Patent Publication Number: US-2005119625-A1

Title: Apparatus and method for preventing free flow in an infusion line

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an apparatus and method for preventing free flow during enteral or parenteral administration solutions through an infusion line. More particularly, the present invention relates to an occluder/valve and method of use for infusion sets and the like, wherein the occluder/valve prevents undesirable free-flow of solution through the infusion set while allowing controlled flow through the infusion set.  
      2. State of the Art  
      The use of infusion sets to administer solutions to patients is well known in the medical arts. Infusion sets are used for both enteral and parenteral applications. Enteral feeding pumps are used to provide patients with nutrition and medication when they are unable, for a variety of reasons, to eat normally. Parenteral (intravenous) solutions are provided to patients to ensure adequate hydration and to provide needed nutrients, minerals and medication. 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. However, emergencies or other distractions may 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 free-flow 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 free-flow 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 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 free-flow condition while allowing controlled flow through the infusion set. There is also a need for such a device which prevents free-flow if an infusion set is not properly mounted in a pump or other regulating means.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide an apparatus and method for occluding infusion sets to prevent an accidental free-flow condition.  
      It is another object of the present invention to provide an occluder which is simple to make and use.  
      It is another object of the present invention to provide such an occluder which is inexpensive and thus disposable.  
      It is still another object of the present invention to provide an occluder which occludes fluid flow through the infusion set unless the infusion set is properly loaded in a flow control mechanism such as an enteral feeding pump.  
      It is still yet another object of the present invention to provide such an occluder which allows for a simple manual override of the occluding function.  
      It is still yet another aspect of the invention to provide an occluder which functions as a valve to effectively control fluid flow through a flexible conduit.  
      The above and other objects of the invention are realized in an apparatus and method for preventing free flow in an infusion set. 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, selectively to allow solutions to pass by the occluder which are pumped by an enteral feeding pump and the like.  
      In accordance with one embodiment of the invention, the occluder is formed by a stop placed in the tubing of the infusion set. The stop limits 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 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 another aspect of the present invention, the occluder can be formed integrally with the infusion set or can be formed of independent piece (s) which are then placed in the infusion set to selectively occlude the flow of solution therethrough.  
      In accordance with still yet another aspect of the invention, the occluder can function as a valve to selectively allow fluid flow therethrough. In one embodiment, a pair of occluders and infusion line can be used in conjunction with a piston or other force applicator to form a linear peristaltic pump which delivers predetermined amounts of fluid to a patient.  
      In accordance with still yet another aspect of the present invention, the occluder and infusion line can be formed to nest in and be opened by a conventional fluid flow pump. 
    
    
     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. 1  shows an perspective view of an infusion set made in accordance with the prior art;  
       FIG. 2A  shows a fragmented, side cross-sectional view of an apparatus and method for preventing free-flow through an infusion set in the form of an occluder mounted in an infusion set with the occluder and infusion set in a closed configuration;  
       FIG. 2B  shows a fragmented, side cross-sectional view of similar to that of  FIG. 2A , wherein the occluder and infusion set are in an open configuration;  
       FIG. 2C  shows a fragmented, side cross-sectional view of an alternate occluder/infusion set configuration made in accordance with the principles of the present invention;  
       FIG. 3A  shows a fragmented, side cross-sectional view of an alternate apparatus and method for preventing free-flow through an infusion set in accordance with the principles of the present invention;  
       FIG. 3B  shows a fragmented, cross-sectional view of an alternate occluder embodiment, with the occluder and infusion set being disposed in a closed configuration;  
       FIG. 3C  shows a cross-sectional view of the occluder embodiment of  FIG. 3A  with the occluder and infusion set being disposed in an open configuration;  
       FIG. 3D  shows a fragmented, side cross-sectional view of another embodiment of an occluder and infusion set made in accordance with the principles of the present invention;  
       FIG. 3E  shows a fragmented, side cross-sectional view of still yet another embodiment of an occluder and infusion set made in accordance with the principles of the present invention;  
       FIG. 4A  shows fragmented, side cross-sectional view of another embodiment of an occluder and infusion set with the occluder in an closed configuration;  
       FIG. 4B  shows a cross-sectional view of the embodiment of  FIG. 4A  in an open configuration;  
       FIG. 5A  shows fragmented side cross-sectional view of an occluder and infusion set made in accordance with one aspect of the present invention with the occluder and infusion set being in a closed position;  
       FIG. 5B  shows a cross-sectional view taken along plane A-A of  FIG. 5A ;  
       FIG. 5C  shows a fragmented, side cross-sectional view of an infusion set with an occluder disposed therein, with the infusion set being mounted in a control mechanism to maintain the infusion set and occluder in an open configuration;  
       FIG. 5D  shows a cross-sectional view taken along the plane B-B of  FIG. 5C ;  
       FIG. 5E  shows a perspective view of a housing of a control mechanism as may be used to hold the infusion set and occluder in an open position as shown in  FIG. 5D ;  
       FIG. 6A  shows a fragmented, side cross-sectional view of an infusion set having an occluder formed therein in accordance with an aspect of the present invention;  
       FIG. 6B  shows a view similar to that shown in  FIG. 6A  with the occluder held in an open position.  
       FIG. 7  shows another configuration of an occluder made in accordance with the principles of the present invention.  
       FIG. 8  shows yet another configuration of an occluder made in accordance with the principles of the present invention;  
       FIG. 8A  shows a cross-sectional view of another configuration of an occluder in accordance with the present invention;  
       FIG. 8B  shows a cross-sectional view of still yet another configuration of an occlude of the present invention;  
       FIG. 9  shows yet another aspect of the invention wherein the occluder forms part of a liquid control valve.  
       FIG. 10  shows a perspective view of a clip for retrofitting existing pumps of use with an occluder of the present invention;  
       FIG. 11  shows a side cross-sectional view of a pair of occluders and infusion line which form a pair of valves, and a force applicator to form a linear peristaltic pump;  
       FIG. 12A  shows a front view of an enteral feeding pump of the prior art with an occludes in accordance with the present invention disposed therein; and  
       FIG. 12B  shows a close-up, cross-sectional view of the occluder, infusion set and a portion of the pump to demonstrate opening of a fluid flow pathway around the occluder.  
    
    
     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. 1 , there is shown a perspective view of an infusion set  10  and related structures in accordance with the teachings of the prior art. Disposed at one end  10   a  of the infusion set  10  is a bag  14  for holding parenteral or enteral solutions. Typically, the bag  14  is supported by a stand  18  which holds the bag approximately 6 feet off the floor.  
      The opposing end  10   b  of the infusion set  10  is connected to a patient (not shown). In a parenteral use, the end of the infusion set  10  would have a needle attached thereto which extends into the patient&#39;s venous system. In a enteral use, the end  10   b  would typically have a fitting which attached to a balloon catheter (not shown) mounted in a stoma in the patient&#39;s stomach. The end may also be connected to a nasoenteric feeding tube.  
      Solution flows under gravity from the upper end  10   a  of the infusion set  10  to the lower end  10   b . The pressure on the fluid is 0.433 psi per foot. Thus, if the bag  14  is disposed five feet higher than the patient, the pressure at the lower end  10   b  of the infusion set  10  is 2.165 psi. From the extreme height of 8 feet to the floor, the solution in the infusion set  10  can reach approximately 3.5 psi.  
      To control the flow of solution through the infusion set  10 , the infusion set is typically mounted through a flow control portion of a pump  22 . The pump  22  selectively allows a metered amount of solution to pass distally (downstream) from the pump. This can be accomplished in multiple ways. For example, many enteral feeding pumps are peristaltic pumps which have a rotor which engages the infusion set  10  with a plurality rollers. Each partial rotation of the rotor allows a predetermined dose to pass to the patient. By controlling the rate at which the rotor turns, the pump can provide highly accurate doses of the solution.  
      Other pumps known in the art control solution flow through the infusion set  10  by a plurality of fingers which engage the infusion set. By controlling the position and frequency of the engagement of the fingers against the infusion set  10 , a highly accurate dose can be provided to the patient.  
      While the pump  22  controls the solution flow through the infusion set  10  when the infusion set is properly loaded, failure to load the infusion set properly in the pump quickly develops a free flow condition in which the solution flows uncontrolled through the infusion set. To prevent free flow, a clamp  26  is disposed along the infusion set  10 . Typically, the clamp  26  is disposed above the pump  22 . On common type of clamp  26  is a roller clamp which allows some control over the presence of flow and flow volume through the infusion set  10 . Other clamps simply provide on/off control.  
      While the infusion set  22  should be mounted in the pump  22  prior to or immediately after opening the clamp, this is not always done. There are many situations in hospital or nursing home setting in which the nurse or physician is called away or otherwise distracted prior to proper placement of the infusion set  10 . The result is that the solution in the bag  18  flows uncontrolled into the patient.  
      In many situations, the free flow of the solution will cause no real threat to the patient. In some situations, however, free flow can cause serious injury on even death to the patient. For example, a critically ill patient may suffer severe shock if a large amount of solution were to suddenly flow into his or her body. Likewise, a patient receiving heavily medicated solution may be seriously injured if a solution that was designed to be delivered over a number of hours were delivered in a few minutes.  
      To resolve such concerns, pinch clips may be disposed on the infusion set  10 . The pinch clip automatically closes the infusion set unless it is properly mounted in the infusion set  10 . An example of such a pinch clip is disclosed in U.S. Pat. No. 5,810,323.  
      While such occluders are a significant advantage over the possibility of free flow, they are relatively expensive to make. While such an occluder may only cost ten to twenty cents, using a new occluder with every infusion set adds a proportionally significant amount to the cost of an infusion set. Thus, there is a need to find an apparatus and method for preventing free flow in an infusion set which is reliable and which is less expensive than the prior art.  
      Turning now to  FIG. 2A , there is shown a fragmented, cross-sectional of an infusion set, generally indicated at  100 , with a stop or occluder  104  disposed therein. The infusion set  100  is formed by an elongate tube  108  made of a flexible, resilient material such as silicone rubber, latex polyurethane, neoprene or numerous similar medical grade materials. (In light of the present disclosure, those skilled in the art will appreciate that the present invention may be used in nonmedical contexts as well. In such situations, the tube made be made of materials which are not medical grade.)  
      The occluder  104  has an exterior diameter which is slightly larger than the interior diameter of the tube forming the infusion set  100 . This causes a portion  108   a  of the tube to stretch slightly as is passes over the occluder  104 .  
      The occluder  104  prevents flow through the infusion set  100  based on gravity. Thus, the size of the occluder  104  will depend on the material used to form the infusion set. In a presently preferred embodiment, the infusion set  100  is formed from a tube made of silicone rubber. The tube has a wall thickness of approximately 0.038 inches and an inner diameter of approximately 0.130 inches. The occluder  104  is preferably formed out of a plastic (e.g. acrylic (PMMA), polycarbonate, etc.) or a stainless steel ball bearing having an outer diameter of 0.141 inches.  
      Because the occluder  104  is larger than the interior diameter of the infusion set  100 , solution which is under only the force of gravity will back-up behind the occluder and not pass. To prevent the occluder  104  from gradually working its way downstream, a projection  112  can be formed in the infusion set  100  or, as explained in detail below, the occluder may be fastened to a connector or some other stationary structure.  
      Because the infusion set  100  is formed by an elongate, resilient tube  108 , increases in pressure will cause the interior diameter of the tube to expand. When the tube  108  expands sufficiently, the portion  108   a  of the tube which passes over the occluder  104  allows the solution to flow around the occluder and into the distal part  100   b  of the infusion set  100  as shown in  FIG. 2B .  
      Preferably, the occluder  104  and infusion set  100  are selected so that up to 4 psi can be maintained upstream of the occluder, i.e. in the proximal portion of the infusion set, before the portion  108   a  of the elongate tube  108  extending over the occluder will expand sufficiently to allow any clinically significant amount of solution to pass.  
      While solution hanging in the bag  18  may develop 2 to 3 psi due to gravity, it will not have enough pressure to pass by the occluder  104  without application of some external force. In contrast, an enteral feeding pump or other type of pump will typically generate between 5 and 10 psi. When the solution is pressurized to 5 to 10 psi by the pump, the solution is under sufficient pressure to go around the occluder  104  for delivery to the patient. In other words, if the infusion set  100  is not properly mounted in the pump so that the pump will generate a higher pressure in the proximal part  10   a  of the infusion set, the occluder  104  inhibits flow to the patient. Thus, there can be no free flow while accommodating flow of solution to the patient when the infusion set  100  is properly mounted in the pump.  
      Turning now to  FIG. 2C , there is shown a fragmented, side cross-sectional view of an alternate configuration of an infusion set, generally indicated at  130 , and the occluder  104 . As with the previous embodiment, the occluder  130  is formed by a small sphere, typically formed of a biologically inert plastic or stainless steel. The infusion set  130  is formed of a first tube  134  and a second tube  138 . The first tube  134  is formed of a resilient polymer or silicone so that the tube may expand with pressure. The second tube  138  is typically slightly smaller than the first tube  134  so that the distal end  134   a  of the first tube can be attached to the exterior of the proximal end  138   a  of the second tube.  
      To ensure that the occluder  104  does not advance distally into the second tube  138 , the second tube  138  is preferably formed from a material which is semi-resilient or nonresilient and therefore will not accommodate advancement of the occluder  104 . To prevent the proximal end  138   a  of the second tube  138  from forming a seal with the occluder  104 , the proximal end preferably has one or more indentations  142  or contours formed therein. The indentations  142  or contours ensure that liquid will be able to flow around the occluder  104  even if the occluder is pressed firmly against the proximal end  138   a  of the second tube  138 .  
      When pressures less than about 4 psi are disposed proximally from the occluder  104 , the first tube  134  engages the occluder and prevents liquid from flowing down stream. Once the pressure on the proximal side of the occluder  104  exceeds approximately 4 psi, the distal end  134   a  of the first tube  134  distends and allows liquid to flow by in the manner demonstrated by arrows  146 . Once the pressure subsides, the first tube  134  returns to its original size and liquid flow terminates until the pressure again is raised above the threshold.  
      In use, the infusion set  130  and occluder  104  prevent free flow unless the infusion set is placed in engagement with a pump that can generate sufficient psi to compel flow around the occluder. Once past the occluder  104 , the pressure of the liquid quickly falls and there is no danger to the patient.  
      Turning now to  FIG. 3A , there is shown a fragmented, cross-sectional view of another embodiment of principle of the present invention. An infusion set  160  has a proximal portion  160   a  and a distal portion  160   b . Disposed between, the proximal portion  160   a  and the distal portion  160   b  is an occluder or stop  164 . The stop  164  is disposed in the infusion set  160  to selectively prevent flow from the proximal portion  60   a  to the distal portion  160   b.    
      The stop  164  includes a proximal end  164   a  and a distal end  164   b . Beginning at the proximal end  164  is a channel  170 . As shown in  FIG. 3A , the channel has a proximal portion  170   a  and two distal portions  170   b  which are in fluid communication with the proximal portion. While the proximal portion  170   a  is disposed in continuous communication with the interior of the proximal portion  160   a , each of the distal portions  170   b  of the stop  164  are typically disposed in communication with the is sidewall of the infusion set  160 . The sidewall of the infusion set  160  normally prevents fluid flow out of the distal portions  170   b  of the channel  170 .  
      Preferably the sidewall will have sufficient resistance to expansion that a pressure of about 4 psi could placed in the channel  170  without causing the infusion set  160  to radially distend. Thus, if the pressure in the proximal portion  160   a  of the infusion set  160  is below about 4 psi, the liquid will not flow through the stop  164 .  
      As shown in  FIG. 3A , the stop  164  is relatively long. To maintain itself in place, the stop  164  frictionally engages the sidewall defining the infusion set  160 . By providing a stop  164  which is long, greater surface area is provided to engage the sidewall and prevent the stop  164  from being slowly moved downstream.  
      Turning now to  FIG. 3B , there is shown a fragmented, side cross-sectional view of an infusion set, generally indicated at  180 . The infusion set  180  includes a proximal (upstream) end  180   a  and a distal (downstream) end  180   b  which are separated by an occluder or stop  184 . The stop  184  is similar to the stop  164  shown in  FIG. 3A  in that it has a channel  190  with a proximal portion  190 a and a pair of distal portions  190   b.    
      Rather than relying on an elongate body and frictional engagement with the sidewall of the infusion set  180 , the stop  184  has at least one projection  194  which extends outwardly from the stop to engage the sidewall of the infusion set and prevent advancement. Preferably, the projection  194  is formed by an annular projection, or a plurality of spaced projections extending radially outwardly from the stop  184 .  
      Turning now to  FIG. 3C  there is shown a cross-sectional view of the infusion set  180  and stop  184  of  FIG. 3B . As the pressure in the proximal portion  180   a  of the infusion set  180  increases to greater than about 4 psi, the infusion set will distend radially. This allows liquid contained in the proximal portion  180   a  of the infusion set  180  to flow into the proximal portion  190   a  of the channel  190 , out the distal portions  190   b  of the channel and into the distal portion  180   b  of the infusion set. Once the pressure drops below about 4 psi, the infusion set  180  will retract and the flow in the channel  190  will be terminated as the sidewall of the infusion set covers the distal portions  190   b  of the channel  190 .  
      In such a manner, the embodiments shown in  FIGS. 3A through 3C  prevent free flow by preventing liquid flow under 4 psi. Once the infusion set  180  is properly mounted in the pump, the increased pressure created by rotation of the rotor (or other pressure source) overcomes the restriction to flow imposed by the stop  184 . When combined with the control provided by the various types of infusion pumps, the occluder or stop  164  or  184  enables a predetermined amount of liquid to flow through infusion set  160  or  180  while preventing the dangers of free flow conditions.  
       FIG. 3D  shows a side cross-sectional view of yet another embodiment of an infusion set, generally indicated at  200 , having an occluder or stop  204  disposed therein. The infusion set  200  includes a proximal portion formed by a first tube  208  and a distal portion formed by a second tube  212 . The proximal end  212   a  of the second tube  212  is mounted about the exterior of the distal end  208   a  of the first tube  208 .  
      Disposed at the distal end  208   a  of the first tube  208  and the proximal end  212   a  of the second tube  212  is the stop  204 . The stop  204  has a channel  216  extending from a proximal end  204  of the stop to a radially lateral position adjacent the distal end  204   b  of the stop. Thus, the channel is in fluid communication with liquid in the first tube  208 , but is normally isolated from the interior of the second tube  212 .  
      When pressures in the first tube exceed about 4 psi, the proximal end  212   a  of the second tube  212  radially expands, thereby opening the distal end of the channel  216  and allowing liquid to flow into the distal portion of the infusion set formed by the second tube  212 .  
      By positioning the stop  204  at the ends of two tube segments, the stop can be adhesively attached to either of the tubes to prevent distal movement of the stop. This can be accomplished without interfering with the ability of the stop to prevent flow below about 4 psi, while allowing pressures above about 4 psi cause liquid to pass through the infusion set.  
      While the embodiments of  FIGS. 3A through 3D  show embodiments in Which the proximal end of the channel is in continuous communication with the upstream flow and the distal end of the channel is normally closed, the stop  164 ,  184  or  204  could be rotated so that the proximal or upstream portion of the channel is normally closed by the sidewall of the infusion set  160 ,  180  or  200  and the distal portion of the channel is always in communication with the distal portion of the infusion set.  
       FIG. 3E  shows yet another embodiment of an infusion set, generally indicated at  230 , and an occluder  234 . The occluder  234  is disposed in the infusion set  230  so as to divide the infusion set  230  into a proximal, upstream portion  230   a  and a distal, downstream portion  230   b.    
      The occluder  234  has a channel  238  which extends from a proximal end  234   a  of the occluder to the distal end  238   b  so as to form a passageway through which an infusion liquid, such as enteral feeding solution, may pass. A wall  242  is disposed along the channel  238  to selectively prevent flow through the channel. In accordance with the principles of the present invention, the wall  242  is pivotably attached to the occluder  234  in such a manner that the wall will not move to allow liquid flow through the channel until the proximal, upstream pressure exceeds 4 psi. (While described as requiring a threshold upstream pressure, in light of the present disclosure those skilled in the art will appreciate that the wall will move based on a pressure differential between the two proximal and distal portions of the infusion set. Thus, the same effect could be generated by developing a vacuum downstream from the occluder  234 ).  
      Once the desired pressure threshold has been reached, the wall  242  will pivot and open the channel  238  to flow. Once the pressure drops, the wall  242  will pivot closed in accordance with one method of use. In accordance with another method of use, however, the wall  242  can have a score  246  formed therein. The wall  242  is designed to remain occluding the infusion set  230  until the pressure threshold is exceeded. Once deflected out of the way, the wall may not return to its original position even after the pressure drop. Because the pressure increase necessary to move the wall  242  is generated by the pump (not shown), the infusion set  230  must have been properly loaded in the pump for the wall to open. When the infusion set  230  is properly loaded in the pump, the pump will prevent free flow. Thus, if the infusion set  230  is properly loaded in the pump, the occluder does not need to continue to prevent free flow.  
      Turning now to  FIGS. 4A and 4B , there are shown fragmented, side cross-sectional views of yet another embodiment of the present invention. An infusion set, generally indicated at  250  has an occluder  254  in the form of a duckbill valve formed therein to divide the infusion set  250  into a proximal, upstream portion  250   a  and a distal, downstream portion  250   b . The occluder  254  is formed of two vanes  258   a  and  258   b  which are biased into engagement with one another.  
      When the pressure in the proximal portion  250   a  of the infusion set  250  is less than about 4 psi, the biasing of the vanes  258   a  and  258   b  keep them in contact as shown in  FIG. 4A . Once the pressure in the proximal portion  250   a  exceeds about 4 psi, the pressure forces the valves  258   a  and  258   b  away from each other, thereby allowing an infusion liquid to flow through the occluder  254  and into the distal portion  250   b  of the infusion set  250  as shown in  FIG. 4B . In order for the occluder  254  to work in such a manner, it is preferable for the vanes  258   a  and  258   b  to extend distally as they engage one another. However, the occluder  254  could be made so that the vanes extend proximally and then buckle once the threshold pressure has been passed.  
      The occluder  254  is shown as being molded integrally with the infusion set  250 . Such a configuration prevents any concern as to whether the occluder  254  may move during use. However, it is feasible to also form such an occluder  254  as a separate unit and then position it within the infusion set  250 . The occluder  254  could be held in place with adhesives or merely a friction fit.  
      Turning now to  FIG. 5A  there is shown a fragmented, side cross-sectional view of an infusion set, generally indicated at  300 , with an occluder  304  disposed therein. Similar to the embodiment shown in  FIG. 2A , the infusion set  300  is made of conventional silicone tubing or some other resilient or semi-resilient material, such as latex, polyurethane, etc.  
       FIG. 5B  shows a cross-sectional view of the infusion set  300  and occluder  304  taken along the plane A-A in  FIG. 5A . As shown, the tube defining the infusion set  300  forms a seal around the occluder  304  and prevents liquid from passing between the occluder and the tube forming the infusion set.  
      Turning now to  FIG. 5C , there is shown a side cross-sectional view of the infusion set  300  and the occluder  304 . Disposed behind the infusion set  300  at the location of the occluder  304  is a wall  308 . As will be discussed in additional detail below, the wall  308 , the occluder  304  and the infusion set  300  form a compression valve for selectively allowing liquid to flow through the infusion set.  
       FIG. 5D  shows a cross-sectional view of the infusion set  300  and the occluder  304  taken along the plane B-B in  FIG. 5C . The infusion set  300  and occluder  304  have been mounted between opposing walls  308  which are spaced apart a distance slightly smaller than the outer diameter of the infusion set. As the infusion set  300  is placed between the opposing walls  308 , the sides of the tubing forming the infusion set are compressed and held against the occluder  304 . This compression also causes the top and bottom  300   a  and  300   b  portions of the tube to extend radially outwardly from the occluder  304 , thereby opening a flow path  312  above and below the occluder. The flow paths  312  enable liquid in the infusion set  300  to flow around the occluder  304  and to flow to the patient.  
      In the event that the infusion set  300  and occluder  304  are pulled out from between the opposing walls  308 , the tube forming the infusion set  300  will return to the position shown in  FIGS. 5A and 5B , thereby terminating flow through the infusion set. Thus, the configuration shown in  FIGS. 5A through 5D  prevents free flow of infusion liquids through the infusion set  300  so long as the infusion set and occluder  304  are properly mounted between the walls  308  (or some analogous engagement surfaces). The infusion set  300  and occluder  304  are typically positioned between the walls  308  as the infusion set is being loaded into the pump (not shown). Once properly loaded, the pump controls flow through the infusion set  300  and prevents free flow.  
      Turning now to  FIG. 5E , there is shown a perspective view of a housing of an enteral feeding pump, generally indicated at  330 , made in accordance with one aspect of the present invention. The housing  330  includes a pair of channels  340  and  344  for holding a portion of an infusion set tube, such as those discussed with respect to  FIGS. 3A through 5D . In use, the tube is placed in one channel  340 , wrapped about a motor unit (not shown) which is placed in the opening  350 , and then positioned in the second channel  344 . If a conventional infusion set is not properly wrapped about the motor unit (or properly installed in other types of pumps) and placed in the channels  340  and  344 , a free-flow condition may develop. However, the present invention prevents such a situation from developing.  
      As shown in  FIG. 5E  in broken lines, the infusion set  354  is mounted in the first and second channels  340  and  344 . At least a portion  340   a  of the channel  340  is sufficiently narrow to form walls, similar to walls  308  in  FIGS. 5A through 5D , which compress the sides of the tube forming the infusion set  354 , thereby creating a flow path around the occluder (not shown) in the infusion set. If desired, the entire length of the walls  360  which form the channel  340  could be sufficiently close together to compress the infusion set  354  and thereby open flow.  
       FIG. 5E  also shows a cover  370  which is connected to the housing  330 . The cover  370  is pivotable with respect to the housing  330  and includes a catch  374  which engages a groove  380  on the housing. When the cover  370  is closed and the catch  374  engaged in the groove  380 , the infusion set  354  is securely held in the housing  330  and it is unlikely that the infusion set may be pulled from the pump.  
      Rather than having the walls  360  of the channel  344  compress the sides of the infusion set  354  to form a compression valve with the sides of the infusion set  354 , a projection  384  can be mounted on the cover  370  so that it is in alignment with the infusion set. When the cover closes, the projection  384  applies a downward force on the infusion set  354  thereby forming an open compression valve with the flow channels being disposed in horizontal alignment, rather than vertical alignment as shown in  FIG. 5D . Thus, liquid flowing through the infusion set  354  passes around the sides of the occluder, as opposed to above and below the occluder.  
      It will be appreciated in light of the present disclosure, that when a projection is used to engage the occluder, the occluder need not be held in a channel. Rather, the infusion set  354  must only be engaged on generally opposing sides so as to open at least one flow path around the occluder, or sufficient pressure must be exerted to cause the infusion set to expand and open a flow path.  
      As long as the catch  374  on the cover  370  engages the groove  380  on the housing  330 , or the projection  384  is maintained in engagement with the infusion set  354  at the location of the occluder, the compression valve will remain open. If the cover  370  is opened, the force holding the compression valve open is gone and the infusion set  354  will retract into the closed position shown in  FIGS. 5A and 5B , thereby preventing free flow through the infusion set  354 .  
      Turning now to  FIGS. 6A and 6B , there is shown yet another embodiment of the present invention. The infusion set, generally indicated at  400 , has an occluder  404  disposed therein. The occluder  404  may be molded in the infusion set  400 , or may be constructed separately and inserted.  
      The occluder  404  is formed by a first vane  408   a  and second vane  408   b  which form a duck-bill valve. The vanes  408   a  and  408   b  are disposed so that they extend proximally (i.e. upstream). As shown in  FIG. 6A , the vanes  408   a  and  408   b  normally engage one other to occlude flow from a proximal portion  400   a  of the infusion set  400  to a distal portion  400   b  of the infusion set.  
      When pressure is applied to the tubing which forms the infusion set  400 , the vanes  408   a  and  408   b  move away from each other sufficiently to allow fluid flow through the infusion set. Thus, in  FIG. 6 , a compression valve is formed by sliding the infusion set  400  between two walls  412  of engagement surfaces so that the vanes  408   a  and  408   b  are held apart, or by forcefully engaging the infusion set with a projection or other structure associated with a door, etc. As long as the infusion set  400  remains between the walls  412 , projections, etc., fluid flow is enabled. If the portion of the infusion set  400  which contains the occluder  404  is pulled from the walls  412  or projections, the occluder will return to the closed position wherein it prevents free flow.  
      Preferably, the infusion set  400  and occluder  404  will be used in a housing, such as that shown in  FIG. 5E . When the infusion set  400  is mounted in a channel defined by restricting sidewalls or when a cover with an aligned projection is closed, flow is enabled through the infusion set. If the infusion set  400  is pulled out of the housing, the occluder  404  will automatically close—thereby preventing free flow through the infusion set.  
      The various embodiments disclosed in accordance with the present invention provide a marked improvement over clamps and other types of external occluders which are commonly used to control fluid flow. The embodiments provide assurance against free flow, are generally easier to handle and are much more cost effective than the external occluders of the prior art.  
      In addition to being usable with housings and other fixed structures which cause the valve to open, the majority of configurations discussed above can also be manually opened by simply squeezing the infusion set adjacent the occluder to open a pathway around the occluder. The availability to manually open the occluder/infusion set is desirable, as it facilitates priming of the infusion set with the liquid being infused. Unlike many of the occluders of the prior art however, simply releasing the infusion set adjacent the occluder is all that is required to terminate flow.  
      Turning now to  FIG. 7 , there is shown another configuration of an infusion set, generally indicated at  400 , and an occluder,  404  made in accordance with the principles of the present invention. The infusion set  400  is formed by an elongate tube  108  made of a flexible, resilient material such as silicone rubber, latex, polyurethane, neoprene or numerous similar materials. Typically, the elongate tube has an inner diameter of approximately 0.130 inches.  
      The occluder  404  has an exterior diameter which is slightly larger than the interior diameter of the tube forming the infusion set  400 , typically about 0.141 inches. This causes a portion  408   a  of the tube to stretch slightly as is passes over the occluder  404 .  
      The occluder  404  prevents flow through the infusion set  400  based on gravity. Thus, the exact size of the occluder  404  will depend on the material used to form the infusion set  460 . In a presently preferred embodiment, the infusion set  400  is formed from a tube made of silicone rubber, and the occluder  404  is formed from a plastic (e.g. acrylic (PMMA), polycarbonate, etc.) cylinder having an outer diameter of 0.141 inches and a length of about 0.282 inches.  
      Because the occluder  404  is larger than the interior diameter of the infusion set  400 , solution which is under only the force of gravity will back-up behind the occluder and not pass. Once sufficient pressure is present—e.g. pressure produced by a pump—the walls of the infusion set will expand to allow fluid flow past the occluder  400  as discussed with respect to  FIG. 2A , etc.  
      While the embodiment shown in  FIG. 2A  is spherical and the embodiment shown in  FIG. 7  is cylindrical, those skilled in the art will appreciate that numerous other embodiments could be used. For example, the dashed line  412  illustrates an occluder which is bullet shaped occluders can also be egg shaped, or any other shape which provides a stop to fluid flow until a predetermined pressure threshold has been reached. It will also be appreciated that the occluder  404  need not have a consistent diameter. By having a portion of the occluder  404  extend radially a greater distance than other parts, a portion of the occluder will always engage the wall of the infusion set  400 , thereby reducing the ability of the occluder to move within the infusion set.  
      Turning now to  FIG. 8 , there is shown still another configuration of an infusion set  420  and occluder  424  made in accordance with the principles of the present invention. The infusion set  420  is formed from an elongate tube  428  which has a first portion  432  and a second portion  436  which are connected together by a connector  440 . The occluder  424  is attached to the connector  440  by a tether  442  to prevent the occluder from advancing along the second portion  436  of the elongate tube  428 .  
      When sufficient pressure is present in a proximal, upstream portion  428   a  of the elongate tube  428 , the second portion  432  will expand sufficiently to allow fluid flow past the occluder  424  and into the distal, downstream portion  428   b  of the infusion set  420 . One advantage of using the connector is that the first portion  428   a  of the elongate tube  428  need not be formed of a material which is resilient, or may use a material which does not expand or contract consistently. In other words, less expensive tubing materials may be used for most of the infusion set  420  without interfering with the interaction between the infusion set and the occluder  424 .  
      While shown in  FIG. 8  as being generally spherical, it should be appreciated that, in accordance with the present invention, the occluder  424  could be a variety of shapes. Additionally, the a single tether  442  or a plurality of tethers could be used to hold the occluder  424  to the connector  440 .  
       FIG. 8A  shows a cross-sectional view of another configuration of an infusion set  420 , and an occluder  444 . Unlike the spherical occluder  424  of  FIG. 8 , the occluder  444  of  FIG. 8A  is disk shaped. To prevent the occluder  444  from rotating in response to fluid pressure and inadvertently opening a fluid flow path, a plurality of tethers  442  are used to secure the disk to the connector  440 .  
      When pressure in the infusion set  420  is sufficient, the tube  428  will expand and allow fluid flow past the occluder  444 . Once the pressure drops below a predetermined threshold, the tube  428  will again engage the occluder  444  and terminate flow.  
       FIG. 8B  shows a cross-sectional view of still yet another configuration of an occluder,  446 , made in accordance with the principles of the present invention. The infusion set  420  and related portions are the same as in  FIGS. 8 and 8 A and are numbered accordingly.  
      The connector  440  is attached by one or more tethers  442  to the occluder  446  to prevent the occluder from moving down stream. The tethers  442  can also be used to keep the occluder  446  in a desired orientation. When sufficient pressure is present, the tube  436  expands to allow fluid flow past the occluder  446 .  
       FIG. 9  shows yet another aspect of the invention wherein the infusion set  450  and occluder  454  forms part of a liquid control valve, generally indicated at  460 . In accordance with the embodiments discussed above, and particularly the discussion surrounding  5 A through  5 E, the occluder  454  normally prevents fluid flow through the infusion set. However, squeezing the infusion set on an opposing sides of the infusion set sidewall  450   a  caused other portions of the sidewall to extend away from the occluder  454 —as demonstrated in  FIGS. 5C and 5D .  
      Disposed adjacent to the infusion set  450  and occluder  454  are a pair of engagement members  464  which are in communication with an actuator  468 , such as a motor. The communication can be electronic, mechanical or pneumatic, so long as the actuator  468  is able to control movement of one or more of the engagement members  464 .  
      When the engagement members are actuated, they apply and inward force to the infusion set  450  at the location of the occluder  454  to open a passage way around the occluder and thereby enable fluid flow through the infusion set. When the engagement members  464  are adjusted to no longer apply sufficient force to the infusion set  450 , the infusion set again surrounds the occluder  454  and prevents fluid flow.  
      By selectively actuating the engagement members  464 , the infusion set  450  and occluder  454  a valve is formed for controlling fluid flow. By applying a pressure sensor or other type of sensor, the valve can be used to regulate flow and flow through the valve can be determined.  
      Turning now to  FIG. 10 , there is shown a perspective view of a clip, generally indicated at  480 , for opening flow between an occluder and infusion set. Those skilled in the art will appreciate that there are a number of enteral and parenteral pumps in the market which use various types of occluders which suffer from the problems identified in the background section. To eliminate these concerns, the clip  480  is configured for retrofitting an existing pump for use with an occluder/infusion set made in accordance with the principles of the present invention. (Of course, with some existing pumps, the occluder and infusion set may be configured to nest in the pump in such a manner that retrofitting is not necessary.)  
      The clip  480  includes a base  484  which is provided for attachment to the housing of a conventional fluid pump. Typically, the base  484  will have an adhesive disposed thereon. If desired, the adhesive may be selected from removable adhesives, such as those known to those skilled in the art, so that the clip  480  can be removed from the pump when an infusion set containing an occluder (such as that represented by the dashed lines  488 ) is not being used with the pump.  
      Extending from the base  484  is a fitting  490  having channel  492  formed therein. The channel  492  is preferably formed with an open end and extends into the clip  480 . As the infusion set, represented in shadow at  488 , is inserted into the channel  492 , walls  494  defining the channel compress the infusion set  488  against the occluder (shown as dashed lines  498 ) to open a pair of flow channels between the occluder and the infusion set as shown in  FIGS. 5A through 5D .  
      As long as the infusion set  488  and occluder  498  remain securely held between the walls  494  defining the channel  492 , fluid flow is enabled between the occluder and the infusion set. If the infusion set  488  is pulled from the channel  492  or is never properly placed in the channel, flow through the infusion set is prevented. Thus, the risk of free flow developing within the system is significantly reduced. Of course, the risk of free flow can virtually be eliminated by placing the clip  480  on the pump in such a manner that the infusion set  488  must be properly loaded in the pump in order to fit within the channel  492 .  
       FIG. 11  shows a side cross-sectional view of yet another embodiment of the present invention which forms an in-line pump, generally indicated at  500 . As shown in  FIG. 11 , a pair of occluders  504  and  508  are disposed in an infusion line  512 . Each of the occluders  504  and  508  is disposed adjacent an actuator  514  and  518 , respectively. The actuators  514  and  518  are configured to selectively apply pressure to the infusion line  512  to selectively open flow channels between the infusion line and the occluder  504  or  508  with which each is associated.  
      In use, liquid in the infusion line  512  will be held in a proximal portion  512   a  which is upstream from the first occluder  504 . The first occluder  504  prevents the liquid from flowing down stream until a drive mechanism  522  causes the first actuator  514  to apply force to the infusion line  512  adjacent the first occluder. Applying force to the infusion line  512  causes a channel to open between the first occluder  504  and the infusion line, thereby allowing fluid flow into a middle portion  512   b  of the infusion line.  
      Once the middle portion  512   b  of the infusion line  512  has had adequate time to fill with liquid, the actuator  514  is adjusted so that it no longer applies sufficient force to the infusion line to enable fluid flow around the occluder  504 .  
      The liquid in the middle portion  512   b  of the infusion line  512  is then isolated from the liquid in the proximal portion  512   a.    
      The liquid in the middle portion  512   b  of the infusion line  512  is prevented from flowing distally or downstream by the second occluder  508  which defines the distal end of the middle portion. However, once the drive mechanism  522  is actuated to move the actuator  518  into forceful contact with the infusion line  512  adjacent the occluder  508 , one or more channels are formed between the occluder and the infusion line. The channel(s) opened by the actuator  518  squeezing the infusion line  512  form a flow path allowing the liquid contained in the middle portion  512   b  to flow into a distal, downstream portion  512   c . Since no occluder or other stop is typically disposed distally from the second occluder  508 , the liquid flowing into the distal portion  512   c  is delivered to the patient.  
      By selectively controlling the application of force by the first actuator  514  on the infusion line  512  and first occluder  504  and the application of force by the second actuator on the infusion line and second occluder  508 , a valve, generally indicated at  526 , is formed which permits a predetermined amount of flow to pass with each series of actuations.  
      In a more preferred embodiment, the valve also includes a force applicator  530 , such as a plunger, roller or similar device, disposed in communication with the middle portion  512   b  of the infusion line  512 . The force applicator  530  applies a compressive force to the middle portion  512   b  of the infusion line  512  to force the liquid contained in the middle portion  512   b  to flow into the distal portion  512   c  of the infusion line  512  and on to the patient. The force applicator  530  ensures that liquid will not simply remain in the middle portion  512   b  when the second actuator  518  causes a flow path to be formed between the second occluder  508  and the infusion line  512 .  
      While applying a compressive force to the middle portion  512   b  of the infusion line  512  helps to force the liquid in the middle portion to flow downstream, it also serves to assist flow into the middle portion. Once a compressive force is no longer applied to the middle portion  512   b , the resilient material forming the infusion line will attempt to return to its original, tubular configuration. By closing the flow path between the second occluder  508  and the infusion line  512  before releasing force applicator  530 , a vacuum is formed within the middle portion  512   b . Once the actuator  514  opens a flow path between the first occluder  504  and the infusion line  512 , the vacuum in the middle portion  512   b  will draw liquid into the middle portion  512   b  as the infusion line returns to its original configuration.  
      In each cycle of the valve  526 , the first actuator  514  will open a flow channel between the first occluder  504  and the infusion line  512  to fill the middle portion  512   b  with liquid. The first actuator  514  will then allow the flow channel to close. The second actuator  518  will then open a flow channel between the second actuator  508  and the infusion line  512  and the force applicator  530  will apply pressure to the infusion line forming the middle portion  512   b  so that the liquid in the middle portion will flow into the distal portion  512   c  and to the patient. The second actuator  518  will then allow the flow channel between the second occluder  508  and the infusion line  512  to close. The process will then be repeated.  
      By controlling the interior diameter of the infusion line  512 , the distance between the first occluder  504  and the second occluder  508 , and the movement/size of the force applicator  530 , one can obtain a predetermined amount of liquid flow with each cycling of the valve  526 . By controlling the number of cycles in a predetermined period of time, the operator is able to provide a highly accurate rate of flow for the solution passing through the valve  526 . Furthermore, because a rotor is not needed to control flow rate, the valve  526  can be used to make an in-line peristaltic pump which is significantly thinner than conventional peristaltic pumps while maintaining the same accuracy.  
      While  FIG. 11  shows two actuators, those skilled in the art will understand, in light of the present invention, that one of the occluders could be configured to allow fluid flow responsive to force if configured properly to prevent back flow. This could be achieved, for example, by controlling the size of the occluders.  
      Turning now to  FIG. 12A , there is shown a perspective view of a pump, generally indicated at  600 , which is designed to control fluid flow through an infusion set, generally indicated at  604 , and into the patient. The pump  600  includes a control panel  608  which has a plurality of buttons  610  or other devices for controlling the actuation of the pump. The pump  600  operates to deliver a predetermined dose of enteral feeding solution to a patient by rotation of a rotor  612 .  
      The infusion set  604  is mounted on the pump so that a resilient portion  604   a  of the infusion set wraps around the rotor  612 . Each rotation or partial rotation of the rotor  612  causes a predetermined amount of enteral feeding solution to be advanced through the infusion set  604  and delivered to the patient.  
      In order to assure that the rotor  604  is providing the proper amount of enteral feeding solution, a drip chamber  620  is formed along the infusion set. An optical sensor  624  is disposed in the enteral feeding pump  600  and monitors the drip rate of the solution in the drip chamber  624 . The drip rate of the solution is used to calculate an actual delivery rate of the solution.  
      As with the prior art, a portion  604   b  of the infusion set disposed distally from the rotor  612  is nested in a channel  630  in the pump housing  600 . In accordance with the present invention, the portion  604   b  has an occluder  634  disposed therein. While the prior art simply used the channel  630  to hold the infusion set  604  in contact with the rotors, the inclusion of an occluder  634  provides an improved measure of safety.  
      In the prior art, if either the portion  604   b  of the infusion set  604  was not properly positioned in the channel  630 , a free flow condition could develop in which fluid flow through the infusion set would be unchecked by the rotor  612 . In the present invention, flow through the infusion set  604  is not permitted until the portion  604   b  with the occluder  634  is nested in the channel  630 . If the portion  604   b  of the infusion set  604  is not properly placed in the channel  630  or is pulled from the channel, the occluder  630  will prevent free flow through the infusion set.  
       FIG. 12B  shows a close-up, cross-sectional view of the portion of the pump  600  having the channel  630  formed therein taken along the line A-A. The channel  630  receives the infusion set  604  in such a manner that it compresses the tube  642  against the occluder  634 . This causes another portion of the tube  642  to extend away from the occlude  634  and thereby open a fluid flow path between the inner wall of the tube and the occluder.  
      As shown in  FIG. 5D , compressing opposing sides of the infusion set can open fluid flow channels both above and below the occluder. In  FIG. 12B , the tube  642  of the infusion set  604  is pressed against one half of the occlude  634 , thereby forming a single fluid flow channel  646  on the opposing side. If the portion  604   b  of the infusion set  604  containing the occluder  634  is pulled from the channel  630 , the infusion set will engage the occluder prevent fluid flow.  
      Thus there is disclosed an improved apparatus and method for preventing free flow in an infusion line. The apparatus and method can be used with infusion control pumps, such as enteral feeding pumps or IV pumps, or as a replacement for such pumps. While the present disclosure discloses embodiments which are currently preferred, those skilled in the art will appreciate numerous modifications which can be made without departing from the scope and spirit of the present invention. For example, the relative size of the infusion set and occluder could be changed by providing an occluder which shrinks sufficiently under pressure to create fluid flow passages. The appended claims are intended to cover such modifications.