TECHNICAL FIELD This invention relates to subcutaneous insertion of catheters into blood vessels such as the femoral or subclavian veins, and more particularly to a dilator for following a guide wire to form a tunnel for receiving the catheter.

The invention will be described with reference to the procedure of inserting a catheter for use in hemodialysis by the Seldinger technique, but it will be recognised that this description is exemplary of procedures for other purposes and that the dilator described here can be used in such other procedures.

BACKGROUND ART

Since Dr. Seldinger introduced his technique in 1953, it has become common practice to use guide wires when inserting catheters into blood vessels. In hemodialysis procedures, a hollow needle is first used to create a small incision in a blood vessel, typically 4 French. This hollow needle allows blood flow to show that the needle has been positioned in the blood vessel. Next a very flexible wire is pushed through the needle, into the blood vessel, and then moved for some distance down the blood vessel to act as a guide for subsequent engagement of a dilator and then a catheter. With the wire in place, the needle is withdrawn leaving behind tissue expanded to about 4 French and an opening in the blood vessel of about the same size. The eventual catheter to be placed is typically 11 French so that dilation to 11 French (or close to this size) must take place. As the dilator is pushed along the wire, blood will flow through the dilator so there is further blood loss as this takes place.

At this point it is worthwhile noting that this is a subcutaneous procedure which means that the leading end of the dilator must first stretch the quite strong skin which requires a significant force and then dilate the underlying tissue, before stretching the blood vessel. The forces required and the

fact that the surgeon is dealing with very flexible and resilient material makes it difficult for the surgeon to sense the dilator following the wire, especially if larger forces are required due to the enlargement being done by a single dilator. The procedure can be very traumatic for the patient if not done properly.

One approach to creating a tunnel is to slide a dilator over the wire. However the difference between 4 French and 11 French makes it difficult to insert an 11 French dilator over the wire for two reasons. Firstly the enlargement demands significant force, and secondly this force reduces the surgeon's tactile sensitivity so that when the catheter is inserted over the wire it can be driven off track taking the wire with the catheter into adjacent tissue. This can result in serious trauma. This problem is emphasized by the fact that the tissue tends to return to its original form after the needle is removed so that the dilation required can possibly be from the wire size to 11 French.

The tactile sensitivity can be improved by the use of a series of dilators of increasing diameter. Such a procedure is slow because each of the dilators must be engaged over the wire, removed, and a new dilator put in place. Because the dilators are forming a tunnel of increasing size, there will be a significant loss of blood. Also, each of the dilators must be handled very carefully because the leading ends enter the blood vessel and if the dilator is pushed too far, it could damage the side of the blood vessel opposite the entry opening.

A second approach to dilation which has been used is to insert the ultimate catheter directly over the wire. This is not a desirable procedure because the design requirements of a catheter used in this way for dilation are contrary to the design requirements of a catheter which make it suitable to be placed in a blood vessel for the time needed for treatment. On the one hand, the tip of the catheter designed for dilation must be quite firm so that when it is pushed along the wire, the tip ^' will dilate the tissue without collapsing the tip. By contrast a catheter designed for prolonged use in a blood vessel should have a very flexible tip so that any movement which causes

contact between the tip of the catheter and the blood vessel will result in the tip flexing to minimize the risk of deforming the blood vessel.

A further approach to dilation has been to provide a set of dilators which fit one over another. A first and smaller dilator is entered over the wire and then this is followed by one or more dilators which are slipped over one another and lead forwardly to a predetermined location so that the resulting combination of dilators represents generally the size of the catheter to be placed. While this combination of dilators has some advantages, it must be remembered that the sizes are very small. The dilator is expanding tissue generally from the size of the needle which is typically 4 French up to about 10 or 11 French. There is very little room for wall thickness in these sizes and consequently the dilators are not simple to handle and the procedure of sliding one over another can be quite dangerous due to the fact that the first dilator is in place in the blood vessel and can cause damage if oscillated sideways or pushed forwardly. As a result of these difficulties there is a need for a single dilator which will follow a wire and form a tunnel of a shape and size which will permit insertion of a catheter directly regardless of the fact that the catheter may have a very flexible tip.

DISCLOSURE OF INVENTION

In one of its aspects the invention provides a dilator for defining a tunnel to receive a catheter having a selected cross-section, the tunnel extending through body tissue and entering a blood vessel, the dilator comprising: an elongate main body having a first cross-section generally equal to said selected cross-section; a tip portion of lesser cross-section than said main body and extending longtiiidinally from the main .body and terminating at a distal end of the dilator; the main body and the tip portion defining a continuous longitudinal opening for .engaging the dilator over a guide wire; the tip portion having a leading taper enlarging from

the distal end about said opening and a trailing taper blending the tip section into the main body; the tip portion having a length selected to permit dilation of the blood vessel and part of said tissue to the cross-sectional shapes of the tip portion, trailing taper, and part of the main body so that the resulting tunnel has an entry corresponding generally to the size of the catheter for initial engagement and so that the catheter will be required to complete dilation only of the tissue and blood vessel in that position of the tunnel where the tip portion formerly resided to thereby facilitate insertion of a relatively soft catheter to which the blood vessel and tissue are sealed by the reaction to dilation by the catheter.

In another of its aspects the invention provides an improvement to catherization procedures. In such procedures involving inserting a catheter into a blood vessel, the method comprising the steps: providing a hollow elongate needle and engaging the needle through the skin, underlying tissue, and into the blood vessel; providing a flexible guide wire and pushing the guide wire through the needle and into the blood vessel until the guide wire has progressed down the blood vessel sufficient to guide a catheter into position in the blood vessel; withdrawing the needle over the guide wire leaving the guide wire in place; providing a dilator having an elongate main body with a first cross-section extending about a longitudinal axis, a tip portion extending from the main body longitudinally and terminating at a distal end of the dilator, and the main body extending from the tip portion to a proximal end of the dilator, and the tip portion having a leading taper enlarging from the distal end towards a second cross-section smaller than the first cross-section, and a trailing taper extending smoothly fron the main body and converging from the first cross-section to the second cross-section; and the dilator defining an opening extending between the proximal and distal ends for receiving the guide wire;

engaging the dilator over the guide wire and moving the dilator along the wire to dilate the skin and adjacent tissue to a first cross-section and the blood vessel and adjacent tissue to the second cross-section so that a tunnel is created about the guide wire; removing the dilator leaving the guide wire in place; providing a catheter having a cross-section larger than said second cross-section and similar to said first cross-section; engaging the catheter over the wire and moving the catheter through the tunnel and into the blood vessel so that the blood vessel and adjacent tissue are dilated to the cross-section of the catheter and the catheter is positioned in the blood vessel; removing the guide wire; and connecting the catheter for conducting the procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.l is a somewhat schematic isometric view of a preferred embodiment of a dilator according to the invention shown partly entered into a subcutaneous tunnel and following a wire which has been engaged in a blood vessel.

BEST MODE FOR CARRYING OUT THE INVENTION The accepted procedure for subcutaneous insertion of a catheter involves engaging a needle into a blood vessel 20 underlying body tissue 22 beneath the skin 24. Typically the needle creates a tunnel 26 of about 4 French and of course once the needle is removed this tunnel tends to collapse around a Seldinger guide wire 28 left behind when the needle is withdrawn. For the purposes of the illustration the tunnel 26 is shown as it would appear with the needle engaged.

A dilator 30 according to the invention consists of an elongate main body 32 extending about a longitudinal axis from a proximal end fitting 34 to a tip portion 36 at the distal end of the dilator. This tip portion has a leading taper 38 spaced from a trailing taper 40 which together combine to dilate the tunnel. The tapers 38 and 40 are separated in this preferred

eiribodiinent by a leading portion 42 which is of reduced cross section compared with the main body 32. Typically the main body is of 12 French and the portion 42 of 10 French and an opening 44 extends longitudinally through the dilator to contain the wire 28 as shown in broken outline. In general, the main body 32 and leading portion 42 are circular in cross-section with the diameter of leading portion being about 40 per cent that of the main bcidy, (e.g. 4 French compared with 10 French.

The opening in the dilator at the leading taper 38 fits snugly about the wire 28. When the dilator is fed along the wire, the dilator initially makes contact with the skin 24 and the leading taper dilates the skin and then commences dilation of the tissue 22. This continues until the trailing taper 40 meets the skin whereupon dilation of the skin to the full size of the body 32 takes place as the taper 38 continues to dilate the tissue. As the dilator progesses, the trailing taper 40 dilates tissue until the leading taper 38 has dilated the blood vessel and entered the blood vessel, thereby dilating the blood vessel to the size of the leading portion 42. At this point the skin and some of the tissue has been dilated to the full size of the dilator and a portion of the tissue and the access opening in the blood vessel have been dilated to the size of the portion 42. The length of the leading portion 42 is selected according to the amount of tissue to be dilated to the size of this portion.

The result is that a subcutaneous tunnel is formed capable of receiving a catheter guided by the wire 28 and which is itself used to dilate only a portion of the tissue and the blood vessel from about 10 French to 11 French. This permits the use of a relatively soft tip catheter and yet permits the catheter to complete the dilation to the size and shape of the catheter. Consequently, if the catheter is not entirely round or the exact shape of the dilator, the stretching will enable the catheter to form an opening in the blood vessel which tends to be self sealing. At the same time the catheter is not required to dilate the skin and all of the tunnel, but only the very last part of the tunnel where it engages the blood vessel. The tissue stretches around the catheter and this combined with

the flexibility of the blood vessel helps to ensure sealing.

It should also be noted that the catheter insertion is done using a single dilator which minimizes time, ensures a good seal, and at the same time makes engagement simple because the lead part is of a small cross section and this follows the existing tunnel and then leads the larger taper 40 along the desired path.

Variations can of course be made to the dilator. In particular the leading portion 42 can have any length consistent with meeting the requirements of having the portion 40 engage through the skin and into the tissue at the time the leading taper 38 engages the blood vessel. Also, portion 42 could itself be slightly tapered resulting in a gradual dilation from the leading end of the dilator through to the main body 32. Procedurally, the dilator helps to ensure a smooth entry of the catheter with minimal trauma. The dilation can be considered to be in three stages: firstly dilation of the complete tunnel to the size of portion 42; secondly, and contemparaneously with the latter part of the dilation to the size of portion 42, dilation of skin and adjacent tissue to the size of body 32; and lastly, dilation of the blood vessel and adjacent tissue to the size of the catheter by the catheter.

The dilator can be made of any suitable material but is preferably of a plastics material such as that sold under the trade mark NYLON. The selected material should have sufficient stiffness to permit insertion and be readily sterlized.

INDU.STRIAL APPLICABILITY

The dilator is used to enlarge a tunnel created initially by a hollow needle which passes through body tissue and into a blood vessel. A single guide wire is fed through the needle before the needle is removed over the guide wire. The needle is as small as possible to minimize trauma and blood loss. The dilator is then fed over the needle until the leading taper 38 enters the blood vessel 20 at which point the blood vessel and an adjacent part of the tissue 22 has been dilated to match the size of the leading portion 42 and the remainder of the tissue 22 has been dilated to the size of the main body 32.

Because the main body is of similar size to the catheter to be placed in the tunnel, an entry is formed and the catheter is required to dilate only the portion of the tissue near the blood vessel, as well as the blood vessel. This permits softer catheters to be inserted over a guide wire and minimizes trauma while enhancing the sealing effects of the blood vessel and tissue about the catheter.

All of these variations are within the scope of the invention as claimed.

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