CA1293898C

CA1293898C - Catheter and method of making the same

Info

Publication number: CA1293898C
Application number: CA000525429A
Authority: CA
Inventors: William Mccormick; Miles C. O'donnell
Original assignee: McCormick Laboratories Inc
Current assignee: McCormick Laboratories Inc
Priority date: 1985-12-17
Filing date: 1986-12-16
Publication date: 1992-01-07
Anticipated expiration: 2009-01-07
Also published as: FR2591492A1; GB2186192B; JPS62176461A; DE3642948A1; GB8629653D0; FR2591492B1; GB2186192A

Abstract

Abstract of Disclosure A catheter and a method of making the same, which catheter has a means for interferring with an electromagnetic field to allow accurate detection of the catheter through tissue, the catheter comprising a first tube extruded over a continuous, solid core material having a diameter equivalent to the desired diameter of the inner passagway of the catheter, bands of metal fused to the first tube at various locations, and a second tube which is extruded over the first and the metal bands. The double-walled continuous tube is then cut into individual tubes and the core material is removed to form the catheter of this invention, which has a smooth outer surface and an embedded metal band.

Description

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Field of the Invention This invention relates to a catheter with a metal element embedded within its wall at a preselected~location in order to allow the catheter to be detected accurately inside a patient, and a method of making the same.
Backqround of the Invention Catheters are used in a variety of medical applications, and in some, they must be precisely positioned initially and kept in that position despite movement of the patient or other factors. One example of such catheters are tracheal tubes. With many medical patients, it is necessary to insure that the breathing passageway is kept open at all times, and this is accomplished by a tracheal tube. The tube is inserted through the patient's mouth or nose, and it extends down into the patient's throat and into the patient's windpipe or trachea. Air can then pass through the tube lumen into and out of the patient's lungs. The principal drawback of these tubes is that there is not much room for error in placement of the~distal or internal end of the tube inside the patient's wlndpipe ln order for the tracheal tube to be effective, ::
particularly with a pediatric patient.

; As might be expected, the positioning and monitoring ; , ~ problem~ are particularly acute with infants or pediatric :, ~ patients, who have such tubes inserted in most critical care ` .J

338~3 situations and for up to three-fourths of all surgery involving general anesthesia. There is much less margin for placement error in infants or pediatric patients because the tracheas are much shorter. Also, the tracheal walls of infants and children are fragile and much more susceptible to mucosal wall irritation and rupture, which could be caused by any abrupt surface discontinuity on the tube. For this and other reasons, tracheal tubes for infants do not have inflatable cuffs to anchor the distal ends in place. Thus, they are more susceptible to movement.
Consequently, proper tube placement and monitoring are much more difficult and critical with pediatric tracheal tubes.
A new method of and apparatus for accurately cletermining the positioning of a tracheal tube inside a trachea is disclosed in~McCormick U.S. Patent No. 4,431,005 and its related patents, Bresler U.S. Patent No. 4,445,501, and Bresler U.S. Patent No.
;4~,416,289. In these, the position of a tracheal tube inside the ~:
trachea is~determined by a device which generates a narrow electromagnetic field and detects disturbances in that field caused by a piece of me-tal placed around the outside of the distal end of the ~tracheal tube. The metal disturbs the narrow field even ~hrough biological tissue. Accordinglyr the position oE the distal end can be determined when the device detects the resulting field disturbance. The tube for use with this device is shown in ; the patents. It has a piece of metal wrapped around and secured to the outside of a commonly used plastic tracheal tube. The metal is then covered by a plastic coating.
Unfortunately, these particular tubes are unsatisfactory, particularly for pediatric patients, for a number of reasons. First, even though it has a thin coating, the metal band can still irritate a child's trachea very easily because it protrudes significantly from the outer wall surface of the tube. Moreover, the metal band cannot be protected by an inflatable cuff. Such cuffs are unsuitable for use with the fragile wall of an infant~s trachea, and they would also cause insertion problems due to the narrow space in which the tube must fit. Further, the pediatric tracheal tubes have narrow lumens and thin walls, making them both flexible and easily comressible. Thus, wrapp1ng the metal band too tightly around' the preformed tube, as might occur occasionally during ~,manufacture, might lead to a compression of the wall and the critical air passageway in the tube. (The allowable tolerance for the inside diameter of such tubes is a mere + .003 inches.) On the other hand, failure to wrap the band tightly might result in serious consequences if the band should dislodge during use.
Summary of the Invention We have discovered a double-walled catheter having a means for interfering with a-electromagnetic field embedded between its walls, the catheter comprises a first tube to which ~:
the means for interfering is fused at a selected location and a ::

4 60412-l~lS
second tube disposed.over the first (and the means for interfering) to complete the double-walled catheter. In addition, depth markings may be printed along the length of the first tube prior to the attachment of the second tube so that in the finished catheter the markings are protectsd by the second tube and thus both isolated from any. tissue and no~ susceptible to erasure. The method for making this catheter generally comprises extruding the first tube, fusing the means for interfering in place and extruding the s~cond tube over the first and the means for interfering. ...
In one aspect, the invention provides, a catheter for insertion into biological ti~s.sue to provide an opening therein, and when 50 inserted, onl~. the distal end of said catheter being detectable outside the. biologica.l tissue by means of a narrow electromagnetic ~ield,~rsaid catheter comprising:
~ a double-walled tubul.ar.section having a proximal end and a :~ distal end~ .
;~ said double-wallad tubular section~ which does not interfere with an electrom~g.netic field, comprising a first tube., said first tube ext~nding.th.e.ent~ire leng.th o~ said catheter from the : ~ proxlmal end to the distal end, said first tube defining an internal passageway.which also extends the. length of said catheter, and hauing. ~n. oute~r surface which extends the length oE
said catheter, a.nd ~ second .tube,~said second tube extending the length of said c~the.~er.and bei.ng connected to the outer surface o.f said first tube over its entire length forming a seam therebetween, said secon.d tube having a smooth outer surface which r.,-~

.
. 4~ - 60412-1615 defines the outer surface of said double-walled tubular section, and a means for interfering with an electromagnetic field, said means for interfering being a small and narrow metal band attached to the outer surEace o,f said first tube on:Ly at the distal end of said catheter, said means for interfering fitting into an indentation in an inn,e,r wall of said second tube at the distal end so as to maintai~ the ,smooth outer surface of said second tube without any protrusio~ at the means for interfering, said means for interf,ering dis.tu~ing a narrow electromagnetic fie.ld directed L . towards it even throug~ biological tissue, but said means for interfering bein,g so ~mall and narrow a metal band ~o as to only , disturb the field when~,the field is directly or nearly directly ; above said means.f.or i,nterfering.
A further as~ect of the invention provides a method of -~aking a cathete~ ,the,,pos.ition of wh.ich can be accurately . determined, comprising~,.
~ ,, creating a con~in~ous core having an outer diameter : approximately e.~.~al,.~o,diameter of the inner passageway of, the catheter,. ': "..
. forming a continu,ous fiLst tube over said core to a :
: substantially un,i~,o.rm.thickness,.
, bonding a means . ar interfering with an elec-tromagnetic field to said first tu,b.,e,at,,selected locations, : applying a c~nti~.~ous second tube over said first tube and said means for interf.ering to creake a continuous double-wall~d tube over said conti~u.ous core, said continuous tube having a cylindrical seam at the interfa.ce of said first and second tubes 1 ~ 3 ~

~ (b) and, cutt-ing said continuous double-walled tube and core into individual catheters a.nd removin~ said core therefrom.
The tube of the preferred embodiment is made by first extruding a continuous, solid core with.an outside diameter equal to the required inner.~iameter for the desired tracheal tube. The core, which is usually several thousand feet long, is then fed into an extruder which.,evenly extrudes a first thin tube of plastic (polyvin~lchloride in the preferred embodiment) around the core over its entire,length~ This first tube has a uniform thickness of about,on,e,half that of the finished catheter. As the core material has a hi,gher melting temperature than the,tube material, the co,rq,rqmains solid during thi,s extrusion proc,ess.
:: At selected intervals~ thin bands of metal foil are then wrapped around the first, t,ub,e,, which is.still in place on the continuous solid core. One.end:~f a,.metal ~oi.l band is fused to the first tube by a high,elect,rical current discharge of short duration..
The band is then wrapp~ed around the first tube until the free end : overlaps the end,,~a,lre,a,dy fused to the.tube. The overIapped porti~ns aro Eu~ed together to secure the : ~ ~

band to the first tube. While the first tube is still on the core, depth markings are printed along the length of the first tube. The first tube and the core are then subjected to another extrusion process whereby a second tube of plastic, having a thickness of about half that of the finished catheter, is added. The second tube fuses to the first during this process, forming a continuous double-walled tracheal tube. A
radiopaque marker in the form of a line extending the length of the tube is coextruded as part of the second tube. This marker is a standard one for such tubes and is used to help identify the tube in an X-ray. The tube is then cut at the appropriate places, and the core is removed to form the completed double-walled tracheal tube.
Description of the Preferred Embodiment Drawin~s I turn now to a description of the preferred embodiments, after first briefly describing the drawingsO
Figure 1 is a perspective view of a double-walled tracheal tube of the invention;
Figure 2 is a lengthwise cross-sectional view of the double-walled tracheal tube of this invention;
Figure 3 is a cross-sectional view taken along lines 3-3 of Figure l;
Figure 4 is a cross-sectional view taken along lines 4-4 of Figure l;
Figure 5 is a perspective view of the end of the tracheal tube of this invention with a portion of the second or outer tube cut away' ;

Figure 6 is a simplified drawing of the extruder for making the inner or first tube.
Figure 7 is a simplified cross-sectional view of the printer unit and assembler unit for adding depth markings and for attaching the metal foil to the inner or first tube respectively;
Figure 8A and 8B are side views taken along lines 8-8 of Figure 7 showing the manner in which the metal foil is fed to the assembler unit;
; Figure 9A to 9D shows the sequence of steps for attaching the metal foil to the inner or first tube.

Referring to Figure 1, a double-walled catheter or tracheal tube according to the invention is shown at 10. The tube lO generally has a connector endpiece 12 at the proximal end 14 of the tube 10 for attachment to a respiratory support system (not shown), and a plastic double-walled tubular section 16 surrounding a central air passageway 18. The tubular section 16 is connected to the endpiece 12, and the passageway 18 extends from the endpiece 12 to a beveled opening 20 located at a distal end 22 of the tube 10. The tip of the distal end ; ~ ~ 22~is identified as 24. A small hole 26, commonly known as a Mu~rphy hole, is also located in the tubular section 16 at its distal end 22, and a cylindrical band of thin metal oil 30, :: :

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having a distal edge 32, is encased within the tubular section 16 of the tube 10 near the distal end 22 and the hole 26. The distance along the length oE the tube 10 between the distal edge 32 of the metal band 30 and the distal tip 24 is determined by the proposed medical use of the catheter tube and the desired anatomical location for the metal band 30.
Also encased within the double-walled tubular section 16 are the depth markings and indicia 34. A radiopaque line 36 is an integral part of the second or outer tube wall in one preerred embodiment. The line 36 extends the length of the tube 10 while the markings and indicia 34 extend between the metal band 30 and the endpiece 12.
Referring to Figure 2, the tubular section 16 of the invention is comprised of an inner or first tube 40 and an outer or second tube 50. The first tube 40 has a uniform wall thickness along its length and an outside surface 42 on which the depth markings and indicia 34 are printed and the metal band 30~is disposed. The second tube 50 also has a uniform wall thickness along its entire leng~h except at an indentation 52 which is occupied by the metal foil 30. The outer surface 54 of the second tube 50 is of uniform dimensions along its entire length resulting in a smooth, continuous outer surface for the double-walled tubular section 16. Because -the second tube 50 ~rovides this indentation 52 for the metal band 30 to occupy, the metal band does not introduce any surface discontinuities in the form of bumps or protrusions to the ~3~

outer surface 54 of tubular section 16. This is important because outside wall smoothness is required in tracheal tubes, particularly in pediatric ones.
As shown in Figure 2, there is a seam 60 between the first tube 40 and the second tube 50. The outside surface 42 of the first tube 40 contacts the inner surface 56 of the second tube 50. The two tubes 40, 50 are fused together at these contacting surfaces to form the cylindrical seam 60 that extends the entire length of the tubular section 16, e~cept in the portion occupied by metal band 30. The seam 60, however, does include the areas of the depth markings and indicia 34.
The searn 60 between the two tubes 40, 50 may be created by any number of well known thermoplastic processes and is ideally formed when outer tube 60 melts partially on top the outside surface 42 of inner tube 40. The specific method by which this is accomplished for the preferred embodiment ~ill be discussed hereinaEter. (In the preferred embodiment, the seam 60 is visible under slight magnification, particularly when the tube is cut cross-sectionally.) Also shown in Figure 3 is the cross section of radiopaque stripe 36 which runs the entire length of tubular section 16. The radiopaque stripe 36 may be included as an integral part of either or both tubes 40, 50 and can be formed by various well known coextrusion processes, the preferred one also to be discussed hereina~ter.
As best shown in Figures 4 and 5, the metal band 30 is attached to the first tube 40 at three fusion sites 6~, 64, 66 _ 9 _ 60412-1615 disposed at about 120 apart around the circumference of the tube 40. (In the preferred embodiment, only fusion site 62 is used. Site~ 64 and 66 are optional.) First, the primary or leading edge 70 o~ the n~etal band 30 is welded to the first tube 40 at fusion site 62. The metal band is then wrapped around the tube 40 and welded to the tu~e ~0 at fusion sites 64 and 66, as shown in Figure 4. When fully wrapped around the tube 40, a trailing edge 72 of the metal band 30 overlaps the primary edge 70 of the band 30. This forms an overlap area 74. A welded overlap joint 68 is made at this overlap area 74, which e~Eectively fuses the metal band 30 to itsel~. There are various means of attaching the metal band 30 to the tube 90.
The preferred process for doing so in this invention is described later.
The tube lO is made in the ~ollowing manner. First, a continuous solid core 80 is made having an outer diameter which i5 identical to the inner diameter of the desired air passageway 18 for the tube lO. The core ~0 itself may be made o~ any of a number of materials including metal wire, which have a higher melting point than the usual materials used for the tube itself, thereby enabling the tube materials to be extruded over it without fusing to the core.
The core 80 is then wrapped on a ~eed spool 82 and fed to the extruder 84 as shown in ~igure 6, which in the preferred embodiment extrudes a polyvinylchloride (PVC) layer over the core 80. This layer is actually the ~irst tube 40.
Polyurethane, silicone-rubber or Te~lon could be used instead.

*Trade Mark - ~93~

In any case, because of the lower melting temperature of the tube material (the PVC in the preferred embodiment), the first tube 40 does not fuse to the core 80 during this process.
Instead, the first tube 40 coats the entir_ core 80 to a uniform thickness over the entire length. The core 80 with the first tube 40 is tlnen drawn up on a take-up spool 88. At thls point, the continuous core and the extruded first tube 40 may be several thousand feet long.
Referring to Figure 7, the take-up spool 88 is then unwound, and the core 80 with the first tube 40 is fed into a printer unit 90. Initially, the core 80 with the first tube 40 moves into a print station 92 in the prin~er unit 90. At the print station 92, the depth markings and indicia 34 are applied to the outer surface 42 of the extruded first tube 40. The :
core 80 with the tube 40 is~then fed into an assembler unit 100. The core 80 and the first tube 40 go through a . ~ :
~ workstat~ion 102 in the unit 100. As shown in Figure 8 (a :
cross-sectional view of Figure 7 taken along lines 8-8), a ;suppl~y reel 104 is disposed near the workstation 102 at a right angle to the ùirection of feed for the core 80 and first tube 40. The supply reel 104 carries several hundred feet of a strlp of metal foil 106. The foil 106 is molypermalloy. The foll~106 is Eed between advance wheels 108, 110 and through a cutting station 112. The cutting station 112 is comprised of a block 114 and a cutting tool 116. The foil 106 passes over the block 114 below the cutting tool 116 so the leading edge 118 of :: :
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9~

the foil 106 is positioned tangentially to (and in contact with) the first tube 40 in the workstation 102. This positioning is just downstream (away from the spool 88) of the depth markings and indicia 34 just added by the printer unit 90.
As shown in Figure 7, a pair of welding heads 120, 122 are positioned above the leading edge 118 of the rnetal foil 106 and the first tube 40 in the workstation 102. When the leading edge 118 of the foil is in place, a controller 124 moves the welding heads 120, 122 down to contact the leading foil edge 118 and the first tube 40, as shown in Figure 8B (for we~ding head 122). Actually, the heads 120, 122 press the leading edge 118 of the foil 106 against th~ first tube 40 at a pressure of 0.20 pounds, and the welding heads 120, 1~2 then briefly ` :discharge an intense current. (The current is actually generated by a:transformer 126 connected to the heads 120, :
122). The current is 500 amps, and it is applied for 0.005 seconds. The welding current causes the foil 106 and the area of the first tube 40 immediately thereunder to fuse together ~

: : :
~ forming weld 62 (as shown in Figure 4). The short duration of ::
'he current, however, confines the melting to the immediate area of the foil and tube and to a depth of only a few thousandths of an inch into~the~tube 40. Thus, while welding at this pressure and current for thls period of time does attach the foil to the~tube, it does not affect the inner :portion of the PVC tube or the core, even with the thinnest PVC
wal]..

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Following the attachment of the leading edge 118 the cutting tool 116 falls, as shown in Figure 8B, and it cuts the foil 106 so that only a short foil strip 130 is actually attached to the tube 40 by the ~eld 62. The strip 130 has a length just exceeding the outside circumference of the first tube 40.
As shown in Figure 9, a rotating wrapping fixture 132 then moves around the first tube 40 and the core 80 in the direction shown by the arrow. This wraps the foil strip 130 around the first tube 40, as shown sequentially in Figures 9B, 9C, and 9D. As has been previously explained, the foil strip 130 is longer than the circumference of the first tube ~0, and there is an area of overlap 74 when the foil strip 130 is wrapped around the tuhe 40, as shown in Figure 4 and 9D. Once this overlap 74 is created, the welding heads 120, 122 are then brought down into contact with it ~only head 122 is shown in Flgure 9~, and the overlap 74 lS fused to the portion of the foil s~trip 130 and tube 40 underneath it in the same manner the leading edge 118 of the foil was originally ~used to the tube :40. The foil strip 130 has now become the me ~l band 30 surrounding the first tube 40. Alternately, other welding heads may be added to provide additional fusion joints at points intermediate between the le~ading edge 118 and the overlap 74. Such optional fusion joints are 64 and 66 shown in Figure 4.

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Once the metal band 30 is attached, that portion of the first tube 40 and the core 80 are then moved out of the workstation 102, and the process of attaching a metal band is repeated on another section of the first tube 40. This process continues until metal bands are attached at intervals along the entire continuous length of the core 80 and first tube 40. The distance between the metal bands is, of course, somewhat greater than the overall length of an individual tracheal tube.
Finally, the banded and printed first tube 40 and core 80 are fed from the workstation 102 to a take-up spaol 134, as shown in Figure 7. The take up spool 134, with the banded and imprinted tube ~0 and core 80, are then fed to another extruder 140 which extrudes a second tube 50 around it. In this extrusion process, the first tube 40 fuses to the second outer tube 50, except where the metal bands 30 are located. The fusion of the two tubes 40, 50 forms the seam 60 resulting in the doubled-walled structure of the tracheal tube 10, the overall wall thickness of which is the same as that of conventional tracheal tubes. Accordingly, the second tube 50 is about half the thickness of the desired wall thickness of .:
the tracheal tube. This extrusion process also forms the indentation 52 in the second tube 50 into which the metal band , :, , : ~
~flts (~see Figure 2). Also, as part of the second extrusion process ~using a crosshead extrusion method), the radiopaque line 36 is coextruded along the length of the second tube 50.
The line 36 may be a barium, a bismuth or a tungsten base of ~' ~
i the type usually used for such markers. The line 36 rnakes it easier ~o detect the tube in an X-ray, and is shown in Figure 3 in cross-section. (The line 36, however, could be coextruded as part of the first tube ~0.) - The resulting continuous double-walled tube is next cut into segments, each slightly longer than a finished catheter. The cllts are made near the metal bands 30 so that when the tube is finished, the metal bands will be near the distal end 22.
The resulting tubes are then completed by removing the core 80, and finishing the tube. The core ~0 is removed by cutting a small piece of tubing away from the core at one end.
The then-protruding core 80 can then be easily pulled out.
Once this is done, the tube is finished by cutting the tip at an angle 20, creating the Murphy hole 26, and adding the endpiece 12. The finlshed tube is smooth both inside and out with very precise internal and external diameter. In particular, the tube has smooth internal and external surfaces with no surface bumps, protrusions or discontinuities, and the metal band is secured within the tube, totally isolated rom the tissùe into which the tube is inserted. At the same time, the depth markings are also protected from erasure and contact with tissue.
Other variations will occur to those skilled in the art.

Claims

1. A catheter for insertion into biological tissue to provide an opening therein, and when so inserted, only the distal end of said catheter being detectable outside the biological tissue by means of a narrow electromagnetic field, said catheter comprising:
a double-walled tubular section having a proximal end and a distal end, said double-walled tubular section, which does not interfere with an electromagnetic field, comprising a first tube, said first tube extending the entire length of said catheter from the proximal end to the distal end, said first tube defining an internal passageway which also extends the length of said catheter, and having an outer surface which extends the length of said catheter, and a second tube, said second tube extending the length of said catheter and being connected to the outer surface of said first tube over its entire length forming a seam therebetween, said second tube having a smooth outer surface which defines the outer surface of said double-walled tubular section, and a means for interfering with an electromagnetic field, said means for interfering being a small and narrow metal band attached to the outer surface of said first tube only at the distal end of said catheter, said means for interfering fitting into an indentation in an inner wall of said second tube at the distal end so as to maintain the smooth outer surface of said second tube without any protrusion at the means for interfering, said means for interfering disturbing a narrow electromagnetic field directed towards it even through biological tissue, but said means for interfering being so small and narrow a metal band so as to only disturb the field when the field is directly or nearly directly above said means for interfering.

2. The catheter of claim 1 wherein said outer surface of said first tube has depth markings printed thereon.

3. The catheter of claim 1 wherein said metal band is fused to said first tube.

4. The catheter of claim 3 wherein said metal band has a leading edge and a trailing edge which are fused to the first tube.

5. The catheter of claim 4 wherein said leading edge and said trailing edge of said metal band overlap when said band is wrapped around said first tube.

6. The catheter of claim 1 wherein a radiopaque stripe is included along the length of either said first tube or said second tube.

7. A method of making a catheter, the position of which can be accurately determined, comprising:
creating a continuous core having an outer diameter approximately equal to diameter of the inner passageway of the catheter, forming a continuous first tube over said core to a substantially uniform thickness, bonding a means for interfering with an electromagnetic field to said first tube at selected locations, applying a continuous second tube over said first tube and said means for interfering to create a continuous double-walled tube over said continuous core, said continuous tube having a cylindrical seam at the interface of said first and second tubes and, cutting said continuous double-walled tube and core into individual catheters and removing said core therefrom.

8. The method of claim 7 wherein said creating a continuous core comprises extruding said core.

9. The method of claim 8 wherein said core is made of a lubricious polymer with a higher melting point than said first tube.

10. The method of claim 7 wherein said first tube is extruded of polyvinylchloride.

11. The method of claim 10 wherein said first tube is extruded so that its thickness is approximately one half that of the overall wall thickness of the catheter.

12. The method of claim 7 wherein said bonding a means for interfering comprises fusing a piece of metal foil to said first tube at a leading edge of said foil and at a trailing edge of said foil.

13. The method of claim 12 wherein said fusing is accomplished by applying an electric weld to said foil so that a small portion of the foil and the adjacent area of the first tube melts together.

14. The method of claim 12 wherein trailing edge of said metal foil overlaps said leading edge and a fusion weld is made at the overlap.

15. The method of claim 12 wherein fusing said metal foil to said first tube is done at location intermediate between said leading and trailing edges.

16. The method of claim 7 wherein applying a continuous second tube comprises extruding a second tube over said first tube and said means for interfering.