Note: Descriptions are shown in the official language in which they were submitted.
1056M 21~ O 9 9 8
F.2074
LARYNGEAL MASK AIRWAY WITH
CONCENTRIC DRAINAGE OF OESOPHAGUS DISCHARGE
Related Case
This application is a continuation-in-part of my
pending application Serial No. 07/919,289, filed July 24,
1992.
Background of the Invention
The invention relates to laryngeal masks,
illustratively of the varieties disclosed in U.K. Patent
2,111,394B (corresponding to U.S. Patent No. 4,509,514) and
in published U.K. Patent Application No. 2,229,367A
(corresponding to U.S. Patent No. 4,995,388). Such masks
are artificial airway devices designed to facilitate lung
ventilation in an unconscious patient by forming a low-
pressure seal around the laryngeal inlet. A seal surrounds
an appropriately shaped mask which fits into the lower
pharynx and is attached to a tube which emerges from the
mouth, as for connection to medical gas-supply tubing.
In practice, these devices have been successful and are
now in daily use in hospitals throughout the United Kingdom.
Such masks have been found effective in achieving a reliable
airway, preventing obstruction in the unconscious patient.
As presently used, such masks are especially effective in
cases where difficulty with the airway is experienced. For
example, the mask has been found to prevent contamination of
the lungs by blood or debris during surgery of the nose or
throat. But it has become apparent that an important
contraindication to its use is the patient who is at risk
from vomiting or regurgitation of stomach contents while
unconscious. Although the device forms an inflatable-cuff
seal around the laryngeal inlet sufficient to permit
~'
2100998
~ inflation of the lungs during artificial ventilation, the
seal is not sufficient to prevent lung contamination in the
event of retching, vomiting or regurgitation. Patients who
are not adequately starved prior to surgery are thus not
suitable for use of the laryngeal mask. In such patients,
an endotracheal tube is still regarded as affording the
safest protection to the patient's airways. However,
insertion of an endotracheal tube is not always without
difficulty, and failure to make a timely insertion can lead
to death or brain damage. In such cases, the laryngeal mask
has proven to be life-saving. And, in cases when it has not
been possible to safely insert an endotracheal tube, it has
been found possible first to install a laryngeal mask, and
then to use the tube of the laryngeal mask as a guide, for
piloted insertion of an endotracheal tube through the mask.
My U.S. Patent No. 4,995,388 describes other means
associated with a laryngeal mask to prevent aspiration of
stomach contents into the lungs. In essence, such means
rely upon a combination of improved peripheral continuity of
seal pressure against the larynx and the provision of
drainage tubing for conduct of gastric contents away from
the laryngeal inlet.
Regardless of the specific purpose to be achieved with
laryngeal masks in use today, the problem of sealing
effectiveness persists, in respect of assuring against entry
of a gastric discharge in the laryngeal inlet. My U.S.
Patent No. 4,995,388 describes laryngeal-mask configurations
with three different embodiments to facilitate drainage of
gastric contents behind the mask. In one of these
embodiments a drainage tube passes directly into the
oesophagus; in a second of these embodiments, a drainage
tube is forked anteriorly of the mask, with drainage
openings on both sides of the mask bowl; and in the third
embodiment, the drainage tube passes behind the mask to
terminate alongside the mask tip.
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But each of these three embodiments has been found to
be less than satisfactory, for one or more reasons. The
disadvantage of l~he first embodiment is that it is more
invasive and breaks the seal which a non-draining inflatable
S mask establishes at the upper oesophageal sphincter. The
disadvantage of the second embodiment is that the drainage
provision is so positioned that it will draw off
regurgitated fluid only after it has already entered the
bowl of the mask, thus risking entry into the trachea of at
least some of this fluid. And the disadvantage of the third
embodiment is that it must be truncated diagonally at its
tip to facilitate mask insertion, thus presenting an
elliptical opening behind the mask tip, so that mask
inflation tends to press this opening against the wall of
the pharynx, thereby blocking the opening and impairing the
desired drainage function.
Aside from the difficulties noted above in respect of
proposals for preventing gastric contents from entry into
the laryngeal inlet, it is important to note some of the
environmental problems encountered by a laryngeal mask,
however well-designed for accuracy of fit to the lower
pharynx, so that when inflated, pressure is exerted on all
surrounding structures, to greater or lesser degrees,
depending on the resistance they offer to displacement. In
broad terms, the structures in front of the mask are
cartilaginous; those surrounding the mask are muscular; and
those behind the mask are bony. Inflation of the cuff of
the mask therefore results in the cartilaginous structures
of the larynx being pushed forward, away from the bony
structures of neck vertibrae, thus stretching and tensing
the surrounding muscles. The seal generated against the
laryngeal inlet therefore depends to some extent upon
stretch resistance of muscles and soft tissues, as cuff-
inflating volume of the mask expands.
If an unconscious patient retches, vomits or
regurgitates gastric contents, the balance of forces
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_ reacting on the inflated cuff is transiently upset. The
muscles surrounding the mask relax, and the sphincteric
mechanism at the lower end of the mask also relaxes, with
consequent loss or degrading of seal effectiveness; and
fluid or semisolids can be forced upward through the
oesophagus during such relaxation. Moreover, the larynx is
itself displaced upwards as part of the vomiting or retching
reflex, and such displacement alone may be sufficient to
disrupt the seal of the mask around the laryngeal inlet.
Still further, and of crucial importance, is the fact
that the airway tube to which the mask is attached offers
resistance to flexure when in its normal position in the
patient's pharynx. The airway tube thus exerts a constant
force against the bony posterior walls of the pharynx. This
means that in the event of a relaxation of the surrounding
structures, the mask will tend to remain firmly in contact
with the posterior wall. Vomited or regurgitated matter may
therefore pass in front of the mask and so enter the
laryngeal inlet.
Brief Statement of the Invention
It is an object of the invention to provide a
laryngeal-mask system with improved ability to prevent lung
soiling by gastric contents.
It is a specific object of the invention to achieve the
above object by providing a gastric-drainage feature for
such a mask system, wherein the drainage feature is in such
sealed relation to the upper sphinctral region of the
oesophagus as to materially reduce the risk of any gastric-
discharge entry into the laryngeal inlet.
Stated in other words, it is a specific object to
achieve such effectiveness in the sealed relation of the
drainage feature to the upper sphinctral region as to assure
that gastric-drainage will be virtually independent of
transient loss of seal effectiveness around the laryngeal
-- 4 --
21009~8
-- inlet, as may be occasioned by changes in surrounding
structures during vomiting, retching or regurgitation.
Another specific object is to achieve the above objects
with a sealed drainage feature in which it can at all times
be observable whether the drainage seal remains intact.
It is also a specific object to provide a laryngeal-
mask system with a gastric-drainage feature that avoids the
noted difficulties of prior drainage systems.
Still another specific object to meet the above objects
with a gastric-drainage feature which involves minimum entry
into the upper sphinctral region and which therefore
presents minimum risk of trauma to the oesophagus.
A general object is to achieve the foregoing objects
with relatively simple structure which is of minor
incremental cost and which is readily and effectively
usable, even in the hands of relatively unskilled paramedic
personnel.
The invention in a first preferred embodiment achieves
these objects in a laryngeal-mask system of the character
indicated wherein the inflatable generally elliptical
annular ring of the mask is provided with an evacuation-tube
which is open through the center of the distal end of the
inflatable ring, thus utilizing the distal end of the
inflatable ring as an inflatable cuff formation which (a)
establishes peripherally sealed engagement to the upper
sphinctral region of the oesophagus, (b) centrally and
resiliently supports the distal end of the evacuation tube,
and (c) which, in the normal condition of operating under
reduced pressure for evacuation purposes, will inherently
draw tissues adjacent the distal-cuff formation into
enhanced oesophageal-sealing effectiveness, thus effectively
tightening the sphincter.
In another preferred embodiment, inflatable-cuff
structure is additionally incorporated in at least a portion
of the backside of the mask. This additional structure is
of softer material than that of the inflatable generally
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_ elliptical annular ring of the mask. The additional
structure inflates to establish a soft profile-conforming
reference to the bony posterior wall of the pharynx, for
gentle application of forwardly directed loading of the
inflatable mask around the laryngeal inlet. As a result,
inflation pressure to establish seal action around the
laryngeal inlet can be at substantially reduced levels,
enabling an enhanced sealing effectiveness of the mask
around the laryngeal inlet. This enhanced seal action is
achieved without detriment to seal engagement to the upper
sphinctral region of the oesophagus, for gastric-drainage
purposes noted above.
Detailed Description of the Invention
The invention will be described in detail for a
preferred embodiment and for other embodiments, all in
conjunction with the accompanying drawings, in which:
Fig. l is a diagrammatic view, generally in side
elevation for a first preferred embodiment of an artificial-
airway device, having a laryngeal mask with a gastric-
drainage feature of the invention, the same being shown in
position for use in a patient;
Fig. 2 is an enlarged fragmentary view of the mask
portion of Fig. l, as seen from the aspect 2-2 of Fig. l;
Fig. 3 is a perspective view of the device of Fig. l,
from a first distal-quarter aspect which reveals the
posterior side of the laryngeal mask;
Fig. 4 is another perspective view of the device of
Fig. l, from a second distal-quarter aspect which reveals
the anterior side of the laryngeal mask;
Fig. 5 is an enlarged fragmentary view in side
elevation, illustrative of the deflated condition of the
cuff formation, in relation to the upper sphinctral region
of the oesophagus;
2I 00998
Fig. 5A is a view similar to Fig. 5, to show the
inflated-cuff formation and its relation to the upper
sphinctral region:
Fig. 5B is another view similar to Fig. 5, to show the
inflated-cuff formation and its relation to adjacent tissues
of the upper sphinctral region, when under the reduced
pressure of gastric-evacuating suction;
Fig. 6 is a fragmentary perspective view of another
embodiment of the invention, as seen from a distal-quarter
aspect which reveals the posterior side of an involved
laryngeal mask;
Fig. 7 is another fragmentary perspective view of the
embodiment of Fig. 6, as seen from a distal-quarter aspect
which reveals the anterior side of the mask;
Fig. 8 is generally a fragmentary plan view of the
posterior side of a further embodiment of the invention;
Fig. 9 is an enlarged sectional view, taken at 9-9 in
Fig. 8;
Fig. 10 is a rear three-quarter perspective view of
another preferred embodiment of the invention, shown
inflated;
Fig. 11 is a similar view of the embodiment of Fig. 10,
for the deflated condition thereof; and
Fig. 12 is a view similar to Fig. 10, for a
modification of the embodiment of Fig. 10.
Referring first to the preferred embodiment of Figs. 1
to 4, the invention is shown in application to an airway
system comprising a laryngeal-mask unit 10 and its airway
tube 11 which is installed through the mouth 12 of a
patient. The mask unit 10 may be generally as described in
either of said U.S. patents and therefore need not now be
described in detail. It suffices to say that mask unit 10
comprises a body portion 13 having a lumen 14 through which
the airway tube 11 can establish a free externally
accessible ventilating passage, via the patient's mouth 12
and throat 15, and past the epiglottis 16 to the larynx 17.
i 2100998
~ The body 13 of mask 10 may be of silicone rubber and
relatively stiff; and body 13 is surrounded by an inflatable
ring 18 which is generally elliptical and which is
circumferentially united to body 13 in essentially a single
plane. The inflatable ring 18 may also be of silicone
rubber, although preferably relatively soft and flexible
compared to body 13. An externally accessible flexible tube
19 is the means of supplying air to the inflatable ring 18
and of extracting air from (and therefore collapsing) ring
18 for purposes of mask insertion in or removal from the
patient; check-valve means 21 in tube 19 will be understood
to hold a given inflation or to hold a given deflation of
ring 18. In the installed position of Fig. 1, the projecting
but blunted distal end 20 of ring 18 is shaped to conform
with the base of the hypopharynx where it has established
locating limited entry into the upper sphinctral region of
the oesophagus 24. The inflated ring establishes a
peripherally sealed closure around the laryngeal inlet,
orienting the axis of the distal end of the airway tube 11
at an acute angle to the general plane of ring 18 and in
substantial alignment with the axis of the laryngeal inlet,
for direct airway communication only with the larynx 17.
In accordance with the invention, provision is made for
an evacuation tube 23 to follow the general course of the
airway tube 11, with sealed entry of the airway tube into
the mask body 13 and passage through the interior of ring 18
near the distal end of the mask. As seen in Fig. 2, the
open distal end of the airway tube 23 is sealed to re-
entrant soft material of ring 18 at a distal central
piercing of ring 18, such that (a) the distal end of tube 23
is concentrically supported by and within the upper
sphinctral region when inflated, and (b) the distal end 23
of tube 23 will be at small offset behind the distal
thus-blunted end of ring 18. Stated in other words, the
described structural arrangement establishes a
circumferentially continuous flexible annulus or cuff
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- formation at the distal end of ring 18 for softly but
concentrically stabilized support of the distal-end of tube
23, all in peripherally sealed engagement to tissues of the
upper sphinctral region. Since passage of evacuation tube
23 through the inflated inner volume of ring 18 necessarily
means that tube 23 will be subject to a crushing pressure
equal to the inflation pressure of ring 18, plus the reduced
pressure relied upon for suction to evacuate any discharge
of gastric products, the tube 23 should be suitably
reinforced or at least of structural strength to withstand
such crushing pressure; in this connection, commercial
plastic tubing having an internal diameter of 5-10 mm and
lined with a reinforcing continuous helix of fine stainless-
steel wire is satisfactory.
Action of the described mask and drainage/evacuation
tube 23 will be better understood from the succession ofdiagrams of Figs. 5, 5A and 5B. In Fig. 5, the relation is
that of the mask having just been inserted into the patient,
while ring 18 is fully deflated, so that the stubby distal
end of the mask has been able to enter the upper sphinctral
region, with less than sealing engagement to said region.
However, once inserted, inflation air should be introduced
via the inflation/deflation tube 19, typically to a pressure
in the range between 80 and 160-mm Hg, so that the mask
installation has the appearance depicted in Fig. 5A;
specifically, at this juncture, ring 18 has not only
developed its sealed engagement around the laryngeal inlet,
but the cuff-like formation 18' at the distal end of the
mask has ~Yr~n~ed into resiliently adapted circumferentially
continuous preliminarily sealed engagement with adjacent
tissues of the upper sphinctral region. Should tube 23 be
under evacuation, the reduced pressure from a suction device
(not shown) at the external end of tube 23 will subject the
oesophagus to the reduced pressure, causing adjacent tissues
to deform into a greater area of sealing the upper
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~ sphinctral region to the bulbous inflated end 18', resulting
in the relation depicted in Fig. 5B.
It is recommended that a simple small-displacement
spring-return bellows (not shown) be first compressed
against spring-return action, to expel the air from its
normally expanded volume, that the compressed bellows be
then connected to the externally exposed end of tube 23, and
that the spring compression should then be released to allow
spring-return action to induce a suction in tube 23. A
proper positioning of mask 10 is then noted if the bellows
fails to expand fully under the force of spring-return
action, because the oesophagus will then have been assuredly
sealed off from communication with the laryngeal inlet.
Having this assurance of proper seal action, the bellows can
be in place as a continuous monitor; alternatively, the
bellows can be replaced with a suitably monitored and
controlled connection to locally available suction means.
In the embodiment of Figs. 6 and 7, a mask 30, having a
connection to an airway tube 31 as in Figs. 1 to 5, also has
a relatively stiff body 32, peripherally surrounded by a
soft flexible ring 33 that is selectively inflated or
deflated via an externally accessible inflation tube 34.
Provision for evacuation or drainage of gastric products
involves two like tubes 35, 36 which conform to and are
carried by airway tube 31. Tubes 35, 36 are the bifurcated
arms of a single evacuation tube formation 37 extending
through the body and the distal end of ring 33, with
centrally sealed connection to the re-entrant fold of
centrally pierced ring-33 material into overlap with the
distal end of tube formation 37, thus establishing the
stubby cuff-like formation 38 at the distal end of mask 30.
Action and use of the embodiment of Figs. 6 and 7 may
be as described for Figs. 1 to S, provided that both of the
tubes 35, 36 are externally connected to a source of
sufficient suction action. Alternatively, a steady flow of
fluid may be drawn from tube 36, having been thereby induced
-- 10 --
2100998
- to flow into the external end of tube 35 (as suggested by
arrows 35', 36' in Fig. 6), thereby at the same time
aspirating, for external collection, analysis and/or
discard, such gastric products as may have entered the
S single central passage 37. Still further alternatively, an
optical or other inspection device (not shown) may have
annularly sealed entry into the bifurcation tube 35, as for
inspection of the sphinctral region adjacent and near the
seal established by the cuff-like formation 38, while the
other bifurcation tube 36 is subjected to continuous
suction, for extraction of gastric products.
In the embodiment of Figs. 8 and 9, two like airway
tubes 40, 41 are in curved, suitably bonded side-by-side
adjacency, with connection in common to the body 42 of a
single laryngeal mask 43 having an inflation ring 44 and
associated inflation/deflation tube connection 45. A single
evacuation tube 46 is secured to and along the length of
both tubes 40, 41 and has sealed entry into, and passage
through ring 44, in the manner previously described for
other embodiments, with distal termination centrally open
within the upper sphinctral seal established by the cuff-
like formation 47.
Use of the embodiment of Figs. 8 and 9 may be as
described for the embodiment of Figs. 1 to 5, except that
the addition of another airway tube affords additional
options such as accommodation of an optical or other
inspection device via one airway tube (40) while the other
(41) serves purely airway functions. Alternatively, in
conditions of anaesthesia, fresh gases can be breathed in at
the level of the larynx by using the tube 40 for fresh-gas
delivery, while using the other tube (41) to carry off waste
gases (carbon dioxide), thus facilitating the elimination of
carbon dioxide.
Figs. 8 and 9 further serve to illustrate that the
three tubes 40, 41, 46 may be the product of a single
extrusion, having the section shown in Fig. 9, wherein all
2100998
three tubes may be of the same internal diameter, or of such
relative proportions as to serve particular special-purpose
applications. By the same token, the tubes 11 and 23 of
Figs. 1 to 5, and 31, 35, 36 of Figs. 6 and 7, may also be
single extruded products.
The described embodiments of the invention will be seen
to afford a number of advantages, including but not limited
to the following:
(a) Regurgitant fluid will tend to pass directly into
the tubular provision (23, 37, 46) without encountering
resistance from the distal tip or end formation of the mask.
(b) Because the distal end of the evacuation tube is
centrally within the distal cuff formation, mask or cuff
inflation results in an even circumferential swelling around
the open distal end of the evacuation tube. This tends to
prevent escape of regurgitated fluid around the sides of the
mask, even in a retching circumstance, thus substantially
reducing the chance of accidental spillage into the larynx.
(c) The oesophagus is a hollow tube which is normally
closed. Application of suction to the outer end of the
evacuation tube produces a negative pressure at the upper
oesophageal sphincter, drawing adjacent tissue walls more
tightly together and thus enhancing the seal which is
otherwise established by inflation engagement to this
sphinctral region. This is an important point because in
the anaesthetized state, the sphincter may relax to
dangerously low pressures, permitting regurgitation in
certain patients.
(d) After laryngeal-mask insertion, it is sometimes
unclear where the distal end of the mask has come to rest.
It is possible that the distal end of the mask has passed
into an undesirable position; for example, it may on
occasion pass into the aperture of the larynx, so that it
comes to lie against the vocal cords, causing obstruction or
damage. Application of negative pressure to the drainage
tube, as in point (c) above, will in such circumstances act
2100998
as a test, since in the incorrect position, air will be
drawn out of the trachea, causing gas flow instead of an
immediate rise in negative pressure. This test (the so-
called Wee test) already exists for an endotracheal tube to
detect malposition in the case that the tube lies in the
oesophagus. This test is therefore readily understood by
clinicians.
(e) Once in place, the laryngeal mask may be used for
positive pressure ventilation of the lungs. However, one of
the dangers of this is that excessive pressures applied to
the airway via the breathing tube of the laryngeal mask may
result in leaks at the mask-to-larynx junction. This is
known to result in some cases in gradual inflation of the
stomach, which may restrict ventilation and ultimately
provoke regurgitation because of increasing intra-gastric
pressure. The present invention avoids this danger because
not only is the evacuation tube capable of establishing a
negative pressure within the oesophagus (thus increasing its
seal), but any gas escaping from the mask-to-larynx junction
will be siphoned away via the evacuation tube before
entering the oesophagus.
A disadvantage of the present invention is that the
mask tip is made more bulbous by the presence of the
evacuation tube at its distal end, even when fully deflated.
This in turn may make it harder to insert without
traumatizing or passing into the entrance to the larynx.
However, if this invention is used in combination with a
rigid tube with handle (Laryngeal Mask Handle as described
in my international application No. PCT/GB92/00242 and
corresponding to U.S. application Ser. No. 869,491, filed
April 20, 1992) in place of the flexible breathing tube of
the standard laryngeal mask, reliable insertion becomes
easier to achieve. In the embodiment of Figs. l to 5, the
airway tube ll is preferably rigid, as of suitably bent
stainless steel, and a handle 22, which may be detachably
connected to the outer exposed end of the airway tube serves
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- for better assurance that the inserted distal end of the
mask can be steered clear of the anterior structures, for
assured entry into the upper sphinctral region.
In adapting an existing laryngeal mask to the
evacuation/drainage purposes of the invention, the tube 23
will be understood to pass through the posterior or
"backplate" of the mask body 13, which may conveniently be
slit to accept tube 23 or, alternatively, be molded with
tube 23 to form a unitary part of it. The curved airway
tube 11 which is secured to the mask body 13 is also
conveniently adapted to carry the evacuation tube 23 in its
posterior or convexly curved wall.
It should also be noted that an installed laryngeal
mask, with provision for evacuation of gastric products may
serve the further purpose of accurately guiding the
insertion of a distally cuffed conventional flexible
endotrachial tube, with axially aligned accuracy through the
lumen of the mask and into the laryngeal inlet, for
subsequent cuff inflation to more assuredly seal the
endotrachial tube in substitution for the lung ventilation
purposes of such a use.
The second, and now more greatly, preferred embodiment
of the invention is shown in Figs. 10 and 11 and may be
identical to the embodiment of Figs. 1 to 4 except for the
addition of a second inflatable cuff 50; all other parts of
Figs. lO and 11 may be as described for Figs. 1 to 4 and
therefore the same reference numbers are used, where
applicable. Cuff 50 is seen to be of longitll~; n~l extent L
which is suitably one-third to one-half the longitudinal
extent of the mask body 13, and cuff 50 is located
intermediate the longitudinal ends of the mask body. Cuff
50 effectively surrounds that circumferential part of the
evacuation tube 23 which is exposed either circumferential
side of tube 23 assembly to the mask body 13. In Fig. lO,
inflation/deflation airflow to and from cuff 50 is provided
by a small tubular passage 51 that is locally integrated
2100998
~ into the structure of the evacuation tube 23; passage 51 has
ported distal connection at 52 to the inflatable ring 18 of
mask 10, and ported proximal connection at 53 to the inner
volume of cuff 50. The same pressure of inflation air via
line 19 thus simultaneously serves ring 18 and cuff 50.
One way to manufacture and assemble cuff 50 to mask 10
is to initially form cuff 50 as a circumferentially
continuous subassembly with the drainage tube 23, complete
with passage 51 and its ported connection 53 to the inner
volume of cuff 50. Thereafter, upon assembly of this
subassembly 23/50 to the backside of the mask body 13, the
ported connection 52 of passage 51 is completed to the inner
volume of inflatable ring 18, and cementing along the course
of adjacency of tube 23 and body 13 renders the assembly
permanent. In the process of such assembly the portion of
cuff 50 adjacent body 13 is squashed, but the assembled cuff
50 survives as a large inflatable arc around the exposed
remaining girth of tube 23.
Preferably, the material of cuff 50 is of lesser
thickness or of softer material, and therefore more softly
compliant than the material of ring 18. This fractional-
gauge relationship, between the material of cuff 50 and the
material of ring 18 is evident from Fig. 11, wherein for the
deflated condition of the mask, the wrinkles and folds of
cuff 50 (as at 50') are seen to be much more thin and narrow
than the wrinkles and folds (as at 18") of ring 18. In
fact, the bulk of cuff 50 in deflated condition is virtually
zero, so that, for a given patient, insertion and removal of
the structure of Fig. 11 is negligibly different from
similar use of the structure of Figs. 1 to 4.
On the other hand, having been inserted in a patient in
the manner described for Figs. 1 to 4, inflation of the
device of Figs. 10 and 11 is found to provide notable
improvement in peripheral sealing efficacy, for mask ring 18
around the laryngeal inlet. And this sealing efficacy is
achieved for a substantially reduced inflation pressure, as
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~ compared with data given above for the embodiment of Figs. 1
to 4. Specifically, the most suitable intra-cuff inflation
pressure thus far experimentally established for the
embodiment of Figs. 10 and 11 is approximately 62 cm H2O,
which will be recognized as very substantially less than the
80 to 160-mm Hg levels described above for the embodiment of
Figs. 1 to 4.
The significance of the improvement realized by the
embodiment of Figs. 10 and 11 will appear from a short
discussion, which of course must involve a comparison with
earlier inflatable-ring structures, as at 18 in Figs. 1 to
4, or as in the patents mentioned above.
In the earlier structures, inflation of the ring of the
laryngeal mask expands the space around it, at the laryngeal
inlet, but posteriorly the relatively hard mask body or
"backplate" is forced in a rather unyielding manner against
the back of the throat. When a drainage tube is added, as
at 23 in Figs. 1 to 4, the drainage tube lies wedged between
the backplate and the throat, further increasing the
potential discomfort and trauma which may be produced,
especially in a prolonged use. By using the second cuff 50
(Figs. 10 and 11), trauma potential is substantially
reduced, not only because inflation pressures are reduced
but also because the soft texture and pressure distribution
afforded by cuff 50 against the backwall of the pharynx
inherently cushions the backwall reference and avoids
drainage-tube (23) contact with the backwall of the pharynx.
Normally, i.e., for a prior inflatable mask ring (18),
without cuff 50, leaks may be expected to occur when gas is
forced into the lungs at pressures excee~ing 2kPa (20 cm
H2O), and I have identified the location of such leaks to be
at approximately the longitudinal mid-point of the mask rin~
(18) and on either or both sides of the mask when viewed
anteriorly; on the anterior side that is viewable in Fig.
10, such a leak point is approximated by the head end of an
arrow 55. Due to this general location of a potential leak
2100998
- point, the new softly compliant inflatable cuff 50 is placed
behind the mask and at the same general longitudinal
location, so that when inflated, cuff 50 will forwardly urge
the laryngeal mask 10 and its inflated ring 18 at the most
advantageous region to prevent leaks.
A further advantage in the structure of Figs. 10 and 11
is the discovery that peripherally sealed engagement of ring
18 to the laryngeal inlet is now possible for substantially
reduced inflation pressures. The ring 18 is necessarily of
greater wall thickness than that of cuff 50 because of the
need to assure against accidental herniation of the wall
during use, causing an obstruction to breathing; the reduced
necessary inflation pressure thus materially reduces the
chance of a herniation in the wall of ring 18. At the same
time, the wall thickness of cuff 50 is preferably much less,
for example, one-third to one-half the wall thickness of
ring, because the consequences of herniation of the wall of
cuff 50 are in no sense to be compared to a herniation of
ring 18; furthermore, by using a thinner-walled, i.e., more
compliant, material for cuff 50, the cuff 50 inflates more
readily and is able to forwardly thrust and displace the
mask for enhanced seal development to the laryngeal
perimeter, before full inflation pressure is developed.
There is some evidence suggesting that the high
pressures which may develop in ring 18, during anaesthesia,
due to absorption of anaesthetic gases, can cause a reflex
relaxation of the oesophagus, making regurgitation more
likely. The thinner and therefore more yieldable material
of cuff 50 acts as a pressure-limiting system, preventing
development of such high pressures in ring 18.
As a further advantage of the structure of Figs. 10 and
11, it is found that by requiring less inflation pressure
within ring 18, it has become possible for ring 18 to
conform itself more closely to the complex contours of the
laryngeal perimeter, instead of stretching tightly against
them. This circumstance avoids the development of high-
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2100998
~ pressure points and yields a more favorable ratio of intra-
ring (18) pressure to laryngeal-inlet seal pressure.
Preliminary experiments have shown a mean leak-developing
pressure of 32 cm H20, for an intra-ring (18) pressure of 60
cm H20; and this is to be compared with use of an inflated
ring 18 without cuff 50, wherein a leak-developing pressure
is encountered at about 18 cm H20, for the same intra-ring
(18) pressure.
The embodiment of Fig. 12 differs from that of Figs. 10
and 11, solely in the fact that separate provision is made
at 21 (and line 19) for inflation of ring 18 apart from
separate provision at 21' (and line 19') for inflation of
cuff 50. This feature will be understood to provide a
degree of flexibility in respect to selective choice of
different inflation pressures to determine a possible
optimum for the inflation pressure at 18, as compared with
the inflation pressure at 50. All other features of Fig. 12
are as described for Figs. 10 and 11.
All of the foregoing sealing advantages of the
structures of Figs. 10 and 11, and of Fig. 12, are achieved
without degrading the drainage-seal engagement to the upper
sphinctral region of the oesophageal inlet.
While it is noted above that in the embodiment of Figs.
1 to S that the airway tube 11 is preferably rigid to permit
use of a manipulating handle, it should be clear that
relative rigidity is desired in all embodiments of the
invention. And it has been found that in situations in
which the two tubes 11 and 23 are adhesively united with
conforming and nested adjacent curvatures, as by using a
silicone adhesive along the curved course of their
adjacency, with the central axes of both tubes in the same
plane, a sufficient rigidity can be achieved for the
adhesively bonded and thus-nested assembly of the two curved
tubes, without necessarily having to additionally rely on
metal reinforcement.
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