled disposable including a cassette and tubing; 
           [0017]      FIG. 5   a  shows a section view of the intermediate pumping chamber; 
           [0018]      FIG. 5   b  shows the check valves and fluid path to the intermediate pumping chambers; 
           [0019]      FIG. 6  shows a cross sectional view of the variable resistance device; 
           [0020]      FIG. 7  shows a preferred embodiment of the flow sensing element; 
           [0021]      FIG. 8   a  shows a graph of the sensor output peaks formed when the element focuses and transmits light to the detector; 
           [0022]      FIG. 8   b  shows a graph of a sensor output peak with the flow object; 
           [0023]      FIG. 8   c  shows a graph of a sensor output peak with one LED illuminated; and 
           [0024]      FIG. 9  shows the IV pole bracket mount for the controllers. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Referring to the drawings, wherein like reference numerals are used to indicate like or analogous components throughout the several views,  FIGS. 1   a  and  1   b  depicts an exemplary volume and flow measurement system in accordance with an exemplary embodiment of the present invention. The full sensor based infusion platform system includes a disposable, a controller, an IV pole mounting bar, and a networked computer. 
         [0026]    Referring now to  FIGS. 1   a  and  1   b , where an exemplary embodiment of the present invention is shown,  FIG. 1   a  is a rear view of the controller with a disposable installed and  FIG. 1   b  shows a front view of the controller with a disposable installed. The controller  1  includes a display  2 , which is preferably an LCD display and more preferably a color LCD display with a touch-sensitive input device, such as a capacitive or resistive touch screen overlay  107  (see  FIG. 3 ). Alternative user input devices are also contemplated, such as a keypad or keyboard, mouse, trackball, touchpad, joystick, or combinations thereof as would be understood by persons skilled in the art. 
         [0027]    The display  2  is housed in a case or housing  3 , e.g., formed of rigid plastic. The controller includes an interface  4  to the pole mount device  60  (see  FIG. 9 ), which both mechanically secures the controller  1  to the IV pole  62  (see  FIG. 9 ). The pole mount  60  may also include a charger for charging the internal batteries or battery pack in the controller, e.g., via charging contacts which are aligned with and electrically couple charging contacts on the controller, or alternatively via induction, when the controller is placed in the mount. Preferably, the charger can charge the internal batteries on either side of the device. The case  3  may include ergonomically designed finger grips or recesses around the circumference to facilitate gripping of the device and may further include a pliable insert either removably or permanently attached to the outer housing  3 , for example, via over-molding, co-molding, or otherwise attaching a flexible or resilient material over the rigid shell  3  to further enhance the grip ability of the device. 
         [0028]    The inlets  5  and  6  and outlet  8  tube of the disposable are also visible in  FIG. 1   b . The primary inlet  5  connects the primary fluid source (not shown) containing a volume of fluid to be delivered to the device through a standard luer fitting as is known in the art. Fluid travels through the cassette housed in the rear of the device and then flows to the patient connection through the outlet  8 . 
         [0029]    The secondary inlet  6  allows a second fluid to be connected to a device independently of and without affecting the current infusion, and then the user can program the device with the second fluid delivery parameters, including start time. At the secondary infusion programmed start time, the controller  1  will temporarily pause delivery of the primary infusion, deliver the secondary infusion per the programmed parameters, and then resume the primary infusion. Other infusion devices on the market require the user to physically hang the second fluid source higher than the first fluid source such that the static pressure of the higher source determines which fluid is delivered. When the hydrostatic head height of second fluid source is not sufficiently higher than that of the primary source, the pump will deliver a mix of both primary and secondary fluids depending on the relative static pressures of the sources, thus not delivering the secondary fluid at the rate—and therefore not delivering the secondary fluid at the desired effective dose—prescribed. This issue, i.e., dependence on the user to manipulate both primary and secondary bag heights, is overcome with this disclosure, as the preferred embodiment will deliver the secondary infusion as programmed independent of the static pressure of the fluid sources. 
         [0030]    Features of the disposable administration set (“disposable”)  16 , and specifically, the cassette portion of the disposable can be seen in  FIG. 1   a , including the variable flow resistor  22 , the flow sensor  23 , the flow sensor  23 , and the intermediate pumping chambers  19 . The variable flow resistor  22  can be automatically adjusted by the controller to match the sensed flow rate with the program flow rate. The flow sensor  23  includes a flow element in the fluid path that moves in response to flow rate and provides the system with both a signal representative of flow rate, but also has a unique signal when air is passing through the sensor. The intermediate pumping chambers  19  pneumatically couple to the controller and act as both pneumatic pumps and additional flow sensors. 
         [0031]      FIG. 1   b  shows the touch-screen display  2  which displays a graphical user interface that is divided into several sections. These sections include information and status displays, status displays that include virtual navigation buttons, and navigation buttons  7 . Color and shading of the user interface intuitively show the user where more information is available. The user can touch an onscreen object such as an icon or button to navigate to pages (e.g., which may be arranged in a hierarchical fashion) with more information and change or update the program parameters if needed. 
         [0032]    Referring now to  FIG. 2 , the controller  1  is shown generally from the back and side, where the interface to the disposable is visible. The rear housing  9  is configured to guide the user in proper placement of the disposable into the controller. The asymmetric recess in the rear housing  9  together with recesses  10 ,  11  provided to allow passage of the primary and secondary inlets  5 ,  6  and the outlet tube  8 , respectively, are three of several features that key the disposable to the controller, thereby preventing the disposable  16  from being installed incorrectly. A rib or spline  12  interlocks with and manipulates the variable flow resistor and is positioned to only allow insertion of a disposable only when the resistor is in the fully closed position (thus preventing uncontrolled flow). Once engaged, the spline  12  does not allow the disposable to be removed from the controller without again fully closing the variable flow resistor. 
         [0033]    The light source array  13  and the optical detector  14  are positioned to allow the movable flow element in the disposable to be located between them. When in use, the light source array  13  can preferentially illuminate specific segments of the array, e.g., based on the anticipated location of the flow element, thus enhancing the ability of the optical detector  14  to accurately sense the location of the flow element and saving power to maximize battery run time. The pneumatic interface  15  to the intermediate pumping chambers (IPC&#39;s) of the disposables include o-ring seals which help both guide the nipple on the disposable and seal the connection. 
         [0034]    Referring now to  FIG. 3 , where more details of the controller  1  architecture can be seen, the pneumatic interface  15  connects to the manifold  104 , housing the valves and sensors, and connecting the pump chamber assembly  102 . Pressure sensors in the manifold  104  allow the system to accurately measure pressure in each of the intermediate pumping chambers in the disposable as well as in a calibration chamber of known volume. Isolating the calibration chamber of known volume from the intermediate pumping chambers using the valves in the manifold  104 , measuring the pressure present in each chamber, then combining the calibration chamber to an intermediate pumping chamber by opening a valve and measuring the resulting pressure allows the system to calculate the volume of fluid in the intermediate pumping chamber using ideal gas laws. As used herein, the term “ideal gas law” is intended to encompass not only the equation PV=nRT, but also special cases of this law, such as Boyle&#39;s Law and Charles&#39; Law. The fluid flow rate is calculated by periodically calculating the volume of fluid entering and leaving the intermediate pumping chambers over time. 
         [0035]    The pump chamber assembly  102  includes the pumps and chambers creating a positive pressure source and a negative pressure source. These pressure sources are connected through the manifold  104  to the intermediate pumping chambers of the disposable. As negative pressure is connected to an intermediate pumping chamber, fluid is drawn from the fluid source. As positive pressure is connected to an intermediate pumping chamber, fluid is expelled from the chamber. Controlling the pressures in each of the sources allows the system to compensate for changes in source height and in changes in outlet back pressure. Controlling the timing of the pressure changes allows the system to change the fluid flow rate through the system. 
         [0036]    A second means of control of fluid flow through the system is accomplished by the inclusion of a variable flow fluid resistor within the fluid flow path that can be manipulated by the variable resistor drive mechanism  103 . The drive mechanism  103  includes a motor and gear mechanism that output torque to a spline  12  (see  FIG. 2 ) that couples with the variable flow resistor on the disposable. As the spline rotates over its 300-degree range of motion, it moves the variable resistor from fully closed to fully open. The resistor is designed to provide a logarithmic response throughout its range of motion, yielding an effective control over a four order of magnitude range (e.g., 0.1-1000 ml/hour) of the system. 
         [0037]    The control board assembly  105  including a processor, microprocessor, or the like, and associated electronics executes the fluid delivery programs sent to it by the user interface (UI) board assembly  106 . The control board assembly  105  also manages inputs from temperature sensors, an external pressure sensor, the intermediate pump chamber pressure sensors, and the flow sensor; determines and executes changes in pneumatic pressure and resistance settings to match the measured flow rate to the programmed flow rate and sends infusion status updates to the UI board assembly  106 . The UI board assembly  106  includes a three axis accelerometer for motion sensing as well as sensors for monitoring the ambient noise level. This data, including the temperature and pressure signals collected and managed on the control board assembly  105 , allows the pump to be situationally aware. 
         [0038]    The UI board assembly  106  drives the display  2  and manages the user interface, allowing users to program new infusions, change the parameters of existing infusions, and view the history and status of infusions run on the device. The UI board assembly  106  also manages communication with the control board assembly  105  and communications to networked computers. The UI board assembly  106  may include one or more wireless, e.g., radio frequency (RF) or infrared (IR) transceivers, and in the preferred embodiment includes both 802.11 (WIFI) and 802.15 (ZIGBEE) radios  108  and  109 , respectively, to enable wireless network communications. Network communication enables the device to send infusion status information to populate electronic medical records, e.g., stored in a network database or remotely located database) and alarm notifications to page the caregiver. Network communications also allows the device to receive updated infusion datasets and software updates. 
         [0039]    If the ZIGBEE  109  network is installed in the hospital or other use environment, the device becomes location aware, and the location of the device can be included in all messages. Since location of the device is often associated with a patient, the device can assist the user in identifying the patient to whom the device is attached. Additionally, ZIGBEE networks—because they are mesh networks—allow the software to warn a caregiver if the same medication in the same location is already being given to the same patient. In acute cases, some patients may be connected to up to 12 infusion devices. Devices currently on the market warn the caregiver if the same drug is already being infused only if it is on the same device as the one being programmed, which can lead to poor outcomes for the patient. 
         [0040]    The ZIGBEE networked advantage of the preferred embodiment herein is to improve safety by having communication between all devices within a specific location, coordinating infusions and communication to caregivers. A further benefit of a ZIGBEE network is the ability to use ZIGBEE frequency RFID devices on caregivers. When a caregiver walks near a ZIGBEE device with the RFID device, the system recognizes and records that that caregiver is associated with a device. Associating caregivers, patients, and infusions helps provide complete electronic documentation. When a caregiver chooses to program a new infusion, the caregiver selects the drug to be infused, e.g., by viewing it on display  2  and using the touch screen  107  to choose it from a dataset on the device, or by using the controller&#39;s bar code imager  111  mounted on the UI board assembly  106  and imaging a bar code, e.g., located on the source of fluid to be infused, through a window in the bottom of the case  3 . The bar code imager  111  preferably is of the type that decodes one and two dimensional bar codes and can be used for patient identification, drug identification, drug infusion programming, and caregiver identification. The depicted controller  1  has a dual battery pack  112 , providing system redundancy and extended runtime. 
         [0041]    Referring now to  FIGS. 4 ,  5   a  and  5   b , the disposable  16  includes an inlet tube which attaches to the inlet. The disposable  16  may also include a drip chamber and spike (not shown), which can either be used to deliver a gravity infusion, or, in combination with the controller  1 , can be used to deliver a sensor based infusion. The disposable  16  has a primary inlet  5  and a secondary inlet  6 , both shown with vented caps  18 . Fluid from the primary or secondary fluid source flows through the respective inlets  5  or  6  and enters the intermediate pumping chambers  19  through a corresponding one of the one-way or check valves  29 . The intermediate pumping chambers  19  are divided by a flexible membrane  25  into two separate volumes  26  and  27 . 
         [0042]    The fluid entering the chamber flows into volumes  26 , and a gas (air) occupies volume  27 . The volume  27  that is filled with gas is separated from the fluid in the fluid volume  26  by the flexible membrane  25  and has a port  20  shaped like a nipple, which couples to the pneumatic interface  15  of the controller  1 . 
         [0043]    When controller  1  applies negative pressure through port  20  to the gas filled volume  27 , the flexible membrane moves toward port  20  drawing fluid from the fluid source to fill the chamber. When the controller applies positive pressure through the port  20  to the gas filled volume  27 , the flexible membrane is driven from port  20  displacing fluid from the chamber. When all fluid is driven from volume  26 , the flexible membrane  25  forms a seal against the fluid outlet of chamber  19 . If positive pressure is left in volume  27 , the outlet sealed by the membrane  25  will prevent fluid flow when flow is not desired. 
         [0044]    Check valves  29  and  30  for each of the primary and secondary flow channels ensure that fluid flows only from the fluid source to the outlet of the disposable  16 . The valves  29  prevent fluid in the volume  26  from exiting the volume  26  via the respective inlets  5 ,  6 , e.g., when a positive pressure is applied to the gas volume  27  during operation Likewise, the valves  30  prevent fluid downstream of the intermediate pumping chamber from being drawn back into the pumping chamber, e.g., when a negative pressure is applied to the gas volume  27  during operation. 
         [0045]    Pressure sensors in the controller can determine the pressure in the gas filled volume  27  of the intermediate pumping chamber  19 . By sensing the pressure in the gas filled volume and the pressure in a known calibration volume in the manifold  104  and then combining the volumes and measuring the resultant pressure of the combined volumes, the volume of gas in the intermediate pumping chamber can be calculated using the ideal gas law. 
         [0046]    If the volume of the rigid IPC is precisely known, it is possible to infer the volume of liquid in the IPC. However, in some instances, e.g., due to manufacturing tolerances variations, it is preferable not to presume that the IPC volume is precisely known and to monitor the flow rate of liquid out of the system using a volume calculation which does not require knowledge of the IPC volume and/or liquid volume. In the preferred embodiment, flow rate is determined by measuring an initial volume of compressible gas in the volume  27  and then monitoring pressure decay in the chamber  27  over time. In reducing the system of the present embodiment to practice, a 500 micro liter combined volume  26  and  27  of the intermediate pumping chambers  19  was selected as being advantageous for both high and low flow rates in that it accommodates the need for flow continuity in the low flow range (e.g., -less than 1 ml/hour) as well as the need to be able to deliver rapid infusions (e.g., greater than 1000 ml/hour), although other volumes are contemplated. 
         [0047]    It can be seen with this design how the system described herein can pause delivery of the primary fluid entering the primary port  5  and being delivered at a primary flow rate, deliver a secondary fluid from the secondary input port  6  at a second flow rate, and then resume delivery of the primary fluid without the need to depend on the user changing the bag heights or otherwise needing to remember to connect, move or otherwise manipulate the primary infusion setup. This arrangement prevents secondary fluid flowing into the primary infusion source, or drawing from both secondary and primary fluid sources at an unknown mix rate, both common occurrences with other systems if the caregiver is not meticulous in system configuration. 
         [0048]    Fluids leaving the intermediate pumping chambers  19  flow through an air-elimination filter  21 . Many systems in use combine a peristaltic mechanism with a silicone pumping member. Silicone is semi permeable to air and when combined with the high pressures typical of a peristaltic device, air becomes entrained in the fluid being infused. Ultrasonic sensors positioned downstream of the pumping mechanism are employed in those devices to transmit through the tubing of the disposable looking for evidence of air. Those devices have been the source of nuisance (false) alarms and the ensuing wasted time, disposables, and medicinal fluids as caregivers have attempted to remedy constant alarms by changing sets. 
         [0049]    This disclosure overcomes those issues by eliminating a high pressure pumping member, which is the root causes of those alarms, instead using low pressure, impervious membranes and incorporation of an air elimination filter. As will be seen, the fluid flow sensor output has a characteristic signature for air and can therefore give an additional layer of safety without an inherent false positive (nuisance) alarm. Fluid passing through the air elimination filter  21  enters the inlet  30  of the variable flow resistor  22 . 
         [0050]    Referring now to  FIG. 6 , when the disposable is used for a gravity infusion (i.e., without the use of the controller), the cap  39  can be manually rotated to increase or decrease flow which can be monitored by viewing the drop rate of fluid moving through the drip chamber. In this view, the piston  34  is shown in the fully closed position. As cap  39  is rotated, threads  41  selectively advance or retract the position of the piston  34  within the cavity of flow resistor body  31 , depending on the direction of rotation, exposing a helical channel or thread  37  to the incoming fluid, which enters the flow resistor body at inlet  33 . 
         [0051]    The groove  37  is made with an increasing pitch, width, and/or depth along its length, to selectively increase or decrease the flow area aligned with the inlet of the resistor, the taper of the pitch, width, and/or depth preferably being selected to create a logarithmically increasing flow path for the fluid as the resistor moves from the closed to fully open position. As the thread  37  is exposed to the fluid, fluid travels in the gap created by the threads  37  and cap  39  to flow into the space between cap  39  and piston  34 . Fluid in this space exits the flow resistor through a central passage  38  in piston  34  to the outlet  32 . 
         [0052]    Piston  34  is sealed by an annular ring or protrusion  35  that slides in the cavity of the resistor body  31 . Cap  39  is sealed by an O-ring  40 . Note that when the cap  39  is rotated, there is no translation of cap  39  with respect to body  31 . Rotation of cap  39  translates the piston  34 , exposing or hiding different portions of the thread  37  to selectively increase or decrease fluid flow through the device. In contrast to mechanisms used in other systems, such as slide clamps and roller clamps, which when activated send a bolus of drug to the patient, movement of piston  34  does not in itself drive fluid. Therefore, no bolus of fluid to the patient can be created by opening the flow resistor. This unique feature adds yet another layer of safety to the patient and differentiates the device in this preferred embodiment. An exemplary fluid flow resistor may be as described in commonly-owned PCT application No. PCT/US2009/068349 filed Dec. 17, 2009, the entire contents of which are incorporated herein by reference. Fluid exiting variable flow resistor  22  via the outlet  32  enters flow sensor body  23  (see  FIG. 7 ). A protrusion  36  rides in a corresponding groove  42  as the piston  34  is translated to prevent rotation of the piston  34  relative to flow axis. 
         [0053]    Referring now to  FIG. 7 , fluid entering flow sensor body  51  is impeded by sensor element  52 , held against the flow opening by spring  57 . Sensor element  52  is generally opaque and houses a transparent transmitting element  53 , which is transparent (as used herein, the terms transparent and opaque are used in reference to the wavelength of light emitted by the light array  13 ) and is designed to transmit light onto the sensor array  14 . The transmitting element is preferably cylindrical and will be described herein primarily by way of reference thereto, however, it will be recognized that the focusing element  53  may be spherical, cylindrical, or other geometric configuration. An alternative embodiment, which has been contemplated, has a transmission region which is fundamentally spherical and thus focuses the transmitted light onto the sensor. In the alternative embodiment the transmitting element  53  may act a refractive lens, or may be a diffractive and/or holographic optical element for focusing light emitted by the array  13  onto the sensor array  14 . 
         [0054]    When disposable  16  is in controller  1 , flow sensor  23  nests between light source array  13  and optical detector array  14  (see  FIG. 2 ). Light emitted from array  13  is gathered by cylindrical element  53  and focused on detector array  14 . As flow increases, sensor element  52  is displaced, compressing spring  57  seated at one end on spring seat  56 . The interior flow channel  55  is tapered toward outlet  58  to allow higher flow as more of the tapered area is exposed by the displaced sensor element  52 . Ribs  54  maintain sensor element  52  alignment with the central flow axis of the flow path. 
         [0055]    There are various alternate embodiments that would be obvious to one skilled in the art, such as the use of a generally cylindrical transparent element in lieu of cylindrical element  53 , allowing the transmission of light through the sensor to the detector without focusing the light. As would be understood by one skilled in the art, a sensor of this type when coupled with the light source array  13  and the optical detector  14  would produce unique output signals when measuring the passage of fluid as versus the passage of air. In addition, since air is compressible, bubbles generate a distinct output signal and the flow sensor herein can therefore additionally function as a bubble detector. 
         [0056]    Referring now to  FIGS. 8   a - 8   c , it can be seen how significantly the signal voltage is enhanced by using a transparent cylindrical element to transmit light. Referring now to  FIG. 8   b , a graph is shown with a clear peak of the optical signal of the flow object. A graph showing a clear peak of the optical signal through TPN, a highly scattering fluid, is shown in  FIG. 8   c.    
         [0057]    Referring again to  FIG. 4 , fluid passing through flow sensor  23  flows through tube  8  to the patient. 
         [0058]    Referring now to  FIG. 9 , controller  1  mounts to pole mount  60  by means of the slide interface  4 . Corresponding slides  61  receive controller  1 . Low voltage DC electric power provided through cord  63  comes from a transformer connected to a standard AC outlet (not shown) and is transferred through the interface  4  and  61  to charge the batteries  112  of the device. Pole mount  60  can be clamped on any standard IV pole  62  and in the depicted embodiment supports up to four controllers. 
         [0059]    A review of adverse infusion events on the FDA&#39;s reporting database (MAUDE) shows that a surprising number of adverse events occur each year as a result of a caregiver forgetting to plug the infusion pump back in after the pump or patient is moved. Other devices use only a tiny light or icon to show when the device is plugged in which can easily be missed. Subsequent battery alarms and battery failure can prevent the patient from timely receiving the medication prescribed. 
         [0060]    The preferred embodiment of this system addresses this unmet need in two manners: first, pumping air to drive the infusion requires significantly less power than compressing a pumping segment with a peristaltic device, allowing for substantially longer battery life; and the device display will automatically go dark—an additional power savings feature—after a time out from input from a user or from sensed moving if it is not plugged in. The infusion will continue, and the display will periodically come to life, but this new behavior will alert the caregiver that the device is not plugged in and is significantly more prominent and therefore useful than a small indicator light or icon as commonly found on conventional devices. 
         [0061]    Another source of adverse events present in other devices but not present in the preferred embodiment of this device is related to occlusions either upstream or downstream that prevent the infusion from proceeding as programmed. There are two associated hazards with other devices on the market with respect to occlusion detection: other devices depend on sensing pressure in the disposable to detect a no-flow condition. Pressure in the disposable will increase over time if there were a downstream occlusion as the pump would continue, filling the compliance available in the disposable until the pressure sensor is able to read sufficient pressure in the line to trip an alarm. When the occlusion is cleared (for example, when the line pinched when the patient was moved is straightened), the pressurized fluid in the line is delivered to the patient as a bolus. This can be a significant hazard as peristaltic pumps can generate high pressure (upwards of 15 psi) which, depending on the compliance of the set and associated delivery catheter and tubing can store and then immediately deliver a significant volume of drug. 
         [0062]    The second hazard associated with pressure sensing as a secondary means of sensing fluid flow is that depending on the flow rate, the pressure alarm settings and the compliance of the tube set, the device can run for over two hours without delivering any medication before sufficient pressure builds in the set to trip the alarm. Some courses of therapy depend on a continuous infusion and a two hour interruption can be a significant source of concern. The preferred embodiment of the system disclosed senses flow directly, both with the flow sensor and with the pressure sensors in the intermediate pumping chambers (redundant flow sensing) and therefore is immediately aware of a no-flow condition regardless of the flow rate or the tubing compliance. Secondly, the pneumatic drive of the system typically operates at one psi, with a maximum of 5 psi available to drive an infusion—a huge improvement in safety as compared to pumps that can deliver fluid in excess of 15 psi. 
         [0063]    Finally, the approach of the preferred embodiment allows for a significantly smaller, lighter, and more cost effective approach to accurately delivering an infusion because it does not require a precision mechanism. In instances where previously there had been a tradeoff in infusion delivery and cost, where infusion data, accuracy, and safety were traded off against the cost of delivering that infusion, the preferred embodiment shifts that economic model. In care situations that previously might use cost to drive the use of a gravity infusion or a simpler infusion device, the economics and simplicity of use of this approach allows the infusion to be given at a similar cost, with the advantages of improved safety and traceable electronic data records further reducing the cost of documentation. 
         [0064]    While there has been shown and described what is considered to be preferred embodiments of the invention, it will of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be construed to cover all modifications that may fall within the scope of the appended claims and their equivalents.