GB2075347A - Improvements in or relating to catheters - Google Patents

Abstract

A catheter suitable for haemodialysis comprises a cannula portion and a hub portion integral with connecting means for providing a secure, lockable connection to a blood line, said hub portion being of resilient material whereby its lumen may be closed by externally applied pressure before or after connection of the hub portion to a blood line.

Description

SPECIFICATION Improvements in or relating to catheters This invention concerns improvements in or relating to catheters and more particularly concerns a catheter suitable for haemodialysis.

During haemodialysis, blood is extracted from the patient through a cannula, processed in a kidney machine and returned to the patient by the same means. The cannula is a plastics tube which is introduced into the patient usually via an arterio-venous fistula, by means of a needle through the lumen of the cannula. After insertion of the device, the needle is withdrawn and the cannula remains in situ to transmit blood, through a hub portion and connecting means, to or from a blood line. For convenience, in this specification the cannula, hub portion and connecting means will be collectively referred to as a catheter, although this term has sometimes been used to denote the plastics tube introduced into the patient.

In haemodialysis, it is essential that the flow of blood can be shut off while the lines from the kidney machine are connected to the catheter. Therefore it has previously been the practice to interpose a short length of tubing, composed e.g. of silicone rubber or other translucent or transparent elastomeric polymer, between the hub portion and the connecting means. In some cases it is necessary to connect two lines to the catheter, in which case the hub is a Y-shaped component having two flexible tubular extension pieces, each having connecting means on their proximal ends.

The production of catheters of this kind is inefficient, requiring a considerable amount of manual assembly work.

The flexible extension pieces also present an obstruction to the flow of blood owing to the change of lumen size at each end. As is well known, stagnant blood is liable to clot with very serious consequences to the patient. There is always the risk that the connections to the extension pieces will leak or even become detached, possibly causing infection or a fatal air embolism.

Sometimes the connecting pieces have been omitted, the blood lines then being plugged directly with the tubular extension pieces. However the connection between the male cone connector of the blood line and the parallel bore of the extension piece is mechanically unsatisfactory and the blood line is easily disconnected by tension on the line or by internal fluid pressure. The extension piece is often made in silicone rubber and the self-lubricating properties of this material in the wet state increase the difficulty of effecting a secure connection.

According to the present invention, a catheter suitable for haemodialysis comprises a cannula portion and a hub portion integral with connecting means for connecting to a blood line, said hub portion being of resilient elastomeric material whereby its lumen may be closed by externally applied pressure before or after connection of the hub portion to a blood line.

Thus in the catheter of the present invention, the use of a separate flexible extension piece is dispensed with, its function being replaced by an elongated hub portion. Not only is this device simpler to manufacture but the flow of blood is unobstructed except by the change of lumen size from blood line to catheter. Thus this invention is based on the surprising and valuable realisation that the resiliently closable portion of the catheter can be formed as an integral part of the hub. Thus the catheter comprising the cannula, hub and connecting means can comprise only two parts; or even a single part if the cannula is moulded integrally with the hub portion.

This compares with the three or four separate parts, often of different materials, which are required for the known construction.

Moreover the lack of steps in the internal bore minimises the destruction of red blood cells by dynamic shearing forces, which is a serious hazard in conventional haemodialysis catheters. The internal bore of the cannula portion should be large enough to ensure adequate blood flow, and will ordinarily be considerably larger than a standard infusion cannula.

The hub portion is preferably made of polyurethane or ethylene/vinyl acetate copolymer.

Other elastomeric polymers can be used, such as silicone rubber. Preferably a portion of reduced wall thickness is provided, on which a clamp may be mounted to close the lumen.

The connecting means for connection to a blood line should provide a secure, lockable connection e.g. a Luer lock or Record lock.

The external ears necessary to engage the internal threads of a Luer lock connector preferably comprise part helical surfaces for engaging securely with the male connector of the blood line. As shown in Figure 3, the ears are preferably wedge shaped, having part helical distal surfaces and circumferentially aligned proximal surfaces.

A self-sealing diaphragm of latex rubber or the like may be provided on the proximal end of the hub portion, for sealingly gripping introducing needles.

Our invention is equally applicable to a haemodialysis catheter having a Y-shaped hub portion, each branch of the hub portion being integral with means for providing a secure, lockable connection for a blood line and the lumen of each branch being closable by externally applied pressure before or after connection of said branch to a blood line.

The invention will now be described by way of example only with reference to the accompanying drawings, wherein Figure 1 is a cross-sectional view of a haemodialysis catheter of known type; Figure 2 is a cross-sectional view of a catheter according to the invention; Figure 3 is a perspective view of the proximal end of the catheter of Figure 2 showing one of the Luer lock ears; Figure 4 is a cross-sectional view of the proximal end of the catheter of Figure 2 having a latex rubber diaphragm attached thereto; and Figure 5 is a cross-sectional view of a catheter according to the invention having a Y-shaped hub.

Referring now to Figure 1, a known haemodialysis catheter comprises a cannula 1 onto which is moulded a hub portion 13 made e.g. of polyp ropylene. An extension piece 14 of silicone rubber tubing can be clamped to shut off the flow of blood and the proximalend 15 can receive a male cone connector on a blood line. As explained above, such connection will not be mechanically sound. There is also an abrupt change of internal section at 16 which can damage the blood flowing past it.

Turning now to Figure 2, the catheter of the invention comprises a cannula 1 onto which is securely moulded the hub portion 2 formed of translucent polyurethane. The region 3 of the hub portion is resiliently compressible so that the lumen 4 extending therethrough can be closed off by squeezing or bending the region 3 between the fingers or by applying mechanical clamping means.

At its proximal end the hub portion 2 is provided with a female Luer taper 5. This is dimensioned to make a fluid tight connection with a corresponding male Luer lock 6 on a blood line 7. The male connector 6 engages with ears 8 moulded onto the hub portion adjacent the proximal end.

Referring now to Figure 3, an ear 8 is shown in more detail. The ear is of generally wedge shaped form, the distal surface 9 being at a helical angle corresponding to the helical angle of the Luer lock connector 6 while the proximal surface 10 is circumferential. This particular configuration of ear enables a secure locking action to be obtained even though the ear is resilient.

In Figure 4 the Luer taper 5 is closed by a rubber diaphragm 11 snap fitted overthe proximal end of the catheter. The ears 8 (not shown) help to retain the diaphragm in position. The diaphragm 11 is self-sealing. Thus when the inserting needle 12 is withdrawn after placement of the catheter is a vein, the diaphragm 11 prevents leakage of blood. The resilient hub is then squeezed by the operator to close off the lumen 4, the diaphragm 11 is removed, and the hub is connected to the Luer lock 6.

In Figure 5 the dual flow catheter has a hub of Y-shape for connection to two blood lines. The compressible portions 3 are of reduced wall thickness to facilitate clamping off the blood flow.

Claims (8)

1. A catheter suitable for haemodialysis comprising a cannula portion and a hub portion integral with connecting means for providing a secure, lockable connection to a blood line, said hub portion being of resilient material whereby its lumen may be closed by externally applied pressure before or after connection of the hub portion to a blood line.

2. A catheter as claimed in claim 1 wherein said resilient material is polyurethane.

3. A catheter as claimed in claim 1 wherein said resilient material is an ethylene/vinyl acetate copolymer.

4. A catheter as claimed in any of the preceding claims including connecting means for providing a secure lockable connection to a Luer lock or Record lock connector.

5. A catheter as claimed in claim 4 wherein said connector comprises external ears having part helical distal surfaces and circumferentially aligned proximal surfaces.

6. A catheter as claimed in any of the preceding claims having a self-sealing diaphragm on the proximal end of the hub portion.

7. A catheter as claimed in any of the preceding claims wherein said hub portion comprises a portion of reduced wall thickness on which a clamp may be mounted to close the lumen.

8. A catheter as claimed in any of the preceding claims having a Y-shaped hub portion, each branch of the hub portion being integral with means for providing a secure, lockable connection to a blood line and the lumen of each branch being closable by externally applied pressure before or after connection of said branch to a blood line.