SUBCUTANEOUS PORT AND CATHETER
The present invention relates to devices for delivering medicaments to a body, preferably subcutaneously, and in particular using subcutaneous ports attached to catheters.
Classically, medicaments that could not be taken orally, for instance because they reacted with acids in the stomach or were degraded by gut enzymes have been injected using a hypodermic needle and a syringe. The hypodermic needle could be inserted either subcutaneously if the medicament was to be placed just under the skin or in the muscle. Alternatively, a hypodermic needle could be inserted directly into a vein in the case where the medicament needed to enter the bloodstream quickly or directly.
However, certain medicaments need to be given either frequently or in large doses. Frequent piercing of the skin, particularly in the small area available over a vein, causes scarring. Scarring has at least two problems associated with it. It is unsightly and it also makes that area of skin more difficult to pierce subsequently because of hardening of the skin in the scar area. Furthermore, recurrent venous cannulations damages veins and can lead to thrombosis, which is dangerous to the patient.
When administering medicaments intravenously, it is important that a hypodermic needle punctures the wall of the blood vessel as well as the skin. Possible targets on a human patient are small and limited and increasing areas of scar tissue make these available targets even scarcer.
Medicaments that need to be given in large doses can cause problems when they are delivered intravenously because a high concentration of the medicament may be found in a small volume of blood, causing unpredictable peak dose effects and that volume of blood to have different properties from normal blood, such as being thinner or thicker or having different flow properties. This can cause serious problems if the volume of blood with the high dosage of medicament finds its way to a sensitive area of the body, such as the brain or the heart or any other organ.
A solution to this latter problem has been proposed: large doses of medicament can be supplied subcutaneously (under the skin) such that the medicament would infuse slowly into the bloodstream. This is referred to as subcutaneous infusion. However, the present inventors have found that there is a
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problem with introducing a large amount of fluid under the skin, namely that a bubble or bulge may form under the skin or in the muscle, causing stretching and discomfort, thereby limiting the amount of medicament that can be administered at a single site.
Recently, the subcutaneous infusion of immunoglobulin (SCIG) has become widely used because of a lower incidence of adverse affects when compared to intravenous infi.jsion of this medicament. To overcome the risks associated with introducing large amounts of fluid under the skin, a process has been proposed wherein a pump is used slowly to infuse the medicament at a site under the skin using a needle. This infusion is performed slowly, which reduces accumulation of medicament within a small area of skin and prevents the bubble or bulge where the fluid builds up. However, this slow infusion of a dose of immunoglobulin may take over 90 minutes to perform and requires a pump. The latter is expensive and the procedure is time consuming, not to mention uncomfortable for the patient, even if several sites are chosen for immunoglobulin delivery and two or more pumps are used.
The problems of scarring near blood vessels and the problem of bulging due to fluid build up can be reduced using a subcutaneously implanted port in combination with a fenestrated catheter attached to the port. The port comprises a small reservoir that has a self-sealing membrane allowing the repeated insertion of hypodermic needles for the administration of drugs or fluids to the reservoir. The membrane can be injected hundreds of times before replacement of the port is required, and does not require scarring near to blood vessels. The fenestrated catheter distributes the fluid over a larger volume until the fluid is absorbed by the body, thus alleviating fluid build up.
However, implantation of such systems can be time-consuming, stressful for the patient, and/or damaging to tissue in the region of implantation. In addition, the injection target associated with the port can be highly localized, leading to high concentrations of scarring when a large number of injections to the port are carried out.
An object of the present invention is to improve methods and devices for introducing fluids to patients, particularly when the fluid needs to be frequently administered, or given in large doses.
According to an aspect of the present invention there is provided a device for enabling the administration and/or removal of fluids, the device comprising: a fenestrated catheter; and a subcutaneously implantable port in fluid communication with the fenestrated catheter, wherein: the port is switchable between a compressed state for insertion through the skin and an uncompressed state.
The fact that all of the parts of the device are subcutaneously implantable means that there are no parts that are emerging from the patient's skin, thus reducing the risk of infection or of catching the port on something if the patient moves. The device enables the infusion of a fluid over a larger area (or volume) than any of: a port on its own, a normal open-ended catheter used with a port, or a hypodermic needle on its own. This larger volume over which the fluid is administered means that bubbles or bulges are less likely to form and larger doses may be administered at a time.
The provision of a port that is switchable between a compressed state for insertion through the skin and an uncompressed state minimizes tissue damage during implantation, while facilitating the provision of a larger port, which provides greater scope for receiving large quantities of fluid and/or providing a larger injection target.
Where a larger injection target is provided, the risk of excessive localized scarring is reduced and the ease of use, particularly for self-injection, is improved.
According to a disclosed variation, the port may comprise a reservoir that is formed as an integral unit with the fenestrated catheter, thus improving manufacturing efficiency and longevity.
According to a further disclosed variation, the port comprises a self-sealing element on a first surface and a puncture resistant element on a surface opposite to the self-sealing element. This approach provides tactile feedback during injection, reducing the risk of insufficient or excessive insertion of the needle, and facilitating the provision of thinner ports, which reduce patient discomfort and/or facilitate the provision of larger injection targets without excessive patient discomfort.
According to a further disclosed variation, the port may comprise a resilient expansion member, preferably having a plane of minor symmetry. The plane of minor symmetry may preferably pass through (or very close to) a point of connection between the port and the catheter. More preferably, the plane of mirror symmetry substantially contains a line lying along an infinitesimal portion of the axis of the catheter starting from the point where the catheter connects to the port (i.e. the line represents the direction that the catheter points initially before it may curve away, for example to follow anatomical features). Preferably, the plane of mirror symmetry lies substantially perpendicular to the largest cross-section of the port. These arrangements help to avoid excessive torques between the port and catheter during insertion/removal, for example, thus improving reliability and/or longevity.
Preferably, the resilient expansion member adopts a substantially deltoid (kite-like) shape.
For subcutaneous administration of normal fluid medicaments, the combined length of the port and a catheter may be 10 to 3 0cm. Preferably, the combined length may be 15 to 25cm. More preferably the combined length is approximately 20cm.
Embodiments of the description will now be described, purely by way of example, and with reference to the Figures, in which: Figure 1 depicts an external injection port and catheter according to the state of the art; Figure 2A is a schematic top view of a switchable port and a fenestrated catheter, with the port in an uncompressed state; Figure 2B is a schematic side view of the port and catheter of Figure 2A; Figure 3A is a schematic top view the port and catheter of Figures 2A and 2B with the port in a compressed state for delivery; Figure 3B is a schematic side view of the port and catheter of Figure 3A; Figure 4A is a schematic top view of an alternative configuration of a switchable port and fenestrated catheter, with the port in an uncompressed state; Figure 4B is a schematic side view of the port and catheter of Figure 4A; Figure 5 is a schematic top view of the port and catheter of Figures 4A and 4B with the port in a compressed state; Figure 6 is a schematic side view of an alternative configuration of a switchable port and fenestrated catheter, wherein the port comprises a self-sealing element, a resilient expansion member and a puncture resistant element; Figure 7A is a cross-sectional end view of a port in a compressed state mounted within a delivery catheter; Figure 78 is a cross-sectional side view of the port of Figure 7A in an compressed state; Figure 8A is a schematic depiction of a first step of a first insertion method, using a delivery catheter into which a port and fenestrated catheter have been mounted;
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Figure SB is a schematic depiction of a second step of the first insertion method, in which the port and fenestrated catheter have been advanced using a plunger, and the delivery catheter has been partially withdrawn; Figure SC is a schematic depiction of a third step of the first insertion method, in which the delivery catheter has been fully withdrawn and the port and feriestrated catheter are in place beneath the skin; Figure 9A is a schematic side sectional view of a port and fenestrated catheter mounted within a delivery catheter for use in a second insertion method; Figure 9B is a schematic side view of the outside of the delivery catheter of Figure 9A, showing a perforated line for splitting of the delivery catheter during withdrawal of the delivery catheter; Figure 9C is a schematic side view of the delivery catheter of Figure 9B, showing an initial tearing of the delivery catheter along the perforated line; and Figure 9D is a schematic side view of the delivery catheter being removed, and progressively torn, to leave the port and fenestrated catheter in place.
Figure 1 shows an external port 2 attached to a catheter 4 according to the prior art. Flange 6 of the port 2 is sewn, taped or otherwise attached to the outside surface of a patient's skin. The catheter 4 is inserted into the skin in such a way that the open end 8 is positioned within a blood vessel. When a fluid is to be introduced to the blood vessel, a hypodermic needle is inserted into the open end 10 of the port 2 and the fluid travels down the catheter 4, out of the open end 8 and into the blood vessel. This system is useful where a patient is in hospital for the duration of the regime of their medication administration. However, this is not useful where the patient is not staying in a hospital, or wishes to be active (such as the case of a child).
This is because the patient must be careful not to knock or infect the port that is on the outside of their body and attached to a catheter that is inside it. Furthermore, this is suitable for a regime where small doses of medication need to be given frequently. If large doses need to be given, this is possible, but the application of the fluid must be done slowly to avoid the problems mentioned above and so administering large doses is cost-and time-consuming.
If a patient wishes to be active between doses of their medicament, or they are children, for example, who would like to play between doses and may be prone to activities that raise the risk of infection, the external port and catheter of the
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prior art would not be suitable. This is also true for people (such as children) who are not willing or able to stay still for long periods of time (e.g. over 90 minutes) while a large dose of medicament is administered.
One solution to these problems has been to implant subcutaneously a port in fluid communication with a fenestrated catheter. However, it has been difficult to implant a port that presents a sufficiently large surface area for injection with minimal tissue damage and discomfort.
The embodiments described below define various ways in which this problem can be addressed. The disclosed embodiments are based on the provision of port that is switchable between a compressed state for insertion through the skin and an uncompressed state, which the port will adopt when in position beneath the skin.
Figures 2A and 2B are top and side views, respectively, of such a port 12 in the uncompressed state, along with a fenestrated catheter 14 in fluid communication therewith.
The catheter 14 may contain a lumen running at least part of the length of the inside of the catheter 14. The lumen may constitute the means by which the catheter 14 is in fluid communication with the port 12. A preferred method of attaching the catheter 14 to the port 12 is with a luer lock. However, many types of attachment may be envisaged, including threaded respective portions, adhesive, friction, snap-fit, etc. Alternatively, the catheter 14 may be formed so as to be integral with a reservoir of the port 12 (an example of this configuration is described below with reference to Figure 6).
Rather than being configured to transmit fluid from the port straight to the end of the catheter (as in the prior art arrangement of Figure 1), the catheter 14 of this embodiment is provided with one or more fenestrations such that fluid that is injected into the port 12 is infused from at least one place within the length of the catheter 14 into a patient's body cavity or under the patient's skin.
The purpose of the fenestrations in the sides of the catheter 14 is to enable the administration of fluid from at least one place other than the end of the catheter 14, thus increasing the volume in which the fluid may be infused into the surrounding tissue or blood (if the catheter is inserted intravenously).
The larger volume of administration prevents fluid from building up in one location and allows all of the fluid to be injected relatively quickly. Various lengths of catheter 14 may be considered, depending on the dose of fluid that is to be
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administered and the desired length of time taken to administer this fluid, as well as to the volume in which the fluid may be administered safely.
The fenestrations may be evenly spaced holes along one or more sides of the catheter 14, or may even be positioned in a spiral around the whole perimeter of the catheter 14 as well as along its length. The fenestrations may be of uniform size or they may be increasing or decreasing in size along the length of the catheter 14. They may be round or any other shape that is possible to incorporate in a catheter wall.
Yet alternatively, the fenestrations may be very small such that they are the size of pores, causing the catheter 14 to be porous. The fenestrations may cause the catheter 14 to be semi-permeable. Fluid that has been injected into the catheter 14 via the port 12 may diffuse through the pores into the surrounding tissue. The pores may be made into a very flexible catheter material such that the catheter 14 may expand to contain the fluid and then contract, thus forcing the fluid out through the pores.
The fenestrations may be achieved by micro-machining or laser machining, punching, melting or any other method which is suitable for making small holes in what is usually a soft, flexible material such as mbber. The fenestrations may be made as part of the manufacturing process (e.g. moulding or extruding) of the catheter 14.
The number and diameter (or area) of the fenestrations may be chosen to allow infusion rates (i.e. the rate at which the fluid is taken up by the tissue) to be in an acceptable range for reasonable injection pressures compatible with hand injection from a standard syringe at the port end.
The port 12 preferably comprises a resilient expansion member 16 that is capable of forcing the port 12 to switch from the compressed state to the uncompressed state after the port 12 has been inserted through the skin. The resilient expansion member 16 may be formed from an elastic material, including one or more of the following: a metal, a polymer. The resilient expansion member 16 may be formed from 316L stainless steel, cobalt-chromium alloy, or titanium-based alloys, for
example.
In the uncompressed state, the port 12 preferably presents a relatively large surface area parallel to the surface of the skin, so as to present a relatively large target for injection, while being relatively thin in the direction perpendicular to the skin surface, so as to minimize possible irritation to surrounding tissue caused by the presence of the port 12. Figures 2A and 2B illustrate a typical configuration, in which the port 12 has a substantially circular cross-section when viewed perpendicular to the skin surface, and a substantially flat surface area when viewed parallel to the skin surface.
The resilient expansion member 16 may be configured to form a closed loop that substantially surrounds the rest of the port 12. In this way, the resilient expansion member 16 can pull the port 12 from the compressed state to the uncompressed state efficiently. For example, the resilient expansion member 16 may be configured such that, when the port 12 is viewed in a direction perpendicular to the largest cross-sectional area of the port 12 in the uncompressed state (i.e. in the direction perpendicular to the skin surface when the port is implanted under the skin), the closed loop substantially surrounds the majority of the largest cross-sectional area.
Figures 3A and 3]3 are schematic top and side views, respectively, of the port 12 and catheter 14 of Figures 2A and 2B, with the port 12 in the compressed state ready for insertion through the skin. This configuration might be achieved, for example, by inserting the port 12 and catheter 14 into the internal lumen of a delivery catheter (see Figures 8A and 8B). In this case, the inner walls of the internal lumen apply radially inward forces that balance the outward restoring forces from the resilient expansion member 16. When the port 12 is pushed out of the delivery catheter into the treatment site, the outward restoring forces from the resilient expansion member 16 will no longer be balanced and the port 12 will switch from the compressed state of Figures 3A and 3B back to the uncompressed state of Figures 2A and2B.
Generally, the largest cross-sectional area will be oriented so as to be parallel to the surface of the skin after implantation, so as to present the largest possible target area for injection of fluid into the port 12.
Figures 4A and 4B are top and side views, respectively, of an alternative configuration for a port 12 and catheter 14, with the port 12 in the uncompressed state.
Figure 5 shows the same port 12 and catheter 14, but with the port 12 in the compressed state. In this configuration, the port 12 comprises a resilient expansion member that adopts a substantially deltoid (kite-like) shape, with a plane of mirror symmetry of the deltoid (in the configuration shown, this plane is perpendicular to the page and contains the broken line 15) substantially containing a line that passes through the axis of the catheter 14 at the point where the catheter 14 connects to the port 12 (broken line 15). In this particular example, the deltoid form is adopted in both the compressed and uncompressed states, but alternative configurations may be such that the port adopts the deltoid form in only one of the two states, i.e. in the compressed state only or in the uncompressed state only.
A benefit of the deltoid shape is that it is relatively easy to manufacture in a form that can switch between an uncompressed state (as in Figures 4A and 4B) and a compressed state (as shown in Figure 5). In Figure 5, arrows 24 and 26 illustrate an example switching mode in which the port 12 is compressed laterally inwards (arrows 24) while at the same time extending forwards longitudinally relative to the point of connection 19 between the catheter 14 and the port 12. The longitudinally forward motion of the port 12 is necessary to accommodate an overall lengthening of the port 12 which occurs in this embodiment as the angles between the forward facing branches 16A, and between the backward facing branches 1613, of the resilient expansion member 16 are reduced as the port 12 is squeezed into the compressed state. However, the port 12 may be configured so that the transition between the compressed and uncompressed states occurs without any change in the length of the port. Alternatively the port may be configured so that the transition from the uncompressed state to the compressed state involves a shortening, rather than a lengthening, of the port in the longitudinal direction.
The increase in the degree of alignment, during compression, of the forward and backward facing branches 16A/16B of the deltoid shown is a specific example of an approach to implementing the compressed state that can be applied more generally (i.e. to shapes other than deltoids). The increased alignment may also be described as an increase in the length of the resilient expansion member 16 in the direction parallel to the axis of the catheter 14 at the point of connection between the catheter 14 and the port 12 when the port 12 is switched from the uncompressed state to the compressed state.
In the example of Figures 4A, 413 and 5, the port 12 is provided with rounded members 18 at the junctions between different branches 16A116B of the resilient expansion member 16, to avoid or reduce the occurrence of sharp corners, which might cause injury or irritation to the patient.
In the example of Figures 4A, 413 and 5, the body of the port 12 comprises support struts 20 that provide a degree of structural rigidity to the port 12. The support struts 20 lead to a flattened area 22, which in this particular example is rectangular when the port 12 is in the uncompressed state. The flattened area 22 helps to limit the depth of the port 12 (i.e. the thickness in the direction perpendicular to the skin surface when the port is implanted), thus reducing uncomfortable bulging and/or tissue stress. However, the struts 20 and flattened area 22 are optional.
The deltoid shaped port 12 is an example of a configuration in which a portion (most or all of the forward facing branches 1 6A) of the resilient expansion member 16 that is located on a side of the port 12 opposite to the point of connection 19 between the catheter 14 and the port 12 is angled obliquely towards (see arrow 1 7A) the point of connection between the catheter 14 and the port 12, so as to facilitate insertion of the device into a delivery catheter and/or removal of the device from a delivery catheter. The oblique angling facilitates insertion into a delivery catheter because it provides a portion against which the delivery catheter can interact when pushed longitudinally to apply an inwards force, Referring to Figure 4A, for example, it is clear that longitudinal movement of the delivery catheter 38 (to the right in the figure) will cause the delivery catheter 38 to engage at points 37 on the forward facing branches 16A of the resilient expansion member 16. Further longitudinal movement (to the right) will cause the delivery catheter 38 to apply an inward force to the forward facing branches 16A due to the angle at points 37, which will be transmitted to the rest of the port 12, causing the port 12 to switch towards the compressed state shown in Figure 5. The angled portion of the resilient expansion member 16 thus facilitates insertion of the port 12 into the delivery catheter 18 in the case where the port 12 is inserted into the delivery catheter 38 in the sense shown in Figure 4A.
Similarly, in the case where the port 12 is withdrawn from the delivery catheter 38 in the opposite sense to that shown in Figure 4A, i.e. via a longitudinal relative movement of the delivery catheter 38 to the left, the restoring force provided by the resilient expansion member 16, which tends to push the forward facing branches 16A of the resilient expansion member 16 outwards with respect to each other, will tend to assist the removal process by applying a longitudinal force to the delivery catheter 38 that is also directed towards the left.
The deltoid shaped port is also an example of a configuration in which a portion (most or all of the backward facing branches 16B) of the resilient expansion member 16 that is located on the same side of the port 12 as the point of connection 19 between the catheter 14 and the port 12 is angled obliquely away (see arrows 1 7B) from the point of connection 19 between the catheter 14 and the port 12, so as to facilitate insertion of the device into a delivery catheter and/or removal of the device from a delivery catheter. The functionality is analogous to that described above in relation to the forward facing branches 16A. The angled nature of the backward facing branches 16B tends to cause an inwards force to be applied to the port 12 when a delivery catheter is pushed over the port 12 from the right to the left (in the sense of the figure). Similarly, when a delivery catheter is withdrawn from the port 12 in the opposite sense (from left to right), the restoring force associated with outward movement of the backward facing branches 16B will tend to apply a longitudinal force (to the right) that assists removal of the delivery catheter.
The deltoid shaped port 12 shown is an example where removal from and/or insertion into a delivery catheter 38 is assisted both by forward facing and backwards facing portions of the port 12. However, this functionality can be provided by shapes that are not deltoid. Furthermore, the port 12 need not be configured so that it can assist with removal from and/or insertion into a delivery catheter 38 in both senses. In altcmative embodiments, the port 12 is configured assist removal from and/or insertion into a delivery catheter 38 in only a single sensor (for example with respect to insertion into a delivery catheter 38 that advances from a side opposite to the point of connection 19 between the fenestrated catheter 14 and the port 12, with respect to removal from a delivery catheter that withdraws from a side opposite to the point of connection 19 between the fenestrated catheter 14 and the port 12, with respect to insertion into a delivery catheter that advances from the same side as the point of connection 19 between the fcnestrated catheter 14 and the port 12, or with respect to removal from a delivery catheter that withdraws from the same side as the point of connection 19 between the fcnestrated catheter 14 and the port 12).
The deltoid shaped port 12 is an example of a more general class of port shapes based on having a plane of mirror symmetry that substantially passes through the point of connection between the fenestrated catheter and port or, preferably, substantially contains the axis of the fenestrated catheter at the point of connection between the fenestrated catheter and the port (i.e. contains a straight line that lies along or contains an infinitesimal portion of the axis starting from the point of connection between the port and the fenestrated catheter), when the port is in the compressed state and/or when the port is in the uncompressed state. Ports with this symmetry tend to lend themselves more naturally to easier insertion and/or removal from delivery catheters according to mechanisms such as those described above in respect of the deltoid shape example, or similar, due to the fact that the symmetry encourages symmetrical distortion and/or symmetrical restoring forces on compression. In addition, this symmetry helps to ensure that longitudinal forces applied to the port tend to act in a direction parallel to the axis of the fenestrated catheter at the point of connection between the fenestrated catheter and the port, the S direction also passing through, or near to, the point of connection between the fenestrated catheter and the port (particularly when the plane contains the axis of the catheter at the point of connection to the port). This configuration thus helps to minimize torques acting between the port and the catheter, which helps reduce undesirable twisting or distortion which could compromise longevity and/or the integrity of the fluid connection between the port and the fenestrated catheter.
Figure 6 is a schematic side view of a port 12 and a fenestrated catheter 14 showing an example internal structure of the port 12 in further detail.
The port 12 comprises a reservoir 32 in a central region. The reservoir 32 may comprise an internal lumen surrounded by a material that is substantially impervious to the fluid to be injected into the reservoir 32 (apart from an opening leading to the catheter 14). Alternatively, the internal lumen may be surrounded by a semi-permeable membrane. The semi-permeable membrane may be formed from a porous material, for example. By "semi-permeable membrane" what is meant is a membrane that allows some but not all substances to pass through it. For example, the semi-permeable membrane may be configured to allow some or all of the injected fluid to flow through the membrane while partially or completely preventing tissue fluid entering the membrane from the region outside of the membrane.
The reservoir 32 and fenestrated catheter 14 may be formed as an integral unit, e.g. in a single manufacturing step, for example by moulding, such that there is substantially no interface between the material of the reservoir 32 and the material of the fenestrated catheter 14. This approach facilitates manufacture and/or enhances longevity. The integral unit may be formed from a material that is substantially impervious to the injected fluid. Alternatively, the integral unit may be formed from a semi-permeable membrane that is configured to allow some or all of the injected fluid to pass though it (and, optionally, partially or completely prevent tissue fluid entering the membrane from the region outside of the membrane).
The port 12 may further comprise a self-sealing element 28 through which the fluid can be injected into the port 12 using a hypodermic needle. The self-sealing element 28 may be made of silicone or another material that may be pierced by a hypodermic needle, but that will reseal itself such that it may be used many times.
The self-sealing element 28 is typically mounted so as to cover the majority of the surface of the port 12 that will be closest to the skin after the port 12 has been implanted.
The port 12 may further comprise a puncture resistant element 30 that is mounted on the opposite side of the port 12 to the self-sealing element 28. The puncture resistant element 30 may be formed from a material that is substantially more difficult to pierce than the self-sealing element 28, such that for all normal injection pressures, the needle will not pass through the port 12 and into tissue beyond the port 12. The provision of a puncture resistant element 30 makes it easier for the person carrying out the injection to determine when the tip of the needle is in an appropriate position for himlher to start injecting fluid. The puncture resistant element 30 is substantially harder to pierce than the rest of the port 12 and so naturally provides tactile feedback when it is encountered. This reduces the possibility of fluid being injected when the tip of the needle is not in the reservoir 32 (either because the needle has not been advanced enough or because the needle has been advanced too far and has pierced all the way through the port 12). The possibility of damage to tissue lying beyond the port 12 is also reduced. The puncture resistant element 30 makes it possible for the port 12 to be made thinner in the direction parallel to the injection direction (perpendicular to the skin surface) because any potential increase in difficulty of use due to the narrower range of depths at which injection into the port 12 can be successful is compensated for by the tactile feedback of the puncture resistant element 30. The appropriate depth for injection (when the tip has reached the puncture resistant element 30) is clearly signalled by the sudden increase in resistance against further inward motion of the tip.
In the example shown in Figure 6 the catheter 14 is connected to the port 12 at a position that is higher than the centre of mass of the port 12 to allow the resilient expansion member 16 to fully encircle the reservoir 32 at the level of the centre of mass of the port 12. However, in alternative embodiments, the catheter 14 is connected to the port 12 at the same level as the centre of mass andlor at the same level as the resilient expansion member 16. In further alternative embodiments, the catheter 14 is connected to the port 12 at a position that is lower than the centre of mass of the port 12 (i.e. further away from the skin when implanted).
Figures 7A and 7B illustrate an alternative configuration for the port 12.
Figure 7A is a schematic, cross-sectional view of the port 12 in a compressed state within a cylindrical inner lumen of a delivery catheter 38. Figure 7B is a schematic side view of the port of Figure 7A in the uncompressed state. In this example, the self-sealing element 28 forms a concave surface extending across an opening in the reservoir 32. The resilient expansion member 16 forms a closed ring around the outer periphery of the reservoir 32. The reservoir 32 is configured to deform on upper and lower surfaces to form upper and lower bulbous regions containing respectively the self-sealing element 28 and the lower surface of the reservoir (which may optionally comprise a puncture resistant element 30).
As mentioned above, the port 12 and fenestrated catheter 14 may be implanted through the skin using a delivery catheter 38. A set may therefore be provided which comprises a port 12, a fenestrated catheter 14, and a delivery catheter 38.
Figure 8A to 8C illustrate an example sequence for a method of implantation of the device. A delivery catheter 38 having a substantially cylindrical inner lumen is provided. In the configuration of Figure 8A, the port 12 and fenestrated catheter 14 are fully loaded (contained) within the delivery catheter 38. The port 12 is positioned behind (further from the skin than) the catheter 14. The system is thus configured so that the catheter 14 is inserted through the skin first, with the port 12 following afterwards. However, alternative configurations may be based on introducing the port 12 first followed by the catheter 14.
In the configuration of Figure 8A a tip of the delivery catheter has been inserted thiough a surface layer 36A of the skin. Optionally, the tip is inserted through a prior formed incision of suitable size. A piston 40 is provided within the lumen of the delivery catheter 38 behind the port 12. In the configuration of Figure 8A, the piston 40 is in a withdrawn position.
Figure SB illustrates a stage in the insertion process subsequent to that shown in Figure 8A. Here, the piston 40 has been pushed forwards causing the port 12 and catheter 14 to advance. The catheter 14 in this example is now substantially clear of the delivery catheter 38. At the same time as the piston 40 is pushed forwards the delivery catheter 38 is gradually withdrawn (arrow 42).
In a final step, the delivery catheter 38 is completely removed from the incision, leaving the port 12 and catheter 14 in the implanted state, between the surface layer 36A of the skin and a deeper layer of tissue 36B. The port 12 will have expanded from the compressed state adopted within the lumen of the delivery catheter 38 (as in Figures 8A and 8B for example) to an uncompressed state (Figure 8C) when released from the confines of the lumen in the implanted state. As described above, a resilient expansion member may assist the transition from the compressed state to the uncompressed state.
Figures 9A to 9D illustrate an alternative implantationlinsertion approach, in which a portion of the delivery catheter 38A138B that houses the port 12 and fenestrated catheter 14 (andlor the whole delivery catheter 38A138B) is completed implanted within the body and subsequently removed leaving the port 12 and fenestrated catheter 14 in place.
Figure 9A is a schematic side sectional view of a delivery catheter 38A138B suitable for use in this method. The delivery catheter 38A138B comprises a first portion 38A capable of housing the port 12 and a second portion 38B, cross-sectionally smaller than the first portion 38A, for housing the fenestrated catheter 14.
The delivery catheter 38A/3 SB is configured to be tearable along a longitudinal line in such a way that the second portion 38B can be pulled over of the port 12 in order to release the port 12 and fenestrated catheter 14 from the delivery catheter 38A138B.
Generally, it is envisaged that the delivery catheter 38A138B will tear progressively during the action of pulling the delivery catheter 38A138B past the port 12.
Figure 9B is a side view of the outside of the delivery catheter 38A138B showing an optional longitudinal tear line 44 for facilitating the tearing process. The longitudinal tear line 44 is configured to provide a lower resistance against tearing than other portions of the delivery catheter 38A138B. For example, the longitudinal tear line 44 may be thinner than other portions of the delivery catheter 38A138B.
Alternatively or additionally, the longitudinal tear line may comprise perforations.
Alternatively, the longitudinal tear line may be omitted.
Figure 9C is a side view of the outside of the delivery catheter 38A138B in the case where a tear 46 has been initiated in the first portion 38A of the delivery catheter 38A/38B, showing the port 12 beneath. A tear 46 may be initiated prior to any pulling or pushing of the delivery catheter 38A138B relative to the port 12 and fenestrated catheter 14, so as to facilitate further tearing (caused, for example, by movement of the port 12 through the second portion 38B of the delivery catheter) andlor help to encourage tearing along the longitudinal tear line (where provided).
Figure 9D is a side sectional view of a delivery catheter 38A138B implanted within a body 52, with the port 12 and fenestrated catheter 14 partly removed from the delivery catheter 3 8A13 8B due to a relative movement therebetween (indicated by arrows 48). Regions 50 show schematically where the delivery catheter 38A138B is being progressively torn as the relatively large port 12 is driven through the narrower second portion 38B of the delivery catheter 38A/38B. The process will be continued until the delivery catheter 38A/38B has been completely removed (at which point it will generally have been torn along its entire length).
In alternative embodiments, the delivery catheter 38A138B may be cut along its length directly (rather than relying on the pressure of the port 12 against the narrower second portion 38B of the delivery catheter 38A138B during removal), for example using a cutting instrument such as a knife, for example as the delivery catheter 38A138B is initially inserted.
The use of a delivery catheter is not essential. In alternative embodiments, for example, the fenestrated catheter is configured to be inserted beneath the skin directly.
Typically, this involves forming the fenestrated catheter of a material that is sufficiently rigid that it can easily be inserted though the incision without buckling.
However, if the fenestrated catheter is very soft, a rigid needle (e.g. made of stainless steel) is inserted first, to create a bore into which the fenestrated catheter may be subsequently inserted. Yet alternatively, a flexible fenestrated catheter may be inserted by being threaded over a rigid needle, the rigid needle being removed from the inside of the fenestrated catheter once the fenestrated catheter is in place. The port may be attached to the fenestrated catheter either before the fenestrated catheter is inserted, or afterwards. The port may be manufactured as one device with the fenestrated catheter. The port may be then tucked into the opening made by the incision, following the fenestrated catheter under the skin. If required, the incision is then sutured or closed by some other means.
To administer the medicament, a hypodermic needle is injected into the port 12 and hand pressure on a syringe or a pump is used to introduce fluid into the reservoir of the port 12. The fluid enters the catheter 14 and is then infused from the catheter t4 via the fenestrations into the surrounding tissue. The larger the number and spread of fenestrations, the larger the volume in the tissue into which the fluid will infuse, generally.
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Once the fenestrated catheter 14 is positioned correctly, the fluid can continue to be infrised optimally into a tissue merely by injecting the fluid into a single location at the implanted injection point. The implanted injection point (i.e. the self-sealing element 28) also offers a stationary target that does not scar as quickly as the surface of a vein, and so it is much easier for the person administering the fluid to be more accurate with the administration of the fluid. Furthermore, this makes self-administration of drugs or fluids much easier for a patient, as they do not need to look for veins or find new areas to inject, and the target provided by the port is easy to find and to use hygienically. In addition, because the port is configured to be inserted in a compressed state and only expanded into the fully expanded state after implantation, the surface area for injection can be made larger without causing excessive discomfort when the device is implanted. In addition, the fact that the port can be made flatter (due for example to the provision of the puncture resistant element 30) means that it can be made larger without causes unacceptable discomfort or tissue irritation.
The catheter may be made of any suitable material. Generally, catheters are made of flexible tubing which will not cause an immune response by the patient and which will allow a certain amount of movement as the patient moves. However, metal, plastic or other inert materials may also be considered if the situation so requires. For example, removing fluid from under a patient's skin may require a different material as compared with the administration of fluid. Different materials may be used for the catheter depending on where in the patient the catheter is intended to go; a stiffer catheter might be required to hard-to-access areas that are not immediately below the skin, or are protected by bone or other structures.
In order to determine the diameter of the catheter 14 and the number, size and position of the fenestrations, the properties of the fluid that is to be administered are considered. The most important property of a liquid that determines its behaviour when flowing under pressure through small tubes is its viscosity. Most liquids exhibit a thickening at lower temperatures and so the viscosity at room and body temperature must both be considered. Whether or not the fluid is a Newtonian fluid is also important in predicting how its viscosity will change over different temperatures and pressures. For example, long-chain molecules or bulky molecules may well not be Newtonian fluids, arid may undergo surprising transformations when compressed.
A second property that affects fluid behaviour in capillaries and orifices is surface tension. Specifically, the size and behaviour of droplets of fluid as they emerge from the fenestrations of the catheter 14 will depend on the surface tension of the fluid injected.
Typical infusion pressures when injecting fluids by band or by infusion pumps are in the range of 100-350 mmHg, or 100-500 cniH2O. A desired injection rate would be to inject, for instance, a 3 ml dose in about 1 minute, at a typical infusion pressure. Assuming a constant pressure, it can be determined that (for instance) human normal immunoglobulin solution ("subgam"), with an average viscosity of 6.2 cP (centipoise) and an average viscosity of 66 mN/rn will have a flow rate of about 3 ml/min with a needle diameter of 0.241 mm (needle gauge 26) with a modest injection pressure of 150 mm Hg. The catheter will therefore need to be able to take this sort of pressure and flow rate. During experiments, it was found that an amorphous biomedical PEEK tube with an inner diameter of approximately 1.2mm was suitable for the purpose, with at least 15 holes each of at least 0.10mm diameter evenly spaced along its length.
The pressure applied at the port end is preferably enough to flush the fluid out through the fenestrations in the catheter so that the fluid does not simply pool in the catheter (or return into the port). One way to apply high pressure is by the pressure applied using the syringe. A second possibility is to provide a diaphragm within the reservoir that expands and is displaced by an amount when a fluid is introduced into the reservoir. The diaphragm may then, by its restoring force, apply pressure to the fluid in the port 12, thus pushing the fluid out of the port 12 and into the fenestrated catheter 14. Alternatively, the self-sealing element 28 itself may expand when the fluid is administered and have a restoring force that imparts pressure onto the injected fluid as the self-sealing element 28 returns to its original shape. It may thereby be the self-sealing element 28 that exerts the pressure to force the fluid out of the holes or pores in the fenestrated catheter 14 at the desired rate.
Yet alternatively, the fenestrated catheter 14 may be flexible enough to expand when a drug is introduced into it. The restoring force of the catheter may then be what gives rise to the pressure that causes the fluid or drug to be squeezed out of the fenestrations.
It can also be important that the fluid does not return to the port 12 under the pressure from the catheter 14 (or surrounding tissue), nor return into the catheter 14 from the port 12 if the device is being used to remove fluid from a patient. One way to ensure a positive flow is to include a one-way valve, for example at the point of the join between the port 12 and the catheter 14. The valve may be a simple flap that is flexible or openable in one direction but not the other. More than one valve can be used, with valves positioned at different places along the catheter. Alternatively, the pressure exerted by the port may be maintained using methods described above such that it is always higher than any negative pressure by the catheter.
In order to encourage the fluid to exit the fenestrations and not just flow out of the end of the catheter 14, the end of the catheter 14 can be plugged, for example with a hot-melt adhesive. Of course, any other method of sealing the end of the catheter 14 may be used or the catheter 14 may be manufactured with one closed end.
The skilled person will understand that the subcutaneous port and fenestrated catheter combination of the present invention is suitable not only for administering fluids, but also for removing fluids from a patient's body. For example, air or fluid trapped in a large area under the skin or at several positions under the skin may be removed more quickly than with a standard open-ended catheter. This is particularly tme where the air or fluid build-up is chronic and must be removed at several instances over a long period of time.