U.S. patent application number 10/225678 was filed with the patent office on 2003-03-20 for laryngeal mask airway device.
Invention is credited to Brain, Archibald Ian Jeremy.
Application Number | 20030051734 10/225678 |
Document ID | / |
Family ID | 26314198 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051734 |
Kind Code |
A1 |
Brain, Archibald Ian
Jeremy |
March 20, 2003 |
Laryngeal mask airway device
Abstract
A laryngeal-mask airway device including provision for drainage
of the oesophagus comprises an inflatable main-cuff and a backplate
having a laryngeal-side and a pharyngeal-side. The backplate also
has an external tube-joint adjacent to the proximal region of the
main-cuff. The backplate is hermetically bonded to the periphery of
the main-cuff establishing separation between a laryngeal-chamber
region and a pharyngeal region. An distally open evacuation tube
includes a distal portion which longitudinally traverses the
interior of the distal region of the main-cuff in sealed relation
therewith for operative engagement and communication with the inlet
of the oesophagus. The evacuation tube traverses the
laryngeal-chamber region generally adjacent to the laryngeal-side
of the backplate and passages through a proximally located
tube-joint to the pharyngeal region. An airway tube also extends
into the tube-joint for communication with an airway port to
provide a flowpath between the airway tube and laryngeal-chamber
region.
Inventors: |
Brain, Archibald Ian Jeremy;
(Surrey, GB) |
Correspondence
Address: |
HALE AND DORR, LLP
60 STATE STREET
BOSTON
MA
02109
|
Family ID: |
26314198 |
Appl. No.: |
10/225678 |
Filed: |
August 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10225678 |
Aug 22, 2002 |
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09289319 |
Apr 9, 1999 |
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6439232 |
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Current U.S.
Class: |
128/207.15 ;
128/200.26 |
Current CPC
Class: |
A61M 16/04 20130101;
A61M 16/0463 20130101; A61M 16/0497 20130101; A61M 16/0443
20140204; A61M 16/0415 20140204; A61M 16/0447 20140204; A61M 16/208
20130101; A61M 16/0434 20130101; A61M 16/0409 20140204; A61M
16/0493 20140204; A61M 16/0486 20140204; A61M 16/0445 20140204 |
Class at
Publication: |
128/207.15 ;
128/200.26 |
International
Class: |
A61M 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 1998 |
GB |
9817537.5 |
Claims
What is claimed is:
1. A laryngeal mask airway device comprising: A. an inflatable
cuff, the cuff defining an anterior side, a posterior side, and a
central aperture, the cuff being insertable through a mouth of a
patient to an inserted location within the patient when the cuff is
deflated, the anterior side of the cuff forming a seal around a
laryngeal inlet of the patient when the cuff is inflated and when
the cuff is at the inserted location; B. a backplate attached to
the cuff, the backplate being attached to the cuff at locations
closer to the posterior side of the cuff than to the anterior side
of the cuff; and C. an airway tube extending from the backplate to
a proximal end, the proximal end of the airway tube being disposed
outside the patient's mouth when the cuff is at the inserted
location, a continuous airway extending from the proximal end of
the airway tube to the central aperture of the cuff.
2. A device according to claim 1, the backplate being attached to
the posterior side of the cuff.
3. A device according to claim 1, further including a drainage tube
extending from a location near a distal end of the cuff to a
location outside the patient's mouth when the cuff is at the
inserted location.
4. A device according to claim 3, further including bite plate, the
bite plate being connected to the airway and drainage tubes, the
bite plate being disposed between the patient's teeth when the cuff
is at the inserted location.
5. A device according to claim 1, the cuff further defining a
posterior bulge at least when the cuff is inflated.
6. A device according to claim 5, the backplate defining a recess,
the posterior bulge extending into the recess at least when the
cuff is inflated.
7. A device according to claim 1, the backplate defining a
generally tubular opening.
8. A device according to claim 7, the airway tube extending into
the tubular opening.
9. A device according to claim 8, the backplate having a strap, a
slot being defined between the strap and the tubular opening.
10. A laryngeal mask airway device comprising: A. an inflatable
cuff, the cuff being insertable through a mouth of a patient to an
inserted location within the patient when the cuff is deflated, the
cuff forming a seal around a laryngeal inlet of the patient when
the cuff is inflated and when the cuff is at the inserted location,
the cuff defining a distal end and a central aperture; B. a
drainage tube extending from a location near the cuff's distal end
to a location outside the patient's mouth when the cuff is at the
inserted location; C. an airway tube having a proximal end, a
continuous airway extending from the proximal end of the airway
tube to the central aperture of the cuff, the proximal end of the
airway tube being disposed outside the patient's mouth when the
cuff is at the inserted location; and D. a bite-plate connected to
the airway and drainage tubes, the bite plate being disposed
between the patient's teeth when the mask portion is at the
inserted location.
11. A device according to claim 10, including a backplate attached
to the cuff.
12. A device according to claim 11, the cuff defining an anterior
side and a posterior side, the backplate being attached to the cuff
at locations closer to the posterior side of the cuff than to the
anterior side of the cuff.
13. A device according to claim 10, the cuff further defining a
posterior bulge at least when the cuff is inflated.
14. A device according to claim 13, the backplate defining a
recess, the posterior bulge extending into the recess at least when
the cuff is inflated.
15. A device according to claim 11, the backplate defining a
generally tubular opening.
16. A device according to claim 15, the airway tube extending into
the tubular opening.
17. A device according to claim 16, the backplate having a strap, a
slot being defined between the strap and the tubular opening.
18. A laryngeal-mask airway device comprising: A. an inflatable
cuff, the cuff defining an anterior side, a posterior side, a
proximal end, a distal end, and a central aperture, the proximal
end of the cuff defining a posterior bulge at least when the cuff
is inflated, the posterior bulge extending in a direction away from
the anterior side, the cuff being insertable through a mouth of a
patient to an inserted location within the patient when the cuff is
deflated, the anterior side of the cuff forming a seal around a
laryngeal inlet of the patient when the cuff is inflated and when
the cuff is at the inserted location; B. a backplate attached to
the cuff, the backplate defining a recess, the protrusion extending
into the recess at least when the cuff is inflated; and C. an
airway tube extending from the backplate to a proximal end, the
proximal end of the airway tube being disposed outside the
patient's mouth when the cuff is at the inserted location, a
continuous airway extending from the proximal end of the airway
tube to the central aperture of the cuff.
19. A device according to claim 18, the backplate being attached to
the cuff at locations closer to the posterior side of the cuff than
to the anterior side of the cuff.
20. A device according to claim 19, the backplate being attached to
the posterior side of the cuff.
21. A device according to claim 18, further including a drainage
tube extending from a location near the cuff's distal end to a
location outside the patient's mouth when the cuff is at the
inserted location.
22. A device according to claim 21, further including bite plate,
the bite plate being connected to the airway and drainage tubes,
the bite plate being disposed between the patient's teeth when the
cuff is at the inserted location.
23. A device according to claim 18, the backplate defining a
generally tubular opening.
24. A device according to claim 23, the airway tube extending into
the tubular opening.
25. A device according to claim 24, the backplate having a strap, a
slot being defined between the strap and the tubular opening.
26. A laryngeal-mask airway device comprising: A. an inflatable
cuff, the cuff being insertable through a mouth of a patient to an
inserted location within the patient when the cuff is deflated, the
cuff forming a seal around a laryngeal inlet of the patient when
the cuff is inflated and when the cuff is at the inserted location,
the cuff defining a central aperture; B. a backplate attached to
the cuff, the backplate defining a generally tubular opening, the
backplate having a strap, a slot being defined between the strap
and the tubular opening; and C. an airway tube extending from the
tubular opening of the backplate to a proximal end, the proximal
end of the airway tube being disposed outside the patient's mouth
when the cuff is at the inserted location, a continuous airway
extending from the proximal end of the airway tube to the central
aperture of the cuff.
27. A device according to claim 26, further including a drainage
tube extending from a location near a distal end of the cuff to a
location outside the patient's mouth when the cuff is at the
inserted location.
28. A device according to claim 27, the drainage tube extending
through the tubular opening.
29. A device according to claim 26, the cuff defining an anterior
side and a posterior side, the backplate being attached to the cuff
at locations closer to the posterior side of the cuff than to the
anterior side of the cuff.
30. A device according to claim 29, the backplate being attached to
the posterior side of the cuff.
31. A device according to claim 27, further including bite plate,
the bite plate being connected to the airway and drainage tubes,
the bite plate being disposed between the patient's teeth when the
cuff is at the inserted location.
32. A device according to claim 26, the cuff further defining a
posterior bulge at least when the cuff is inflated.
33. A device according to claim 32, the backplate defining a
recess, the posterior bulge extending into the recess at least when
the cuff is inflated.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to laryngeal mask airway devices
(LMA-devices). Such devices are useful in facilitating lung
ventilation in unconscious patients by forming a low pressure seal
around the patient's laryngeal inlet, avoiding the known harmful
effects of the endotracheal tube, which forms a seal within the
windpipe (trachea).
[0002] LMA-devices of the types disclosed in UK Patent Nos. 2111394
and 2205499 have become accepted items of equipment for rapidly and
reliably establishing an unobstructed airway in a patient in
emergency situations and in the administration of anaesthetic
gases, and have found use in most countries of the world. A
disadvantage associated with the use of such a mask is encountered
in a patient who is at risk from vomiting or regurgitating stomach
contents while unconscious since although the device forms a seal
around the laryngeal inlet sufficient to permit artificial
ventilation of the lungs, the seal is sometimes insufficient to
prevent lung contamination during retching, vomiting or
regurgitation.
[0003] A partial solution to this problem is disclosed in U.S. Pat.
No. 4,995,388 in which reliance is made upon a combination of an
improved peripheral continuity of seal pressure against the
laryngeal inlet and the provision of a drainage tube to conduct
gastric contents away from the laryngeal inlet. However, one
embodiment of such a system is itself disadvantaged by the fact
that the removal of such gastric discharges can be achieved only
after the seal between the LMA device and the laryngeal
inlet/oesophagus has been breached. Another embodiment provides for
removal of gastric drainage without breaching the seal between the
LMA device and laryngeal inlet/oesophagus, but this proved awkward
to insert and caused throat irritation.
[0004] A more successful solution to this problem has been provided
by the gastro-laryngeal mask airway device disclosed in U.S. Pat.
No. 5,241,956 and European Patent 651664. In that device, a
drainage tube passes through the posterior aspect of the mask and
through the distal end of the inflatable cuff of the mask to open
in alignment with the patient's oesophagus. However, the drainage
tube must be sufficiently rigid at its distal end to withstand the
pressure within the inflated cuff and it has been found that this
may make proper insertion of the deflated device into the patient's
throat more difficult than either necessary or desirable.
[0005] In a modified gastro-laryngeal mask airway device disclosed
in International Patent Application WO 97/12680, provision is made
for the distal half of the mask to be of softly compliant
construction, and to ensure against collapse of the drainage tube
when the cuff is inflated. Also, the mask has a flexible leading
edge for facilitating correct insertion into the throat of the
patient.
[0006] European Patent Application 796631 and U.S. Pat. No.
5,632,271 disclose an LMA device which further facilitates
insertion into the throat of the patient, an LMA device includes a
drainage tube, which opens into the distal tip of the mask, passes
along the posterior aspect of the flexible airway tube and emerges
from the mouth of the patient just below the upper incisor teeth.
For practical purposes this device works well but has the following
limitations.
[0007] A disadvantage of this back-to-back tube orientation is that
it confers a degree of instability to the mask when the device is
in place, permitting the possibility of loss of seal between the
mask and laryngeal inlet. Another disadvantage of the back-to-back
tube configuration is that it confers to the tubular elements of
the device an undesirable degree of stiffness so that movements of
the head and neck of the patient occasioned, for example, by
surgical manipulation or positioning, may result in undue harmful
pressure being exerted on the surrounding tissues of the upper
airway passages.
[0008] Another disadvantage is that the inserting index finger
tends to slip off the airway and drainage tube due to lack of
purchase. A still further disadvantage is that the inserting index
finger may be damaged by the teeth of the patient because of the
greater combined diameter of the back-to-back tubes.
SUMMARY OF THE INVENTION
[0009] The present invention has as its overall objective to
provide an LMA device of the types described above, i.e.,
incorporating means for draining gastric discharge from the region
of the oesophageal inlet of the patient, which substantially avoids
the disadvantages described above in relation to various of the
known types of LMA-devices.
[0010] In accordance with the invention, this objective is achieved
by first modifying the bowl of the mask such that its interior
curvature has a significantly deeper shape than previous
constructions. This is accomplished by either making the posterior
wall or backplate of the mask to generally the same peripheral
dimensions to permit its attachment to the posterior aspect of the
inflatable cuff formation (in contrast to attachment to the inner
rim or equator of the cuff formation), or by changing the cross
section shape of the cuff so that its seam is placed at offset from
the major or equatorial plane. Hence, the backplate is located
substantially behind, i.e., posteriorly of the cuff and not, as
previously, within the annulus of the cuff. The backplate edge, or
rim, is attached roughly tangentially with respect to the roughly
ring-shaped cross-section of the inflatable toroidal shape of the
cuff annulus. It will be evident that with this construction, the
depth of the bowl of the mask, i.e., the distance between the
anterior aspect of the cuff when inflated and the anterior aspect
of the backplate, will be greater than in previous constructions by
approximately half the posterior-anterior dimension of the inflated
cuff. Since most adult-size LMA devices have cuff inflation
diameters in the range of 12 to 16 millimeters, it is clear that
the additional bowl depth will be of the order of 6 to 8
millimeters. This additional bowl depth permits the gastric drain
tube to be on the anterior surface of the backplate instead of
running posteriorly as in previous designs, increasing the
stability of the mask when installed in the throat of the patient
and reducing the tendency of the installed device to migrate
outwardly.
[0011] This anterior placement of the drain tube also eliminates
the requirement to guard the aperture of the airway tube against
obstruction by the anatomical structure known as the epiglottis. To
prevent such obstruction, former cuffs were provided with paired
parallel bars running across the airway aperture. These bars proved
effective in preventing epiglottis obstruction but offered unwanted
resistance to airflow and tended to obstruct passage of suction or
inspection tubing. Anterior positioning of the drain tube allows it
to act as an epiglottic prop, holding back the epiglottic rim from
the floor of the mask and the airway port. The paired bars
described above were not able to prevent obstruction occurring as a
result of the epiglottic rim lying in contact with the bowl or
floor of the mask. The anterior location of the drain tube in the
present invention overcomes the problems of epiglottic misplacement
more effectively than the previous design.
[0012] The second modification to the backplate is to replace the
single tube-joint port adapted to accept the flexible airway tube
with a double-barrelled port in which said ports are arranged
side-by-side, that is to say laterally, permitting easy assembly of
said side-by-side airway and drainage tubes. This provides better
correspondence with the cross section space within the throat, the
major axis of which runs laterally, and reduces stiffness and
consequent pressure on the throat from movements of the head and
neck of the patient. Also, the side-by-side adjacency reduces the
pressure exerted on the drainage tube by the incisor teeth of the
patient, and facilitates manufacturing since the portions of the
tubes in the throat of the patient describe similar radii.
[0013] The double-barrelled tube-joint additionally provides a
desirable locating point for the tip of the index finger used to
insert the device, thus reducing possible slipping of the finger on
the tube-joint. Also, the reduced transverse diameter in the
vertical direction between the teeth of the patient resulting from
the side-by-side adjacency of the drainage and airway tubes reduces
possible injury to the finger from contact with the teeth.
[0014] A third modification to the backplate is the incorporation
of a well or depression covering an area of approximately 3 square
centimeters and having a 2 to 5 millimeters depth situated in the
anterior surface of the backplate under the drain tube where it
connects with the distal end of the drain port of the backplate.
The well has the dual functions of permitting gas circulation and
allowing secretions from the trachea to be drained away.
[0015] The LMA device of the invention is readily distinguished
from the devices proposed hitherto in which the backplate of the
mask has been located within the annulus of the inflatable cuff,
and in which the gastric drainage tube has been routed across the
posterior surface of the backplate.
[0016] According to the invention, therefore, there is provided a
laryngeal mask airway device equipped for drainage of gastric
discharge, the device comprising an inflatable main-cuff and a
backplate having a laryngeal-side and a pharyngeal-side. The
backplate also has an external tube-joint adjacent to the proximal
end of the main-cuff. The backplate is hermetically bonded to the
periphery of the main-cuff establishing separation between a
laryngeal-chamber region and a pharyngeal region. A distally open
evacuation tube includes a distal portion which longitudinally
traverses the interior of the distal region of the main-cuff in
sealed relation therewith for operative engagement and
communication with the inlet of the oesophagus. The evacuation tube
traverses the laryngeal-chamber region generally adjacent to the
laryngeal-side of the backplate and passages through a proximally
located tube-joint to the pharyngeal region. An airway tube also
extends into the tube-joint for communication with an airway port
to provide a flowpath between the airway tube and laryngeal-chamber
region.
[0017] These and other objects, features, and advantages of the
invention will be more fully understood from the following
description of certain specific embodiments of the invention taken
together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the drawings:
[0019] FIG. 1 is a simplified overall view to show an LMA-device of
the invention, installed in a patient whose relevant anatomical
features are shown by phantom outlines;
[0020] FIG. 2 is a perspective view showing the LMA-device of FIG.
1 installed in a patient, the patient being shown in the quarter
neck direction from the front right-side omitting most neck
structures and showing a sagittal section of the larynx, the
epiglottis being shown displaced anteriorly relative to the
main-cuff to show the internal-drain tube (normally, the epiglottis
extends into the main-cuff), the right lateral portion and proximal
region, including the hemispherical posterior bulge, of the
main-cuff being shown;
[0021] FIG. 3 is a plan view of the anterior side of the LMA-device
of FIG. 1, the main-cuff being inflated and illustrated in enlarged
scale relative to FIG. 1, the airway and external-drain tubes being
cut-off, the well hidden behind the internal-drain tube also being
shown;
[0022] FIG. 4 is an enlarged perspective view of a detail of FIG. 3
with the airway and evacuation tubes removed, showing the anterior
surface of the tube-joint and the posterior bulge of the
main-cuff;
[0023] FIG. 5 is an enlarged plan view of a detail of FIG. 3 with
the airway and evacuation tubes removed, showing the anterior
surface of the tube-joint and the posterior bulge of the
main-cuff;
[0024] FIG. 6 is an enlarged end view of a detail of FIG. 3 with
the airway and evacuation tubes removed, showing the proximal end
surface of the tube-joint and the posterior bulge of the
main-cuff;
[0025] FIG. 7 is a plan view of the posterior side of the device of
FIG. 1, in the same inflated condition as and to the scale of FIG.
3, the portions of the airway tube and the external- and
internal-drain tubes hidden in the tube-joint being shown, the well
hidden behind the backplate also being shown;
[0026] FIG. 8 is a lateral view in partial section, in the plane
indicated by the line 8-8 of FIG. 7 which is parallel to the
sagittal plane and which coincides with the central longitudinal
axis of the evacuation tube, except in the distal region of the
main-cuff where the evacuation tube is transversely offset from the
sagittal plane, showing the longitudinal traverse of the
internal-drain tube along the backplate;
[0027] FIG. 9 is a view corresponding to FIG. 8 with portions
broken away to show the anterior-posterior dimension of the
internal-drain tube relative to a plane containing the anterior
surface of the main-cuff;
[0028] FIG. 10 is a sectional plan view in the plane indicated by
the line 10-10 of FIG. 9 showing the location of the
anterior-posterior dimension of FIG. 9 relative to the proximal
region of the main-cuff;
[0029] FIG. 11 is a distal view in cross section, in the plane
indicated by the line 11-11 of FIG. 7 showing the engagement
between the internal-drain tube and backplate, and the adjacency
between the seam in the main-cuff and backplate;
[0030] FIG. 12 is a distal view in cross-section of a second
embodiment of the backplate and back-cuff in a plane corresponding
to the plane indicated by line 11-11 of FIG. 7, showing a reduced
wall thickness of the backplate in the sagittal plane, and the
back-cuff tethered to the backplate;
[0031] FIG. 13 is a distal view in cross section, in the plane
indicated by the line 13-13 of FIG. 7 showing a portion of the
LMA-device between lines 11-11 and 13-13, the clearance between the
internal-drain tube and base of the well being illustrated;
[0032] FIG. 14 is an enlarged fragmentary view of a detail of FIG.
8 showing the connection between the external-drain tube and distal
region of the main-cuff, the angles between selected parts and
respective reference planes also being shown;
[0033] FIG. 15 is an enlarged fragmentary view of a detail of FIG.
8 showing the connection between the internal and external-drain
tubes;
[0034] FIG. 16 is an anterior perspective view of the backplate
removed from the LMA-device of FIGS. 3 and 7;
[0035] FIG. 17 is a perspective view, in the aspect indicated by
line 17 of FIG. 16, showing the recessed heel portion and well, and
also showing the double-barrelled passage for the connections of
the airway and external-drain tubes;
[0036] FIG. 18 is an anterior view of a second embodiment of the
backplate of FIG. 16;
[0037] FIG. 19 is a perspective view of the second embodiment of
the backplate illustrated in FIG. 18, in the aspect indicated by
line 20, showing the recessed heel portion, and the
double-barrelled passage for the connections for the airway and
external-drain tubes;
[0038] FIG. 20 is a perspective view of the anterior surface of the
LMA-device of FIGS. 3 and 7 in a deflated condition;
[0039] FIG. 21 is a lateral view of the main-cuff in the direction
indicated by line 22 of FIG. 20 showing the preferred deflection
characteristic of the main-cuff;
[0040] FIG. 22 is a perspective view in the aspect of FIG. 20
showing the LMA-device of FIGS. 3 and 7 in an inflated
condition;
[0041] FIG. 23 is a plan view of the anterior side of a third
embodiment of the LMA-device of FIGS. 3 and 7 showing one-way
valves incorporated in the anterior wall of the main-cuff; and
[0042] FIG. 24 is a lateral view of the main-cuff of the embodiment
illustrated in FIG. 23 in the direction indicated by line 23-23
showing one of the one-way valves and its associated housing.
[0043] Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0044] As used herein, the anatomical terms "anterior" and
"posterior", with respect to the human body, refer to locations
nearer to the front of and to the back of the body, respectively,
relative to other locations. The term "anterior-posterior (A-P)"
refers to a direction, orientation or the like pointing either
anteriorly or posteriorly. The anatomical terms "proximal" and
"distal", with respect to applying an instrument to the human body,
refer to locations nearer to the operator and to the inside of the
body, respectively. Alternatively, "distal", as opposed to
"proximal", means further away from a given point; in this case,
"distal" is used to refer to positions on the LMA-device 20 or in
the body relative to the extreme outer or connector end of the
LMA-device. "Proximal" is the opposite of "distal". The term
"lateral" refers to a location to the right or left sides of the
body, relative to other locations. Alternatively, "lateral" means
to one or other side of the mid-line, with respect to the major
axis of the body, or to a device lying in the body's major axis.
The term "bilateral" refers to locations both to the left and right
of the body, relative to the sagittal plane. The term "sagittal" or
"sagittally" refers to a vertical longitudinal plane through the
center or midline of the body that divides a bilaterally
symmetrical body into right and left halves. The sagittal plane is
the plane passing antero-posteriorly through the middle of the body
in its major axis. The term "medial" means nearer to the
mid-line.
[0045] A laryngeal-mask airway device (LMA-device) of the present
invention, is designated generally by the reference numeral 20 in
FIGS. 1 and 2. The LMA-device 20, in a deflated condition, is
inserted into the throat 32 the upper surface of which is bounded
by hard and soft palates 192, 195. The LMA-device 20 is lodged in
the pharynx 197 of the throat 32 at the base of the hypo-pharynx
212 where the throat divides into the trachea 36 (i.e., windpipe)
and oesophagus 57. A lower portion of the LMA-device 20 reaches to
the base of the hypo-pharynx 212. After the LMA-device 20 is so
lodged in the pharynx 197 such that the lower portion of the
LMA-device reaches the base of the hypo-pharynx 212, the LMA-device
is inflated. Disposed in the junction between the throat 32 and
trachea 36 is the flexible epiglottis 35 (i.e., a lid-shaped
structure) which forms the upper border of the larynx 37, entry
through which is provided by the laryngeal inlet 67. To facilitate
understanding of the relations between the LMA-device 20 and
anatomy of the throat 32 and related structures, a glossary of the
anatomical structures related to the LMA-device is provided herein
below.
[0046] Referring to FIGS. 1 and 2, the laryngeal-mask airway device
(LMA-device) 20 is shown comprising an airway tube 22, installed
through the mouth 25 of a patient. The LMA-device 20 further
comprises a backplate 27 having an airway port 30 through which the
airway tube 22 can establish a free externally accessible
ventilation passage, via the patient's mouth 25 and throat 32, and
past the epiglottis 35 to the larynx 37. The backplate 27 is
preferably of an elastomer such as silicone rubber and relatively
stiff, for example, of 80 Shore durometer.
[0047] As further shown in FIGS. 3 and 7, the backplate 27 is
surrounded by a main-cuff 40 comprising an inflatable ring which,
when inflated, has the shape of a torus generated by an
asymmetrical oval or ellipse having a wider proximal region 42 and
narrower distal region 45. The main-cuff 40 is circumferentially
united to the backplate 27 in essentially a single plane, except
for the portion of the main-cuff extending into a recess 47 in a
heel 50 of the backplate 27. The portion of the main-cuff 40
extending into the recess 47 may or may not be united to the
backplate 27, as described further hereinbelow.
[0048] The main-cuff 40 may also be of silicone rubber, although
preferably relatively soft and flexible compared to the backplate
27. The material of the main-cuff 40 is preferably of 20 to 30
Shore durometer. Except for a plastic connector (not shown)
attached to the proximal end of the airway tube 22 and a check
valve 52, all parts of the LMA-device 20 disclosed herein are
preferably made of silicone, possibly with different additives.
[0049] An externally accessible tube 55 and inflation port 56 on
the main-cuff 40 are the means of supplying air to the main-cuff
and of extracting air from (and therefore collapsing) the main-cuff
for purposes of insertion in or removal from the patient. The
check-valve 52 is disposed in the tube 55 for holding a given
inflation or holding a given deflation of the main-cuff 40.
[0050] In the installed position of FIGS. 1 and 2, the projecting
but blunted distal region 45 of the main-cuff 40 is shaped to
conform with the base of the hypo-pharynx 212 where it has
established limited entry into the upper sphincteral region of the
oesophagus 57. The pharyngeal-side 60 of the backplate 27 is
covered by a thin flexible panel 62, as shown in FIGS. 7, 11 and
13, which is peripherally bonded to a margin 63 on the posterior
surface of the main-cuff 40, to define an inflatable back-cuff 65
comprising a cushion which assures referencing to the posterior
wall of the pharynx and thus is able to load the inflated main-cuff
forward for enhanced effectiveness of sealing engagement to the
inlet 67 of the larynx 37. The inflated main-cuff 40, thus-engaged
to the laryngeal inlet 67, orients a distal-end 72 of the airway
tube 22 at an acute angle to a mid-line major plane 75 of the
main-cuff 40 and in substantial alignment with the axis of the
laryngeal inlet 67, for direct airway communication only with the
larynx 37.
[0051] The major plane 75 is a plane containing the major axis 77
of main-cuff 40 extending between proximal and distal regions 42,
45. The major plane 75 is disposed between, and parallel to, the
anterior and posterior surfaces of the main-cuff 40. Additionally,
the major plane 75 is equidistant from the anterior and posterior
surfaces of the main-cuff 40, except for posterior bulge 100.
[0052] The LMA-device 20 is of the GLM (gastro-laryngeal mask)
variety in which an evacuation tube, designated generally by 80, as
shown in FIGS. 1, 2, 3 and 7, serves for extraction and external
removal of gastric-discharge products from the oesophagus 57.
Additionally, the evacuation tube 80 provides a pathway into the
oesophagus 57 for insertion, for example, of a gastric feeding
tube, suction catheter, temperature probe or other monitoring
device, probes carrying stimulating electrodes such as pacing
wires, sengstaken balloons, or other catheters bearing inflatable
cuffs, fiber optic endoscopes or medication. The evacuation tube 80
follows the general course of the airway tube 22, with sealed entry
through the backplate 27 alongside the airway tube, on the
laryngeal-side 81 of the backplate, and with sealed passage through
the interior of the main-cuff 40 and open through the distal region
45 of the main-cuff. Inflation-air supply to the back-cuff 65 may
be via the same tube 55 as for the main-cuff 40, or separate
inflating means (not shown) may be provided for the back-cuff 65.
The disclosures of U.S. Pat. Nos. 5,241,956, and 5,632,271, and
5,878,745 disclosing various laryngeal mask devices, are hereby
incorporated by reference herein.
[0053] More specifically, the toroidal-shaped main-cuff 40 is
formed by first moulding it in an intermediate stage having
opposing edges, each of which has an elliptical shape. The opposing
edges of the main-cuff 40, when in generally edge-to-edge relation,
are welded together to form a seam 85, as shown in FIGS. 5, 11 and
13. The seam 85 defines an oval contained in a plane which is
parallel to the major plane 75, corresponding to the internal
surface of the main-cuff 40. When the backplate 27 is attached to
the main-cuff 40, the seam 85 abuts the periphery of the oval
portion 87 in anterior relation to the backplate, as best shown in
FIGS. 11 and 13. The seam 85 may be inserted in a corresponding
groove in the oval portion 87. Alternatively, the backplate 27 and
main-cuff 40 may be extruded as a single, unitary piece.
[0054] As used herein, the term "welding" describes the bonding
together of two components having the same or similar chemical
compositions, either by adhesive having the same or similar
chemical composition as the components, or by high pressure or
temperature fusion, or a combination of any of them.
[0055] A separate tube (not shown), preferably with multiple
perforations along its length, may be contained within the
main-cuff 40 between the opening of the tube 55 into the main-cuff
such that each perforation communicates with a port between the
interiors of the main-cuff and back-cuff 65. Such a separate tube
preserves a flowpath between the tube 55 and back-cuff 65 if the
main-cuff 40 is completely collapsed from deflation, thereby
providing for further deflation of the back-cuff 65 via the tube
55. Alternatively, a channel (not shown) may be formed on the inner
surface of the main-cuff 40 between the opening of the tube 55 into
the main-cuff and at least one of the one or more ports between the
interiors of the main-cuff and back-cuff 65. Such a channel
preserves a flowpath between the tube 55 and back-cuff 65 if the
main-cuff 40 is completely collapsed from deflation.
[0056] The backplate 27 has a one-piece, integral spoon-shape
which, with the oval portion 87, also has an external tube-joint
92. The tube-joint 92 is oriented proximally relative to the oval
portion 87. Opposite sides of the oval portion 87 are defined by a
convex pharyngeal-side 60 and concave laryngeal-side 81. The
periphery of the oval portion 87 is hermetically bonded to the
periphery of the main-cuff 40 to establish separation between the
laryngeal-chamber region 110 and pharyngeal region 112.
[0057] The periphery of the oval portion 87 of the backplate 27
abuts, in proximal relation to, the seam 85 of the main-cuff 40 in
its inflated condition, as shown in FIGS. 10 and 12. This more
posterior location of the backplate 27, as compared to locating the
periphery of the oval portion 87 in the major plane 75, provides
additional space for the internal-drain tube 115. The oval portion
87 may be located at various positions in the anterior-posterior
direction relative to the main-cuff 40 because of the generally
constant cross-section of the laryngeal-chamber region 110 in
planes parallel to major plane 75, as shown in FIGS. 10 and 12.
[0058] Formed in the laryngeal-side 81 is a well 95 defined by a
depression adjacent to the tube-joint 92. The well 95 faces the
evacuation tube 80 such that the well is offset relative to the
sagittal plane 97 of the main-cuff 40. The well 95 thereby provides
a radial clearance between the evacuation tube 80 and
laryngeal-side 81.
[0059] The portions of the laryngeal-side 81 which are proximal and
distal of the well 95 are inclined relative to the base of the well
such that the laryngeal-side ramps anteriorly as it approaches the
well in the distal and proximal directions, as shown in FIG. 8.
[0060] The periphery of the oval portion 87 adjacent to the
tube-joint 92 is included in the heel 50. A portion of the heel 50
contiguous with its anterior edge is removed to define a
crescent-shaped recess 47. The proximal region 42 of the main-cuff
40 has an approximately hemispherical posterior bulge 100 arising
from its posterior surface, as shown in FIG. 8. The posterior bulge
100 extends posteriority symmetrically relative to the sagittal
plane 97 to fit into the mid-line groove 102 forming part of the
anterior surface of the double-barrelled tube-joint 92 of the
backplate 27. The mid-line groove 102 is shown in FIG. 16. The
posterior bulge 100 also extends into the crescent-shaped recess 47
to compensate for the reduced support provided by the backplate 27
resulting from the recess 47.
[0061] Less than the entire width of the main-cuff 40 extends
posteriorly from the proximal region 42 because the recess 47 of
the backplate 27 allows space for the main-cuff 40 to extend
posteriorly in the approximately hemispherical posterior bulge 100.
The posterior bulge 100 is partially supported bilaterally by the
backplate 27 thus preventing ballooning-out of this portion of the
main-cuff 40. Such ballooning-out of the main-cuff 40 would result
in the flow of internal gases from other interior regions of the
main-cuff resulting from redistribution of the pressure in the
main-cuff, thereby resulting in an uneven seal between the
main-cuff and the tissues surrounding the laryngeal inlet 67. Such
an uneven seal might result in loss of seal, particularly at the
pointed distal end of the main-cuff 40.
[0062] The recess 47 and mid-line groove 102 together form a
partial socket which provides mechanical support posteriority,
bilaterally and distally for the posterior bulge 100.
[0063] The posterior bulge 100 may be separable from the recess 47
to define a normally closed and therefore self-sealing port for
insertion of an elongate member such as a probe, endotracheal tube,
endoscope or the like from the pharyngeal-region 112 into the
laryngeal-chamber region 110. This enables such-an elongate member
to be inserted into the laryngeal-chamber region 110 without
occupying the interior of the airway tube 22 which may obstruct air
flow through the airway tube. Additionally, throughout insertion of
such an elongate member through the port and the laryngeal-chamber
region 110, the elongate member is anterior of the internal-drain
tube 115.
[0064] In comparison, if such an elongate member is inserted
through the airway port 30 into the laryngeal-chamber region 110,
upon entry into the laryngeal-chamber region, the distal end of the
elongate member lies substantially parallel to the internal-drain
tube 115. Accordingly, shortly after entry into the
laryngeal-chamber region 110, upon continued insertion into the
laryngeal-chamber region, the insertion direction of such an
elongate member must normally be sharply changed to enable entry
into or viewing of the larynx 37 or bronchial tree. Additionally,
insertion of such an elongate member through the airway port 30
into the laryngeal-chamber region 110 results in the elongate
member being laterally offset from the sagittal plane 97 since the
airway port is so offset from the sagittal plane. Such an elongate
member must therefore be suitably steered if it is to be aligned in
the sagittal plane 97. Aligning such an elongate member in the
sagittal plane 97 may facilitate its further insertion through the
larynx 37 into the trachea.
[0065] The elongate tube-joint 92 is formed on the pharyngeal-side
60 and extends posteriorly and proximally relative to the oval
portion 87. The tube-joint 92 includes a longitudinal passageway
105 extending from its proximal end 107 distally to the concave
laryngeal-side 81. The passageway 105 has a double-barrelled cross
section for supporting the airway tube 22 and evacuation tube 80,
described more fully herein below. The longitudinal central axis of
the passageway 105 is contained in the sagittal plane 97 and
inclined posteriority at an angle of approximately 30 degrees
relative to the major plane 75, as viewed in the sagittal plane
97.
[0066] A strap 200 is moulded to the external anterior surface of
the proximal tube-joint 92 in arching relation over the mid-line
groove 102. The moulding of the strap 200 onto the anterior surface
of the proximal portion of the tube-joint 92 defines an introducer
tool slot 201. The distal edge of the strap 200 has an internal
curved edge 203 against which abuts the posterior bulge 100 (which
is an extension of the main cuff 40), as shown in FIGS. 4, 6 and
16. The introducer tool slot 201 and curved edge 203 avoid becoming
dirt trap because when the main-cuff 40 is deflated, the posterior
bulge 100 (i.e, the main-cuff extension) pulls away from the strap
200, thus avoiding the formation of a blind pocket which could be a
dirt trap.
[0067] FIGS. 18 and 19 show a second embodiment of the backplate
27b. Parts in FIGS. 18 and 19 having corresponding parts in FIGS.
16 and 17 have the same reference numeral with the addition of
suffix b. The backplate 27b is similar to the backplate 27
illustrated in FIGS. 16 and 17 except that the backplate 27b does
not a strap similar to strap 100.
[0068] The evacuation tube 80 comprises an internal-drain tube 115
extending between the tube-joint 92 and the distal region 45 of the
main-cuff 40 on the laryngeal-side 81 of the backplate 27. The
internal-drain tube 115 longitudinally traverses the interior of
the distal region 45 of the main-cuff 40 in sealed relation
therewith for operative engagement and communication with the inlet
of the oesophagus 57. The internal-drain tube 115 is anterior
relative to the seam 85 of the main-cuff 40 such that the seam is
disposed between the internal-drain tube and the distal end of the
oval portion 87.
[0069] The internal-drain tube 115 therefore pierces the distal
region 45 at the proximal crotch-region 117 and the longitudinally
opposing distal crotch-region 120, both of which are portions of
the distal region 45. The edges of the main-cuff 40 in the
crotch-regions 117, 120 surrounding the internal-drain tube 115 are
hermetically sealed to the tube such that the enclosure of the
main-cuff 40 is defined in part by the external cylindrical surface
of the internal-drain tube.
[0070] The internal-drain tube 115 terminates in an oblique distal
orifice 123 opening out on the anterior distal aspect of the distal
region 45 of the main-cuff 40. The oblique distal orifice 123
results in partial flattening of the distal region 45 such that the
flattening is in a transverse plane inclined relative to the major
plane 75 by an angle a of preferably approximately 45 to 50 degrees
when main-cuff 40 is inflated, as shown in FIG. 14. When the
main-cuff 40 is deflated, angle a is preferably approximately 40 to
45 degrees. In adult sizes of the LMA-device 20, the surface area
of the distal region 45 removed to accommodate the orifice 123 is
approximately 1 square centimeter which is therefore no longer
available to contribute to expansion of the main-cuff 40 when the
main-cuff is inflated for sealing around the laryngeal inlet 67.
Accordingly, to prevent inspired gas leakage across the distal
region 45 resulting from insufficient local expansion of the
main-cuff 40, additional circumferential area of the anterior
surface of the distal region may be required for sealing. This may
be provided by inversion of the anterior-facing lip 127 of the
distal region 45 surrounding the orifice 123 resulting from
longitudinal withdrawal of the intra-cuff portion 130 of
internal-drain tube 115 approximately 3.5 millimeters relative to
the plane containing the distal end of the distal region 45 of the
main-cuff 40. This inversion produces a corresponding lateral
bulging of the distal region 45 around the orifice 123. The
anterior position of the distal orifice 123 ensures less
compressive force resulting from the fluid pressure inside the
main-cuff 40 on the intra-cuff portion 130 in the
anterior-posterior direction, thus compensating for
anterior-posterior compression from anatomical structures in the
throat 32 so that the internal-drain tube 115 is subject to
approximately equal compressive forces laterally and
anterior-posteriorly, hence avoiding collapse.
[0071] The part of the intra-cuff portion 130 containing the distal
orifice 123 has a longitudinal central axis inclined relative to
the plane containing the distal orifice by an angle .gamma. of
preferably 60 degrees, and inclined relative to the major plane 75
by an angle .DELTA. of preferably 20 degrees. The longitudinal
central axis of the intra-cuff portion 130 is contained in the
sagittal plane 97.
[0072] The distal orifice 123 has diametrically opposed posterior
and anterior apexes 135, 137. The distal orifice 123 is contained
in a transverse elliptical plane preferably inclined by an angle
.beta., which is preferably 40 degrees, relative to the major plane
75, as shown in FIG. 14. The inclination of the distal orifice 123
is such that the posterior apex 135 is offset distally relative to
the anterior apex 137 along the longitudinal axis of the portion of
the internal-drain tube 115 containing the distal orifice 123.
[0073] Integral with the external anterior surface of the
intra-cuff portion 130 adjacent to the distal orifice 123 is a
semicircular transverse shoulder 142, as shown in FIG. 9. The
anterior and the adjacent lateral portions of the distal edge of
the distal region 45 of the main-cuff 40 are bonded to the proximal
surface of the shoulder 142. The posterior and remaining lateral
portions of the distal edge of the distal region 45 are bonded to
the unshouldered external surface adjacent to the distal orifice
123.
[0074] The lateral termination of each end of the shoulder 142
facilitates collapse of the distal orifice 123 in the major plane
75 when the main-cuff 40 is deflated since the un-reinforced
posterior portion of the intra-cuff portion 130 is able to collapse
more readily when the pressure inside the main-cuff 40 is reduced
(i.e., negative pressure is applied to the main-cuff). Also, by
limiting the circumferential dimension of the shoulder 142, its
peripheral length which must be deflected is reduced. In contrast,
if the shoulder 142 extended posteriorly a sufficient amount such
that it traversed the major plane 75, the portions of the shoulder
that traversed the major plane would require closure to close
distal orifice upon deflation of the main-cuff 40. Such closure of
such a shoulder would require significantly more force than
required to flatten the shoulder 142, shown in FIG. 14. Such
increased force may require stronger material for the main-cuff 40
and application of higher deflation vacuums to the main-cuff.
[0075] The distal orifice 123 is withdrawn proximally relative to
the distal region 45 of the main-cuff 40 resulting in the portion
of the distal region 45 adjacent to the distal orifice 123 being
invaginated when the main-cuff 40 is inflated, as shown in FIG. 14.
The bonding of the distal end of the distal region 45 to the distal
surface of the shoulder 142 results in the transversely-arcuate
inverted anterior-facing lip 127 of the invaginated surface having
the greatest radial bulge. The transversely-arcuate lateral
portions 145, 147 of the invaginated surface have the next largest
radial bulge with the transversely-arcuate posterior portion 150
having the least radial bulge. The opposed lateral portions 145,
147 are symmetrical about the sagittal plane 97 of the main-cuff
40.
[0076] The portion of the internal-drain tube 115 longitudinally
traversing the interior of the distal region 45 of the main-cuff 40
defines intra-cuff portion 130. The outer surface of the intra-cuff
portion 130 has at least one circumferential strengthening rib 152
proximal of the shoulder 142 to resist radial collapse of the
intra-cuff portion 130 by internally directed radial forces
resulting from the fluid pressure within the main-cuff 40. The rib
152 is contained in a transverse elliptical plane preferably
inclined at an angle 0, preferably of 60 degrees and equal to angle
.gamma., relative to the longitudinal axis of the intra-cuff
portion 130, as shown in FIG. 14. The inclination of the rib 152
enables its posterior pivoting about its posterior apex during
deflation of the distal region 45 to facilitate flattening of the
main-cuff 40.
[0077] The portion of the internal-drain tube 115 proximal of the
intra-cuff portion 130 is laterally offset from the sagittal plane
97, as shown in FIGS. 3 and 7. The portion of the internal-drain
tube 115 where it emerges from the proximal crotch-region 117 and
extends to the well 95 is received in a groove 157 formed in the
oval portion 87, as shown in FIG. 7. The groove 157 is defined
laterally by fillets 160 which laterally abut the internal-drain
tube 115. As much as 50% of the posterior portion of the
cross-sectional area of the internal-drain tube 115 may be
contained in the distal portion of the groove 157, except where its
circumference is free posteriority, i.e., where it runs over the
well 95. In one size of the main-cuff 40, the longitudinal
dimension of the groove 157 is 2.5 centimeters. The internal-drain
tube 115 is welded to the groove 157.
[0078] The fillets 160 resist anterior deflection of the oval
portion 87 since the fillets provide increased surface area for the
weld between the internal-drain tube 115 and oval portion. This
additional resistance compensates for the reduced resistance
resulting from a reduction in the anterior-posterior thickness of
the part of the oval portion 87 defining the base of the groove
157. Such reduced anterior-posterior thickness is desirable to
increase the anterior-posterior dimension a between the anterior
surface of the main-cuff 40, and the portion of the internal-drain
tube 115 between the proximal crotch region 117 and well 95, shown
in FIG. 8, especially at the location of dimension b, shown in
FIGS. 9 and 10, which should have a depth of at least 10
millimeters in adult sizes, described further herein below.
[0079] FIG. 12 illustrates a second embodiment of the LMA-device
20a in which the flexible panel 62a is tethered to the backplate
27a. The parts in FIG. 12 having corresponding parts in FIGS. 1 to
11 have the same reference numeral with the addition of suffix a.
Tethering of the panel 62a to the backplate 27a provides additional
resistance to anterior inversion of the oval portion 87a. This
enables further reduction in the anterior-posterior thickness of
the part of the oval portion 87a defining the base of the groove
157a. As discussed above, such reduced anterior-posterior thickness
is desirable to increase the anterior-posterior dimension,
corresponding to the dimension a in FIG. 8.
[0080] A longitudinal portion of the internal-drain tube 115
extends over well 95, as shown in FIG. 8. The anterior-inclination
of the portions of the laryngeal-side 81 proximal and distal of the
well 95, described herein above, anteriorly props the portion of
the internal-drain tube 115 extending over the well to increase the
anterior-posterior clearance between the internal-drain tube and
base of the well. The internal-drain tube 115 arches over the well
95 defining a slight posterior curve and simultaneously curving
laterally to its insertion in the tube-joint 92.
[0081] The evacuation tube 80 includes an external-drain tube 165
having a distal end 167 connected in end-to-end relation to the
proximal end 170 of the internal drain-tube 115. The joint between
the internal and external-drain tubes 115, 165 is located where the
tube-joint 92 opens into laryngeal-chamber region 110, as shown in
FIGS. 8 and 15.
[0082] The inner diameters of the internal-drain tube 115 and
external-drain tube 165 are the same. The outer diameter of the
internal-drain tube 115 is less than the outer diameter of the
external-drain tube 165. The distal end 167 of the external-drain
tube 165 has an internal countersunk portion 172 defined by a
bevelled internal axial wall, as shown in FIG. 15. The outer
diameter of the countersunk portion 172 is greater than the outer
diameter of the internal-drain tube 115. The proximal end 170 of
the internal-drain tube 115 abuts the countersunk portion 172
resulting in coaxial self-alignment of the central longitudinal
axes of the distal and proximal ends 167, 170.
[0083] As shown in FIGS. 8 and 15, the external-drain tube 165 is
supported in the cylindrical drain barrel 175 of the
double-barrelled passageway 105 which is longitudinally offset from
the well 95 at an angle of approximately 9 degrees. The
internal-drain tube 115 is thereby disposed anteriorly of the well
95 and is also offset at 9 degrees from the major axis of drain
barrel 175 to increase the lateral clearance.
[0084] The evacuation tube 80 is preferably moulded to the
backplate 27. Alternatively, for making a prototype, assembly of
the evacuation tube 80 to the backplate 27 may be by first welding
the distal portion of the internal-drain tube 115 into the distal
region 45 of the main-cuff 40. Before connecting the proximal end
of the internal-drain tube 115 to tube-joint 92, the main-cuff 40
is welded to the backplate 27. The external-drain tube 165 is then
welded into the drain barrel 162 of the tube-joint 92, for example,
by an adhesive 173. Hardening of these welds effectively clamps and
fixes the distance between the distal end of the proximal
crotch-region 117 of the main-cuff 40 and the distal end 167 of the
external-drain tube 165. The internal-drain tube 115 is cut, as
needed, such that it is slightly longer than this distance. The
proximal end 170 of the internal-drain tube 115 is then inserted
into the countersunk portion 172 of the external-drain tube 165
with the countersunk portion resulting in coaxial self-alignment of
the longitudinal central axes of the distal and proximal ends 167,
170. The internal-drain tube 115 is then welded to the tube-joint
92, for example, by an adhesive 174.
[0085] The slightly longer length of the internal-drain tube 115
relative to the distance between the proximal crotch-region 117 and
distal end 167 results in a slight longitudinal compression of the
internal-drain tube causing lateral curvature of it away from the
adjacent side-wall 177 of the backplate 27. Lateral curvature of
the internal-drain tube 115 away from the adjacent side-wall 177
increases the lateral clearance between them, reducing the
likelihood of dirt collecting between them.
[0086] As shown in FIGS. 3 and 7, the airway tube 22 is supported
in the cylindrical airway barrel 180 of the double-barrelled
passageway 105 in communication with the airway port 30 defined by
the opening of the airway barrel 180 into the laryngeal-side 81.
Such communication provides a flowpath between the airway tube 22
and laryngeal-chamber region 110. The airway tube 22 is connected
to the tube-joint 92 by welding using an adhesive or,
alternatively, connected by high-pressure or temperature
fusion.
[0087] The airway tube 22 and external-drain tube 165 are welded
together in side-by-side tangential relation, as shown in FIG. 2.
The welding is accomplished by depositing adhesive in one or both
of the crevices defined by the outer surfaces of the tubes 22, 165
adjoining the line of tangential contact between them. The adhesive
preferably extends longitudinally from the tube-joint 92 proximally
for approximately 41/4 inches. Alternatively, the tubes 22, 165 may
be connected together by high pressure or temperature fusion. Also,
the tubes 22, 165 may be manufactured by simultaneous extrusion.
Additionally, the tubes 22, 165 may remain separate for certain
clinical applications, e.g., operations on the tongue 202 in the
mid-line or other mid-line structures in the pharynx 197.
[0088] The airway tube 22 and external-drain tube 165 are inserted
through a bite-plate 176 comprising a sleeve which is
telescopically fitted around the tubes 165, 176, as shown in FIG.
2. The bite-plate 176 is positioned longitudinally on the tubes 22,
165 such that, when the LMA-device 20 is completely inserted into
the throat 32 and pharynx 197, the bite-plate is positioned between
the upper and lower teeth, described further herein below.
[0089] In embodiments in which the airway tube 22 is bonded to the
external-drain tube 165, the tubes 22, 165 are bent away from one
another, laterally at the proximal extent of the adhesive to
facilitate routing of the airway tube to a ventilating apparatus
(not shown) and the external-drain tube 165 to a suction-apparatus
(not shown), if required. The separation of the airway tube 22 and
external-drain tube 165 is achieved by placing a sleeve 182 on the
airway tube to cover the proximal 3 centimeters of the airway tube.
The sleeve 182 is proximally oriented relative to the bite-plate
176. Connected to the distal end of the sleeve 182 is a triangular
wedge 185 oriented toward the external-drain tube 165 to force the
softer external-drain tube to incline away from the airway tube 22
by an angle C, preferably approximately 15 degrees. The sleeve 182
and wedge 185 are a single moulding and are welded to the airway
tube 22. Additionally, the wedge 185 is welded to the
external-drain tube 165. The sleeve 182 also stiffens the proximal
end of the airway tube 22 to reduce the likelihood of kinking at
its attachment to the ventilating apparatus (not shown).
[0090] The portions of the airway tube 22 and external-drain tube
165 in side-by-side tangential relation each have the same outer
diameter. The inner diameter of this portion of the airway tube 22
is greater than the inner diameter of the adjoining portion of the
external-drain tube 165. These portions of the airway tube 22 and
external-drain tube 165 each have approximately the same stiffness
and resistance to longitudinal bending. A metallic cylindrically
helical wire 190 is provided between inner and outer surfaces of
the airway tube 22 in coaxial relation therewith to increase the
kink resistance of the thinner-wall airway tube. The kink
resistance of this portion of the airway tube 22 may be further
increased by forming it of a material having a harder durometer of
silicone. It may also be possible for the chemical compositions of
these portions of the tubes 22, 165 to be approximately the same
if, for example, the helical wire 190 sufficiently increases the
stiffness of airway tube.
[0091] A hard plastic or polycarbonate cylindrical fitting (not
shown) is inserted in the end of the airway tube 22 proximal of the
triangular wedge 185. The fitting is inserted into the airway tube
22, and has a radial flange which abuts the proximal end of the
airway tube to longitudinally limit the insertion of the fitting
into the airway tube. The fitting facilitates connection to the
ventilating apparatus (not shown).
[0092] In use, an inflation/deflation device is actuated to apply a
vacuum, via the tube 55, to the main-cuff 40 sufficient to fully
deflate it prior to insertion of the main-cuff through the mouth of
the patient. Such a vacuum extends to the space enclosed by the
flexible panel 62 and backplate 27, via the channel 90 in the
main-cuff 40, deflating the back-cuff 65 to collapse it onto the
pharyngeal-side 60 of the backplate 27 and posterior surface of the
main-cuff.
[0093] The main-cuff 40 is preferably deflated into a predetermined
shape by using the forming tool disclosed in U.S. Pat. No.
5,711,293, the entire disclosure of which is hereby incorporated by
reference herein.
[0094] The flattened sheet, comprising fully deflated the main-cuff
40, backplate 27 and internal-drain tube 115, is passed easily
through the mouth 25 of the patient because of the reduced
compressible antero-posterior dimension of the part of the
LMA-device 20 having the largest anterior-posterior dimension,
i.e., the generally proximal region 42 of the main-cuff 40 and the
heel 50. This reduced compressible antero-posterior dimension
results from the recess 47 of the heel 50. The deflated main-cuff
40, backplate 27 and internal-drain tube 115 is pressed against the
hard and soft palates 192, 195 as it is pushed inwardly, resulting
in the deflated main-cuff being guided distally by the soft palate
onto the posterior wall of the pharynx 197. Such deflection of the
main-cuff 40 is normally only reliably achieved if the total
stiffness of the LMA-device 20 is within certain predetermined
limits.
[0095] The main-cuff 40 is preferably urged through the throat 32
by placement of either the operator's index finger or an insertion
tool inserted into the strap 200 against the heel 50, because the
side-by-side airway tube 22 and internal-drain tube 115 are
normally not sufficiently stiff to be used as a rod to direct the
main-cuff through the throat.
[0096] The main-cuff 40 is preferably positioned in the throat 32
by inserting the a sufficient length of the index finger of the
operator through the introducer tool slot 201 such that the finger
is placed on the mid-line groove 102 of the tube-joint 92 and the
end of the finger abuts the heel 50, as shown in FIG. 16. Inserting
the finger through the introducer tool slot 201 enables the finger
to be partly wedged into the strap 100 to secure the index finger
to the mid-line groove 102. Placement of the index finger on the
mid-line groove 102 of the tube-joint 92 and against the heel 50
assists in locating and stabilizing the finger against the proximal
region 42 of the main-cuff 40. This reduces the risk of finger
slippage from its intended position on the backplate 27 due to the
presence of slippery secretions in the mouth 25 and/or the
application of lubricant, to assist smooth passage of the
LMA-device 20 during its insertion into the patient and to avoid
the risk of injury to the patient or of damage to the LMA-device.
During such insertion, the proximal region 42 of the main-cuff 40
provides a fulcrum.
[0097] An alternative and equally preferable way to position the
main-cuff 40 in the throat 32 is by an introducer tool (not shown)
including a relatively rigid elongate member having a distal end
adapted for removable keyed engagement with the heel 50 and strap
200 adjacent to the tube-joint 92 for insertional guidance of the
main-cuff 40. During such insertion, as with placement of the
operator's finger against the heel 50, the proximal region 42 of
the main-cuff 40 provides a fulcrum. The introducer tool and
LMA-device 20 may both be included in a kit.
[0098] Preferably, the deflated main-cuff 40 and backplate 27 are
sufficiently flexible that they do not overcome the resistance
provided by the soft palate 195. The main-cuff 40 and backplate 27
are preferably flexible similar to a palette knife such that, when
the main-cuff and backplate are urged or tensed against the soft
palate 195, the distal region 45 is deflected downward by the soft
palate rather than being forcibly driven into it, which may bruise
the soft palate. Also preferable is for the deflated main-cuff 40
to itself bend smoothly around (i.e., in the shape of) an arc 196,
as shown in FIG. 21, also similar to a palette knife.
[0099] Further, the deflated main-cuff 40 and backplate 27 resist
kinking. Kinking results in the main-cuff 40 and backplate 27,
during their insertion through the throat 32, collapsing on the
tongue 202 rather than arching over it. To avoid kinking, a
specific overall stiffness and long-axis gradation of stiffness in
the delated main-cuff 40 is required, which in turn depends on the
shape of the backplate 27. The primary factors or considerations to
be balanced when designing the backplate 27 are (i) desirability of
long-axis gradation of stiffness (i.e., linear tapering-off
distally of resistance to flexure), (ii) adequate stiffness and
appropriate architecture to prevent anterior herniation from fluid
pressure within the inflated back-cuff 65, and (iii) minimal
thickness in the anterior-posterior dimension to reduce overall
resistance to flexure.
[0100] The relative stiffness of the airway tube 22, external-drain
tube 165 and backplate 27 facilitate piloting and guiding of the
substantially flattened, deflated main-cuff 40 to smoothly ride or
track posterior contours of the throat 32 and pharynx 197 and to
assure that the deflated main-cuff enters and locates immediately
above the upper oesophageal sphincter 207 and adjacent to the
laryngeal inlet 67, as shown in FIGS. 1 and 2.
[0101] Additionally, the backplate 27, internal-drain tube 115 and
main-cuff 40 are sufficiently flexible to allow anterior and
posterior deflection of the distal region 45 in the sagittal plane
97 when the main-cuff is fully deflated, as shown in FIG. 21. Such
deflection further facilitates riding or tracking of the distal
region 45 of the main-cuff 40 over the posterior contours of the
throat 32 by allowing the distal region to deflect as necessary to
conform to protrusions or recesses in the posterior surface of the
throat.
[0102] The deflated main-cuff 40 further enters into its correct
position opposite the laryngeal inlet 67 without colliding with
anterior structures such as the posterior surface of the tongue
202, epiglottis 35, or arytenoids 205. Insertion of the deflated
main-cuff 40 is facilitated by forming the main-cuff 40 and
attaching it to the backplate 27 such that the seam 85 abuts the
backplate, as shown in FIGS. 12, 13 and 14. As a result, when the
main-cuff 40 is fully deflated, the anterior surface of the
main-cuff is uninterrupted by the seam 85, i.e., the seam is buried
between the backplate 27 and the deflated main-cuff. Accordingly,
the likelihood is reduced of the anterior surface of the deflated
main-cuff 40 scraping or catching on the anatomical structures of
the throat 32, such as the epiglottis 35 and arytenoids 205.
Further disclosure of insertion of the deflated main-cuff 40
through the throat 32 may be had by reference to U.S. Pat. No.
5,632,271, the entire disclosure of which is hereby incorporated by
reference herein.
[0103] When the LMA-device 20 is fully inserted in the throat 32,
the side-by-side airway tube 22 and external-drain tube 165 extend
proximally from the tube-joint 92 in contacting relation with the
soft palate 195, and lie against the hard palate 192, i.e., the
roof of the mouth 25. The tubes 22, 165 are spaced inwardly of the
sides of the throat 32 to avoid damage to the lingual nerves. The
tubes 22, 165 rest lightly against the posterior aspect of the
upper teeth, usually close to parallel with the inner surface of
the upper incisors, and emerge from the mouth 25 between the
teeth.
[0104] The bite-plate 176 is positioned at the emergence of the
tubes 22, 165 from the mouth 25 such that the bite-plate is
disposed between the upper and lower teeth and the tubes. The teeth
thereby directly contact the bite-plate 176, rather than the tubes
22, 165, to provide protection to the tubes.
[0105] When the main-cuff 40 is correctly positioned, the distal
orifice 123 of the internal-drain tube 115 contacts the upper
oesophageal sphincter 207 and lies posterior to the cricoid
cartilage 210. The bevelled distal region 45 of the main-cuff 40,
including the distal orifice 123 of the internal-drain tube 115,
forms a wedge-shape of approximately 45 degrees when the main-cuff
40 is deflated. This facilitates insertion of the main-cuff 40 and
backplate 27 behind the cricoid cartilage 210 because such
insertion requires the cricoid cartilage to be gently forced
anteriorly to allow passage of the wedge-shaped distal region 45,
including the distal orifice 123, behind it. Further disclosure of
positioning the LMA-device 20 may be had by reference to U.S. Pat.
No. 5,241,956, the entire disclosure of which is hereby
incorporated by reference.
[0106] When the LMA-device 20 is completely inserted, the main-cuff
40 contacts the base of the hypo-pharynx 212 with the distal region
45 being wedged into the upper opening of the upper oesophageal
sphincter 207, a constriction which is however much too small to
permit the LMA-device 20 to pass through it. Complete insertion of
the LMA-device 20 is thereby detected by the operator as a
resistance to insertion of the main-cuff 40 into the upper
oesophageal sphincter 207. The main-cuff 40 is then inflated with
sufficient air, via the tube 55, to obtain a seal against the
laryngo-pharyngeal perimeter. The LMA-device 20, when completely
inserted in the pharynx 197, lies in the sagittal plane 97.
[0107] Inflation of the main-cuff 40 causes expansion of the distal
region 45 enabling it to lie against and adapt to the pharynx 197
and hypo-pharynx 212. Additionally, inflation of the main-cuff 40
causes the gas or fluid to flow into the space enclosed by the
flexible panel 62 and backplate 27, for example, via one or more
ports in the main-cuff, resulting in inflation of the back-cuff 65.
Inflation of the back-cuff 65 initially causes engagement between
the flexible panel 62 and posterior surface of the pharynx 197.
Further inflation of the back-cuff 65 urges the main-cuff 40
anteriorly to press it against the tissue surrounding the laryngeal
inlet 67. This tightens the sealing engagement between the
main-cuff 40 and the tissue surrounding the laryngeal inlet 67,
thereby reducing leakage between such tissue and the main-cuff. The
sealing engagement is further improved by provision of the
increased anterior-posterior space between the oval portion 87 of
the backplate 27 and the anterior surface of the main-cuff 40,
permitting accommodation of the posteriorly bulging posterior
surface of the cricoid cartilage 210 which is located distally
relative to the laryngeal inlet 67.
[0108] If the back-cuff 65 is overinflated, the oval portion 87 may
bulge anteriorly outward resulting in anterior displacement of the
internal-drain tube 115 relative to the main-cuff 40, and loss of
the advantageously increased anterior-posterior space between the
oval portion 87 and the anterior surface of the main-cuff 40,
described above. The anterior-posterior dimension a between the
anterior tangency of the internal-drain tube 115 and a plane
containing the anterior surface of the main-cuff 40, shown in FIG.
8, must not decrease below a minimum level since such may result in
the internal-drain tube undesirably impinging against anatomical
structures of the throat 32 normally present in the
laryngeal-chamber region 110. For example, if the main-cuff 40 is a
standard adult size and is inflated to 40 millimeters Hg (mercury),
at a point b contained in the sagittal plane 97 and located 40
millimeters distally from the distal end of the proximal region 42
of the main-cuff 40, shown in FIG. 9, the minimum
anterior-posterior distance b must not approach 8 millimeters, is
preferably at least 10 millimeters and ideally at least 10.7
millimeters.
[0109] The transversely arched profile, degree of hardness, and
increased anterior-posterior thickness of the distal portion of the
oval portion 87 are all factors chosen to offer adequate resistance
to such anterior bulging thereby limiting such resulting anterior
displacement of the internal-drain tube 115 near the distal region
45 of the main-cuff 40 where the internal-drain tube is nearest to
the anterior surface of the main-cuff. Fillets 160, 160a and
tethered panel 62a, shown in FIGS. 11 and 12, also limit anterior
displacement of the internal-drain tube 115 relative to the
main-cuff 40. Anterior-posterior dimension a, shown in FIG. 8,
should be maintained above a minimum amount to avoid anterior
displacement of the arytenoids 205 which may obstruct flow of gases
through the larynx 37, and to avoid anterior displacement of
anatomical structures relative to the main-cuff 40 which may reduce
the tightness of the seal between the main-cuff and the tissues
surrounding the laryngeal inlet 67. Additionally, the backplate 27
is preferably sufficiently flexible to deflect in the
anterior-posterior direction during insertion into the throat 32 to
follow its contours, e.g., to bend around the soft palate 195.
[0110] The backplate 27 is reinforced because the prior LMA-devices
(such as is disclosed in U.S. Pat. No. 4,509,514) did not have a
back-cuff, such as back-cuff 65. The back cuff 65 of the LMA-device
20 causes pressure to be applied to the oval portion 87 of the
backplate 27, which may cause the oval portion to herniate
anteriorly. The backplate 27 must therefore be designed to resist
such herniation, preferably to pressures within back-cuff 65 of up
to 100 centimeters of water. Techniques for preventing such
herniation of the backplate 27 include arching the backplate 27
such that it has a concavity facing anteriorly, making the
backplate of a high durometer silicone or other plastics material,
thickening the backplate sufficiently to resist herniation (but not
so much that it becomes too stiff to bend easily around the back of
the tongue 202), and possibly also providing the backplate with a
midline longitudinally running 30 groove for accurately locating
adhesive to weld to it the back cuff 65. In addition, the back cuff
65 may be made of a thin elastomeric sheet material capable of
considerable elongation in response to the pressure within it,
resulting in minimal herniation of the backplate 27.
[0111] The anteriorly facing laryngeal-chamber region 110 of the
main-cuff 40 is wider than the transverse distance between the
edges of the laryngeal inlet 67 as defined by the so-called
aryepiglottic folds which bilaterally border the laryngeal inlet
thus encouraging a sealing contact between the main-cuff and the
pharyngeal tissues as well as the tissues bordering the laryngeal
inlet. The main-cuff 40 is thus functionally a pharyngo-laryngeal
mask airway forming an end-to-end seal against the larynx 37.
[0112] FIGS. 23 and 24 illustrate a third embodiment of the
LMA-device 20c. Parts in FIGS. 23 and 24 having corresponding parts
in FIGS. 1 to 22 have the same reference numeral with the addition
of suffix c. The main-cuff 40c may have soft and yielding ridges
(not shown) bilaterally disposed on the anteriorly-facing distal
region 45c of the main-cuff which are suitably contoured to fill
the anatomical grooves known as the pyriform fossae to increase the
sealing efficacy of the main-cuff. The LMA-device 20c exploits the
triangular cross-section of the grooves of the pyriform fossae
which are roofed over and isolated by the anterior surface of the
main-cuff 40c bilaterally. The entire length of the grooves of the
pyriform fossae are covered by the main-cuff 40c such that a
respective cavity is defined by each groove and the contiguous
portion of the anterior surface of the main-cuff. Incorporation of
one or more one-way valves 215, such as a reed or duck-bill valve,
in the anterior wall of the main-cuff 40c facing the grooves of the
pyriform fossae permits the operator to evacuate residual gas from
the cavities by anterior neck pressure so causing the low pressure
in the cavities to pull or draw the main-cuff anteriorly enhancing
the seal. One-way valves 215 may be duck-bill valves of the type
sold by Accusil.RTM. Incorporated of Merriville, Ind., U.S.A.
[0113] Attached to the interior surface of the anterior wall of the
main-cuff 40c are respective cylindrical housings 217, shown in
FIG. 24, each surrounding a respective one of the one-way valves
215. Deflation of the main-cuff 40c draws its posterior wall toward
the housings 217 and one-way valves 215, eventually causing the
posterior wall to seat on the open posterior ends of the housings
217, as illustrated by a portion of the posterior wall being shown
in phantom line in FIG. 24 in dashed lines. Seating of the
posterior wall of the main-cuff 40 on the open posterior ends of
the housings 217 hermetically seals the respective one-way valves
215 from the remainder of the interior of the main-cuff. Each of
the one-way valves 215 thereby becomes isolated from the reduced
pressure inside the main-cuff 40c. This prevents the reduced
pressure within the main-cuff 40c from drawing gases external of
the main-cuff in the vicinity of the one-way valves 215 through the
one-way valves into the main-cuff thereby enabling the reduced
pressure inside the main-cuff to deflate it.
[0114] In an alternative embodiment (not shown), one-way valves 215
and their associated housings 217 may be replaced by ports or
apertures, the ends of which within the main-cuff 40c are each
connected to a tube also within the main-cuff. The tubes connected
to the ports or apertures communicate via a tube or, less
preferably, multiple tubes which extend through the wall of the
main-cuff to a point outside of the main-cuff 40c such that the
ports or apertures, and the tubes connected to them, are isolated
from the interior of the main-cuff. A source of suction may then
applied to the tube or tubes outside of the main-cuff 40c to
evacuate residual gas from the cavities defined by each groove of
the pyriform fossae and the contiguous portion of the anterior
surface of the main-cuff.
[0115] The sealing efficacy of the main-cuff 40 may be further
increased by an optional wedge-shaped crescent (not shown) in
sealing contact with the anterior surface of substantially the
proximal one-half of the main-cuff.
[0116] The epiglottis 35, a leaf-like structure which normally
projects proximally and posteriorly, is supported against the
anterior surface of the internal-drain tube 115. The internal-drain
tube 115 thereby defines a stop to prevent the epiglottis 35 from
interfering with communication between the airway tube 22, via the
airway port 30, and the laryngeal inlet 67. This creates adequate
space in the laryngeal-chamber region 110 posterior to the
epiglottis 35 for passage of gases between the airway port 30 and
laryngeal inlet 67.
[0117] Such passage of gases between the airway port 30 and
laryngeal inlet 67 is mainly in the portion of the
laryngeal-chamber region 110 lateral of the sagittal plane 97 and
containing the airway port. If, however, the epiglottis 35 slides
laterally from its propped position against the internal-drain tube
115 into the lateral portion of the laryngeal-chamber region 110
containing the airway port 30, gas passage between the airway port
and laryngeal inlet in this portion of the laryngeal-chamber region
may be obstructed. If so, gases may circulate between the airway
port 30 and laryngeal inlet 67 via the radial clearance between the
internal-drain tube 115 and well 95, and through the portion of the
laryngeal-chamber region 110 laterally of the sagittal plane 97
offset from the airway port 30. An alternative circulation flowpath
is thereby provided to permit adequate and free gas communication
between the airway tube 22 and laryngeal inlet 67, while
simultaneously preventing obstruction to such gas flow by the
epiglottis 35. The contour of the laryngeal-side 81 of the
backplate 27 props the internal-drain tube 115 away from the
laryngeal-side to facilitate sufficient radial clearance between
the internal-drain tube 115 and well 95 thereby to provide the
adequate and free gas communication between the airway tube 22 and
laryngeal inlet 67.
[0118] The oval portion 87 of the backplate 27 has a sufficiently
large anterior-posterior depth to contain the internal-drain tube
115 such that the drain tube does not bear against other laryngeal
structures and interfere with gas flow.
[0119] The well 95 also provides a route for drainage of secretions
from the trachea, which may enter the laryngeal-chamber region 110
via the laryngeal inlet 67. Such secretions normally collect in the
well 95 since, when the LMA-device 20 is fully installed and the
patient is supine, the laryngeal-side 81 of the backplate 27 faces
upward. In the absence of the well 95, such secretions would
collect between the laryngeal-side 81 of the backplate 27 and
internal-drain tube 115.
[0120] The adequately-sized well 95 is provided behind the
internal-drain tube 115 to allow gases or secretions to pass
between the internal drain tube and the backplate 27. This improves
drainage of secretions emerging from the trachea 36 and improves
gas exchange if there is any obstruction due to the epiglottis 35
falling into the laryngeal-chamber region 110 close to the
distal-end 72 of the airway tube 22 adjacent to the airway port
30.
[0121] Inflation of the main-cuff 40 causes expansion of the distal
region 45 including the anterior-facing lip 127, lateral portions
145, 147, and posterior portion 150 of the invaginated end, as
shown in FIGS. 8 and 14. The hermetic seal between the oblique
distal orifice 123 of the internal-drain tube 115 and the distal
region 45 of the main-cuff 40 obstructs communication between the
oesophagus 57 and laryngeal-chamber region 110. Accordingly,
leakage, e.g., of contents from the oesophagus 57 into the
laryngeal-chamber region 110, and via the laryngeal inlet 67 into
the trachea is obstructed.
[0122] The invagination and 45 degree angulation of the distal end
of the main-cuff 40 reduces the likelihood of leakage between the
distal orifice 123 of the internal-drain tube 115 and the
laryngeal-chamber region 110 of the main-cuff 40 which may result
from the expansion of the main-cuff being hampered at the narrower
distal region 45 and distal end by the presence of the distal
orifice. Also, the angle formed by the main-cuff 40 when deflated
was sufficiently large to impede insertion of the LMA-device 20 to
its correct location in the pharynx 197 opposite the laryngeal
inlet 67. The desired insertion characteristics are obtained by
invagination by 3.5 millimeters (size 4) of the wall of the
main-cuff 40 forming the anterior lip 127 of the distal orifice 123
produced an increased expandable area around the distal orifice of
the internal-drain tube 115, improving the seal and, by drawing
proximally only the anterior lip 127, sufficiently sharpening the
angle of the distal tip of the deflated main-cuff.
[0123] The side-by-side bonded adjacency of the airway tube 22 and
external-drain tube 165 conforms to the cross-sectional shape of
the mouth 25 and throat 32 facilitating insertion into and
displacement through the throat. The side-by-side adjacency of the
airway tube 22 and external-drain tube 165 also reduces the
likelihood of kinking when they bend.
[0124] After positioning the main-cuff 40 opposite the laryngeal
inlet 67 as described herein above, the ventilating apparatus (not
shown) is actuated, as needed, to provide anesthesia gas to the
trachea, via the laryngeal inlet, through the airway tube 22.
[0125] The evacuation tube 80 has the following functions:
[0126] (i) the evacuation tube 80 allows gases to be administered
to the lungs through the airway tube 22 under positive pressure
without the risk of inflating the stomach, via the upper
oesophageal sphincter 207, since gases escaping from the
laryngeal-chamber region 110 between the main-cuff 40 and the
tissues surrounding the laryngeal inlet 67 into the hypo-pharynx
212 will be ducted out through the evacuation tube instead of being
forced through the upper oesophageal sphincter 207 into the
oesophagus 57, the latter of which may occur with other known
LMA-devices such as is disclosed in U.S. Pat. No. 4,509,514 which
is hereby incorporated by reference herein;
[0127] (ii) conversely, if there is no evidence of gases being
ducted through the evacuation tube 80 during positive pressure
ventilation through the airway tube 22, this indicates proper
positioning of the main-cuff 40 with its distal end of the distal
region 45 pressed into the base of the hypo-pharynx 212. The
evacuation tube 80 thus provides monitoring of correct placement of
the LMA-device 20;
[0128] (iii) In the event of unexpected regurgitation though the
upper oesophageal sphincter 207, gastric contents are likely to
follow the path of least resistance and enter into the evacuation
tube 80 through the oblique orifice 123 rather than the larynx 37
via the laryngeal inlet 67, the latter of which may occur with
other known LMA-devices such as is disclosed in U.S. Pat. No.
4,509,514 which is hereby incorporated by reference herein; and
[0129] (iv) If desired, a suction catheter (not shown), probe for
monitoring temperature or other parameter (not shown), or endoscope
(not shown) may be inserted through the evacuation tube 80 provided
the outer diameter of any such inserted device is less than the
internal diameter of the evacuation tube.
[0130] An additional drain tube (not shown) may also be inserted
though the airway tube 22 in a distal direction to emerge through
the airway port 30 adjacent to the well 95. A suction may be
applied to such additional drain tube to remove secretions which
may collect in the well 95. The different inner diameters of the
airway tube 22 and external-drain tube 165 facilitate their
respective identifications by the operator so to facilitate
insertion into the proper tube of such additional drain-tubes or
endoscope.
[0131] The internal- and external-drain tubes 115, 165 have
different external but the same internal diameters because the
external-drain tube must be soft in order to bend around the tongue
202 without exerting undue pressure on it. For example, a
disadvantage of the airway tube of the LMA-device disclosed in U.S.
Pat. No. 4,509,514 is that it may be too stiff. If the
external-drain tube 165 is too soft, however, it may kink unless it
has a sufficient wall-thickness. The airway tube 22 must be of
maximum internal diameter for optimal gas flow through it but of
minimum outside diameter to reduce its cross-sectional area and
consequent bulk. The resulting outer diameter of the airway tube
22, about 11 millimeters (for #4), is therefore applied to the
outer diameter of the external-drain tube 165. The tubes 22, 165
therefore have the same or similar outer diameter, but for
different reasons.
[0132] The portion of the internal-drain tube 115 contained in the
laryngeal-chamber region 110, however, preferably also has a
reduced outer diameter to prevent it from interfering with free
passage of gases within the laryngeal-chamber region. Additionally,
the inner diameter of the internal-drain tube 115 is the same as
the inner diameter of the external-drain tube 165 because if the
inner diameter of the internal-drain tube is less than the inner
diameter of the external-drain tube, the clinician will not know if
a catheter inserted through the external-drain tube from outside
the mouth will pass through the internal-drain tube. If the inner
diameter of the internal-drain tube 115 is less than the inner
diameter of the external-drain tube 165, then a catheter just able
to pass through the external-drain tube (e.g., the catheter having
an outer cross-sectional area which is slightly smaller than that
of the external-drain tube) will become obstructed when it reaches
the internal-drain tube having the narrower internal
cross-section.
[0133] Conversely, if the inner diameter of the internal-drain tube
115 is larger than the inner diameter of the external-drain tube
165, then the outer diameter of the internal-drain tube must be
correspondingly larger resulting in the internal-drain tube having
a larger outer cross-sectional area thereby occupying additional
space in the laryngeal-chamber region 110 (free space within the
laryngeal-chamber region is precious). The additional internal
cross-sectional area of the internal-drain tube 115 resulting from
its larger inner diameter would, however, limited use since, for
example, the gastric flow volume through the internal-drain tube
would be limited by the smaller internal cross-sectional area of
the external-drain tube 165.
[0134] Anatomical Structures
[0135] Ary-epiglottic folds--wings of tissue joining the arytenoid
cartilages 205 to each side of the epiglottis 35.
[0136] Arytenoid Cartilages 205--a pair of pyramid-shaped
cartilages bordering the posterior rim of the laryngeal inlet 67.
Arytenoid cartilages 205 are attached anteriorly to the vocal cords
which they open, close, lengthen and shorten by rotation and
sliding actions, pulled by the laryngeal muscles. The most
important of the arytenoid cartilages 205 is the posterior
crico-arytenoid muscle, which draws the vocal cords open to permit
air to enter and leave the lungs.
[0137] Cervical vertebrae--the neck bones, of which there are seven
counting from above downwards. The sixth vertebral body lies
opposite the cricoid cartilage 210 and the distal tip of the
LMA-device 20 lies between the two when correctly inserted.
[0138] Constrictor muscles--three cylinders of muscle stacked
within each other like plastic cups surround the interior space of
the pharynx 197 and act sequentially to squeeze swallowed food into
the oesophagus 57. The lower pharyngeal constrictor muscle is the
one which mostly wraps around the inserted LMA-device 20. The
lowest part of this muscle (most distal part) forms a complete ring
and defines the upper oesophageal sphincter 207, also known as the
crico-pharyngeus muscle.
[0139] Cricoid cartilage 210--a ring of cartilage which acts as the
container or chamber of the larynx 37. Cricoid cartilage 210 is
attached distally to the trachea or wind-pipe 36. From the lateral
sides of the cricoid cartilage 210, the membrane forming the vocal
cords stretches upwards and medially. Proximally, the thyroid
cartilage surrounds the cricoid cartilage 210 but overlaps it on
either side postero-laterally. Posteriorly, the broad flat surface
(lamina) of the cricoid cartilage 210 carries the paired posterior
crico-arytenoid muscles, which are separated in the mid-line by a
ridge. There is normally no space between the muscle-covered lamina
an the posterior wall of the pharynx 197, so when the LMA-device 20
enters this area of the pharynx, the LMA-device 20 must squeeze in
between these two normally contiguous surfaces. Hence the need to
make the deflated LMA-device 20 form a suitable wedge-shape with
sufficient resilience to slip in behind (posterior to) the cricoid
210. The part of the internal-drain tube 115 which is enclosed by
the distal region 45 of main-cuff 40 of the LMA-device 20 lies
immediately posterior to the mid-line ridge on the back of the
cricoid cartilage 210. Were the LMA-device 20 to lie to one or
other side, it might compress one or other of the vitally important
posterior crico-arytenoid muscles.
[0140] Cricopharingeus muscle--same as upper esophageal sphincter
207. Part of the inferior constrictor muscle of the pharynx
197.
[0141] Epiglottis 35--a fibro-elastic cartilage often described as
leaf-shaped, whose pointed end is firmly attached to the posterior
surface of the front of the thyroid cartilage and whose lateral
borders are suspended between the ary-epiglottic folds, so that its
free posterior surface projects proximally and posteriorly. This
free posterior surface acts like a shield preventing food entering
the glottis but can also cause obstruction to air-flow especially
when the pharyngeal space sags inwardly as surrounding muscles
weaken during anaesthesia. If the space available inside the
LMA-device 20 is inadequate, the epiglottis 35 potentially causes
obstruction, particularly if it is large and floppy as may be the
case in elderly males. The epiglottis 35 may be downfolded over the
laryngeal vestibule if the distal tip of main-cuff 40 catches it
and flips it downwards during insertion. Correct deflation and
insertion of the LMA-device 20 minimise this risk, as does a good
design permitting the optimal wedge-shape of the deflated
LMA-device.
[0142] Oesophagus 57--muscular tube which is normally closed,
unlike the trachea 36 which lies immediately anterior to it. The
muscular coat is thickened to form the upper oesophageal sphincter
207 and lower oesophageal sphincter. Stimulating the upper
oesophageal sphincter 207 excessively by insertion of a bulky
device or inflation of the LMA-device 20 to too high a pressure may
cause the upper oesophageal sphincter 207 and lower oesophageal
sphincter to open reflexively, making regurgitation of gastric
contents more likely. Also, the esophageal muscles tend to relax
during anaesthesia, so if there is any obstruction to inspiration,
as caused for example by closure of the glottis or a misplaced
LMA-device 20, the chest movement of inspiration may cause such a
high negative pressure within the chest cavity that the thin-walled
oesophagus 57 is literally sucked open, encouraging fluids to be
drawn up into it from the stomach. A correctly placed LMA-device 20
with a hole in the distal end, e.g., distal orifice 123,
communicating with the oesophagus 57 may prevent this cycle of
events from occurring, since it permits air to be drawn into the
oesophagus from above.
[0143] Glottis--the constriction of the airway tube 22 which occurs
in the region of the vocal cords. The larynx 37 is the structure
which surrounds and controls the movements and shape of the glottic
opening.
[0144] Hard Palate 192--the dome shaped bony vault which arches
over the upper surface of the tongue 202. The soft palate 195 is
attached to it posteriorly and it stretches down to the dental
arcades anteriorly and laterally. The anterior surface of the hard
palate 192 blends with the gums and is innervated with nerves which
trigger deglutition. Hence the importance of stimulating the
anterior surface of the hard palate 192 when inserting the
LMA-device 20, which must be designed so that when deflated, its
posterior surface forms a smooth broad sheet which imparts a soft,
atraumatic feel to the surface of the hard palate 192, stimulating
the acceptance of the LMA-device 20 by triggering deglutition
reflexes rather than rejection of the LMA-device, e.g., triggering
vomiting reflexes.
[0145] Hyoid bone--a semicircular ring of bone vital to the
mechanical 0.5 functions of swallowing, including opening of the
mouth 25. The hyoid bone lies above, i.e., proximal to, the thyroid
cartilage and is attached above to the base of the tongue 202, the
front of the mandible and the base of the skull. The lower part of
the hyoid bone is attached to the chest wall, the thyroid cartilage
and the pharyngeal constrictor mechanism. The lateral wings of the
hyoid bone press into the sides of the inflated main-cuff 40 of the
LMA-device 20 near the proximal region 42 of the main-cuff 40. The
hypoglossal nerves pass near the inner ends of the hyoid bone,
limiting the pressure which should be safely generated within the
main-cuff 40 and the lateral expansion permissible in any device
inflated in this region of the pharynx 197.
[0146] Hypo-pharynx 212--the region of the pharynx 197 lying behind
the larynx 37, and normally a closed sack at the level of the
cricoid 210. Adjacent to the base of hypo-pharynx 212 is the closed
upper oesophageal sphincter 207. The hypo-pharynx 212 is surrounded
by the middle and lower constrictor muscles. Anteriorly, the distal
region of the hypo-pharynx 212 is bordered by the posterior surface
of the cricoid cartilage 210. Also anteriorly, the proximal region
of the hypo-pharynx 212 is bordered by the laryngeal vestibule.
[0147] Inter-arytenoid muscle--the muscle joining the two arytenoid
cartilages 205 posteriorly and transversely, and proximal to the
upper border of the cricoid cartilage 210. The inter-arytenoid
muscle consists of two parts, a straight transverse part and an "X"
shaped part, both of which enable closure of the glottis. The
distal end of the bowl which defines the posterior surface of the
laryngeal-chamber region 110 of the LMA-device 20 must have
adequate depth to avoid interfering with the inter-arytenoid muscle
or with the arytenoid cartilages 205 which lie immediately anterior
to it. Bruising of the overlying mucosal surface is common with
improper insertion of the LMA-device 20.
[0148] Larynx 37--the apparatus responsible for protecting the
entrance to the lungs from contamination and for vocalisation. The
principle advantage of the LMA-device 20 is that it permits the
larynx 37 to retain these functions, of which the first is the most
important. Endotracheal intubation prevents effective coughing,
which is an airways-cleaning mechanism vital to our survival.
[0149] Laryngeal inlet 67--the rim of tissue surrounding the
vestibule of the larynx 37, consisting of the ary-epiglottic folds
laterally, the tip of the epiglottis 35 proximally, and the
arytenoids 205 and inter-arytenoid notch distally.
[0150] Laryngeal vestibule--a pocket of space above the vocal cords
bounded laterally by the quadrate membranes, proximally by the
epiglottis 35 and distally by the vocal cords. The distal tip of
the LMA-device 20 may lodge in the laryngeal vestibule if the tip
does not pass posterior to the arytenoids 205. The laryngeal
vestibule closes during swallowing, partly by the action of the
ary-epiglottic muscle which acts like a sphincter and partly by the
elevation of the larynx 37. This closure of the laryngeal vestibule
is observed when the LMA-device 20 is inserted prematurely.
[0151] Posterior crico-arytenoid muscle--the most important muscle
of the larynx 37 because it acts to separate the vocal cords. The
posterior crico-arytenoid muscle lies as a pair of muscles on the
posterior surface of the cricoid lamina, which is the broad
posterior region of the cricoid cartilage 210. The distal tip of
the LMA-device 20 presses against the cartilaginous ridge which
separates the two muscles. Excessive pressure in the main-cuff 40
might drive blood out of the muscle, depriving it of the necessary
oxygen to function, though such a complication has yet to be
reported.
[0152] Pyriform fossae--gutters lying on either side of the
entrance to the larynx 37, bounded medially by the ary-epiglottic
folds and laterally by the membranes stretching between the thyroid
horns and the hyoid bones.
[0153] Quadrate membrane--the side-walls of the laryngeal
vestibule. The quadrate membrane is bounded below by the rima
glottidis, posteriorly by the ary-epiglottic folds, and anteriorly
by the epiglottis 35.
[0154] Rima glottidis--the space between the vocal cords.
[0155] Soft palate 195--a muscular wedge of tissue extending
posteriorly from the posterior edge of the hard palate 192. The
surfaces of the soft palate 195 converge to the mid-line
posteriorly and distally to end in a mid-line triangular structure
known as the uvula. The soft palate 195 acts like a bridge arching
across the space separating the nasal cavity from the rest of the
pharynx 197 and completely closes this gap during swallowing.
Insertion of the LMA-device 20 relies on the resistance offered by
the oral surface of the soft palate 195 to distally guide the
distal tip of LMA-device 20. If the deflated LMA-device 20 is too
rigid, or incorrectly deflated, the soft palate 195 cannot guide it
downwards, thereby impeding insertion of the LMA-device 20 into the
pharynx 197.
[0156] Thyroid cartilage--a shield-like structure whose lower
border bilaterally overlaps the cricoid cartilage 210. The thyroid
cartilage has two posterior-directed horns, the lower of which
articulates with the sides of the cricoid 210, so that the whole
structure can hinge on the cricoid in the manner of a visor of a
helmet. This articulation produced by the crico-thyroid muscle
serves to lengthen the vocal cords. The epiglottis 35 is attached
to the anterior prominence of the thyroid, also known as the
"Adam's Apple", because it projects more sharply in males.
[0157] Trachea 36--the wind-pipe, connected directly to the lower
rim of the cricoid cartilage 210.
[0158] Upper esophageal sphincter 207--guards the entrance to the
oesophagus 57. The upper esophageal sphincter 207 is normally
closed, even when the LMA-device 20 is in place and pressed into
the upper surface of the upper esophageal sphincter. The upper
esophageal sphincter 207 can open to approximately 1.5.times.1.0
centimeters.
[0159] Vocal cords--folds of tissue which represent the upper free
borders of a membrane arising from the cricoid 210, i.e., the
crico-vocal membrane. The vocal cords vibrate, lengthen and shorten
(for speech), adduct (to prevent soiling of the airway or trachea
36 and to allow coughing), and abduct (to admit air to the lungs).
The crico-thyroid muscle lengthens the vocal cords by activating
the visor-like hinging action of the crico-thyroid joint. The
thyro-arytenoid muscle shortens the vocal cords by pulling the
arytenoids 205 anteriorly. The vocalis muscle thickens the vocal
cords to affect vibration frequency. The posterior crico-arytenoids
abduct the vocal cords. The transverse arytenoids and lateral
crico-arytenoids draw the arytenoids 205 together to close the
vocal cords.
[0160] While the invention has been described by reference to
certain preferred embodiments, it should be understood that
numerous changes could be made within the spirit and scope of the
inventive concept described. Accordingly, it is intended that the
invention not be limited to the disclosed embodiments, but that it
have the full scope permitted by the language of the following
claims.
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