Patent Publication Number: US-2010114027-A1

Title: Fluid medication delivery systems for delivery monitoring of secondary medications

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119 of U.S. Ser. No. 61/111,377 filed Nov. 5, 2008. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to a flow sensor assembly, such as a differential pressure based flow sensor assembly, and method for monitoring medication delivery from a secondary medication reservoir utilizing a system containing the flow sensor assembly, and more particularly to a differential pressure based flow sensor assembly that has a disposable portion and a reusable portion and may be utilized to measure fluid flow from a secondary medication reservoir. 
     BACKGROUND 
     Modern medical devices, including medical pumps, are increasingly being controlled by microprocessor based systems to deliver fluids, solutions, medications, and drugs to patients. A typical control for a medical pump includes a user interface enabling a medical practitioner to enter the dosage of fluid to be delivered, the rate of fluid delivery, the duration, and the volume of a fluid to be infused into a patient. Typically, drug delivery is programmed to occur as a continuous infusion or as a single bolus dose. 
     It is common for a plurality of medications to be infused to a patient by using a multi-channel infusion pump or using a plurality of single channel infusion pumps where a different fluid is administered from each channel. Another method of delivering multiple medications to a patient is to deliver a first medication using an infusion pump, and additional medications through single bolus doses. 
     A further common medication delivery system utilizes a primary medication reservoir and a secondary medication reservoir. Medication from the secondary medication reservoir is delivered to a patient after the primary medication reservoir is stopped, such as by clamping the line from the primary reservoir, and resetting the pump to deliver the secondary medication at an appropriate rate for the secondary medication. Once the secondary medication reservoir is empty, the line from the primary medication reservoir is reopened, and medication flows once again from the primary reservoir once the pump is re-programmed to resume the delivery rate appropriate for the first reservoir. This type of system requires a caregiver to manually operate the valves to ensure that flow of medication is coming from the appropriate reservoir, and that the pump is operating at the correct rate for the primary or secondary medication. 
     However, in other applications involving a secondary medication reservoir, the secondary medication reservoir is simply placed higher than the primary medication reservoir so that the pump draws the medication from the higher secondary medication reservoir until the secondary reservoir is empty, and then flow will resume from the lower primary medication reservoir. Such a system requires that a caregiver carefully monitor the flow to ensure that medication from the appropriate reservoir is being delivered to the patient. In this type of system, it is possible for the wrong medication to be delivered, or the proper medication may be delivered at an inappropriate rate. 
     Thus, under both previous approaches, a caregiver had to carefully monitor the fluid delivery to ensure that medication being delivered to a patient was coming from the appropriate source, and to further ensure that the medication is being delivered to the patient at the appropriate flow rate. Even with careful oversight from a caregiver, it may be difficult to ensure that the appropriate medication is being delivered to the patient, particularly if the flow rate is low. When the flow rate of the medication is low, a great deal of time may pass prior to the caregiver being able to visually notice a change in volume of medication in a particular reservoir. Also, events where both reservoirs are contributing to the fluid volume drawn through the pump can be very difficult to discern visually. Thus, if medication is being delivered to the patient from an incorrect medication reservoir, a long period of time may pass before corrective action is taken. It is important to confirm that flow has been initiated from the appropriate reservoir and that this reservoir continues to be the active fluid source for as long as desired. 
     Further, even if the proper medication is being delivered, a caregiver may not be able to discern that the medication is not being delivered at a proper rate. Thus, medication may be delivered too rapidly, or too slowly, and a caregiver may only notice subsequent to a reservoir being empty sooner than planned, or still containing medication when the reservoir should be empty. Thus, a sensor within the flow path from the secondary medication reservoir to the patient, that is capable of measuring flow rate through the flow path, would be helpful to ensure that both the correct medication source is being used, and that the correct amount of the medication is being delivered. Further, it is desirable to provide a robust flow rate sensing methodology that is low cost and in particular introduces low incremental cost to the disposable medication delivery tubing set. Further, it is desirable to provide a flow rate sensing methodology that is capable of accurately sensing the flow rate of fluids that have a range of physical properties, including fluid viscosity, which may not be known precisely. Further, it is desirable to confirm that actual flow from secondary reservoirs is captured and communicated to the caregiver and the electronic medication administration record of the patient in an automated fashion. Further, it is desirable to subject secondary medications to the framework of safety software. Therefore, a need exists for a fluid flow sensor system adapted for monitoring medication delivery. 
     SUMMARY 
     According to one embodiment, a fluid medication delivery system comprises a primary medication reservoir, a secondary medication reservoir, an infusion pump, a first valve assembly, a second valve assembly, a first y-site, and a fluid flow sensor assembly. The primary medication reservoir has a first fluid. The secondary medication reservoir has a second fluid. The infusion pump pumps fluid from at least one of the primary medication reservoir and the secondary medication reservoir. The first valve assembly controls the flow of fluid from the primary medication reservoir in a first fluid line segment. The second valve assembly controls the flow of fluid from the secondary medication reservoir in a second fluid line segment. The fluid flow sensor assembly determines the flow rate of a fluid from the secondary medication reservoir in the second fluid line segment. In one embodiment, the fluid flow sensor assembly is a differential pressure based fluid flow sensor assembly. 
     According to another embodiment, a fluid medication delivery system comprises a primary medication reservoir, a secondary medication reservoir, an infusion pump, a first valve assembly, a second valve assembly, a first y-site, and a drip counter assembly. The primary medication reservoir has a first fluid. The secondary medication reservoir has a second fluid. The infusion pump pumps fluid from at least one of the primary medication reservoir and the secondary medication reservoir. The first valve assembly controls the flow of fluid from the primary medication reservoir in a first fluid line segment. The second valve assembly controls the flow of fluid from the secondary medication reservoir in a second fluid line segment. The drip counter assembly determines the flow rate of a fluid from the secondary medication reservoir in the second fluid line segment by counting drops of fluid that flow past the drip counter assembly in a portion of the second fluid line segment. 
     According to a further embodiment, a fluid medication delivery system comprises a primary medication reservoir, a secondary medication reservoir, an infusion pump, a first valve assembly, a second valve assembly, a first y-site, and a load cell assembly. The primary medication reservoir has a first fluid. The secondary medication reservoir has a second fluid. The infusion pump pumps fluid from at least one of the primary medication reservoir and the secondary medication reservoir. The first valve assembly controls the flow of fluid from the primary medication reservoir in a first fluid line segment. The second valve assembly controls the flow of fluid from the secondary medication reservoir in a second fluid line segment. The load cell assembly determines the change in weight of the secondary medication reservoir over time to determine the flow rate of a fluid from the secondary medication reservoir. 
     According to yet another embodiment, a fluid medication delivery system comprises a medication reservoir, an adjustable valve assembly, and a fluid flow sensor assembly. The medication reservoir has a first fluid. The adjustable valve assembly has a slider to allow for the adjustment of the flow rate of the first fluid through the valve. The second valve assembly controls the flow of fluid from the secondary medication reservoir in a second fluid line segment. The fluid flow sensor assembly determines the flow rate of a fluid from the medication reservoir and has a display to provide a visual indication of the fluid flow rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view that illustrates a patient connected to IV line having a flow sensor assembly according to one embodiment; 
         FIG. 2  shows a closer, more detailed pictorial view of the flow sensor assembly of the embodiment of  FIG. 1 ; 
         FIG. 3  is an isometric view of the flow sensor assembly of the embodiment of  FIG. 1 ; 
         FIG. 4  is an isometric cross-sectional view taken along line  4 - 4  of  FIG. 3 ; 
         FIGS. 5   a - 5   e  illustrate cross-sections of flow restricting elements within differential pressure based flow sensor assemblies according to various embodiments; 
         FIG. 6  is a pictorial view illustrating delivery of medication to a patient via an IV push or bolus through an IV line having the flow sensor assembly of  FIG. 1 ; 
         FIG. 7  schematically illustrates a method of delivering medication using a system having a flow sensor assembly according to one basic process; 
         FIG. 7   a  schematically illustrates a method of delivering medication using a system with flow sensor assembly, according to a more elaborate process than  FIG. 7 ; 
         FIGS. 8   a - 8   b  schematically illustrate a method of delivering medication using a system having a flow sensor assembly according to another process; 
         FIG. 9  is a pictorial view that illustrates a medication delivery system having a differential pressure based flow sensor assembly located in a secondary medication reservoir fluid flow path according to one embodiment; 
         FIG. 10  is a pictorial view that illustrates a medication delivery system having a drip counter sensor located in a secondary medication reservoir fluid flow path according to another embodiment; 
         FIG. 11  is a pictorial view that illustrates a medication fluid delivery system having a load cell in communication with a secondary medication reservoir according to a further embodiment; 
         FIG. 12  is a pictorial view that illustrates a medication delivery system having a differential pressure based flow sensor assembly located in a secondary medication reservoir fluid flow path according to yet another embodiment; 
         FIG. 13  is a pictorial view that illustrates a medication delivery system having a drip counter sensor located in a secondary medication reservoir fluid flow path according to yet a further embodiment; 
         FIG. 14   a  is a pictorial view that illustrates a gravity fed medication delivery system having a flow sensor and an adjustable valve according to one embodiment; and 
         FIG. 14   b  is a detailed view of the manually adjustable valve shown in  FIG. 14   a.    
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described an example of the invention. The present disclosure is to be considered as an example of the principles of the invention. It is not intended to limit the broad aspect of the invention to the examples illustrated. 
       FIG. 1  is a pictorial representation of a patient  10  connected to a medication delivery system  1  and receiving a first medication via an infusion pump  12  from a medication reservoir  14 . A first fluid line segment  16  delivers the first medication from the reservoir  14  to the infusion pump  12 . The second fluid line segment  18  delivers the medication from the infusion pump  12  to a differential pressure based flow sensor assembly  100 . A third fluid line segment  22  delivers the medication from the differential pressure based flow sensor  100  to the patient  10 . While three fluid lines segments are described in connection with  FIG. 1 , it is contemplated that the number of fluid lines or line segments used in connection with the present invention may vary, and may be more or less than three fluid lines. It is further contemplated that fluid lines  16 ,  18 , and  22  can be integrated in manufacturing to present a single common tubing set or line-set. The third fluid line segment  22  is typically connected to the patient  10  through a connector valve  23  and a patient access device such as a catheter  25 . 
     The second fluid line segment  18  has a connection  20  adapted to receive a second medication from a second source. The connection illustrated in  FIG. 1  is typically referred to as a Y-Site, although it is contemplated that other connection types and configurations may be used in connection with the present invention. 
     The connection  20 , shown in additional detail in  FIG. 2 , may receive a second medication from a syringe  24  in the form of a manual IV push or bolus by a caregiver  26  (see  FIG. 6 ). It is further contemplated that the second medication may be provided in another fashion, such as from a secondary medication reservoir or other known medication delivery source. The medication delivery system  1  further has a differential pressure based flow sensor assembly  100 . In the illustrated embodiment, the differential pressure based flow sensor assembly  100  is located downstream of the connector  20  and is secured on the patient  10 . Thus, the flow sensor assembly is adapted to have both the first and the second medication pass through the sensor assembly  100 . However, the sensor assembly  100  could also be disposed in any number of locations including but not limited to upstream of the fluid junction between the first and second medication, connected between the second source and the connector  20 , or integrally formed on or within one of the branches of the connector  20 . The flow sensor assembly  100  need not be secured to the patient  10  directly. 
     Turning next to  FIG. 3  and  FIG. 4 , the differential pressure based flow sensor assembly  100  is shown in additional detail. The differential pressure based flow sensor assembly  100  has a disposable portion  102  and a reusable portion  104 . As used herein reusable is defined as a component that is capable of being safely reused. For example, the same reusable portion  104  can be used multiple times on the same patient with the disposable portion  102  being changed at least every 72 hours or so. The same reusable portion  104  can be used hundreds or even thousands of times on different patients, subject to the cleaning policies recommended by the manufacturer or the healthcare institution, by installing a new disposable portion  102 . This is possible since the reusable portion  104  is designed to be robust and to prevent fluid ingress. As may best be seen in  FIG. 4 , the disposable portion  102  has a fluid inlet  106  an upstream fluid chamber  108 , an upstream fluid pressure membrane  110 , a flow restricting element  112 , a downstream fluid chamber  114 , a downstream fluid pressure membrane  116 , and a fluid outlet  118 . The membranes  110  and  116  are fluid impermeable. Although full membranes are shown, it is contemplated that other types of seals, including but not limited to one or more gaskets and O-rings, would suffice to keep fluid out of the housing of the reusable portion. Any exposed areas could be swabbed with a cleaning solution, if necessary. 
     As shown in  FIG. 4 , medication enters the disposable portion  102  through the fluid inlet  106 . The medication flows into the upstream fluid chamber  108  from the fluid inlet  106 . Next, the medication flows through the flow restricting element  112  and into the downstream fluid chamber  114 . The flow of the medication through the flow restricting element  112  results in a drop in fluid pressure as the fluid flows from the upstream fluid chamber  108  to the downstream fluid chamber  114  through the flow restricting element  112 . Thus, during forward fluid flow under normal conditions, the fluid pressure within the upstream fluid chamber  108  is generally greater than the fluid pressure within the downstream fluid chamber  114 . The fluid pressure within the upstream fluid chamber  108  presses against the upstream fluid pressure membrane  110 . Similarly, the fluid pressure within the downstream fluid chamber  114  presses against the downstream fluid pressure membrane  116 . 
     It is contemplated that a variety of materials may be utilized for the manufacture of the disposable portion  102 . The disposable portion  102  may comprise a thermoplastic. It is contemplated that the flow restricting element  112  may be made of the same thermoplastic as the rest of the disposable portion  102 , or may be a different material than the disposable portion  102 . Non-limiting examples of the material that may be utilized to form the flow restricting element  112  include silicon, glass, and medical grade thermoplastics and elastomerics. The fluid pressure membranes  110 ,  116  may comprise a variety of polymeric or elastomeric materials, such as TPE, or silicone. 
     It is additionally contemplated that the flow restricting element  112  may be formed integrally with the rest of the disposable portion  10 , or the flow restricting element  112  may be a separate component mounted and sealed within the disposable portion  102 . In either approach, all fluid passing between the fluid inlet  106  and the fluid outlet  118  is routed through the flow restricting element  112 . 
     As may also be seen in  FIG. 4 , the reusable portion  104  of the differential pressure based flow rate sensor assembly  100  has an upstream pressure sensor  120 , a downstream pressure sensor  122 , a circuit board  124 , and an electrical connection  126 , all contained within a housing  128 . The upstream pressure sensor  120  is adapted to interact with the upstream fluid pressure membrane  110  to generate a reading of fluid pressure within the upstream fluid chamber  108 . Similarly, the downstream pressure sensor  122  is adapted to interact with the downstream fluid pressure membrane  116  to generate a reading of fluid pressure within the downstream fluid chamber  114 . The circuit board  124  receives output from both the upstream pressure sensor  120  and the downstream pressure sensor  122 . The circuit board  124  may calculate a pressure difference between the upstream fluid chamber  108  and the downstream fluid chamber  114 , or the circuit board  126  may generate an output signal that is transmitted to another device with a processor, such as the infusion pump  12 , that calculates the pressure difference between the upstream chamber  108  and the downstream chamber  114 . Output of the circuit board  124  passes through electrical connection  126  to the infusion pump  12  ( FIG. 1 ). 
     Although a wired electrical connection  126  is shown in  FIG. 4 , the system may optionally comprise wireless electrical connection and communication with the infusion pump  12  or other system components. It is additionally contemplated that according to some alternative embodiments, the reusable portion  104  may further contain additional electronics, such as, batteries, one or more memories, amplifiers, signal conditioning components, analog-to-digital converters, power converters, LED indicators, a display, sound generating components, a wireless communication engine, inductive coils for receiving power from the infusion pump  12  or another source, and active or passive radio frequency identification devices (RFID). It will be appreciated that the calculations and processing described herein can take place on the circuit board  124 , in the infusion pump  12 , in a remote processor (not shown), or be concentrated in only one of the system components, or distributed among one or more of the system components as needed or desired. 
     The components of the reusable portion  104  are contained within the housing  128 . The housing  128  may be manufactured from a polymeric material such as polycarbonate, polyethylene, polyurethane, polypropylene, acrylic, or other known materials. It is further contemplated that an upstream reusable portion membrane  130  may separate the upstream fluid pressure membrane  110  from the upstream fluid pressure sensor  120 . Likewise, a downstream reusable portion membrane  132  may separate the downstream fluid pressure membrane  116  from the downstream fluid pressure sensor  122 . It is also contemplated that the upstream reusable portion membrane  130  and the downstream reusable portion membrane  132  can be combined into a single unitary membrane or gasket. 
     Referring next to  FIG. 5   a,  a cross-section of a disposable portion  202  is schematically illustrated with a flow restricting element  212   a  to illustrate the profile of the flow restricting element  212   a.  The flow restricting element  212   a  may be identical to the flow restricting element  112 , but may also vary. The flow restricting element  212   a  is in the form of an orifice. An orifice may be a beneficial flow restricting element, as orifice performance varies less between fluids of different viscosities than other flow restricting elements, such as capillary channels. That is to say, the measured pressure differential across an orifice for a given flow rate will be largely independent of the viscosity of the active solution, where the pressure difference measured across alternate restrictions such as capillaries will demonstrate a strong dependence upon fluid viscosity. The flow restricting element  212   a  has a front face  214   a  located on an upstream side of the flow restricting element  212   a,  and a rear face  216   a  on the downstream side of the flow restricting element  212   a.  An opening  218   a  is formed through the flow restricting element  212   a  to allow fluid to flow through the flow restricting element  212   a.    
     The opening  218   a  may have a variety of aerial shapes, but a circular opening is commonly used as it provides a maximum flow area versus perimeter length. In order to help reduce the effect of fluid viscosity on the flow of the fluid through the opening  218   a  of the flow restricting element  212   a,  the opening  218   a  may have a ratio of a perimeter of the opening  218   a  to the length the fluid travels though the opening  218   a  of from about 100:1 to about 2000:1. That is, the perimeter of the opening is sufficiently larger than the length of fluid flow though the opening  218   a,  such that the pressure drop through the opening  218   a  is less dependent on the fluid, and more dependent on the geometry of the opening  218   a.  An opening  218   a  having a perimeter to flow length ratio of about 1000:1 has been found to be effective. For example, a 430 micron diameter circular orifice with a length in the flow dimension of 12 microns will accommodate flow rates in the hundreds to thousands of ml/hr. A smaller diameter orifice would be needed for smaller flow rates and applications. 
     The thickness of the opening  218   a  of the flow restricting element may vary from about 5 microns to about 25 microns. An opening  218   a  having a thickness of about 12 microns has been found to be effective. In order to demonstrate the desired flow characteristics, it is important to provide a flow orifice or opening in a solid geometry. The ratio of the inlet height, which is to say the minimum internal inlet flow plenum geometry at the orifice plate, to the effective hydraulic diameter of the orifice should be rather large, such as at least 10:4 or about 5:1. However, a constant-thickness membrane, of thickness equal to the length of the desired orifice, may become mechanically weak if the overall area of the membrane is large. Once the orifice opening is established, the membrane material in which the orifice resides can be thicker as one moves away from the orifice perimeter. As a result, the orifice itself can provide the desired restrictive fluid path length, while the membrane in which the orifice resides is thicker than the length of the orifice at a location away from the orifice. Thus, it is contemplated that various other geometries may also be used to form a flow restricting element. 
     As shown in  FIG. 5   a,  the flow restricting element  212   a  transitions from a thicker cross sectional shape to a thinner cross sectional shape near the opening  218   a.  Creating such a geometry for the flow restricting element  212   a  allows for various low cost manufacturing approaches for the flow restricting element  212   a.  Creating such a geometry has a limited effect on performance of the flow restricting element  212   a,  as such a geometry does not introduce a significant pressure difference for fluids having different viscosities, but having the same fluid flow rate. Thus, the thinness of the flow restricting element  212   a  near the opening  218   a  limits the effect of fluid viscosity on pressure drop through the opening  218   a,  while thicker material away from the opening  218   a  increases the overall strength of the flow restricting element  212   a.    
       FIGS. 5   b - 5   e  illustrate alternative flow restricting elements  212   b - 212   e  that function similarly to flow restricting element  212   a.  Flow restricting element  212   b  maintains a constant thickness, while flow restricting elements  212   c - 212   e  are thinner near the openings  218   c - 218   e.  Assuming that flow occurs generally from left to right in these figures, the geometry of the rear face  216   a - 216   e  does not have a great effect on flow characteristics through openings  218   a - 218   e.  This is because flow through the opening  218   a - 218   e  typically features well-defined fluid velocity profiles with minimal fluid/wall dynamic interaction on the orifice backside, as long as the rear face  216   a - 216   e  geometry is sloped away from the orifice appropriately, and therefore minimizes viscosity induced pressure losses. Some of these orifice geometries lend themselves to manufacturing advantages. For example, orifice  218   a  can be formed efficiently via silicon processing techniques such as etching, lithography, masking and other MEMS operations. Orifice  218   b  can be formed efficiently by laser machining thin flat stock material. Orifices  218   c  and  218   d  could be formed easily with photo-imaging glass processing techniques. Orifices  218   c,    218   d,  and  218   e  could be formed using molding or embossing techniques. Further combinations of techniques could be utilized within the scope of the invention. 
     While many embodiments have been described in connection with an upstream pressure sensor, a flow restricting element, and a downstream pressure sensor within a common assembly, it is further contemplated according to a further alternative embodiment, that these components may be separate standalone components within a fluid flow system. The methods and processes of measuring fluid flow rates and the volume of fluid flow are generally identical to those previously described according to this alternative embodiment. Thus, by monitoring the difference in pressure between a standalone upstream pressure sensor and a standalone downstream pressure sensor generated by fluid flowing through a standalone flow restricting element, the fluid flow rate may be calculated. 
     Turning next to  FIG. 6 , an IV push or bolus is shown being delivered to the patient  10 . The caregiver  26  connects the syringe  24  to the second fluid line  18  via the connection  20 . The caregiver  26  then delivers the mediation within the syringe  24  to the patient through the connection  20 . The medication passes through the differential pressure based fluid flow sensor  100  and the third fluid line  22  to the patient  10 . The differential pressure based fluid sensor assembly  100  monitors the flow rate of the medication through the sensor assembly  100 . By monitoring the flow rate through the sensor assembly  100 , the volume of medication delivered to the patient  10  may be calculated. 
     The flow rate of the fluid through the pressure sensor assembly  100  may be calculated by the following equation: 
     
       
         
           
             
               Q 
               = 
               
                 A 
                  
                 
                     
                 
                  
                 
                   C 
                   D 
                 
                  
                 
                   
                     
                       2 
                        
                       Δ 
                        
                       
                           
                       
                        
                       P 
                     
                     ρ 
                   
                 
               
             
             , 
           
         
       
     
     where Q is the volumetric flow rate, ΔP is the pressure differential between an upstream pressure sensor and a downstream pressure sensor, ρ is the fluid mass density, C D  is an opening discharge coefficient, and A is the area of the opening. The use of an orifice for the opening has been empirically shown to minimize the dependence of the induced pressure differential on fluid viscosity, and the discharge coefficient remains essentially constant, thus making the flow rate a function of pressure, density, and area. 
     Once the flow rate Q has been calculated, the volume of the flow may be determined by integrating the flow rate over a period of time using the following equation: V=∫Qdt. Using this equation, both forward and backward flow thorough the sensor assembly  100  may be calculated. A negative flow rate would indicate that the pressure at the downstream sensor  122  is higher than the pressure at the upstream sensor  120 , and thus fluid is flowing backwards through the sensor assembly  100 , away from the patient  10 . 
     In order to provide a more accurate ΔP, a pressure tare, or calibration of the sensors, may be performed, preferably in a zero flow condition. A pressure tare subtracts the average pressure of both the upstream pressure sensor  120  and the downstream pressure sensor  122  from the readings of the respective upstream and downstream pressure sensors  120 ,  122  during fluid delivery. Utilizing such a pressure tare reduces the occurrence of signal drifts from pressure supply drifts, amplification, temperature variance, or residual pressures from any priming steps prior to delivering and recording a bolus dose. 
     Reverse flow of fluid through the sensor can be also measured with ΔP being negative. In this case, the flow is computed by taking the absolute value of ΔP and moving the negative sign outside the square root, 
     
       
         
           
             Q 
             = 
             
               
                 - 
                 A 
               
                
               
                   
               
                
               
                 C 
                 D 
               
                
               
                 
                   
                     
                       2 
                        
                       
                          
                         
                           Δ 
                            
                           
                               
                           
                            
                           P 
                         
                          
                       
                     
                     ρ 
                   
                 
                 . 
               
             
           
         
       
     
     Negative flow rates are important to aggregate in the computation of true net forward volume delivery from the syringe, as they may impact the accuracy of total net volume delivered from the syringe. Additionally, an occlusion condition (i.e., the catheter  25  or the patient&#39;s vein being closed or occluded) can be detected using a back draw of the syringe prior to forward fluid delivery, a typical clinical practice. Under normal conditions, reverse flow of the fluid can be directly measured and aggregated into the net forward volume delivery. However, under occlusion scenarios, the occluded reverse flow can be quickly detected by the sensor using threshold negative limits of the downstream and upstream sensors drawing a negative vacuum pressure. 
     The outputs of the upstream pressure sensor  120  and the downstream pressure sensor  122  may further be monitored for detection of motion artifacts to distinguish such artifacts from true flow patterns. To detect motion artifacts, a ratio of the upstream pressure sensor  120  output to the downstream pressure sensor  122  output is monitored. If, for example, the ratio is less than a predetermined threshold, such as 3:1, it is likely that any changes in pressure indicated by the upstream pressure sensor  120  and the downstream pressure sensor  122  are the results of motion artifacts within the sensor assembly  100 , not forward fluid flow. Thus, flow is only indicated when the ratio of the pressures indicated by the upstream pressure sensor  120  and the downstream pressure sensor  122  is greater than a threshold amount. This is because once flow is initiated, the flow restricting element  112  causes the pressure at the upstream pressure sensor  120  to be significantly higher than the pressure at the downstream pressure sensor  122 . Alternatively, reverse fluid flow is similarly distinguished from motion artifacts, if the ratio of the downstream pressure sensor to the upstream pressure sensor is less than a limit threshold, such as 3:1, and otherwise the signal is considered motion artifacts. Pressure values obtained due to motion artifacts may be excluded from the flow rates and aggregate volume computation. Motion artifacts events are also distinguished from events indicating the true onset of flow, which is used to gate or determine the start of bolus delivery via the syringe  24 . 
     Algorithms also are contemplated to detect the start and end of a single bolus dose. Such an algorithm may rely on a first derivative and a short term mean value of the flow rate. If the mean value of the flow rate is above a certain threshold, such as for example 300 ml/hr, and the mean value of the derivative of the flow rate is above another threshold value, such as 50 (ml/hr)/sec, this flow rate and flow rate derivative indicate a start of a bolus dose. The threshold values are selected based upon the finding that typical bolus dose deliveries have a flow rate between about 300 ml/hr to about 5000 ml/hr, while a human injecting a bolus dose is typically incapable of delivering the injection at a rate less than about 50 ml/hr, on a per second basis. 
     The outputs of the differential pressure sensor assembly  100  may also be used to monitor both the delivery of medication via a single bolus dose, and via an infusion pump. Such an algorithm would indicate that a flow rate below a threshold level, such as for example 300 ml/hr, is not from a bolus dose. Similarly, infusion pump cycles provide a consistent sinusoidal pattern of deliveries with every pumping cycle. Utilizing an approach that analyzes the output of the sensor assembly  100  in a frequency domain, such as through a Fourier transform, pump infusion cycles appear at a much higher frequency than flow rates introduced through a single bolus dose. A low pass filter with a cutoff frequency separating the frequency band due to an infusion pump action, versus manual delivery via a single bolus dose, can segregate the flow rate signal due to each source. Alternatively, an inverse Fourier transform of the frequencies in the band below the frequencies affected by the pump action can recover a time domain flow rate signal from the differential pressure based sensor assembly  100  to quantify the amount of flow from a single bolus dose. Such an algorithm to isolate flow due to a pump source from flow due to manual injection could also be utilized to verify an infusion pump flow rate. Similarly, pressure pulsations occurring as a result of arterial pulsations when the sensor is in direct fluidic connection with an arterial vessel can be detected and mathematically compensated for using frequency domain low pass filtering below a cutoff frequency, since manual injections are usually lower frequency than arterial pulsations. Alternatively, linear weighted averaging of pressure values measured at the sensor is a form of filtering or smoothing that can be applied on the signal to reduce the effect of pulsations. Typical infusion pumps do not measure flow volume, but rather estimate flow volume based upon pump fluidic displacement. Thus, a differential pressure based flow sensor assembly  100  may verify infusion pump function, or be used in a closed feedback loop to control pump flow rate. 
     Yet another algorithm contemplated allows the differential pressure based sensor assembly  100  to be used to detect air pockets within fluids flowing through the sensor assembly  100 . An air pocket typically is much less dense than a fluid passing through the sensor assembly  100 . Thus, an air pocket or bubble within a fluid medium generates an abrupt change in pressure value, followed by a return to expected levels. The start and end of the abrupt change in pressure values is detected by monitoring the first derivative and the second derivative of the output of the upstream pressure sensor  120  and the downstream pressure sensor  122 . An abrupt change in pressure would first be noticed on the upstream pressure sensor  120 , followed by an abrupt change in pressure on the downstream pressure sensor  122 . These pressure changes would be followed by an abrupt resumption back to pressure levels prior to air pocket reception, once the air pocket is passed. The duration of the deviation from typical pressures is indicative of the size of the air pocket. 
       FIG. 7  shows a basic process of utilizing a differential pressure based sensor assembly  100  to determine the instantaneous flow rate and/or volume of a fluid flow delivered through a bolus or other delivery. The process provides a differential pressure based flow sensor assembly  100  in step  602 . Fluid flows through the sensor assembly in step  604 . The output of the upstream pressure sensor  120  is measured in step  606 A, and the output of the downstream pressure sensor  122  is measured in step  606 B. The signals from the sensors  120 ,  122  can be filtered, amplified, or otherwise processed (for example as described above) in step  608 . A timestamp is associated with the measurements in step  610 . A differential pressure is calculated based upon the observed measurements in step  612 . The instantaneous fluid flow rate is calculated in step  614 . The flow rate is integrated over time to derive the volume deliver during the time period of interest in step  616 . In step  618 , the sensor signals or measurements, timestamp information, differential pressure, flow rate and/or volume delivered are communicated to a memory, which can be located in the sensor assembly  100 , in the infusion pump  12 , or another computer. 
     Turning now to  FIG. 7   a,  a process of utilizing a differential pressure based sensor assembly to deliver a fluid is depicted, including monitoring for possible occlusions within the delivery system. The process provides a differential pressure based flow sensor in step  702 . Fluid flows through the sensor in step  704  and the output of both the upstream fluid pressure sensor and the downstream fluid pressure sensor are monitored in step  706 . The process determines whether the outputs of both the upstream fluid pressure sensor and the downstream fluid pressure sensor are within expected ranges in step  708 . If so, the process calculates the fluid flow rate, utilizing the algorithm previously described, in step  710 . Once the flow rate has been determined, the process derives the volume that has passed through the sensor assembly  100  over a given period of time in step  712 . As described above with respect to  FIG. 7 , the sensor signals or measurements, timestamp information, differential pressure, flow rate and/or volume delivered are communicated to a memory, which can be located in the sensor assembly  100 , in the infusion pump  12 , or another processor. 
     If the outputs of the upstream and downstream fluid pressure sensors do not fall within expected ranges, the process determines if the output of the upstream fluid pressure sensor is above a minimum level in step  714 . If the pressure is not above a preset minimum level, an error signal is generated in step  716 , indicating that a possible obstruction exists upstream of the differential pressure based flow sensor assembly  100 . However, if the output of the upstream fluid pressure sensor is above a minimum level, the process in step  718  determines if the output level of the downstream fluid pressure sensor is above a preset minimum level. If the output of the downstream fluid pressure sensor is not above a preset minimum level, an error signal is generated in step  720  that indicates an obstruction may be present at the flow restricting element  112 . However, if the downstream fluid pressure sensor detects a pressure above the preset minimum level, an error signal is generated in step  722  indicating that an obstruction may be present downstream of the differential pressure based flow sensor assembly  100 . 
     Thus, utilizing the process illustrated in  FIG. 7   a,  the flow rate of a fluid as well as the volume of the fluid delivered through a differential pressure based flow sensor assembly may be calculated, and an error message may be provided when an occlusion occurs. 
     As shown in  FIGS. 8   a - 8   b,  a method of delivering medication to a patient utilizing a medication delivery system having an infusion pump is depicted in block diagram form. The process provides a differential pressure based flow sensor assembly in step  802 , such as sensor assembly  100  previously described herein. A first medication is provided through the flow sensor assembly to the patient  10  in step  804 . The flow through the sensor assembly is sensed in step  806 . In step  808 , the process controls an infusion pump delivering the first medication via a processor. The amount or volume of the first medication delivered to the patient is calculated in step  810  using the processor and signals received from the differential pressure based flow sensor assembly  100 . Information about a second medication to be delivered to the patient is provided to the processor in step  812 . The information provided about the second medication is compared to information within the patent&#39;s treatment plan in step  814 . The process determines in step  816  whether the second medication is on the patient&#39;s specific treatment plan, such as by checking whether the patient has a medical order or prescription for the second medication. If the second medication is not found on the patient&#39;s treatment plan, an error message is provided in step  818  indicating that the second medication is not found on the patient&#39;s treatment plan, and the caregiver should check with a physician or other caregiver to determine if it is appropriate to provide the second medication to the patient. It is contemplated that the system may allow the caregiver to override the warning and deliver the second medication. Such an override could be set by the hospital, or other healthcare facility, so as to allow some caregivers to deliver certain medications to a patient even if that medication is not found on the patient&#39;s treatment plan. Thus, a balance may be reached between providing a patient a potentially important medication dose, with protecting the patient from the delivery of an unnecessary medication. If the second medication is found on the patient&#39;s treatment plan, guidelines for delivering the second medication are generated or displayed in step  820 . The guidelines can include but are not limited to a target delivery rate with upper and/or lower limits, a total volume or amount to be delivered during the bolus, and a time period over which to deliver the IV push or bolus. 
     Continuing now to  FIG. 8   b,  the second medication is delivered to the patient in step  822 . The process calculates the delivery rate of the second medication using the differential pressure based flow rate sensor assembly  100  in step  824 . As described with respect to  FIG. 7  above, the delivery flow rate calculations can be stored in memory. A comparison is performed in step  826  to determine if the delivery rate of the second medication conforms to the delivery guidelines. If the delivery rate does not conform to the delivery guidelines, a delivery rate warning is provided to the caregiver in step  828 . If the delivery rate warning is provided, the patient&#39;s electronic medication administration record (eMAR) is updated in step  830  to show that the second medication was delivered at a rate inconsistent with the delivery guidelines or protocols. The amount of the second medication delivered to the patient can also be calculated in step  832 . The process in step  834  compares the amount of the second medication delivered to the amount of the second medication the patient was scheduled to receive. If the amount of the second medication the patient received does not conform to the patient&#39;s treatment plan, a dosage warning is provided to the caregiver at step  836 . This warning can indicate that the patient was provided an underdose of the second medication, or that the patient was provided with an overdose of the second medication. The patient&#39;s electronic medication administration record (eMAR) is updated in step  838  to include the amount of the second medication that was provided to the patient, as well as information to indicate that the dosage of the second medication did not conform to the patient&#39;s treatment plan. If the amount of the second medication delivered to the patient conforms to the patient specific guidelines, the patient&#39;s electronic medication administration record (eMAR) is updated in step  840  to indicate that a proper dosage of the second medication was delivered to the patient. It is contemplated that every update to the patient&#39;s electronic medication administration record (eMAR) will note the time a medication was delivered to the patient, as well as the caregiver responsible for delivering that medication to the patient. 
     According to a further embodiment, a disposable infusion tubing set is provided that has a disposable portion of a differential pressure based flow sensor assembly. The tubing set would include at least a first tube adapted to connect to a primary medication reservoir, and a connection site to allow a second medication to be introduced into the first tube of the tubing set upstream of the disposable portion of the differential pressure based flow sensor assembly. The disposable infusion tubing set further has a second tube adapted to connect to a patient access device. The second tube is adapted to be positioned downstream of the disposable portion of the differential pressure based flow sensor assembly. As discussed above, the disposable portion of the differential pressure based flow sensor assembly can be disposed in other locations within the disposable infusion tubing set, depending on the line pressure conditions, delivery flow rates, or fluid volume delivery amounts of interest. 
     According to yet another embodiment, a differential pressure based flow rate sensor assembly is replaced by a pressure based event detection sensor. A pressure based event detection sensor allows an event, such as a bolus, to be detected noting a spike in pressure. Such an event detection sensor would not allow the computation of the volume of medication delivered, but will place a notation onto a patient&#39;s record that some medication was delivered at a specific time. Thus, a record will exist confirming that a patient was provided with medication. 
     According to yet a further embodiment, a differential pressure based flow sensor assembly may be powered by an inductive power source. Such an embodiment would contain many of the same features as the differential pressure based flow sensor assembly  100  described herein. Similarly, it is contemplated that a wireless differential pressure based flow sensor assembly may transmit information regarding a pressure at an upstream pressure sensor and information regarding a downstream pressure sensor to other components within a system. Finally, it is contemplated that the portion  104  of the differential pressure based flow sensor assembly  100  could be produced using MEMS, integrated circuits or other technology in a miniaturized and low cost manner, such that the portion  104  might be considered disposable as well. 
     Turning now to  FIG. 9 , a medication delivery system  900  is shown having an infusion pump  902 , a primary medication reservoir  904  and a secondary medication reservoir  906 . The medication delivery system  900  allows a patient to receive medication from the primary medication reservoir  904 , or the secondary medication reservoir  906 , through various fluid line portions  908   a - 908   d  depending on the settings of a first valve  910   a  or a second valve  910   b.  A first drip chamber  914   a  and a second drip chamber  914   b  are in fluid communication with each of the respective primary and secondary medication reservoirs  904 ,  906 . A first fluid line segment  908   a  delivers a first medication from primary medication reservoir  904  through the first valve  910   a  to a y-site  916 . The first valve  910   a  allows the flow of the first medication in the first fluid line segment  908   a  to be controlled. 
     A second fluid line segment  908   b  delivers a second medication from a secondary medication reservoir  906  to the y-site  916 . The second fluid line segment  908   b  causes fluid to pass through a differential pressure based fluid flow sensor assembly  912 , such as the sensor assembly  100  described above. The second fluid line segment  908   b  additionally has the second valve  910   b,  to allow flow through the second line segment to be controlled. 
     The first fluid line segment  908   a  and the second fluid line segment  908   b  fluidly join together at the y-site  916 . A third fluid line segment  908   c  provides a fluid path from the y-site  916  to the pump  902 . The pump  902  may be generally identical to the pump  12  described above. The pump  902  may be controlled by the caregiver to deliver medication at a predetermined flow rate. 
     A fourth fluid line segment  908   d  delivers fluid from the pump  902  to the patient. The fourth fluid flow path  908   d  has a second y-site  918  to allow another fluid line or fluid source, such as a syringe bolus, to connect to the fourth fluid line segment  908   d  and be supplied to the patient. 
     In use a first medication, or other fluid, in the primary medication reservoir  904  is delivered to the patient via the first fluid line segment  908   a,  the third fluid line segment  908   c,  the pump  902  and the fourth fluid line segment  908   d.  The pump  902  will monitor and control the flow rate as well as the volume of the first medication that passes through the pump  902 . 
     When a fluid from the secondary medication reservoir  906  is to be delivered to the patient, the pump  902  is stopped, and the first valve  910   a  is closed. The second valve  910   b  is opened and the pump is reprogrammed, after which fluid flows from the secondary medication reservoir  906  to the patient. The fluid from secondary medication reservoir  906  flows at a predetermined rate based on the characteristics of the second fluid, and the patient&#39;s clinical needs, through the fluid flow sensor assembly  912 . The fluid flow sensor assembly  912  may be generally identical to the differential pressure based flow sensor assembly  100  described above, or may be a different type of flow sensor assembly. The fluid flow sensor assembly  912  allows the flow rate of the fluid from the secondary medication reservoir  906  to be monitored, and thus, the volume of fluid delivered may be calculated. Further, this flow rate calculations can be compared to the known pump rate and provide confirmation that substantially all of the fluid routing through the pump is in fact originating from secondary reservoir  906 . 
     Once the fluid flow sensor assembly  912  has sensed that the proper amount of fluid from the secondary medication reservoir  906  has been delivered, or the secondary medication reservoir  906  is about to become empty, the caregiver will stop the pump  902 , close the second valve  910   b,  and reopen the first valve  910   a  to allow the medication in the primary medication reservoir  904  to again be delivered to the patient. The fluid flow sensor assembly  912  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the second medication, the flow rate of the delivery of the second medication, and the volume of the second medication that was delivered to the patient. Updating the patient&#39;s electronic medication administration record in such a manner helps to prevent errors in medication delivery, by reducing the likelihood that a patient has received a medication that is not indicated in the patient&#39;s medical records, or conversely, has not received a medication that the patient&#39;s medical record shows was delivered. 
     In addition to simply monitoring the flow rate of medication from the secondary medication reservoir  906 , the fluid flow sensor assembly  912  may also be set to alert the caregiver to changes in flow conditions that may indicate that the caregiver needs to take some action. For instance, if a differential pressure based fluid flow sensor is used for the fluid flow sensor assembly  912  and the pressure of the upstream chamber drops below a predetermined level, the caregiver may be alerted that the fluid level in the secondary medication reservoir  906  is becoming low. Further, monitoring of the flow conditions of medication from the secondary medication reservoir  906  allow the caregiver to be alerted if the flow rate differs from an expected flow rate, such as if an occlusion is present in the fluid line. 
     Turning next to  FIG. 10 , a medication delivery system  1000  according to a further embodiment is shown. The medication delivery system  1000  is shown having an infusion pump  1002 , a primary medication reservoir  1004  and a secondary medication reservoir  1006 . The medication delivery system  1000  allows a patient to receive medication from the primary medication reservoir  1004 , or the secondary medication reservoir  1006 , through various fluid line portions  1008   a - 1008   d,  depending on the settings of a first valve  1010   a  or a second valve  1010   b.  A first drip chamber  1014   a  and a second drip chamber  1014   b  are in fluid communication with each of the respective primary and secondary medication reservoirs  1004 ,  1006 . A first fluid line segment  1008   a  delivers a first medication from primary medication reservoir  1004  through the first valve  1010   a  to a y-site  1016 . The first valve  1010   a  allows the flow of the first medication in the first fluid line segment  1008   a  to be controlled. 
     A second fluid line segment  1008   b  delivers a second medication from a secondary medication reservoir  1006  to the y-site  1016 . The second fluid line segment  1008   b  causes fluid to pass through a drop counter sensor assembly  1012  that is adapted to count each drop of fluid from the secondary medication reservoir  1006  that enters the second fluid line portion  1008   b.    
     According to one embodiment, the drop counter sensor assembly  1012  estimates the flow rate by assuming each fluid drop has a predetermined volume, thus, based on the number of fluid drops that pass the sensor over a given period, a flow rate may be calculated. According to a different embodiment, it is contemplated that the drop counter assembly  1012  calculates the flow rate by estimating the volume of each fluid drop that passes by the drop counter assembly  1012 . By estimating the volume of each fluid drop, a more accurate fluid flow rate may be calculated, as some variation commonly occurs in the size of the fluid drops. 
     The second fluid line segment  1008   b  additionally has the second valve  1010   b,  to allow flow through the second line segment  1008   b  to be controlled. 
     The first fluid line segment  1008   a  and the second fluid line segment  1008   b  fluidly join together at the y-site  1016 . A third fluid line segment  1008   c  provides a fluid path from the y-site  1016  to the pump  1002 . The pump  1002  may be generally identical to the pump  12  described above. The pump  1002  may be controlled by the caregiver to deliver medication at a predetermined flow rate. 
     A fourth fluid line segment  1008   d  delivers fluid from the pump  1002  to the patient. The fourth fluid flow path  1008   d  has a second y-site  1018  to allow another fluid line or fluid source, such as a syringe bolus, to connect to the fourth fluid line segment  1008   d  and be supplied to the patient. 
     In use a first medication, or other fluid, in the primary medication reservoir  1004  is delivered to the patient via the first fluid line segment  1008   a,  the third fluid line segment  1008   c,  the pump  1002  and the fourth fluid line segment  1008   d.  The pump  1002  will monitor the flow rate as well as the volume of the first medication that passes through the pump  1002 . 
     When a fluid from the secondary medication reservoir  1006  is to be delivered to the patient, the pumping operation of the pump  1002  is ceased, and the first valve  1010   a  is closed. The second valve  1010   b  is opened, and subsequent to reprogramming the pump  1002 , fluid flows from the secondary medication reservoir  1006  to the patient at the appropriate secondary rate. The fluid from secondary medication reservoir  1006  flows through the drop counter assembly  1012 . The drop counter sensor assembly  1012  allows the flow rate of the fluid from the secondary medication reservoir  1006  to be monitored, and thus, the volume of fluid delivered may be calculated. The flow rate observed by the drop counter sensor assembly  1012  can be compared to the anticipated flow rate controlled by the pump  1002 , thus allowing the system  1000  to confirm that substantially all of the fluid progressing through the pump  1002  originates within the secondary reservoir  1006 . In the event that the system  1000  detects that the pump  1002  is drawing fluid from a source other than the secondary reservoir  1006  the caregiver may be notified, or the pump  1002  may cease pumping operations, as appropriate based on the medication involved and the healthcare facility or hospital policy. 
     Once the drop counter sensor assembly  1012  has sensed that the proper amount of fluid from the secondary medication reservoir  1006  has been delivered, or the secondary medication reservoir  1006  is about to become empty, the caregiver will stop the pump  1002 , close the second valve  1010   b,  and reopen the first valve  1010   a  to allow the medication in the primary medication reservoir  1004  to again be delivered to the patient subsequent to a reprogramming of the pump infusion rate. The drop counter sensor assembly  1012  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the second medication, the flow rate of the delivery of the second medication, and the volume of the second medication that was delivered to the patient. Updating the patient&#39;s electronic medication administration record in such a manner helps to prevent errors in medication delivery, by reducing the likelihood that a patient has received a medication that is not indicated in the patient&#39;s medical records, or conversely, has not received a medication that the patient&#39;s medical record shows was delivered. 
     In addition to simply monitoring the flow rate of medication from the secondary medication reservoir  1006 , the fluid flow sensor assembly  1012  may also be set to alert the caregiver to changes in flow conditions that may indicate that the caregiver needs to take some action. These alerts could include reductions in flow from the reservoir, which could indicate a near-empty reservoir state, or a mode in which the pump is drawing from both reservoirs. 
     As shown in  FIG. 11 , a further embodiment of a medication delivery system  1100  is depicted. The medication delivery system  1100  is shown having an infusion pump  1102 , a primary medication reservoir  1104  and a secondary medication reservoir  1106 . The medication delivery system  1100  allows a patient to receive medication from the primary medication reservoir  1104 , or the secondary medication reservoir  1106 , through various fluid line portions  1108   a - 1108   d  depending on the settings of a first valve  1010   a  or a second valve  1110   b.  A first fluid line segment  1108   a  delivers a first medication from the primary medication reservoir  1104  through the first valve  1110   a  to a y-site  1116 . The first valve  1110   a  allows the flow of the first medication in the first fluid line segment  1108   a  to be controlled. 
     A second fluid line segment  1108   b  delivers a second medication from a secondary medication reservoir  1106  to the y-site  1116 . The secondary medication reservoir  1106  is connected to a load cell  1112 . The load cell  1112  is adapted to measure the weight of the secondary medication reservoir  1106 . The load cell  1112  is adapted to record the weight of the secondary medication reservoir  1106  over time, thus allowing the flow rate of fluid out of the secondary medication reservoir  1106  to be calculated, by monitoring the change in weight over time of the secondary medication reservoir  1106  and dividing that result by the density of the fluid within the secondary medication reservoir  1106 . Further, the total volume of fluid delivered may be calculated by dividing the total change in weight by the density of the fluid. 
     The second fluid line segment  1108   b  causes fluid to pass through the second valve  1110   b  to allow the flow of the fluid from the secondary reservoir  1106  to be controlled. 
     The first fluid line segment  1108   a  and the second fluid line segment  1108   b  fluidly join together at the first y-site  1116 . A third fluid line segment  1108   c  provides a fluid path from the first y-site  1116  to the pump  1102 . The pump  1102  may be generally identical to the pump  12  described above. The pump  1102  may be controlled by the caregiver to deliver medication at a predetermined flow rate. 
     A fourth fluid line segment  1108   d  delivers fluid from the pump  1102  to the patient. The fourth fluid flow path  1108   d  has a second y-site  1118  to allow another fluid line or fluid source, such as a syringe bolus, to connect to the fourth fluid line segment  1108   d  and be supplied to the patient. 
     In use a first medication, or other fluid, in the primary medication reservoir  1104  is delivered to the patient via the first fluid line segment  1108   a,  the third fluid line segment  1108   c,  the pump  1102  and the fourth fluid line segment  1108   d.  The pump  1102  will monitor and control the flow rate as well as the volume of the first medication that passes through the pump  1102 . 
     When a fluid from the secondary medication reservoir  1106  is to be delivered to the patient, the pump  1102  is stopped, and the first valve  1110   a  is closed. The second valve  1110   b  is opened and fluid flows from the secondary medication reservoir  1106  to the patient, subsequent to reprogramming of the pump  1102 . The load cell  1112  allows the flow rate of the fluid from the secondary medication reservoir  1106  to be monitored, and thus, the volume of fluid delivered may be calculated. Additionally, when the secondary medication reservoir  1106  is positioned upstream of the pump  1102 , the output of the load cell  1112  may be compared to the flow rate calculated by the pump  1102  to ensure that only medication from the secondary reservoir  1106  is being delivered to the patient. 
     While fluid is being delivered from the secondary medication reservoir  1106 , the pump  1102  is restarted, and pumps the fluid from the secondary medication reservoir  1106  at a predetermined rate based on the characteristics of the second fluid, and the patient&#39;s clinical needs. 
     Once the load cell  1112  has indicated that the proper amount of fluid from the secondary medication reservoir  1106  has been delivered, or the secondary medication reservoir  1106  is about to become empty, the care giver may stop the pump  1102 , close the second valve  1110   b,  and reopen the first valve  1110   a  to allow the medication in the primary medication reservoir  1104  to again be delivered to the patient. The load cell  1112  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the second medication, the flow rate of the delivery of the second medication, and the volume of the second medication that was delivered to the patient. 
     In addition to simply monitoring the flow rate of medication from the secondary medication reservoir  1106 , the load cell  1112  may also be set to alert the caregiver to changes in flow conditions that may indicate that the caregiver needs to take some action. 
     Yet another embodiment of a medication delivery system  1200  is depicted in  FIG. 12 . The medication delivery system  1200  generally identical to the medication delivery system  900  depicted in  FIG. 9 , except the secondary medication reservoir connects to the fluid line portion at the second y-site  1218  downstream of an infusion pump  1202 . The medication delivery system  1200  is shown having the infusion pump  1202 , a primary medication reservoir  1204  and a secondary medication reservoir  1206 . The medication delivery system  1200  allows a patient to receive medication from the primary medication reservoir  1204 , or the secondary medication reservoir  1206 , through various fluid line portions  1208   a - 1208   d  depending on the settings of a first valve  1210   c,  a second valve  1210   b,  or a third valve  1210   c.  A first fluid line segment  1208   a  delivers a first medication from the primary medication reservoir  1204  through the third valve  1210   c  to a y-site  1216 . The third valve  1210   c  allows the flow of the first medication in the first fluid line segment  1208   a  to be controlled. It is contemplated that the first valve  1210   a  may not be required if the pump  1202  has check valves to limit the backflow in the second fluid line segment  1208   b  when fluid flows from the secondary medication reservoir  1206 . Additionally, the pump  1202  itself may sufficiently limit backflow, even if the pump  1202  does not contain check valves, to allow the elimination of the first valve  1210   a.    
     A second fluid line segment  1208   b  runs from the infusion pump  1202  to the second y-site  1218 . The second fluid line segment  1208   b  contains the first valve  1210   a  that allows the flow of fluid in the second fluid line segment  1208   b  to be controlled. 
     The third fluid line segment  1208   c  delivers a second medication from a secondary medication reservoir  1206  to a second y-site  1218 . The third fluid line segment  1208   c  causes fluid to pass through a differential pressure based fluid flow sensor assembly  1212 , such as the sensor assembly  100  described above. The third fluid line segment  1208   c  additionally has the second valve  1210   b,  to allow flow through the third line segment  1208   c  to be controlled. The second valve  1210   b  may be a proportional or analog valve to allow the caregiver to vary the rate of the fluid flow from the secondary reservoir  1206 . 
     The second fluid segment  1208   b  and the third fluid line segment  1208   c  fluidly join together at the second y-site  1218 . A fourth fluid line segment  1208   d  delivers fluid from the second y-site  1218  to the patient. 
     In use, a first medication, or other fluid, in the primary medication reservoir  1204  is delivered to the patient via the first fluid line segment  1208   a,  the second fluid line segment  1208   b,  the pump  1202  and the fourth fluid line segment  1208   d.  The pump  1202  will monitor and control the flow rate as well as the volume of the first medication that passes through the pump  1202 . 
     When a fluid from the secondary medication reservoir  1206  is to be delivered to the patient, the pump  1202  is stopped, and the first valve  1210   a  and the third valve  1210   c  are closed. The second valve  1210   b  is opened, and fluid flows from the secondary medication reservoir  1206  to the patient. The fluid from secondary medication reservoir  1206  flows through the fluid flow sensor assembly  1212 . The fluid flow sensor assembly  1212  may be generally identical to the differential pressure based flow sensor assembly  100  described above, or may be a different type of flow sensor assembly. The fluid flow sensor assembly  1212  allows the flow rate of the fluid from the secondary medication reservoir  1206  to be monitored, and thus, the volume of fluid delivered may be calculated. Flow rate information derived by the sensor can be communicated via a user interface, including a user interface on the pump  1202 . 
     While fluid is being delivered from the secondary medication reservoir  1206 , the pump  1202  remains stopped, and gravity feeds the fluid from the secondary medication reservoir  1206  to the patient. Alternatively, a pressure cuff may be applied to the secondary bag to increase the infusion rate. This is particularly useful in treatments requiring high continuous flow rates of delivery. During the initiation of flow from the secondary medication reservoir  1206 , the flow sensor  1212  output may be monitored and the valve  1210   b  adjusted to provide an appropriate fluid flow from the secondary reservoir  1206 . 
     Once the fluid flow sensor assembly  1212  has sensed that the proper amount of fluid from the secondary medication reservoir  1206  has been delivered, or the secondary medication reservoir  1206  is about to become empty, the care giver may close the second valve  1210   b,  and reopen the first valve  1210   a  and the third valve  1210   c  to allow the medication in the primary medication reservoir  1204  to again be delivered to the patient, subsequent to re-initiation of the infusion pump  1202 . The fluid flow sensor assembly  1212  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the second medication, the flow rate of the delivery of the second medication, and the volume of the second medication that was delivered to the patient. Updating the patient&#39;s electronic medication administration record in such a manner helps to prevent errors in medication delivery, by reducing the likelihood that a patient has received a medication that is not indicated in the patient&#39;s medical records, or conversely, has not received a medication that the patient&#39;s medical record shows was delivered. 
     In addition to simply monitoring the flow rate of medication from the secondary medication reservoir  1206 , the fluid flow sensor assembly  1212  may also be set to alert the caregiver to changes in flow conditions that may indicate that the caregiver needs to take some action. For instance, if a differential pressure based fluid flow sensor is used for the fluid flow sensor assembly  1212  and the pressure of the upstream chamber drops below a predetermined level, the caregiver may be alerted that the fluid level in the secondary medication reservoir  1206  is becoming low. Further, monitoring of the flow conditions of medication from the secondary medication reservoir  1206  allow the caregiver to be alerted if the flow rate differs from an expected flow rate, such as if an occlusion is present in the fluid line. 
     Referring now to  FIG. 13 , yet a further embodiment of a medication delivery system  1300  is depicted. The medication delivery system  1300  is generally identical to the medication delivery system  1000 , except the secondary fluid reservoir connects to the system downstream of the infusion pump  1302 . 
     The medication delivery system  1300  is shown having an infusion pump  1302 , a primary medication reservoir  1304  and a secondary medication reservoir  1306 . The medication delivery system  1300  allows a patient to receive medication from the primary medication reservoir  1304 , or the secondary medication reservoir  1306 , through various fluid line portions  1308   a - 1308   d  depending on the settings of a first valve  1310   a,  a second valve  1310   b,  and a third valve  1310   c.  A first drip chamber  1314   a  and a second drip chamber  1314   b  are in fluid communication with each of the respective primary and secondary medication reservoirs  1304 ,  1306 . A first fluid line segment  1308   a  delivers a first medication from primary medication reservoir  1304  through the third valve  1310   c  to a first y-site  1316  and finally to the infusion pump  1302 . The third valve  1310   c  allows the flow of the first medication in the first fluid line segment  1308   a  to be controlled. 
     A second fluid line segment  1308   b  runs from the infusion pump  1302  to the second y-site  1318 . 
     A third fluid line segment  1308   c  delivers the second medication from the secondary medication reservoir  1306  to the second y-site  1318 . The third fluid line segment  1308   c  causes fluid to pass through a drop counter sensor assembly  1312  that is adapted to count each drop of fluid from the secondary medication reservoir  1306  that enters the third fluid line portion  1308   c.    
     According to one embodiment, the drop counter sensor assembly  1312  estimates the flow rate by assuming each fluid drop has a predetermined volume, thus, based on the number of fluid drops that pass the sensor over a given period, a flow rate may be calculated. According to a different embodiment, it is contemplated that the drop counter assembly  1312  calculates the flow rate by estimating the volume of each fluid drop that passes by the drop counter assembly  1312 . By estimating the volume of each fluid drop, a more accurate fluid flow rate may be calculated, as some variation commonly occurs in the size of the fluid drops. 
     The third fluid line segment  1308   c  additionally has the second valve  1310   b,  to allow flow through the third line segment  1308   c  to be controlled. 
     The second fluid line segment  1308   b  and the third fluid line segment  1308   c  fluidly join together at the second y-site  1318 . The pump  1302  may be generally identical to the pump  12  described above. The pump  1302  may be controlled by the caregiver to deliver medication at a predetermined flow rate. 
     The fourth fluid line segment  1308   d  delivers fluid from the second y-site  1318  to the patient. 
     In use, a first medication, or other fluid, in the primary medication reservoir  1304  is delivered to the patient via the first fluid line segment  1308   a,  the pump  1302 , the second fluid line segment  1308   b,  and the fourth fluid line segment  1308   d.  The pump  1302  will monitor and control the flow rate as well as the volume of the first medication that passes through the pump  1302 . 
     When a fluid from the secondary medication reservoir  1306  is to be delivered to the patient, the pump  1302  is stopped, and the first valve  1310   a  and the third valve  1310   c  are closed. The second valve  1310   b  is opened, and fluid flows from the secondary medication reservoir  1306  to the patient. The fluid from secondary medication reservoir  1306  flows through the drop counter assembly  1312 . The drop counter sensor assembly  1312  allows the flow rate of the fluid from the secondary medication reservoir  1306  to be monitored, and thus, the volume of fluid delivered may be calculated. 
     While fluid is being delivered from the secondary medication reservoir  1306 , the pump  1302  remains off, and gravity causes the fluid flow from the secondary medication reservoir  1306 . Alternatively, a pressurized cuff may be used to increase the pressure driving the fluid from the secondary medication reservoir  1306 . This is particularly useful in treatments requiring high continuous flow rates for delivery of fluid from the secondary medication reservoir  1306 . During the initiation of the flow of fluid from the secondary medication reservoir  1306 , the flow sensor  1312  output may be monitored to allow the caregiver to adjust the valve  1310   b  to provide appropriate fluid flow. 
     Once the drop counter sensor assembly  1312  has sensed that the proper amount of fluid from the secondary medication reservoir  1306  has been delivered, or the secondary medication reservoir  1306  is about to become empty, the caregiver closes the second valve  1310   b,  and reopens the first valve  1310   a  and the third valve  1310   c  to allow the medication in the primary medication reservoir  1304  to again be delivered to the patient subsequent to re-initiation of the infusion pump  1302 . The drop counter sensor assembly  1312  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the second medication, the flow rate of the delivery of the second medication, and the volume of the second medication that was delivered to the patient. Updating the patient&#39;s electronic medication administration record in such a manner helps to prevent errors in medication delivery, by reducing the likelihood that a patient has received a medication that is not indicated in the patient&#39;s medical records, or conversely, has not received a medication that the patient&#39;s medical record shows was delivered. 
     In addition to simply monitoring the flow rate of medication from the secondary medication reservoir  1306 , the fluid flow sensor assembly  1312  may also be set to alert the caregiver to changes in flow conditions that may indicate that the caregiver needs to take some action. 
     Finally, turning to  FIGS. 14   a  and  14   b,  still yet another embodiment of a medication delivery system  1400  is depicted. As shown in  FIG. 14   a,  the medication delivery system has a fluid reservoir  1402 , a flow sensor assembly  1404 , that may be a differential pressure based flow sensor assembly operationally similar to the flow sensor  100  described above, an adjustable control valve  1406 , and fluid line portions  1408   a  and  1408   b.  An optional y-site  1410  fluidly joins a first fluid line portion  1408   a  to a second fluid line portion  1408   b.  The y-site  1410  allows another fluid line or fluid source, such as a syringe bolus to connect to the second fluid line segment  1408   b  to be supplied to the patient. 
     In use, a medication, or other fluid, in the reservoir  1402  is delivered to the patient via the first fluid line segment  1408   a  and the second fluid line segment  1408   b.  The adjustable valve  1406  allows the flow rate of the fluid to be adjusted based on the clinical needs of the patient. As shown in  FIG. 14   b,  the flow sensor assembly  1404  additionally has a display  1412 . The display may show a real time flow rate as determined using the sensor assembly  1404 . By observing the displayed flow rate in real time on the display  1412 , the caregiver may adjust the position of a slider  1414  of the adjustable control valve  1416  to either increase or decrease the flow rate. Thus, the medication delivery system  1400  allows a gravity fed medication delivery to occur with a flow rate based on a patient&#39;s clinical needs. For example, if the display  1412  shows that the flow rate is higher than desired, the caregiver may adjust the valve slider  1414  to partially close the valve  1406  until the display  1412  indicates the desired flow rate. Similarly, if the display  1412  indicates that the flow rate is lower than desired, the care giver may adjust the valve slider  1414  to partially open the valve  1406  until the display  1412  indicates the desired flow rate. 
     Once the fluid flow sensor assembly  1404  has sensed that the proper amount of fluid from the reservoir  1402  has been delivered, or the reservoir  1402  is about to become empty, the caregiver may close the adjustable valve  1406 . Depending on the patient&#39;s medical needs, the caregiver may then replace the reservoir  1402  with another reservoir, or may simply remove the empty reservoir  1402 . The fluid flow sensor assembly  1404  allows data monitored by the sensor to be communicated electronically to a patient&#39;s electronic medication administration record, such that the patient&#39;s medical records accurately reflect when a patient was given the medication, the flow rate of the delivery of the medication, and the volume of the medication that was delivered to the patient. Updating the patient&#39;s electronic medication administration record in such a manner helps to prevent errors in medication delivery, by reducing the likelihood that a patient has received a medication that is in not indicated in the patient&#39;s medical records, or conversely, has not received a medication that the patient&#39;s medical record shows was delivered. While infusion data from an infusion pump may easily be captured and communicated to caregivers and electronic patient records, the present embodiments outline cost-effective and practical techniques by which to capture medication delivery data not subject to pump based infusions. 
     It should be noted that the systems may not require or utilize the manual liquid valves described above, as a pump may draw fluid from whichever reservoir is physically positioned at a higher elevation. In such a mode of operation, a flow sensor provides similar information that allows the source of the fluid flow to be identified. 
     While the foregoing has described what is considered to be the best mode and/or other examples, it is understood that various modifications may be made and that the subject matter disclosed herein may be implemented in various forms and examples, and that they may be applied in numerous other applications, combinations and environments, only some of which have been described herein. Those of ordinary skill in that art will recognize that the disclosed aspects may be altered or amended without departing from the true scope of the subject matter. Therefore, the subject matter is not limited to the specific details, exhibits and illustrated examples in this description. It is intended to protect any and all modifications and variations that fall within the true scope of the advantageous concepts disclosed herein.