Plunger rod for arterial blood collection syringes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to arterial blood collection syringes. More particularly, the present invention relates to a one-piece plunger rod for efficient use of an arterial blood collection syringe.

2. Description of Related Art

Arterial blood collection syringes are used for withdrawing and collecting arterial blood samples from the body of a patient. Once the blood sample is collected, it is subjected to diagnostic analysis for gases, electrolytes, metabolites, and other elements that are indicative of a condition of a patient. Various types of syringes have been devised for collecting arterial blood samples, which mainly comprise elements from a hypodermic syringe, i.e., a plastic or glass syringe barrel, a sealing elastomeric stopper, and a plunger rod. Additionally, certain arterial blood collection syringes include a self-sealing filter that allows passage of air out of the syringe during blood collection, while still preventing the passage of blood. This latter type of syringe having a filter allows for an anaerobic arterial sample to be collected without the need to aspirate the syringe, as is required with a syringe having a plunger rod and a plunger stopper.

Typical arterial blood collection syringes include a two-piece plunger rod assembly comprised of an elastomeric sealing stopper attached to a plunger rod. The sealing stopper and plunger rod must be assembled together in a separate operation prior to assembly with a syringe barrel. In addition, a silicone lubricant is usually used on the interior wall of the syringe barrel to facilitate easy slidable movement of the elastomeric sealing stopper against the interior wall of the syringe barrel. Such syringes typically involve an active step for obtaining a blood sample. For example, a needle connected to such a syringe accesses a patient's blood vessel, and the syringe is thereafter aspirated by drawing the plunger rearwardly within the syringe barrel so as to draw a blood sample into the syringe barrel for analysis. United States Patent No. 5,314,416 to Lewis et al. discloses a low friction syringe assembly having a typical two-piece plunger rod and a plunger tip assembly.

Arterial blood samples can also be obtained passively through the use of a syringe having a plunger with a porous filter to collect blood by way of the blood pressure of a patient from whom the blood is being collected. In such a syringe, the plunger mechanism is typically hollow, and includes a porous filter therein. A separate elastomeric sealing stopper is typically attached to the front end of the plunger mechanism for sealing within the syringe barrel, with air channels in the stopper for air passage through the filter. In use, the plunger is set at a certain position against a graduated scale of the syringe barrel, so that the desired volume of the sample to be collected is represented by the cavity within the syringe. Once a blood vessel of a patient is accessed by an appropriate needle attached to the syringe, arterial blood will fill the syringe under its own pressure. As the cavity within the syringe fills, air within the syringe is allowed to escape from the syringe by way of a gas permeable filter. When the blood sample contacts the filter, the filter seals, thereby preventing escape of blood and ingress of air and other contaminants into the collected sample. United States Patent No. 4,821,738 to Iwasaki et al. discloses an arterial blood gas syringe including a typical two-piece assembly for use. The arterial blood gas syringe is comprised of a plunger rod and an elastomeric sealing plug having channels formed in an upper surface for use in removing air as arterial blood is received in the syringe. The channels extend in a generally radial direction and converge near the center of a sealing plug to allow the passage of air to and through a filter element contained within the sealing plug. United States Patent Nos. 5,377,689 and 5,529,738, both to Mercereau, disclose a sampling syringe including a plunger cap having an air permeable filter attached to a plunger rod, which is in slidable communication with the inner wall of a syringe barrel.

The separate rubber sealing stopper on the plunger in such assemblies provides an effective seal to contain the blood sample within the syringe. However, while such syringe assemblies are useful, the separate rubber sealing stopper typically requires a silicone lubricant for sliding movement within the syringe barrel, and further requires costly manufacturing and assembly steps. Accordingly, there is a present need for an arterial blood collection syringe which is inexpensive to manufacture and easy to assemble, and which is simple to operate.

SUMMARY OF THE INVENTION

Generally, the present invention is directed to an arterial blood collection syringe including a one-piece plunger rod assembly having an integrally molded sealing mechanism, all comprised of a single material, which is easy to manufacture and is simple to operate, with or without a silicone lubricant. The invention is an improvement over the prior art as it reduces the manufacturing costs of assembly because the plunger rod can be molded as a single part, from a common material, thereby eliminating the cost of manufacturing a separate rubber sealing stopper. The invention is a further improvement over the prior art because it eliminates the need for assembling the sealing stopper with a plunger rod in a separate assembly step. The invention is an even further improvement over the prior art because it eliminates the need for use of a silicone lubricant on the interior wall of the syringe barrel, which is traditionally used to lubricate the sealing stopper and allow smooth movement of the plunger through the syringe. Silicone oils, when used as a plunger lubricant, may enter the blood analyzer during testing of a sample within a syringe and cause contamination of the surface of the sensitive electrodes within the analyzer. The combination of a lubricating additive with the plunger rod raw material during the injection molding process may eliminate the need for silicone oils as lubricants within the syringe barrel.

The plunger rod of the present invention includes an elongated, hollow cylindrical rod comprising a rigid tubular wall defining an internal lumen and extending between an open rear end and a non-elastomeric, rigid closed front end. The front end is desirably a tapered front end having a conical profile. The plunger rod includes a plurality of vents extending through the rigid tubular wall adjacent the front end of the rod and in fluid communication with the internal lumen. Desirably, the plurality of vents extend through the rigid tubular wall at an intersection of the closed front end with the rigid tubular wall, thereby forming the vents about the perimeter of the front end. Alternatively, the plurality of vents can be equally radially spaced about the circumference of the rigid tubular wall, and extend through the rigid tubular wall at a location axially spaced from the closed front end of the rod.

The plunger rod assembly further includes a porous filter member maintained within the internal lumen at the front end of the plunger rod and adjacent the plurality of vents. The porous filter member is desirably adapted to filter fluid passing between the plurality of vents and the internal lumen of the rod. The porous filter member desirably contacts an interior surface of the closed front end within the internal lumen such that the plurality of vents are adjacent the porous filter member at a location spaced from a front surface of the porous filter member. The porous filter member is desirably constructed of a matrix which is pervious to air, and which is capable of becoming impervious to air and blood after being contacted with a blood sample.

The plunger rod may further include at least one sealing ring extending circumferentially about an external surface thereof. Preferably, the sealing ring is integrally formed with the plunger rod or, alternatively, is comprised of an elastomeric o-ring affixed to an external surface of the rod.

In a further embodiment, the invention is directed to a syringe assembly which includes such a plunger rod in combination with a syringe barrel. The syringe barrel includes a barrel having an internal chamber extending between an open rear end and a closed front end having an opening extending therethrough. At the front end, the syringe barrel includes structure for connecting the syringe assembly with a medical device, such as a needle assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plunger rod within a syringe barrel in accordance with the present invention;

FIG. 2A is a longitudinal cross-section of the plunger rod within a syringe barrel as shown in FIG. 1;

FIG. 2B is an enlarged view of the cross-section of the front end of the plunger rod showing the filter therein as shown in Fig. 2A;

FIG. 3 is a perspective view of the plunger rod;

FIG. 4 is a partial sectional view of the plunger rod as shown in FIG. 3;

FIG. 5 is an enlarged, partial sectional view of the front end of the plunger rod as shown in FIG. 4;

FIG. 6 is a longitudinal section of the plunger rod assembly as shown in FIG. 4;

FIG. 7 is an enlarged, perspective view of the front end of a further embodiment of a plunger rod having vents radially positioned in the tubular side wall of the plunger rod;

FIG. 8 is an enlarged, sectional view of the front end of the plunger rod as shown in FIG. 7; and

FIG. 9 is an enlarged, perspective view of a further embodiment of a plunger rod having an o-ring.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in which like reference characters refer to like parts throughout the several views thereof, FIG. 1 illustrates an arterial blood collection syringe assembly <b>10</b> comprised of a plunger rod <b>58</b> in slidable communication with a syringe barrel <b>12</b> having a standard luer fitting <b>34</b> at the closed front end <b>22</b> for connection to an arterial access device, such as a needle assembly <b>38</b>. The present invention is generally described in terms of an arterial blood collection syringe assembly <b>10</b>. While described herein in terms of a preferred embodiment of an arterial blood collection syringe assembly <b>10</b> intended for use with a needle assembly <b>38</b>, the syringe assembly <b>10</b> of the present invention may be used with or may incorporate other medical devices, such as another medical device assembly that includes a piercing element or allows for attachment to a catheter.

As shown in FIG. 1, the two primary components of the arterial blood-collection syringe assembly <b>10</b> include a plunger rod <b>58</b> in slidable communication with a syringe barrel <b>12</b>. Syringe barrel <b>12</b> may be constructed of any suitable material such as glass or plastic, and is of a suitable size for collection of blood or other fluid samples.

A particular embodiment of syringe barrel <b>12</b> is shown in detail in FIGS. 1 and 2A and includes an elongated, hollow, cylindrically-shaped tube having an open rear end <b>20</b> and a generally closed front end <b>22</b>. The cylindrically-shaped tube of syringe barrel <b>12</b> comprises a rigid tubular wall <b>24</b> that defines an internal space extending between open rear end <b>20</b> and front end <b>22</b>. The rigid tubular wall <b>24</b> of syringe barrel <b>12</b> defines an internal surface <b>28</b> for slidably receiving the plunger rod <b>58</b>. A flange <b>32</b> is provided at the open rear end <b>20</b> of syringe barrel <b>12</b> for manipulation of the arterial blood collection syringe assembly <b>10</b>.

Front end <b>22</b> of syringe barrel <b>12</b> is generally closed-ended with an opening <b>32</b> extending therethrough. Front end <b>22</b> includes a fitting for attachment with an appropriate arterial access device such as a needle. For example, a standard luer fitting including a male luer taper <b>34</b> and an internally threaded luer lock <b>36</b> may be provided at front end <b>22</b> of syringe barrel <b>12</b>, for removeably receiving a corresponding fitting of an arterial access device. More particularly, an arterial access device such as a needle assembly <b>38</b> as shown in FIG. 1 may include a rearward end <b>40</b> and a forward end <b>42</b>. The forward end defines a needle cannula <b>44</b> beveled at the forward end <b>42</b> to define a sharp puncture tip <b>46</b> for intravenous puncture into the blood vessel of a patient, such as an artery. Puncture tip <b>46</b> is designed to provide ease in insertion and minimal discomfort for the patient during arterial access. The rearward end <b>40</b> of the needle assembly <b>38</b> includes a hub fitting <b>48</b>, which includes an internal female luer taper <b>50</b> and a pair of opposing flanges <b>52</b>. In this manner, needle assembly <b>38</b> can be releasably attached to the front end <b>22</b> of syringe barrel <b>12</b> by the corresponding interfitting engagement between male luer taper <b>34</b> and female luer taper <b>50</b>, as well as through the locking engagement between luer flanges <b>52</b> and luer lock <b>36</b>, as is well known in the art. As such, fluid communication can be established between the interior lumen of needle cannula <b>44</b> and the internal space <b>26</b> of collection assembly <b>10</b>.

The arterial blood collection assembly <b>10</b> of the present invention further includes plunger rod <b>58</b> slidably received within the internal space <b>26</b> defined by tubular wall <b>24</b> of syringe barrel <b>12</b>. The particular features of plunger rod 58 are shown in detail throughout FIGS. 4-6. Plunger rod <b>58</b> generally includes an elongated, hollow, cylindrically-shaped rod as shown in the sectional view of FIG. 4. The plunger rod <b>58</b> comprises a rigid tubular wall <b>64</b> extending between a closed front end <b>68</b> and an open rear end <b>69</b> establishing therein an interior lumen <b>72</b> as shown in FIG. 4. The plunger rod <b>58</b> has a circular cross-section with an external diameter that is slightly smaller than the internal diameter <b>28</b> of the syringe barrel <b>12</b>. In a preferred embodiment, the closed front end <b>68</b> of plunger rod <b>58</b> includes a conical profile <b>90</b>. Plunger rod 58 is desirably constructed of a suitable polymeric material, and may be manufactured by injection molding with a suitable polymer material known in the art. The plunger rod <b>58</b> may further include a flange <b>74</b> extending about the perimeter of the open rear end <b>69</b> of the plunger rod <b>58</b>, which provides a means or mechanism to manipulate and axially displace the plunger rod <b>58</b> relative to the syringe barrel <b>12.</b>

The plunger rod <b>58</b> further includes at least one vent, and preferably a plurality of vents <b>62</b> extending through the rigid tubular wall <b>64</b> of the plunger rod <b>58</b> at a location adjacent front end <b>68</b> thereof. Vents <b>62</b> are desirably spaced equally and radially about a circumference or perimeter of the front end <b>68</b> of the plunger rod <b>58</b> as illustrated generally in FIGS. 3-5. In a preferred embodiment, the plurality of vents <b>62</b> are positioned about the closed front end <b>68</b> of the plunger rod <b>58</b> at the intersection between the conical-profiled, closed front end <b>90</b> and the rigid tubular wall <b>64</b> of the plunger rod <b>58</b>. The plurality of vents <b>62</b> extend through the rigid tubular wall <b>64</b> of the plunger rod <b>58</b>, thereby providing fluid communication into the interior lumen <b>72</b> created by the rigid tubular wall <b>64</b> of the plunger rod <b>58</b>.

In an alternate embodiment as shown in FIGS. 7 and 8, the plurality of vents <b>62a</b> are equally-positioned circumferentially in the rigid tubular wall <b>64a</b> of the plunger rod <b>58a</b> at a location spaced from the front end. In this embodiment, the plunger rod <b>58a</b> is also shown as including a flat profiled front end <b>92a</b>, with the plurality of vents <b>62a</b> positioned in the rigid tubular wall <b>64a</b> of the plunger rod <b>58a</b>. Such positioning of the vents spaced from the first end is possible in the plunger rod due to the sealing mechanism between the plunger and the syringe barrel being located a position spaced from the front end of the plunger rod, as compared with typical prior art assemblies. It is contemplated that in any embodiments of the invention, the front end of the plunger rod can include such a flat profiled front end, or a conical profiled front end as described in connection with FIGS. 3-5.

A porous filter member <b>66</b> is housed within the interior lumen <b>72</b> of the plunger rod <b>58</b> as illustrated by FIGS. 4-6. The porous filter member <b>66</b> is located within the interior lumen <b>72</b> at a position toward the front end <b>68</b> thereof, and is desirably positioned fully within the interior lumen <b>72</b> and contacting the inner surface of the front end <b>68</b> within interior lumen <b>72</b>. The porous filter member <b>66</b> is positioned so as to be in fluid communication with the plurality of vents <b>62</b>. The porous filter member <b>66</b> permits air and other gases to flow from within internal space <b>26</b> of syringe barrel <b>12</b> through the vents <b>62</b> and through the interior lumen <b>72</b> out to the external environment, as will be described in more detail herein. Desirably, the porous filter member <b>66</b> is positioned within the interior lumen <b>72</b> of the plunger rod <b>58</b> by insertion of the porous filter member <b>66</b> through the open rear end <b>69</b> of the plunger rod <b>58</b> and sliding the porous filter member <b>66</b> up to the closed front end <b>68</b> of the interior lumen <b>72</b>, so that an interference fit is formed between the two components.

The porous filter member <b>66</b> is constructed of a material which is permeable to gases, such as air, but is desirably impermeable to liquids, such as blood. Porous filter member <b>66</b> may be a one-way vent, in which air flows only in one direction, or more desirably may be a two-way vent, in which air is able to flow in both directions. While the porous filter member <b>66</b> permits air and gas to flow therethrough, it acts as a barrier for liquid flow in either direction. Also, once a liquid specimen such as blood contacts and/or saturates the porous filter member <b>66</b>, the vent will seal to any further gas flow therethrough. As such, no air will be able to flow in or out of the vent, even once the liquid specimen has been removed.

Porous filter member <b>66</b> may be made out of any suitable material which is permeable to gases (in particular air) and impermeable to liquids (in particular blood). For example, the porous filter member <b>66</b> may be manufactured from a sintered polymer matrix with a self-sealing additive. Alternatively, any other type of porous filter member suitable for self-sealing in connection with exposure to blood or other fluid that is known in the art may also be used as the porous filter member. These types of self-sealing filters are commonly used in arterial blood collection syringes and in many other applications. Non-limiting examples of useful materials include carboxymethyl cellulose, high density polyethylene, high density polypropylene, and the like.

The plunger rod <b>58</b> further includes at least one, and more desirably two sealing rings <b>80, 84</b> extending circumferentially about the external surface of rigid tubular wall <b>64</b>, as best depicted in FIGS. 3-5. Sealing rings <b>80</b>, <b>84</b> are positioned circumferentially near the closed front end <b>68</b> of the plunger rod <b>58</b> at a position between the plurality of vents <b>62</b> and the open rear end <b>69</b>. Sealing rings <b>80, 84</b> may be seperately attached to plunger rod <b>58</b>, or more desirably are integrally molded into the exterior surface of the rigid tubular wall <b>64</b> of the plunger rod <b>58</b>. The sealing rings <b>80, 84</b> are of a diameter approximately equal to or only slightly smaller than that internal diameter <b>28</b> of the syringe barrel <b>12</b> as shown in FIGS. 2A and 2B. The sealing rings <b>80, 84</b> of the plunger rod <b>58</b> slidably contact the internal surface <b>28</b> of the syringe barrel <b>12</b> and provide a fluid-tight seal between the plunger rod <b>58</b> and the internal surface <b>28</b> of the syringe barrel <b>12</b> so that a sample can be held within the cavity <b>82</b> formed within the internal space <b>26</b> between front end <b>22</b> of syringe barrel <b>12</b> and closed front end <b>68</b> of plunger rod <b>58</b>, thereby preventing the sample from leaking from the syringe assembly <b>10</b>. The first sealing ring <b>80</b> nearest to the closed front end <b>68</b> of the plunger rod <b>58</b> creates a primary seal between the cavity <b>82</b> formed between the plunger rod <b>58</b> and the syringe barrel <b>12</b>. The second sealing ring <b>84</b> provides a secondary seal and assists in the stabilization of the plunger rod <b>58</b>, thereby centralizing the plunger rod <b>58</b> during slidable movement of the plunger rod <b>58</b> relative to the syringe barrel <b>12</b>.

A lubricating additive may be incorporated into the plunger rod <b>58</b> during molding thereof to assist the slidable movement of the plunger rod <b>58</b> relative to the syringe barrel <b>12</b>. Such a lubricating additive eliminates the need for silicone lubricants within the syringe barrel <b>12</b>, thereby preventing sample contamination and entry of such silicone lubricants into instrumentation used for sample analysis.

In an alternative embodiment shown in FIG. 9, the plunger rod <b>58b</b> may include an o-ring seal <b>86b</b> positioned on the outer diameter of the closed front end <b>68b</b> of the plunger rod <b>58b</b>. Such an o-ring seal is desirably constructed of an elastomeric material, such as rubber or the like. The o-ring seal <b>86b</b> is of a diameter equal to or greater than the internal diameter of the syringe barrel, thereby providing the formation of a liquid-tight seal while relying on the resistance between the o-ring seal <b>86b</b> and the internal surface of the rigid tubular wall of the syringe barrel. The o-ring seal <b>86b</b> is in slidable communication with the internal surface of the syringe barrel.

Assembly of the arterial blood collection assembly <b>10</b> is accomplished by inserting the porous filter member <b>66</b> within the interior lumen <b>72</b> of the plunger rod <b>58</b> through the open rear end <b>69</b> of the plunger rod <b>58</b> and forcing the porous filter member <b>66</b> up to the closed front end <b>68</b> of the interior lumen <b>72</b>, so that an interference fit is formed between the two components. The plunger rod <b>58</b> having the porous filter member <b>66</b> fixed therein can then be slidably inserted into the interior space <b>26</b> of the syringe barrel <b>12</b> through open rear end <b>20</b>. The assembly can then be packaged for later use. When assembled as such, fluid communication is generally established throughout the length of the assembled arterial blood collection syringe assembly <b>10</b>. Specifically, fluid communication is provided through front opening <b>32</b> at the front end of syringe barrel <b>12</b> (and likewise through needle cannula <b>44</b> attached thereto), into the internal space <b>26</b>, and more particularly the cavity <b>82</b>, in the syringe barrel <b>12</b>, through the plurality of vents <b>62</b> and the porous filter member <b>66</b>, through the interior lumen <b>72</b> of the plunger rod <b>58</b> and out the opened rear end <b>69</b> of the plunger rod <b>58</b>.

In use, the syringe assembly <b>10</b> can be used to either passively or actively collect a blood sample from a patient. More particularly, the present invention can be used to collect blood passively by removing the syringe assembly from the packaging and drawing the plunger rod <b>58</b> rearwardly relative to the syringe barrel <b>12</b> so that a cavity <b>82</b> is formed within the syringe barrel <b>12</b> (as shown in FIGS. 1 and 2A) that equals the volume of the sample to be collected from a patient. A suitable arterial access device such as needle assembly <b>38</b> is connected by interfitting female luer taper <b>50</b> over male luer taper <b>34</b> and threading luer flanges <b>52</b> within the internal threads within luer lock <b>36</b> at the front end <b>22</b> of the syringe barrel <b>12</b>. The needle cannula <b>44</b> can then be positioned within a vessel of a patient for sample collection.

Upon entry of the needle cannula <b>44</b> into the patient's blood vessel, in particular an artery, collection of the blood sample into the cavity <b>82</b> within the syringe barrel <b>12</b> is immediately facilitated passively by the blood pressure of the patient. In particular, the air within the cavity <b>82</b> of the syringe barrel <b>12</b> is displaced through the plurality of vents <b>62</b> and the porous filter member <b>66</b> into the interior lumen <b>72</b> of the plunger rod <b>58</b> as the blood enters the cavity <b>82</b> of the syringe barrel <b>12</b>.

More particularly, the blood within the patient's artery is pumping at physiological pressure, which is greater than normal atmospheric or ambient pressure. Since the cavity <b>82</b> of collection assembly <b>10</b> is vented to the external environment through the plurality of vents <b>62</b>, the air pressure within cavity <b>82</b> is at ambient pressure. When the blood within the patient's artery is in fluid contact with the cavity <b>82</b>, the higher pressure of the patient's artery forces the blood into the lower ambient pressure cavity <b>82</b>. As such, the blood transfer occurs based on the patient's blood pressure.

During such transfer of blood into the cavity <b>82</b>, it is necessary to displace the air within the cavity <b>82</b> in order to prevent the pressure therein from building to a pressure which would be above the blood pressure and therefore prevent further blood flow into cavity <b>82</b>. Accordingly, during such blood flow, the air, and any other gases present within cavity <b>82</b>, must be displaced from within cavity <b>82</b>. This displacement occurs by venting such air from within cavity <b>82</b> through the plurality of vents <b>62</b>, through the porous filter member <b>66</b>, through the interior lumen <b>72</b> and out through closed rear end <b>69</b> of plunger rod <b>58</b>.

As the cavity <b>82</b> of the syringe barrel <b>12</b> is gradually filled by the blood sample being collected and the air within the cavity <b>82</b> is displaced, the blood sample will eventually contact the conically profiled front end <b>90</b> of the plunger rod <b>58</b> or, in an alternative embodiment, the flat profiled front end of the plunger rod. The plurality of vents <b>62</b> are designed in close proximity to the internal surface <b>28</b> of the syringe barrel <b>12</b> to ensure that all air is expelled from the cavity <b>82</b> before the porous filter member <b>66</b> becomes sealed. Accordingly, in any manner that the syringe assembly <b>10</b> is held, one of the plurality of vents <b>62</b> will always be positioned at a higher position within the syringe barrel <b>12</b>. This arrangement is further facilitated by positioning the sealing ring <b>80</b> spaced from the front end, such that vents <b>62</b> can be located directly adjacent the internal surface <b>28</b> of syringe barrel <b>12</b> when plunger rod <b>58</b> is assembled therewith, either adjacent the front end <b>90</b> or spaced from the front end <b>90</b> (such as vents <b>62a</b> in Fig. 1). Due to the inherently higher surface tension of the blood sample as compared to the air, any air that is trapped within the cavity <b>82</b> of the syringe barrel <b>12</b> will rise to the uppermost point of the cavity <b>82</b> and be displaced out of the cavity <b>82</b> before blood within the cavity <b>82</b> reaches and flows through the highest vent of the plurality of vents <b>62</b> and, ultimately, contacts the porous filter member <b>66</b>.

During sampling, the blood will rise within the cavity <b>82</b> until it is full, at which point the blood will contact all of the vents <b>62</b> and therefore the entire vented surface of the porous filter member <b>66.</b> Such contact will cause the porous filter member <b>66</b> to become gas impermeable, thereby preventing any further blood to enter cavity <b>82</b> since no further air can be displaced therefrom. Also, such feature serves to protect the blood sample within the cavity <b>12</b> when a two-way filter is used, since no further air will be able to enter into the cavity <b>12</b> through the now-sealed filter member <b>62.</b> Once the self-sealing porous filter member <b>66</b> is sealed, an aseptic sample is present in the cavity <b>82</b> of the syringe barrel <b>12</b> that can be used for analysis of the blood collected from the patient.

Alternatively, the present invention can be used actively to collect blood from a patient by aspiration like a traditional blood sampling hypodermic syringe. In such a procedure, the plunger rod <b>58</b> is be positioned in the forwardmost position relative to the syringe barrel <b>12</b>. The operator of the syringe assembly <b>10</b> must then place a thumb over the hole at the open rear end <b>69</b> of the plunger rod <b>58</b> to seal the opening to the passage of air. While maintaining a seal on the opened rear end <b>69</b> of the plunger rod <b>58</b>, the operator then draws the plunger rod <b>58</b> rearwardly relative to the syringe barrel <b>12</b> thereby creating a vacuum within the cavity <b>82</b> to aspirate a sample of blood from a patient. A cavity <b>82</b> is formed within the syringe barrel <b>12</b> as the plunger rod <b>58</b> is moved rearwardly and then held in a position that will create a cavity <b>82</b> within the syringe barrel <b>12</b> that equals the desired volume of the sample to be collected from a patient. As previously discussed, the blood sample will enter the cavity <b>82</b> of the syringe barrel <b>12</b> through the needle cannula <b>44</b>. As the blood contacts the porous filter member <b>66</b>, the self-activating seal will form, thereby sealing an aseptic blood sample in the cavity <b>82</b> for analysis.

The present invention provides an arterial blood gas syringe which is inexpensive to manufacture and easy to assemble. By constructing the plunger rod out of a one-piece assembly with the vents integrally formed therein, the need for a separate elastomeric plunger sealing tip is eliminated. As such, manufacturing and assembly are simplified. By providing sealing rings about the exterior surface of the plunger rod, and in particular integrally formed therewith, an effective seal can be maintained without the need for the elastomeric plunger sealing tip. By eliminating the elastomeric plunger sealing tip, cost savings are achieved, and the plunger mechanism can slide more freely within the syringe barrel, eliminating the need for separate silicone lubricants which can contaminate the sample contained therein.

While the present invention is satisfied by embodiments in many different forms, there is shown in the drawings and described herein in detail the preferred embodiments of the invention, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. Various other embodiments will be apparent to and readily made by those skilled in the art without departing from the scope and spirit of the invention. The scope of the invention will be measured by the appended claims and their equivalents.