Abstract:
A feeding set adaptor and related system for delivering solutions utilize a feeding set adaptor which engages a pump engaging portion of an infusion set and the feeding set adaptor structure to provide monitoring portions for detecting pressures within the infusion set, a sample cell for determining the presence of air within an infusion set, and an anti-freeflow device for selectively preventing freeflow through the infusion set. The feeding set adaptor is configured for mounting on an infusion pump which moves solution through the infusion set for delivery to a patient.

Description:
RELATED APPLICATIONS 
   The present application is a divisional of U.S. patent application Ser. No. 10/606,262, filed Jun. 25, 2003, now U.S. Pat. No. 6,852,094, which is a continuation application of U.S. patent application Ser. No. 09/836,851, filed Apr. 16, 2001, now U.S. Pat. No. 6,659,976. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to systems for feeding solutions to patients. More particularly, the present invention relates to a feeding set adaptor which is used in association with a medical solution pump. The pump and an infusion set which is acted on by the pump typically form a system for the monitoring of fluid pressures, for bubble detection and for selective flow occlusion of solutions being fed to a patient. Specifically, the invention relates to an adaptor which is used to connect various parts of an infusion set and to integrate them with the pump to enable the monitoring of fluid pressures, the detection of bubbles, and the selective occlusion of fluid flow to prevent freeflow conditions. 
   2. State of the Art 
   There are numerous situations in which a solution must be fed to a patient over a period of time. In some situations, the solution is provided directly into the blood stream of the patient. Saline solutions and medications supplied in such a manner are typically referred to as parenteral solutions. 
   In contrast to a parenteral system, an enteral feeding system is used to provide nutrient solutions to patients who, for one reason or another, are unable to eat for themselves. Such a system typically includes a pump which is attached to an input tube connected to a supply container and to an output tube which is connected to a patient. The pump draws nutrient solution from the supply container and delivers the solution to the patient. By adjusting the number of rotations of the motor, or the frequency of rotations, in the pump, an enteral feeding pump can adjust its output to deliver a predetermined amount of nutrient solution (or even medication) at a desired rate. 
   A significant problem with many currently available enteral feeding systems, is that the intake and output tubes may become occluded. Unlike parenteral solutions, enteral feeding solutions have a relatively high viscosity, as they must carry sufficient nutrition to sustain the patient. Occlusion can occur, for example, if a fibrous substance is included in the enteral feeding solution and somehow combines to interfere with flow through the tube. Occlusion can also occur if a tube is bent sufficiently to interfere with flow therethrough, or if a roller clamp (as is commonly used for intravenous applications) is not sufficiently opened. Because of the viscosity of the solution, the amount of kinking of the tube or other interference required to interfere with solution flow is significantly less than that required in a parenteral infusion set. 
   If the intake tube becomes occluded, insufficient solution may be supplied to the pump, and thus to the patient. If the output tube becomes occluded, the flow of solution may be blocked, or the solution may be delivered suddenly at unusually high pressures. Additionally, medical personnel may fail to notice that the supply container is out of solution, or may not properly mount the intake and/or output tubes in the pump, thereby preventing the proper amount of solution from being delivered to the patient. Any of these scenarios can have tragic consequences if allowed to continue for a prolonged period of time. 
   Yet another concern with enteral feeding systems is that of viscosity of the solution and viscosity changes as a container full of solution is pumped to a patient. Knowing the viscosity of the fluid being pumped through the enteral feeding system is important because different viscosities are pumped at different rates by the enteral feeding pump. For example, a lower quantity of a highly viscous solution will be pumped by a given number of rotations of the enteral feeding pump motor than will be moved by the same pump when the solution has low viscosity. In other words, the amount of solution fed to the patient can differ substantially depending on the solution&#39;s viscosity. Thus, unless the pump is able to accurately determine and compensate for viscosity changes in the solution (i.e. by increasing or decreasing the rotations of the pump rotor in a given period of time), it is difficult to know exactly how much of the solution has been fed to the patient. 
   Yet another problem which is of concern during the administration of enteral feeding solutions is the presence of air bubbles. While very small air bubbles will not cause harm, large bubbles entering the blood stream can cause serious medical complications and even death. Thus, it is important to monitor the solution to ensure that any bubbles present do not exceed the desired threshold. 
   Still another problem which is present in enteral feeding systems, and the like, is freeflow. Often, the infusion set is placed in a free standing arrangement in which gravity forces the solution into the patient. The rate at which the solution enters the patient can be roughly controlled by various clamps, such as roller clamps, which are currently available on the market. 
   In many applications, it is necessary to precisely control the amount of solution which enters the patient. When this is the case, a regulating device, such as an enteral feeding pump, is placed along the infusion set to control the rate at which the solution is fed to the patient. In applications where a pump, etc., is used, the clamps used to regulate flow are typically opened to their fullest extent to prevent the clamp from interfering with the proper functioning of the pump. The clamp is opened with the expectation that the enteral feeding pump will control fluid flow through the infusion set. 
   It is not uncommon, for emergencies or other distractions to prevent the medical personnel from properly loading the infusion set in the enteral feeding pump. When the infusion set is not properly loaded in the pump and the clamp has been opened, a situation known as freeflow often develops. The force of gravity causes the solution to flow freely into the patient unchecked by the pump or other regulating device. Under a freeflow condition, an amount of solution many times the desired dose can be supplied to the patient within a relatively short time period. This can be particularly dangerous if the solution contains potent medicines and/or the patient&#39;s body is not physically strong enough to adjust to the large inflow of solution. 
   Numerous devices have been developed in an attempt to prevent free flow conditions. Such devices, however, typically add significantly to the overall cost of the infusion set and some provide only marginal protection against free flow. Thus, there is a need for a device that prevents a freeflow condition while allowing controlled flow through the infusion set. There is also a need for such a device which prevents freeflow if an infusion set is not properly mounted in a pump or other regulating means. Furthermore, there is a need for a device which prevents freeflow and which is inexpensive and easy to use. 
   The fluid flow monitoring mechanism disclosed in U.S. Pat. No. 5,720,721 and the anti-freeflow mechanism described in U.S. Pat. No. 5,704,584 (both of which are expressly incorporated herein) provided a significant improvement in monitoring for enteral feeding pumps and in control of freeflow situations. 
   As shown in  FIG. 1A , the pump taught in U.S. Pat. No. 5,720,721 uses two pressure sensors to monitor viscosity and occlusions, and to enable the enteral feeding pump to compensate for the varying amount of solution which will pass through the pump with each rotation of the rotor. The pressure sensors engage the elastic tube of the infusion set and monitor changes in the strain on the infusion set by occlusions and viscosity changes. The strain information can then be processed by the pump and adjustments made to the number of rotations of the pump rotor to compensate. In the event that the occlusion is too severe to compensate by modification of the rotor rotations, the pump is shut down and an alarm signal generated so that replacement tubing may be provided. 
   Also included was an air detector which was disposed in the pump. The air detector was disposed in communication with the pump and used ultrasonic energy to determine if bubbles were present in the conduit. 
   While the pressure sensor system of U.S. Pat. No. 5,720,721 is a significant improvement over the art, it does have limitations. The pressure sensors described in the &#39;721 patent are relatively expensive and must be properly mounted in the pump. Additionally, the person loading the pump must make sure that the upstream and downstream portions of the infusion set are properly loaded in the pump housing so that they engage the pressure sensors in the proper manner. Failure to properly load the infusion set can interfere with the functioning of the pressure sensors. In particular, if the clinician overly stretches the tubing as he or she wraps it around the pump, the tube on one side of the pump rotor will be stretched to a greater degree than the opposing side. This, in turn, can effect pump accuracy if too severe. 
   One manner for decreasing the costs of pressure sensors is to use an optical sensors. While there are several methods for using optical sensors to determine the presence of occlusions, each has significant drawbacks. Some methods only allow the mechanism to determine when the pressure exceeds a certain threshold. This is done by detecting when the expanding tube of the infusion set engages a surface, thereby modifying reflection or refraction of light. Other methods require complex calculations of refraction indexes or otherwise provide relatively limited information on small pressure changes. Additionally, some methods can vary based on the material from which the infusion set is formed, or based on whether the tube of the infusion set is opaque or transparent. 
   In addition to the above, many mechanisms for monitoring pressure within an infusion set lack an inherent failure detector. For example, if a sensor is configured to sense only when the expanding infusion set tube engages a transparent surface, the failure to record a reflected signal may mean that the tube has not expanded. In certain situations, however, the lack of reflected signal could also mean that the sensor has failed and is either not sending the signal or is not receiving the reflected signal. 
   In addition to the concerns with pressure sensing technology of the prior pumps, the pumps also used ultrasonic technology for bubble detection. While this technology is highly accurate, it is also expensive. An ultrasonic sensor can cost as much as 50 times as much as an optical sensor. 
   In addition to the above, the anti-freeflow technology discussed in U.S. Pat. No. 5,704,584 has limitations. While the occluder mechanism works well, it is relatively expensive to form a separate mechanism to selectively stop flow through the infusion set. A separate pinch clip occludes such as that shown in  FIG. 1B  can add fifteen to twenty percent to the cost of an infusion set. While the cost per unit is rather small, daily replacement of the infusion set can add up to significant costs. In a highly competitive medical environment, even a few cents per unit can dramatically effect sales quantities. 
   Thus, there is a need for a mechanism which can enable improved pressure monitoring, improved air detection and improved flow occlusion. Such a mechanism should be relatively inexpensive and should lessen the likelihood of errors in use of the pump and infusion set. Furthermore, it should enable the use of infusion sets made from a variety of materials. 
   SUMMARY OF THE INVENTION 
   Thus, it is an object of the present invention to provide a mechanism which allows improved method monitoring viscosity and/or occlusions in an infusion set. 
   It is another object of the present invention to provide such a mechanism which facilitates the monitoring of viscosity and occlusions with an optical sensor system. 
   It is another object of the present invention to provide a mechanism which facilitates the optical monitoring of solution to determine the presence of bubbles in the solution. 
   It is another object of the present invention to provide a mechanism which prevents free flow through an infusion set unless fluid flow through the infusion set is being driven by the pump. 
   It is yet another object of the present invention to provide an integrated adaptor which is disposed along an infusion set which facilitates pressure monitoring, bubble monitoring and an anti-free flow device. 
   The above and other objects of the present invention are realized in specific illustrated embodiments of a feeding set adaptor configured for attachment to an upstream portion, a down stream portion and a pump engaging portion of an infusion set. 
   In accordance with one aspect of the invention, the feeding set adaptor is attached to a flexible tube which forms the pump engaging portion of the infusion set. The flexible tube is mounted to the adaptor in such a manner that the tube is not disproportionately stretched on either side of the pump mechanism when it is loaded on the pump mechanism. 
   In accordance with another aspect of the invention, the flexible tube of the infusion set attached to the feeding set adaptor has at least one monitoring portion which is held by the adaptor to prevent stretching of the tube. The monitoring portion is disposed adjacent a sensor which allows the pump to monitor pressure within the tube. Preferably, this is done by an optical sensor which is positioned to monitor the diameter of the tube. By sensing changes in the diameter of the tube, the pump can determine the pressure within the tube. If the pressure sensed is above or below predetermined thresholds, the pump can determine that there is an occlusion and will generate an alarm. 
   In a preferred embodiment, the flexible tube is secured for monitoring both upstream and downstream from the pump rotor (or other pump mechanism). Thus, the pump can monitor upstream and downstream occlusions. The pressure monitoring can also be used in conjunction with movement of the pump mechanism to more accurately determine solution flow through the pump system. 
   In a preferred embodiment, the feeding set adaptor is configured to hold the tube in such a position that the tube neither obstructs all light flow nor allows complete light flow between the two sides of the optical sensor. Between the two extremes of receiving a full optical signal and no optical signal, the signals generated by the optical signal receiver indicate the extent to which the optical signal sent by the optical signal emitter have been obstructed by the tube. If, however, a full reading is received, the pump can indicate that the feeding set adaptor and the associated tube have not been properly mounted in the pump. In contrast, if no reading is received, the pump can generate an alarm indicating that the sensor is malfunctioning, or that the infusion set tube has expanded well beyond the desired threshold. 
   In accordance with another aspect of the invention, the feeding set adaptor includes a sample cell through which solution being pumped by the pump is passed. The sample cell is configured for monitoring the solution to determine the presence of bubbles. Preferably, the sample cell has a pair of angled sidewalls. The angled sidewalls are preferably disposed at an angle of 47 to 70 degrees from each other, depending on the indices of refraction of the material used, and are most preferably angled 50 to 60 degrees from one another. 
   The sample cell is configured to fit into a void on a housing disposed adjacent to an optical sensor. Light from the optical sensor passes through the housing and the sample cell in such a manner that it is refracted in one direction if the sample cell is full of liquid and another angle if a bubble is present in the sample cell. Thus, the pump is able to monitor for bubbles and to make appropriate corrections in pump flow rate or to generate an alarm if the amount of air present in the solution exceeds desired thresholds. 
   In accordance with one aspect of the invention, an occluder is disposed within the infusion set. The occluder is configured to prevent free flow of fluids in the infusion set past the occluder. The occluder is also configured, however, to selectively allow solutions to pass by the occluder which are pumped by an enteral feeding pump and the like. 
   In accordance with another aspect of the invention, the feeding set adaptor includes an occluder which prevents fluid flow through the infusion set when the infusion set has not been disposed in proper engagement with the pump mechanism of the infusion pump, thereby giving control of fluid flow through the infusion set to the pump. 
   In one embodiment of the invention, the occluder is formed by a stop attached to the feeding set adaptor and placed in the tubing of the infusion set. The stop limits flow through the tube by limiting flow around and/or through the stop when the solution is subject to flow due to gravity. However, when greater pressures are placed on the solution, such as those produced by a pump, the solution is able to flow around and/or through the stop, thereby delivering the solution to the patient. 
   In accordance with another embodiment of the present invention, an occluding valve is formed as part of the feeding set adaptor and is disposed in the infusion set. The valve prevents free flow through the infusion set due to gravity, while allowing controlled flow of solution through the infusion set. 
   In accordance with another aspect of the invention, the occluder is configured to stop fluid flow until the infusion set has been properly loaded into a control mechanism such as a pump. Once properly placed, the interaction between the occluder and the infusion set effectively opens the infusion set to allow solution to flow therethrough. 
   In accordance with still yet another aspect of the invention, a plurality of the aspects discussed above are integrated into a single feeding set adaptor. By integrating the various aspect discussed above, the health care professional or patient who loads the pump with the infusion set can be assured that the safety and monitoring aspects discussed above are being accomplished without the need to check multiple systems. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which: 
       FIG. 1A  shows a top view of an enteral feeding pump housing formed in accordance with the principles of the prior art; 
       FIG. 1B  shows a top view of a top of an enteral feeding pump housing and a pinch clip occluder formed in accordance with the principles of the prior art; 
       FIG. 2A  shows a top perspective view of a feeding set adaptor configured in accordance with the principles of the present invention; 
       FIG. 2B  shows a bottom perspective view of the feeding set adaptor shown in  FIG. 2A ; 
       FIG. 2C  shows a side view of the pump engaging portion of the infusion set; 
       FIG. 3  shows a bottom view of an enteral feeding set adaptor having the pump engaging portion of the infusion set disposed therein for mounting on an infusion pump in accordance with the principles of the present invention; 
       FIG. 4  shows a fragmented perspective view of an infusion set and a perspective view of a feeding set adaptor and an enteral feeding pump made in accordance with principle of the present invention; 
       FIGS. 5 and 5A  show close-up, cross-sectional views of the adaptor, flexible tubing and portion of the enteral feeding pump relating to the pressure monitoring mechanism associated with feeding set adaptor; 
       FIGS. 6 and 6A  show a close-up, cross-sectional view of the adaptor and the enteral feeding pump portions relating to the detection of air bubbles passing through the infusion set; 
       FIGS. 7 and 7A  show close-up, cross-sectional views of the adaptor and infusion set relating to the anti-freeflow mechanism of the present invention; 
       FIG. 7B  shows a close-up, cross-sectional view of the adaptor, infusion set and enteral feeding pump providing an alternate embodiment of the anti-freeflow mechanism of the present invention; and 
       FIG. 7C  shows a close-up, cross-sectional view of yet another embodiment of the anti-freeflow mechanism of the present invention. 
   

   DETAILED DESCRIPTION 
   Reference will now be made to the drawings in which the various elements of the present invention will be given numeral designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the pending claims. 
   Referring to  FIG. 1A , there is shown a top view of an enteral feeding system taught in U.S. Pat. No. 5,720,721. The enteral feeding system, generally indicated at  4 , has a delivery set  8  including an intake (upstream) tube  10  and an output (downstream) tube  14  connected together by a pair of connectors  18  and a pump tubing segment within an enteral feeding pump  20 . The position of the pump tubing segment disposed inside of the pump  20  is represented by the dashed lines  16 . 
   The enteral feeding pump  20  includes a housing  24  with a conventional motor unit, generally indicated at  28 . The motor unit  28  includes a rotor  30  with a plurality of peristaltic rollers  34  disposed about an exterior of the rotor to move liquid through the enteral feeding pump  20 . The rotor  30  is connected by a shaft  32  to a motor (not shown). The section  38  of the pump tubing segment  16  is disposed about the rotor  30  and rollers  34  and is usually made of a flexible silicone material. Rotating the rotor  30  in the direction indicated by the arrows directionally squeezes the tube section  38  and causes solution to be pushed through the output tube  14 . 
   Also shown in  FIG. 1  is an air detector  40  provided in a proximal position (upstream) from the motor unit  28  along the intake tube  10  to warn medical personnel of an empty supply container or a large bubble in the infusion set. 
   In addition to these elements, the enteral feeding pump  20  of the present invention includes a pair of pressure sensors  50 . In a preferred embodiment, two pressure sensors  50   a  and  50   b  are disposed along the pump tubing segment  16  adjacent the intake/output tubes to 1) ensure that the tubes are properly mounted in the pump  20 ; 2) monitor any changes in viscosity which are significant enough to alter the amount of liquid moved by each rotation or partial rotation of the rotor  30 ; and 3) detect any occlusions in the intake tube  10  or the output tube  14  of the delivery set  8 . A retention plate  54  ( FIG. 1 ) is attached to the housing  24  by a screw  58  to hold the pressure sensors  50   a  and  50   b  in place. 
   While the pressure sensor system of U.S. Pat. No. 5,720,721 was a significant improvement over the art, it does have limitations. Specifically, the pressure sensors are relatively expensive and the accuracy depends on the proper loading of the tube in the pump. Additionally, the air detector used ultrasonic energy and ultrasonic sensors are relatively expensive. Furthermore, as the health care professional or patient loaded the pump, he or she could effect the relative stretching of the tube as it was wrapped around the rotor of the pump. This, in turn, could effect the strain detected by the pressure sensors. 
   In addition to the above, the pump required some sort of anti free flow mechanism to prevent solution from running through the infusion set when the tube was not securely engaging the pump rotor. Thus, a pinch clip occluder, as shown in  FIG. 1B  at  96  was taught in U.S. Pat. No. 5,704,584. While the pinch clip occluder shown is highly effective, it is relatively expensive compared to the cost of the infusion set. 
   Turning now to  FIGS. 2A and 2B  there are shown a top perspective view and a bottom perspective view of a feeding set adaptor, generally indicated at  100 , which improves upon the prior art. The feeding set adaptor has a connector portion  104  having a first connector  108  and a second connector  112 . The first connector portion  104  also preferably has a small handle  116  which can be used to pull the feeding set adaptor  100  from a pump if necessary. 
   The first connector  108 , a functional proximal end  108   a  which engages the functional distal end of an inflow line (not shown) of an infusion set. The opposing end of the infusion line is typically disposed in communication with a fluid container which holds the solution being delivered to the patient. The first connector  108  will typically be approximately the same diameter as the inflow tube, and the inflow tube is mounted on the first connector by being stretched over the distal end  108   a  of the connector. 
   The first connector  108  also has a functional distal end  108   b . The distal end  180   b  is preferably configured with an annular barb  108   c  and a neck portion  108   d  positioned proximally from the annular barb. The annular barb  108   c  and neck portion  108   d  are used to secure a pump engagement portion of the infusion set, which is discussed below regarding  FIG. 2C . As shown in  FIG. 1 , the distal end  108   b  of the first connector  108  has conduit  120  which is generally triangular. 
   Disposed within the first connector  108  is a sample cell  124 . As will be discussed in additional detail below, the sample cell  124  is used in conjunction with an optical sensor (not shown) to optically determine the presence of air bubbles within the conduit  120 . The sample cell  124  is preferably triangular and has sidewall which are offset from one another at an angle of between about 47–70 degrees. In a presently preferred embodiment, the sample cell  124  is made with a wall which forms an equilateral triangle with two sidewalls being disposed at an angle of about 50 to 60 degrees. Such an angle allows light emitted from the optical sensor to be refracted in a first direction if the conduit  120  is filled with liquid, and a second direction if the conduit has any appreciable amount of air. The refracted light, or relative absence thereof, indicates the relative size of the air bubble. A more detailed discussion regarding bubble detection is found in U.S. patent application Ser. No. 09/836,840, now U.S. Pat. No. 6,531,708, which is expressly incorporated herein. 
   Disposed functionally distally (i.e. downstream) from the distal end  108   b  of the first connector  108  is a first tube engagement member  130 . The first tube engagement member  130  preferably includes a wall  132  having generally U-shaped opening  134  which is sized to receive the pump engagement portion of the infusion set. 
   The first tube engagement member  130  also preferably includes a pair of flanges  138  which extend inwardly to partially obstruct the opening and to form a recess which receives a collar (see  FIG. 2C ) of the pump engagement portion of the infusion set. 
   The pump engagement portion of the infusion set, which is generally indicated at  200  in  FIG. 2C  includes an elongate tube portion  204 . The tube portion  204  is preferably a flexible tube made from a medical grade material, such as silicone. Such tubes are commonly used in enteral feeding pumps. 
   Unlike most enteral feeding pump tubes, however, the tube portion  204  has a first fitting  208  disposed at a functionally proximal end (i.e. upstream). The first fitting  208  is preferably used by a machine to secure the tube portion  204  and to attach a proximal end  204   a  of the tube to the distal end  108   b  of the first connector  108 . 
   Disposed distally from the first fitting  208  is a first abutment member  212 , which is preferably in the form of a collar  216 . (In light of the present disclosure, those skilled in the art will appreciate that numerous other abutment configurations could be used to secure the tube portion  204  as described). The abutment member  212  in particular, and the collar  216  specifically, are designed to nest in the recess  142  against the wall  132  of the first tube engagement member  130 . When nested in the recess, the tube portion  204  which is proximal to the collar  216  is held taut between the first tube engagement member  130  and the first connector  108 . 
   When the pump engaging portion  200  of the infusion set is attached to the distal end  108   b  of the first connector  108 , it is stretched slightly until the collar  216  is slightly passed the flanges  134  of the first tube engagement member  130 . The tube portion  204  is then moved between the flanges  134  and the tube released so the contraction of the tube pulls the collar  216  into the recess  142 . 
   Disposed distally from the first tube engagement member  130  is a second tube engagement member  150 . As with the first tube engagement member  130 , the second tube engagement member preferably includes a wall  152  with a generally U-shaped opening  154  which is sized to receive the pump engagement portion of the infusion set. 
   The second tube engagement member  150  also preferably includes a pair of flanges  158  which extend inwardly to partially obstruct the opening and to form a recess  162  which receives an abutment member  220 , which is preferably in the form of a collar  224  ( FIG. 2C ). (Those skilled in the art will appreciate that other abutment members such as arms, nubs or flanges could also be used). As shown in  FIG. 2B , the recess  162  preferably faces the recess  142  in the first tube engagement member and works with the collar  224  to prevent the portion of the tube portion  204  disposed proximally adjacent to the collar from being stretched to any significant degree when the central working portion  230  of the pump engaging portion  200  of the infusion set. Likewise, when the pump rotor rotates, the stretching of the tube portion  204  proximally from the collar  224  is minimized. 
   Because the proximal collar  216  prevents proximal movement and the distal collar  224  prevents distal movement, the portion  234  of the tube disposed therebetween is held against movement, this portion forms a relatively isolated monitoring portion  234 . 
   To properly determine the flow through an infusion set, and to properly determine the presence of occlusions in an infusion set, it is advantageous to monitor pressure within the infusion set. This can be accomplished either by pressure sensors, such as those discussed in U.S. Pat. No. 5,720,721, or by an optical detector as discussed in co-pending U.S. patent application Ser. No. 09/836,852, now U.S. Pat. No. 6,523,414, As is explained more fully in the co-pending application, the pressure in the infusion set can be determined by having the tube occlude light in an optical sensor. As the tube expands due to increased pressure or contracts due to a vacuum caused by occlusions, etc., the amount of light which is received by the optical sensor changes, thereby indicating the change in pressure in the tube. 
   Using the diameter of the tube to determine pressure can provide highly accurate readings. However, the accuracy of such readings is diminished if the tube is being stretched inconsistently because having the tube under tension will change the extent to which it expands and contracts due to pressure changes. This is resolved in the present invention by the first and second tube engagement members  130  and  150  and the abutment members  212  and  220  (collars  216  and  224 ). These structures interact so that the monitoring portion  234  is held relatively unstretched, regardless of tension from either side. Because most of the tension will occur due to loading the central working portion  230  of the pump engagement portion  200  and rotation of the pump rotator, the second tube engagement member  150  is more critical than the first pump engagement portion. Thus, it will be appreciated that the first pump engagement portion  130  could be omitted while maintaining most of the benefits of the present invention. 
   The feeding set adaptor  100  also includes a third tube engagement member  170 . The third tube engagement member preferably includes a wall  132  defining a generally U-shaped opening  174  which is sized to receive the pump engagement portion of the infusion set. The third tube engagement member  170  also preferably includes a pair of flanges  178  which extend inwardly to partially obstruct the opening and to form a recess  182  which receives an abutment member  240 , which is preferably in the form of a collar  244  ( FIG. 2C ). 
   As shown in  FIG. 2B , the recess  182  preferably faces in the same direction as the recess  162  in the second tube engagement member  150 . When the pump engaging portion  200  of the infusion set is properly loaded, the collars  224  and  244  are disposed in recesses  162  and  182 . This substantially isolates the central working portion  230  and prevents rotation of the pump rotor from causing tension either upstream or downstream from the collars  224  and  244 , respectively. 
   The feeding set adaptor  100  further comprises a fourth tube engagement member  186 . The fourth tube engagement member  186  preferably includes a wall having a generally U-shaped opening  188 . A pair of flanges  190  are disposed adjacent the U-shaped opening to partially obstruct the opening and to form a recess  192 . The pump engaging portion  200  of the infusion set includes an abutment member  250  in the form of a collar  254  which is configured to nest in the recess  192 . 
   The recess  192  of the fourth tube engagement member  186  faces the same direction as first tube engagement member  130  and the third and fourth tube engagement members act together in the same manner as the first and second engagement members to isolate a second monitoring portion  260  on the tube  204 . Thus, the infusion pump is able to optically monitor both the upstream pressure between the first and second engagement members  130  and  150 , and the downstream pressure between the third and fourth engagement members. Thus, the pump can readily determine if an occlusion in the infusion set is inhibiting delivery of solution to the patient. 
   The feeding set adaptor  100  also includes an anti-freeflow mechanism  300 . As shown in  FIGS. 2A and 2B , the anti-freeflow mechanism  300  is in the form a small ball  304  which is attached to the proximal (i.e. upstream) end  112   a  of the second connector  112  by a small wall  308 . The wall  308  is configured to provide minimal resistance to flow of liquid into the proximal end  112   a  of the second connector  112 . 
   In order to prevent freeflow through the infusion set, the anti-freeflow mechanism  300  is inserted into the distal end  204   b  of the tube portion  204 . The tube portion  204  is then advanced until the distal end  204   b  passes over an annular barb  112   c  and rests on the neck  112   d  of the second connector  112 . A second fitting  268  on the tube portion  204  is typically used so that a machine can readily mount the distal end  204   b  of the tube portion  204  on the proximal end  112   a  of the second connector  112 . 
   Once the tube is in place, the small ball  304  will prevent solution flow through the tube portion  204  unless the solution is under sufficient pressure. Thus, the small ball  308  will prevent flow through the tube portion  204  if the solution is simply subject to gravity. However, if the solution is placed under sufficient pressure, the flexible material (typically silicone) of the tube portion  204  will expand and allow solution to flow past the small ball  308 . This is accomplished as the pump drives solution through the infusion set. If the pump is not properly engaging the central working portion  230  of the tube portion  204 , there will not be enough pressure to bypass the anti-freeflow mechanism  300 . In other words, unless the pump is in control of the fluid flow, no fluid will flow through the infusion set and a freeflow situation will not develop. 
   While the workings of the anti-freeflow mechanism  300  are discussed in additional detail below, numerous different embodiments of anti-freeflow mechanisms which can be used with the present invention are discussed in U.S. patent application Ser. No. 09/569,332, now U.S. Pat. No. 6,595,950 and U.S. patent application Ser. No. 09/836,850, both of which are expressly incorporated herein. 
   Once the solution in the tube portion  204  has been driven past the anti-freeflow mechanism  300 , the solution passes into the proximal end  112   a  of the second connector  112 . The distal end (downstream)  112   b  of the second connector  112  is disposed in engagement with a patient portion of the infusion set (not shown). Typically, the patient portion of the infusion set is slid over the second connector  112  and retained in a frictional engagement. It can, however, be attached by other means. 
   Turning now to  FIG. 3 , there is shown a bottom view of an enteral feeding set adaptor  100  having the pump engaging portion  200  of the infusion set disposed therein for mounting on an infusion pump in accordance with the principles of the present invention. The central working portion  230  of the pump engaging portion  200  extends outwardly from the feeding set adaptor  100  in a loop. 
   In the prior art configurations, the portion of the infusion set which engages the pump rotor can be stretched unevenly as it is mounted on the pump. This can interfere with monitoring of pressure within the infusion set. Additionally, stretching the tube and wrapping it around the pump rotor can take some coordination. 
   In contrast, the feeding set adaptor  100  and pump engaging portion  200  of the infusion set is loaded by simply engaging the far side of the loop  230   a  against the pump rotor and pulling the feeding set adaptor  100  until it can be inserted in the pump. With such a configuration, the risk of the central working portion  230  being stretched unevenly is virtually eliminated. Additionally, it takes very little coordination to properly load the feeding set adaptor  100  in the pump. The user simply loops the end  230   a  of the looped central working portion  230  over the rotor and pulls back on the feeding set adaptor  100  until it is in alignment with a cavity on the pump, and releases the feeding set adaptor. 
   Turning now to  FIG. 4 , there is shown a fragmented perspective view of an infusion set, generally indicated at  310  and a perspective view of a feeding set adaptor  100  and an enteral feeding pump, generally indicated at  320 , made in accordance with principle of the present invention. The infusion set  310  includes an inflow tube  314  which is typically connected to a solution container (not shown), such as a plastic bag holding enteral feeding solution, and an outflow tube  318 , which is generally connected to an adaptor (not shown) which engages a balloon catheter which traverses the abdominal wall of the patient. 
   The inflow tube  314  is connected to the pump engaging portion  200  of the infusion set  310  by the first connector  108 . As discussed above, the solution passing through the inflow tube  314  and the first connector  108  passes through the sample cell  124 . Due to the configuration of the feeding set adaptor  100 , the sample cell  124  nests in a channel  324  of the infusion pump  320 . A portion of the channel  324  defines a housing  328  which is preferably made of a generally translucent plastic. The housing  328  serves the dual purpose of protecting an optical sensor (not visible in  FIG. 4 ) from liquids, and of refracting light which is emitted and received by various parts of the optical sensor. 
   As the solution passes through the sample cell  124 , the optical sensor sends light through the housing  328  and sample cell  124 . If liquid is in the sample cell  124 , most of the light will travel in such a path that it is not reflected back to an optical detector. The sample cell  124  is specifically designed so that it always sends some light to the optical detector to provide an integrity check of the optical sensor. If a bubble is present, however, a light emitted by the optical sensor is refracted to the optical detector. The amount of light which is refracted gives a reliable indication of whether a bubble is present, and the size of the bubble. If the bubble exceeds desired thresholds, the pump  320  can generate an alarm. The alarm may be audible, or simply appear on a display screen  332  on the pump  320 . 
   Once the solution has passed through the sample cell  124 , it passes out of the first connector  108  and into the monitoring portion  230  of the pump engaging portion  200  of the infusion set  310 . The monitoring portion  234  is disposed between the first and second tube engagement members  130  and  150 , and is disposed in a distal section  324   a  of the channel  324 . Disposed in the walls of the distal section  324   a  of the channel  324  is an optical sensor (not shown). The optical sensor sends light between an optical signal emitter and an optical signal detector. As the monitoring portion  234  of the tube is disposed in the distal section  324   a  of the channel  324 , it is positioned to partially obstruct the light flow between the optical signal emitter and the optical signal detector. 
   The diameter of the monitoring portion  234  changes as pressure changes within the tube. The change in diameter of the monitoring portion  234  changes the amount of light which is detected by the optical detector and allows the pump  320  to determine pressure within the monitoring portion without direct contact. For example, if the inflow line  314  of the infusion set  310  were to be kinked or otherwise occluded, flow through the inflow line would be reduced. As the pump rotor  340  of the infusion pump  320  rotates, it will develop a vacuum upstream from the rotor. Because the inflow line  314  is occluded, the vacuum created by the rotation of the rotor  340  will be greater in magnitude and will remain longer than if flow through the inflow tube were not obstructed. 
   The vacuum will cause the monitoring portion  234  of the pump engaging portion  200  to collapse to a greater degree and remain in a collapsed state for a longer period of time. The optical sensor detects the collapse because more light will be detected by the optical detector and for a longer period of time. The pump  320  monitors the readings of the optical sensor. If the readings of the optical detector fall outside of a predetermined range, the pump  320  will generate an alarm indicating the presence of an occlusion. It may also automatically stop the pump  320  until the occlusion situation has been resolved. A more detailed discussion of the interaction between the optical sensor and the monitoring portion  234  of the infusion set  310  is set forth below. Additionally, co-filed U.S. patent application Ser. No. 09/836,852, now U.S. Pat. No. 6,523,414 contains a detailed discussion of numerous different applications of such a pressure sensor and is expressly incorporated herein. 
   As the solution passes out of the monitoring portion  234 , it passes into the central working portion  230  of the pump engaging portion  200  of the infusion set  310 . The central working portion  230  is engaged by a plurality of rollers  344  on the pump rotor  340 . As the rotor  340  rotates, the rollers  344  pinch off sections of the tube and advance theoretically known volumes of solution with each rotation. (The actual volumes moved are partially dependent on the pressures on the solution both upstream and downstream from the rotor  340 ). By controlling the number of rotations of the rotor  340 , and making modifications for detected pressures, the pump  320  can deliver a known volume of solution to the patient. 
   Once the solution has been moved downstream of the rotor  340 , it passes into the second monitoring portion  260  which is disposed between the third and fourth tube engagement portions  170  and  186 . The second monitoring portion  260  rests in a channel  354  in the pump  320  which is preferably disposed parallel to channel  324 . The channel  354  also has an optical sensor which functions in substantially the same manner as the sensor discussed in association with the monitoring portion  234 . The only signficiant difference between the two is that which the monitoring portion  234  will generally collapse due to vacuum created by the pump rotor  340  and upstream occlusions, the second monitoring portion  260  will generally expand due to solution being forced down stream by the pump rotor  340  and any occlusions downstream which inhibit the downstream flow of solution. 
   Once the solution passes out of the second monitoring portion  260 , it must flow around the anti-freeflow device  300 . As mentioned above, gravity alone is insufficient to develop flow around the anti-freeflow device  300 . However, the rotation of the pump rotor  340  pushes solution downstream with sufficient force that the tube  204  adjacent the anti-freeflow device will expand and create a channel around the ball  304 , thereby allowing the solution to flow down stream to the patient. 
   Once past the anti-freeflow device  300 , the solution flows through the second connector  112  and into the outflow portion  318  of the infusion set  310  which delivers the solution to the patient. 
   Turning now to  FIGS. 5 and 5A , there are shown close-up, cross-sectional views of the feeding set adaptor  100 , flexible tubing  204  of the pump engaging portion  200  and a portion of the enteral feeding pump  320  relating to the pressure monitoring mechanism associated with feeding set adaptor. The enteral feeding pump  320  has two channels  324  and  354  which receive the feeding set adaptor  100 . 
   As shown in  FIGS. 5 and 5A , the monitoring portion  230  of the flexible tubing  204  of the pump engaging portion  200  is disposed in the first channel  324 . Disposed on opposing sides of the first channel  324  is an optical sensor  400 . The optical sensor includes a optical signal emitter  404  and an optical signal detector  408 . Each is provided with leads  412  for communication with the enteral feeding pump. 
   In response to an electrical signal from the pump  324 , the optical signal emitter  404  emits light energy, indicated by dashed line  420 . Those skilled in the art will appreciate that various wavelengths of light may be used. Currently, it is anticipated that infrared light will be preferred. 
   The flexible tube  204  forming monitoring portion  230  is positioned to obstruct some of the light. The extent to which the light is obstructed, of course, depends on the diameter of the flexible tube  204  in the monitoring portion  230 . This diameter, depends on the pressure within the tube. Thus, by monitoring the amount of light which is obstructed, the voltage or other readings of the sensor correlates with the pressure inside of the tube. 
   In a preferred embodiment, the flexible tube  204  forming the monitoring portion  230  is disposed so that it always obstructs some light, but does not obstruct all light flow between the optical signal emitter and the optical signal detector. This can be used to verify the integrity of the sensor and proper loading of the tubing. If the optical signal detector  408  gives the maximum voltage reading, the tubing  204  is not loaded properly. If, in contrast, no optical signal is received by the optical signal detector  408 , the sensor  400  is defective and must be serviced or replaced. 
   Turning specifically to  FIG. 5A , there is shown a view similar to that of  FIG. 5 . However, with respect to the monitoring portion  230 , the diameter of the tube  204  has decreased. This typically occurs with each rotation of the pump rotor ( FIG. 4 ) as a temporary vacuum is created as solution is forced through the infusion set. The extent of the vacuum and its duration, however, is related to the presence of occlusions, and/or the viscosity of the solution. The sensor  400  detects the extent of the reduced diameter of the tube  204  in the monitoring portion  230  by the amount of light received by the optical signal detector  408 . The optical sensor  400  is thereby able to determine the negative pressure within the tube. The pump  320  is then able to make adjustments to rotor rotations to ensure accurate volume delivery. It can also detect an occlusion that should be resolved and generate an alarm. 
   The pump  320  also has a second optical sensor  400 ′ which is disposed along the second monitoring portion  260  which is down stream from the pump rotor ( FIG. 4 ). The sensor  400 ′ has an optical signal emitter  404  and an optical signal detector  408  which have leads  412  for communicating with the pump. The sensor  400 ′ operates in substantially the same manner as the optical sensor  400  and is therefor not discussed in detail. 
   One difference between the practical applications of the sensor  400 ′ and sensor  400  is that, because the sensor  400 ′ is downstream, the sensor  400 ′ will detect pressure increase in the second monitoring portion  260  with each rotor rotation, instead of the pressure decreases associated with the first monitoring portion  230 . Thus, as the rotor ( FIG. 4 ) rotates, the pressure in the second monitoring portion  260  will increase. As shown in  FIG. 5A , the increase in pressure causes the diameter of the second monitoring portion to increase and decreasing the amount of light received by the optical signal detector  408 . 
   The sensor  400 ′ and monitoring portion  260  can be configured in a variety of ways to achieve the goals of the present invention. In a preferred configuration, the tube  204  is positioned within the sensor such that it will always occlude some light, but will never fully occlude all light from the optical signal emitter  404  to the optical signal emitter  408 . Thus, a full voltage reading indicates that the tube  204  forming the monitoring portion  260  is not properly loaded. A zero reading indicates that the sensor  400 ′ has malfunctioned and must be serviced or replaced. 
   Between the two extremes is a range of values which correlate with acceptable pressures which the pump  320  can use to ensure accuracy in volumetric delivery. This is also a threshold which indicates a pressure which exceeds acceptable pressure in the infusion set. If the threshold is surpassed, the pump  320  will generate an alarm and warn the user that the infusion set is obstructed. 
   Those skilled in the art will appreciate that the tube  204  and sensor  400 ′ could be disposed in communication such that the threshold pressure occludes all light and therefore generates an alarm. While such a configuration meets the requirements of generating an alarm and/or shutting off the pump  320  when the pressure is too high, it has the disadvantage of not distinguishing between a faulty sensor in the pump and an unacceptably high pressure in the infusion set. 
   Those skilled in the art will also realize that numerous modifications could be made to the presently preferred embodiment disclosed herein. The sensors need not be disposed adjacent each other and could be disposed in other locations along an infusion set. 
     FIGS. 6 and 6A  show a close-up, cross-sectional view of the adaptor and the enteral feeding pump portions relating to the detection of air bubbles passing through the infusion set. Specifically, the sample cell  124  is disposed in the channel  324  of the pump. The channel  324  has a portion  324   b  which is defined by a sloped housing  430 . The sloped housing  430  is preferably formed of a clear plastic, such as ABS and has walls  430   a  and  430   b  which are offset from one another at an angle of between about 45–100 degrees (most preferably about 60 degrees), and preferably between 40 and 67.5 degrees from horizontal, and a base  432 . The housing also preferably has a flanged portion  434 . The housing  430  helps both with bubble detection as explained below, and prevents water or other hazzards from entering the pump  320 . 
   Disposed adjacent the housing  430  is an optical sensor  440 . The optical sensor  440  has an optical signal emitter  444  and an optical signal detector  448  which are disposed on opposing sides of the housing  430 . Leads  452  are provided for the optical sensor  440  and pump  320  to send electronic signals to one another. 
   The sample cell  124  is placed in the channel  324  so that it is spaced away from the housing  430  slightly and forms an air chamber  458  between the sample cell and housing. While it is preferred that the conduit  460  formed by the sample cell  124  has a cross-section which forms an inverted equilateral triangle and the sample cell  124  preferably has two walls disposed at  60  degrees from one another, the walls defining the conduit need not form a triangle. As shown in  FIG. 6 , the walls have a base  464  which is formed at the bottom of the inverted triangle. Additionally, the top wall  468  could be curved or vaulted to provide the conduit with a diamond shape. Also, as set forth in more detail in U.S. patent application Ser. No. 09/836,840, now U.S. Pat. No. 6,531,708, numerous different configurations can be used. It is most desirable, however, that the sidewalls be disposed at an angle less than normal to the plane along which the light is emitted to refract the light back to an optical detector when air is present in the sample cell. 
   In use, light is emitted by the optical signal emitter  444  and is refracted by a sidewall of the housing  430  and again by the air of the air chamber  458 . The light is again refracted as it enters into the sidewall  430   a  of the housing. If the conduit  460  is filled with solution, the light undergoes very little refraction as it passes from the sidewall  430   a  of the housing  430  into the solution. Thus, the light travels in a generally straight path which prevents the light from contacting the optical signal receiver  448  as shown by the dashed line in  FIG. 6 . 
   If, however, the conduit  460  is filled with air, the difference indices of refraction of the plastic sample chamber  124  and the air in the conduit  460  causes the air to be refracted to a much greater degree as shown by the upper dashed line in  FIG. 6A . The light is then refracted again as it passes from the air in the conduit to the opposing sidewall  430   b , through the air chamber  458  and through the housing  430 . The refraction is such that the light is directed to the optical signal detector  448 . If an air bubble is present in the conduit  460 , it will direct an increased amount of light to the optical signal detector  448 . The amount of light refracted to the optical signal detector  408  is proportional to the size of the air bubble. Thus, the voltage reading obtained from the optical signal detector  448  is proportional to the size of the bubble. 
   The base  464  of the sample cell  124  assists in the important role of integrity checking the optical sensor  440 . The base  464  is positioned so that it will always allow some light through to impact the optical signal detector  448  as shown by the lower dashed line in  FIG. 6A . Thus, if the optical signal detector  448  indicates a reading of zero, an alarm can be generated indicating that the sensor  440  has failed. Likewise, the refraction of light is controlled so that too high of a reading indicates that the sample cell  124  has not been properly loaded in the channel  324 . 
   Turning now to  FIGS. 7 and 7A , there are shown close-up, cross-sectional views of the feeding set adaptor  100  and the pump engaging portion  200  of the infusion set  310  as they relate to the anti-freeflow mechanism  300  of the present invention. It is important to prevent an infusion set from providing uncontrolled solution to the patient. While many enteral feeding systems have roller clamps or other pinch clip occluders, most devices do not affirmatively prevent fluid flow when the pump is not controlling the flow. In contrast, the anti-freeflow mechanism  300  only allows fluid flow when the pump is actively driving solution through the system. 
   The anti-freeflow mechanism shown in  FIGS. 7 and 7A  is a small substantially ball-shaped member  304  which is sized slightly larger than the inside diameter of the flexible tube  204  which forms the pump engaging portion  200  of the infusion set  310 . As such, the ball-shaped member  304  prevents fluid flow under gravity pressures. If, however, a pressure well above that caused by gravity is developed in the flexible tube  204 , the flexible tube will expand and develop a channel  480  about the exterior of the ball-shaped member  304 . (It will be appreciated that other shapes may also be used). 
   The channel  480  is opened each time the pump rotor drives solution through the pump engaging portion  200  of the infusion set  310  and allows solution to flow downstream. Unlike other clamps which are manually controlled or which open by closing of the pump housing, the configuration is advantageous because it will not allow a freeflow condition to develop, even if the feeding set adaptor  100  is properly mounted in the pump  320  and the pump engaging portion  200  of the infusion set  310  has simply been pulled out of engagement with the pump rotor. 
   Turning now to  FIG. 7B , there is shown a cross-sectional view of the adaptor  100 , pump engaging portion  200  of the infusion set  310  and enteral feeding pump  320  providing an alternate embodiment of the anti-freeflow mechanism of the present invention. While the embodiment discussed with respect to  FIGS. 7 and 7A  is presently preferred, there may be situations in which it is not desired to force the solution to open a channel around the anti-freeflow mechanism. In such situations, the channel can be opened by interaction of a pump cover  500 , the anti-freeflow mechanism  300  and the channel  354  of the pump  320 . The cover  500  preferably has an engagement member  504  which is configured to forcefully engage the flexible tube on the opposite side of the tube from the anti-freeflow mechanism. The channel  354  also may have a stop  510  which engages the outside of the flexible tube  204  opposite the anti-freeflow mechanism  300 . 
   As the flexible tubing  204  gets compressed between the engagement member  504  and the anti-freeflow mechanism  300  and between the stop  510  and the anti-freeflow mechanism, the flexible tubing will bow outwardly along the sides of the anti-freeflow mechanism  300  and form channels for the solution to flow around the anti-freeflow mechanism. Thus, once the cover  500  is closed and secured, solution flow passed the anti-freeflow mechanism  300  can occur regardless of whether the pump rotor  340  is properly engaging the pump engaging portion  200  of the infusion set  310 . 
   Turning now to  FIG. 7C , there is shown a close-up, cross-sectional view of yet another embodiment of the anti-freeflow mechanism  300 ′ of the present invention. Instead of using a ball-shaped member  304  inside of the tube, the embodiment shown in  FIG. 7C  shows a flap  304 ′ which is disposed in the connector  112 . The flap is configured to substantially prevent fluid flow through the connector if pressures are equal to or less than typically encountered due to gravity. If a desired pressure threshold is passed, the flap  304 ′ is forced open and allows solution to flow down stream. Those skilled in the art will appreciate that the flap  304 ′ could be configured to remain open once deflected by the solution pressure, or could be mounted such that the flap  304 ′ returns to its original position once the solution pressures are insufficient to hold the flap open. 
   Thus there is disclosed an improved feeding set adaptor. The adaptor enables the integration of the various functions discussed above, and provides improved pressure monitoring, anti-freeflow and bubble detection at a price well below the systems of the prior art. Additionally, the feeding set adaptor increases the ease of loading and unloading the tube engaging portion of the infusion set. While numerous different embodiments of the present invention have been disclosed, those skilled in the art will appreciate numerous modifications which can be made without departing from the scope and spirit of the present invention. The appended claims are intended to cover such modifications.