GB2290030A

GB2290030A - Guide for needle assembly

Info

Publication number: GB2290030A
Application number: GB9508667A
Authority: GB
Inventors: Christopher Stratton Turnbull
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1994-06-09
Filing date: 1995-04-28
Publication date: 1995-12-13
Anticipated expiration: 2015-04-28
Also published as: GB2290030B; GB9508667D0

Abstract

A guide 3 for aiding insertion of an epidural cannula into a needle 1 is made of a transparent resilient plastics material so that the forward portion 30 of the guide can be inserted in a luer-tapered bore 20 through the needle hub 2 and be located close to its end, leaving little space for the cannula to bend or kink in the bore of the hub. The forward portion 30 of the guide 3 has ridges 33 to make insertion easier. <IMAGE>

Description

NEEDLE ASSEMBLIES This invention relates to needle assemblies and to guides for needle assemblies.

The invention is more particularly concerned with epidural needle assemblies comprising an epidural needle and a guide for use in inserting an epidural cannula into the needle.

An epidural cannula is inserted to the epidural space through a hollow needle, which is subsequently withdrawn. The epidural cannula is a flexible plastics tube with a very small diameter, typically about 0.8mm. The needle is usually provided at its proximal or machine end with a female luer taper hub adapted to receive the nose of a syringe. The syringe is used during insertion to detect correct insertion by the loss-of-resistance technique or by aspiration. The syringe is removed after the needle as been correctly located; the cannula is then inserted through the hub into the bore ofthe needle. Because the cannula is very flexible, there is a tendency for it to bend and kink when axial pressure is applied to it.In order to facilitate insertion ofthe cannula into the hub ofthe needle, it is usual to use a hollow guide that is fitted in the hub. The guide has a bore through it aligned with the bore through the needle, the guide projecting rearwardly from the hub. The rear ofthe guide adjacent the rear end of its bore is relatively thin compared with the hub so that both the cannula and the guide can be engaged between the finger and thumb when the cannula is being inserted. In this way, the portion of the cannula immediately to the rear of the opening of the bore is supported between the finger and thumb during insertion so that the risk of bending at the opening is reduced.

Although such a guide can reduce the risk of the cannula bending where it is inserted, there is still a risk that the cannula can bend within the hub. This arises because the forward end of the guide does not extend completely to the forward end of the luer bore in the hub, leaving a gap in which bending of the catheter is possible. This gap occurs because the guide is a luer slip fit in the hub and because there must be sufficient room to accommodate variations in dimensions caused by manufacturing tolerances, whilst also ensuring that the guide is a secure fit in the hub.

It is an object of the present invention to provide an improved needle assembly and guide.

According to one aspect ofthe present invention there is provided a needle assembly comprising a hollow needle with a hub at its rear, machine end, the hub having a bore with a luer-tapered portion communicating with a bore through the needle, the assembly including a guide having a bore extending therethrough, the guide having a forward portion for location in the bore ofthe hub and a rear end projecting rearwardly from the hub with a guide surface surrounding the rear opening of the bore so that a cannula can be pushed into the opening of the bore with a finger and thumb ofthe user engaging the guide surface, and at least the forward end of the guide being of a compressible material such that the forward portion of the guide can be pushed into the hub with the forward end ofthe guide closely at or beyond the forward end ofthe luer tapered portion ofthe hub.

The entire guide is preferably of the compressible material and may be of a transparent plastics material. The forward portion ofthe guide may have a frusto-conical portion and may have a plurality of longitudinal ridges extending along a part at least ofthe length ofthe forward portion.

According to another aspect of the present invention there is provided a guide for an assembly according to the above one aspect ofthe invention.

An epidural needle assembly according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional side elevation view of the assembly before assembly ofthe guide; Figure 2 is a plan view of the guide of the assembly; Figure 3 is an end view of the guide from the left; and Figure 4 is a transverse cross-section along the line IV - IV ofFigure 1.

The epidural needle assembly comprises a needle 1 moulded at its rear, machine end into a hub 2, and a guide 3 that is insertable into and removable from the hub.

The needle 1 is a conventional Tuohy needle of stainless steel, which is 60mm long and has a forward, patient end 10 bent to one side. The needle has a bore 11, of diameter lmm, extending along its entire length and has markings at 5mm intervals, in the usual way. The bore 11 of the needle 1 is sufficient to allow smooth passage along its length of an epidural cannula of diameter 0.8mm. The rear IOmm of the needle 1 is moulded into the hub 2, the rear end 12 of the needle being flared outwardly.

The hub 2 is of a transparent, rigid plastics material, such as polycarbonate, and has a bore 20 extending along its length. The bore 20 is aligned with, and communicates with, the bore 11 through the needle, the forward portion 21 ofthe bore 20 having the same diameter as the bore 11 of the needle. An intermediate portion 22 of the bore flares rearwardly to a larger diameter of 3.5mm. The rear portion 23 of the bore 20 has a luer taper of 6% and increases in diameter rearwardly to 4.3mm over a distance of 7.5mm. The rear luer-tapered portion 23 of the bore 20 is adapted to receive the nose of a syringe (not shown), which is coupled to the hub 2 during insertion of the needle to the epidural space, the syringe being used to detect correct location by the loss-of-resistance technique or by aspiration of fluid.

The guide 3 is a one-piece, integral moulding of a resilient, compressible material such as E.V.A., with a hardness of 35 Shore "D"' (or 90 Shore "A"). The material of the guide is preferably transparent or semi-transparent so that a cannula inserted through the guide can be seen. The guide 3 is about 23mm long and has a forward portion 30 about 14mm long and of circular section. At the forward end ofthe forward portion 30 there is a frusto-conical nose portion 31, which is about 3mm long, with a diameter of about 2.25mm and has a taper angle e of310.

The rear part 32 of the forward portion tapers from a diameter of 3.4mm at its forward end to a diameter of 5.3mm at its rear end. Four small surface projections in the form of longitudinal ridges 33 extend along the rear part ofthe forward portion. The ridges 33 are equally disposed around the forward portion 30 and are about 0.2mm high.

The rear end ofthe guide 3 is provided by a finger grip 35 of generally rectangular shape with a shallow flange 36 around its forward end. The grip 35 extends transversely ofthe forward portion 30, being about l2.4mm wide and 5.5mm thick at its forward end just rearwardly ofthe flange 36. The grip 35 has two flat surfaces 37 and 38, which slope towards one another at an angle of 150 as far as a location about lmm from the rear end of the guide where the grip is 8.5mm wide and 2.6mm thick. Rearwardly ofthis point, the surfaces ofthe grip slope towards one another more steeply, forming two narrow finger-engaging surfaces 39 and 40 that extend to a flat end surface 42, which is 2.2mm deep and 7.3mm wide.

An axial bore 43, 1.35mm in diameter, extends through the entire length ofthe grip, opening at the forward end ofthe forward portion 30 and centrally ofthe end surface 42 ofthe grip 35. At its rear end, the bore 43 is flared outwardly to form an opening 44 the periphery of which merges with the edge of the end surface 42.

The dimensions of the forward portion 30 and the nature of the material from which it is formed enable it to be pushed into the bore 20 in the luer-tapered hub 2 until the nose portion 31 enters the intermediate portion 22 ofthe bore. Pushing the guide 3 into the hub 2 compresses the forward portion 30 slightly to accommodate any dimensional tolerances and enables the forward end of the forward portion to be located at or beyond the forward end of the luer-tapered portion 23 ofthe bore 20. The ridges 33 reduce the friction required to insert the grip and give it slightly more resilience in radial directions. In this position, the bore 43 through the guide 3 is aligned with the bore 20 in the hub 2 and with the bore 11 in the needle 1.The lateral dimension of the bore 20 in the hub 2 just forwardly of the forward end of the guide 3 is typically only about 2.5-3mm.

An epidural cannula (not shown) is introduced to the needle 1 by gripping the cannula between the finger and thumb close to the forward end of the cannula. The forward end of the cannula is pushed into the opening 44 at the rear end of the guide 3 until the finger and thumb contact the finger-engaging surfaces 39 and 40 over which they can slide down to the flat surfaces 37 and 38. In this way, the cannula can be held between the finger and thumb very close to the point where it enters the bore 43 so that it is fully supported against bending.

When the cannula emerges out of the forward end of the guide 3 into the bore 20 through the hub 2, it passes into the bore through the needle 1. Because the guide 3 extends beyond the end of the luer-taper portion 23, the cannula emerges into a confined region, which does not allow it to bend sufficiently to deviate from an axial path through the hub 2.

When the cannula emerges from the forward end of the needle, it might meet resistance if the tip of the needle were located close to body tissue. With previous assemblies, this could lead to bending of the cannula in the bore through the hub, as force is applied to overcome the resistance. In the assembly ofthe present invention, however, there is very little risk of bending in this region because the guide can be pushed further into the hub than previous guides, thereby reducing the space available within the hub for bending of the cannula. This makes it possible for the user to apply a greater force to the cannula without a risk of bending within the needle assembly.

Claims

1. A needle assembly comprising a hollow needle with a hub at its rear, machine end, the hub having a bore with a luer tapered portion communicating with a bore through the needle, wherein the assembly includes a guide having a bore extending therethrough, wherein the guide has a forward portion for location in the bore of the hub and a rear end projecting rearwardly from the hub with a guide surface surrounding the rear opening ofthe bore so that a cannula can be pushed into the opening ofthe bore with a finger and thumb of the user engaging the guide surface, and wherein at least the forward end ofthe guide is of a compressible material such that the forward portion of the guide can be pushed into the hub with the forward end ofthe guide closely at or beyond the forward end ofthe luer tapered portion ofthe hub.

2. A needle assembly according to Claim 1, wherein the entire guide is of a compressible material.

3. A needle assembly according to Claim 1 or 2, wherein the guide is of a transparent plastics material.

4. A needle assembly according to any one of the preceding claims, wherein the forward portion of the guide has a frusto-conical nose portion.

5. A needle assembly according to any one of the preceding claims, wherein the forward portion of the guide has a plurality of longitudinal ridges extending along a part at least ofthe length ofthe forward portion.

6. A needle assembly substantially as hereinbefore described with reference to the accompanying drawings.

7. A guide for a needle assembly according to any one of the preceding claims.

8. A guide substantially as hereinbefore described with reference to the accompanying drawings.

9. Any novel feature or combination of features as hereinbefore described.