Abstract:
A method for withdrawing a fluid sample from a patient is disclosed comprising the steps of: a) providing a sampling device ( 10 ) having a housing ( 20 ) and a needle ( 40 ) having a sharpened tip for piercing the skin of the patient; b) withdrawing fluid from the patient into the housing; c) retracting the needle so that the sharpened tip of the needle is enclosed within the housing; and d) expelling the fluid from the housing after the needle is retracted.

Description:
This application is a continuation of International Patent Application No. PCT/US99/02566, filed May 2, 1999, which claims priority to U.S. Provisional Application No. 60/073,749, filed Feb. 5, 1998, which are hereby incorporated herein by reference. 

   FIELD OF INVENTION 
   The present device relates to the field of medical devices for fluid sampling. More specifically, the present invention relates to such medical devices having a retractable needle, so that the device is rendered safe after use. In particular, the present invention relates to a device for drawing blood from a patient, wherein after use the needle retracts so that the contaminated needle is enclosed thereby preventing inadvertent contact with the contaminated needle. 
   BACKGROUND 
   The present invention relates to a type of medical device that is used to take a sample of arterial blood. An arterial blood collection is done commonly in emergency room settings, as well as hospitals to test for various conditions, such as blood oxygen levels and pH. The standard devices currently used are coated with heparin to prevent blood clotting and the fit between the plunger piston and the barrel is loose enough to allow the arterial blood pressure to move the piston as the device fills with arterial blood. These requirements complicate the reaction of the needle. 
   SUMMARY OF THE INVENTION 
   In light of the foregoing, the present invention provides an apparatus and method for collecting fluid samples from a patient. The device comprises a housing, a plunger slidably displaceable within the housing and a needle having a sharpened tip for piercing a patient. The needle is operable to pierce the skin of a patient. Fluid from the patient collects in a fluid chamber within the housing. After the sample is collected, the needle is retracted into the housing so that the sharpened tip is enclosed. After the needle is retracted a pair of seals prevent the sample from leaking from the fluid chamber. In addition, the seals preferably operate to prevent air from entering the fluid chamber after the needle is retracted. The fluid can then be expelled from the fluid chamber by displacing the plunger within the housing. 

   
     DESCRIPTION OF THE DRAWINGS 
     The foregoing summary as well as the following detailed description of the preferred embodiment can be best understood when read in connection with the following drawings in which: 
       FIG. 1  is a top view of a fluid sampling medical device having a retractable needle; 
       FIG. 2  is a side view of the fluid sampling medical device shown in  FIG. 1 ; 
       FIG. 3   a  is a side view of the device shown in  FIG. 1 , illustrating the device prior to use; 
       FIG. 3   b  is a side view of the device shown in  FIG. 3   a , illustrating the device after a quantity of fluid has been withdrawn; 
       FIG. 3   c  is a side view of the device shown in  FIG. 3   a , illustrating the device with the needle in a retracted position; 
       FIG. 3   d  is a side view of the device shown in  FIG. 3   a , illustrating the device after the fluid sample has been expelled; 
       FIG. 4  is a side view of a second embodiment of a fluid sampling medical device having a retractable needle; 
       FIG. 5   a  is a side view of the device shown in  FIG. 4 , illustrating the device prior to use; 
       FIG. 5   b  is a side view of the device shown in  FIG. 5   a , illustrating the device after a quantity of fluid has been withdrawn; 
       FIG. 5   c  is a side view of the device shown in  FIG. 5   a , illustrating the device with the needle in a retracted position; 
       FIG. 5   d  is a side view of the device shown in  FIG. 5   a , illustrating the device after the fluid sample has been expelled; 
       FIG. 6  is a side view of third embodiment of a fluid sampling medical device having a retractable needle; 
       FIG. 7   a  is a side view of the device shown in  FIG. 6 , illustrating the device prior to use; 
       FIG. 7   b  is a side view of the device shown in  FIG. 7   a , illustrating the device after a quantity of fluid has been withdrawn; 
       FIG. 7   c  is a side view of the device shown in  FIG. 7   a , illustrating the device with the piston separated from the plunger; 
       FIG. 7   d  is a side view of the device shown in  FIG. 7   a , illustrating the device with the needle in a retracted position; 
       FIG. 8  is a side view a fourth embodiment of a fluid sampling medical device having a retractable needle; 
       FIG. 9  is an enlarged fragmentary sectional view of the device shown in  FIG. 8 ; 
       FIG. 10  is a cross-sectional view of the device shown in  FIG. 9 , taken along the line  10 — 10 ; 
       FIG. 11  is a side view of the device shown in  FIG. 8 , illustrating the device with the needle in a retracted position; 
       FIG. 12   a  is an exploded side view of a combination syringe and removable needle assembly; 
       FIG. 12   b  is a side view of the device shown in  FIG. 12   a , illustrating the needle assembly attached to the syringe; 
       FIG. 12   c  is a side view of the device shown in  FIG. 12   a , illustrating the needle in a retracted position; 
       FIG. 13   a  is a side view of a second embodiment of removable needle assembly; and 
       FIG. 13   b  is a side view of the needle assembly shown in  FIG. 13   a , illustrating the needle in a retracted position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings and to  FIGS. 1–3   d  specifically, a fluid sampling device is designated generally  10 . The device  10  comprises a barrel  20  and a needle  40  projecting forwardly from the forward end of the barrel. A plunger  30  is slidably displaceable within the barrel  20 . Fluid is sampled through the needle. For instance, the device may be used to withdraw a quantity of fluid from a patient. The needle  40  pierces the skin of a patient, and blood from the patient flows into the barrel  20 . After a sufficient amount of blood has been withdrawn, the needle  40  is retracted into the barrel  20  so that the needle is enclosed, preventing inadvertent contact with the contaminated sharpened point of the needle. 
   Referring now to  FIGS. 1 and 2 , the barrel  20  is an elongated generally cylindrical hollow housing. The forward end of the barrel  20  forms a reduced diameter nose piece  22 . The nose piece  22  is generally closed, having an aperture for receiving the needle  40 . 
   The plunger  30  has a hollow forward stem  31 . An elastomeric piston  32  is attached to the forward end of the plunger stem  31 . The piston  32  forms a fluid-tight seal with the interior wall of the barrel  20 . The stem is integrally formed with the rearward portion of the plunger, which is an elongated hollow cylindrical portion, which forms a needle chamber  34  for receiving the needle after the needle is retracted. The rearward end of the needle chamber is closed to prevent the needle from being displaced rearwardly of the needle chamber. An actuator  36  is formed at the forward end of the needle chamber  34 . The actuator is generally wedge-shpaed and is formed to matingly cooperate with a needle retainer  50  that releasably retains the needle. 
   The needle  40  includes a side port  42  formed in the side wall of the needle. In addition, the rearward end of the needle is plugged. The needle is disposed so that the side port  42  is located forward of the piston. A variable volume is formed in the barrel between the piston  32  and the forward end of the barrel  20 . Accordingly, fluid flowing through the needle is discharged through the side port  42  into the fluid chamber between the piston  32  and the nose  22 . 
   The needle  40  is operable between a projecting position in which the sharpened tip of the needle projects forwardly from the nose  22  of the barrel  20 , and a retracted position in which the needle is enclosed within the barrel. A spring  60  circumscribes the needle  40 , biasing the needle rearwardly toward the retracted position. The needle retainer  50  releasably retains the needle  40  in the projecting position against the bias of the spring  60 . When the actuator  36  engages the needle retainer  50 , the needle retainer releases the needle  40 , allowing the spring to propel the needle rearwardly into the needle chamber  34 . 
   The needle retainer  50  is rigidly connected to the barrel  20  so that the needle retainer is fixed axially relative to the barrel. The interior wall of the barrel  20  includes a recess that forms a seat  25  for receiving the needle retainer  50 . As shown in  FIG. 1 , the needle retainer  50  comprises a pair of connecting tabs  58  that form a snap fit or friction fit with the seat  25  in the wall of the barrel. The connecting tabs  58  project through a pair of slots  38  in the side walls of the plunger  30 . The slots allow the plunger to be displaced axially relative to the needle retainer. 
   The needle retainer  50  includes at least one finger or latch  52  for releasably retaining the needle. In the present instance, the fingers  52  are bonded to the needle by UV curable epoxy. Alternatively, a block can be attached to the needle and the finger can abut the block to retain the needle against rearward axial displacement. 
   The forward end of the fingers form a tapered actuation surface  56  that cooperates with the tapered actuator  36  on the plunger. When the plunger is displaced rearwardly, the actuator  36  engages the tapered actuation surface  56  of the needle retainer, wedging the fingers apart. In this way, the fingers are displaced radially outwardly out of engagement with the needle. The spring then propels the needle rearwardly into the needle chamber  34 . 
   The needle retainer  50  further includes a spring housing  54  projecting forwardly from the fingers  52 . The forward end of the spring housing  54  form a bearing surface against which the forward end of the spring  60  bears. The rearward end of the spring is bonded to the needle. Alternatively, if a block is attached to the needle, the rearward end of the spring may bear against the block. 
   As shown in  FIGS. 1 and 2 , in the projecting position, the forward end of the needle projects from the forward end of the barrel  20 . The needle also projects through the piston  32  and into the needle retainer  50 . The piston  32  includes a pierceable septum that forms a fluid-tight seal with the exterior surface of the needle to prevent fluid from leaking from the barrel into the plunger  30 . In addition, in the projecting position, the needle pierces a nose seal  24  disposed within the nose  22  of the barrel. The nose seal forms a fluid-tight seal with the exterior surface of the needle to prevent fluid from leaking from the barrel through the nose  22 . 
   The device can be designed to operate in two different manners. In the first manner, the plunger is withdrawn to form a fluid chamber of a particular volume. The needle is then inserted into a patient and blood flows through the needle and into the barrel, filling the fluid chamber. When designed to be used in this manner, a hydrophobic vent is included to prevent the device from becoming airlocked, which would impede the flow of blood into the fluid chamber. The vent is air permeable, but is not permeable to blood The vent allows air from the fluid chamber to be discharged from the fluid chamber as the blood enters the fluid chamber, but prevents blood from leaking from the fluid chamber. 
   Alternatively, the device  10  can be configured to operate so that the blood pressure displaces the plunger rearwardly as blood enters the fluid chamber. During such use, the plunger is displaced forwardly so that the piston is disposed at the forward end of the barrel, engaging the forward wall of the barrel. The needle is then inserted into the patient and blood flows into the barrel, displacing the piston  32  rearwardly as blood enters the barrel. When designed to be used in such a manner, the device does not need a vent for venting air from the fluid chamber. In addition, the piston or the barrel wall is lubricated to reduce the friction between the piston and the barrel to facilitate displacing the plunger. 
   Referring now to  FIGS. 3   a – 3   d , the device operates as follows. In  FIG. 3   a , the device is shown prior to use. The needle  40  is inserted into a patient&#39;s blood vessel, and blood flows into the fluid chamber in the barrel as shown in  FIG. 3   b . Referring to  FIG. 3   c , the plunger is then displaced axially rearwardly so that the actuator  36  engages the needle retainer  50  displacing the fingers  52  radially outwardly to release the needle. The spring  60  then propels the needle rearwardly into the needle chamber so that the needle is enclosed with in the barrel. After the needle retracts, the septum of the piston that was pierced by the needle reseals to prevent blood from leaking into the plunger. In addition, the nose seal  24  reseals to prevent blood from leaking through the nose  22 . In this way, the sample is sealed within the fluid chamber against contact with the air. Referring now to  FIG. 3   d , after the needle is retracted, the sample can discharged from the syringe so that the sample can be tested. The sample is discharged by displacing the plunger forwardly. Displacing the piston forwardly creates sufficient fluid pressure to expel the fluid through the hole in the nose seal membrane that was formed by the needle. 
   Referring now to  FIGS. 4–5   d , a second embodiment  110  of a fluid sampling device is shown. The device  110  includes a barrel  120  and a retractable needle  140  projecting forwardly from the barrel. A plunger  130  is slidably displaceable within the barrel. After a fluid sample is collected in the device, the needle is retracted into the barrel so that the needle is enclosed to prevent inadvertent contact with the contaminated needle. After the needle is retracted, the fluid is sealed within a fluid chamber in the barrel. The fluid sample can then be discharged so that the sample can be tested. 
   The plunger  130  includes a tapered hollow stem  132 . An elastomeric piston  132  is removably attached to the forward end of the stem. The piston forms a fluid-tight seal with the interior of the barrel. Preferably, a hydrophobic plug  136  extends through the piston, providing a vent for gases in the fluid chamber between the piston and the forward end of the barrel. An inwardly projecting annular flange or stop ring  125  limits the rearward axial displacement of the piston. After the piston engages the ring stop  125 , continued rearward displacement of the plunger detaches the piston from the plunger. 
   The plunger stem projects forwardly from the rearward portion of the plunger, which is an elongated generally cylindrical hollow portion, forming a needle chamber  134 . The stem  132  is also hollow, forming a forward chamber  137  for receiving the rearward end of the needle when the needle  140  is disposed in the retracted position. The forward end of the forward chamber is smaller in diameter than a block  146  attached to the rearward end of the needle. In this way, upon rearward displacement of the plunger, the interior wall of the forward chamber  137  engages the block  146  on the needle urging the needle rearward. This in turn displaces the needle out of engagement with a needle retainer  150  so that continued rearward displacement of the plunger retracts the needle rearwardly. 
   The forward end of the barrel  120  forms a reduced diameter nose  122 . The needle projects forwardly from the nose  122  in the projecting position. In this position, the needle passes through an opening in the forward end of the piston. The forward opening in the piston is smaller in diameter than the needle, so that the piston forms a fluid-tight seal around the exterior of the needle. 
   A needle retainer  150  releasably retains the needle in the projecting position. In the present instance, the needle retainer comprises a pair of receptacles  152  that cooperate with and engage a spherical detent  144  fixed to the needle. 
   The device  120  operates as follows. Referring to  FIG. 5   a , the device  110  is shown prior to use. The plunger  130  is displaced rearwardly to provide a fluid chamber for receiving the fluid sample. The needle is then inserted into the artery of the patient. Blood flows through the needle into the fluid chamber through a side port in the needle to collect the sample, as shown in  FIG. 5   b . Referring to  FIG. 5   c , after the sample is collected, the plunger is displaced rearwardly to detach the piston from the plunger. The plunger is further displaced rearwardly to retract the needle into the barrel. Referring to  FIG. 5   d , the sample can then be expelled by driving the plunger forward to re-engage the piston and then drive the piston forwardly. 
   Referring now to  FIGS. 6–7   d , a third embodiment of a fluid sampling medical device  210  is illustrated. The device includes a barrel  220  and a retractable needle  240  projecting from the forward end of the barrel. A plunger  230  is slidably displaceable within the barrel. After a fluid sample is collected from the patient, the needle retracts into the barrel to enclose the contaminated needle. 
   The barrel is generally cylindrical and hollow. The plunger  230  includes an elastomeric piston  234  that forms a fluid-tight seal with the interior wall of the barrel. The plunger  230  is hollow, having a forward chamber  239  housing the spring before the needle is retracted, and a rearward needle chamber  237  for receiving the needle after the needle is retracted. 
   A spring  260  circumscribing the needle biases the needle rearwardly towards the retracted position. The spring is disposed about the needle  240  between a fixed spring block  228  and a needle block  244  connected to the rearward end of the needle. The spring block  228  is fixedly attached to the barrel  220 . Accordingly, slots  233  are formed in the side of the plunger  230  to provide clearance for the spring block  228  when the plunger is displaced within the barrel. 
   A needle retainer  250  releasably retains the needle in the projecting position against the bias of the spring  260 . In the present instance, the needle retainer is epoxy that bonds the needle to the nose  222 . 
   Referring to  FIGS. 7   a – 7   d , the device operates as follows. In  FIG. 7   a , the device is illustrated prior to use. The plunger  230  is withdrawn to provide a fluid chamber between the piston  234  and a resealable seal  224  that is disposed in the nose of the barrel and provides a fluid-tight seal with the exterior of the needle  240 . Referring to  FIG. 7   b , the needle  240  is inserted into a patient&#39;s artery, and blood flows through a side port  242  in the needle  240  and into the fluid chamber. Once the sample is collected the needle is withdrawn from the patient. Referring to  FIG. 7   c , the plunger  230  is then displaced rearwardly. The rearward displacement brings the piston  234  into engagement with an annular flange projecting inwardly from the interior wall of the barrel. Continued rearward displacement of the plunger detaches the piston  234  from the stem  232  of the plunger. In addition, the rearward displacement brings an annular flange  238  into engagement with the needle block  244 . Referring to  FIG. 7   d , further rearward displacement of the plunger breaks the bond between the nose  222  and the needle, releasing the needle from the needle retainer  250 . The spring then propels the needle rearwardly into the needle chamber. The nose seal  224  reseals to prevent the sample from leaking through the nose  222  of the barrel. In addition, the forward end of the piston  234  reseals to prevent the sample from leaking into the plunger. In this way, the nose seal  224  and the piston  234  seal the sample within the fluid chamber to prevent the sample from contacting the air. After the needle is retracted, the sample can be expelled from the barrel into equipment for testing the sample by driving the plunger forwardly. 
   Referring now to  FIGS. 8–11 , a fourth embodiment of a fluid sampling device  310  is shown. The device includes a barrel  320 , a retractable needle  340  and a plunger  330  slidably displaceable within the barrel. This third embodiment allows the operator to actuate retraction of the needle regardless of the axial position of the plunger. 
   The barrel  320  is generally cylindrical. The forward end of the barrel is generally closed, forming a reduced diameter opening. A female Luer-type fitting  322  projects from the forward end of the barrel  320 . An elastomeric seal threadedly engages the Luer fitting  322 . The seal  324  includes a pierceable membrane through which the needle  340  projects. The membrane forms a fluid-tight seal with the exterior of the needle  340 . 
   The plunger  330  includes a piston  332  that forms a fluid-tight seal with the interior wall of the barrel. In addition, the piston  332  includes a pierceable membrane through which the needle projects. The piston membrane forms a fluid-tight seal with the exterior of the needle. In addition, the piston includes a hydrophobic plug  336  that allows gas to vent from the fluid chamber between the piston and the nose seal  324 . Referring to  FIGS. 10 and 11 , the plunger  330  is a generally U-shaped channel, having a needle chamber  334  for receiving the retracted needle  340 . A longitudinal, axially elongated rib  335  projects upwardly into the needle chamber  334 . 
   Referring now to  FIGS. 8–10 , a manually operable needle retainer  350  releasably retains the needle in the projecting position against the bias of the spring  360  biasing the needle rearwardly toward the retracted position. The needle retainer  350  comprises an actuating lever  354  and a latch that engages a block  344  attached to the needle. As shown in  FIG. 9 , the latch  354  engages the needle block  344  to releasably retain the needle. By operating the actuator lever  352 , the latch  357  pivots radially outwardly out of engagement with the needle block  344 . The spring  360  then propels the needle rearwardly toward the retracted position. 
   The latch  357  is biased into engagement with the needle block  344 . In the present instance, a spring finger  359  biases the latch into engagement with the needle block. The spring finger  359  is integral with the latch and projects rearwardly from the latch. The spring finger  359  resiliently flexes and engages the interior wall of the barrel  320 . When the actuating lever  354  is operated, the latch displaces radially outwardly, thereby resiliently deforming the spring finger  359 . 
   Referring to  FIG. 10 , the needle retainer  350  is attached to the barrel  320  by mounting brackets  352 . The mounting brackets  352  engage a slot  326  formed in the top of the barrel. The mounting brackets  352  fix the needle retainer relative to the plunger  330 . A transverse spring block  351  is connected to the needle retainer assembly. The spring block forms a forward bearing surface for the spring  360 . The actuating lever  354  is attached to the spring block  351  by a flexible web or living hinge  355 . The web  355  forms a pivot point for the actuating lever  354 . 
   The device operates as follows. The plunger  330  is withdrawn to provide a fluid chamber for receiving a blood sample from a patient. The needle  340  is inserted into a patient&#39;s artery. Blood flow through a side port  342  in the needle and into the fluid chamber. Once a sufficient amount of blood is withdrawn, the needle is withdrawn from the patient. The actuating lever is depressed to pivot the latch  357  thereby releasing the needle from the needle retainer  350 . The spring  360  then propels the needle rearwardly into the needle chamber. After the needle is retracted, the nose seal  324  reseals to prevent from blood from leaking from the fluid chamber. The fluid sample can then be expelled from the device into separate device to test the sample. The sample is expelled by driving the plunger forwardly within the barrel. 
   Referring now to  FIGS. 12   a – 12   c , a device for collecting a fluid sample such as blood is designated generally  410 . The device  410  comprises a syringe  420  and a removably connectable needle assembly  430 . The needle assembly  430  comprises a retractable insertion needle  460  for piercing a patient&#39;s skin. When the needle assembly  430  is connected to the syringe  420 , the insertion needle  460  is in fluid communication with the interior of the syringe. After the fluid sample is collected in the syringe  420 , the insertion needle  460  can be retracted into the housing of the needle assembly  430  to prevent inadvertent contact with the contaminated insertion needle. The needle assembly  430  can also be removed from the syringe  420  after the fluid sample is collected. The fluid sample can then be transferred to where the sample is to be tested. The sample can then be expelled from the syringe  420  and tested. 
   The syringe  420  is similar to a typical syringe, having a barrel  422 , a plunger  424  with a piston  425  slidably displaceable within the barrel and a Luer-type fitting  428  on the nose of the barrel. The piston  425  forms a fluid-tight seal with the interior wall of the barrel  422 , and driving the plunger forward expels fluid from the syringe  420 . 
   The needle assembly  430  is adapted to connect to the Luer fitting  428  of the syringe so that the needle assembly can be utilized with standard syringes that are already in widespread use throughout the medical field. Accordingly, the housing  440  of the needle assembly  430  includes an opening at the rearward end, forming a socket  442  for engaging the Luer fitting  428  of the syringe. A seal  445  having a pierceable resealable membrane is disposed within the socket  442 . The seal  445  is externally threaded having threads that cooperate with the Luer fitting  428 . 
   The needle assembly  430  comprises two needles a forward insertion needle  460  that projects forwardly from the front end of the housing  440 , and a fixed needle  450  disposed within the housing  440 . The fixed needle  450  projects into the socket  442 , piercing the Luer seal  445 . The fixed needle  450  is attached to a fixed needle tube  452  that is fixedly attached to the housing  440 . The rearward end of the fixed needle tube is generally closed, having a reduced diameter through which the fixed needle  450  projects. The fixed needle is fixedly connected to the fixed needle tube  452  to form a fluid-tight connection between the exterior surface of the fixed needle and the generally closed rearward end of the fixed needle tube. 
   The insertion needle  460  is fixedly connected to a telescoping needle tube  462  that telescopingly engages the interior of the fixed needle tube  452 . A needle seal  456  disposed within the forward end of the fixed needle tube  452  provides a fluid-tight seal between the fixed needle tube and the telescoping needle tube. The insertion needle projects forwardly from the forward end of the telescoping needle tube  462 . An annular flange  464  projects outwardly from the telescoping needle tube  462 . A spring  480  circumscribing the telescoping needle tube  462  is disposed between the flange  464  and the interior of the forward end of the housing. The spring  480  bears against the flange  464  biasing the telescoping needle tube  462  and the attached insertion needle  460  rearwardly. 
   A needle retainer  470  releasably retains the insertion needle  460  against the bias of the spring  480 . The needle retainer  470  comprises an actuator button  472  and a latch  474 . The latch  474  has an aperture through which the telescoping needle tube  462  projects. In the latched position, the latch  474  is disposed so that the rim of the aperture engages the flange  464  to retain the telescoping needle tube against the bias of the spring. Depressing the actuator button  472  displaces the latch  474  downwardly so that the latch aperture is aligned with the annular flange  464 . The spring  480  then propels the telescoping needle tube rearwardly into the fixed needle tube, so that the insertion needle is enclosed within the housing  440 . 
   Accordingly, the device  410  operates as follows. The plunger  424  is disposed so that the piston  425  is located at the forward end of the syringe barrel  422 . The needle assembly  430  is connected to the front end of the syringe  420 . The rear fixed needle  450  projects through the Luer seal  445  and into the barrel. The insertion needle  460  is then inserted into a patient&#39;s artery and blood flows from the patient into the interior of the syringe. The pressure of the blood flow drives the piston and plunger  424  rearwardly as the blood enters the syringe  420 . After a sufficient amount of blood is collected, the insertion needle is withdrawn from the patient. The actuator button  472  is depressed to actuate retraction of the insertion needle. The insertion needle then retracts into the housing. The needle assembly  430  is then detached from the syringe  420 . The Luer seal  445  remains on the Luer-fitting  428  of the syringe, sealing the forward end of the syringe to prevent fluid from leaking out of the nose of the syringe  420 . The piston  425  forms a fluid-tight seal with the barrel to prevent fluid from leaking out of the rearward end of the syringe. The sealed fluid sample can then be transported to an area for testing the sample and then expelled from the syringe by driving the plunger forwardly within the barrel. 
   Referring now to  FIGS. 13   a  and  13   b  a second embodiment of a needle assembly that is operable in connection with a syringe is designated generally  510 . The needle assembly includes a housing  520  and a retractable needle  540  projecting forwardly from the housing. The rearward end of the housing forms a socket  522  for connecting the needle assembly to a syringe similar to the manner described above in connection with the device designated  410  and illustrated in  FIGS. 12   a – 12   c . However, in the present instance, the socket  522  is configured as a female tapered Luer-type fitting to cooperate with a male Luer-type fitting on a syringe. 
   The needle assembly  510  includes a generally cylindrical nose piece  530  attached to the forward end of the housing  520 . A nose seal  532  forms a fluid-tight seal with the exterior of the needle  540 . A generally cylindrical needle tube  545  is disposed within the housing  520  and projects into the rearward end of the nose piece  545 . The forward end wall of the socket  522  has a reduced diameter opening so that the needle tube  545  is in fluid communication with the socket. An annular detent  542  projects inwardly into the needle tube adjacent the forward end of the needle tube  545 . An elastomeric valve  550  seals the forward end of the needle tube  545 . The valve  550  has an external circumferential groove  552 . The annular detent  542  engages the circumferential groove to releasably retain the valve  550 . 
   The rearward end of the needle  540  projects into the valve  550 . The forward end of the needle  540  projects forwardly from the nose piece. A spring  560  attached to the needle biases the spring rearwardly to a retracted position within the housing  520 . A needle retainer  570  releasably retains the needle in the projecting position against the bias of the spring. 
   The needle retainer  570  is configured similarly to the needle retainer described above in connection with the previous device  410 . The retainer  570  comprises a button actuator  572  and a latch  574 . The latch has an aperture. In the latched position, the rim of the latch aperture engages the end of the spring  560 . When the actuator button  572  is depressed, the latch is displaced downwardly, aligning the latch aperture with the spring, thereby allowing the spring to propel the needle rearwardly as shown in  FIG. 13   b.    
   Accordingly, the device operates as follows. The needle assembly  510  is attached to a syringe. The needle is then inserted into a patient&#39;s artery. Blood flows through the needle  540 , and through the valve  550  into the needle tube  545 . From the needle tube the blood flows into the syringe, where the sample collects. After a sufficient amount of blood is removed, the needle  540  is removed from the patient. The actuator button  572  is depressed to release the needle  540 . The spring  560  propels the needle rearwardly. The needle is driven further within the valve, sealing the rearward end of the needle. In addition, the spring biases the valve against the opening into the socket to seal the socket opening. The needle assembly thereby operates as a seal, sealing the forward end of the syringe. The needle assembly can be detached if desired. The syringe can then be sealed with a cap and transported to an area where the sample is to be tested. The sample can then be expelled from the syringe by driving the plunger forward. 
   While particular embodiments of the invention have been illustrated and described above, it is not intended to limit the invention to such disclosure. It will be recognized that changes and modifications may be made within the scope of the following claims.