Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2002-05-08
2003-06-10
Tapolcai, William E. (Department: 3744)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
Reexamination Certificate
active
06575945
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical implants and to methods for their use. More particularly, the present invention relates to preventing or inhibiting infections internal to the patient in the vicinity of subcutaneously implanted devices or associated with the use of such devices and to configurations of devices that prevent or alleviate localized internal infections. As used herein, the phrase “inhibiting infection” and variations thereof refer both to prophylactic treatment to avoid infection and to therapeutic treatment to eliminate an established infection. More specifically, this invention relates to preventing or inhibiting infections in the vicinity of implanted hemodialysis ports.
2. Description of Related Art
Subcutaneously and transcutaneously implanted devices are utilized for a wide variety of purposes, e.g., drug infusion and hemodialysis access. Heart pacemakers have become commonplace. All such implanted devices are at some risk for infection.
The focus of interest for use of the current invention is hemodialysis access systems for access to human or animal patient's vascular system for high fluid flow rate exchange of blood between the vascular system and an external processing apparatus Various improved access devices have been developed and described in numerous prior art documents.
Such a device is typically a subcutaneously implanted port connected to a blood vessel or other body lumen or cavity usually using a catheter. The port has an aperture for receiving a percutaneous access tube, e.g., a needle. Typical access port apparatuses are disclosed in U.S. Pat. Nos. 5,180,365; 5,226,879; 5,263,930; and 5,281,199.
Ports represent a significant advance over transcutaneous catheters and have a number of common fundamental design features. The ports themselves are made from a variety of materials, e.g., titanium, ceramics, and various plastic materials, e.g., polysulphone, and comprise a housing which forms a reservoir. A surface of the reservoir may be enclosed by a high-density, self-sealing septum, typically made of silicone rubber. Connected to the port housing is typically an implanted catheter that communicates with a vein or other site within the patient where the infusion of therapeutic agents is desired. Implantation of such devices generally proceeds by making a small subcutaneous pocket in an appropriate area of the patient under local anesthesia. The implanted catheter is tunneled to the desired infusion site. When the care provider desires to infuse or remove materials through the port, a hypodermic needle which pierces the skin over the infusion port and docks with the port is inserted.
Recently, improved devices of this class addressing these problems have been developed and described in U.S. Pat. No. 5,954,691 and U.S. patent application Ser. No. 09/083,078, filed May 21, 1998, the disclosures of which are incorporated herein by reference in their entirety. These inventions are directed to a hemodialysis access system for access to a human or animal patient's vascular system for high fluid flow rate exchange of blood between the vascular system and an external processing apparatus at a volumetric flow rate in excess of 250 ml/minute.
Notwithstanding improvements in the construction of subcutaneous ports, problems still remain that retard their full usefulness in medical practice. Specifically, from time to time infections develop in the capsules or pockets surrounding the implanted devices. Such infections are difficult to treat for the reasons discussed herein and often require the removal of the port or other implanted device.
It is well known that a relatively hard tissue capsule or “pocket” usually forms around an artificial object or device implanted under the skin if the exterior surface of the device is impermeable to tissue in-growth, e.g., where the surface is both hard and non-porous. Pocket formation typically takes place within a few weeks of the implantation of the object in subcutaneous tissue. The capsule, approximately 1 mm thick, forms tightly around the implanted object. Such a capsule is usually white or pinkish and quite slippery to the touch on the inside. The outside of the capsule is attached to the patient's normal subcutaneous tissue. The matrix of the capsule is normally without blood vessels or is very poorly vascularized. When the implanted device comprises a non-porous metal, plastic or elastomer, the capsule usually does not stick or adhere to the artificial material. To a large extent, but not completely, the pocket seals the implanted device off from the surrounding living tissue.
It is also known that infections of subcutaneously implanted ports arise most frequently from skin bacteria transported through the skin by needle penetration. Bacteria, having entered the space between the external surface of the device and the opposed tissue surface, can then attach to the port outer surface and grow into colonies in a layer or film form called biofilm.
While initially localized within the pocket formed around a device, such a colony may not cause symptoms or manifest as an infection for a long time. However, bacteria from the biofilm colony may shed and cross the pocket membrane, whereby an infection will manifest itself. Such an infection can become a local tissue infection indicated by local swelling, pus formation, local heating and pain, and so on, and it can also lead to systemic blood infection. These latter infections are very serious and if not treated often lead to morbidity and ultimately death.
One of the inventors herein, Dr. Sodemann, examined a surgical site at autopsy of a 79 year old patient who had an implanted hemodialysis port for approximately 6 months. There had been no incidents or symptoms which would have suggested an active infection at any time. After autopsy, however, it was found that the outer surface of the implant had been colonized with bacteria. It was concluded that bacteria had not propagated to surrounding tissue outside of the capsule and hence infection had not been suspected.
Infections near a subcutaneously implanted device have frequently been treated by systemic administration of antibiotics after somatic symptoms appear. Often such treatment does not work and the implanted device must be removed, subjecting the patient to additional trauma and leaving the patient without benefit of the device for the time it takes to clear the infection and replace the removed implant with another device. Moreover, the need to administer antibiotics frequently to patients is expensive and patients who suffer from repeated infections often develop strains of bacteria resistant to antibiotics.
Dr. Sodemann conducted a clinical study of a new port for hemodialysis patients, the Dialock®, aided by a proprietary catheter lock solution to prevent infection and clotting inside the indwelling catheter. The method of using the proprietary antimicrobial locking solution in all patients for the first 14 months of the study was to instill the locking solution only in the catheter at the end of a dialysis session and discard it at the beginning of the next session. This study enrolled some 65 patients (the individual implant time ranged from a few weeks to 2 years) for an accumulated experience of approximately 60 patient-years. This study showed an overall infection rate of approximately 0.9 infection episodes per 1000 days of hemodialysis treatment using Dialock® as an access with the proprietary catheter locking solution. The breakdown was approximately 0.1 episodes per 1000 days for blood infections and 0.8 episodes per 1000 days for pocket infection. These infection results compare very favorably with results reported in review papers published in peer reviewed journals, namely, 2 to 10 episodes per 1000 days.
The inventors concluded from the foregoing observations that the risk of pocket infection remained problematic, however. Patients are at risk of having their tissue exposed to bacteria or fungi during each acce
Estabrook Brian K.
Polaschegg Hans-Dietrich
Prosl Frank R.
Sodemann Klaus
Biolink Corporation
Burns & Levinson LLP
Lan Yan
Williams Frederick C.
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