GB2426199A

GB2426199A - Urinary catheter with reduced encrustation and blockage

Info

Publication number: GB2426199A
Application number: GB0510359A
Authority: GB
Inventors: Alexander Robert Ead Blacklock; Aniruddha Chakravarti
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-20
Filing date: 2005-05-20
Publication date: 2006-11-22
Also published as: GB0510359D0

Abstract

A urinary catheter comprises a tube 4 having a proximal opening for the outlet of urine and a distal opening 10 for the inlet of urine, and two electrodes 12, 14 inside the tube and connected to a power source 16, wherein a plane AA perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode. In use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation and subsequent blockage of the catheter. In a preferred embodiment the power source such as a watch battery is attached to the tube. Various preffered voltages, currents and dimensions are disclosed.

Description

Urinary Catheter

Technical field

The present invention relates to a urinary catheter comprising a tube having a proximal opening for the outlet of urine and a distal opening for the inlet of urine, and two electrodes inside the tube and connected to a power source, wherein a plane perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode. In use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation and subsequent blockage of the catheter. In a preferred embodiment the power source is attached to the tube.

Background art

Encrustation of long term indwelling urinary catheters is a well known problem resulting in catheter blockage. Consequently, urinary retention, incontinence due to catheter bypassing and sepsis endangers the quality of life of patients requiring long term urinary catheters and places considerable demands on the health care services in terms of recurrent catheter change, bladder washouts in the community, and hospital admissions for more serious problems like bleeding or sepsis.

Approximately half the patients undergoing this form of long term bladder management will experience recurrent encrustation and blockage of catheters.

Catheter encrustations resemble infection induced stones in their crystalline structure. Without wishing to be bound by theory, the encrustation process is believed to start with infection by ureasplitting bacteria, which colonise the eye and inner surface of the catheter, forming biofilm communities embedded in a polysaccharide matrix. Enzymatic hydrolysis of urea by bacterial urease generates an alkaline environment in which calcium and magnesium salts crystallize out and become trapped in the organic matrix which surrounds the bacterial cells, followed by alkali induced gel stabilized crystallization of calcium and magnesium phosphates. Amongst all urease producing organisms, Proteus mirabilis has been found to be most capable of blocking catheters with crystalline biofilms.

Attempts have been made to make urethral catheters less attractive to bacteria by applying coatings of hydrophiic hydrogels or antibacterial agents such as silver, with varied success.

The lethal effect of electric fields and iontophoresis on bacteria has been demonstrated by some investigators. An electric field is believed to cause a bactericidal effect by damaging the cell membrane of the organisms, resulting in leakage of the intracellular contents. The killing of organisms is not believed to be due to heating or electrolysis and is independent of the current density and energy input. lontophoresis is defined as the introduction of an ionised substance into intact cells or tissues using direct current. lontophoresis of silver, gold, platinum, copper, nickel and stainless steel using weak direct current has been found to be bactericidal and also able to eliminate Candida albicans in synthetic urine. This is believed to be due to the oligodynamic property of the heavy metal ions.

Oligodynamic properties are the ability of small amounts of heavy metals to exert a lethal effect on bacteria.

As a result of the bactericidal effect of an electric field, a number of catheters incorporating electrodes have been designed with the intention of preventing bacterial infection. For example, US 4 411 648 discloses a urinary catheter containing two internal heavy metal electrodes disposed proximate to the distal inlets of the catheter, the electrodes being connected to a remote external power supply. The catheter is designed to prevent catheter associated bacterial infection during the course of catheterjsatjon. A. Shafik (The electrified catheter, World J. Urol., 1993, vol. 11, pages 183-185) discloses a similar catheter containing two silver-silver chloride electrodes connected to a small 9V battery fixed to the abdomen of the patient. The catheter is used to decrease the incidence of catheter- induced urinary infections. Neither of these catheters, however, is designed to prevent catheter encrustation and blockage.

GB 2 339 696 and GB 2 339 698 disclose a urethral catheter comprising two electrodes located internally along the length of the lumen of the catheter, connected to a power supply mounted upon the catheter. The catheter is designed to prevent catheter encrustation and blockage. The electrodes in this catheter do not, however, extend as far as the distal inlets of the catheter so as to prevent catheter encrustation around the eye of the catheter.

There therefore remains a serious need for a urinary catheter, which is less prone to encrustation and subsequent blockage and therefore suitable for long term use.

Summary of the invention

A first aspect of the invention provides a urinary catheter comprising a tube having a proximal opening for the outlet of urine and a distal opening for the inlet of urine, and two electrodes inside the tube and connected to a power source, wherein a plane perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode, and wherein in use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation of the catheter. Preferably, the catheter further comprises a power source connected to the electrodes.

Preferably, the power source is attached to the tube.

For the purposes of the present invention, the term to intersect' means to be coincident with' in the sense that a plane perpendicular to the longitudinal axis of the tube is coincident with the distal opening and at least one electrode.

For the purposes of the present invention, the term encrustation' of the catheter refers to the build up of deposits upon the external and/or internal surfaces of the catheter such that, if left unchecked, the build up will eventually lead to a blockage of the catheter.

For the purposes of the present invention, the term attached to the tube' used in relation to a power source or battery refers to a power source or battery fixed to and supported by the tube.

A second aspect of the invention provides a urinary catheter comprising a tube having a proximal opening for the outlet of urine and a distal opening for the inlet of urine, two electrodes inside the tube, and a power source connected to the electrodes and attached to the tube, wherein a plane perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode.

Preferably, in use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation of the catheter.

Preferably, in either the first or second aspect of the invention, the urinary catheter is a urethral catheter.

Also preferably, the voltage of the power source is about I to 20V, more preferably about 3 to 15V, more preferably about 6, 7, 8, 9, 10, 11 or 12V, even more preferably about 8, 9 or IOV, most preferably about 9V. The current of the power source is preferably about 10 to 1000 mA, more preferably about 50 to 500 mA.

The current of the power source may be either continuous or pulsed, preferably it is continuous. The power source may be an AC (alternating current) or DC (direct current) supply, more preferably a DC supply.

In a preferred embodiment, the catheter has two distal openings for the inlet of urine.

Preferably, the two electrodes are located on substantially opposite sides of the longitudinal axis of the tube. If the catheter has two distal openings for the inlet of urine, preferable these are located on substantially opposite sides of the longitudinal axis of the tube. Preferably, the two electrodes arc located substantially equidistant from the two distal openings, preferably such that the two distal openings and the two electrodes are located substantially at right angles to each other.

Preferably, at least one electrode extends along the longitudinal length of the distal opening or distal openings, more preferably both electrodes extend in this way. As used herein, the term longitudinal length' of the distal opening refers to the length of that opening along the longitudinal axis of the tube.

Preferably, at least one electrode extends along the longitudinal length of the distal opening or distal openings and further towards the proximal end of the tube by at least about 1 cm, more preferably by at least about 2 cm. Preferably both electrodes extend in this way.

In a preferred embodiment, the power source is a battery, more preferably a watch battery. Preferably, the power source is attached to the most proximal 1/3 of the tube, more preferably to the most proximal 1/5 of the tube, such that in use the battery remains outside of the patient.

Generally, the electrodes are connected to the power source by wires. Preferably, the wires are located within the outer circumference of the tube, more preferably either on the internal surface of the tube or within the wall of the tube, most preferably the wires are located on the internal surface of the tube. Preferably, the wires are made from the same metal as the electrodes.

The catheter is designed such that in use the electrodes generate an electric field across the distal opening or distal openings. Urine passing through the distal opening or distal openings comes into contact with the electrodes completing the electric circuit by providing an electrolytic pathway. In this manner, the current provided to the electrodes generates an electric field across the distal opening or distal openings, which leads to the prevention, reduction or lessening of encrustation of the catheter.

Ideally, the catheter is suitable for long-term use, which means that the catheter can be used for at least 1, 2, 3, 4, 5 or 6 months without blocking. Preferably the catheter can be used for at least 6 months without blocking.

Preferably, the electrodes are located on the internal surface of the tube. Preferably, the electrodes are located substantially within the most distal 1/2 of the tube, preferably within the most distal 1/3 of the tube, more preferably within the most distal 1/5 of the tube.

Preferably, the electrodes are about 4 to 6 mm wide, more preferably about 5 mm.

Preferably, the electrodes are about 0.25 to 0.3 mm thick, more preferably about 0.28 mm. Preferably, the electrodes are about 2 to 3.5 cm long, more preferably about 3 cm.

In a preferred embodiment, the electrodes are made from metal, preferably the metal is silver, gold, platinum, copper, nickel or stainless steel, more preferably the metal is silver or platinum, most preferably the metal is silver. Preferably, at least one electrode is made from silver. The two electrodes need not be made from the same metal, however, preferably they are.

The tube may be made from any material suitable for use in forming a urinary catheter. Preferably the tube is made from plastic, silicone or latex, more preferably from silicone. Optionally, the tube is coated with silicone, Teflon or hydrogel.

In a preferred embodiment, the catheter further comprises means for holding the catheter in place during use. Preferably, the means for holding the catheter in place comprises an inflatable balloon. The inflatable balloon may be attached radially around the tube towards the distal end of the tube and it may be inflated or deflated during use of the catheter via a secondary fluid passageway.

A third aspect of the invention provides a method of preventing, reducing or lessening encrustation of a urinary catheter, the method comprising the steps of: a) inserting a catheter according to the first or second aspect of the present invention into a patient, and b) providing a current to the electrodes of the catheter.

Preferably, when the method of the invention is carried out, the electrodes generate an electric field across the distal opening or distal openings of the catheter thereby preventing, reducing or lessening encrustation of the catheter.

Brief description of the drawings

The present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective view of a preferred embodiment of a urethral catheter according to the present invention.

Figure 2 is a cross-sectional view of a preferred embodiment of a urethral catheter according to the present invention, illustrating the arrangement of the wires and the electrodes.

Figure 3 is a cross-sectional view of the preferred embodiment of Figure 2 taken along plane A-A.

Figure 4 is a graph showing the variation with time of the silver ion concentration in parts per million (ppm) measured by absorption spectroscopy in the urine in test models of the Example. The x-axis represents time in hours, the y-axis represents ppm.

Figure 5 is a graph showing the variation with time in urine pH of the control and test models of the Example. The x-axis represents time in hours, the y-axis represents the pH values of the urine samples (T test catheter, C = control catheter, CW = control catheter with electrodes not connected to DC source. 1, 2 and 3 = 1st, 2nd and 3rd experiment respectively).

Figure 6 is a scanning electron micrograph of a section of a control catheter (from the Example) across the eyelet.

Figure 7 is a scanning electron micrograph of a section of a test catheter (from the Example) across the eyelet.

Figure 8 is a scanning electron micrograph of a section of a control catheter (from the Example) 2 cm below the eyelet.

Figure 9 is a scanning electron micrograph of a section of test catheter (from the Example) 2 cm below the eyelet.

Detailed description of the invention

Figure 1 is a perspective view of a preferred embodiment of a urethral catheter 2 according to the invention. The catheter comprises a tube 4 having a proximal opening 6 for the outlet of urine and two distal openings 8 and 10 for the inlet of urine.

As illustrated in Figure 2, two electrodes 12 and 14 are located on the internal surface of the tube and connected to a power source 16. Both electrodes extend along the longitudinal length of the distal openings and further towards the proximal end of the tube by about 2 cm.

As illustrated in Figure 3, the two distal openings 8 and 10 are located on substantially opposite sides of the longitudinal axis of the tube, with the two electrodes 12 and 14 also located on substantially opposite sides of the longitudinal axis of the tube and substantially equidistant from the two distal openings 8 and 10, such that the two distal openings 8 and 10 and the two electrodes 12 and 14 are located substantially at right angles to each other.

The power source 16 is a 9V DC battery providing a current in the range of about to 500 mA. It is mounted towards the proximal end of the tube such that, during use of the catheter, the battery remains outside of the patient.

Both electrodes 12 and 14 are made of silver. The electrodes are connected to the power source by wires 18 and 20. Like the electrodes 12 and 14, the wires 18 and 20 are made of silver.

The catheter 2 further comprises an inflatable balloon 22 for holding the catheter in place during use. The inflatable balloon 22 is attached radially around the tube 4 towards the distal end of the tube and may be inflated and deflated during use of the catheter via a secondary fluid passageway 24. In this manner, when inflated, the balloon 22 is able to hold the catheter in place during use.

The catheter is suitable for long-term use. The tube 4 may be made from any material suitable for use in forming a urinary catheter, such as plastic, silicone or latex.

The catheter is designed such that in use the electrodes 12 and 14 generate an electric field across the distal openings 8 and 10. Urine passing through the distal Openings comes into contact with the electrodes completing the electric circuit by providing an electrolytic pathway. In this manner, the current provided to the electrodes 12 and 14 generates an electric field across the distal openings 8 and 10, which leads to the prevention, reduction or lessening of encrustation of the catheter 2.

Example

Using aseptic precautions under laminar air flow, a length of wire (0. 25mm diameter, 99.9% soft silver wires from The Scientific Wire Company, London) was passed through the lumen of a I 6F silicone catheter and brought out through the eyelet of the catheter until about 2cm of the wire was out of the eyelet. Another length was passed alongside the catheter and fixed to the sidewall with insulating tape, allowing 2cm to remain exposed alongside the eyelet. Such arrangement was made so that the wires remain insulated and separated all along the lumen of the catheter, allowing flow of current only across the eyelet. Three such catheters were prepared for each experiment, two of which were connected to a source of 9V DC supplying a steady current of I 50niA through a self- regulating circuit, the current being monitored with a galvanometer throughout the process. The third catheter was left wired but not connected to a power source. - 10-

The four bladder models used were glass fermentation flasks maintained at 37 C by a water jacket, as described by C. Winters et a!. (Some observations on the structure of encrusting bioflims of Proteus Mirabilis on urethral catheters, Cells and Materials, 1995, vol. 5, pages 245-253). They were sterilized by autoclaving and catheters were inserted into the flask through a section of silicone tubing ("urethra") attached to a glass outlet at the base of the flask. One model had a normal 16F silicone catheter as control, while the other three had 16F silicone catheters with silver wires of which two were connected to power sources. Thus, there was one "control" catheter, one "wired control" catheter and two "test" catheters for each experiment.

The catheter balloons were then inflated, securing the catheter in position and sealing the outlet from "the bladder".

Sterile artificial urine was pumped into the bladder by a peristaltic pump at O.5rnl/min. In this way, residual volume of 30m1 collected in the bladder below the eyelet of the catheter, and then flowed through the lumen into collecting bags with a closed drainage system. Artificial urine was used throughout the experimental procedure based on the artificial urine devised by D.P. Griffith et al. (Urease: the preliminary cause of infection-induced urinary stones, Invest. Urol., 1976, vol. 13, pages 346-350). The constituents are described in Table 1.

Table 1: preparation of artificial urine 1. Deionjsed water - autoclaved 2. 2.30 g/l di-sodium sulphate added, dissolved, then 0.49 g/l calcium chloride, 0.65 g/l magnesium chloride hexahydrate, 4.6Og/l sodium chloride, 0.65 g/l tn-sodium citrate dehydrate, 0.02 g/l di-sodium oxalate, 2.80 g/l potassium dihydrogen phosphate, 1.60 g/l potassium chloride, 1.0 g/l ammonium chloride and 25.0 g/l urea added in succession and dissolved using a magnetic stirrer.

3. pH adjusted to 6.10 4. gelatine 5 g/l then added and temperature raised to 50 C.

5. when gelatine has dissolved, solution is filtered through a sterile 0. 2 micron Sartorius capsule filter.

6. Tryptone soya broth then added to a final concentration of 1 g/l.

The test organism, Proteus mirabilis NSM6, had been isolated from a patient's encrusted catheter. For experimental purposes, cells were subcultured onto cysteine_lactoseelectrolyte deficient (CLED) agar (Oxoid, UK) from stock suspensions in 5% glycerol. Sets of models were assembled and bladders primed with 20m1 of artificial urine. They were then inoculated with I Oml of 4 hour urine culture of the test strain. After one hour to allow the organisms to establish themselves in the model, urine was supplied at 0.5m1/min.

The pH, viable bacterial cell count and silver ion concentration of the urine in the bladder chamber were checked in each model every 24 hours, samples being retrieved by a pipette from the top. The models were run until the catheters blocked. The time to blockage for each catheter was noted. The mean times to blockage were statistically analysed using analysis of variance. The experiment was repeated three times. Encrustation was assessed visually on a fourth set of catheters (run until one of the catheters blocked) using low vacuum scanning electron microscopy. Catheters were sectioned at the level of the eyelet and 2cm below the eyelet. These sections were mounted on carbon disks on aluminium stubs and viewed directly using low vacuum setting of a JEOL 5200 LV SEM at 20kV.

Results The control catheter blocked within 22 to 48 hours. The catheters which had silver wires not connected to a DC source behaved in the same manner, getting blocked in 24 to 48 hours. However, the test catheters, which had a constant flow of 150mA of direct current, took up to 156 hours to block. The minimal blockage time for the test catheters was 96 hours. Thus, the test catheters lasted about five to seven times longer than controls in an environment with low urine output and Proteus mirabilis infection. The difference in blockage times was found to be statistically significant

(p<O.OO2) (Table 2).

Experiment Time the catheters took to block in models number infected with Proteus mirabijis (hours) Control catheters Catheters with Catheters with with no electrodes electrodes but no electrodes and ____________________ current applied current applied 1 22 24 156 2 24 48 96 3 48 48 144 Mean Values SD 31 14.5 40 13.9 133 31.8 -

Table 2

The effect of electrification of catheters on the rate of blockage by encrustation.

The viable bacterial cell counts of the inocula were from 1.92 x iO to 2. 2 x iO cfu/ml. Bacterial colony counts in the urine with control catheters at blockage ranged from 3.2 x i08 to 2.73 x iO cfu/ml. In the urine with electrified catheters, the viable bacterial cell counts ranged from 9.89 x iO to 6.96 x 108 cfu/ml.

The silver ion concentration in urine with the catheter containing silver wires only was negligible. Silver ion concentration measured by absorption spectroscopy in parts per million gradually dropped every 24 hours in the urine in test models as the silver electrodes oxidised and turned black and brittle (see Figure 4).

Urine pH, which was 6.1 at the start in all models, sharply rose to between 8.5 and 9 in control models over a period of 24 hours, but stayed under 6.5 for up to 70 to hours in the test models and then rose to 8.75 (average) when the test models eventually blocked (see Figure 5).

Catheter encrustations were also visually evaluated by scanning electron micrographs of sections across the eyelets and 2cm below the eyelets when the control catheters blocked. The micrographs showed considerable encrustation starting at the eyelets and growing down the lumen in control catheters, whereas the test catheters were virtually encrustation free (see Figures 6 to 9).

Thus, successful iontophoresis was demonstrated by the concentration of silver ions in the urine with test catheters. The bacterial cell count increased from 1.92 x io cfu/ml in the inocula to 2.73 x iO cfu/ml in the control where bacterial growth was - 13 - unhindered, whereas in the test models iontophoresis or direct current per se was bactericidal, reducing the viable bacterial cell count down to 9.89 x 1O cfu/ml.

This has also been reflected in the p1-I of the urine in control and test catheters. As the urease producing organisms grew in the controls, the pH rose sharply, whereas killing of the organisms in the test models managed to keep the pH down to 6.5.

The most noteworthy phenomenon was seen as time elapsed. With the effect of constant direct current, the silver electrodes oxidised and turned black.

Consequently, the concentration of silver ions fell in the test sample, the pH of the urine started rising indicating bacterial growth, viable cell counts increased and eventually the catheters blocked. Therefore, as long as the silver electrodes were active they prevented the inevitable encrustation caused by bacterial colonisation at the eye of the catheters. This phenomenon also indirectly suggests that iontophoresis of metals is probably the most important factor in prevention of bacterial growth and encrustation rather than direct current per Se.

It will be understood that the present invention has been described above by way of example only. The examples are not intended to limit the scope of the invention.

Various modifications and embodiments can be made without departing from the scope and spirit of the invention, which is defined by the following claims only.

Claims

- 14 - Claims 1. A urinary catheter comprising: a) a tube having a

proximal opening for the outlet of urine and a distal opening for the inlet of urine, and b) two electrodes inside the tube and connected to a power source, wherein a plane perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode, and wherein in use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation of the catheter.
2. A catheter as claimed in claim 1, further comprising a power source connected to the electrodes.
3. A catheter as claimed in claim 2, wherein the power source is attached to the tube.
4. A urinary catheter comprising: a) a tube having a proximal opening for the outlet of urine and a distal opening for the inlet of urine, b) two electrodes inside the tube, and c) a power source connected to the electrodes and attached to the tube, wherein a plane perpendicular to the longitudinal axis of the tube intersects the distal opening and at least one electrode.
5. A catheter as claimed in claim 4, wherein in use a current is provided to the electrodes thereby preventing, reducing or lessening encrustation of the catheter.
6. A catheter as claimed in any of claims I to 5, wherein the urinary catheter is a urethral catheter.
7. A catheter as claimed in any of claims 1 to 6, wherein the voltage of the power source is about I to 20V.

- 15 -
8. A catheter as claimed in claim 7, wherein the voltage of the power source is about 3 to 15V.
9. A catheter as claimed in claim 8, wherein the voltage of the power source is about 6, 7, 8, 9, 10, 11 or 12V.
10. A catheter as claimed in claim 9, wherein the voltage of the power source is about 8, 9 or 1OV.
11. A catheter as claimed in claim 10, wherein the voltage of the power source is about 9V.
12. A catheter as claimed in any of claims I to 11, wherein the current of the power source is about 10 to 1000 mA.
13. A catheter as claimed in claim 12, wherein the current of the power source is about 50 to 500 mA.
14. A catheter as claimed in any of claims I to 13, wherein the current of the power source is either continuous or pulsed.
15. A catheter as claimed in claim 14, wherein the current of the power source is continuous.
16. A catheter as claimed in any of claims I to 15, wherein the power source is an AC or DC supply.
17. A catheter as claimed in claim 16, wherein the power source is a DC supply.
18. A catheter as claimed in any of claims 1 to 17, having two distal openings for the inlet of urine.

- 16 -
19. A catheter as claimed in claim 18, wherein the two distal openings are located on substantially opposite sides of the longitudinal axis of the tube.
20. A catheter as claimed in claim 18 or 19, wherein the two electrodes are located on substantially opposite sides of the longitudinal axis of the tube.
21. A catheter as claimed in any of claims 18 to 20, wherein the two electrodes are located substantially equidistant from the two distal openings.
22. A catheter as claimed in any of claims 18 to 21, wherein the two distal openings and the two electrodes are located substantially at right angles to each other.
23. A catheter as claimed in any of claims I to 22, wherein at least one electrode extends along the longitudinal length of the distal opening or distal openings.
24. A catheter as claimed in claim 23, wherein both electrodes extend along the longitudinal length of the distal opening or distal openings.
25. A catheter as claimed in any of claims I to 24, wherein at least one electrode extends along the longitudinal length of the distal opening or distal openings and further towards the proximal end of the tube by at least about 1 cm.
26. A catheter as claimed in claim 25, wherein the at least one electrode extends further towards the proximal end of the tube by at least about 2 cm.
27. A catheter as claimed in any of claims I to 26, wherein both electrodes extend along the longitudinal length of the distal opening or distal openings and further towards the proximal end of the tube by at least about 1 cm.
28. A catheter as claimed in claim 27, wherein both electrodes extend further towards the proximal end of the tube by at least about 2 cm.
29. A catheter as claimed in any of claims I to 28, wherein the power source is a battery.
30. A catheter as claimed in claim 29, wherein the power source is a watch battery.
31. A catheter as claimed in any of claims 1 to 30, wherein the power source is attached to the most proximal 1/3 of the tube.
32. A catheter as claimed in claim 31, wherein the power source is attached to the most proximal 1/5 of the tube.
33. A catheter as claimed in any of claims 1 to 32, wherein the electrodes are connected to the power source by wires.
34. A catheter as claimed in claim 33, wherein the wires are located within the outer circumference of the tube.
35. A catheter as claimed in claim 33 or 34, wherein the wires are made from the same metal as the electrodes.
36. A catheter as claimed in any of claims 1 to 35, wherein in use the electrodes generate an electric field across the distal opening or distal openings.
37. A catheter as claimed in any of claims I to 36, wherein the catheter is suitable for long-term use.
38. A catheter as claimed in claim 37, wherein the catheter can be used for at least 6 months without blocking.
39. A catheter as claimed in any of claims 1 to 38, wherein the electrodes are located on the internal surface of the tube. - 18-
40. A catheter as claimed in any of claims I to 39, wherein the electrodes are located substantially within the most distal 1/2 of the tube.
41. A catheter as claimed in claim 40, wherein the electrodes are located substantially within the most distal 1/3 of the tube.
42. A catheter as claimed in claim 41, wherein the electrodes are located substantially within the most distal 1/5 of the tube.
43. A catheter as claimed in any of claims I to 42, wherein the electrodes are about 4 to 6 mm wide, about 0.25 to 0.3 mm thick, and/or about 2 to 3.5 cm long.
44. A catheter as claimed in claim 43, wherein the electrodes are about 5 mm wide, about 0.28 mm thick, and about 3 cm long.
45. A catheter as claimed in any of claims I to 44, wherein the electrodes are made from metal.
46. A catheter as claimed in claim 45, wherein the metal is silver, gold, platinum, copper, nickel or stainless steel.
47. A catheter as claimed in claim 46, wherein the metal is silver or platinum.
48. A catheter as claimed in claim 47, wherein the metal is silver.
49. A catheter as claimed in any of claims 1 to 48, wherein at least one electrode is made from silver.
50. A catheter as claimed in any of claims I to 49, wherein both electrodes are made from the same metal.
51. A catheter as claimed in any of claims I to 50, wherein both electrodes arc made from silver.
52. A catheter as claimed in any of claims I to 51, wherein the tube is made from plastic, silicone or latex.
53. A catheter as claimed in claim 52, wherein the tube is made from silicone.
54. A catheter as claimed in any of claims I to 53, further comprising means for holding the catheter in place during use.
55. A catheter as claimed in claim 54, wherein the means for holding the catheter in place comprises an inflatable balloon.
56. A catheter substantially as hereinbefore described with reference to any one of Figures 1 to 3.
57. A method of preventing, reducing or lessening encrustation of a urinary catheter, the method comprising the steps of: a) inserting a catheter according to any of claims I to 56 into a patient, and b) providing a current to the electrodes of the catheter.
58. A method as claimed in claim 57, wherein the electrodes generate an electric field across the distal opening or distal openings of the catheter.