The present invention relates generally to medical devices and more particularly to needle safety devices and positive flushing mechanisms.
Implantable vascular access systems are used extensively in the medical field to facilitate the performance of recurrent therapeutic tasks inside the body of a patient. Such vascular access systems generally include an implantable vascular access port attached to a vascular catheter. A typical vascular access port has a needle-impenetrable housing that encloses a fluid reservoir that is accessible from the exterior of the access port through a needle-penetrable elastomeric septum.
The entirety of the system, both the vascular access port and the catheter attached thereto, is implanted in the body of a patient. The distal tip of the catheter is disposed at a predetermined location where therapeutic activity is to be effected. Once the vascular access system is implanted, the tip of a hypodermic needle can then be employed selectively and repeatedly to access the fluid reservoir of the access port by penetrating the skin at the implantation site for the access port and then by being advanced through the septum of the access port itself.
While often times syringe-type devices are utilized for vascular access ports in acute or short-term situations, a special type of device is utilized for longer term infusion therapy. Such an infusion assembly device generally consists of a needle and wing assembly that lies flat against the skin in an insertion position, the needle having a proximal end attached to a wing assembly that is in angular relation to the needle shank, the angle being approximately 90°. As mentioned, when this longer term needle device is inserted into the vascular access port, it lies flat against the patient's skin and is adhered thereto as described, for example, in U.S. Pat. No. 4,710,176 to Quick.
With respect to the needle tip of the needle used in infusion assemblies for vascular access ports, a non-coring configuration is generally utilized due to repeated entry of the needle into the septum of the vascular access port. When the tip of a hypodermic or other traditional needle advances through the septum, coring occurs if any portion of the septum material is forced inside the shaft of the needle through the opening in the tip thereof. That portion of the septum material forced inside a needle in this process is in effect severed from the rest of the body of the septum material. Such septum coring produces small, detached particles of the septum that are likely to enter the fluid that is infused by the implanted vascular access system into the vascular system of the patient. These particles can obstruct fluid flow through the outlet stem of the vascular access port, or if escaping through the outlet stem of the vascular access port, can become trapped in the cardiovascular system of the patient.
In addition, septum coring produces small passageways through the body of a septum. On occasion these passageways extend entirely through the septum, from the exterior thereof to the fluid reservoir inside the vascular access port. The inwardly directed forces imposed on the installed septum by the housing of a vascular access port should initially urge the material of the body of the septum inwardly upon itself to close such passageways after the shaft of the needle is withdrawn therefrom. Nonetheless, continued coring eventually leads to various forms of septum failure that cannot be overcome by such inwardly directed forces. The material continuity of the septum is increasingly compromised, resulting in crumbled areas of the septum matrix. Eventually, leakage of fluid can be expected through the septum from the fluid reservoir in the vascular access port. Once such fluid escapes to the exterior of the vascular access port, necrosis will occur of the tissue surrounding the subcutaneous pocket in which the vascular access port is implanted, causing many undesirable consequences. Therefore, non-coring or Huber needles are preferably used in conjunction with infusion assemblies for vascular access ports. These needles, in contradistinction to the standard or traditional hypodermic needles pierce the septum like a knife, facilitating the resealing thereof so that the aforementioned problems are largely averted.
As with any needle-type device, there exists the problem of inadvertent needle sticks, which generally occurs when the needle-type device is withdrawn from the patient prior to appropriate disposal thereof. Of course, inadvertent needle sticks introduce a variety of concerns due to unwanted transmission of blood from the patient to the medical practitioner. Inadvertent needle sticks can occur because of carelessness on the part of the medical practitioner or due to accidents in the handling of devices with exposed needle tips. With respect to Huber needles specifically, needle stick accidents can occur due to difficulty in removal as well. This difficulty results from the configuration of the Huber needle, which gets hooked into the port making it difficult to remove. Increased pulling force on behalf of the medical practitioner to dislodge the needle from the port results in less control over the tip of the needle when freed from the port, causing the inadvertent needle stick.
To address the inadvertent needle stick problem in winged infusion assemblies, such as those described herein, various safety devices have been designed to encase the needle after it is withdrawn from the port. One such safety device is described in U.S. Pat. No. 5,755,694 to Camus. Camus discloses a needle base disposed over a segment of the needle at its proximal end, comprising two generally flat wings made of flexible material with one hinge connecting each of the wings to the needle base. Upon removal of the needle from the patient the wings flex against a moveable member that keeps them adjacent the needle until the needle is completely removed from the skin of a patient after which the wings surround the needle to prevent the tip from making contact outside of the needle base.
Another type of safety device is described in U.S. Pat. No. 5,951,522 to Rosato et al., in which the particular configuration of the Huber needle is also taken into account. Rosato et al. discloses a safety enclosure comprising a wing assembly mounted to the aft end of a angled Huber needle, the wing assembly having a configuration consisting of either a single integral member having a plurality of spaced apart fold lines which divide the member into a plurality of interconnected panels, or a pair of wing members mounted in a scissors-type arrangement. In each embodiment, when the medical practitioner removes the needle from the patient, the wing assembly closes around the needle and locks together, encasing it therein.
While many advancements have been made in the area of needle devices for use with vascular access ports, such as those described herein, there remains a heretofore unsolved problem related to removal of the needle device from the vascular access port. When the needle is inserted through the septum, it occupies a volume equal to the external dimensions thereof present in the fluid reservoir positioned underneath the septum. When the needle is removed from the vascular access port, the needle volume is evacuated without replacement, causing an equivalent volume of venous fluid to be drawn into the catheter tip at the distal end thereof. This infiltration of venous fluid is suspected to cause or contribute to thrombus formation at the catheter tip, which blocks the flow of fluid therethrough and results in early removal of the port and catheter from the patient. Early removal is costly, invasive and time-consuming and otherwise extremely undesirable.
One solution to this problem of unwanted venous fluid being drawn into the catheter tip has been to implement a positive flushing technique as the needle is withdrawn. This technique generally consists of the medical practitioner inserting a syringe into the port and injecting a solution such as heparin while simultaneously withdrawing the needle. This technique, however, can be quite cumbersome and complicated and in fact may require more than one operator, as many of the infusion sets for use with vascular access ports require two hands to withdraw. For these reasons and others, it is known that a significant population of medical practitioners forego the practice of the described technique despite the adverse consequences that could result, as outlined herein. Therefore, it would be desirable to incorporate a flushing mechanism into a needle infusion set for use with a vascular access port so that flushing upon removal of the needle from the septum is assured.
In particular, it would be desirable to incorporate a positive flushing mechanism into various needle assemblies, one of which being an improved infusion needle assembly for use with a vascular access port that also provides a safety feature to prevent needle sticks.