WO1993014710A1

WO1993014710A1 - Fine gauge needles and cannulae

Info

Publication number: WO1993014710A1
Application number: PCT/IE1993/000003
Authority: WO
Inventors: Muthafar Muflih Al-Rawi
Original assignee: Al Rawi Muthafar Muflih
Priority date: 1992-01-29
Filing date: 1993-01-29
Publication date: 1993-08-05
Also published as: AU3366193A

Abstract

The invention discloses a needle (10, 20, 20', 30, 40, 50, 60) or cannula (100, 100', 110, 110', 120, 120', 200, 210, 220) comprising a hollow shaft with an interface hub (18, 28, 28', 38, 48, 58, 68, 114, 114', 124, 124', 214, 224), the shaft having a fine gauge portion (12, 22, 22', 32, 42, 52, 62, 112, 112', 212) at its distal end and a reinforced portion (16, 26, 26', 36, 46, 56, 66, 122, 122', 222) at or near its proximal end. A cannula sleeve (122, 122', 222) is provided to reinforce a standard cannula (C). A larbe bore cannula (120) and an insertion means is disclosed, which insertion means causes a small puncture wound and reduces risk of accidental injury. Improved needles (10, 20, 20', 30, 40, 50, 60, 310, 320, 330, 340, 350, 360) and cannulae (200, 210, 200, 220) for nerve stimulation and needles (310, 320, 330, 340, 350, 360) to minimize the risk of puncture damage are also disclosed.

Description

FINE GAUGE NEEDLES AND CANNULAE

The present invention relates to surgical needles and more particularly to fine gauge needles for use in spinal anaesthesia, nerve stimulation and peripheral nerve blocks and to needles and cannulae for use in intravenous and intra-arterial cannulation.

Large bore needles, which are relatively easy to use, result in post-operative side effects such as backache and postdural puncture headache when used for the administration of a local anaesthetic agent for spinal anaesthesia. Postdural puncture headache is attributed to a fall in pressure of cerebro-spinal fluid due to leakage through the puncture hole in the dura. Additionally, accidental dural puncturing may occur when attempting to access the epidural space only.

Fine gauge needles are known to provide many advantages over large bore needles and have been used for many years. For example, after spinal anaesthesia the incidence of postdural puncture headache using a 26-gauge needle is 3-10% compared to less than 1% incidence using a 29-gauge or 30-gauge needle. Unfortunately, fine gauge needles are technically and clinically difficult to use and their use is often restricted to experienced aneasthesiologists. Th factor limiting the gauge of a needle in which a stylet is required is the diameter of the stylet. The stylet is use to prevent blocking of the lumen of the needle. Presently, the finest needle available with a stylet is a 29-gauge needle. A 30-gauge or 32-gauge needle is too fine for a stylet. Another disadvantage associated with fine gauge needles is their flexibility. The flexing of the needle shaft while handling makes it difficult to use and incurs a loss of "feel". This flexing is accentuated by a relatively heavy metal hub which interfaces with a syringe. With large bore needles the metal hub may be replaced by a transparent or translucent hub. These hubs allow the user to assess the anatomical position of the point of the needle by observing the meniscus of cerebro-spinal fluid as soon as fluid enters the hub from the metal needle shaft. Transparent or translucent hubs are not yet available for fine gauge needles above 27-gauge as a resilient bonding between the needle shaft and hub is difficult to establish.

A known solution to the problem of postdural puncture headache is to ensure that the puncture made in the dura is small. As stated above, fine gauge needles are difficult to use and the following are a number of arrangements which seek to alleviate the risk of dural puncture headache. In a first arrangement, as disclosed in CA-A-2,037,052, a cannula is inserted through a relatively large hollow needle. This cannula houses a catheter which is provided with a puncturing wire or stylet. A disadvantage of this arrangement is that the relative positions of the needle, cannula and catheter are difficult to maintain and those positions are easily disturbed especially when withdrawing the puncturing wire or stylet. A similar arrangement is disclosed in US-A-4,973,312. In a second arrangement a coaxially disposed cannula and catheter are provided with a centrally disposed trocar (as disclosed in US-A-5,135,525) or guide wire (as disclosed in US-A-4,994,036) . However, this trocar or guide wire must be sufficiently resilient to prevent the coaxial cannula and catheter from flexing. Further known arrangements provide hollow needles down which a catheter tube is fed thus requiring relatively ^r+ large bore needles. The above arrangements provide certai disadvantages with respect to accidental injury as detaile hereinbelow. 5

It is known that cutting tips or needles tear the fibres o membranes through which they pass. A solution to this problem is to provide a needle tip which reduces the cutting or tearing action of the tip. A known needle,

10 called the Whitacre needle, provides a needle point which is closed at its distal end and has an aperture defined on the shaft of the needle to allow fluid to flow. A disadvantage of this needle is that very fine gauge needle of this type are not realisable and that the aperture is

15 too small to allow adequate fluid flow. An improvement on the Whitacre needle is the Sprotte needle which again has closed needle tip but has a larger aperture defined on the needle shaft. Unfortunately, the large aperture causes a weakness in the needle which may bend or break along the

20 shaft opposite the aperture. Additionally, when the

Sprotte needle is being withdrawn, fibres of the punctured membrane may be torn by the edges of the aperture. A needle similar to the Sprotte needle is disclosed in US-A-5, 100,390.

25

Fine gauge cannulae also have disadvantages associated with their flexibility. When a fine gauge needle associated with a fine gauge cannula is withdrawn, the cannula shaft or sleeve can be easily bent or twisted which disrupts the

30 flow of fluid therethrough. Additionally, the durability of fine gauge cannulae is low and in use cannulae may have to be replaced regularly.

1*

Where a situation presents a requirement for the use of a large bore cannula it is standard procedure to use a large bore needle to insert the cannula even in situations where the target is small or difficult to locate which makes cannulation difficult. A disadvantage of large bore needles is that they create large puncture wounds.

In general, there is a high risk of accidental injury when handling needles. Personnel handling needles run a risk of needle-stick injury. Needles are often left unprotected for a time after they have been used and may thus expose those personnel to risk of infection. Larger bore needles tend to inflict more severe injuries than fine gauge needles.

It is an object of the present invention to seek to alleviate the above disadvantages and to provide fine gauge needles that are relatively easy to use for anaesthesia, nerve stimulation and similar uses.

It is a further object of the present invention to seek to provide improved fine gauge cannulae and associated needles for use in intravenous and intra-arterial cannulation.

It is a yet further object of the present invention to seek to minimize needle puncture damage.

The present invention provides a needle or cannula comprising a hollow shaft and an interface hub, the shaft having proximal and distal ends, characterised in that the shaft comprises a fine gauge portion at or towards the distal end and a reinforced portion at or near the proximal end.

An optional intermediate reinforced portion may be provided between said proximal and distal ends of the shaft.

The needle and cannula may be adapted for use in the administration of local anaesthetic agents for spinal anaesthesia.

Advantageously, a transparent or translucent hub may be provided on the reinforced portion.

The needle and cannula of the present invention may be adapted for use with existing needles and cannulae.

The reinforced needle and cannula of the present invention may be adapted for use in nerve stimulation.

The invention further provides a cannula for use as a sleeve with a standard cannula to reinforce said standard cannula, comprising a cannula shaft which is shorter than standard cannula shaft and an interface hub which receives the interface hub of a standard cannula, a needle or a syringe.

The present invention further provides a cannula and means for insertion thereof, the insertion means comprising a blunt-tipped needle which is coaxially and slidingly house in the cannula, the needle housing a fine gauge sharp-tipped needle or trocar for puncturing, the needle o trocar protruding from the blunt end of the blunt-tipped needle whereby a small puncture wound is created by the fine gauge needle or trocar, the insertion means being advanced such that the puncture wound is stretched about the blunt-tipped needle to accommodate the bore of the cannula without tearing the puncture wound. Advantageously, the fine gauge needle or trocar has an operational and inoperational position within the blunt-tipped needle, characterised in that, in the inoperational mode, a biasing means moves the fine gauge needle or trocar rearwardly into the blunt-tipped needle and, in the operational mode, a user moves the needle or trocar relative to the blunt-tipped needle against the biasing means.

In a yet further aspect, the present invention provides a needle comprising an atraumatic tip having a substantially conical or rounded profile, so that where the needle tip is applied against a target membrane, the membrane fibres are separated to allow passage of the needle.

Conveniently, the needle comprises a stylet coaxially housed within the shaft of the needle, so that the stylet and the needle tip together form the distal end of the atraumatic tip.

Advantageously, the stylet may protrude from the substantially conical or rounded profile of the needle tip.

Typically, the stylet protrudes from the needle tip a distance in the range of from about 0.1mm to about 2mm.

The profile of the needle tip may be a pencil-point tip, a rounded tip or a diamond-shaped tip.

In a preferred embodiment, the stylet is electrically isolated from the needle and is provided with a connector to allow connection to a voltage or current source.

The invention will now be described more particularly with reference to the accompanying drawings which show, by way of example only, six embodiments of fine gauge needle, two embodiments of cannula and six embodiments of atraumatic needle according to the invention. In the drawings:

Figures 1a to 1c are cross-sectional side elevations of a prior art fine gauge needle, a stylet and a needle and stylet combination, respectively;

Figure 2a is a cross-sectional side elevation of a first embodiment of needle;

Figure 2b is a cross-sectional side elevation of the needl of Figure 2a in use with a modified introducer needle;

Figure 3 is a cross-sectional side elevation of a second embodiment of needle;

Figures 4a to 4b are cross-sectional side elevations of a needle similar to that of the second embodiment to be used independently and in conjunction with a modified introducer needle, respectively.

Figure 5 is a cross-sectiohal side elevation of a third embodiment of needle having a larger internal diameter at the proximal end of the needle shaft;

Figure 6 is a cross-sectional side elevation of a fourth embodiment of needle;

Figure 7 is a cross-sectional side elevation of a fifth embodiment of needle with a modified stylet;

Figure 8 is a cross-sectional side elevation of a sixth embodiment of needle with a modified stylet;

Figure 9 is a cross-sectional side elevation of a prior art cannula and needle;

Figure 10a is a cross-sectional side elevation of a first embodiment of cannula;

Figure 10b is a cross-sectional side elevation of a modification of the first embodiment of cannula;

Figure 11a is a cross-sectional side elevation of a further arrangement of cannula and needle;

Figure 11b is a cross-sectional side elevation of a modified arrangement of that of Figure 11b;

Figure 12 is a cross-sectional side elevation of a second embodiment of cannula;

Figure 13a and 13b are cross-sectional side elevations of a prior art cutting tip needle with an associated stylet in a standard configuration and in a configuration having a stylet in an extended position, respectively; and

Figure 1 a to 1 f are cross-sectional side elevations of a first to a sixth embodiment of needle tip with their associated stylets, respectively.

Referring initially to Figures 1a to 1c, a prior art standard fine gauge needle and stylet are shown separately and in use. The needle comprises a needle shaft NS and a syringe interface hub NH. In use, the needle, with stylet S in place, is inserted through an introducer needle (not shown) . A 30mm introducer needle is often used with a 90m needle. When the needle is in position the stylet S is withdrawn and a syringe is inserted to the hub. As the hu is not made of transparent or translucent material on most fine gauge needles, the user must rely on another method o observation. A common method is to carefully aspirate using a 1 or 2 ml syringe attached to the needle.

Often it is not necessary to use the full length of the needle and the flexible needle shaft will protrude from th introducer needle. The position of the needle may be critical and both withdrawing the stylet and inserting a syringe may disturb the position of the needle.

Additionally, if the^user aspirates with a first syringe and then changes to a syringe containing local anaesthetic the position of the needle within the introducer may change. A first method of observing any unwanted movement involves placing a dew-drop of liquid, preferably local anaesthetic, half-way along the exposed length of needle shaft. Any movement in this arrangement results in unequa lengths of needle shaft on each side of the dew-drop. The dew-drop must be small enough not to move from its initial position even if the needle shaft is moved from a horizontal to a vertical position. A mechanical device is also available to lock the hub of the fine gauge needle to the hub of the introducer needle but this device is cumbersome and heavy relative to the introducer needle and fine gauge needle.

A first embodiment of reinforced fine gauge needle 10 is shown in Figure 2a. The needle shaft comprises a first fine gauge portion 12 and a second reinforced portion 16. In use, this needle may be inserted to a shortened introducer needle. Flexing of the needle in position is reduced. Additionally, the syringe interface hub 18 may comprise transparent or translucent material which will be supported by the reinforced portion 16 of the shaft. The first embodiment of needle 10 is shown in conjunction with a shortened introducer needle I in Figure 2b. An example of this embodiment is a 90mm long spinal needle which comprises a fine gauge (29-gauge) portion 12 having a length of 45mm and an approximate external diameter of 0.3mm and a reinforced portion 16 having a length of 45mm and an approximate external diameter of 0.7mm. The modified introducer I comprises a shortened standard introducer needle (e.g. 19-gauge) having a length of 20mm.

Referring now to Figure 3, a second embodiment of reinforced fine gauge needle 20 is shown. In this embodiment the needle shaft comprises three portions. A first fine gauge portion 22, an intermediate gauge portion 24 and a reinforced portion 26. Similarly, to the first embodiment, the needle hub 28 supports a transparent or translucent hub and is used solely or in conjunction with a modified introducer needle. An example of the present embodiment of needle 20 is a 90mm long spinal needle comprising a fine gauge (29-gauge) portion 22 having a length of an intermediate reinforced portion 24 having a length of 10mm and an external diameter of approximately 0.45mm and a reinforced portion 26 having length of 35mm and an external diameter of approximately 0.77mm. The modified introducer needle I again comprises, for example, a 19-gauge 20mm long needle.

A modification of the second embodiment of needle 20' is shown in Figures 4a and 4b. As before, the needle comprises a fine gauge portion 22' , an intermediate gauge portion 24', a reinforced portion 26' and an interface hub 28'. The fine gauge portion 22' is not as long as the fin gauge portion 22 of the second embodiment of needle 20. For example, a 90mm long needle comprises a fine gauge (29 gauge) portion 22' having a length of 25mm, an intermediat gauge (25-gauge) portion 24' of 10mm and a reinforced (22- gauge) portion 26' of 55mm. Alternatively, the reinforced portion 26' has a length of 45mm and the intermediate gaug portion has a length of 20mm. The fine gauge portion 22' is supported more efficiently in this arrangement and is less likely to flex in use. The needle 20' is used alone or in conjunction with an introducer needle I as shown in Figures 4a and 4b, respectively.

A third embodiment of fine gauge reinforced needle 30 is shown in Figure 5. In use, the cerebro-spinal fluid may not flow sufficiently well through the lumen of the needle due to its small diameter. The needle shaft comprises a fine gauge portion 32, a first reinforced portion 34 having an external diameter similar to the proximal reinforced portion of the first 10 and second 20 embodiments, a second reinforced portion 36 which houses a relatively large internal diameter portion 37 and supports the needle shaft, and a syringe interface hub 38. In the present embodiment of needle 30, the cerebro-spinal fluid may be drawn up the fine gauge portion 32 by careful aspiration. When the cerebro-spinal fluid reaches the relatively large inner diameter portion 37 the fluid flows through an aperture 39 in the lumen of the needle such tha flow is not restricted and the fluid will be obvious to th user when it reaches the hub 38. Aspiration is also simplified. A fourth embodiment of reinforced fine gauge needle 40 is shown in Figure 6. This needle is similar to the first 10 and second 20 embodiments having a first fine gauge portion 42, a reinforced portion 46 and a syringe interface hub 48. The reinforced portion 46, however, comprises a variable cross-sectional area along its length to provide a substantially conical reinforced portion with its base abutting the hub 48. As with the first 10 and second 20 embodiments the fourth embodiment 40 of reinforced needle has a constant internal diameter throughout the length of the needle shaft. Additionally, each embodiment may support a transparent or translucent hub by virtue of the reinforced portion of the needle shaft.

Referring now to Figure 7, a fifth embodiment of fine gauge needle 50 is shown, said fine gauge reinforced needle 50 comprises a first fine gauge portion 52, a second reinforced portion 56 and a syringe interface hub 58. The reinforced portion 56 comprises a variable cross-sectional area along its length to provide a substantially conical reinforced portion having its base abutting the hub 58. The internal diameter of the needle is constant through the length of the fine gauge portion 52 of the needle 50. However, the internal diameter of the needle varies in the reinforced portion 56 to provide a substantially conical internal profile having its base at the interface hub 58. The thickness of the reinforced needle wall along the length of the reinforced portion 56 may increase toward the hub 58. A stylet S5 having a diameter conforming closely to the internal profile of the needle may be provided.

This arrangement provides improved flow and aspiration is also simplified.

A sixth embodiment of fine gauge needle 60 is shown in Figure 8. This needle 60, comprising a variable gauge needle shank 62 and a syringe interface hub 68, is very similar to the needle 50 of Figure 7 except that the needl shank 62 is not divided into two separate portions (fine gauge portion 52 and reinforced portion 56) but has a constantly increasing needle shank wall thickness towards its interface hub 68. A stylet S6 is provided which conforms closely to the internal profile of the needle shank 62. Again improved aspiration and fluid flow are provided.

A prior art cannula C and associated fine gauge needle N are shown in Figure 9. The prior art cannula C comprises an interface hub CH and a cannula sleeve CS. Fine gauge cannulae tend to deteriorate rapidly and may easily restrict flow if the cannula sleeve CS is bent or twisted. Cannulae must therefore be replaced regularly which is both time consuming and costly. The cannula sleeve CS has constant internal and external diameters. A needle N with shaft NS and syringe interface hub NH is shown in position in the cannulae. In use, the cannula sleeve CS and the needle shaft NS are inserted into a patient's artery or vein and the needle N is withdrawn.

A first embodiment of cannula 100 is shown in Figure 10a. This embodiment of cannula is designed for use with standard fine gauge needles N. The cannula 100 comprises a first inner cannula 110 and a second outer cannula 120. The inner cannula 110 comprises a standard cannula sleeve 112 and an interface hub 114 adapted to receive the hub 124 of the outer cannula 120. The outer cannula sleeve 112 is shorter than that of the inner cannula 110 but its length may be from 90% to 20% of said inner cannula sleeve 112. In use, a relatively small puncture wound is made by the tip of the fine gauge needle shaft NS, the punctured membrane is then stretched about the first cannula sleeve 112 and subsequently about the second cannula sleeve 122 as the cannula 110, 120 are urged forward and the needle N is withdrawn. When the cannulae are f lly inserted the first cannula 110 is withdrawn to provide improved fluid flow through the relatively large bore of the second cannula 120. In general, due to the elasticity of the punctured membrane, when the cannula 120 is withdrawn after use, the puncture wound remaining has a diameter similar to that of the fine gauge needle N.

A modified embodiment of cannula 100' is shown in Figure 10b having features similar to those of the first. embodiment of cannula 100 above. However, the first and second cannulae 110' 120' are fused together along the lengths of their sleeves 112', 122' and at their hubs 114', 124'. This arrangement provides a reinforced cannula which is less prone to wear, kinking and buckling. Fluid flow, however, is equal to the fluid flow through the fine gauge cannula 110'.

Referring now to Figure 11a in which an arrangement of needles and cannula are shown which prevents excessive puncture damage. The arrangement comprises a first fine gauge needle N having a sharp-tipped needle shaft NS and an interface hub NH, a second larger gauge needle N' having a blunt-tipped needle shaft NS' and an interface hub NH' and a large bore cannula 120 having a large bore cannula sleeve 122 and an interface hub 124. In use, the sharp tip of the first needle N is used to puncture the target membrane and the arrangement is advanced until the blunt end of the second needle N' abuts the membrane. The punctured membrane stretches over the blunt end of the needle tip onto the needle shaft NS' . The inner fine gauge needle N is then withdrawn into the lumen of the second needle N' . Figure 11b shows a modification of the arrangement of Figure 11a where a force must be applied to the interface hub NH of the fine gauge needle N to overcome the biasing force of a spring 150 provided within a modified hub NH' o the second N' such that the sharp point of the fine gauge needle N protrudes beyond the blunt end of the second needle N' .

Referring now to Figure 12, a second embodiment of reinforced fine gauge cannula 200 is provided for use with fine gauge needles N. The cannula 210 comprises a first inner cannula 210 provided with a sleeve 212, having a varying diameter increasing from its fine gauge distal end to its proximal end which abuts a first interface hub 214, and a second outer cannula 220 provided with a relatively shorter cannula sleeve 222 which reinforces the first cannula sleeve 212. The cannula 200 may be used with standard fine gauge needles or fine gauge needles of the present invention.

In both embodiments of cannulae 100, 200 the inner and outer cannula sleeves may be separate or fused according t their use. In further embodiments (not shown) the cannulae 100,100' ,110'110* ,120' 120' ,200,210,220 are provided with reinforced cannula sleeves or shafts. The cannula shafts are provided with a first fine gauge portion and a second reinforced portion abutting the cannula hub. Optionally an intermediate reinforced portion is provided on the cannula shaft between the fine gauge portion and the reinforced portion. The interface hubs of all embodiments disclosed herein may be interfaced with infusion device feed lines.

The reinforced needles of the invention may be modified for nerve stimulation. Nerve stimulation comprises passing a low voltage current through a nerve and must be restricted to a localised area. Nerve stimulation may be used to identify the subarachnoid space and peripheral nerves. The needle modification may be accomplished in a number of ways. The lumen of the fine gauge needle may be coated with an insulating material and the stylet connected to a current source. The stylet protrudes from the lumen at the needle point bringing it into electrical contact with the area immediately adjacent the end of the needle shaft. The needle modification may also be accomplished by insulating the reinforced shaft (stylet and introducer needle may also be insulated) . The tip of the needle may then be electrically isolated from the body of the needle. A current is passed to the isolated tip through the needle shaft or stylet to provide a localised low voltage current source. An uninsulated needle may also be used for nerve stimulation when used with an insulated introducer needle or cannula.

As shown in Figure 12, a modified needle N and cannula 210, 220 arrangement may be used for nerve stimulation. In this case, the tip of the needle shaft NS protrudes beyond the insulated cannula sleeve 212. The needle tip is supplied with a low voltage current by connecting the needle shaft NS to an electrical source (not shown) . Where an insulated needle N is being used for nerve stimulation, a standard cutting tip needle provides certain disadvantages. As shown in Figures 13a and 13b a prior art standard cutting needle N is provided with a bevelled needle tip NT and stylet S. Should the stylet S be moved from its standard position (Figure 13a) to an extended position (Figure 13b) the tip of the stylet does not extend sufficiently beyond the needle tip NT. A needle N with an extended stylet S would cause substantial puncture wound damage if inserted in this configuration. Additionally, the cutting action o the needle of Figure 13a creates a puncture wound having a diameter substantially equal to the needle shaft diameter.

Figures 14a, 14b and 14c show first, second and third embodiments of atraumatic needle 310, 320, 330, respectively. Each embodiment comprises a needle shaft 312, 322, 332 having a needle tip 314, 324, 334 and an associated stylet 316, 326, 336. The needle tip 314, 324, 334 and stylet 316, 326, 336 form an atraumatic tip having a pencil-point, a rounded and diamond-shaped profile, respectively. Similarly, Figures 14d, 14e and 14f show fourth, fifth and sixth embodiments of atraumatic needle 340, 350, 360, respectively. Each embodiment again comprises a needle shaft 342, 352, 362 having a needle tip 344, 354, 364 and an associated stylet 346, 356, 366. In these embodiments the stylets are extended beyond the needle tips by a distance approximately equal to the diameter of the needle shaft. For example, for a 29-gauge needle the stylet may protrude from the tip by about 0.3 to 0.5mm. More typically, however, the stylet is extended beyond the tip a distance in the range of about 1 to 2mm. In each of the embodiments of atraumatic needle 310, 320, 330, 340, 350, 360 the stylet 316, 326, 336, 346, 356, 366 is utilized to provide a localized point for nerve stimulation when the stylet is electrically isolated from the needle shaft 312, 322, 332, 342, 352, 362. The profiles of these needles tend to separate the fibres of a target membrane rather than cut through the fibres as does the prior art needle tip. When in place, a low voltage current is passed through the stylet for localised nerve stimulation.

It will be seen that the atraumatic needles disclosed herein may be used in conjunction with the needles and cannulae of the present invention and that the atraumatic needles may be used advantageously in spinal anaesthesia,

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.

Claims

CLAIMS :

1. A needle (10,20,20' ,30,40,50,60) or cannula (100,100',110,110*,120,120*,200,210,220) comprising a hollow shaft and an interface hub (18,28,28' ,38,48,58, 68,114,114',124,124* ,214,224), the shaft having proximal and distal ends, characterised in that the shaft comprises a fine gauge portion (12,22,22' ,32,42,52,62,112,112' ,212) at or towards the distal end and a reinforced portion (16,26,26* ,36,46,56,66,122,122' ,222) at or near the proximal end.

2. A needle or cannula as claimed in claim 1 characterised in that an intermediate reinforced portion (24,24',34) is provided between said proximal and distal ends of the shaft.

3. A needle or cannula as claimed in claim 1 or claim 2, characterised in that a transparent or translucent hub (18,28,28' ,38,48,58,68,124,124' ,224) is provided on the reinforced portion (16,.26,26',36,46,56,66,122, 122' ,222).

4. A needle or cannula as claimed in any of claims 1 to 3, adapted for use with a standard cannula (C) or needle (N) , for use in nerve stimulation or for use in the administration of local anaesthetic agents.

5. A cannula as claimed in claim 4 for use as a sleeve (120, 220) with a standard cannula (C) to reinforce said standard cannula (C), comprising a cannula shaft (122,222) which is shorter than a standard cannula shaft CS and a interface hub (124,224) which receives the interface hub (CH,NH) of a standard cannula (C), a needle (N) or a syringe .

6. A cannula (120) and means for insertion thereof, the insertion means comprising a blunt-tipped needle (N¹ ) which is coaxially and slidingly housed in the cannula (120), the needle (N' ) housing a fine gauge sharp-tipped needle (N) or trocar for puncturing, the needle (N) or trocar protruding slightly from the blunt end of the blunt-tipped needle (N¹ ) whereby a small puncture wound is created by the fine gauge needle (N) or trocar, the insertion means being advanced such that the puncture wound is stretched about the blunt-tipped needle (N' ) to accommodate the bore of the cannula (120) without tearing the puncture wound.

7. A cannula and insertion means as claimed in claim 6, in which the fine gauge needle N or trocar has an operational and inoperational position within the blunt-tipped needle (N'), characterised in that, in the inoperational mode, a biasing means (150) moves the fine gauge needle (N) or trocar rearwardly into the blunt-tipped needle (N' ) and, in the operational mode, a user moves the needle (N) or trocar relative to the blunt-tipped needle (N' ) against the biasing means.

8. A needle (310,320,330,340,350,360) comprising an atraumatic tip having a substantially conical or rounded profile, so that where the needle tip (314, 324,334,344,354,364) is applied against a target membrane, the membrane fibres are separated to allow passage of the needle.

9. A needle as claimed in claim 8, characterised in that the needle (310,320,330,340,350, 360) comprises a stylet (316,326,336,346,356,366) coaxially housed within the shaft (312,322,332,342,352,362) of the needle, so that the stylet (316,326,336,346,356,366) and the needle tip (314,324,334,344,354,364) together form the distal end of the atraumatic tip.

10. A needle according to claim 8, characterised in that the stylet (346,356,366) protrudes from the substantially conical or rounded profile of the needle tip (344,354,364).

11. A needle as claimed in any one of claims 8 to 10 in which the substantially conical or rounded profile of the needle tip (314,324,334,354,364) or stylet (316,326,336,346,356,366) is either a pencil-point tip (314,316,344,346), a rounded tip (324,326,354,356) or a diamond-shaped tip (334,336,364, 366).

12. A needle as claimed in any one of claims 1 to 4 and 8 to 11, characterised in that the stylet

(S,S5,S6,316,326,336,346,356,366) is electrically isolated from the needle and is provided with a connector to allow connection to a voltage or current source.