Extra-corporeal vascular conduit

Details Extra-corporeal vascular conduit Extra-corporeal vascular conduit

2001-02-09

2004-07-13

Bennett, Henry (Department: 3743)

Surgery

Blood drawn and replaced or treated and returned to body

C604S006160, C623S001360, C623S003260

Reexamination Certificate

active

06761700

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an artificial vessel and, in particular, to an apparatus and method for permitting long-term extracorporeal circulation of blood flow from and to the vasculature of a patient.
2. Description of the Related Art
It is often necessary to divert the flow of blood from a patient's blood vessel back to the same or a different blood vessel as part of treating a patient suffering from one or more of numerous health impairments, including cardiovascular ills. In many cases, such efforts involve using artificial means for carrying the blood between vessels. The materials selected for doing so depend often on whether the application is acute (short-term) or chronic (long-term). In either case, it is beneficial to employ biocompatible materials, although the extent of biocompatibility differs depending upon the duration of intended or expected use with the patient. Biocompatibility is generally measured by how little the synthetic material adversely affects the patient's blood and tissues. Materials that eventually destroy red blood cells or body tissues are generally not suitable particularly for long-term applications.
For short-term or acute applications, a wide range of polymer materials are available, such as polyethylene, silicone and polyvinyl chloride (PVC). While the level of biocompatibility for such polymer materials is not particularly high, for short-term use, the adverse effects on the patient tend to be minimal. For chronic or long-term applications of artificial blood vessels used for the diversion of blood, the need for a higher level of biocompatibility rises dramatically. Indeed, an entire industry has evolved around the development of biocompatible materials that may be formed as conduits to function as artificial vessels for carrying diverted blood to and from a patient's vascular system on a long-term basis. Examples of such materials are ePTFE (expanded polytetrafluroethylene) such as that manufactured by Bard Impra and woven polyester such as that manufactured by W. L. Gore. Discussions of such synthetic biocompatible materials may be found in U.S. Pat. Nos. 5,718,973, 5,629,008 and 5,549,657.
In many cases, the blood being diverted remains entirely within the patient's body; i.e., intracorporeal application, using a graft. Under those circumstances, the material chosen for long-term, purely internal, application need only withstand the conditions of a singular environment—the interior of the patient. In some cases, a portion of the patient's existing vascular system is used to divert the blood, ensuring complete biocompatibility. In other cases, synthetic materials are used for the graft, such as ePTFE or woven polyester. In one method of application, both ends of the artificial vessel are grafted directly to the patient's blood vessels. Where the artificial vessel is applied entirely within the patient's thorax, the vessel is often applied during open-chest surgery. In some cases, the artificial vessel is applied to blood vessels in a manner that does not require open-chest surgery. In those cases, the graft may be tunneled under the skin and surgically applied at both ends to the respective blood vessels. While common graft materials such as ePTFE and woven polyester are somewhat porous, it is not a problem as the pores in the wall of the graft eventually clot off.
Where there is a desire or need to divert the flow of blood externally to the patient for some period of time during treatment, the material selected to carry the blood should be capable of withstanding the conditions of two environments, that inside the body and that outside the body. Presently, the short-term application of diverting blood extracorporeally, such as perisurgical environments where the blood is diverted through an oxygenator outside the body, e.g., during cardiac surgery, an artificial vessel made of PVC is used to carry the blood. The connection to the patient's vascular system is typically made, under such circumstances, with cannulas temporarily inserted into the vasculature of the patient for both the inflow and the outflow. An example of such an artificial vessel is made by Medtronic, Inc. The nature of the PVC material is such that it is not porous, so there is no risk of blood seeping through the walls of the artificial vessel or contaminants passing to the blood from the external environment.
The long-term application of diverting blood extracorporeally involves the use of a bi-material conduit, where one portion of the conduit is made of a biocompatible material, such as ePTFE, and the other portion of the catheter is made of a polymer material such as PVC. Typically, the ePTFE portion is anastamosed to the patient's vasculature to permit fluid communication. The polymer portion of the catheter is used to connect to a pump and/or other device through which the blood passes.
There is one artificial vessel system manufactured by MEDOS AG, Germany that includes a closed end at the proximal end of the catheter, in which a small orthogonally positioned hole is provided to permit the physician to grasp the closed end with a hook. A tunneling guide is used to create a tunnel below the patient's skin through which the cannula may reside. The guide is then used to grasp the closed end of the vascular conduit and pull the proximal end of the vascular conduit through the tunnel created by the guide. A hemostat is placed over the proximal end of the conduit to seal the inner lumen and the closed end is then sliced off, permitting the proximal end of the cannula to be connected to a pump or other device. The hemostat can then be released to permit blood flow to the pump or the other device. This system provides a means for attaching the vascular conduit to the patient at a location different than the location where the vascular conduit exits the body. Where it is desired to locate the exit site proximate the connection site, no tunneling may be necessary.
Typical graft materials such as ePTFE and woven polyester are effective at diverting blood flow without adversely affecting the properties of the blood or the characteristics of the flow. However, as alluded to above, common graft materials are porous and are not successful in applications outside the body because of fluid communication with the ambient environment. Materials such as ePTFE and woven polyester, however, are simply not capable of withstanding extracorporeal environments without adversely affecting blood flow characteristics or without contamination of the blood. Contact of the blood with air may lead to contamination and infection or may lead to the more serious event of introducing air emboli into the blood stream. Thus, the industry presently relies upon the non-porous polymer materials to carry the blood outside the body. While easy to use, the problem with such materials is that they eventually have an adverse effect on the blood during prolonged use. Moreover, such materials eventually lead to poor sustained blood flow due to resulting thrombosis within the artificial vessel. Should the thrombus break away, it could lead to blood clots in other parts of the circuit or in the patient, the well known adverse results of which include occlusion of blood vessels potentially leading to stroke or myocardial infarction. In some cases, when using such polymer materials, a heparin coating has been applied to the polymer graft to minimize thrombosis. The long-term effectiveness of such an application is not certain.
SUMMARY OF THE INVENTION
Overcoming many if not all of the limitations of the prior art, the present invention comprises an extracorporeal vascular conduit for circulating blood outside a patient's body over an extended period of time in a manner that minimizes risk of thrombosis and inflammatory response and maximizes the ability of a patient to be ambulatory during recovery stages. The inventive vascular conduit solves the needs described above by employing a single lumen va

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