Patent Publication Number: US-8523823-B2

Title: Indwelling device

Description:
This application is a continuation of application Ser. No. 10/916,631, filed Aug. 12, 2004, now pending, that application is a continuation-in-part of application Ser. No. 10/074,017, filed Feb. 14, 2002, now abandoned, the entire contents of which are hereby incorporated by reference in this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention is in the field of medical devices, and more specifically relates to indwelling medical devices. 
     BACKGROUND OF THE INVENTION 
     There are many medical devices that are inserted into the body and left indwelling for a prolonged period of time. These include, for example, various types of catheters, cannulae, drains, implants, stents, pacemakers, electrodes and other devices. Some of these devices, such as a urinary catheter, when in use, extend from the exterior of the body into the body interior, passing through an orifice on the body surface. The orifice may be a natural orifice (e.g. mouth, meatus, nostrils, etc.) or an artificial orifice (e.g. a hole formed in the skin by a surgical incision). Other indwelling devices, such as a pacemaker or stent, are completely enclosed inside the body during use. Accessing these devices typically requires surgical incising or other invasive approaches. 
     Although using indwelling devices is a common medical procedure, it is often limited due to formation of biofilm such as calcifications and other debris, and colonization of microorganisms, such as bacteria and fungi, on the surface of the device. This may cause inflammation and further infection around the device. The formation of biofilm and contamination is common with exposed indwelling devices, limiting the amount of time that they may be left in the body before having to be removed and possibly replaced with a new device. 
     Contamination of the device and tissues surrounding it may occur as the device is inserted into the body. For example, the end of a urethra closest to the meatus is naturally contaminated with various infectious agents, while the remainder of the urethra, nearer to the urinary bladder is normally sterile. During insertion of a catheter through the urethra to the urinary bladder, the catheter contacts infectious agents in the beginning of the urethra and spreads them up the urethra into the normally sterile portion and into the bladder. In order to reduce the spread of microorganisms up the urethra during insertion of a urinary catheter, it is known to first insert a hollow sheath into the beginning of the urethra that extends in the urethra to just beyond the contaminated region. A urinary catheter is then inserted through the sheath into the normally sterile part of the urethra, and into the bladder. The sheath thus intervenes between the catheter and the microorganisms in the infected part of the urethra, and thus decreases the chance of microorganisms spreading into the normally sterile portion of the urethra and into the bladder. After insertion of the catheter, the sheath is withdrawn from the body. Such sheaths are disclosed, for example, in U.S. Pat. No. 5,417,666. 
     Microorganisms may also migrate along an exposed indwelling device after its insertion along the outside surface of the device at its interface with the surrounding tissue. In order to inhibit the migration of microorganisms along the device, it is known to impregnate the device with antiseptic substances that are released from the catheter over time. A catheter designed to release antiseptic substances is disclosed, for example, in U.S. Pat. No. 3,598,127. Antiseptic impregnation, however, is not effective in the prevention of biofilm formation and is of very limited value in preventing infection due to the development of resistance among the microorganisms to the antibiotic. 
     SUMMARY OF THE INVENTION 
     It has now been found that it is possible to prevent the build-up of biofilm on the surfaces of indwelling medical devices by means of providing removable covers. By means of this arrangement, biofilm components become deposited on the surface of a cover instead of on the surface of the medical device itself. This cover may then be removed without disturbing the positioning or functioning of the indwelling device to which said cover was attached, thereby removing the built-up biofilm from the region of the device, and from the body. The act of removing the cover exposes either a further cover, enabling the removal process to be repeated, or, the external surface of the indwelling device itself. Unexpectedly, the inventors have found that it is possible to construct a covered device, such that the desired functioning thereof (for example the passage of fluids through a catheter or the mechanical dilatory action of a stent) is not affected or influenced by the presence of one or more covers on the surface of the device. 
     The term “biofilm”, explained hereinabove, refers to the build-up of biologically-derived matter such as calcified material and other debris, as well as microorganisms, such as bacteria and fungi, on the surface of the device. This may cause inflammation and further infection around the device. In certain locations and in certain circumstances the biofilm and associated inflammatory processes may lead to undesirable blood clot formation. 
     The present invention is thus primarily directed to indwelling medical devices having an outer surface, at least a portion of which is protected by a manually detachable cover. During insertion, the cover is attached to the surface so as to prevent relative movement of the surface and the cover. This allows the integrity of the device and cover to be maintained during insertion. Once the covered device (e.g. catheter, stent, drain etc.) has been inserted into the desired operating location, said device may be manipulated or operated in the normal manner, without any hindrance or loss of functionality arising from the presence of the cover. At any time after insertion, the cover may be detached from the shaft and removed from the body, leaving the device in place. Removing the cover from the device removes the biofilm and contamination that has accumulated on the cover. 
     The cover is preferably made from non-allergic biocompatible materials such as natural rubber, silicone rubber, latex, woven metal mesh, parylene, polyvinylchloride, polyurethane, mylar, nylon and the like. The cover may be impermeable to body fluids or microorganisms. The cover may have a rough or smooth surface. 
     The covered device provided by the present invention may comprise any of the different types of indwelling medical devices known in the art. In particularly preferred embodiments, however, the medical device is selected from the group consisting of:
         (a) a catheter (e.g. a urinary catheter, venous catheter, arterial catheter dialysis catheter);   (b) a cannula;   (c) a drain;   (d) a stent;   (e) a pacemaker; and   (f) an electrode.       

     In a preferred embodiment, the device has an outer surface that is protected by a stack of two or more sequentially detachable covers. A first, innermost, cover is in direct contact with the outer surface of the device. A second detachable cover is in contact with the first cover, so that the first cover is between the second cover and the surface. Additional covers may also be present, as required. At any time after insertion of the device into the body, the outermost cover may be detached from the surface and removed from the body, leaving the device in place with one less cover over the surface. The newly exposed outermost cover may, later on, be detached from the surface and removed from the body. This process may be repeated until all of the covers have been removed. When using multiple covers, the covers may be made from the same material as the surface of the device or from a different material. The covers may be identical or different. They may be made from different materials or the same material. The thickness of each layer may be the same or different. 
     A detachable cover for a device may be made using a pre-formed cover that is applied to the surface. A cover may be formed having a lumen that is dimensioned to receive the entire device, or a portion of it in the lumen. Alternatively, a liquid coating substance may be applied to the device or to a portion of its surface and allowed to solidify by curing, polymerizing, or drying. For example, a 2:1 solution of silicone rubber:toluene may be applied to the surface and allowed to dry and cure. The coating substance may be applied to the device or an outermost detachable cover previously applied to the surface, for example, by brushing, immersion, spraying, or any other method of deposition. 
     Two adjacent members (a detachable outermost cover and the surface of the device, or two adjacent detachable covers on a multiple coated device), may be reversibly attached to each other by any known method. For example, an adhesive may be introduced between the members and allowed to cure. The bond formed by the adhesive is subsequently broken when desired, for example, by applying an axial or radially outward force to the outermost member so as to break the bond. Alternatively, the bond may be broken by introducing a fluid between the members that breaks the bond either chemically or mechanically. As yet another alternative, the bond may be broken over time, either spontaneously or during prolonged contact of the adhesive with body fluids such as blood plasma or urine. 
     The reversible attachment of the two adjacent members may extend along the entire contact area between the members, or only at specific regions between the members. For example, one or more clips may be disposed on the device that presses the outermost cover to the underlying member at various locations. The clips may be formed, for example, by a rubber ring that may be rolled onto the outermost layer. The outermost layer is detached by cutting the ring or by rolling it off the outermost layer. The clip may be a toroidal balloon that constricts the members when inflated and releases the attachment when deflated. 
     A detachable cover may be made from an elastic material. An elastic cylinder may be stretched over the shaft of a catheter or over detachable covers already present on the shaft and allowed to contract with the shaft and any previously existing detachable covers in its lumen. In this case, a reversible attachment is formed between the new cover and an adjacent member by the elastic forces of the new outermost cover. The attachment may be broken by making a longitudinal cut along the outermost cover. The cover may have one or more lines of preformed perforations that are easily torn by splaying apart an end of the coating. 
     The mechanical removal of the detachable cover(s) may also be achieved by means of the use of a fixed, proximally-located knife blade. This blade is shaped and disposed such that the proximal end of the outermost cover may be pulled towards the blade, and subsequently split longitudinally by the action of the stationary blade on the proximally-drawn cover. In this manner, the apposition and attachment of the outermost cover to the adjacent cover or external surface of the indwelling device is disrupted, thus allowing the removal of said outermost cover from said device and from the body. 
     The space between the device and a cover or between two adjacent covers may contain material to reinforce the attachment or to enhance relative sliding. The material may repel deposits, and/or contain pharmaceutically-active agents, including but not limited to anti-microbial agents such as antibiotics. The interface material can be the same or different, for each pair of adjacent members. For example, mineral oil may be present to enhance sliding and prevent penetration of contamination between the members. 
     In a particularly preferred embodiment of the device of the present invention, sealing elements are present at the distal and/or proximal extremities of the covered device. The presence of these sealing elements prevents the ingress of liquids such as blood, urine, tissue fluid and so on into the space between pairs of adjacently-disposed covers or into the space between the innermost cover and the external surface of the medical device itself. 
     In another aspect, the present invention is also directed to indwelling medical devices having an inner or luminal surface, at least a portion of which is protected by either one manually detachable cover or a stack of two more sequentially detachable covers. This particular embodiment of the device of the invention is particularly suitable for use in applications where it is desirable to prevent the formation and growth of blood clots on the luminal surface of indwelling devices such as venous and arterial catheters. During insertion, the cover is attached to the surface so as to prevent relative movement of the surface and the cover. This allows the integrity of the device and cover to be maintained during insertion. Once the covered internal device (e.g. internal surface of a catheter or drain) has been inserted into the desired operating location, said device may be manipulated or operated in the normal manner, without any hindrance or loss of functionality arising from the presence of the cover. At any time after insertion, the cover may be detached from the shaft and removed from the body, leaving the device in place. Removing the cover from the device removes any blood clots, contamination and other biofilm deposits that may have accumulated on the cover. All of the various different embodiments and technical features described above in relation to the devices having external covers also apply to the devices having internal covers as described immediately hereinabove. 
     In a further aspect, the present invention also provides a method for preventing biofilm buildup on the surface of an indwelling medical device that has been inserted into the body of a subject, said method comprising the steps of: 
     a) providing a medical device fitted with a detachable cover attached to at least a portion of its outer surface, such that the presence of said cover does not interfere with the intended function of said device; 
     b) inserting said device together with its attached cover into the body of the subject; 
     c) detaching the cover from the outer surface of the medical device and removing said cover from the body together with any biofilm deposited on the surface of said cover, while leaving the device inside the body such that it may continue to fulfill its intended function. 
     The present invention also provides a further method for preventing biofilm buildup on the surface of an indwelling medical device that has been inserted into the body of a subject, said method comprising the steps of: 
     a) providing a medical device fitted with a stack of two or more sequentially detachable covers, such that the innermost cover is attached to at least a portion of its outer surface, and wherein the presence of said stack of covers does not interfere with the intended function of said device; 
     b) inserting said device together with its attached cover into the body of the subject; 
     c) detaching the outermost cover from the stack of sequentially detachable covers and removing said cover from the body together with any biofilm deposited on the outer surface thereof, while leaving the device inside the body such that it may continue to fulfill its intended function; 
     d) subsequently repeating step (c) for the one or more remaining outermost covers. 
     In a preferred embodiment of the above-disclosed methods for preventing biofilm buildup on the surface of an indwelling medical device, said device is selected from the group consisting of: 
     (a) a catheter; 
     (b) a cannula; 
     (c) a drain; 
     (d) a stent; 
     (e) a pacemaker; and 
     (f) an electrode. 
     In one particularly preferred embodiment of the method of the present invention, the device is a urinary catheter. In another particularly preferred embodiment, the device is a venous catheter. In a further particularly preferred embodiment, the device is a dialysis catheter. 
     All the above and other characteristics and advantages of the present invention will be further understood from the following illustrative and non-limitative examples of preferred embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, preferred embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: 
         FIGS. 1   a - 1   d  show an indwelling device having a tearable cover in accordance with one embodiment of the invention; 
         FIGS. 2   a - 2   c  show an indwelling device having a cutable cover in accordance with another embodiment of the invention; 
         FIGS. 3   a - 3   d  show an indwelling device having a rollable cover in accordance with another embodiment of the invention; 
         FIGS. 4   a - 4   c  show an indwelling device having a helical cover in accordance with another embodiment of the invention; 
         FIGS. 5   a - 5   e  show an indwelling device having a cover attached with internal balloons in accordance with another embodiment of the invention; 
         FIG. 6  shows use of a clamp securing the distal end of a cover to a surface; 
         FIGS. 7   a  and  7   b  show an indwelling device having a cover attached on an inner surface; 
         FIGS. 8   a - 8   d  show an indwelling device having a tearable cover in accordance with another embodiment of the invention; 
         FIGS. 9   a - 9   c  show a system for preparing a cover on a mandrel in accordance with one embodiment of the invention; and 
         FIGS. 10   a - 10   h  show a system for transferring a cover from a mandrel onto a device. 
         FIGS. 11   a - 11   d  show an indwelling device having a cover attached to its outer surface, said cover being fitted with proximal and distal sealing elements and a fixed cutting blade. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The invention will now be described by non-limiting embodiments. For the sake of clarity, the invention is exemplified by devices having a slender shaft such as catheters, cannulae, and drains. This is by way of example only, however, and the invention is not limited to such devices. Other devices having detachable covers are included within the scope of the invention, such as implants, stents, and pacemakers. 
     First Embodiment 
       FIG. 1   a  shows an indwelling device  100  in accordance with a first embodiment of the invention. The device  100  has a proximal end  102 , a distal end  104 , and a cylindrical shaft  105  that may be solid or hollow. The shaft  105  is contained in an outer cover  110  having the general shape of a thin cylindrical shell. The outer cover  110  is formed from a biocompatible, elastic material, such as latex, that was stretched over the shaft  105 , and allowed to contract on the shaft  105 . The outer cover  110  is reversibly attached to the shaft  105  by circumferential elastic forces in the outer cover  110  that are exerted on the shaft  105 . This prevents slipping of the outer cover  110  over the shaft  105  during insertion of the device  100  into the body, and maintains the outer cover  110  on the shaft  105  after insertion. 
     The outer cover  110  is formed from two materials. The first material is used to form the cover except in a narrow strip  125  that is formed from a second material. The two materials are joined at two parallel seams  120   a  and  120   b  extending along the length of the outer cover  110 . The strip of  125  formed from the second material preferably extends circumferentially for less than one quarter of the circumference of the outer cover  110 . The first material has a relatively high tear stress, for example, a silicone rubber having a tear stress of 25 to 50 kN/M. The second material is a material having a relatively low tear stress, such as a silicone rubber with a tear stress of less than 5 kN/M. The preparation of silicone rubbers and other materials having a particular tear stress are known in the art. 
     Between the shaft  105  and the outer cover  110  is a cord  130 . The cord is attached at one of its ends to the distal end of the strip  125 . At its other end, the cord extends beyond the proximal end of the coating. A ring  150  holds the end of cord  130  on the shaft  105 . As shown in  FIG. 6 , the device  100  may optionally comprise a distally located annular clamp  610  that secures the distal end of the outer cover  110  to the shaft  105  and prevents debris from accumulating under the distal end of the outer cover  110  during insertion. 
       FIG. 1   b  shows the catheter of  FIG. 1   a  after insertion into the body. The catheter  100  was inserted into the body through a hole  135  on the body surface  140 . The hole  135  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the cord  130  extends through the hole  135  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the cord  130 . Relative movement of the shaft  105  and the outer cover  110  is prevented during insertion due to the circumferential elastic forces of the outer cover  110  on the shaft  105 . 
     At any time after insertion, the outer cover  110  may be detached from the device  100  by removing the ring  150  and pulling the distal end of the cord  130 . Pulling the cord  130  away from the body draws the distal end of the strip  125  into the space between the coating  110  and the shaft  105 , tearing the distal ends of the seams  120   a  and  120   b . ( FIG. 1   c ). As the cord  130  continues to be pulled, tearing of the seams  120   a  and  120   b  progresses from the distal end towards the proximal end, until the entire strip  125  has been detached from the rest of the layer  110  and removed from the body ( FIG. 1   d ). This detaches the outer cover  110  from the shaft  105 . The proximal end of the torn outer cover  110  may now be grasped and manually removed from the body leaving the device  100  in place. If after removal of the outer cover  110 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
       FIG. 9  shows a system, generally indicated by  900 , for preparing the cover  110 . A reservoir  905  contains a first liquid suspension  910  for preparing the first material in the cover  110 . A cylindrical mandrel  915  is used upon which the cover  110  is to be formed. The mandrel  915  has a diameter corresponding to the inner diameter of the cover  110 . A length of the mandrel  915  is submerged in the suspension  910 . As the mandrel  915  is withdrawn from the suspension  910 , a layer  920  of the first material coating the mandrel is formed. 
     A wiper blade  925  is used to remove a portion of the coating  920  as the mandrel  915  is withdrawn from the suspension  910 . Above the wiper  925 , a narrow strip  930  of the surface of the mandrel  915  thus becomes exposed. 
     A second reservoir  935  contains a second suspension  940  that is used to form the second material of the coating  110 . The second suspension  940  is delivered to the surface of the mandrel  915  through a tube  945 . A nozzle  950  applies the second suspension to the exposed strip  930  of the mandrel  915  surface, as the mandrel  915  is withdrawn from the first suspension  910 . The second suspension  940  thus forms a coating  955  on the mandrel  915  in the exposed strip  930  created by the wiper  925 . 
       FIG. 9   c  shows the mandrel  915  after having been removed from the reservoir  905 . A cylindrical coating  960  has been formed on the mandrel  915 . The coating consists of the first portion  920  formed by the first suspension  910  and the second portion  955  formed by the second suspension  940 . The mandrel  915  is then placed in an oven in order to allow the coating to cure so as to form the cover  110 . The first suspension  910  thus formed the first material of the cover, and the second suspension  940  formed the second material. 
       FIG. 10  shows a system, generally indicated by  1000 , for transferring the cover  110  from the mandrel  915  to the shaft  105  of the device  100 . The system  1000  is shown in plan view in  FIG. 10   a  and in cross-section in  FIG. 10   b . The system  1000  has a housing  1005 . A cylindrical tube  1010  passes through the housing  1005  and has a diameter configured to alternately receive the coated mandrel  915  and the shaft  105  of the device  100 , as described below. 
       FIG. 10   b  shows the interior  1015  of the system  1000 . A cylindrical space  1020  surrounds the cylinder  1010 . The wall  1022  that is common to the space  1020  and the cylinder  1010  contains a plurality of pores  1025  allowing the flow of air between the interior  1015  of the cylinder  1010  and the space  1020 . When the ends of the cylinder  1010  are sealed, as described below, the chambers  1015  and  1020  may be evacuated by removing air in the chambers through a tube  1027  that is connected to a source of negative pressure (not shown). 
       FIG. 10   c  shows the system  1000  after the mandrel  915  has been inserted into the cylindrical tube  1010 . As described above, the mandrel  915  is contained in the cover  110  that is to be transferred from the mandrel  915  to the shaft  105  of the device  100 . 
     As shown in  FIG. 10   d , the ends  128  of the cover  110  are then rolled off the mandrel  915  and onto the ends of the tube  1010 , thus sealing the ends of the cylinder  1010 . The chamber  1020  is then evacuated causing the cover  110  to dissociate from the mandrel  915  and associate with the inner surface of the cylinder  1010 , as shown in  FIG. 10   e . Dissociation of the cover  110  from the mandrel  915  may be enhanced if the mandrel is formed with a hollow core  1030  that is confluent with the exterior by pores  1035  in the wall of the mandrel  915 , as shown in  FIG. 10   f . A source of positive pressure (not shown) is applied to the core  1030  by means of a tube  1040 . The mandrel is then removed from the cylinder  1010  leaving the cover  110  mounted on the inner surface of the cylinder  1010 , as shown in  FIG. 10   f.    
     Now the shaft  105  of the device  100  is inserted into the cylinder  1010  as shown in  FIG. 10   g . The source of negative pressure is then disconnected from the tube  1027 , causing the cover  110  to dissociate from the wall of the cylinder  1010  and associate with the shaft  105  of the device  100 , as shown in  FIG. 10   h . The ends of the cover  110  are then unrolled from the cylinder  1010  onto the shaft  105 , and the shaft  105  is removed from the interior of the cylinder  1010  with the cover  110  in place. 
     Second Embodiment 
       FIG. 2   a  shows an indwelling device  200  in accordance with another embodiment of the invention. The device  200  has a proximal end  202 , a distal end  204 , and a cylindrical shaft  205  that may be solid or hollow. The shaft  205  is contained in an outer cover  210  having the general shape of a thin cylindrical shell. The outer cover  210  is formed from a biocompatible, elastic material, such as latex, that was stretched over the shaft  205 , and allowed to contract on the shaft  205 . The outer cover  210  is reversibly attached to the shaft  205  by circumferential elastic forces in the outer cover  210  that are exerted on the shaft  205 . This prevents slipping of the outer cover  210  over the shaft  205  during insertion of the device  200  into the body, and maintains the outer cover  210  on the shaft  205  after insertion. 
     As shown in the insert  FIG. 2   a -I of  FIG. 2   a , the shaft has a longitudinal groove  215  that forms a track for a blade  220 . The blade  220  is slidable along the groove  215 . During insertion into the body, the blade  220  is positioned at the distal end of the groove  215 . Between the shaft  205  and the outer cover  210  is a cord  230 . The cord is attached at one of its ends to the blade  220 . At its other end, the cord  215  extends beyond the proximal end of the coating. 
       FIG. 2   b  shows the device  200  after insertion into the body. The device  200  was inserted into the body through a hole  235  on the body surface  240 . The hole  235  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the cord  230  extends through the hole  235  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the cord  230 . Relative movement of the shaft  205  and the outer cover  210  is prevented during insertion due to the circumferential elastic forces of the outer cover  210  on the shaft  205 . 
     At any time after insertion, the outer cover  210  may be detached from the device  200  by pulling the proximal end of the cord  230 . Pulling the cord  230  away from the body draws the blade  220  towards the proximal end of the shaft  205  thus making a longitudinal cut  233  in the cover  210 . ( FIG. 2   c ). A guard  222  ( FIG. 2   a -I) on the blade prevents the blade from cutting any underlying covers. As the cord  230  continues to be pulled, cutting of the cover  210  progresses from the distal end towards the proximal end, until the cut extends along the entire length of the cover  210 . This detaches the outer cover  210  from the shaft  205 . The proximal end of the cut outer cover  210  may now be grasped and manually removed from the body leaving the device  200  in place. If after removal of the outer cover  210 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Third Embodiment 
       FIG. 3   a  shows a device  300  in accordance with another embodiment of the invention. The device  300  has a proximal end  302 , a distal end  304 , and a cylindrical shaft  305 . The shaft  305  is contained in an outer cover  310  having the general shape of a thin cylindrical shell. The outer cover  310  is formed from a biocompatible, elastic material, such as latex. The outer cover  310  was formed from an inner cylindrical shell  322  and an outer cylindrical shell  324 . The inner and outer shells  322  and  324  are welded together at a first circular seam  326  at its distal end and a second circular seam  327  at its proximal end. The outer cover  310  was stretched over the shaft  305 , and allowed to constrict on the shaft  305 . The outer cover  310  is reversibly attached to the shaft  305  by circumferential elastic forces in the outer cover  310  that are exerted on the shaft  305 . This prevents movement of the outer cover  310  relative to the shaft  305  during insertion of the device  300  and maintains the outer cover  310  on the shaft  305  after insertion. 
       FIG. 3   b  shows the device of  FIG. 3   a  after insertion into the body. The catheter  300  was inserted into the body through a hole  335  on the body surface  340 . The hole  335  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). The proximal end of the outer cover  310  extends through the hole  335  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the outer cover  310 . Relative movement of the shaft  305  and the outer cover  310  is prevented during insertion due to the circumferential elastic forces of the outer cover  310  on the shaft  305 . 
     At any time after insertion, the outer cover  310  may be detached from the device  300  by causing the outer cylindrical shell  324  to slide proximally over the inner cylindrical shell  322 . As shown in  FIG. 3   c , this may be accomplished by placing a thumb  330  and an index finger  332  on the outer cylindrical shell  324  and urging the outer cylindrical shell  324  to slide proximally over the inner cylindrical shell  322 , as indicated by the arrow  342  This draws the distal end of the inner cylindrical shell  322  into the outer shell  324 , while the remainder of the inner shell remains stationary, relative to the shaft  305 . As the outer shell  324  continues to slide proximally, the shaft  305  becomes progressively more exposed at its distal end, as shown in  FIG. 3   d . This process continues until the shaft  305  has been completely exposed and the outer cover  310  has been removed from the body. If after removal of the outer cover  310 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Fourth Embodiment 
       FIG. 4   a  shows an indwelling device  400  in accordance with another embodiment of the invention. The device  400  has a proximal end  402 , a distal end  404 , and a cylindrical shaft  405  that may be solid or hollow. The shaft  405  is contained in an outer cover  410  having the general shape of a thin cylindrical shell. The outer cover  410  is formed from a strip of biocompatible material, such as latex or silicone rubber. The outer cover  410  is formed by winding the strip of biocompatible material in a helical pattern around the length of the shaft  405 . Consecutive turns of the helix overlap so as to completely cover the shaft  405 . The distal end  411  of the strip is tucked under the first few turns of the helix, so as to immobilize the distal end of the strip as shown in the insert to  FIG. 4   a . The proximal end of the strip is held in place by a ring  425 . The ring  425  has a lumen dimensioned to fit snugly on the shaft  405  and the proximal end of the outer cover  410 . This prevents slipping of the outer cover  410  over the shaft  405  during insertion of the device  400  into the body, and maintains the outer cover  410  on the shaft  405  after insertion. 
       FIG. 4   b  shows the device of  FIG. 4   a  after insertion into the body. The device  400  was inserted into the body through a hole  435  on the body surface  440 . The hole  435  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the device  400 , including the ring  425 , extends through the hole  435  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the device  400  and the ring  425 . Relative movement of the shaft  405  and the outer cover  410  is prevented during insertion due to the radial force of the ring  425  on the proximal end of the outer cover  410 , and the radial force of the last few turns of the helix on the distal end of the outer cover  410 . 
     At any time after insertion, the outer cover  410  may be detached from the device  400 . Referring to  FIG. 4   c , the ring  425  is removed from the shaft  405  and the outer cover  410  is unwound from its proximal end  408 . ( FIG. 4   c ). The outer cover  410  continues to be unwound, until the distal end of the outer cover  410  is freed. The proximal end of the outer cover  410  may now be grasped and manually removed from the body leaving the device  400  in place. If after removal of the outer cover  410 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Fifth Embodiment 
       FIG. 5   a  shows an indwelling device  500  in accordance with another embodiment of the invention. The device  500  has a proximal end  502 , a distal end  504 , and a cylindrical shaft  505  that may be solid or hollow. The shaft  505  is contained in an outer cover  510  having the general shape of a thin cylindrical shell. The outer cover  510  is formed from a biocompatible, rigid material, such as plastic or metal. One or more balloons  515  are located in a space  520  formed between the outer cover  510  and the shaft  505 . In  FIG. 5   a , the balloons are shown in their deflated state. As shown in  FIG. 5   b , before inserting the device  500  into the body, the balloons  515  are inflated with a fluid such as air or water. A syringe  525  containing the fluid  530  is inserted into a valve  570 . 
     The balloons are inflated by opening the valve  570  and depressing the plunger  550  of the syringe. The fluid  530  is conducted from the syringe  525  through a first tube  560  and then through a second tube  565  running along the shaft  505  and then into each of the balloons  515 . When inflated, the balloons apply a pressure to both the shaft  515  and the outer cover  510 . The valve  540  is then closed to prevent fluid from leaving the balloons. The outer cover  510  thus becomes reversibly attached to the shaft  505  by the balloons  515  that are lodged between the outer cover  510  and the shaft  505 . 
       FIG. 5   c  shows the device of  FIG. 5  and b after insertion into the body. The device  500  was inserted into the body through a hole  535  on the body surface  540 . The hole  535  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the device extends through the hole  535  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the cover  510 . 
     At any time after insertion, the outer cover  510  may be detached from the device  100  by deflating the balloons  515 . This may be done, for example, by inserting the syringe  530  into the valve  570  and drawing the fluid from the balloons so as to puncture the balloon by pulling on the plunger  550 . Once the balloons have been deflated, the proximal end of the device  500  may be grasped and manually removed from the body leaving the device  500  in place. If after removal of the outer cover  510 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Sixth Embodiment 
       FIG. 7  shows an indwelling device  700  in accordance with another embodiment of the invention. The device  700  has a proximal end  702 , a distal end  704 , and a hollow cylindrical shaft  705 . The shaft  705  has a lumen  708 . In this embodiment, the cover  710  lines the inner surface of the hollow shaft  705 . The lumen  708  contains a cover  710  having the general shape of a thin cylindrical shell covering the wall of the lumen  708 . The cover  710  is formed from a biocompatible, rigid material, such as plastic. The proximal end of the cover  710  is glued to the lumen of a restraining ring  711 . A circumferential clamp  750  around the ring  711  secures the ring  711  to the proximal end  702  of the device  700 . 
       FIG. 7   b  shows the catheter of  FIG. 7   a  after insertion into the body. The catheter  700  was inserted into the body through a hole  735  on the body surface  740 . The hole  735  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the device extends through the hole  735  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the device  700 . 
       FIG. 7   b  further shows removal of the outer cover. The ring  711  is detached from the proximal end  702  of the device  700 , and the ring  711  is removed from the device  700  together with the cover  710  attached to it. As the ring  711  continues to be pulled away from the proximal end  702  of the device  700 , the cover  710  becomes attenuated and detaches from the inner surface of the shaft lumen  708 . If after removal of the outer cover  710 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Seventh Embodiment 
       FIG. 8   a  shows an indwelling device  800  in accordance with a further embodiment of the invention. The device  800  has a proximal end  802 , a distal end  804 , and a cylindrical shaft  805  that may be solid or hollow. The shaft  805  is contained in an outer cover  810  having the general shape of a thin cylindrical shell. The outer cover  810  is formed from a biocompatible, elastic material, such as latex, that was stretched over the shaft  805 , and allowed to contract on the shaft  805 . The outer cover  810  is reversibly attached to the shaft  805  by circumferential elastic forces in the outer cover  810  that are exerted on the shaft  805 . This prevents slipping of the outer cover  810  over the shaft  805  during insertion of the device  800  into the body, and maintains the outer cover  810  on the shaft  805  after insertion. 
     The outer cover  810  has a line of perforations  820  extending along the length of the outer cover  810 . A ring  811  located on the shaft  805  contains a cord  830  that fixes the proximal end of the cover  810  onto the shaft  805 . As shown in  FIG. 6 , the device  800  may optionally comprise a distally located annular clamp  615  that secures the distal end of the outer cover  810  to the shaft  805  and prevents debris from accumulating under the distal end of the outer cover  810  during insertion. 
       FIG. 8   b  shows the device  800  after insertion into the body. The device  800  was inserted into the body through a hole  835  on the body surface  840 . The hole  835  may be a natural hole on the body surface (e.g. mouth, meatus, nostrils, etc.) or an artificial hole (e.g. a hole formed in the skin by a surgical incision). After insertion, the proximal end of the device  800  extends through the hole  835  and is exposed on the body surface. This is by way of example only, and the device may in use be completely enclosed within the body. In this case, a surgical cut is made in order to access the proximal end of the cord  830 . Relative movement of the shaft  805  and the outer cover  810  is prevented during insertion due to the circumferential elastic forces of the outer cover  810  on the shaft  805 . 
     At any time after insertion, the outer cover  810  may be detached from the device  800 . The cord  830  is released as shown in  FIG. 8   c . The proximal end of the perforation  820  is then torn. The cover  810  is then made to slide proximally over the shaft  805  as shown in  FIG. 8   d . This causes a new region of the perforation  820  to be exposed outside the body. This section of the perforation is then torn, and the cover  810  is then made to slide proximally over the shaft  805  ( FIG. 8   d ). This process continues until all of the perforation  820  is completely torn and the cover is removed from the body. If after the removal of the outer cover  810 , a new detachable outer cover (not shown) becomes exposed on the shaft, the newly exposed detachable layer may later on be removed from the device. 
     Eighth Embodiment 
       FIG. 11   a  depicts a further embodiment of the device of the present invention, comprising an elongate catheter  1100  bearing an outer cover  1110  on its external surface. The cover  1110  is situated in close apposition to the outer surface of catheter  1100  along almost the entire length thereof. In some versions of this embodiment, the cover may extend over the entire length of the device. In addition, two sealing elements—a distal sealing tip  1120  and a proximal sealing element  1130 —ensure that cover  1110  and the outer surface of catheter  1100  are in very close contact at their distal and proximal ends respectively, thus preventing the passage of possibly contaminating fluids (e.g. blood, urine, tissue fluid) between said catheter and said outer cover. In the typical device according to this embodiment shown in  FIG. 11   a , the distal sealing tip  1120  is elongate in shape, while the proximal sealing element  1130  is depicted as an annular ring.  FIG. 11   b  depicts an alternative version of elongated distal sealing tip  1120 . The function of the perforations  1140  present in the distal half of this version of the sealing element is to provide a fluid pathway for use in cases in which it is desired that substances such as pharmaceutical agents and the like will be released from the indwelling device into the blood stream, duct or tissues. In yet other alternative forms of the distal sealing tip  1120 , the internal side of the distal half of the sealing tip, in which are present one or more apertures or perforations, may be covered with a mesh, thereby providing mechanical support and strength without interfering with the desired fluid flow channel provided by said apertures. It is to be further noted that it is possible to use many other shapes and forms of sealing elements, all of which are included in the scope of the present invention. 
     According to one preferred embodiment of the invention, a thin layer of mineral oil or similar biocompatible fluid is present between each adjacent pair of covers (in the case that the device is fitted with a sequential stack of covers, as described hereinabove) and/or between the innermost cover and the indwelling medical device itself. The presence of the inter-layer oil is advantageous both in providing an extra mechanism for preventing the ingress of contaminating fluids, as well as acting as a lubricant in order to facilitate the removal of the layer(s) from each other and/or from the surface of the medical device. In the case that mineral oil is incorporated into the device as described herein, the sealing elements may usefully be constructed of an oil-absorbing material. 
     In one particularly preferred embodiment of this type of device, both the outer cover  1110  and the distal sealing tip  1120  are made of medical grade polyurethane. In such a case, however, the polyurethane used to construct the cover  1110  will usually be of a harder grade (i.e. have a higher Shore rating) than that used to manufacture the sealing tip  1120 . However, other biocompatible materials such as silicones, PVC, mylar and nylon may also be used to manufacture the outer cover  1110  and distal sealing tip  1120 . 
     The proximal sealing element  1130  is most conveniently manufactured from polyurethane, but any other suitable material such as silicones, PVC, mylar and nylon may also be employed, and as such fall within the scope of the present invention as claimed. 
     The abovementioned materials that may be used to construct the medical device (e.g. catheter), outer cover and proximal and distal sealing elements may be used in any of the available degrees of hardness and color (including colorless transparent). In addition, any of these materials may be prepared such that they incorporate radio-opaque substances, for use as markers, as is known in the art. The embodiment of the device shown in  FIG. 11   a  also incorporates a stationary cutting blade  1150  in its proximal, preferably extra-corporeal, portion. As shown in  FIG. 11   a , the proximal sealing element  1130  may be situated external to (and separate from) the blade. Alternatively, said element may be mounted close to the blade, within the blade housing itself (not shown). 
     Blade  1150  is used to assist in the removal of the outer cover  1110  (together with its attached biofilm deposits) in the following manner. Firstly, in the event that proximal sealing element  1130  is situated external to blade  1150  (as indicated in  FIG. 11   a ), said element is opened and removed from the device and (if necessary) from the body. In the event that the proximal sealing element exists as an integral part of the blade housing, this stage is not required. In a further version of this embodiment of the invention, the proximal sealing element is constructed such that it may adopt two different conformations. In the first of these conformations, the sealing element is capable of preventing ingress of fluids into the space between the proximal end of the covers(s) and the medical device. In the second of these conformations, the proximal sealing element adopts a position such that the tight seal between the cover and underlying medical device is lost in the region of said element, thereby facilitating the removal of the cover layer and any biofilm attached thereto. Consequently, when the device is constructed in this manner, the first stage of the cover removal process consists of changing the conformation of the proximal sealing element from the first conformation to the second conformation. 
     The proximal margins of the outer cover  1110  are then grasped between the operator&#39;s fingers and drawn in a proximal direction toward the blade  1150 . Upon making contact with the blade, outer cover  1110  is incised at its free edge. This initial incision becomes elongated as the proximal margins of cover  1110  are drawn still further in a proximal direction, until the entire length of said cover has been cut longitudinally, and removed from contact with the catheter  1100  and finally entirely withdrawn from the body. 
       FIG. 11   c  illustrates the shape and form of cutting blade assembly  1150  in greater detail. The distal, ramp-like portion  1160  of the blade possesses a rounded, non-sharp profile which leads into the cutting edge  1170  of the blade assembly. It will thus be appreciated that when, as described hereinabove, the outer cover  1110  is drawn in a proximal direction towards cutting blade assembly  1150 , the distal, ramp-like portion  1160  will serve to guide the free proximal margin of said cover towards cutting edge  1170 . This guiding mechanism serves to prevent the kinking or buckling of cover  1110  that might otherwise occur if the proximal margin of said cover were to encounter a sharp, angled blade. 
     The cutting blade  1150  may be constructed from any suitable material that will permit said assembly to function as described hereinabove. In a preferred embodiment, however, the material used to construct the cutting blade  1150  is constructed from a sharpened metal such as medical grade stainless steel. In other embodiments, the blade may be constructed from other suitable biocompatible metals, as well as from rigid plastic materials. 
     The cutting blade assembly  1150  may be mounted in a stationary position at any convenient point at the proximal end of the device. In a particularly preferred embodiment, as shown in the exploded view given in  FIG. 11   d , cutting blade assembly  1150  is located within a multiple luer lock fitting  1180 , of any of the types that are well known in the art. 
     It is to be emphasized that the various components described in this embodiment of the device of the invention (i.e. the distal and proximal sealing elements and the stationary cutting blade) may all be incorporated into a single device, as illustrated in  FIG. 11   a . Alternatively, a single device may incorporate only one or two of the three elements disclosed hereinabove. It should further be noted that the presently-described embodiment is suitable for use both in conjunction with a single cover and with a stack of covers, as is the case with the other embodiments disclosed and described hereinabove. 
     While specific embodiments of the invention have been described for the purpose of illustration, it will be understood that the invention may be carried out in practice by skilled persons with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.