Abstract:
An I.V. flush syringe assembly includes a barrel having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end with a passageway therethrough in fluid communication with the chamber. An elongate plunger having a proximal end, a distal end and a stopper is slidably positioned in fluid-tight engagement with the inside surface of the barrel for drawing fluid into and out of the chamber by movement of the stopper relative to the barrel. The plunger includes anti-reflux structure for minimizing stopper deflection when fluid has been delivered from the chamber and the stopper is being forced against the distal end of the chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/117,257 filed May 8, 2008, now U.S. Pat. No. 8,512,298, issued on Aug. 20, 2013, which is a continuation of U.S. application Ser. No. 10/530,831 filed Apr. 8, 2005, now abandoned, which is a 371 off Application No. PCT/US03/29725 filed Sep. 23, 2003 which claims priority from U.S. Provisional Application No. 60/417,954, filed Oct. 11, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to syringe assemblies and particularly to syringe assemblies for use in I.V. flush procedures. 
     An I.V. catheter is a commonly used therapeutic device. Many patients, in accordance with their therapy, have an I.V. catheter connected to a vein ready for use in various procedures or in fluid communication with an I.V. system for infusing liquids and medication. Many I.V. sets have I.V. ports which are in fluid communication with a catheter and allow access for the purpose of injecting medication into the patient, and for use in flushing techniques to maintain catheter integrity. Healthcare facilities have flushing protocols which depend on the amount of time the catheter will remain in the patient and the type of catheter being used. For example, a peripherally inserted central catheter (PICC) is a long flexible catheter, which is typically inserted into the central venous system (optimally with the tip terminating in the superior vena cava) via the superficial veins of the antecubital fossa. PICC lines are designed for use when intermediate or long-term therapy is prescribed. 
     These catheter lines must be periodically flushed with saline flush solution and/or heparin lock flush solution depending on the protocol. Among other things, flushing saline solution removes blood from the catheter and heparin helps prevent the formation of future blood clots. The most common I.V. ports are covered by pierceable septums or pre-slit septums and are known in the art and sometimes referred to as “PRN” from the Latin pro re nata meaning “as the need arises”. The septum is preferably made of rubber or another elastomeric material which permits insertion of a sharp needle cannula in order to infuse fluids into or to withdraw fluids from the catheter. Upon withdrawal of the needle cannula the septum seals itself. Ports having pre-slit septums are used with blunt cannula. Typically, the blunt cannula is attached to a syringe and the syringe is moved to place a gentle pressure on the pre-slit septum which is forced open by the blunt cannula to establish fluid communication. Also, some I.V. sets have access valves which are responsive to the frusto-conically shaped tip of a syringe barrel for allowing fluid communication between the interior of the syringe and the catheter without the use of a cannula. 
     Catheters are flushed using syringe assemblies filled with various fluids. In some cases, different fluids are injected sequentially in accordance with the protocol. For example, a saline solution followed by an anticoagulant such as heparin. The size of the syringe used to flush I.V. lines varies by various factors including the size and length of the catheter. Typically syringes of 1 ml, 3 ml, 5 ml and 10 ml volume are used. 
     It is important in the flush procedure not to draw blood back into the catheter where it can clot and seal the catheter, commonly referred to as “reflux”. In order to prevent blood reflux into the catheter the user is encouraged to maintain a positive pressure in the line during the flush procedure. This may involve slowly withdrawing the syringe and cannula from the I.V. port while still applying pressure to the syringe plunger rod during the flush procedure. When using a syringe with an elastomeric stopper, the stopper is often compressed when it contacts the distal end of the syringe barrel at the completion of the flush procedure. When a user relieves the pressure to the plunger after the flush procedure is completed, the stopper will expand back to its normal size drawing liquid from the catheter into the syringe barrel. This is undesirable, since it can cause blood to enter the catheter at the catheter distal end (reflux). 
     Therefore there is a need for simple, straight forward easy-to-manufacture syringe assemblies which helps reduce or eliminate reflux of blood into the catheter during and after the flushing procedure has occurred without changing flush protocols and procedures. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a syringe for use in flush applications. The syringe reduces or eliminates compression of distal end of the stopper at the completion of the flush procedure thereby reducing or eliminating reflux of blood into the catheter. Compression of the stopper is eliminated, or greatly reduced, by the presence of a compressible or flexible portion disposed on the plunger to absorb the compression forces usually absorbed by the stopper. Since compression of the stopper is translated to a portion of the plunger, reflux is reduced or eliminated. 
     An I.V. flush syringe assembly includes a barrel having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall with an elongate tip extending distally therefrom having a passageway therethrough in fluid communication with the chamber. A plunger including an elongate body portion having a proximal end, a distal end and a stopper is slidably positioned in fluid-tight engagement with the inside surface of barrel for drawing fluid into and driving fluid out of the chamber by movement of the stopper relative to the barrel. The elongate body portion of the plunger extends outwardly from the open proximal end of the barrel. The I.V. flush syringe includes anti-reflux means for minimizing stopper deflection when fluid has been delivered from the chamber and the stopper is in contact with the distal wall. Such anti-reflux means provides a portion of the stopper and/or plunger which is more flexible than the distal end of the stopper so that distally directed forces on the plunger will not cause distortion of the distal end of the stopper because anti-reflux structure between the distal end of the stopper and the proximal end of the plunger rod deflects in response to the force. 
     The anti-reflux structure can include the stopper being supported by a flexible base at the distal end of the plunger wherein the base is more flexible than the stopper in response to proximally directed forces on the stopper. 
     The anti-reflux structure may include a stopper having a recess in its proximal end and a flexible base extending distally from the plunger wherein the base is positioned at least partially in the recess of the stopper and the base is softer than the stopper and deflectable upon application of a proximally directed force on the stopper. 
     The anti-reflux structure may include the stopper being connected to a base at the distal end of the plunger wherein the stopper is configured to be more flexible at its proximal end than at its distal end in response to proximally directed forces on the stopper. 
     The anti-reflux means may include a resilient portion in the plunger between the proximal end and the distal end of the plunger wherein the resilient portion is more deflectable than the stopper and deflectable upon application of a proximally directed force on the stopper. 
     A method of flushing a catheter of the present invention comprises the steps of providing a syringe assembly having an inside surface defining a chamber for retaining fluid, an open proximal end and a distal end including a distal wall with an elongate tip extending distally therefrom having a passageway therethrough in fluid communication with the chamber, a plunger including an elongate body portion having a proximal end, a distal end and a stopper slidably positioned in fluid-tight engagement with the inside surface of the barrel for drawing fluid into and driving fluid out of the chamber by movement of the stopper relative to the barrel, the elongate body portion extending outwardly from the open proximal end of the barrel, a quantity of flush solution in said chamber, and anti-reflux means for minimizing stopper deflection when the flush solution has been delivered from the chamber and the stopper is in contact with and pressed against the distal wall. The method further includes providing a catheter having a proximal end, a distal end and a passageway therethrough and a housing having a hollow interior in fluid communication with the passageway, the housing having an access valve capable of engaging the elongate tip of the barrel for allowing fluid communication with the hollow interior of the housing. The method further includes the steps of placing the distal end of the catheter in a blood vessel; engaging the elongate tip of the barrel with the access valve so that the passageway in the tip is in fluid communication with the hollow interior of the housing; applying force to the plunger to move the plunger in a distal direction with respect to the barrel so that the flush solution in the chamber flows through the passageway into the hollow chamber of the housing and through the passageway of the catheter; continuing to apply force to the plunger until the stopper contacts and presses against the distal wall of the barrel; and disengaging the barrel from the access valve. 
     An alternative method may include the step of attaching a needle assembly to the elongate tip of the barrel. The needle assembly includes a cannula having a proximal end, a distal end and a lumen therethrough and a hub having an open proximal end containing a cavity and a distal end attached to the proximal end of the cannula so that the lumen is in fluid communication with the cavity. The attachment of the needle assembly to the barrel is through frictional engagement between the cavity in the hub and the elongate tip. This alternative method is used with a catheter having a proximal end, a distal end and a passageway therethrough and a housing having a hollow interior connected to the catheter and in fluid communication with the passageway of the catheter. The housing further includes a septum for allowing fluid communication with the hollow interior. Fluid communication is established by forcing the distal end of the cannula through the septum so that the lumen of the cannula is in fluid communication with the hollow interior of the housing. Also, the cannula may be permanently attached to the barrel tip with or without the use of a hub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a syringe assembly according to one embodiment of the invention. 
         FIG. 2  is a partially cross-sectioned perspective view of the syringe assembly of  FIG. 1  with a needle assembly attached. 
         FIG. 3  is an enlarged partial cross-sectional side elevation view of the distal end of the syringe assembly of  FIG. 2 . 
         FIG. 4  is a side-elevational view illustrating the syringe assembly in use with a catheter injection site. 
         FIG. 5  is a cross sectional side elevation view of the distal end of a plunger and stopper according to another embodiment of the invention 
         FIG. 6  is a perspective view of a syringe assembly according to another embodiment of the invention. 
         FIG. 7  is partially cross-sectioned side-elevation view of the syringe assembly of  FIG. 6 . 
         FIG. 8  is the syringe assembly of  FIG. 7  shown after flush solution has been delivered. 
         FIG. 9  is a partial cross-sectional view of the proximal end of the syringe assembly of  FIG. 8  with the plunger deflected. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a syringe  20  according to the present invention generally comprising a barrel  22  and a plunger  24 . The barrel  22  has a generally elongate body including an open proximal end  28  having finger grips  29 , a distal end  30  having a distal wall  31  and an inside surface  32  defining a chamber  33  for retaining fluid. The distal end  30  further includes a tip  36  having a passageway  38  in fluid communication with the chamber. The distal end of barrel  22  preferably, but not necessarily includes a locking luer type collar  40  concentrically surrounding tip  36 . The inside surface of the collar includes at least one thread  43 . A cannula  26  includes a proximal end  42 , a distal end  44  and a lumen  46  therethrough. The distal end may include a sharp tip or a blunt tip  48  as shown. The cannula may be connected directly to the tip of the syringe barrel to establish fluid communication between the lumen and the chamber. Also, the cannula may be part of a needle assembly  27  including a hub  34  having an open proximal end  37  containing a cavity  41  and a distal end  39  attached to the proximal end of the cannula so that the lumen of the cannula is in fluid communication with the cavity. The cavity of the hub can be removably frictionally engaged to the tip of the barrel as illustrated in  FIGS. 2-3 . 
     Plunger  24  includes an elongate body portion  25 , a proximal end  50  having a flange  51 , and a distal end  52 . A flexible base  53  extends axially from distal end  52  of the plunger  24 . Base  53  has a diameter smaller than the diameter of the plunger  24  and may include threads. 
     A stopper  54  is disposed on flexible base  53  at distal end  52  of the plunger, preferably via threading engagement. Thus, the flexible base  53  supports the stopper  54  at its center. Stopper  54  includes a plurality of ribs  56  on its outside diameter. The stopper  53  may be made of any material suitable for providing sealing characteristics while under compression. For example, the stopper may be made of thermoplastic elastomers, natural rubber, synthetic rubber, silicon or thermoplastic materials. The base in this embodiment is preferably made of material which is more flexible than the stopper such as thermoplastic elastomers, natural rubber, synthetic rubber, polyurethane, silicone and the like. 
     In operation, syringe  20  is connected to a hypodermic needle assembly and filled with flush solution using known methods. The flush solution may be any solution intended for flushing. It is preferred that the flush solution be selected from the group consisting of saline flush solution and heparin lock flush solution. These solutions are known in the art and readily available. An example of a saline flush solution is 0.9% Sodium Chloride USP. An example of a heparin lock flush solution is 0.9% Sodium Chloride with 100 USP units of Heparin Sodium per ml or 10 USP units of Heparin Sodium per ml. The syringe with needle assembly attached is used to pierce the pierceable septum or a blunt cannula may be inserted into a pre-split septum of a vial containing flush solution and the flush solution is drawn into the syringe barrel by pulling plunger rod flange  51  in the proximal direction while holding barrel  22 , to draw fluid through the needle cannula into the fluid chamber  34 . 
     Alternatively, the syringe may be filled with flush solution during the manufacturing of the syringe via a sterile filling method. Such prefilled syringes may be supplied with a tip cap such as tip cap  23  releasably connected to tip  36  sealing passageway  38 . It is preferred that the tip cap is formed of material selected from the group of thermoplastic materials and elastomeric materials such as natural and synthetic rubber and thermoplastic elastomers. 
     The syringe is now ready for use in flushing a catheter of an I.V. set. I.V. sets can be very complicated and may include multiple injection ports, a valve and/or other components. For the purpose of illustrating the present invention a simplified I.V. set  64  is illustrated in  FIG. 4 . I.V. set  64  comprises an I.V. site  65  which includes a housing  67  having a hollow interior  68  and a septum  69  at its proximal end. A catheter  70  having a conduit therethrough extends from the distal end of the housing. For this I.V. set septum  69  is pre-slit for use with blunt cannula. The I.V. site may be a valve having structure for accepting the syringe barrel tip and being activated by the insertion of the tip to establish fluid communication with the catheter, such as the valve taught in U.S. Pat. No. 6,171,287. 
     Blunt tip  48  of cannula  26  may be inserted through pre-split septum  69  of I.V. set  64 . Alternatively, a sharp tip of a needle cannula may be used to pierce a septum that is not pre-split or the tip of the barrel may be engaged with a valve in the IV site. This establishes fluid communication between the interior  68  of the I.V. set and the chamber of the syringe barrel. The syringe barrel  22  is preferably held via finger grips  29 . Pressure is then applied to flange  51  of the plunger, for example by a thumb, in the distal direction. This moves the plunger  24  having the stopper  54  on its distal end forcing the liquid such as flush solution  35  in the chamber  34  out of the chamber, through cannula  26  and into interior  68  of the I.V. set and then through catheter  70 . 
     Referring to  FIG. 3  the position of the plunger and stopper at the completion of the flush procedure is shown. As shown, the flange  51  does not contact the proximal end of the barrel at the completion of the flush procedure. It is preferable, however, that the flange  51  of the plunger bottoms out on the proximal end of the plunger at the completion of the flush procedure. When the distal face of the stopper  54  contacts the distal end  30  of the barrel  22 , compressive force generated by this contact is translated to the flexible base  53 . Thus, compression of the stopper  54  and its ribs  56  is reduced. The flexible base  53 , therefore, absorbs compressive forces so that compression of the stopper face and the outside diameter of the stopper is reduced. Since the stopper  54  does not compress substantially, there is little or no reflux of liquid into the catheter that typically results from the expansion of the stopper after compression. 
       FIG. 5  shows another embodiment of the invention. A distal end  152  of a plunger  124  is shown having a base  153  extending therefrom. A stopper  154  is disposed on the base. Base  153  includes threads  155  for threading engagement with the interior of the stopper. Stopper  154  includes one or more ribs  156  on its outer diameter. The stopper further includes an annular groove  157  concentrically surrounding base  153 . As shown, the proximal end of the stopper  154  is displaced from the proximal end of the base by a distance denoted as D. 
     In operation, the flush procedure is carried out as described above. At the completion of the flush procedure, stopper  154  contacts the distal end of the barrel. When distal face  158  of the stopper contacts the distal wall of barrel, compressive force generated by this contact is translated to the proximal end of the stopper in the area of the annular groove which is, by virtue of its structure more flexible than the distal end of the stopper. The annular groove  157  and relief D act to create a structure wherein the proximal end of the stopper as it is connected to the base, is more flexible than the distal end of the stopper to absorb much of the compressive force. Thus, the distal end of stopper  154  and its ribs  156  are subject to less compression. The flexible proximal end of the stopper absorbs most of the compression forces so that the outside diameter near the face of the stopper does not compress. Since the distal end of stopper  154  does not compress as much as a more rigid stopper design, there is little or no reflux of liquid into the barrel  22 . 
       FIGS. 6-9  show another embodiment of the present invention, where like elements are similarly numbered. In this embodiment of the invention, the plunger  224  comprises a flexible or compressible portion  260  at its proximal end  250 . The compressible portion  260  may be, for example a compressible spring such as a coil spring or flexible members. As shown, the compressible portion  260  comprises a compressible spring including a plurality of ribs  262 . 
     In operation, after the syringe barrel has been filled with flush solution as discussed above, the sharp tip  248  of the cannula  226  may be inserted through a septum of an I.V. set. Alternatively, a blunt tip of a needle cannula may be used to pierce a pre-slit septum. This establishes fluid communication between the catheter of the I.V. set and the chamber  33  of the syringe barrel. The syringe barrel  22  is preferably held via finger grips  29 . Pressure is then applied to the flange  251  of the plunger, for example by a thumb, in the distal direction. This moves the plunger  224  having the stopper  254  on its distal end forcing the liquid in the chamber  33  out of the chamber, through the cannula  226  and into the conduit of the I.V. set through the catheter. 
     At the completion of the flush procedure, the distal end of the stopper contacts and presses against the distal wall of the barrel. The compressible portion  260  absorbs more of the compressive forces generated by this stopper contact rather than the stopper  254 . In addition, if stopper  254  does in fact compress, any relaxation that is caused by the compression of stopper  254  can be translated to and absorbed by the compressible portion  160 . 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as disclosed.