Abstract:
A needle assembly includes a transparent or translucent housing with a fluid inlet end, a fluid outlet end, a flashback chamber and a venting mechanism therebetween. Substantially axially aligned inlet and outlet cannulas extend from the housing and communicate with the chamber. A sealable sleeve covers the external end of the outlet cannula. Relative volumes of the cannulas, the chamber and the sleeve are selected to provide rapid reliable flashback indicative of venous entry with an internal vent plug over the outlet of the flashback chamber to inhibit leakage of blood from the needle on withdrawal from the patient.

Description:
The present application is a Continuation application based upon U.S. application Ser. No. 10/919,088, filed Aug. 16, 2004, entitled “Flashback Blood Collection Needle”, now U.S. Pat. No. 7,615,033. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for collecting blood samples by performing venipuncture on a patient. More particularly, the present invention relates to a needle assembly for multiple sample blood collection that allows a phlebotomist to determine whether vein entry has occurred when collecting a blood sample from a patient into an evacuated blood collection tube. 
     2. Description of Related Art 
     Venipuncture is the primary method used for acquiring blood samples for laboratory testing. In performing venipuncture procedures, a phlebotomist must follow several steps simultaneously. Such steps include assessing the patient&#39;s overall physical and psychological condition so as to properly select a venipuncture site and technique. The phlebotomist must also select the proper corresponding equipment, perform the technique so as to control bleeding, and properly collect and identify fluid specimens for testing. The phlebotomist must ascertain all of these coinciding factors, as such factors may adversely affect the distension of the vein and the length of the venipuncture procedure. 
     Various venipuncture devices have been developed to address the above-described problems. These devices include products intended to assist the phlebotomist in confirming that vein entry has been made see e.g. U.S. Pat. Nos. 5,222,502 and 5,303,713. Such a device contains a needle assembly with a housing that defines a chamber therein. A single cannula pointed at both ends, is affixed to the housing. The intravenous (IV) end of the cannula is adapted for penetration of a patient&#39;s vein. The non-patient end of the cannula has a sealable sleeve and is adapted for penetration of a penetrable stop positioned within an evacuated container. 
     Upon vein entry with the intravenous end of the cannula, blood will flow through the cannula, into the sealable sleeve and into the housing chamber, which is clear or translucent for visualization (“flashback”). Once air is vented from the flashback chamber, the blood therein is pressurized each time the sealable sleeve is pushed toward the housing chamber upon activation of an evacuated container. 
     Due to the length of time between vein entry and flashback, the phlebotomist may erroneously believe that satisfactory vein entry has not been achieved since there is no immediate indication of vein entry in the see-through chamber. The phlebotomist may therefore unnecessarily repeat the venipuncture procedure, requiring replacement of the evacuated container and/or the needle assembly itself. Such a repetitive process prolongs the physical and emotional discomfort endured by the patient. In such cases, a phlebotomist may use a blood collection set to provide some entry indication, and will then incur the cost of the blood collection set, as well as the cost of a discard tube. 
     It would therefore be desirable to provide an improved blood collection device that permits blood flow through a relatively short needle directly into a flashback chamber, thereby providing immediate indication of successful vein entry. 
     SUMMARY OF THE INVENTION 
     The invention provides a needle assembly for the extraction of at least one fluid sample into an evacuated container for laboratory testing. The needle assembly provides a clear or translucent housing with sufficient dead space for blood to flow into a flashback chamber for visualization by the user to confirm successful vein entry, with an internal vent mechanism over the outlet of the flashback chamber to inhibit leakage of blood from the IV needle on withdrawal from the patient. As used herein vent mechanism indicates one or more features or elements that provide venting of air, but which, typically, prevent fluid from passing through. The actual element that vents the air in the venting mechanism may be for example a vent plug or a one-way valve. At the same time there will be very little residual blood in the housing after use as the vent mechanism retains the blood within the relatively small flashback chamber. 
     According to the invention a needle assembly includes a housing which in turn is comprised of a housing interior, a flashback chamber in communication with the housing interior; and either (i) a first cannula mounted in the housing in communication with the flashback chamber and a second cannula mounted in the housing in communication with the flashback chamber, or (ii) a single cannula mounted in the housing with an opening in communication with the flashback chamber. These elements are configured such that the sole communication path between the housing interior and the external environment is via the flashback chamber. A vent mechanism is located in the communication path between the flashback chamber and the housing interior; so that upon contact with blood, this venting mechanism seals against the flow of air from the housing interior into the flashback chamber. 
     In use, the intravenous (IV) cannula (or IV portion of a single cannula). punctures the patient&#39;s skin to make a vein entry. Upon satisfactory vein entry, air that is at atmospheric pressure within the lumen of the IV cannula, flashback chamber, housing interior and the lumen of the non-patient cannula (or non-patient portion of a single cannula) experiences compression due to the influence of venous pressure and therefore flows through the IV cannula into the flashback chamber and through the vent plug into housing interior. Because the venous pressure exceeds the atmospheric pressure within flashback chamber, blood flows into the chamber. Blood flow into the housing interior is prevented by the vent mechanism, which while allowing air to flow through it, seals on contact with blood thereby trapping the compressed air at venous pressure in the housing interior. This inhibits leakage of the blood or fluid sample from the N cannula on removal from the patient, which might otherwise occur due to decompression of the air from the housing interior through the N cannula. 
     The volumes defined by the lumens through the cannulas, the chamber, the housing interior and the sleeve are selected to achieve a very rapid indication of vein entry. The first and second cannulas are typically in axial alignment with one another to provide an axial fluid flow path therebetween along a length of the housing. The second cannula typically includes a sealable sleeve. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a typical embodiment of the needle assembly of the present invention. 
         FIG. 2  is a cross-sectional view of a second embodiment. 
         FIG. 3  is a cross-sectional view of a third embodiment. 
         FIG. 4  is a cross-sectional view of a fourth embodiment. 
         FIG. 5  is a schematic view of the needle assembly of  FIG. 1  prior to use. 
         FIG. 6  is a schematic view similar to  FIG. 5 , but showing the first sign of venous entry. 
         FIG. 7  is a schematic view of a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The invention provides a needle assembly for blood collection that, provides a visual indication of vein entry (“flashback”) upon collection of a blood or other fluid sample from a patient into one or more evacuated blood collection tubes and inhibits leakage of the blood or fluid sample from the IV cannula on removal from the patient. 
     Various embodiments of the present invention are shown in  FIGS. 1-7 , With reference to  FIG. 1 , this embodiment is directed to a needle assembly  210  with a housing  212  having a fluid inlet end  214 , a fluid outlet end  216  and a frustum-shaped exterior wall  218  extending between the ends. Exterior wall  218  defines the housing interior  220 . Housing  212  further includes a cylindrical interior wall  224  that extends in the housing interior  220  from fluid inlet end  214  substantially concentrically with cylindrical exterior wall  218  to a vent plug  900 . Cylindrical interior wall  224  and vent plug  900  define a flashback chamber  226 . 
     Needle assembly  210  also includes a fluid inlet cannula  236  having an exterior end that defines a sharpened bevel and an interior end  244  that is mounted fixedly in fluid inlet end  214  of housing  212 . Fluid inlet cannula  236  is characterized further by a substantially cylindrical lumen extending between the ends and communicating with the interior of housing  212 . 
     Needle assembly  210  further includes a fluid outlet cannula  252 . Outlet cannula  252  concludes a blunt interior end  254 , an exterior end defining a sharpened bevel and a substantially cylindrical lumen extending between the ends. Portions of outlet cannula  252  between the ends are securely affixed in outlet end  216  of housing  212 . Outlet cannula  252  is mounted so that interior end  254  passes substantially coaxially into interior wall  224  and so that interior end  254  of outlet cannula  252  substantially aligns axially with interior end  244  of inlet cannula  236 . Additionally, interior end  254  of outlet cannula  252  is spaced only a small distance from interior end  244  of inlet cannula  236 . An axial gap between interior end  254  of outlet cannula  252  and interior end  244  of inlet cannula  236  that is less than 0.5 mm may result in a flashback that is inconsistent. 
     Cylindrical interior wall  224  is dimensioned relative to outlet cannula  252  to achieve both desirable flow of blood through assembly  210  and to achieve effective flashback indication. In particular, cylindrical interior wall  224  preferably is dimensioned to provide a radial gap around outlet cannula  252  of about 0.2 mm, as indicated by dimension “c” in  FIG. 1 . This gap achieves a substantially laminar blood flow within flashback chamber  226  and prevents blood hemolysis. Additionally, the small radial gap between cylindrical inner wall  224  and outlet cannula  252  enables a drop of blood to be spread thinly across the radial gap in flashback chamber  226  to provide a magnified flashback indication with a very small volume of blood. Thus, an easily visualized flashback indication is achieved quickly at the first appearance of blood from interior end  244  of inlet cannula  236 . 
     Needle assembly  210  further includes a sealable sleeve  261  mounted to fluid outlet end  216  of housing  212  and covering exterior end  258  of outlet cannula  252  when sealable sleeve  261  is in an unbiased condition. However, sealable sleeve  261  can be collapsed in response to pressure exerted by the stopper of an evacuated tube for urging exterior end  260  of outlet cannula  252  through both sealable sleeve  261  and stopper of an evacuated tube, as known in the art. 
     The above embodiment is described in terms of a vent plug. However, any vent mechanism is suitable. The vent mechanism may be, for example, a porous vent plug formed from a matrix or carrier material, typically hydrophobic, that is coated with, impregnated with, or otherwise, contains a hydrophilic material that swells on contact with aqueous or water containing substances. The hydrophobic carrier material can be but is not limited too, high-density polyethylene, polytetrafluoroethylene, ultra-high molecular weight polyethylene, Nylon  6 , polypropylene, polyvinylidine fluoride and polyethersulfone. The swellable nature of the hydrophilic material thereby provides the sealing function in the vent upon contact with blood. It is also possible to use a porous vent plug that becomes sealed upon contact with blood using biological phenomena, e.g., by clotting and/or cell agglutination that blocks the vent; a superabsorbant material to seal the vent by swelling on contact with an aqueous fluid; or a one-way valve, (e.g., a thin flap such as plastic film covering a vent, a deformable seal such as a rubber or plastic duckbill valve, or a deformable wrap over a vent). Is should be noted that any combination of these various mechanisms is also possible. 
       FIGS. 2-4  show embodiments with varying vent plugs.  FIG. 2  shows a vent plug  900   a , which is located at the end of the cylindrical inner wall  224   a  and fitted into a recess  301  in the housing interior non-patient wall  300 .  FIG. 3  shows a vent plug in a similar location to that of  FIG. 2  however Vent plug  900   b  has a shoulder  901   b .  FIG. 4  shows a vent plug  900   c  that is located both within the cylindrical inner wall  224   c  and the recess  301  in the housing interior non-patient wall  300 , and has a shoulder  901   c . The vent plug location in each of these embodiments is such that no air can flow out of the flashback chamber  226  into the housing interior  220  without passing through the vent mechanism ( 900   a,b,c ). 
       FIGS. 5 and 6  provide schematic representations of the needle assembly  210  of  FIG. 1  before and after a conventional venipuncture, in which, the needle assembly  210  is connected to a holder (not shown) and punctures the patient&#39;s skin to make a vein entry. Upon vein entry, blood enters the IV cannula  236  and flows toward the flashback chamber  226 . The blood flows from inlet cannula  236  into the space between inlet and outlet cannula, such that blood flows both into the outlet cannula  252  and into flashback chamber  226 . At this point in time, Flashback chamber  226  indicates successful vein entry and reduces the volume of air present in housing  212  shown in  FIG. 6 . Air that was at atmospheric pressure within the lumen of the N cannula  248 , flashback chamber  226  housing interior  220  and the lumen of the non-patient cannula  262  prior to vein entry. Thus experiences compression due to the influence of venous pressure and this air is therefore forced through the IV cannula  236  shown in  FIG. 6  into the flashback chamber  226  and through the vent plug into chamber  220 . Blood flow into housing interior  220  is prevented by the vent plug  900 , which allows the pressurized air to flow through it, but seals on contact with blood, thereby trapping the compressed air (at venous pressure) in housing interior  220 . Blood flow in the entire needle assembly ceases once the pressure within chamber  226  and the venous pressure are equal. 
     Once the steps set forth in the previous paragraph occur, and venous entry is visually confirmed by the phlebotomist, an evacuated container (not shown), is then inserted into the holder such that exterior end  260  of second cannula  252  penetrates stopper of the container, as known in the art. Upon penetration of the stopper by second cannula  252 , a negative pressure gradient is transmitted to chamber  226 , causing blood to flow from chamber  226  into the container. 
     The needle assemblies described above desirably should be small for convenient use, but should be constructed to ensure reliable and rapid flashback. The occurrence of flashback in the needle assemblies described and illustrated above operate pursuant to the ideal gas law. In particular, at very low densities all gases and vapors approach ideal gas behavior and closely follow the Boyle&#39;s and Charles&#39; laws given by:
 
P 1 V 1 =P 2 V 2  
 
where:
         P 1  denotes the pressure of air within the needle assembly before needle insertion,   P 2  denotes the pressure of air within the needle assembly after vein entry;   V 1  denotes the volume of air within the needle assembly before vein entry; and   V 2  denotes the volume of air within the needle assembly after vein entry.       

     Design parameters should keep the needle device as small as possible for easy use, while ensuring an appropriate volume as specified by the preceding equation.  FIGS. 5 and 6  provide schematic representations of the needle assembly  210  of  FIG. 1  for purposes of depicting the application of the ideal gas law. In this regard, A identifies the volume of lumen  248  through inlet cannula  236 . B denotes the total volume of the housing interior  220 , flashback chamber  226 , lumen  242  through outlet cannula  252  and sealable sleeve  261 . Referring again to the preceding equation, P 1  is the pressure within needle assembly  210  before use, and hence substantially equals atmospheric pressure. Atmospheric pressure will vary slightly from time to time and from location to location. However, for purposes of this analysis, atmospheric pressure P 1  will be assumed to be 760 mm Hg. P 2  in the preceding equation is the volume of the dead space in needle assembly  210  after vein entry. More particularly, after vein entry, blood will fill lumen  248  of inlet cannula  236 , thereby reducing the volume to be occupied by gas in remaining portions of needle assembly  210  and hence increasing the pressure of air in the remaining portion of needle assembly  210 . A needle assembly with dimensions approximately as shown in  FIG. 1  will have a pressure P 2  of about 790 mm Hg at venous pressure (with tourniquet). V 1  in the preceding equation defines, the volume of the total dead spaced in needle assembly  210  before use, and hence will equal A+B as shown in  FIG. 5 . V 2  defines the dead space in the device after vein entry, and with lumen  248  of inlet cannula  236  filled with blood. Hence, V 2  in the preceding equation will equal B. These input parameters can be employed to define a minimum desired size for the respective components of needle assembly  200  as shown in the following application of the ideal gas law equation.
 
P 1 V 1 =P 2 V 2  
 
 P   1   /P   2   =V   2   /V   1  
 
760/790= B /( A+B )
 
0.962= B /( A+B )
 
0.962( A+B )= B  
 
0.038B=0.962A
 
B=25.3A
 
Therefore, dead space in housing  212 , outlet cannula  252  and sleeve  261  advantageously is at least 25.3 times the volume defined by lumen  248  through inlet cannula  236 , and most advantageously is about 26 times the volume of lumen  248 . However, other configurations are possible and will function as described herein.
 
     The immediate response when an evacuated tube is placed in communication with outlet cannula  252  is to draw blood from the vein into tube (not shown). The highest-pressure gradient is always maintained between the vein and the evacuated tube. An axially aligned inlet cannula  236  and outlet cannula  252 , therefore provide an unobstructed path for blood flow from the vein into evacuated tube. 
     When the requisite tubes are filled with blood, the needle assembly is removed from the vein. The sealed nature of the vent plug  900  inhibits the pressurized air within housing interior  220  from then moving into the flashback chamber  226  and into the Inlet cannula  236 , which could promote dripping of blood from the IV cannula tip. 
     The preceding embodiments show structurally separate inlet and outlet cannulas that are axially aligned with one other and placed in close end-to-end relationship with one another. However, the principals of the invention described above also can be achieved with a single cannula formed with a transverse slot or aperture within the flashback chamber. For example,  FIG. 7  schematically shows a needle assembly  310  with a housing  312  that is substantially identical to housing  212  described and illustrated above. Needle assembly  310  differs from needle assembly  210  in that a single double end needle cannula  336  is provided and passes entirely through housing  312 . More particularly, needle cannula  336  includes a venous entry end  338 , a non-patient end  340  and a lumen  342  extending therebetween. Portions of cannula  336  within inner wall  324  include a slot or aperture  344  to provide communication between lumen  342  and flashback chamber  336  within inner wall  324 . Needle assembly  310  functions substantially in the same manner as needle assembly  210  described and illustrated above. 
     The relative dimensional calculations, volumes and pressures apply to both illustrated and unillustrated embodiments of the invention. Accordingly, the scope of the as defined by the appending claims is not limited to the specific illustrated embodiments. Various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention.