GB2120947A - Catheter assembly - Google Patents

Abstract

A catheter with a blunt tip is provided with a fairing to facilitate entry through tissue and thereafter to convert to a dispersible fluent form in contact with body fluid. An intended use is for suprapubic entry to the bladder, the relevant body fluid being urine. The catheter 10 is suitably inserted with the aid of an instrument 12 located in its lumen and projecting from the catheter tip as a trocar, the catheter and instrument having mutually engageable shoulders for entry, the fairing 15 being mounted around the trocar to flair the same to the tip, and the fairing being separable from the catheter upon instrument withdrawal. <IMAGE>

Description

SPECIFICATION Catheter assembly Catheters are commonly of blunted shape at the tip to reduce the possibility, when in situ, of irritation or damage to adjacent tissue which could otherwise be caused by sharp edges or shapes. However the use of a blunted tip can itself cause difficulty during entry of the catheter through the tissue to its intended location. This difficulty is partly ameliorated by the use of associated instrumentation for the purposes of entry, but some difficulty can remain. If, for example, the instrumentation involves a cannula through which the catheter is entered, the assembly is of greater diameter than the catheter per se and a correspondingly larger incision is made, and remains after withdrawal of the cannula: this may be undesirable.If, on the other hand, the instrumentation passes internally of the catheter to a trocar, the instrumentation must be of lesser overall diameter than the catheter to allow withdrawal proximally and there will still be a significant blunted discontinuity towards the tip of the assembly.

An object of the present invention is to improve this situation and to this end provides, in or for a catheter assembly, a fairing to facilitate entry of the catheter through tissue and thereafter to convert to a dispersible fluent form in contact with body fluid.

The invention has in fact been conceived in connection with a form of catheter usually referred to as an "Argyle" and it is convenient to describe the invention further in this context.

The argyle catheter is widely used for suprapubic entry through the abdominal wall into the bladder in order to drain the same in a patient suffering from urine retention. The catheter consists of a flexible tube with an opening at its tip of reduced diameter compared to the communicating lumen to form an inwardly facing shoulder. The catheter is used with an entry instrument in the form of a rod or other relatively stiff member passing therethrough and projecting from each end, the tip portion of this member being of reduced diameter, to provide a shoulder complementary to that of the catheter, and being tapered towards its tip to form a trocar. The trocar initiates entry of the assembly, with the shoulders of the catheter and instrument engaging to carry the former forwardly with the latter through the tissue, whereafter the instrument is withdrawn rearwardly.

The catheter tip has a blunted shape which creates a stepped configuration at its junction with the trocar and this configuration can produce a need for the application of a large force to effect tissue penetration nowithstanding the pre-entry of the trocar.

Moreover, when the tissue does part to allow entry of the catheter, the applied force is released and can cause the catheter to over-run and damage the opposite side of the bladder.

This particular difficulty is reduced by use of the present invention in a form comprising a fairing of urine-dispersible material mounted around the trocar to smooth the junction thereof with the catheter tip, the fairing being separable upon withdrawal of the entry instrument.

This last form of the invention is clarified by the accompanying drawings which are given by way of example and in which: Figure 1 schematically illustrates one embodiment of an Argyle catheter in assembly with an entry instrument; Figure 2 similarly illustrates the catheter assembly supplemented by a fairing according to the invention; and Figure 3 further illustrates the same assembly with the fairing separated upon withdrawal of the instrument.

The assembly of Figure 1 is largely selfexplanatory on the basis of the above description.

The flexible tube of the catheter is denoted at 10 and the inwardly facing shoulder at 11, adjacent the tip opening of reduced diameter. The entry instrument comprises a rod 12 stepped down through a complementary shoulder 13 to a trocar 14 projecting through the tip opening of the catheter.

It will be noted that the catheter tip is partly tapered by a chamfer or rounding, but this serves only to remove the sharp edge which may otherwise occur and still leaves a blunted shape forming a stepped configuration at its junction with the trocar.

In Figure 2 the catheter assembly is supplemented by the provision of a fairing component 15 of axially-bored frusto-conical shape. This shape is such that the fairing can be engaged over the trocar with the conical base abutting the catheter tip and the conical taper substantially smoothing the stepped configuration down to the trocar.

The fairing is to be separably mounted on the trocar and against the catheter such that it is disengaged when the entry instrument is withdrawn as shown in Figure 3 after entry of the catheter into the bladder. The fairing can, for this purpose, be mounted by a sliding fit. Alternatively, the fairing may be lightly adhered or otherwise held in place such that it is not readily dislodged during preinsertion handling but is, nevertheless, separated by withdrawal of the entry instrument without undue force.

Also, the fairing is to be made of a material which converts to a dispersible fluent form in contact with urine so that it becomes flushed from the bladder through the catheter during subsequent drainage.

This material should, of course, at the same time afford adequate mechanical integrity for the fairing to facilitate entry of the catheter.

Materials for this purpose can be made in accordance with Patent Application GB 210851 7A.

One example of such a material has been made and tested against a requirement for a machineable biodegradable tough hydrogel akin to hard rubber which would dissolve in urine in a period of two or three weeks. A sample of the tested hydrogel was prepared first by mixing 0.2520 g anhydrous FeCI3 with 8.6567 g of dried hexane triol which was dissolved in about 15 minutes in an oven at 95 C, whereafter 200.0 g of polyethylene glycol (Mn = 3100) as added and throughly mixed. Lastly, 43.3534 g of 3,4-dihydro-2H-pyran carboxylate derivative was added slowly while carefully stirring the mixture by hand, and the final mixture was poured into moulds and cured at 95 C for 41/2 hours.

In vitro testing involved placing a 0.5433 g slice of the cured hydrogel in a sealed sample bottle containing male human urine in an ambient condition and thereafter shaking the bottle once or twice a day Following initial swelling in a few hours, the hydrogel started to fragment after about 3-4 days and eventually degraded to a very fine powder after 14 days, which powder can be expected to be drained or excreted with urine. While this test result does not lead to total dissolution, the degradation appears to allow satisfactory dispersion.

It is interesting to note that a further 0.6890 g slice of the hydrogel placed in a sample bottle containing distilled water and kept in a shaker path at a constant temperature of 250C showed no visually discernible degradation during a period of 21 days.

Other testing with an embodiment as illustrated has been found to result in a 50-70% reduction in the force necessary to pierce tissue compared to the same assembly with no fairing.

While the invention has been described largely with reference to a particular form of catheter it will be appreciated that this is not intended as a limitation insofar as the invention can clearly find application to other forms subject to a similar difficulty in use.

Claims (5)

1. In or for a catheter assembly, a fairing to facilitate entry to the catheter through tissue and thereafter to convert to a dispersible fluent form in contact with fluid.

2. A catheter fairing or assembly according to Claim 1 wherein said body fluid is urine.

3. A catheter assembly comprising a catheter having a blunted tip and a lumen extending wholly longitudinally therethrough to an opening in said tip, an elongate member located in said lumen and terminating in a trocar projecting through said opening, said catheter and member having respective mutually complementary shoulder formations engageable to move the catheter forwardly with the member while allowing rearward separation of the member from the catheter, and a fairing mounted around said trocar to smooth the junction of the latter with said tip, said fairing being made of a material convertible to a dispersible fluent form in contact with urine.

4. An assembly according to Claim 3 wherein saidfairing is of substantially frusto-conical shape.

5. An assembly according to Claim 3 or 4 wherein said fairing is mounted to separate from said catheter upon separation of said membertherefrom.