Patent Application
20060229573
1. Field of the Invention
This invention relates generally to the field of infusion catheters. More specifically, this invention relates to an improved device and method for administering a medication or other therapeutic fluid to a targeted region in a patient's body, such that the fluid is dispersed throughout the targeted region.
2. Background of the Invention
Infusion catheters for delivery of medication to a targeted region in a patient's body are well known in the art. These catheters are typically comprised of a flexible tube containing one or more axial lumens that allow fluid to flow from the proximal end of the catheter to the distal end. A source of fluid under pressure, such as a syringe or infusion pump, is connected to the proximal end of the catheter and provides fluid flow to the distal end of the catheter, which is inserted into the patient's body. The distal portion of the catheter is provided with one or more exit holes that create fluid communication between the fluid-carrying axial lumen(s) and the portion of the patient's body that surrounds the exterior of the catheter. As seen in the prior art, these exit holes may take a wide variety of forms such as an opening at the end of the axial lumen, holes or slits cut through the side wall of the lumen or tube, spaces between the coils of a spring wound to form a tube, or microscopic openings through a porous membrane shaped to form a tube.
Catheters Providing Even Delivery of Fluid Over an Extended Infusion Segment.
For certain medical treatments, it is beneficial to deliver a slow drip of fluid medication or other therapeutic fluid as evenly as possible over an extended area. For example, infusion of pain medication directly into the surgical site is commonly used to provide post-operative pain management. For surgical procedures involving a long incision or a relatively broad region (several square inches or more) of disturbed tissue, clinical studies have demonstrated improved pain relief when pain medication is infused at a slow rate (typically on the order of magnitude of 1-10 cc/hr), dripping along the full length of the incision or across the entire disturbed region. An infusion catheter that only provides a few exit holes is incapable of providing the broad fluid dispersion required in these instances. Simply adding numerous exit holes over an extended length typically results in most of the fluid dripping from only a small number of those holes, thereby depriving adequate fluid contact to other portions of the targeted area and failing to satisfy the clinical need. The prior art shows a variety of infusion catheters that attempt to provide an even dispersion of fluid throughout an extended segment of several inches or more along the length of the catheter. A discussion of several relevant prior art devices follows below.
The Wundcath infusion catheter manufactured by Micor (U.S. Pat. Nos. 6,676,643 and 6,689,110 to Brushey) provides a catheter body comprised of a flexible plastic tube with open proximal end and closed distal end, forming a single axial lumen, with a multitude of holes formed along an extended fenestrated segment near the distal end of the tube. A fine wire coil spring, wound with each adjacent coil touching or nearly touching the next, is positioned within the lumen and extends the full length of the catheter body. The majority of the fluid flowing into the catheter travels down the inside of the wire coil spring, and weeps out between the coils to flow out through the holes in the catheter body. The weeping action caused by the coil spring tends to spread the fluid more evenly between all of the holes along the fenestrated catheter segment, whereas the majority of the fluid would flow out of the first few holes if the coil spring were not in place.
The Soaker catheter sold by I-Flow (U.S. Pat. No. 6,626,885 to Massengale) provides a catheter body comprised of a flexible plastic tube with open proximal end and closed distal end, forming a single axial lumen, with a multitude of holes formed along an extended segment near the distal end of the tube. A microporous tube, made of a porous material formed into a tubular shape with open ends, is positioned within the lumen at the distal end of the catheter and extends slightly further than the fenestrated catheter segment. The majority of the fluid flowing into the catheter travels down the inside of the microporous tube, and weeps out through the micropores to flow out through the holes in the catheter body. The weeping action caused by the microporous tube tends to spread the fluid more evenly between all of the holes along the fenestrated catheter segment, whereas the majority of the fluid would flow out of the first few holes if the microporous tube were not in place.
The UniFlo catheter sold by Sorenson (Merit Medical) (U.S. Pat. Nos. 6,179,816 and 5,957,901 to Mottola et al.) provides a catheter body comprised of a flexible plastic tube with open proximal end and closed distal end, forming a single axial lumen, with a multitude of holes formed along an extended segment near the distal end of the tube. Unlike the Wundcath and Soaker, which use a separate element inside the catheter body to help disperse fluid evenly, the UniFlo controls fluid dispersion along the fenestrated catheter segment by controlling the size of the holes. For a comparably-sized catheter (e.g., 20G diameter with approximately 30 holes over a 5 inch-long segment), the holes in the UniFlo catheter are an order of magnitude smaller than the holes in the Wundcath and Soaker catheters (on the order of 0.001 in. vs. 0.01 in.). The small size of each individual hole, which increases the flow resistance through each hole and thereby reduces the maximum rate of flow through each hole, forces fluid to flow more evenly between all of the holes along the fenestrated catheter segment, whereas the majority of the fluid would flow out of the first few holes if the holes were larger.
A number of other prior art references disclose other catheter configurations that attempt to provide reasonably even dispersion of fluid flow along an extended infusion segment. While most of these prior art devices do not perform as well as the above referenced devices (at least when delivering fluid at relatively slow flow rates) or are significantly more expensive to manufacture, they are hereby incorporated as further examples of means to achieve even fluid dispersion along an extended infusion segment in a catheter.
Catheters Providing an Adjustable-Length Infusion Segment.
For certain medical treatments where fluid medication or other therapeutic fluid is to be delivered over an extended area using an infusion catheter with an extended infusion segment, it would be desirable to be able to match the length of the extended infusion segment to the need at hand. For example, when infusing pain medication along the length of an incision to provide post-operative pain relief, it would be desirable to adjust the length of the fenestrated catheter segment to match the length of the incision, so that medication is delivered along the full length of the incision. The Wundcath, Soaker, and UniFlo catheters described above do not provide any mechanism for adjusting the length, but instead are available in two or three models, each with a different, fixed, fenestrated catheter segment length. Models typically available provide a fenestrated catheter segment of 2.5, 5, or 10 inches in length. The prior art shows a variety of other catheters, typically designed for thrombolysis or infusion of medication to a confined segment inside a blood vessel, that do provide for adjustment of the length of the infusion segment. A discussion of several relevant prior art devices follows below.
The IV catheter taught by Huss et al. (U.S. Pat. No. 4,968,306) is designed for intravenous infusion of medication to a selected segment of a blood vessel at a flow rate of approximately 80 cc/hr. The Huss device provides a catheter having a guide wire; a catheter body formed by an inner and outer elongated tube sealed together at the distal end, such that the guide wire fits inside the inner tube and an annular fluid conduit is formed between the inner and outer tubes; a plurality of exit holes in the outer tube that create fluid communication between the fluid-carrying annular conduit and the region outside the catheter body; and a sliding sheath that fits over the catheter body and slides along the length of the catheter body, such that a selectable portion of the fenestrated catheter segment can be covered or uncovered.
For several reasons, the Huss device is not practical for certain medical applications such as delivery of anesthetic agents to a surgical site for post-operative pain management. First, the Huss device does not provide a means for ensuring even distribution of fluid along the fenestrated catheter segment. This is not an issue at high flow rates in the 80 cc/hr range (the intended use of the Huss device), but is an issue at the low flow rates in the 1-10 cc/hr range typically used for delivering anesthetic agents for post-operative pain relief.
Second, the Huss device does not provide a means for adequately sealing the sliding sheath against the catheter body. The device is described as typically having a sheath ID of 0.059 in. and a catheter body OD of 0.059 in. Such a “line-to-line” fit may provide an adequate seal for short bursts of fluid infusion in the 80 cc/hr range (the intended use of the Huss device), but will not provide an adequate seal for slow infusions that continue for hours or days. When normal manufacturing tolerances are taken into account, gaps of at least 0.001 in. and more likely up to 0.005 in. or more would be expected, providing enough of a leak path for the covered exit ports to provide a substantial amount of fluid flow, which will drip out the end of the sheath. Providing an interference or compression fit between the sheath and the catheter body is necessary to ensure a good seal, but is impractical in the Huss design because the parts could not be assembled if sized with an interference fit.
The Huss device is relatively expensive to manufacture, due to the large number of components, the tolerances required on the components, and the processes used to assemble the components. The manufacturing cost of the Huss catheter may be acceptable for its intended use in treating life-threatening vascular thrombosis, where a catheter selling for hundreds of dollars or more is accepted in the marketplace, but it is not acceptable for applications such as delivery of anesthetic agents for post-operative pain management, where the device must be produced in the $1-10 range to be cost competitive.
SociDal Finally, the Huss device includes a tightenable collar at the proximal end of the sheath. This collar is twisted to tighten down on the catheter body to seal the proximal end against leakage (note the need for this feature is further evidence that the design of the sheath itself does not provide for a good seal against the catheter body). In addition to being an added expense, the design of this collar creates a bulky component that reduces patient comfort and convenience. In the post-operative pain management application, the catheter is secured against the patient's skin and left in place for a period of hours or days, during which time the patient is often mobile. Securing the collar against the skin could cause abrasion and irritation to the skin, especially if the patient is moving around and the collar rubs against the skin. The bulk of the collar can also be inconvenient, as any significant protrusion above the skin surface can tend to catch on clothing, dressings, bed linens, etc.
The catheter disclosed by Zhan et al. (U.S. Pat. No. 5,626,564) is similar to the Huss device and suffers the same shortfalls when evaluated against the present invention. The device disclosed by Ouriel et al. (U.S. Pat. No. 6,755,813) provides yet another similar device also suffering some of the same shortfalls.
The catheter taught by Elsberry (U.S. Pat. Nos. 6,594,880, 6,093,180 and 6,056,725) is designed for infusion of medication to a parenchymal target, such as in treatment of a brain tumor, Alzheimer's disease, or other neurological applications. This catheter design is typically implanted in the patient's body for long-term treatment using an implanted infusion pump. The Elsberry device provides a catheter having a closed-end porous tube held in the open end of a second, non-porous tube. The second tube is formed of a material that expands when heated or exposed to a specific chemical, then returns to its original shape when the heat or chemical is removed. When the second tube is expanded, the user can slide the porous tube in or out to match the exposed length to the size of the parenchymal target; the heat or chemical is then removed and the second tube tightens over the first tube to hold it in the adjusted position. For several reasons, the Elsberry device is not practical for certain medical applications such as delivery of anesthetic agents to a surgical site for post-operative pain management.
The Elsberry device requires that the user apply a controlled amount of heat or a chemical solvent prior to adjusting the length of the infusion segment, then maintain the adjustment position and wait until the expansion effects of the heat or chemical dissipate. This is impractical in a typical surgical setting because: (a) a controlled heat source or specific chemical solvent is not normally available in the operating room, and would thus have to be specially provided at added cost and inconvenience, and (b) clinician and operating room time are typically at a premium, with high associated cost, therefore the added time needed to perform the adjustment steps is not cost effective.
In addition, the Elsberry device teaches a “zero tolerance” (i.e., “line-to-line”) fit between the porous tube and the second tube, and the porous tube does not extend to the proximal end of the catheter (where it could be directly affixed to the catheter connector) but rather is held in place only by contact with the second tube. This may provide adequate fixation for the delicate positioning and manipulation involved with implanting a catheter in the brain, and implantation of the catheter may eliminate the majority of the external forces that could tend to dislodge the catheter from its placement. However, in applications such as delivery of anesthetic agents to a surgical site for post-operative pain management, the catheter is exposed to significant external forces during placement and removal, and also during use (especially if the patient is mobile). A catheter of the Elsberry design, if used in these types of applications, would likely suffer inadvertent separation of the porous tube from the rest of the catheter either during use or during removal, requiring follow-up surgery to remove the portion left inside the patient's body.
The Elsberry device is limited in the choice of materials for the second tube to those that will expand significantly when exposed to heat or a specific chemical, then return to the original shape when the heat or chemical is removed. Elsberry teaches the potential material options as polyacrylonitrile, silicone elastomer, or polyurethane. Catheters used for applications such as delivery of anesthetic agents to a surgical site for post-operative pain management typically require a combination of high tensile strength, high elongation, kink resistance, flexibility and lubricity. In the small sizes typically used for these types of applications (19-21G catheters being most commonly used), silicone and polyacrylonitrile will not provide an adequate combination of these properties. Some polyurethanes are useful for catheters for these applications, but it is unlikely that the material could be optimized for both the material properties needed for these applications and the chemically-induced expansion properties needed for adjustability.
There exists an unmet need for an infusion catheter that delivers fluid along an extended-length infusion segment, provides even dispersion of the fluid delivery along the full length of the infusion segment, and allows the user to easily adjust the length of the infusion segment at the time of use. To provide broad applicability for use in a wide range of surgical procedures, this improved infusion catheter must function well when provided with a suitably long infusion segment of at least 10-12 inches and a suitably small catheter diameter of approximately 19-21G, and when used with an infusion system that delivers fluid at a relatively slow flow rate in the 1-10 cc/hr range. Further, the manufacturing cost for this improved catheter must not be significantly higher than the cost for the referenced Wundcath, Soaker and UniFlo prior art catheters.
The present invention provides an infusion catheter and method of use thereof that disperses fluid throughout a targeted region by providing exit holes along an extended section of the distal portion of the catheter. The extended section can be adjusted by the user so that the fluid-dispersing section can be adjusted from a relatively short length to a relatively long length as dictated by the requirements of the application at hand. This provides an adjustment mechanism that is inexpensive to manufacture, easy to use, comfortable and convenient for the patient, and provides even dispersion of the fluid infusion along the fluid-dispersing catheter segment at low flow rates and low fluid-driving pressures.
The present catheter provides an elongated, flexible, tubular catheter body with an axial lumen extending from the proximal end to the distal end. A distal portion of the catheter body is fenestrated with fluid passageways extending from the lumen through the catheter body walls, providing a multitude of pathways for expulsion of fluid from inside the catheter body to the area outside the fluid body. An exterior, sliding sheath is formed of a flexible tube with inside diameter equal to or slightly larger than the outside diameter of the catheter body. The ends of the sheath are necked down to an inside diameter slightly smaller than the outside diameter of the catheter body, so that when the sheath is fitted over the catheter body, the necked down sheath ends form a fluid-tight but slidable seal against the outside of the catheter body. The length of the sheath is greater than the length of the fenestrated section of the catheter body, but shorter than the portion of the catheter body proximal to the fenestrated section. When the sheath is slid distally to cover the entire fenestrated section, all of the fluid passageways are covered and fluid in the lumen cannot be expelled outside the catheter. When the sheath is slid proximally to uncover a portion or all of the fenestrated section, the fluid passageways are uncovered and fluid can be expelled from the lumen through each uncovered passageway. By adjusting the position of the sheath, the user can selectively uncover the desired portion of the fenestrated section, to provide an infusion length appropriately matched to the body region targeted for the infusion.
In the preferred embodiment, the catheter body is formed of an extruded polymeric tube, with a closed end formed at the distal tip, and the fluid passageways are formed by a series of micro-holes passing through the wall of the tube. A plurality of micro-holes is provided along a predetermined length of the catheter body (the fenestrated section). The size and number of the micro-holes are chosen to ensure even dispersion of fluid throughout the fenestrated section.
In the preferred embodiment, the sheath is formed of an extruded, heat-shrinkable polymeric tube. Short segments at the proximal and distal ends of the sheath are shrunk using selectively-applied heat during the manufacturing process, to provide a fluid-tight seal between the sheath and the catheter body.
In another embodiment, the ends of the sheath can be formed with relatively thick circumferential end rings to form the seal between the sheath and the outer surface of the tubular catheter body. In addition, the lubricity of the sheath material and/or the catheter body can be increased to allow the sheath to better slide along the catheter body and still provide the necessary fluid seal.
In the preferred embodiment, the proximal end of the catheter body connects to a standard connector such as a Tuohy-Borst connector or a Luer lock connector, which mates to the distal connection on the fluid source.
These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.
The present invention can be more readily understood in conjunction with the accompanying drawings, in which:
Turning now more specifically to the drawings,
The catheter body 100 is preferably formed of a material that is flexible, suitably biocompatible for prolonged contact with body tissues, cost-effective, and manufacturable with standard catheter production techniques such as extrusion and tip forming. Suitable materials include but are not limited to nylon, polyether block amide, polyurethane, polyimide, PVC, FEP and PTFE.
The sheath 200 is preferably formed of a material that is flexible, heat shrinkable, suitably biocompatible for prolonged contact with body tissues, cost-effective, and manufacturable with standard tubing production techniques such as extrusion. Suitable materials include but are not limited to polyester, PTFE, FEP, and polyolefin.
In the preferred embodiments, the proximal connector 300 is a female luer-lock connector. The proximal connector 300 is preferably formed of a material that is suitably biocompatible for contacting fluid that is then delivered to body tissues, is cost effective, and is manufacturable with standard production techniques such as injection molding and solvent or adhesive bonding. Suitable materials include but are not limited to acrylic, polycarbonate, ABS, PVC, polyethylene and polypropylene. The proximal connector may be permanently attached to the catheter body, such as a female luer-lock connector adhesively bonded to the catheter body, or it may be removably connected to the catheter body, such as a Tuohy-Borst connector.
The user adjusts the position of the sheath 200 along the catheter body 100 by grasping the sheath and pulling it in the desired direction. The catheter body or proximal connector is also held to provide tension when sliding the sheath, but this is omitted from the illustration to provide a better view of the device. As the sheath is slid distally, the fenestrated section 165 of the catheter body is partially or completely covered by the sheath. The degree of coverage is dependent on the axial position of the sheath. In
Referring now to
The actual size and placement of the fenestrations 160 must be selected to balance the conflicting needs of providing a uniform flow distribution throughout the fenestrated area (which requires the fenestration size to be minimized) and ensuring that the flow restriction created by the fenestrations does not cause a clinically significant reduction in the rate at which the fluid is delivered to the infusion site (which requires that the fenestration size be maximized). In the preferred embodiments, the size of each fenestration 160 is in the range of 0.0002 in. to 0.005 in., with optimal fenestration size dependent on the thickness of the catheter body wall 140, the number of fenestrations provided (including the expected range in number of uncovered fenestrations for typical usage), the range of desired flow rates of fluid through the catheter, and the fluid pressure created by the infusion device 700. The size and spacing of individual fenestrations may vary throughout the fenestrated area or section 165 in order to improve flow uniformity; for example, the distal portions of the fenestration section may have more or larger fenestrations 161 to balance the fluid pressure loss as fluid flows distally or to provide for sufficiently low flow restriction when only a relatively small number of fenestrations are left uncovered at the distal end.
While the illustrated embodiments incorporate a closed, rounded tip 122 at the distal end of the catheter body, alternate tip configurations such as a smooth, open tip or a tip with a small fenestration 124 at the end are also acceptable. For embodiments where the tip is not closed, the sheath cannot be used to completely stop the infusion as the tubular sheath cannot block the distal tip of the catheter body.
Still referring to
In the preferred embodiments, the interference fit or seal 167 between the necked-down sections 220 and the catheter body 100 is in the range of 0.0005 in. to 0.005 in., with optimal interference dependent on the dimensions (such as wall thickness and overall diameter) of the catheter body and the sheath, the modulus and yield strength of the catheter body and sheath materials, the elasticity of the sheath material after heat-shrinking, the coefficient of friction between the catheter body and the sheath, and the maximum potential fluid pressure created by the infusion device 700.
Referring now to
Referring now to
Referring now to
In addition, the ends 166 of the sheath 200 can have a thickened circumferential end portion 168 to form the fluid seal. The thickened end portion 168 will have an inside diameter that is smaller than the outside diameter of the tube 100. This will still allow the sheath 200 to slide along the surface of the tube 100. The thickened end portion 168 can be used with or without the shrinking of the ends 166 of the sheath seal 200.
In the preferred embodiments, both the catheter body and the sheath material are formed of a material with a relatively low coefficient of friction, or are coated with a lubricious coating. This aspect of the invention allows for a heavier interference fit between the necked-down sheath ends and the catheter body, which provides a better seal that remains fluid tight under higher pressures, without requiring an unreasonably high force to slide the sheath along the catheter body. The low-friction material or lubricious coating also reduces the potential for the catheter to stick to bodily tissue or implants inside the patient, thereby reducing the amount of force needed to remove the catheter from the patient's body at the end of the therapy (and associated occurrences of catheter breakage when the user pulls too hard on the catheter).
The sheath is preferably formed of a colored or opaque material 169 that provides high contrast with the color or transparency of the catheter body. This aspect of the invention improves user friendliness by ensuring that the sheath position can be readily determined at a glance.
The catheter of this invention can be made in a wide range of sizes. The preferred size for the catheter is dependent on the clinical application for which it is to be used. The fenestrated section may vary from less than 1 inch long to more than 1 foot long, depending on the body sites that are being targeted. The preferred size for infusion of pain medications into a surgical site, to provide broad applicability for a wide range of surgical procedures, is' a fenestrated section approximately 10-15 inches long with a sheath slightly longer than the fenestrated section. The preferred catheter body size range for infusion of pain medications into a surgical site is between 15G and 24G, with sizes between 18G and 21G most commonly preferred by clinicians. The length of the catheter body must be at least equal the length of the sheath plus the length of the fenestrated section, to provide room for the entire sheath to be positioned proximal to the fenestrated section so all fenestrations are uncovered. The length should also be adequate to reach from the infusion site to a convenient location for the infusion device, without being so long as to hinder patient convenience with large amounts of loose tubing. For situations where the patient may be ambulatory during the infusion, a length in the range of 18 to 60 inches is typically appropriate, with a range of 24 to 36 inches being adequate for most applications.
The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims.
The present application is based on, and claims priority to the Applicant's U.S. Provisional Patent Application Ser. No. 60/669,840, entitled “Adjustable Infusion Catheter,” filed on Apr. 8, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60669840 | Apr 2005 | US |
