Catheters and methods of manufacture.

0001This invention relates to epidural catheters of the kind comprising a flexible plastics tube.

0002Epidural catheters are used to convey an anaesthetic agent to the epidural space of a patient. The catheter conventionally comprises a small bore, flexible, plastics tube the tip of which is introduced to the epidural space through a hollow metal needle that is subsequently removed.

0003The catheter must be sufficiently rigid to enable it to be manipulated and introduced without kinking but it must also be sufficiently flexible to enable it to be diverted, on insertion to the epidural space, without puncturing veins, dura or other obstacles.

0004The patient end of an epidural catheter usually opens in one of two different ways. It either has an axial opening at its tip, or a closed tip with several eyes through the wall of the catheter spaced apart from one another along the catheter in a region close to the tip.

0005Previous epidural catheters suffer from various problems. Firstly, it has not been possible, hereto fore, to achieve a low-cost catheter that is sufficiently flexible to prevent any risk of puncturing whilst also preventing the catheter kinking and ensuring occlusion free flow along the catheter. One form of catheter that attempts to address this problem comprises a tightly wound helical coil of wire embedded in the wall of the catheter to give it radial strength. The coils of the wire are opened out at the patient end to render it more flexible. This form of catheter is, however, expensive to make.

0006A second problem arises because, if the tip of the catheter does penetrate, for example, the dura, this may initially go undetected. It is usual practice for the anaesthetist to aspirate through the catheter to check for the presence of cerebro-spinal fluid (indicating penetration of the dura) or blood (indicating penetration of a vein). If this fails to indicate incorrect insertion, the anaesthetist will usually inject a small test dose (typically, about 2 cc) of anaesthetic agent which may also include adrenalin. If the catheter lies in the dura or a vein, this will cause a rapid, readily noticeable effect on the patient, indicating false insertion, without fatal consequences. Any blockage of the catheter will be apparent by increased resistance of the syringe used to aspirate or introduce the test dose. However, if the cannula has several eyes it may be that only one of these is blocked by being located in the dura, the other eyes being unblocked and located in the epidural space. It can be difficult to detect such a situation since flow can occur out of the catheter through the two unblocked eyes. Where anaesthetic agent is only injected slowly it may flow out of the patient end of the cannula entirely through the unblocked eyes, without harm to the patient. Where, however, a higher pressure, top-up dose, is given, the pressure may be sufficient to allow some of the drug to flow into the dura through the patient-end eye with often fatal results.

0007Those catheters opening through only the patient end tip, are more likely to be occluded. Furthermore, the open end of such catheters tends to encourage jetting at the tip.

0008It is an object of the present invention to provide a catheter that can be made at low cost with a more flexible tip so as thereby to reduce the risk of puncturing a view or the dura. It is another object of the present invention to provide a method of making such a catheter.

0009According to one aspect of the present invention there is provided an epidural catheter of the above-specified kind, characterised in that the tube has a plurality of elongate slits through the wall of the tube, that a substantial part at least of each slit extends along the same region along the length of the catheter at its patient end, and that slits are disposed around the circumference such that the flexibility of the catheter is thereby increased over the region.

0010The slits preferably extend parallel to one another and to the longitudinal axis of the tube.

0011According to another aspect of the present invention there is provided an epidural catheter comprising a flexible plastics tube, characterised in that the tube has at least one slit that extends helically about the tube at its patient end such that the flexibility of the patient end of the catheter is thereby increased.

0012The patient end tip of the catheter is preferably closed. The or each slit may be formed without removal of material. The catheter may include an aperture located rearwardly of the slits.

0013According to a further aspect of the present invention there is provided a method of making an epidural catheter comprising the steps of: providing a flexible plastics tube with an open patient end tip, forming a plurality of slits through the wall of the tube each slit extending from the open patient end tip along substantially the same region along the length of the tube and being separated from one another by segments of the tube, and closing the patient end tip of the tube by joining the patient end of the segments while leaving the slits open along a major part of their length such that the flexibility of the catheter is increased over a region at the patient end of the catheter.

0014The slits are preferably made by pushing the patient end of the tube along its length over an arrangement of crossed biades. The patient end of the segments are preferably subsequently joined together by end forming in a heated die.

0015An epidural catheter and a method of manufacture of the catheter, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Figure 1 is a side elevation view of the catheter;</li><li>Figure 2 is an enlarged transverse cross-section of the catheter along the line II-II in Figure 1;</li><li>Figure 3 illustrates the catheter in use;</li><li>Figure 4 are side views of the patient ends to 6 of alternative catheters;</li><li>Figure 7 and 9 illustrate steps in the manufacture of one form of catheter;</li><li>Figure 10 and 11 illustrate steps in the manufacture of another form of catheter; and</li><li>Figure 12 is a side elevation view of a alternative form of catheter</li></ul>

0016With reference first to Figures 1 and 2, the epidural catheter comprises a tube 1 of a flexible plastics material, such as nylon, and is about 850 mm long, being circular in section with an external diameter of 1 mm and an internal diameter of 0.58 mm. The machine end 2 of the catheter is square, plain and open enabling it to be joined to any conventional epidural connector.

0017The patient end 3 of the catheter has a smoothly rounded closed tip 4 and has four slits 5 to 8 formed through the wall of the tube 1. The slits 5 to 8 are formed without removal of any material from the wall of the tube 1 and are equally spaced from one another around the catheter. The slits 5 to 8 are 10 mm long and each extend parallel to one another and to the catheter longitudinal axis from just rearwardly of the tip 4. The slits 5 to 8 thereby extend along the same region along the length of the catheter and define four segments 15 to 18 between them around the catheter.

0018With reference now also to Figure 3, the patient end 3 of the catheter is introduced to the epidural space 10 in the usual way. When fluid is supplied to the machine end 2 of the catheter it is free to flow out of the patient end 3 through the slits 5 to 8. The length of the slits 5 to 8 and the nature of the material from which the catheter is made are such as to ensure that some at least of the slits are sufficiently open to allow free flow of injected fluid out of the catheter. The pressure of fluid within the catheter may also help to open the slits 5 to 8 slightly. The slits 5 to 8 increase the flexibility at the patient end 3 of the catheter so that it is more easily deflected if it should meet an obstruction on insertion. In this way, the risk of veinepuncture and dural puncture are substantially reduced.

0019It will be appreciated that fluid will be delivered through the slits 5 to 8 at very much the same location along the catheter, regardless of injection pressure. The catheter is also less likely to be occluded than those catheters having a single opening. Furthermore, dispersal of fluid from the slits 5 to 8 is improved and jetting is avoided. Because the opening of the catheter is of a shorter length than the region over which eyes are located in conventional multiple eye catheters, there is less risk of false test injection result being obtained.

0020Various modifications are possible within the scope of the present invention. For example, the slits could be formed by removal of material from the wall of the tube.

0021An aperture 20 could be formed in the catheter to the rear, distally, of the slits 5 to 8, as shown in Figure 4. This has the advantage of reducing the risk, when suction is applied to the machine end 2 to aspirate the catheter, of the segments 15 to 18 being sucked inwardly, blocking the bore through the catheter. It also prevents the edges of the four segments 15 to 18 sealing with each other to form a closed ended cylinder.

0022Figure 5 shows an alternative way in which the catheter can be prevented from closing an aspiration. In this arrangement, two of the segments 16 and 18 have been removed thereby producing enlarged slits 26 and 28.

0023The tip of the catheter at the patient end 3 could be open in the manner shown in Figure 6. In this arrangement, the slits 5 to 8 extend to the open end 24 of the catheter so that the segments 25 to 28 are free at their patient end. Such an arrangement also reduces the risk of the catheter closing on aspiration.

0024A catheter of the kind shown in Figures 1 to 3 may be made in the manner shown in Figures 7 to 9. A plain square-ended tube 30, of the kind shown in Figure 7, is provided and cut diameterically along a part of its length. This is done by pushing the tube 30 through an outer support tube 31 so that the open end of the tube impinges on a cruciform arrangement 32 of crossed, pointed blades. The four slits 5 to 8 thereby formed extend to the open patient end of the tube 30. The patient end of the tube 30 is closed, as shown in Figure 9, by end forming, such as in a heated die 33 have a rounded concave recess 34 of the desired profile of the finished catheter. The temperature of the die 33 is sufficient to cause softening and flow of the material of the tube so that the ends of the segments 15 to 18 flow into one another and become joined after cooling. It has been found preferable to form the slits before closing the patient end, in the way described above, since this makes it easier to ensure that the slits 5 to 8 extend close to the tip of the catheter than if the slits are produced after closing the end of the catheter.

0025A catheter having a tip of the kind shown in Figure 5 can be formed in a similar way, as shown in Figures 10 and 11. Following cutting the slits, in the manner described above with reference to Figure 8, two of the segments 16 and 18 are cut away to leave the remaining two segments 15 and 17 separated by enlarged slits 26 and 28. The patient end of the two segments are then bridged together using the heated die 33, as shown in Figure 11. This produces a catheter with a closed patient end and with enlarged slits 26 and 28 extending from close to the patient end.

0026It will be appreciated that various modifications could be made to the arrangements described above. For example, the slits could be staggered from one another slightly along the length of the catheter providing they overlap substantially.

0027Instead of having a plurality of slits, a single helical slit 41 extending about the patient end of the catheter could be used, as shown in Figure 12.