SYRINGE WITH COLLAPSIBLE PLUNGER TIP

Abstract: A blood collection syringe of the present invention minimizes contact of the blood during and after collection with extraneous gases. In a preferred embodiment of a syringe (20) of the present invention, a plunger tip (22) is mounted on a plunger (40) positioned in a syringe barrel (24). The plunger tip (22) includes a hollow sealing member (42) having leading (44) and trailing members (52) with a resilient wall (60) extending therebetween. An interior chamber is defined by the wall (60), the leading (44), and trailing members (52). Circumferential sealing rings extend from the leading and trailing member for sealing engagement with the syringe barrel. At least one slit (66) is formed in and extends through the leading member. When the plunger (40) is fully extended into the syringe barrel (24), the resilient wall (60) collapses so that the leading (44) and trailing members (52) of the plunger tip (22) become positioned near each other at the head of the syringe barrel and the volume of the interior chamber is minimized.

Description: SYRINGE WITH COLLAPSIBLE PLUNGER TIP Field of the Invention The present invention relates to blood collection syringes and to plunger tips for blood collection syringes. More particularly, the present invention relates to techniques for minimizing contact of blood collected in a blood collection syringe with extraneous gases. Background of the Invention When drawing blood samples from an arterial line to a blood collection syringe, there may well be air trapped in the line which was present before blood was allowed to flow through the line. In addition, when using stopcock arrangements with such lines, for example, when multiple samples are taken from an indwelling catheter, air can also be trapped in the stopcock. Air may also reside in the nose of the syringe itself, prior to collection of the blood in the syringe When the blood to be sampled is to be analyzed for blood gases, it is important to minimize contact of the blood with air in the line or in the syringe. Air contact with the blood, either before or after sampling, can result in an exchange of gases into and out of the blood. Such gas exchange may well result in subsequent blood gas analyses which are inaccurate and misleading. Conventional practice is to first collect the blood and then evacuate air from the blood collection reservoir. For example, one conventional technique in which extraneous gases collected with blood in a blood collection syringe are vented after sample collection is the utilization of a vented tip cap. When using such devices, after the blood sample is collected in the syringe, the syringe tip is pointed upwardly, the plunger is depressed further into the syringe barrel, and extraneous gases are expelled out the tip until the blood in the tip contacts the vented tip cap. Although this technique prevents extended contact of the blood collected in the syringe with the extraneous gases previously residing in the syringe, some contact and gas exchange will be expected to have occurred during blood collection and prior to expulsion of the gases out the vented tip cap. Thus, the content of the various blood gases in the blood sampled may have already been altered by contact with the air during blood collection and prior to venting. Another technique used to remove extraneous gases from biood collected in a blood collection syringe is the removal of gases during sample collection through passageways in the plunger tip into an interior chamber of the plunger tip and then out past the plunger rod through the rear port in the syringe barrel. Typically, a reactive material is placed in the passageways that seals upon contact with blood or other physiological fluid. With such configurations, the syringe plunger is set in a retracted position prior to sample collection, and blood and gases fill the syringe under arterial pressure. Gases flow along the passageways and into the interior of the plunger tip until blood contacts the reactive material in the passageway. At that point, a barrier is formed in which neither gases nor blood flows beyond the plunger tip. However, the foregoing technique is limited by the possibility that premature contact of the reactive material with blood may cause the passageways to occlude before all extraneous gases are removed from the barrel of the syringe. This can occur, for example, when the syringe is held in an improper orientation. In addition, gas exchange may well take place at the beginning of sampling, when both blood and air are passing into the barrel of the syringe. Furthermore, some gas exchange may well take place in the passageways, adjacent the reactive material, after blood collection is complete. For these reasons, the technique does not prevent all contact of the blood sample with extraneous gases. Another limitation to syringe configurations where initial blood flow is trapped inside a reactive membrane is that anticoagulant present in the syringe reacts with the first blood introduced into the syringe. This same blood then flows into passageways, interior chambers, and/or reactive membranes, where it is effectively separated from the blood subsequently collected in the syringe. The blood which is subsequently collected in the syringe may not come into contact with anticoagulant. The net result is that waste blood initially collected is fully anticoagulated, and blood subsequently collected is insufficiently anticoagulated. In attempting to develop techniques for removal of extraneous gases from blood collection syringes like those described above, plunger tip designs are often modified to accommodate specially shaped air permeable membranes, hydrophobic materials and membranes, liquid reactive materials, and the like. In other cases, the plunger tips are not integrally formed, but rather are a combination of two or more pieces. Such designs require additional assembly, which adds to the both the labor and materials costs of blood collection syringes. It is against this background that the significant improvements and advancements of the present invention have taken place in the field of blood collection. Summary of the Invention It is an object of the present invention to prevent contact of a fluid to be collected in a syringe with extraneous gases after blood collection. It is a further object of the present invention to remove air trapped in blood collection lines before allowing blood to flow through the blood collection lines and thereby prevent contact of the blood with extraneous gases before biood collection is begun. It is a yet further object of the present invention to prevent contact of blood with extraneous gases with a blood collection syringe in which a preferred orientation need not be maintained. It is a still further object of the present invention to achieve the foregoing objectives while providing for a syringe plunger tip which is of unitary construction and economical assembly. In accordance with the foregoing objects, a fluid collection technique of the present invention minimizes contact of the fluid during and after collection with extraneous gases. In a preferred embodiment of a syringe which utilizes the fluid collection technique of the present invention, a plunger tip is mounted on a plunger positioned in a syringe barrel. The plunger tip includes a hollow sealing member having leading and trailing members with a resilient wall extending therebetween. An interior chamber is defined by the wall and the leading and trailing members. Circumferential sealing rings extend from the leading and trailing member for sealing engagement with the syringe barrel. At least one slit is formed in and extends through the leading member. To prepare the preferred syringe and plunger of the present invention for fluid collection, the plunger is first fully extended to the head of the syringe barrel until the resilient wall of the plunger tip collapses and the leading and trailing members of the plunger tip are adjacent to each other. Upon collapse of the resilient wall of the plunger tip, the volume of the interior chamber becomes minimized. Then, as the plunger is released, the resilient wall of the plunger tip returns to its extended position parallel with the barrel wall of the syringe, the trailing member slides rearwardly away from the leading member, the volume of the interior chamber increases, and the air in the leading portion of the collection chamber and adjacent the syringe tip passes through the slit into the interior chamber, evacuating the leading portion of the collection chamber and the area adjacent the syringe tip. Fluid subsequently collected in the syringe does not contact gases previously residing in the leading portion of the collection chamber and the area adjacent the syringe tip. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of a fluid collection syringe of the present invention, including a preferred plunger tip, wherein contact of the fluid to be collected with extraneous gases is prevented. FIG. 2 is an exploded view of the syringe shown in FIG. 1. FIG. 3 is an isometric view of the plunger tip component of the syringe shown in FIG. 1. FIG. 4 is a vertical section view of the plunger tip shown in FIGS. 2 and 3, taken substantially along the line 4-4 of FIG. 3. FIG. 5 is a vertical section view of the syringe shown in FIGS. 1 and 2, showing the plunger tip fully inserted to the leading wall of the syringe barrel, with the walls of the plunger tip compressed, the volume of the interior chamber of the plunger tip minimized, and air previously residing in the interior chamber expelled out the syringe tip. FIG. 6 is a vertical section view of the syringe shown in FIG. 5 after the syringe has been connected to a tube containing fluid to be collected in the syringe, the plunger tip has been released and gases in the tip of the syringe and leading fluid in the tube has collected in the interior chamber of the plunger tip. FIG. 7 is a vertical section view of the syringe shown in FIG. 6 after the plunger assembly of the syringe has been drawn rearwardly and fluid has been collected in the syringe barrel. FIG. 8 is an isometric view of an alternative embodiment of a plunger tip of the present invention. FIG. 9 is an isometric view of an alternative embodiment of a syringe of the present invention containing the alternative embodiment of the plunger tip shown in FIG. 8, along with an alternative plunger rod containing a plurality of longitudinal ribs. DETAILED DESCRIPTION A presently preferred embodiment of a syringe 20 and a plunger tip 22 of the present invention adapted for collecting blood for subsequent chemical analysis is illustrated in FIGS. 1 -7. Referring now to FIGS. 1 -2, it can be seen that syringe 20 includes a tubular barrel 24 defining an elongated and generally cylindrical blood collection chamber 26 having a diameter D1. Barrel 24 of syringe 20 tapers at its forward end to form a leading barrel wall 28. Extending centrally and outwardly from leading barrel wall 28 is a hollow syringe tip 30 which terminates in a delivery port 32. A leading portion 34 of collection chamber 26 is that portion of the collection chamber 26 adjacent leading wall 28. A tip portion 35 of collection chamber 26 is that portion of collection chamber 26 circumscribed by hollow syringe tip 30. Extending inwardly from barrel 24 into collection chamber 26 are a pair of spaced apart, ridge-like barrel stops 36 spaced apart a distance of arc length A1 . Barrel 24 terminates at its back end at a rear port 37 from which outwardly extend transverse and opposing barrel flanges 38. Rear port 37 is sized to receive an elongated syringe plunger 40 to which plunger tip 22 is mounted, as is described in further detail below. It should be understood that although syringe 20 and its components are described herein with reference to leading, rear, forward, backward, and the like, such modifiers are for convenience in describing the orientation of such components relative to each other. In actual use when plunger tip 22 is assembled on plunger 40 and plunger 40 is inserted in syringe 20, syringe 20 can be operated in most any orientation. Referring now to FIGS. 3 and 4, it can be seen that plunger tip 22 essentially comprises a hollow sealing member 42. Sealing member 42 includes a leading member 44 having an exterior surface 46, an interior surface 48, and a circumferential outer edge 49. An annular leading sealing ring 50 having a diameter D2 is formed in leading member 44, with leading sealing ring 50 preferably coextensive with outer edge 49. Sealing member 42 also includes a trailing member 52 having an outer surface 54 and an inner surface 56. An annular trailing sealing ring 58 having a diameter D3 is formed in trailing member 52. A thin, flexible and resilient plunger tip wall 60 of thickness T1 extends from leading member 44 to trailing member 52, defining therebetween an interior chamber 62 of the sealing member 42. Plunger tip 22 is preferably made from a thermoplastic elastomer such as Kraton ™ or other resilient material. Leading member 44 of plunger tip 22 is preferably conical, conforming generally with leading wall 28 of syringe barrel 24. A plurality of slits 66 are also formed in leading member 44, with slits 66 extending from exterior surface 46 to interior surface 48. Preferably, slits 66 each radially extend from adjacent depression 64 towards circumferential outer edge 49 of leading member 44. Trailing member 52 of plunger tip 22 is preferably disk-shaped and includes an aperture 70 extending from inner surface 56 to outer surface 54. Aperture 70 is defined by a collar 72 and has an aperture diameter D4. An inner rim 74 of collar 72 has a thickness T2 and surrounds aperture 70. Plunger 40 (FIG. 2) includes an elongated substantially cylindrical plunger rod 76. A pair of opposed, spaced apart, ridge-like plunger stops 78, each having an arc length A2 are formed on plunger rod 76. A plunger handle 80 having an elongated face 82 extends transversely from a rear portion of plunger rod 76. Formed in a forward portion of plunger rod 76 is a forward plunger member 83 which comprises a disk 84 having a forward face 86 from which a plunger neck 88 longitudinally and forwardly extends. Plunger neck 88 has a neck diameter D5 and a neck height H 1 . Plunger neck 88 terminates in a plunger boss 90. Referring now to FIG. 2, it can be seen that to assemble syringe 20 prior to use, plunger boss 90 of forward plunger member 83 is inserted in aperture 70 of plunger tip 22. After insertion, as is shown in FIG. 1 , the plunger boss 90 rests in sealing engagement on inner collar rim 74 of trailing member 52, with forward face 86 of plunger 40 in contact with outer surface 54 of trailing member 52. A seal is created between the forward portion of plunger 40 because neck height H1 is slightly smaller than thickness T2 of inner rim 74. Plunger 40, with plunger tip 22 is then inserted through rear port 37 into blood collection chamber 26 of syringe 20. In the preferred embodiment, leading sealing ring diameter D2 and trailing sealing ring diameter D3 are equal and slightly larger than diameter D1 of collection chamber 26, so that both leading and trailing sealing rings form an effective seal with the barrel wall 24 of the syringe 20. It is also preferred that neck diameter D5 of plunger neck 88 be slightly larger than aperture diameter D4 of plunger tip aperture 70 and that neck height H 1 is slightly smaller than thickness T2 of inner rim 74 of collar 72 of trailing member 52, so that an effective seal is formed between the interior chamber 62 of plunger tip 22 and the forward face 86 of plunger 40. In the preferred embodiment, arc length A1 which is the distance between adjacent barrel stops 36 is slightly larger than arc length A2 which is the arc length of plunger stops 78. As will be further appreciated below, the smaller width of arc length A2 are sized to pass between the distance A1 between adjacent barrel stops 36 when the plunger 40 is rotated in the collection chamber 26 of syringe 20. As will be further appreciated when the operation of syringe 20 is described below in connection with FIGS. 5-7, it is preferred that the when the walls 60 of plunger tip 22 are fully extended (i.e., not collapsed) the volume of interior chamber 62 is equal to or slightly greater than the total volume of the "dead space" at the head of syringe 20. This "dead space" is the total of the expected volume of tip portion 35 of collection chamber 26, plus leading portion 34 (if any) of collection chamber 26, plus any other "dead space" in the line to which syringe tip 30 is attached. An alternative embodiment of a plunger tip 22' is shown in FIG. 8. Plunger tip 22' includes a plurality of slits 66' formed in leading member 44'. Each slit 66' is concentric with a portion of circumferential outer edge 49' of leading member 44'. Plunger tip 22' also differs from plunger tip 22 in that it is substantially frustoconical, and includes a depression 100 centrally formed in leading member 44' which receives lyophyilized anticoagulant 101. Despite this variation, the use and benefits of the present invention, described further below, relate to plunger tip 22' as well as other embodiments of the present invention. An alternative embodiment of a syringe 20' which includes a plunger tip 22' is shown in FIG. 9. Syringe 20' includes plunger 40' having a plurality of longitudinal ribs 92. In the preferred form of this alternative embodiment, four longitudinal ribs 92 are present, in cross section forming an "X" with adjacent ribs forming a 90 ° angle. A pair of opposing, web-like, wedge-shaped plunger stops 94, each having an arc length A2 are formed on ribs 92, with each plunger stop 94 extending between a pair of adjacent ribs 92. A plunger handle 80' having a elongated face 82' extends transversely from a rear portion of plunger rod 76'. The construction of the disk 84' to which a plunger tip 22' is attached is the same as that of plunger 40, with the use and benefits of the present invention, described further below, relate to plunger 40' as well as other embodiments of the present invention. Use of the syringe 20 in performance of the technique of the present invention is now described with reference to a conventional technique for collection of blood with a blood collection syringe from an indwelling arterial catheter. It should be understood, however, that the technique of the present invention, applies also to collection of a single sample with a syringe to which a needle is attached and to other systems in which a syringe is attached to a fluid sampling line. For purposes of illustration, and as shown in FIGS. 6 and 7, a syringe 20 is attached by a luer lock 95 to a third line 96 of a three-way stopcock 97. Tubing (not shown) from an arterial line (not shown) feeds into a first line 98 of three-way stopcock 97. A second line 99 of the three-way stopcock feeds into a waste collection syringe (not shown) attached by a luer lock (not shown) to second line 99. Stopcock 97 provides selective fluid communication from the arterial line into either second line 99 and thence into the waste collection syringe, or into the third line 96 and thence into syringe 20. Prior to connection of syringe 20 to third line 96 of three-way stopcock 97, with elongated plunger handles 80 aligned with flanges 38 of syringe 20, plunger 40 is fully depressed into syringe barrel 24, until (a) exterior surface 46 of leading member 44 contacts leading wall 28 of barrel 24, (b) resilient wall 60 of plunger tip 22 collapses, and (c) plunger 40 snaps into a locked position after plunger stops 94 ride over barrel stops 36. At that point, inner surface 56 of trailing member 52 is adjacent, preferably touching interior surface 48 of leading member 44, and the volume of interior chamber 62 of plunger tip 22 is minimized, i.e. , reduced from a maximum when wall 60 is not collapsed to a minimum when upon collapsing of wall 60. Air previously present in interior chamber 62 is expelled by this action out slits 66 and out delivery port 32 of syringe tip 30. In this locked position, syringe 20 is attached to third line 96, by engagement of luer lock 95 with third line 96, as is shown in FIG. 5. Blood is then allowed to flow from the arterial line through first line 98 of stopcock 97 into the waste collection syringe, thereby forcing air from the first and second lines 98 and 99 into the waste collection syringe. Air remains, however, in third line 96. Stopcock 97 is opened to direct flow of blood from the first line 98 into third line 96. Next, as is shown in FIG. 6, plunger 40 is turned a quarter turn (90 ° ) thereby unlocking/disengaging plunger stops 78 from barrel stops 36. The resiliency of resilient wall 60 of plunger tip 22 causes plunger 40 to travel backwards along barrel wall 24 until plunger tip 22 is in a fully extended position. As the volume of interior chamber 62 increases by this operation until the volume of interior chamber 62 is at its maximum with wall 60 in its uncollapsed, fully extended position, air and extraneous gases present in third line 96, in tip portion 35 of syringe collection chamber 26, and in the leading portion of the collection chamber 26, if any, is drawn by the air pressure differential into interior chamber 62 through slits 66. A small portion of blood may also flow through slits 66 into interior chamber 62, until the differential in pressure from interior chamber 62 to first line 98 is minimal. Thereafter, slits 66 close, preventing air and blood in interior chamber 62 from flowing out slits 66 into collection chamber 26. Referring now to FIG. 7, it can be seen that as plunger 40 is further retracted, blood collected in collection chamber 26 is substantially free of extraneous gases. Post collection venting of the syringe is not required. As can now be appreciated, utilization of the above technique prevents contact of blood or other fluid collected as described above with extraneous gases. Indeed, such extraneous gases are removed before the blood or other fluid is introduced into a collecting syringe. In this way, subsequent gas analysis of the blood or other fluid can be expected to be reliable. In addition, because extraneous gases are maintained in an interior chamber of a plunger tip which does not contact the barrel wall of the syringe, there is minimal risk of gas exchanges along the barrel wall during and after collection. Moreover, the benefits just described are achieved with a syringe and plunger tip construction which is economical to manufacture and assemble. The preferred plunger tip is of a unitary construction without need for special membranes, materials or inserts. As can now also be appreciated, the syringe of the present invention can be operated in most any orientation. For example, the syringe tip need not be maintained in an upwardly pointing orientation in order to maintain any extraneous gases at the syringe tip for later manual expulsion. Also by way of example, the syringe tip need not be maintained in a downwardly or laterally pointing orientation during fluid collection to prevent premature contact of fluids with the plunger tip during fluid collection, thereby prematurely occluding the plunger tip and preventing gases from flowing therethrough. Presently preferred embodiments of the present invention and many of its improvements have been described with a degree of particularity. It should be understood, however, that the present invention is defined by the spirit and scope of the following claims.

Claims: What is claimed is: 1. A syringe adapted for collecting blood samples, comprising: an elongated barrel having a barrel wall and a leading wall and defining a blood collection chamber, a barrel tip of said barrel terminating in a delivery port and defining a tip portion of said collection chamber; an elongated plunger rod slidably mounted in said barrel, said plunger having a plunger handle at one end and a forward member at an opposing end positioned in said barrel; a hollow sealing member comprising a leading member having an interior surface and having exterior surface conforming substantially to said leading wall of said barrel, a trailing member mounted to said forward plunger end, and a resilient wall defining an interior chamber of said hollow sealing member; and at least one slit formed in said leading member providing selective communication between said tip portion of said collection chamber and said interior chamber, wherein said plunger tip has a first operational position in which said wall is fully extended, said leading and trailing members are positioned a maximum distance from each other, and said interior chamber has a maximum volume, and a second operational position in which said wall is at least partially collapsed, said leading and trailing members are a distance which is less than said maximum distance, and said interior chamber has a volume which is less than said maximum volume. 2. A syringe in accordance with claim 1 wherein said resilient wall of said plunger tip is cylindrical. 3. A syringe in accordance with claim 1 wherein said resilient wall extends from said leading member to said trailing member. 4. A syringe in accordance with claim 3 wherein said leading and trailing members contact each other in said second operational position. 5. A syringe in accordance with claim 1 wherein said leading and trailing members contact each other in said second operational position. 6. A syringe in accordance with claim 1 wherein a plurality of slits are formed in said leading member. 7. A syringe in accordance with claim 6 wherein said slits are formed in said leading member in a radial pattern. 8. A syringe in accordance with claim 6 wherein said first member has an outer circumference and said slits are each concentric with a portion of said outer circumference. 9. A syringe in accordance with claim 1 wherein said leading member has a depression formed in its exterior surface for receiving an anticoagulant. 10. A plunger tip adapted for use with a blood collection syringe, said syringe having a barrel wall terminating in a syringe tip and defining a collection chamber having a tip portion thereof adjacent said syringe tip, said plunger tip comprising: a hollow sealing member which includes a leading member having an exterior surface and an interior surface, a trailing member, a resilient plunger tip wall extending from said leading member to said trailing member, an interior chamber of said hollow sealing member defined by said plunger tip wall, said leading member and said trailing member, and at least one slit formed in said leading member and extending from said exterior surface to said interior surface of said leading member to provide selective communication between said tip portion of said collection chamber and said interior chamber of said plunger tip, wherein said plunger tip has a first operational position in which said plunger tip wall is fully extended, said leading and trailing members are positioned a maximum distance from each other, and said interior chamber has a maximum volume, and a second operational position in which said plunger tip wall is at least partially collapsed, said leading and trailing members are a distance which is less than said maximum distance, and said interior chamber has a volume which is less than said maximum volume. 1 1. A plunger tip in accordance with claim 10 wherein said plunger tip wali is cylindrical. 12. A plunger tip in accordance with claim 1 1 wherein said leading and trailing members contact each other in said second operational position. 13. A plunger tip in accordance with claim 10 wherein said leading and trailing members contact each other in said second operational position. 14. A plunger tip in accordance with claim 10 wherein a plurality of slits are formed in said leading member to form a radial pattern. 15. A plunger tip in accordance with claim 10 wherein said leading member has an outer circumference and a plurality of slits are formed concentric with a portion of said outer circumference. 16. A plunger tip in accordance with claim 10 wherein said leading member has a depression formed in its exterior surface for receiving an anticoagulant. 17. A plunger tip in accordance with claim 10 wherein said leading member also includes a circumferential first sealing ring for sealing engagement with said barrel wall and said trailing member also includes a circumferential second sealing ring for sealing engagement with said barrel wall. 18. A method of minimizing contact of blood to be collected in a blood collection syringe having a syringe barrel having a leading wall and defining a collection chamber, a syringe tip extending from said leading wall and defining a tip portion of said collection chamber, a hollow plunger tip having an interior chamber circumscribed by a collapsible plunger tip wail and mounted to a plunger rod inserted in said barrel, said method including the steps of: depressing said plunger rod in said barrel until said plunger tip is adjacent said leading wall of said syringe barrel; collapsing said plunger tip wall; minimizing a volume of said interior chamber; locking said plunger rod in place, with said interior chamber volume minimized and said plunger tip wall collapsed; maintaining said plunger rod in said locked position; releasing said plunger rod; collecting air present in said tip portion of said collection chamber in said interior chamber of said plunger tip; and maintaining said air in said interior chamber of said plunger tip while blood is collected in said collection chamber.

Inventors: GEIST LEROY D, KAMINSKI ROGER P, GEIST, LEROY, D., KAMINSKI, ROGER, P.
Applicants: GEIST LEROY D, KAMINSKI ROGER P, VITAL SIGNS INC, GEIST, LEROY, D., KAMINSKI, ROGER, P., VITAL SIGNS, INC.
Application year: 1997
Main classification: A61M5
IPC codes: A61B5, A61M5