Blood withdrawal apparatus

Abstract: A blood withdrawal apparatus provided which a blunt cannula or needle (58) is adapted to penetrate an elastomeric septum (40) into a pressurized flow channel (26), such as an arterial line. After blood has been sucked into the attached syringe (60), the needle tip (78) is partially withdrawn from the septum (40) until an indication is detected, for example by engagement of a detent (90) on a shroud (80) surrounding the cannula or needle (58), with a detent (54) on the housing (34) for the septum (40). The nurse can then depressurize the syringe (60) by operating the piston (70) and thus prevent blood-spurt when the needle tip (78) is subsequently fully withdrawn from the septum (40).

Description: The invention relates to aspiration of blood samples through an elastomeric septum from pressurized flow channels such as arterial lines. Such aspiration thas 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sampling technique, a needle or cannula is inserted into the flow channel through the elastomeric septum, and blood withdrawn into a blood collection device such as a syringe attached to the needle or cannula.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 the 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. Such a device is known from WO-A-91/00115, which falls under Article 54(3) EPC. 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. According to the invention, there is provided a blood aspiration assembly for aspirating a sample of blood from a flow channel into an interior chamber of a blood storage container, the flow channel being adapted for communication through a catheter with the lumen of a blood vessel of a patient, the blood vessel lumen containing blood under pressure, said aspiration assembly comprising: a housing containing at least a portion of said flow channel and having an internal passage in communication with said flow channel portion; a cannula having a distal tip, first and second openings, and a bore through said cannula extending between said first and second openings, said second opening being located adjacent said distal tip of said cannula; an elastomeric element in said housing normally occluding said internal passage and adapted to be penetrated by said cannula so that at least a portion of said cannula can enter and pass through said element to locate said second opening in said flow channel portion to place said bore of said cannula in communication with the flow channel portion so that blood from said flow channel portion can enter said bore through said second opening for passage through said bore and through said first opening; means carried by the cannula for connecting said cannula to a blood storage container so that said cannula bore will lie in communication with an interior chamber of the blood storage container through said first opening; means for precluding communication between said cannula bore and said flow channel; and means carried to the aspiration assembly for indicating when communication between said cannula and said flow channel portion is precluded. The cannula 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. The needle occlusion indication means is preferably provided on the housing, but may be provided along the outer surface of the needle. In a 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. (Thus, the detents are an example of means which are cooperable between the needle and the housing for positively inhibiting withdrawal of the needle from the septum when communication between the needle and the flow channel portion is precluded. Such cooperable means may be present as an alternative to the occlusion indicator means defined above.) 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. Whilst it is preferable that the means for occluding the passage in the housing, and hence isolating the blood pressures on opposite sides of the septum, is formed by the septum itself, any other suitable means may be used for this purpose. Thus, in another aspect the apparatus of the invention includes means for isolating the pressurized blood passing through the bore of the needle from the blood vessel of the patient and means carried by the aspiration assembly for indicating when the pressurized blood in the bore of the needle has been isolated from the blood vessel of the patient. Preferred embodiments of the invention will now be described in detail, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a preferred apparatus in accordance with the invention; Figure 2 is an enlarged part-sectional view of the aspiration assembly of figure 1, ready for withdrawing blood from the flow channel; Figure 3 is a similar view to that of Figure 2, showing the needle tip occluded by the septum; and Figure 4 is a perspective view of another preferred embodiment of the apparatus of the invention. 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 40 extends from mthe atmospheric interface 48 of the septum 40 to the flow channel interface 44. The outer surface 52 of housing 34 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 intergral 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 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 detend 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 withdraws 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 the 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' may have a shallow slot 100 to receive a post 110 on the inner surface of shroud 80'. The slot 100 can angulate sharply at a predetermined angle point 120 along the housing 34'. At the position at which the post 110 engages the angle point 120 during withdrawal of the needle 58' from the septum 40', the distal opening (not shown) in the needle bore (not shown) is occluded by the septum 40' 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' should temporarily stop and the syringe chamber should be decompressed, as previously discussed, before the shroud 80' is rotated past the angle point 120 and is completely removed from over housing 34'.

Claims: A blood aspiration assembly for aspirating a sample of blood from a flow channel (26) into an interior chamber (79) of a blood storage container (60), the flow channel (26) being adapted for communication through a catheter (24) with the lumen of a blood vessel (20) of a patient, the blood vessel lumen containing blood under pressure, said aspiration assembly comprising: a housing (34) containing at least a portion of said flow channel and having an internal passage (38) in communication with said flow channel portion (26); a cannula (58) having a distal tip (78), first and second openings, and a bore (69) through said cannula (58) extending between said first and second openings, said second opening (74) being located adjacent said distal tip (78) of said cannula; means (40,50,74) for precluding communication between said cannula bore and said flow channel, said means for precluding comprising an elastomeric element (40) in said housing (34) normally occluding said internal passage (38) and adapted to be penetrated by said cannula (58) so that at least a portion of said cannula can enter and pass through said element to locate said second opening in said flow channel portion to place said bore of said cannula in communication with the flow channel portion so that blood from said flow channel portion can enter said bore through said second opening for passage through said bore and through said first opening; means (68) carried by the cannula for connecting said cannula to a blood storage container (60) so that said cannula bore will lie in communication with an interior chamber of the blood storage container through said first opening; and means (54,90; 100,110,120) carried by the aspiration assembly for indicating when communication between said cannula and said flow channel portion is precluded. An assembly according to claim 1 in combination with a blood storage container (60) having said interior chamber (79) and including means (70) coupled to said blood storage container (60) for inducing a negative pressure within said interior chamber (79) of said blood storage container. An assembly according to claim 2, wherein said blood storage container comprises a syringe and said negative pressure inducing means comprises a piston for said syringe in said interior chamber. An assembly according to claim 1, wherein said means for precluding is responsive to at least partial withdrawal of said cannula from said flow channel portion. An assembly according to claim 1, wherein at least one of said cannula and said housing comprise said means for indicating. An assembly according to claim 5, wherein said elastomeric element (40) seals about said second opening (74) of said cannula when said second opening is positioned within said element during said at least partial withdrawal of said cannula from said element to preclude communication between said cannula bore and said flow channel portion. An assembly according to any preceding claim, wherein said indicating means further indicates when said second opening (74) of said cannula is sealed by said elastomeric element (40). An assembly according to any preceding claim, further including a shroud (80) connected to said cannula (58) and extending in a direction toward said distal tip (78) and about said cannula, said shroud being sized to receive at least a portion of said housing (34) when said elastomeric element (40) is penetrated by said cannula (58). An assembly according to claim 8, wherein said indicating means comprises detents (90, 54) on said shroud and said housing, respectively, said detents being engageable with one another during said at least partial withdrawal of said cannula from said element, when communication between said cannula bore and said flow channel portion is precluded. An assembly according to claim 9, wherein said elastomeric element (40) seals about said second opening (74) of said cannula when said second opening (74) is positioned within said element (40) during said at least partial withdrawal of said cannula (58) from said element (40), said detent (90) on said shroud and said detent (54) on said housing engaging one another during said at least partial withdrawal of said cannula from said element when said elastomeric element (40) seals about said second opening (74). An assembly according to any preceding claim, wherein said elastomeric element seals against said cannula about said second opening when said second opening is positioned within said element, and means cooperable between said cannula and said housing for inhibiting withdrawal of said cannula relative to said elastomeric element when said second opening is sealed by said element. An assembly according to any preceding claim, wherein said elastomeric element has an outer face (48), an inner interface (44) in said flow channel portion and a normally sealed perforation (50) extending from said outer faces through said element to said interface for receiving said cannula.

Inventors: LYNN LAWRENCE A, LYNN, LAWRENCE A.
Applicants: LYNN LAWRENCE A, LYNN, LAWRENCE A.
Application year: 1991
Main classification: A61B5
IPC codes: A61M5, A61B5, A61M39