WO2004064652A1

WO2004064652A1 - A cannula

Info

Publication number: WO2004064652A1
Application number: PCT/GB2003/005709
Authority: WO
Inventors: Prakash Punjabi
Original assignee: Hammersmith Hospital's Nhs Trust
Priority date: 2003-01-17
Filing date: 2003-12-31
Publication date: 2004-08-05
Also published as: GB0301070D0; AU2003295172A1

Abstract

A cannula (12), has an end region (15) of sufficient dimensions as to be located, in use, in an aperture (16) of body tissue to channel fluid through the aperture and adapted so that an operator applying appropriate tension on one or more threads woven in the tissue can draw the tissue around the aperture to control any fluid escape between the cannula and the body; characterised by the provision of one or more members (21, 22) adjacent the said end region of the cannula which are carried by or form part of the cannula adapted to hold the or each thread in tension once the operator is satisfied that the engagement of the cannula end region with the tissue defining the aperture is appropriate.

Description

A CANNULA

Field of the Invention

The invention relates to cannulas which may be attached to an aperture of body tissue to channel fluid through the aperture and more particularly to cannulas used in conjunction with cardiopulmonary by-pass machines.

Background to the Invention

Figure 1 presents a prior art cannula 1 destined to operate with a cardiopulmonary by-pass machine (not illustrated in the Figure). The cannula is shown attached to body tissue 2. The attachment of cannula 1 to the body tissue 2 involves a number of steps and several separate pieces of apparatus. The attachment presented in Figure 1 shows the cannula with two flexible tubes 3 and 4 which are located along the outer surface of the wall of the cannula and which are not carried by the cannula but are initially separate from it and are secured in place on it only when threads 5 and 6 are tied around the tubes and cannula as shown.

The steps involved in attaching the cannula to the body tissue are in essence as follows:

1. Placing purse string stitches at the site of insertion of the cannula. 2. Threading the excess thread from the stitches through two separate pieces of small diameter, flexible plastic tubes 5 and 6.

3. Carrying out the incision and inserting the cannula 1.

4. Locating the threads 10 and 11 from the purse string stitches into the notches 7 and 8 of the end region 9 of the cannula.

5. Drawing the purse strings tight by hand to seal the cannula in place so that the flexible tubes push against the end region of the cannula.

6. Securing the threads 10 and 11 and the flexible tubes 3 and 4 in place by tying them to the trunk of the cannula using threads 5 and 6 or by clamping them using (instead of the threads 5 and 6) arterial clamps.

This prior art cannula has the following drawbacks:

• Any attachment of the cannula to body tissue involves five separate pieces of equipment not including the final tying of threads.

• Any attachment of the cannula to body tissue is multi-step, cumbersome and requires extensive training to enable sound judgement regarding the tension required to hold the cannula in place without damage to the tissue.

• The attachment of the prior art cannula results in variable thread tension which may lead to leakeage.

It is an objective of the present invention to present a cannula whose configuration reduces the number of processes required to secure the cannula to body tissue.

It is a further objective of the present invention to present a cannula whose attachment is simplified and is generally more compact when attached to the body tissue and prior to attachment.

The invention also has as an objective to render the cannula more readily adjustable and removable. It is also an objective of the present invention to provide means for maintaining a constant tension when the cannula is in use in order to reduce any risk of leakage.

The invention also aims at providing a cannula, for which the skills required in its operation may more rapidly be learnt.

Summary of the Invention

h its broadest aspect, the invention covers a cannula having an end region of sufficient dimensions as to be located, in use, in an aperture of body tissue to channel fluid through the aperture and adapted so that an operator applying appropriate tension on one or more threads woven in the tissue can draw the tissue around the aperture to control any fluid escape between the cannula and the body; characterised by the provision of one or more members adjacent to the said end region of the cannula which are adapted to hold the or each thread in tension once the operator is satisfied that the engagement of the cannula end region with the tissue defining the aperture is appropriate.

Employing a cannula of this configuration will reduce the number of steps required to attach it in the aperture of body tissue. Any such operation will involve steps which are less cumbersome as those associated with the prior art system. It will be, in particular, easier to adjust during the operation and to remove thereafter. Furthermore, the usage of this cannula may more readily be learnt by trainees.

In a subsidiary aspect, the or each member employed in holding the or each thread is a tube which is sufficient in diameter to receive, in use, a portion of thread which is sufficiently flexible so that, in use, when appropriate pressure is applied to the tube's walls by any appropriate pressure applying means, these are crushed against a portion of thread received, in use, by the tube; characterised in that the flexible tube is joined to the rest of the cannula by a portion which is sufficiently weakened to allow the rapid removal of the flexible tube - for example in a so-called tear-off action.

This configuration is particularly advantageous as it provides practical means for achieving the required tension in the thread and achieves advantageous flexibility to allow the tubes to be readily removed.

In a further subsidiary aspect, the cannula incorporates a region - for example an end region adjacent to the end region of the cannula - which concertinaes to allow the tube effectively to extend or contract in its overall length to a limited extent during use.

This configuration advantageously allows the tube to vary in length during use which may be particularly advantageous when the body tissue is one which periodically displaces.

In a further subsidiary aspect, the or each member comprises a projection extending from the cannula and so sized and shaped that the thread may be wound quickly around it.

This configuration is advantageous because it further simplifies the manner in which the thread is anchored so as to remain in tension during the use of the cannula as it involves no extra threads. The operation of winding thread around the projection has the additional benefit of being of the type that is readily learnt by trainees.

In a further subsidiary aspect, the or each projection is at least partially cut into the exterior of the cannula wall.

This configuration renders the cannula more compact while retaining the advantageous characteristics of anchoring the thread by means which are relatively straightforward to learn.

In a further subsidiary aspect, the or each projection is an eye. Utilising an eye is particularly advantageous in this context as it will allow the projection itself to be easily localised so as to allow rapid anchoring of the thread in tension.

In a further subsidiary aspect, the or each member incorporates an over-centre- action clamp.

Employing this kind of clamp is advantageous because it allows the anchoring of the threads without requiring complex multi-handed knots to be carried out.

This type of system is also particularly practical in terms of releasing the thread and then the cannula from its attachment with body tissue.

In a further subsidiary aspect, the or each member incorporates a clamp in which at least one of the j aws has a resili entry biased closing action.

In the context of the present invention, employing a clamp in this manner may be more easily manufactured while presenting a cannula which is compact and whose use is straightforward to learn.

In a further subsidiary aspect, at least one jaw incorporates a first, relatively rigid portion and a second, relatively resilient portion, the second portion being destined to engage the thread when the thread is located in the jaws and being also composed of material whose frictional thread-gripping characteristics are such as to tend to anchor the thread in the jaws on engagement therewith.

This configuration is advantageous because it allows the anchoring of thread without requiring the thread to be unduly wound around a projection as some of the preceding aspects consider. Such a cannula is particularly compact and straightforward to operate.

In a further subsidiary aspect, the or each member is located on a collar whose diameter allows it to be mounted on the cannula' s wall. Brief Description of the Drawings

Figure 1 shows a prior art cannula in perspective view.

Figure 2 shows a cannula in cross-section according to a first embodiment of the present invention.

Figure 3A shows a partial cross-sectional view of a cannula in accordance with a second embodiment.

Figure 3B shows a flexible tube in cross-section.

Figure 4 shows a cannula in cross-section in accordance with a further embodiment.

Figure 5 shows a perspective view of a cannula according to a further embodiment.

Figure 6 shows a cross-sectional view of a cannula in accordance with a further embodiment of the present invention.

Figure 7 shows a side elevation of part of a cannula clamp.

Figure 8 shows a partial cross-sectional view of a cannula in accordance with a further embodiment.

Figure 9 shows a perspective view of part of a cannula in accordance with a further embodiment.

Detailed Description of the Drawings

Figure 1 is discussed in detail in one of the preceding sections entitled 'Background to the Invention'. Figure 2 presents a cannula generally referenced 12. The cannula comprises a thick- walled portion or trunk 13 forming a central channel 14 through which a fluid may flow. At its end region 15, the cannula engages an aperture created by an insertion in tissue 17. There is also provided in the end region 15 a flange 18 which overlaps the tissue region defining the aperture 16. The flange 18 extends essentially in the radial direction and is interrupted only by two diametrically opposite notches 19 and 20. These notches allow the passage of threads which would result from purse string stitches carried out in the tissue 17 and which are not represented in the drawings for clarity.

The threads resulting from the purse string stitches may be drawn through flexible tubes 21 or 22. When the threads are in appropriate tension, a further thread may be wound about the periphery of the cannula and tightened so as to crush the flexible tubes 21 and 22 in order to trap the thread in tension. When the threads are sufficiently tight, the purse strings stitches cause the tissue 17 to be drawn against the end region 15 of the cannula so as to effectively prevent the passage of fluid between the tissue 17 and the outer surface 24 of the cannula. The fluid is therefore constrained to flow through channel 14.

Flexible tubes 21 and 22 form an integral part of the cannula. The section between the flexible tubes and the trunk 13 of the cannula may include perforations such as that referenced 23 which may permit an operator to tear the flexible tubes away from the trunk. The section joining the flexible tubes to the trunk may be modified by the person skilled in the art so as to employ other similar means to permit ready detachment of the flexible tubes from the trunk.

Figure 3A shows a portion of cannula trunk 25 with a flexible tube 26 of advantageously modified kind. The lower extremity of the flexible tube 15 is equipped with a concertina member 27 which has a number of fold lines 28 which run along the periphery of the tube and allow it to be extended or collapsed. This embodiment is particularly advantageous because when the lower extremity of the flexible tube enters into contact with the outer surface of the tissue, the tube will remain in contact even when the tissue regularly displaces. Concertina member 27 is designed in order to be tapered so as to reduce the area of contact onto the tissue.

Figure 3B shows a further flexible tube 29 which has a concertina member 30 which widens out at its lower extremity 31 and thereby achieves a greater surface of contact as compared with concertina member 27 described above in the context of Figure 3 A.

Figure 4 presents a cannula 32 with a trunk 33. Out of trunk 33 extend radially two diametrically opposite projections 34 and 35. These projections have at their outer extremities portions 36 and 37 which are of greater diameter than portions 38 and 39 located radially inwards. Around these projections, the thread resulting from the purse string stitches may be retained by winding these around radially inward portions 38 and 39. This configuration would allow the threads to be maintained at the appropriate level of tension selected by the skilled operator of the cannula.

Figure 5 presents a cannula generally referenced 40 with a channel 41 and a trunk 42. The cannula further incorporates a projection 43 which is cut into the exterior of the trunk 42. This manufacturing material saving configuration may permit the attachment of the purse string threads in a similar fashion to that presented in Figure 4. This projection may also be made sufficiently resilient so that it may act as a jaw for clamping the threads between the projection and the trunk of the cannula.

Figure 6 presents a cannula 44 with a ribbed end region 45. This cannula incorporates a clamp 46 with a radially outer jaw 47 and a radially inner jaw 48. At the upper extremity of the gap between the jaws, the gap widens sufficiently so that the operator may readily locate the threads in the clamp.

Once the operator locates the threads in the wide upper extremity, the operator may readily push the threads down the gap of the clamp against the resilience or friction of the jaws. This particular clamp has a so-called 'over-centre' action. That is, jaw 47 is biased towards closure beyond a certain stage of its approach towards jaw 48; and biased towards opening when moved beyond that same stage in the opposite direction. Once the operator releases the threads, these find themselves crushed between the jaws of the clamp which effectively anchor the threads therein.

Figure 7 shows in more detail a possible clamp arrangement 49 extending from trunk 50 (partially shown in the drawing). Arrangement 49 comprises a relatively rigid portion 51 and a relatively resilient portion 52 which is shown engaging a thread 53. Portion 52 incorporates a first half 54 and a second half 55 which define at their upper extremity a N shaped notch to facilitate the location of the threads into the clamp. Halves 54 and 55 will be selected from material with a frictional thread-gripping characteristic sufficient to tend to anchor the thread between the halves on engagement.

Figure 8 shows part of a cannula 56 with a tube 57 above which a projecting eye extends radially from the camiula and may be advantageously used to improve the localisation of the projection and to ease the way in which the threads may be wound round the projection.

Figure 9 shows part of a cannula 60 and a collar 61 sufficient in internal diameter to be placed about the cannula's wall 62. The cannula's wall 62 is provided with a flange 63 which prevents collar 61 of being moved downwards past its upper surface 64.

In order to prevent the collar from rotating when it is placed in a position where it abuts against surface 64, there are provided two diametrically opposite spigots 65 and 66 on collar 61 which may become trapped in corresponding recesses provided on wall 62 of the cannula such as that referenced 67. Two diametrically opposite eyes 68 and 69 are also provided on the collar and are destined to be employed in the operation of holding the thread (not illustrated in the drawing) in tension.

Claims

1. A cannula, having an end region of sufficient dimensions as to be located, in use, in an aperture of body tissue to channel fluid through the aperture and adapted so that an operator applying appropriate tension on one or more threads woven in the tissue can draw the tissue around the aperture to control any fluid escape between the cannula and the body; characterised by the provision of one or more members adjacent the said end region of the cannula which are carried by or form part of the cannula adapted to hold the or each thread in tension once the operator is satisfied that the engagement of the cannula end region with the tissue defining the aperture is appropriate.

2. A cannula according to claim 1, wherein the or each member employed in holding the or each thread is a tube which is sufficient in diameter to receive, in use, a portion of thread and which is sufficiently flexible so that, in use, when appropriate pressure is applied to the tube's walls by any appropriate pressure applying means, these are crushed against a portion of thread received, in use, by the tube; characterised in that the flexible tube is joined to the rest of the cannula by a portion which is sufficiently weakened to allow the rapid removal of the flexible tube - for example in a so-called tear-off action.

3. A cannula according to claim 2, characterised in that incorporates a region - for example an end region adjacent the end region of the cannula - which concertinaes to allow the tube effectively to extend or contract in its overall length to a limited extent during use.

4. A cannula according to any preceding claim, characterised in that the or each member comprises a projection extending from the cannula and so sized and shaped that the thread may be wound quickly around it.

5. A cannula according to claim 4, wherein the or each projection is at least partially cut into the exterior of the cannula wall.

6. A camiula according to claim 4 or 5, wherein the or each projection is an eye.

7. A cannula according to any preceding claim, wherein the or each member incorporates an over-centre-action clamp.

8. A cannula according to any preceding claim, wherein the or each member incorporates a clamp in which at least one of the jaws has a resiliently biased closing action.

9. A cannula according to claim 9, wherein at least one jaw incorporates a first, relatively rigid portion and a second, relatively resilient portion, the second portion being destined to engage the thread when the thread is located in the jaws and being also composed of material whose frictional thread- gripping characteristics are such as to tend to anchor the thread in the jaws on engagement therewith.

10. A cannula according to any preceding claim wherein the or each member is located on a collar whose diameter allows it to be mounted on the cannula's wall.

11. A cannula as herein before described with reference to and/or illustrated in any appropriate combination of the accompanying text and/or figure 2 onwards