Abstract:
A blood withdrawal apparatus and method in which a blunt cannula or needle penetrates an elastomeric septum into a pressurized flow channel such as an arterial line. After blood is withdrawn into the attached syringe, the needle tip is withdrawn into the septum until an indication is detected, for example by engagement of a detent on a shroud surrounding the cannula or needle with a detent on the housing for the septum. The nurse can then depressurize the syringe by operating the piston and thus prevent blood spurt when the needle tip is subsequently fully withdrawn from the septum.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to aspiration of blood samples through an elastomeric septum from pressurized flow channels such as arterial lines. 
     Such aspiration has become an important method of blood sampling. In this sampling technique, a needle or cannula is inserted into the flow channel through the elastomeric septum, and blood is withdrawn into a blood collection device such as a syringe attached to the needle or cannula. The needle tip is thus inserted into the flow channel through the elastomeric septum, and blood is drawn into the syringe through the bore of the needle. The needle is then removed from flow channel and septum and the sample is transported to the lab for analysis. 
     One major problem which exists with this technique is that the elevated pressure within the flow channel is transmitted through the bore of the needle into the syringe. Since syringes and needles commonly have a small amount of dead air space within them, a bubble of air will be displaced into and trapped within the syringe when blood is drawn into the syringe through the needle. The transmitted pressure from the flow channel into the syringe through the needle bore can compress the air bubble when the needle bore is in fluid communication with the flow channel. When the needle is removed from the pressurized flow channel and the needle tip exits the septum, the bore of the needle is exposed to atmospheric pressure which may be substantially lower than the pressure within the syringe which has now been pressurized. The pressurized air bubble within the syringe expands rapidly upon the reduction of pressure at the opening of the bore of the needle near the needle tip thereby forcing blood out of the needle through the exposed opening. This rapid expansion of the bubble within the syringe therefore causes blood to spurt from the needle tip. This spurt of potentially infectious blood may strike the nurse or spray onto the bedsheets resulting in substantial blood exposure to hospital personnel. 
     Pending U.S. patent application Ser. No. 07/302,835 filed Jan. 27, 1989, describes a novel aspiration system comprising an aspirator receiver and blunt aspirator for use with a pressurized flow channel such as an arterial line. This design substantially reduces the risk of needlestick injury but is still subject to the blood spurting problem as described above. The present invention is an improved blood aspiration system and technique which is designed to eliminate the blood spurting problem. 
     Blood cannot spurt if the pressure in the syringe is relieved while the needle tip is occluded by the septum. Therefore, detecting and indicating when the tip is so occluded is very useful. 
     The blood aspiration system of this invention provides an occlusion indicator as well as an aspirator receiver means in fluid communication with a flow channel. The flow channel is connectable to a catheter in fluid communication with a blood vessel having an elevated internal fluid pressure. The system further includes a blood aspirator having a proximal and a distal end and a bore extending from the proximal end to an distal opening near the distal end. The occlusion indicator indicates when the aspirator is positioned within the septum such that distal opening of the bore of the aspirator is occluded. 
     In the preferred embodiment the aspirator receiver includes a housing having a passage extending from a proximal opening to an interface with the flow channel. The passage is occluded with an elastomeric septum having a perforation for receiving a blood aspirator which is preferably a needle having a blunt distal tip. The blunt needle has a bore extending from a proximal hub to an opening near the distal tip of the needle. The hub is preferably connectable to and may be permanently attached to a conventional syringe having a piston and internal chamber. The needle further includes means defining a space extending distally about the needle. The space defining means is preferably a cylindrical shroud sized to be received over the housing of the aspirator receiver. The shroud is connected to the needle and preferably extends beyond the needle tip. 
     A needle occlusion indication means indicates the position of the needle within the septum wherein the tip of the needle is occluded, and is preferably provided on the housing, but may be provided along the outer surface of the needle. In the preferred embodiment, the occlusion indicator means comprises a detent on the outer surface of the housing of the aspirator receiver and a corresponding detent on the inner surface of the shroud. The detents are specifically positioned such that withdrawal of a needle which has been received over the aspirator receiver is inhibited at a position wherein the distal opening of the needle bore is fully within the elastomeric septum and is occluded by the septum. This, therefore, provides a tactile indication that the needle tip is located at a position wherein the opening near the tip is occluded. At this point the nurse can stop withdrawing the needle and hold the shroud and needle in position while retracting the syringe piston. This will effectively decompress any trapped air within the chamber of the syringe. The nurse can then apply additional force to withdraw the shrouded needle completely from the septum. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1-4 the blood aspiration system with aspirator occlusion indicator 10 is shown generally. Catheter 14 is shown with its tip 18 within a blood vessel 20 of a patient. Conduit 24 is connected to catheter 14 placing flow channel 26 (FIG. 2) of conduit 24 into fluid connection with blood vessel 20 (FIG. 1). The conduit 24 extends to an aspirator receiver 30 integral with conduit 24. Housing 34 of aspirator receiver 30 has passage 38 occluded by elongated elastomeric septum 40 extending from a flow channel interface 44 to an atmospheric interface 48. A central perforation 50 (FIG. 3) through septum 4 extends from the atmospheric interface 48 of the septum 4 to the flow channel interface 44. The outer surface 52 of housing 34 has annular housing detent 54. 
     The blunt needle aspirator 58 is shown connected to a conventional syringe 60. The syringe 60 includes syringe tip 62 shown inserted into dead space 63 and needle hub 68. A needle bore 69 extends from hub 68 to a distal bore opening 74 near needle tip 78. Piston 70 is mounted within syringe 60 defining syringe chamber 79 below piston 70. Needle 58 is integral with shroud 80 which extends beyond needle tip 78 to define a space 84. The inner surface 86 of shroud 80 has annular shroud detent 90. Shroud 80 is sized to be snugly received over housing 34. The housing detent 54 is positioned along the outer surface 52 of housing 34 such that the distal opening 74 of needle bore 69 is occluded by septum 40 when the detents 54 and 90 are engaged as in FIG. 3. 
     In the preferred embodiment, the housing detent 54 is shaped to provide an initial slow elevation 94, a summit 96, and a sharp descent 98. Shroud detent 90 is therefore easily pushed past housing detent 54 as the needle tip 78 is advanced through the perforation 50 of septum 40, as the needle 58 is advanced to the position of FIG. 2. wherein the opening 74 of the needle bore 69 is within the flow channel 26 when needle tip 78 is maximally advanced through septum 40. The distance from shroud detent 90 to housing detent 54 is greater than the distance from the septum flow channel interface 44 to the distal bore opening 74. However, during the withdrawal of the needle 58 from the septum 40, the withdrawal is inhibited when the shroud detent 90 engages the housing detent 54, as shown in FIG. 3. This provides a tactile indication that the distal bore opening 74 of the needle bore 69 is in a position such that the bore opening 74 is occluded by the septum 40, as shown in FIG. 3. At this point the syringe chamber 79 is completely sealed so that withdrawal of the piston 70 will not draw blood or air into the syringe 60 but will rather induce a negative pressure within the syringe chamber 79. 
     This negative pressure will be transmitted to the air bubble (not shown) which is commonly trapped within the syringe chamber 79. As will be described, this trapped bubble now will contain a partial vacuum rather than an elevated pressure. The bubble will therefore enlarge when the bore opening 74 exits the septum atmospheric interface 48 upon further withdrawal of the needle 58. This causes the syringe chamber 79 to actually suck residual blood from the atmospheric interface 48 of the septum 40 as the bubble contracts in response to the relief of the relative vacuum within the bubble by air entry through the bore opening 74. The relative ease with which the piston 70 moves within the syringe 60 will determine, in part, the extent to which the bubble will retain a negative pressure since this negative pressure will have a tendency to cause the piston 70 to advance toward the negative pressure to relieve it. In any case, the positive pressure which causes the spurt of blood will be eliminated by this novel design and technique and at least some negative pressure is likely to remain within the bubble. 
     The unique system is operated by inserting the blunt needle 58 attached to the syringe 60 through the perforation 50 in the septum 40 so that the distal opening 74 of the needle bore 69 is in fluid connection with the pressurized blood within the flow channel 26. The piston 70 of the syringe 60 is then retracted to cause blood to enter the chamber 79 of the syringe 60. (In practice the elevated pressure within the flow channel 26 may cause the piston 70 to be forced upward without manual retraction.) Some air will enter the syringe chamber 79 from the dead space 63 within hub 68 and from within needle bore 69. When the nurse stops retracting piston 70 of the syringe 60, the pressure within the flow chamber 26 will rapidly equilibrate with the syringe chamber 79 effectively compressing the air bubble trapped within the syringe chamber 79. The nurse then begins to withdraw the syringe 60 and the attached needle 58 out of the septum 40 until the nurse feels shroud detent 90 engaging the housing detent 54. The nurse then stops withdrawing the syringe 60. Then while holding the syringe 60 and needle 58 in place the nurse manually retracts piston 70. The distal opening 74 of the needle bore 69 is occluded by the septum 40 when the detents are so engaged, therefore, neither air nor blood can enter the syringe chamber 79. The retraction of the piston 70 will, therefore, depressurize the syringe chamber 79 and actually induce a negative pressure within the trapped air bubble. The nurse then further withdrawals the syringe 60 and the attached shrouded needle 58 past the housing detent 54 until the needle tip 78 exits the septum 40. With this technique, the needle bore opening 74 will exit the septum 40 without the spurt of blood which so often accompanies conventional technique. 
     Many modifications can be made to provide visual, tactile, auditory, or other indication that the needle bore opening 74 is occluded. A visual indicator, such as a red line (not shown) could be provided on the needle 58 or the housing 34 at a predetermined point to indicate occlusion of the distal opening 74 of the needle bore 69. Also a variety of detents can be provided for tactile and/or auditory indication of needle bore occlusion. For example, as in FIG. 4, the housing 34&#39; may have a shallow slot 100 to receive a post 110 on the inner surface of shroud 80&#39;. The slot 100 can angulate sharply at a predetermined angle point 120 along the housing 34&#39;. At the position at which the post 110 engages the angle point 120 during withdrawal of the needle 58&#39; from the septum 40&#39;, the distal opening (not shown) in the needle bore (not shown) is occluded by the septum 40&#39; in a manner similar to the that described for the preferred embodiment. The nurse is therefore notified that, at this position, withdrawal of the needle 58&#39; should temporarily stop and the syringe chamber should be decompressed, as previously discussed, before the shroud 80&#39; is rotated past the angle point 120 and is completely removed from over housing 34&#39;.