U.S. patent number 3,890,976 [Application Number 05/434,937] was granted by the patent office on 1975-06-24 for catheter tip assembly.
This patent grant is currently assigned to Medical Products Corporation. Invention is credited to Seymour Bazell, Edward M. Goldberg, Ralph G. Ostensen.
United States Patent |
3,890,976 |
Bazell , et al. |
June 24, 1975 |
Catheter tip assembly
Abstract
A catheter having an improved tip structure. The catheter tube
has a relatively low durometer tubular body portion and a separate
higher durometer molded tip thereon which does not collapse when it
strikes an obstruction during insertion. Preferably, the tip
assembly is precision molded from a suitable plastic, such as PVC,
acrylates, urethanes, styrenes or the like, having a durometer
greater than the tube body, and an inwardly tapering contour to
provide for ease of insertion. The distal aperture of tips for
endotrachael-type tubes also have non-beaded, chamfered leading
edges. The tips may be color coded to the internal diameter of the
catheter tube for easy operating room identification, and may be
radio-opaque. The tube body is precurved into a hyperbolic shape
with the distal end being the "straight" part of the hyperbolic
curve, terminating in the molded tip.
Inventors: |
Bazell; Seymour (Skokie,
IL), Ostensen; Ralph G. (Morton Grove, IL), Goldberg;
Edward M. (Glencoe, IL) |
Assignee: |
Medical Products Corporation
(Skokie, IL)
|
Family
ID: |
26972198 |
Appl.
No.: |
05/434,937 |
Filed: |
January 21, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
301172 |
Oct 26, 1972 |
|
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|
Current U.S.
Class: |
128/207.15;
604/103.1; 604/915; 604/523 |
Current CPC
Class: |
A61M
25/0068 (20130101); A61M 25/10 (20130101); A61M
25/008 (20130101); A61M 25/0108 (20130101); A61M
2025/1093 (20130101); A61M 25/0069 (20130101) |
Current International
Class: |
A61M
25/00 (20060101); A61M 25/10 (20060101); A61M
25/01 (20060101); A61m 025/00 () |
Field of
Search: |
;128/239,348-351 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truluck; Dalton L.
Attorney, Agent or Firm: Molinare, Allegretti, Newitt &
Witcoff
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of our co-pending application Ser.
No. 301,172, filed Oct. 26, 1972.
Claims
We claim:
1. An improved tracheal tube comprising:
a. a flexible, tubular body portion with a durometer of above 60 to
about 85 having a central passage extending axially therein from a
proximal to a distal end;
b. an inflatable cuff positioned on the tubular body portion;
c. means for inflating said cuff;
d. a separate molded tip secured to the distal end of the flexible
tubular body portion,
i. said tip having a distal portion and having an aperture therein
communicating with the central passage of said tube body
portion,
ii. said tip being resilient material having a durometer higher
than the durometer of said flexible tube body portion, and in the
range of from about 75 to about 95,
iii. said distal portion having a distally extending inward taper
and a chamfered leading edge of uniform thickness around its entire
circumference oriented transverse to the axis of the aperture for
ease of insertion into a body, and
iv. said tip also having a proximal portion with an inwardly
beveled edge abutting and heat sealed to the distal end of said
tube body portion,
v. said heat seal providing a smooth transition between the tubular
body portion and the tip on both the exterior and the interior
thereof;
e. said tip providing a tracheal tube wherein the tip does not fold
over upon striking an obstruction when inserted into the body.
2. A tracheal tube as in claim 1 wherein said tip is color coded to
identify the inner diameter of the tube body central passage for
ease of recognition and size selection for surgical use.
3. A tracheal tube as in claim 1 wherein said tip material is
radio-opaque to render the position of said tip locatable when in
use.
4. A tracheal tube as in claim 1 wherein said tube body and said
tip assembly are polyvinyl chloride plastic-containing materials.
Description
FIELD OF THE INVENTION
This invention relates to catheter tubes useful in medical
situations, such as endotracheal tubes, tracheostomy tubes, Foley
catheters and the like, where a tube is inserted into the body for
medical reasons. More particularly, the invention relates to
improved cuff and catheter tip assemblies, methods of construction
and retrofitting of the cuffs to the tubes. Most specifically, the
invention relates to providing a special silicone rubber cuff which
may be employed with dissimilar plastic, rubber, or metal tubes to
which the silicone rubber is normally nonbondable to provide a cuff
which produces transmural pressures upon sealing inflation of
values which tend not to induce substantial tissue pressure
necrosis. The tip assembly is precision molded of a plastic,
rubber, or silicone rubber material of equal or higher durometer
than is used for the body portion of the tube itself, and is
characterized by a tapered profile to reduce tissue lesions upon
insertion or removal, and precision molded chamfered edges and
openings. The tip may also have a medially extending tapered collar
or bevel for fitting or sealing the tip to the body portion of the
tube.
BACKGROUND OF THE INVENTION
Catheters are extremely important and useful medical tools for the
input or withdrawal of fluids from the body of a patient.
Generically, catheters are tubular in shape and have a retaining
and/or sealing inflatable balloon cuff near the distal
(intracorporeal) end of the tube. Often the catheters must remain
in place for substantial periods of time. Present catheters have
not been entirely satisfactory since they tend to cause tissue
necrosis from pressure or biochemical incompatibility of the
inflatable balloon cuffs. For example, standard rubber cuffs of
endotracheal tubes in place for as little as 72 hours can cause
severe necrosis. Latex material is chemically irritating, and
polyvinylchloride plastic cannot elongate sufficiently to provide
adequate low pressure balloon volumes, has no memory and prunes
upon deflation.
Physicians and anesthesiologists are only just now becoming aware
of the severe damage which catheter tubes may cause at the time of
insertion or withdrawal from the body and of the damage which
inflated cuffs may cause on the adjacent tissues with which they
come into contact.
In early tubes of rubber material construction, for example the
Rusch-type tubes, the tube, tip, and inflatable cuff were made of
uniform durometer material. However, the durometer had to be
selected to be sufficiently hard for ease of insertion into the
body. When the tube is too soft, insertion of an endotracheal tube
(taken by way of illustration) becomes exceedingly difficult since
the tube tip may collapse or the tube may kink upon being forced
past the vocal chords.
With the advent of newer plastic materials such as
polyvinylchloride (PVC), attempts were made to provide all-PVC
tubes, i.e. tube, cuff and tip of PVC. Although the PVC was well
suited to make the body of the tube, PVC cuffs were not suitable
because the PVC is of low extensibility. The PVC cuffs are
extremely hard and transmit pressures sufficient to cause venous
collapse in the surrounding tissues. This venous collapse is then
followed by buildup of edema which in turn results in back pressure
sufficient to cause capillary collapse. The vascular beds adjacent
to the site of contact of such cuffs become sufficiently
constricted in normal use that pressure necrosis and ischemia occur
causing medically significant damage to the tissues. This is well
documented in the literature.
One approach to attempting to solve the problem was to provide
nonextensible, large residual volume (oversized) cuff
constructions. These oversized cuffs were characterized by having
the PVC plastic, latex, or rubber in an enlarged, baggy or folded
condition prior to insertion. It was postulated that relatively
high volumes of intra-cuff air would be required to expand those
loosely folded cuffs into contact with the trachea walls, as in the
case of endotracheal or tracheostomy tubes. However, there was no
full recognition of how low the critical pressure had to be; i.e.
pressure which could be transmitted safely to the adjacent tissues
without causing significant tissue pressure necrosis. For example,
Cooper et al, in "Experimental Production and Prevention of Injury
Due to Cuffed Tracheal Tubes", Surg., Gyn. & Obst., December
1969, p. 1235-1241, considered that intramural pressures on the
order of 40 mm. of mercury would be permissible. However, these
pressures are far too high. Efferent venous collapse occurs at a
range of 4-7 mm. mercury; in the supine individual (e.g. during
surgery) venous collapse occurs at pressures from about 8-15 mm.
mercury, with the average being above about 10 mm. mercury. The
capillary bed constriction commences at approximately 20-25 mm.
mercury.
However, typical prior art material such as rubber and
polyvinylchloride produce transtracheal or transmural pressures,
measured by the difference between the pressure at seal and the
contact pressure, of from about 29-210 mm. mercury. This is from
145 to 1050 percent greater than the critical 20 mm. mercury
pressure for commencement of capillary bed constriction.
A further problem with the oversized tube of cuffs is that the
insertion procedure is "blind", i.e. the anesthesiologist is unable
to view the vocal chords upon insertion of the tube. Consequently,
the vocal chords can be damaged upon insertion. As a natural
reaction to this, the anesthesiologist usually picks a tube which
is quite small relative to the size of the trachea. However, this
defeats the purpose of the oversized cuffs, since upon inflation,
the cuffs are not extensible and do not have the slack with which
they were designed to permit low volume inflation. In order to make
full seal, additional air volume must be applied. But the pressures
transmitted by the cuff to the trachea walls then exceeds the
critical pressure of vascular constriction.
If proper sized tracheal tubes are used with the oversized cuffs,
the cuffs upon inflation have wrinkles and folds in them which may
promote leakage and imperfect seal. In order to compensate for
this, the anesthesiologist in actual operation tends to overinflate
the cuff in order to flatten the wrinkles against the inside of the
trachea tube. In the process, uneven pressures are developed. More
significantly, from a medical view, pressures in excess of critical
vascular constrictive pressures are developed.
Because of the inelasticity of PVC, it cannot be used in
satisfactory standard non-oversized type construction form of
endotracheal tubes. But even in oversized forms, the anesthetist in
actual practice attempts prestretching the very hard PVC plastic
film used for the cuff by heating it, for example, by holding it
under hot tap water. However, this renders the endotracheal tube
non-sterile, and permits the PVC to expand non-uniformly and take
an improper "set" when it cools. Neither are conducive to medical
safety. Martinez, in Anesthesiology 34, p.p. 488-89 (1971) reports
extensive tracheal necrosis associated with a prestretched
tracheostomy tube cuff.
In short, the prior art went in the direction of constructional
design changes (oversized cuffs) in an attempt to overcome the poor
properties of PVC and rubber then in use, e.g. hardness and
inelasticity. But in so doing, they were insensitive to the actual
surgical problems that the resulting oversized cuffs presented.
These problems led to overinflation which is a full-circle return
to the hard inelastic properties of PVC and rubber then in use.
There is still another problem associated with the PVC plastic
catheters. Normally the tube in an endotracheal or trachestomy tube
has an end which is cut on a bias in order to facilitate ease of
insertion. The tubes are normally extruded and the insertion ends
are bias-cut and heat treated to smooth the rough-cut ends with RF,
infrared, resistance heating or flame. However, the heat treating
of the tip of the plastic PVC tube causes a bead-like thickening at
the edge. This tends to make the outside diameter of the tip larger
than the nominal diameter of the tube, and at the same time renders
the internal opening in the tube of smaller diameter than the
nominal diameter of the tube. The former means that the tube is
larger and tends to cause more damage upon insertion. The latter
means that tubes passed down the central lumen of the tracheostomy
tube or endotracheal tube, e.g. drainage tubes or the like, must be
smaller than maximum capacity in order to pass through the
constricted opening at the tip. Still further, there is no
completely consistent way of production line control of heat
treatment for each tube. That is, the heat treatment results in
each tube having a somewhat different confirmation and degree of
enlargement. Thus, since no two tubes have the same configuration,
the anesthetist or doctor using the tube may not rely on past
experience in making judgments about the sizes of tubes to use in a
given medical situation.
Still further, constructing the tube body, from distal to proximal
ends of the identical material evidences a failure to recognize
that different portions of the tube must have different properties
because of differing functions. As noted above, the cuff should be
of a type which does not have necrosis inducing pressures in the
adjacent tissues. We have also recognized that the main body of the
tube should be relatively flexible, of a moderate durometer to be
easily bent to conform to natural variations in the longitudinal
(axial) shape of the trachea or other opening or passage through
which the tube is being inserted. However, we have discovered that
the tip must be of a durometer equal to or higher than the body so
as to provide for ease of insertion and prevent the tip from being
folded back upon itself upon striking an obstruction. In contrast,
the prior PVC tubes, being heat treated at the end present
substantially the same durometer for the tips as for the main body
portion of the tube. In cases where the heat treatment is
excessive, the PVC may actually be degraded and the durometer
lowered thus aggravating the problem of having too soft a tip.
In our co-pending application, Ser. No. 128,898 we have disclosed
and claimed catheter tubes constructed entirely of silicone rubber
having a special conformable type cuff of a silicone rubber which
has properties which generate transmural pressures that tend not to
induce tissue pressure necrosis in the site of cuff inflation. More
specifically, we have therein disclosed our discovery that a
silicone rubber of low modulus, having properties of a Shore A
hardness of less than about 30, a tensile strength of below about
700 psi, an elongation of above about 1000 percent, and a stress
value upon sealing inflation of less than about 30 percent of the
breaking stress of said cuff material permits providing a
conformable, extensible, standard (non-oversized) type of cuff
which produces sealing pressures upon inflation that do not tend to
induce tissue pressure necrosis.
However, it has long been impossible, on a practical commercial
basis to sealingly bond silicone rubber to polyvinylchloride
plastic or to other plastics, rubber or metal tubes on a
consistent, medically reliable basis. While all-silicone rubber
catheters are useful as such, they are relatively expensive and
thus present some hindrance to single use, throw-away application.
In addition, many hospitals already have catheters which employ
cuffs that develop pressures too high for medical safety.
Therefore, there is a need for a low pressure, low volume,
extensible, conformable silicone rubber cuff of special properties
which develop pressures which are below those which tend to induce
any substantial tissue pressure necrosis, and yet may be applied to
dissimilar catheter tube body materials, and may be combined with
special durometer tips of precise, medically non-injurious
dimensions, and which may be retrofit onto existing tubes having
high pressure, medically injurious cuffs and/or tips.
SUMMARY
One aspect of this invention includes a silicone rubber cuff
assembly in which the silicone rubber portion contacting the body
tissue into which the catheter is inserted has special properties
such that the transmural pressure developed by the balloon upon the
initial full seal does not tend to induce tissue pressure necrosis.
A special inner seal sleeve member, or a plurality of seal rings,
or bands, of high modulus and durometer silicone rubber are
provided and an outer, low modulus and durometer rubber is bonded
thereto. The inner seal member is generally tubular in shape and
has a 5-50 percent compression factor, that is, the unassembled
diameter of the seal member is 5-50 percent less than the tubular
portion of the catheter body on which it is to be mounted. The
inner seal member or rings are stretched over the tube for mounting
and the circumferential tension thereof provides a frictional,
mechanical type of bond to the tube which prevents inflation fluid
leakage, and prevents the cuff from being dislodged during use.
This permits the cuff to be mounted on tubes of materials which
ordinarily do not permit reliable sealing thereto, as by chemical
gluing or bonding. Special provision is also made for providing a
smooth transition between the distal and proximal ends or margins
of the cuff and the catheter tube body on which it is carried.
The invention also includes a specially molded tip plastic equal or
harder durometer than standard extruded platic or molded tubes. The
special tip is characterized by a tapered profile which assists in
ease of insertion. The leading edge of the tip has precision molded
chamfers which provide for medically smooth traveling edges.
The invention also includes a combination polyvinylchloride tube
having the cuff assembly of this invention mounted thereon and a
specially molded selected durometer polyvinylchloride tip secured
to the distal end thereof. Such tubes may be constructed having a
hyperbolic curve or set to the tubes with the proximal end being
more curved than the distal, tip and cuff-carrying end. This
assists in inserting and lessens tip necrosis in use. This in
contrast to the tubes of the prior art which naturally carry a
semicircular set resulting from manufacturing processes employed by
PVC tube manufacturers. The tips may be color coded to facilitate
identification and size mistakes, and may also be rendered
radio-opaque for fluoroscopic location during use.
THE INVENTION
OBJECTS
It is therefore an object of this invention to provide improved
cuff and catheter tip assemblies for catheter tubes of all
types.
It is another object of this invention to provide an improved cuff
of a silicone rubber material which produces transmural pressures
at substantially full initial seal of values that do not tend to
induce substantial tissue pressure necrosis at the site of cuff
inflation in the body.
It is another object of this invention to provide a special
catheter cuff assembly of silicone rubber material which may be
applied to dissimilar catheter tube materials, or retrofit on to
existing catheter tubes.
It is another object of this invention to provide a special
catheter tip of generally equal or harder durometer than used for
catheter tubes to facilitate ease of insertion and withdrawal of
the tube in the body and which avoids collapsing upon encountering
obstructions upon insertion.
It is another object of this invention to provide improved catheter
tips which are molded of durometer material equal or harder than
the catheter tube body which have precisely molded tapered
configurations and the openings in which have smoothly chamfered
edges which are not enlarged as in prior art tips.
Still further and other objects of this invention will become
evident from a review of the detailed description which
follows.
FIGURES
The description below has reference to the following figures in
which:
FIG. 1 is a perspective view of one embodiment of the present
invention showing a plastic catheter tube having placed thereon a
special silicone rubber cuff of this invention and the distal end
of which employs the special tip of this invention.
FIG. 2 is a section view of a cuff assembly embodiment taken along
the line 2--2 of FIG. 1.
FIG. 3 is a section view of one embodiment of the special cuff and
tip assembly placed near the distal end of a catheter tube body of
dissimilar plastic material and shows in detail the mounting
features of both the cuff and the tip.
FIG. 4 shows partly in perspective and partly in section
constructional details of one embodiment of the special tip of this
invention.
FIG. 5 shows partial closure of the tip of a prior art catheter
wherein the body of the catheter and tip are made of a single
material of relatively low durometer.
FIG. 6 is a section view of a retrofit cuff assembly and separate
inflation lumen in accordance with this invention.
FIG. 7 shows several aspects of the retrofit silicone rubber cuff
of FIG. 6 in use upon a catheter body of dissimilar material. This
figure also shows the free shape of the cuff, the shape upon
initial contact, upon initial full seal, and the shape upon
overinflation.
FIG. 8 shows in section three embodiments of the marginal seal of a
retrofit balloon on a catheter body of dissimilar material.
FIG. 9 shows in section three embodiments of a retrofit cuff which
provides for smooth, non-irritating edge seal of the cuff to
dissimilar catheter body materials.
FIG. 10 shows in section two other embodiments of the cuff
construction of this invention.
FIG. 11 shows in plan view the generally hyperbolic shape of the
catheter tube of this invention as compared to the generally
semicircular shape of prior catheters.
FIG. 12 shows in section another embodiment of the tip of this
invention and a method of securing the tip to a catheter tube
body.
DETAILED DESCRIPTION
The following detailed description makes particular reference to a
polyvinylchloride or stainless steel catheter tube. This
description is by way of example only and is not meant as limiting
of the invention since the principles shown herein may be
applicable to catheter tubes of various materials. The selected
durometer tips as described in this invention are described as
constructed of polyvinylchloride by way of example only. It should
be understood that they may be made of any plastic or elastomeric
material which permits them to be bonded to the main body of the
catheter tube as by chemical bonding, solvent bonding, thermal
treatment, or mechanical interlock. It should also be understood
that while the description is made herein with reference to an
endotracheal tube, this description is by way of example only and
the principles of this invention may be applied to all types of
catheter tubes, including tracheostomy tubes, Foley catheters,
endotracheal tubes, urethral catheters, and catheters for use in
gastric, esophageal, pharyngeal, nasal, intestinal, rectalcolonic,
choledochal, arterial, venous, cardiac and endobronchial
applications.
FIG. 1 shows, by way of example an endotracheal or tracheostomy
tube 1 which is composed of main body portion 2, broken into
several parts so as to show within the space available the proximal
end assembly 3, distal end assembly 4, and inflation assembly 5.
The proximal assembly 3 may include a connection 6 for attachment
to a source of oxygen or vaporous anesthetic for administration to
the patient by way of the lungs. This connector 6 may be inserted
into the proximal end 7 of the main body portion 2, which end is
terminated normal to the long axis of the tube. The inflation
assembly 5 includes a pilot tube 8 connecting medially of the main
portion 2 with an inflation lumen 9 which is formed in the wall of
the main body portion. The proximal end of the pilot tube 8 is
terminated in an appropriate connector 10 for attachment of a cuff
inflating device, such as a syringe for inflating the cuff with air
or fluid, such as water or saline solution. As discussed herein,
the inflation medium for the endotracheal tubes is air,
administered by way of hypodermic syringe (not shown) attached to
the connector 10. Also by way of example, the description herein is
of a main body portion 2 extruded from polyvinylchloride plastic of
a durometer suitable for flexibility in use in medical situations,
yet not so soft and flexible that the tube collapses in use. For
example the durometer of the PVC tube typically ranges from 60-85
Shore A hardness. The inflation lumen 9 is normally formed during
the extrusion operation.
It should be understood, however, that the inflation lumen 9 may be
disposed in any manner desired in association with the main body
portion 2. For example, the inflation lumen need not be in the wall
11 of the body 2, but may be formed by attaching the pilot tube 8
to the body portion 2 along the side, extending in the direction of
the proximal and until it connects to the cuff assembly. Likewise,
as shown in FIGS. 6 and 7, the pilot tube 8 with inflation lumen 9
may be contiguous to the tube 2 but not connected thereto.
The cuff assembly 12 is placed medially of the distal end of the
main body portion 2 and the interior of the cuff communicates with
the inflation lumen 9 by means of one or more apertures 13, 13'.
FIG. 1 also shows one embodiment of the frictional securing means
for the silicone rubber cuff comprising a pair of high durometer
and modulus sealing rings 14, 15. The outer cuff member 16 is the
low durometer and modulus silicone rubber member (Shore A hardness
less than about 30) which contacts tissue, such as the tracheal
wall, and has special properties (as described in more detail
below) which tend to lessen inducing tissue pressure necrosis by
vascular flow cutoff in tissues adjacent to areas of contact of the
inflated cuff. The outer silicone rubber cuff member is chemically
bonded to the securing inner member or members by the use of an
adhesive silicone rubber which may be air-dried and/or heat-cured
to provide bonds 17, 17' (see FIG. 3) which are permanent under
conditions of use. For example, a Dow-Corning "Silastic" brand
medical grade type A adhesive may be used, or any suitable RTV type
may be used.
The distal end assembly 4 includes a precision molded tip 19
secured to the distal end 18 of the body 2 (see FIG. 3). The tip
may be seen in more detail in FIGS. 3, 4 and 7. With reference to
FIG. 4, the tip 19 is precision molded of a plastic or elastomeric
material of equal or harder durometer than the main body portion 2.
Whereas the typical durometer of polyvinylchloride body portion
tubes ranges from a Shore A hardness of above 60 to about 85 the
durometer of tip 19 will range from 60-95. We prefer the tip
durometer to be greater than the body durometer, in the range of
from about 75 to about 95. While the tip is shown and described
herein by way of example as constructed of polyvinylchloride, it
should be understood that the tip may be of any moldable plastic or
elastomeric material which can be secured to the body portion 2 as
by adhesive, solvent bonding, thermal bonding, (such as infrared,
resistance heating, RF, and including spin welding), or frictional
and mechanical interlock with the body portion 2. We prefer bonding
of tip 19 to the distal end 18 of body 2 by means of compatible
adhesives, solvents or plasticizers.
The tip 19 may include a proximal flange portion 20 which may be
tapered inwardly from approximately the region of the shoulder 21
to the proximal edge 22. The proximal edge 22 is typically normal
to the axis of the tip and body portion 2. The distal portion 23
has an inwardly tapered profile and terminates in a transverse
leading edge 25, in the case of endotracheal or tracheostomy tubes.
The transverse leading edge 25 has both an outer chamfer or rounded
edge 26 and an inner chamfer or rounded edge 27. The axial bore 28
of the tip 19 has an inner diameter the same as the inner diameter
29 of the body portion 2 (see FIG. 3). The precision molded leading
edge and tapered profile provides for ease of insertion and
withdrawal of the catheter tube from the body while the relatively
long, in the axial direction, flange portion 29 provides for
adequate mechanical or chemical seal to the body portion 2.
The chamfered leading edge is precision molded thus providing
catheter tubes having identical insertion tips. The leading edges
of the tubes of this invention are not irregular in shape, rough or
sharp due to a transverse cut, nor are they larger on the outside
than the main body portion, while at the same time smaller at the
inner diameter, due to beading from flame or other thermal
smoothing of the transverse cut edge. In addition, the increased
hardness (durometer) prevents folding over of the tip upon striking
an obstruction when inserted into the body, as seen for example in
FIG. 5. Prior PVC tips have a transversely cut end 31, and trailing
edge 32 of which may be relatively sharp, while the leading edge
typically illustrates the beading 33, and folding as shown at 34 in
FIG. 5.
It should be understood that while the tip flange portion 20 may
have an inward taper such that the proximal edge 22 has a wall
thickness thinner than the distal portion of flange 20, the flange
may be of equal thickness throughout as shown by uniform wall
thickness 36 in FIG. 7. This wall thickness may be varied to
provide for smooth transition between the tip and the body portion
2 or the cuff assembly 12. As shown in FIG. 1, there may be a gap
37 between the proximal edge of the tip 19 and the distal end of
the cuff assembly 12. As seen in FIGS. 3 and 7, the flange portion
20 may extend proximally far enough to abut the cuff assembly 12.
Where the cuff assembly 12 is spaced from the proximal edge 22 of
the tip flange portion to leave a gap 37 (see FIG. 8), that gap
optionally may be filled with a material to provide a smooth
transition therebetween. For example, a silicone rubber adhesive
material 38 may be applied at this juncture to provide a smooth
transition. Although the silicone rubber adhesive may not bond to
the polyvinylchloride tip or to the polyvinylchloride or metal body
portion 2, it will bond to the silicone rubber cuff members and
provide a smooth transition.
FIG. 12 illustrates another embodiment of the tapered tip 19. In
this embodiment, flange 20 is replaced by proximally extending
bevel 71. To secure this tip form to tube body portion 2, tip 19 is
slipped over mandrel 69 which is then fitted into bore 29 of tube
2. The mandrel may be spring biased axially in the medial direction
of tube 2, as shown by the arrow on the right of FIG. 12. Heat is
applied circumferentially from source 70, 70' to the bevel and
distal end 18 of the tube 2. Upon softening sufficient to weld the
tube to the tip, the biasing force presses the parts together to
make a secure joint. The mandrel is sufficiently tight fitting that
there is substantially no flashing or narrowing of the bore at the
joint. Alternately, the bevel may be filled with glue or adhesive,
as at 72 in FIG. 12.
Whether collar or bevel type preformed tips are used, the assembly
time is on the order of 3-5 seconds, as compared to 8-15 seconds
for cutting and tip heat-smoothing operations of the prior art. The
same principles apply to tips for other types of catheters, such as
eyelet type tips for Foley-type catheters.
In addition to the medically smooth insertion tip providing for a
transition between the transversely leading edge and the main body
portion of the catheter, we may provide the main body portion with
an appropriate preformed curve, as seen in FIG. 11. As shown by the
dotted curve 39, prior tubes had a set which was a portion of a
semicircular arc of radius about 12-18 inches. In contrast, we
provide a preformed curve or set to the main body portion which is
generally hyperbolic for this type of tube. This more nearly
conforms to the general shape of the trachea while the patient is
in the supine position in surgery. The hyperbolic curve is
preformed in the polyvinylchloride tube by warming the tube,
placing it in the appropriate hyperbolic form and letting it cool
until the curve is set in the plastic. Because of the circular
curve of prior tubes they exhibit drag of the tip along the trachea
during insertion, or upon retraction of the insertion obdurator.
After obdurator retraction, the tips may rest against the trachea
wall causing severe necrosis. See McGinnis et al., An Engineering
Analysis of Intratracheal Tube Cuffs, Anaesthesia & Analgesia,
Current Researches, 50, 557-64 (1971). The hyperbolic curve 40 of
our tubes is set into the tube such that the short "radius" portion
of the curve 42 is near the proximal end while the relatively
straight portion of the curve 41 is at the distal end. With the
precision molded tip 19 of this invention, the tube terminates in
an axially straight portion which minimizes side wall drag during
insertion and tip necrosis.
FIG. 3 also shows in more detail one embodiment of the inflation
cuff and in accordance with this invention. The cuff assembly 12
basically comprises two elements, a sealing element and an outer
cuff member which expands upon inflation to provide the desired
seal. As shown in FIGS. 6-9, the inner seal member 43 comprises a
cylindrical tube extending axially substantially the length of the
outer cuff member 16. However, as shown in FIGS. 1-3, the inner
seal member 43 may also be composed of two seal rings 14 and 15
rather than an inner continuous cylindrical tube. In both
embodiments, the sealing function is essentially similar. Either
rings 14 and 15, or the inner seal 43 grippingly engage the tube
body 2 securing the cuff member 12 thereto and preventing leakage
of inflation fluid from either the proximal or distal margins of
the cuff assembly 12. The seal member has a compression factor of
from 5-50 percent, that is, the relaxed I.D. of the seal member is
5-50 percent less than the O.D. of the catheter tube on which it is
fit, depending on durometer, such that the harder the durometer of
the tube the greater the compression factor. We prefer compression
factors in the range of from 10-30 percent for normal durometer
range of PVC tubes.
Turning first to the embodiment of the cuff assembly shown in FIGS.
1-3, the inner seal member of this embodiment includes a plurality
of rings 14 and 15 one of each being disposed adjacent the proximal
and distal ends of the cuff assembly, respectively. In both
embodiments, the inner seal members are constructed of a silicone
rubber of higher modulus and durometer than the cuff, and which has
a compression factor of 5-50 percent in proportion to the tube
durometer. The outer, extensible cuff member 16 is bonded to the
inner seal member tube 43 or rings 14, 15 by means of an
appropriate adhesive or curable silicone rubber material. Since
both members, cuff and seal, are silicone rubber, they can be
bonded by conventional techniques. The rings or tubular inner seal
member is then expanded mechanically and placed over the tube, or
the tube inserted through the expanded seal member. The mechanical
expansion is then released and the rings or sleeve firmly grips the
outside surface of the body member. In the case of
polyvinylchloride, an excellent frictional fit is provided due to
its slightly "tacky" surface characteristics. Since these bands do
not come into contact with the tissue walls, they may be of
properties which lend themselves to gripping the tube and provide
for integrity of inflation fluid seal.
As seen in FIG. 3, the rings 14 and 15 may extend beyond the ends
of the outer cuff member 16 to provide for a step-wise transition
between the outer surface 44 and the outer surface of the cuff 16.
In the alternative, the ring 14 may be placed inwardly of the end
of the outer cuff member 16 so that a margin 45 of the outer cuff
member overlaps to provide for a tapered, smooth transition. As
shown in FIG. 3, the margin 45 may be extended axially sufficiently
far to abut the proximal edge 22 of the tip assembly 19.
FIGS. 6-9 illustrate another embodiment of the invention in which
the inner seal member is tubular in configuration. FIG. 6 shows a
retrofit assembly comprising the inner sleeve seal member 43, which
is secured to the outer extensible cuff member 16 along margins
adjacent the proximal end 46 and the distal end 47 thereof by means
of a suitable adhesive 17, 17'. This provides for inflation space
48 which may be inflated by means of the pilot tube 8 and inflation
lumen 9 connected to appropriate inflation means such as a syringe
(not shown). Like the ring form of sealing member, the inner seal
sleeve member 43 has a compression factor of 5-50 percent, with the
inner diameter 49 of the seal being smaller than that of the tube.
The sealing sleeve member 43 securely grips the outer surface of
the tube 2 providing for a full seal. This is more particularly
illustrated in the lower portion of FIG. 7 which shows the cuff in
its freely inflated shape. The arrows also show a hydrostatic
assist effect wherein the inflation fluid serves both to expand the
outer cuff member 16, while at the same time pressing inwardly on
the sealing sleeve member 43, thereby increasing the seal of the
cuff to the tube body.
The inner seal sleeve member 43 and rings 14, 15 are typically
constructed of a high modulus silicone rubber which may be molded
or extruded having a durometer, expressed as a Short A hardness, in
the range of 40-90 typically 60-80. While the seal member material
may be molded or extruded, we prefer to extrude the seal members
and heat cure them. One manner of placing the sealing member
sleeves or rings over the tube is by slipping them over the tapered
tip assembly 19 and onto the tube body portion. Since the tip is
tapered, it facilitates the insertion of the tube 1 into the
reduced diameter sleeve or rings.
The upper portion of FIG. 7 illustrates the high degree of true
conformability of the outer cuff member 16 when in contact with
tissue, such as trachea wall 50. As the cuff is inflated, the outer
cuff member 16 expands outwardly until it touches the trachea wall.
Characteristic of our outer cuff materials is the fact that this
first contact occurs at relatively low pressure and low volume. The
pressure at first contact may be measured and identified as
P.sub.C. Since the trachea is not round, but rather is generally
triangular with the apices of the triangle having rounded corners
of short radius, the initial contact along the walls leaves gaps at
these apices. Continued inflation, however, presses our outer cuff
member into contact and complete conformity with all the walls of
the trachea. The pressure at this initial full seal may also be
measured, and it is identified as P.sub.S. The longitudinal (axial)
shape of the cuff of this invention may be seen in FIG. 7 at both
initial contact the P.sub.C shape shown on the right hand side of
FIG. 7, and at initial full seal, the P.sub.S shape identified in
dotted lines at the left side of FIG. 7.
Our cuff material is constructed of a low modulus silicone rubber
material of relatively low durometer, high elongation, low
strength, and low stress upon sealing, which values may be selected
to provide a cuff which, at initial substantially full seal,
provides a transmural pressure P.sub.T, defined as the seal
pressure minus the contact pressure (P.sub.S -P.sub.C), of values
below those which tend to induce vascular cutoff pressures which
produce medically significant tissue pressure necrosis. Normally,
this would be below about 30 mm. Hg. pressure transmitted to
capillary beds, or the equivalent value of about 10-15 mm. Hg.
transmitted to the efferent venous system adjacent the cuff-tissue
contact area. We prefer that this transmitted pressure be below
about 20-25 mm. Hg. relative to the capillary bed site or about 10
mm. mercury compressive pressure transmitted at the efferent venous
site.
A typical composition suitable for cuffs having below the above
critical transmural pressure values is one which is of a low
modulus, molded silicone rubber having a Short A hardness of less
than about 30, an elongation of greater than about 1000 percent, a
tensile strength of below about 700 psi, and a stress value upon
sealing inflation of less than about 30 percent of the breaking
stress of the cuff material. Other compositions producing the below
critical pressure values may also be employed.
The importance of being below the critical value can also be seen
from the left hand side of FIG. 7. Since the anesthetist in actual
practice is not able to precisely gauge in each instance the exact
moment of initial full seal, he is apt to overinflate the cuff to
ensure that a seal is made. This is particularly true of prior art
catheters employing oversize, large residual volume, cuffs. Since
in order to have visibility upon insertion of oversize-cuff-type
tubes, the anesthetist selects undersized catheter tube bodies,
i.e., those with a small outer diameter. But with small O.D. tubes,
the overinflation reaches or exceeds the elastic limits of the PVC
or latex outer cuff prior to full seal, and over-critical pressures
are generated. In contrast, our silicone rubber outer cuff member
conforms generally to the outer shape of the tube i.e. is not
oversized, thus permitting insertion visibility. At the same time
our cuffs are low volume, low pressure, and highly conformable due
to their low modulus and hardness, and high extensibility. Thus the
anesthetist may select one of our catheters having an outer
diameter more nearly approximating the size of the trachea. This
provides for maximum air inflow through the lumen of the
endotracheal tube and full seal at extremely low volumes. Since the
transmural pressure generated by the cuffs of our invention at full
seal are generally below critical, the anesthetist has ample margin
for error to over-inflate the cuff without generating over-critical
pressures. For example, actual measurements have shown that the
anesthetist may have up to about 55 percent leeway to overshoot
initial seal as to pressure and/or volume injected into the cuff.
In addition, the high conformability and extremely elastic nature
of our silicone rubber causes the cuff to extend laterally, rather
than radially outwardly, upon over-inflation. This illustrated by
the over-inflated shape in the upper left in FIG. 7. In descriptive
parlance, the cuff "hotdogs" laterally (axially), rather than
"ballooning", i.e. expanding only radially as in the case of prior
art PVC or latex cuffs. The cuff of our invention conforms to the
trachea shape, rather than forcing the trachea to its shape.
FIG. 6 shows the inner seal member 43 terminating at either end 46,
47 co-extensively with the proximal and distal ends of the outer
cuff member 16. In another embodiment shown in FIG. 7, axial
margins of either cuff member 16 or inner seal sleeve member 43 may
extend beyond the other to provide for more smooth transition
between the outer surface of the tube body 2 and the outer cuff
member 16. For example, in the upper half of FIG. 7, the outer cuff
member 16 has a proximal margin 51, a distal margin 52 each of
which extends beyond the ends 46, 47 respectively, of the seal
sleeve member 43. The distal margin 52 is shown as abutting the
proximal edge 22 of the precision molded tip 19. This provides for
an extremely smooth transition between the tip and the outer cuff
member 16.
The lower portion of FIG. 7 shows a step-wise transition with
proximal margin 53 and distal margin 54 of the inner seal sleeve
member 43 extending beyond the ends of the outer cuff member
16.
FIG. 8 shows still another embodiment of the retrofit assembly
shown in FIG. 6. In this embodiment, the pilot tube 8 may be
omitted and aperture 55 provided in the seal sleeve member 43 for
communication with inflation lumen 9 provided in the wall of a
stainless steel tracheotomy tube 56. The upper left portion of FIG.
8 shows a step-wise transition with the proximal margin of the
sleeve member 43 extending beyond the outer cuff member 16. In
contrast, the upper right hand portion of FIG. 8 shows the reverse
overlap with distal margin 52 of the outer cuff member 16
overlapping the seal sleeve member 43. The lower half of FIG. 8
shows the gap 37 between the proximal edge of the tip 19 being
filled with a silicone rubber adhesive material 38.
FIG. 9 illustrates still further embodiments of the invention with
provisions for providing a smooth transition between the cuff and
the tube body. In FIG. 9 various types of grooves and overlaps of
the cuff and sleeve members are shown. The upper left hand portion
of FIG. 9 shows a generally U-shaped groove 57 molded or incised
into the body of the plastic, elastomeric or metal tube 56. In this
embodiment, the proximal margin 51 of the outer cuff 26 overlaps
slightly the sealing sleeve member 43. A smooth transition is
provided as shown. At the upper right of FIG. 9, an oblique
V-shaped groove 58 is molded or incised into the tube body wall,
and co-extensively terminating outer cuff member and sealing
members fit snugly therein to provide a smooth transition. The
lower portion of FIG. 9 shows on the left hand end the reverse
overlap in a U-shaped groove, and the right hand end shows
co-incident termination of both the outer cuff member and the
sleeve member in a U-shaped groove.
FIG. 10 shows still another embodiment of the cuff of this
invention wherein the sealing rings 14, 15 have been molded
integrally or cured with the outer cuff member 16, placed medially
thereof, and the outer surfaces of which are tapered to provide for
smooth transition. The outer cuff member 16 is molded or cured to a
proximal thickened margin portion 59 and a distal thickened margin
portion 60 which have the properties attributed to the securing
rings 14 and 15, respectively. As shown in the upper half of FIG.
10 these thickened portions may be inset into one or more grooves
61, 62 and 63 incised or molded into the body of the tube. At the
upper left hand portion of FIG. 10, there can be seen a plurality
of inwardly projecting feet 64 and 65 which mate with the grooves
63 and 62 respectively. A larger, single foot 66 is shown in groove
61 in the upper right hand portion of FIG. 10. The outer edges of
the thickened margin portions 67 and 68 are chamfered to provide
for smooth transition between the outer surface of the tube body
and the outer cuff member 16. The lower half of FIG. 10 shows this
type of cuff placed on a standard tube, the outer surface of which
has no special grooves.
Several other advantages to the precision molded tip of this
invention are important. First, it is possible to provide the tip
with radio-opaque properties such that it may be seen by x-ray or
fluoroscope. For example, the PVC composition may be compounded
with a barium sulfate filler material. This permits the very tip of
the catheter to be located when the tube is in place in the body.
In addition, the thermoplastic polyvinylchloride material, after
injection into the precision mold, may be cooled rapidly by running
cooling water through the walls of the steel mold. The rapid
cooling promotes a very fine surface crystallization which gives
the tip a frosted appearance. This frosted appearance is actually a
microscopic surface texturing or slight "deformation". This surface
texturing is extremely helpful in the insertion of the tube into
the body since it promotes ease of sliding due to a mechanical
wettability effect. Normally, polyvinylchloride of moderate
durometer is relatively tacky to the touch, and it is difficult to
insert a suction or other type of tube of similar material through
the center lumen of the trachea tube. In order to permit the tubes
to slide one against the other, the surface of one or both should
be microscopically roughened. Similarly, the outer surface of the
tube is advantageously roughened. This is particularly critical of
the tube tip since it meets initial resistance upon insertion. By
the frosting effect achieved by mold temperature control, we are
able to promote ease of insertion. Likewise, this frosted effect
can be produced by slight chemical etching or mechanical abrading
of the mold surface. The tips may also be color coded for size or
type by use of conventional dyes for ease of selection and
prevention of error in use. For example, a different color may be
used to identify each of the 12 sizes of tracheal tubes ranging
from 5 to 12 mm. I.D.
It should be understood that various modifications within the scope
of this invention can be made by one of ordinary skill in the art
without departing from the spirit thereof. We therefore wish our
invention to be defined by the scope of the appended claims as
broadly as the prior art will permit, and in view of this
specification if need be.
* * * * *