US20080060655A1 - Laryngeal mask airway device - Google Patents

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.

Description

CROSS-REFERENCE SECTION
• This application is a continuation of currently pending U.S. patent application Ser. No. 11/350,470, filed Feb. 9, 2006, which is a continuation of U.S. patent application Ser. No. 10/225,678, filed Aug. 22, 2002, which is a continuation of U.S. patent application Ser. No. 09/289,319, filed Apr. 9, 1999, now U.S. Pat. No. 6,439,232. This application also claims the benefit of United Kingdom patent application 9817537.5, filed Aug. 13, 1998.
BACKGROUND OF THE INVENTION
• 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).
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• In the drawings:
• 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;
• FIG. 2 is a perspective view showing the LMA-device ofFIG. 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;
• FIG. 3 is a plan view of the anterior side of the LMA-device ofFIG. 1, the main-cuff being inflated and illustrated in enlarged scale relative toFIG. 1, the airway and external-drain tubes being cut-off, the well hidden behind the internal-drain tube also being shown;
• FIG. 4 is an enlarged perspective view of a detail ofFIG. 3 with the airway and evacuation tubes removed, showing the anterior surface of the tube-joint and the posterior bulge of the main-cuff;
• FIG. 5 is an enlarged plan view of a detail ofFIG. 3 with the airway and evacuation tubes removed, showing the anterior surface of the tube-joint and the posterior bulge of the main-cuff;
• FIG. 6 is an enlarged end view of a detail ofFIG. 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;
• FIG. 7 is a plan view of the posterior side of the device ofFIG. 1, in the same inflated condition as and to the scale ofFIG. 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;
• FIG. 8 is a lateral view in partial section, in the plane indicated by the line8-8 ofFIG. 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;
• FIG. 9 is a view corresponding toFIG. 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;
• FIG. 10 is a sectional plan view in the plane indicated by the line10-10 ofFIG. 9 showing the location of the anterior-posterior dimension ofFIG. 9 relative to the proximal region of the main-cuff;
• FIG. 11 is a distal view in cross section, in the plane indicated by the line11-11 ofFIG. 7 showing the engagement between the internal-drain tube and backplate, and the adjacency between the seam in the main-cuff and backplate;
• 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 line11-11 ofFIG. 7, showing a reduced wall thickness of the backplate in the sagittal plane, and the back-cuff tethered to the backplate;
• FIG. 13 is a distal view in cross section, in the plane indicated by the line13-13 ofFIG. 7 showing a portion of the LMA-device between lines11-11 and13-13, the clearance between the internal-drain tube and base of the well being illustrated;
• FIG. 14 is an enlarged fragmentary view of a detail ofFIG. 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;
• FIG. 15 is an enlarged fragmentary view of a detail ofFIG. 8 showing the connection between the internal and external-drain tubes;
• FIG. 16 is an anterior perspective view of the backplate removed from the LMA-device ofFIGS. 3 and 7;
• FIG. 17 is a perspective view, in the aspect indicated byline17 ofFIG. 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;
• FIG. 18 is an anterior view of a second embodiment of the backplate ofFIG. 16;
• FIG. 19 is a perspective view of the second embodiment of the backplate illustrated inFIG. 18, in the aspect indicated byline20, showing the recessed heel portion, and the double-barrelled passage for the connections for the airway and external-drain tubes;
• FIG. 20 is a perspective view of the anterior surface of the LMA-device ofFIGS. 3 and 7 in a deflated condition;
• FIG. 21 is a lateral view of the main-cuff in the direction indicated byline22 ofFIG. 20 showing the preferred deflection characteristic of the main-cuff;
• FIG. 22 is a perspective view in the aspect ofFIG. 20 showing the LMA-device ofFIGS. 3 and 7 in an inflated condition;
• FIG. 23 is a plan view of the anterior side of a third embodiment of the LMA-device ofFIGS. 3 and 7 showing one-way valves incorporated in the anterior wall of the main-cuff; and
• FIG. 24 is a lateral view of the main-cuff of the embodiment illustrated inFIG. 23 in the direction indicated by line23-23 showing one of the one-way valves and its associated housing.
• Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
• 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-device20 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.
• A laryngeal-mask airway device (LMA-device) of the present invention, is designated generally by thereference numeral20 inFIGS. 1 and 2. The LMA-device20, in a deflated condition, is inserted into thethroat32 the upper surface of which is bounded by hard andsoft palates192,195. The LMA-device20 is lodged in thepharynx197 of thethroat32 at the base of the hypo-pharynx212 where the throat divides into the trachea36 (i.e., windpipe) andoesophagus57. A lower portion of the LMA-device20 reaches to the base of the hypo-pharynx212. After the LMA-device20 is so lodged in thepharynx197 such that the lower portion of the LMA-device reaches the base of the hypo-pharynx212, the LMA-device is inflated. Disposed in the junction between thethroat32 andtrachea36 is the flexible epiglottis35 (i.e., a lid-shaped structure) which forms the upper border of thelarynx37, entry through which is provided by thelaryngeal inlet67. To facilitate understanding of the relations between the LMA-device20 and anatomy of thethroat32 and related structures, a glossary of the anatomical structures related to the LMA-device is provided herein below.
• Referring toFIGS. 1 and 2, the laryngeal-mask airway device (LMA-device)20 is shown comprising anairway tube22, installed through themouth25 of a patient. The LMA-device20 further comprises abackplate27 having anairway port30 through which theairway tube22 can establish a free externally accessible ventilation passage, via the patient'smouth25 andthroat32, and past theepiglottis35 to thelarynx37. Thebackplate27 is preferably of an elastomer such as silicone rubber and relatively stiff, for example, of 80 Shore durometer.
• As further shown inFIGS. 3 and 7, thebackplate27 is surrounded by a main-cuff40 comprising an inflatable ring which, when inflated, has the shape of a torus generated by an asymmetrical oval or ellipse having a widerproximal region42 and narrowerdistal region45. The main-cuff40 is circumferentially united to thebackplate27 in essentially a single plane, except for the portion of the main-cuff extending into arecess47 in aheel50 of thebackplate27. The portion of the main-cuff40 extending into therecess47 may or may not be united to thebackplate27, as described further hereinbelow.
• The main-cuff40 may also be of silicone rubber, although preferably relatively soft and flexible compared to thebackplate27. The material of the main-cuff40 is preferably of 20 to 30 Shore durometer. Except for a plastic connector (not shown) attached to the proximal end of theairway tube22 and a check valve52, all parts of the LMA-device20 disclosed herein are preferably made of silicone, possibly with different additives.
• An externallyaccessible tube55 andinflation port56 on the main-cuff40 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-valve52 is disposed in thetube55 for holding a given inflation or holding a given deflation of the main-cuff40.
• In the installed position ofFIGS. 1 and 2, the projecting but blunteddistal region45 of the main-cuff40 is shaped to conform with the base of the hypo-pharynx212 where it has established limited entry into the upper sphincteral region of theoesophagus57. The pharyngeal-side60 of thebackplate27 is covered by a thinflexible panel62, as shown inFIGS. 7, 11 and13, which is peripherally bonded to amargin63 on the posterior surface of the main-cuff40, to define an inflatable back-cuff65 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 theinlet67 of thelarynx37. The inflated main-cuff40, thus-engaged to thelaryngeal inlet67, orients a distal-end72 of theairway tube22 at an acute angle to a mid-linemajor plane75 of the main-cuff40 and in substantial alignment with the axis of thelaryngeal inlet67, for direct airway communication only with thelarynx37.
• Themajor plane75 is a plane containing themajor axis77 of main-cuff40 extending between proximal anddistal regions42,45. Themajor plane75 is disposed between, and parallel to, the anterior and posterior surfaces of the main-cuff40. Additionally, themajor plane75 is equidistant from the anterior and posterior surfaces of the main-cuff40, except forposterior bulge100.
• The LMA-device20 is of the GLM (gastro-laryngeal mask) variety in which an evacuation tube, designated generally by80, as shown inFIGS. 1, 2,3 and7, serves for extraction and external removal of gastric-discharge products from theoesophagus57. Additionally, theevacuation tube80 provides a pathway into theoesophagus57 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. Theevacuation tube80 follows the general course of theairway tube22, with sealed entry through thebackplate27 alongside the airway tube, on the laryngeal-side81 of the backplate, and with sealed passage through the interior of the main-cuff40 and open through thedistal region45 of the main-cuff. Inflation-air supply to the back-cuff65 may be via thesame tube55 as for the main-cuff40, or separate inflating means (not shown) may be provided for the back-cuff65. 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.
• More specifically, the toroidal-shaped main-cuff40 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-cuff40, when in generally edge-to-edge relation, are welded together to form aseam85, as shown inFIGS. 5, 11 and13. Theseam85 defines an oval contained in a plane which is parallel to themajor plane75, corresponding to the internal surface of the main-cuff40. When thebackplate27 is attached to the main-cuff40, theseam85 abuts the periphery of theoval portion87 in anterior relation to the backplate, as best shown inFIGS. 11 and 13. Theseam85 may be inserted in a corresponding groove in theoval portion87. Alternatively, thebackplate27 and main-cuff40 may be extruded as a single, unitary piece.
• 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.
• A separate tube (not shown), preferably with multiple perforations along its length, may be contained within the main-cuff40 between the opening of thetube55 into the main-cuff such that each perforation communicates with a port between the interiors of the main-cuff and back-cuff65. Such a separate tube preserves a flowpath between thetube55 and back-cuff65 if the main-cuff40 is completely collapsed from deflation, thereby providing for further deflation of the back-cuff65 via thetube55. Alternatively, a channel (not shown) may be formed on the inner surface of the main-cuff40 between the opening of thetube55 into the main-cuff and at least one of the one or more ports between the interiors of the main-cuff and back-cuff65. Such a channel preserves a flowpath between thetube55 and back-cuff65 if the main-cuff40 is completely collapsed from deflation.
• Thebackplate27 has a one-piece, integral spoon-shape which, with theoval portion87, also has an external tube-joint92. The tube-joint92 is oriented proximally relative to theoval portion87. Opposite sides of theoval portion87 are defined by a convex pharyngeal-side60 and concave laryngeal-side81. The periphery of theoval portion87 is hermetically bonded to the periphery of the main-cuff40 to establish separation between the laryngeal-chamber region110 andpharyngeal region112.
• The periphery of theoval portion87 of thebackplate27 abuts, in proximal relation to, theseam85 of the main-cuff40 in its inflated condition, as shown inFIGS. 10 and 12. This more posterior location of thebackplate27, as compared to locating the periphery of theoval portion87 in themajor plane75, provides additional space for the internal-drain tube115. Theoval portion87 may be located at various positions in the anterior-posterior direction relative to the main-cuff40 because of the generally constant cross-section of the laryngeal-chamber region110 in planes parallel tomajor plane75, as shown inFIGS. 10 and 12.
• Formed in the laryngeal-side81 is a well95 defined by a depression adjacent to the tube-joint92. The well95 faces theevacuation tube80 such that the well is offset relative to thesagittal plane97 of the main-cuff40. The well95 thereby provides a radial clearance between theevacuation tube80 and laryngeal-side81.
• The portions of the laryngeal-side81 which are proximal and distal of the well95 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 inFIG. 8.
• The periphery of theoval portion87 adjacent to the tube-joint92 is included in theheel50. A portion of theheel50 contiguous with its anterior edge is removed to define a crescent-shapedrecess47. Theproximal region42 of the main-cuff40 has an approximatelyhemispherical posterior bulge100 arising from its posterior surface, as shown inFIG. 8. Theposterior bulge100 extends posteriority symmetrically relative to thesagittal plane97 to fit into themid-line groove102 forming part of the anterior surface of the double-barrelled tube-joint92 of thebackplate27. Themid-line groove102 is shown inFIG. 16. Theposterior bulge100 also extends into the crescent-shapedrecess47 to compensate for the reduced support provided by thebackplate27 resulting from therecess47.
• Less than the entire width of the main-cuff40 extends posteriorly from theproximal region42 because therecess47 of thebackplate27 allows space for the main-cuff40 to extend posteriorly in the approximatelyhemispherical posterior bulge100. Theposterior bulge100 is partially supported bilaterally by thebackplate27 thus preventing ballooning-out of this portion of the main-cuff40. Such ballooning-out of the main-cuff40 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 thelaryngeal inlet67. Such an uneven seal might result in loss of seal, particularly at the pointed distal end of the main-cuff40.
• Therecess47 andmid-line groove102 together form a partial socket which provides mechanical support posteriority, bilaterally and distally for theposterior bulge100.
• Theposterior bulge100 may be separable from therecess47 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-region112 into the laryngeal-chamber region110. This enables such-an elongate member to be inserted into the laryngeal-chamber region110 without occupying the interior of theairway tube22 which may obstruct air flow through the airway tube. Additionally, throughout insertion of such an elongate member through the port and the laryngeal-chamber region110, the elongate member is anterior of the internal-drain tube115.
• In comparison, if such an elongate member is inserted through theairway port30 into the laryngeal-chamber region110, upon entry into the laryngeal-chamber region, the distal end of the elongate member lies substantially parallel to the internal-drain tube115. Accordingly, shortly after entry into the laryngeal-chamber region110, 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 thelarynx37 or bronchial tree. Additionally, insertion of such an elongate member through theairway port30 into the laryngeal-chamber region110 results in the elongate member being laterally offset from thesagittal plane97 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 thesagittal plane97. Aligning such an elongate member in thesagittal plane97 may facilitate its further insertion through thelarynx37 into the trachea.
• The elongate tube-joint92 is formed on the pharyngeal-side60 and extends posteriorly and proximally relative to theoval portion87. The tube-joint92 includes alongitudinal passageway105 extending from itsproximal end107 distally to the concave laryngeal-side81. Thepassageway105 has a double-barrelled cross section for supporting theairway tube22 andevacuation tube80, described more fully herein below. The longitudinal central axis of thepassageway105 is contained in thesagittal plane97 and inclined posteriority at an angle of approximately 30 degrees relative to themajor plane75, as viewed in thesagittal plane97.
• Astrap200 is moulded to the external anterior surface of the proximal tube-joint92 in arching relation over themid-line groove102. The moulding of thestrap200 onto the anterior surface of the proximal portion of the tube-joint92 defines anintroducer tool slot201. The distal edge of thestrap200 has an internalcurved edge203 against which abuts the posterior bulge100 (which is an extension of the main cuff40), as shown inFIGS. 4, 6 and16. Theintroducer tool slot201 andcurved edge203 avoid becoming dirt trap because when the main-cuff40 is deflated, the posterior bulge100 (i.e, the main-cuff extension) pulls away from thestrap200, thus avoiding the formation of a blind pocket which could be a dirt trap.
• FIGS. 18 and 19 show a second embodiment of thebackplate27b. Parts inFIGS. 18 and 19 having corresponding parts inFIGS. 16 and 17 have the same reference numeral with the addition of suffix b. Thebackplate27bis similar to thebackplate27 illustrated inFIGS. 16 and 17 except that thebackplate27bdoes not a strap similar tostrap100.
• Theevacuation tube80 comprises an internal-drain tube115 extending between the tube-joint92 and thedistal region45 of the main-cuff40 on the laryngeal-side81 of thebackplate27. The internal-drain tube115 longitudinally traverses the interior of thedistal region45 of the main-cuff40 in sealed relation therewith for operative engagement and communication with the inlet of theoesophagus57. The internal-drain tube115 is anterior relative to theseam85 of the main-cuff40 such that the seam is disposed between the internal-drain tube and the distal end of theoval portion87.
• The internal-drain tube115 therefore pierces thedistal region45 at the proximal crotch-region117 and the longitudinally opposing distal crotch-region120, both of which are portions of thedistal region45. The edges of the main-cuff40 in the crotch-regions117,120 surrounding the internal-drain tube115 are hermetically sealed to the tube such that the enclosure of the main-cuff40 is defined in part by the external cylindrical surface of the internal-drain tube.
• The internal-drain tube115 terminates in an obliquedistal orifice123 opening out on the anterior distal aspect of thedistal region45 of the main-cuff40. The obliquedistal orifice123 results in partial flattening of thedistal region45 such that the flattening is in a transverse plane inclined relative to themajor plane75 by an angle a of preferably approximately 45 to 50 degrees when main-cuff40 is inflated, as shown inFIG. 14. When the main-cuff40 is deflated, angle a is preferably approximately 40 to 45 degrees. In adult sizes of the LMA-device20, the surface area of thedistal region45 removed to accommodate theorifice123 is approximately 1 square centimeter which is therefore no longer available to contribute to expansion of the main-cuff40 when the main-cuff is inflated for sealing around thelaryngeal inlet67. Accordingly, to prevent inspired gas leakage across thedistal region45 resulting from insufficient local expansion of the main-cuff40, 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-facinglip127 of thedistal region45 surrounding theorifice123 resulting from longitudinal withdrawal of theintra-cuff portion130 of internal-drain tube115 approximately 3.5 millimeters relative to the plane containing the distal end of thedistal region45 of the main-cuff40. This inversion produces a corresponding lateral bulging of thedistal region45 around theorifice123. The anterior position of thedistal orifice123 ensures less compressive force resulting from the fluid pressure inside the main-cuff40 on theintra-cuff portion130 in the anterior-posterior direction, thus compensating for anterior-posterior compression from anatomical structures in thethroat32 so that the internal-drain tube115 is subject to approximately equal compressive forces laterally and anterior-posteriorly, hence avoiding collapse.
• The part of theintra-cuff portion130 containing thedistal orifice123 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 themajor plane75 by an angle Δ of preferably 20 degrees. The longitudinal central axis of theintra-cuff portion130 is contained in thesagittal plane97.
• Thedistal orifice123 has diametrically opposed posterior andanterior apexes135,137. Thedistal orifice123 is contained in a transverse elliptical plane preferably inclined by an angle β, which is preferably 40 degrees, relative to themajor plane75, as shown inFIG. 14. The inclination of thedistal orifice123 is such that theposterior apex135 is offset distally relative to theanterior apex137 along the longitudinal axis of the portion of the internal-drain tube115 containing thedistal orifice123.
• Integral with the external anterior surface of theintra-cuff portion130 adjacent to thedistal orifice123 is a semicirculartransverse shoulder142, as shown inFIG. 9. The anterior and the adjacent lateral portions of the distal edge of thedistal region45 of the main-cuff40 are bonded to the proximal surface of theshoulder142. The posterior and remaining lateral portions of the distal edge of thedistal region45 are bonded to the unshouldered external surface adjacent to thedistal orifice123.
• The lateral termination of each end of theshoulder142 facilitates collapse of thedistal orifice123 in themajor plane75 when the main-cuff40 is deflated since the un-reinforced posterior portion of theintra-cuff portion130 is able to collapse more readily when the pressure inside the main-cuff40 is reduced (i.e., negative pressure is applied to the main-cuff). Also, by limiting the circumferential dimension of theshoulder142, its peripheral length which must be deflected is reduced. In contrast, if theshoulder142 extended posteriorly a sufficient amount such that it traversed themajor plane75, the portions of the shoulder that traversed the major plane would require closure to close distal orifice upon deflation of the main-cuff40. Such closure of such a shoulder would require significantly more force than required to flatten theshoulder142, shown inFIG. 14. Such increased force may require stronger material for the main-cuff40 and application of higher deflation vacuums to the main-cuff.
• Thedistal orifice123 is withdrawn proximally relative to thedistal region45 of the main-cuff40 resulting in the portion of thedistal region45 adjacent to thedistal orifice123 being invaginated when the main-cuff40 is inflated, as shown inFIG. 14. The bonding of the distal end of thedistal region45 to the distal surface of theshoulder142 results in the transversely-arcuate inverted anterior-facinglip127 of the invaginated surface having the greatest radial bulge. The transversely-arcuate lateral portions145,147 of the invaginated surface have the next largest radial bulge with the transversely-arcuate posterior portion150 having the least radial bulge. The opposedlateral portions145,147 are symmetrical about thesagittal plane97 of the main-cuff40.
• The portion of the internal-drain tube115 longitudinally traversing the interior of thedistal region45 of the main-cuff40 definesintra-cuff portion130. The outer surface of theintra-cuff portion130 has at least onecircumferential strengthening rib152 proximal of theshoulder142 to resist radial collapse of theintra-cuff portion130 by internally directed radial forces resulting from the fluid pressure within the main-cuff40. Therib152 is contained in a transverse elliptical plane preferably inclined at an angle θ, preferably of 60 degrees and equal to angle γ, relative to the longitudinal axis of theintra-cuff portion130, as shown inFIG. 14. The inclination of therib152 enables its posterior pivoting about its posterior apex during deflation of thedistal region45 to facilitate flattening of the main-cuff40.
• The portion of the internal-drain tube115 proximal of theintra-cuff portion130 is laterally offset from thesagittal plane97, as shown inFIGS. 3 and 7. The portion of the internal-drain tube115 where it emerges from the proximal crotch-region117 and extends to the well95 is received in agroove157 formed in theoval portion87, as shown inFIG. 7. Thegroove157 is defined laterally byfillets160 which laterally abut the internal-drain tube115. As much as 50% of the posterior portion of the cross-sectional area of the internal-drain tube115 may be contained in the distal portion of thegroove157, except where its circumference is free posteriority, i.e., where it runs over the well95. In one size of the main-cuff40, the longitudinal dimension of thegroove157 is 2.5 centimeters. The internal-drain tube115 is welded to thegroove157.
• Thefillets160 resist anterior deflection of theoval portion87 since the fillets provide increased surface area for the weld between the internal-drain tube115 and oval portion. This additional resistance compensates for the reduced resistance resulting from a reduction in the anterior-posterior thickness of the part of theoval portion87 defining the base of thegroove157. Such reduced anterior-posterior thickness is desirable to increase the anterior-posterior dimension a between the anterior surface of the main-cuff40, and the portion of the internal-drain tube115 between theproximal crotch region117 and well95, shown inFIG. 8, especially at the location of dimension b, shown inFIGS. 9 and 10, which should have a depth of at least 10 millimeters in adult sizes, described further herein below.
• FIG. 12 illustrates a second embodiment of the LMA-device20ain which the flexible panel62ais tethered to the backplate27a. The parts inFIG. 12 having corresponding parts in FIGS.1 to11 have the same reference numeral with the addition of suffix a. Tethering of the panel62ato the backplate27aprovides additional resistance to anterior inversion of theoval portion87a. This enables further reduction in the anterior-posterior thickness of the part of theoval portion87adefining the base of the groove157a. As discussed above, such reduced anterior-posterior thickness is desirable to increase the anterior-posterior dimension, corresponding to the dimension a inFIG. 8.
• A longitudinal portion of the internal-drain tube115 extends over well95, as shown inFIG. 8. The anterior-inclination of the portions of the laryngeal-side81 proximal and distal of the well95, described herein above, anteriorly props the portion of the internal-drain tube115 extending over the well to increase the anterior-posterior clearance between the internal-drain tube and base of the well. The internal-drain tube115 arches over the well95 defining a slight posterior curve and simultaneously curving laterally to its insertion in the tube-joint92.
• Theevacuation tube80 includes an external-drain tube165 having adistal end167 connected in end-to-end relation to theproximal end170 of the internal drain-tube115. The joint between the internal and external-drain tubes115,165 is located where the tube-joint92 opens into laryngeal-chamber region110, as shown inFIGS. 8 and 15.
• The inner diameters of the internal-drain tube115 and external-drain tube165 are the same. The outer diameter of the internal-drain tube115 is less than the outer diameter of the external-drain tube165. Thedistal end167 of the external-drain tube165 has an internalcountersunk portion172 defined by a bevelled internal axial wall, as shown inFIG. 15. The outer diameter of the countersunkportion172 is greater than the outer diameter of the internal-drain tube115. Theproximal end170 of the internal-drain tube115 abuts the countersunkportion172 resulting in coaxial self-alignment of the central longitudinal axes of the distal and proximal ends167,170.
• As shown inFIGS. 8 and 15, the external-drain tube165 is supported in thecylindrical drain barrel175 of the double-barrelledpassageway105 which is longitudinally offset from the well95 at an angle of approximately 9 degrees. The internal-drain tube115 is thereby disposed anteriorly of the well95 and is also offset at 9 degrees from the major axis ofdrain barrel175 to increase the lateral clearance.
• Theevacuation tube80 is preferably moulded to thebackplate27. Alternatively, for making a prototype, assembly of theevacuation tube80 to thebackplate27 may be by first welding the distal portion of the internal-drain tube115 into thedistal region45 of the main-cuff40. Before connecting the proximal end of the internal-drain tube115 to tube-joint92, the main-cuff40 is welded to thebackplate27. The external-drain tube165 is then welded into the drain barrel162 of the tube-joint92, for example, by an adhesive173. Hardening of these welds effectively clamps and fixes the distance between the distal end of the proximal crotch-region117 of the main-cuff40 and thedistal end167 of the external-drain tube165. The internal-drain tube115 is cut, as needed, such that it is slightly longer than this distance. Theproximal end170 of the internal-drain tube115 is then inserted into the countersunkportion172 of the external-drain tube165 with the countersunk portion resulting in coaxial self-alignment of the longitudinal central axes of the distal and proximal ends167,170. The internal-drain tube115 is then welded to the tube-joint92, for example, by an adhesive174.
• The slightly longer length of the internal-drain tube115 relative to the distance between the proximal crotch-region117 anddistal end167 results in a slight longitudinal compression of the internal-drain tube causing lateral curvature of it away from the adjacent side-wall177 of thebackplate27. Lateral curvature of the internal-drain tube115 away from the adjacent side-wall177 increases the lateral clearance between them, reducing the likelihood of dirt collecting between them.
• As shown inFIGS. 3 and 7, theairway tube22 is supported in thecylindrical airway barrel180 of the double-barrelledpassageway105 in communication with theairway port30 defined by the opening of theairway barrel180 into the laryngeal-side81. Such communication provides a flowpath between theairway tube22 and laryngeal-chamber region110. Theairway tube22 is connected to the tube-joint92 by welding using an adhesive or, alternatively, connected by high-pressure or temperature fusion.
• Theairway tube22 and external-drain tube165 are welded together in side-by-side tangential relation, as shown inFIG. 2. The welding is accomplished by depositing adhesive in one or both of the crevices defined by the outer surfaces of thetubes22,165 adjoining the line of tangential contact between them. The adhesive preferably extends longitudinally from the tube-joint92 proximally for approximately 4¼ inches. Alternatively, thetubes22,165 may be connected together by high pressure or temperature fusion. Also, thetubes22,165 may be manufactured by simultaneous extrusion. Additionally, thetubes22,165 may remain separate for certain clinical applications, e.g., operations on thetongue202 in the mid-line or other mid-line structures in thepharynx197.
• Theairway tube22 and external-drain tube165 are inserted through a bite-plate176 comprising a sleeve which is telescopically fitted around thetubes165,176, as shown inFIG. 2. The bite-plate176 is positioned longitudinally on thetubes22,165 such that, when the LMA-device20 is completely inserted into thethroat32 andpharynx197, the bite-plate is positioned between the upper and lower teeth, described further herein below.
• In embodiments in which theairway tube22 is bonded to the external-drain tube165, thetubes22,165 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 tube165 to a suction-apparatus (not shown), if required. The separation of theairway tube22 and external-drain tube165 is achieved by placing asleeve182 on the airway tube to cover the proximal 3 centimeters of the airway tube. Thesleeve182 is proximally oriented relative to the bite-plate176. Connected to the distal end of thesleeve182 is atriangular wedge185 oriented toward the external-drain tube165 to force the softer external-drain tube to incline away from theairway tube22 by an angle C, preferably approximately 15 degrees. Thesleeve182 andwedge185 are a single moulding and are welded to theairway tube22. Additionally, thewedge185 is welded to the external-drain tube165. Thesleeve182 also stiffens the proximal end of theairway tube22 to reduce the likelihood of kinking at its attachment to the ventilating apparatus (not shown).
• The portions of theairway tube22 and external-drain tube165 in side-by-side tangential relation each have the same outer diameter. The inner diameter of this portion of theairway tube22 is greater than the inner diameter of the adjoining portion of the external-drain tube165. These portions of theairway tube22 and external-drain tube165 each have approximately the same stiffness and resistance to longitudinal bending. A metallic cylindricallyhelical wire190 is provided between inner and outer surfaces of theairway tube22 in coaxial relation therewith to increase the kink resistance of the thinner-wall airway tube. The kink resistance of this portion of theairway tube22 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 thetubes22,165 to be approximately the same if, for example, thehelical wire190 sufficiently increases the stiffness of airway tube.
• A hard plastic or polycarbonate cylindrical fitting (not shown) is inserted in the end of theairway tube22 proximal of thetriangular wedge185. The fitting is inserted into theairway tube22, 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).
• In use, an inflation/deflation device is actuated to apply a vacuum, via thetube55, to the main-cuff40 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 theflexible panel62 andbackplate27, via the channel90 in the main-cuff40, deflating the back-cuff65 to collapse it onto the pharyngeal-side60 of thebackplate27 and posterior surface of the main-cuff.
• The main-cuff40 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.
• The flattened sheet, comprising fully deflated the main-cuff40,backplate27 and internal-drain tube115, is passed easily through themouth25 of the patient because of the reduced compressible antero-posterior dimension of the part of the LMA-device20 having the largest anterior-posterior dimension, i.e., the generallyproximal region42 of the main-cuff40 and theheel50. This reduced compressible antero-posterior dimension results from therecess47 of theheel50. The deflated main-cuff40,backplate27 and internal-drain tube115 is pressed against the hard andsoft palates192,195 as it is pushed inwardly, resulting in the deflated main-cuff being guided distally by the soft palate onto the posterior wall of thepharynx197. Such deflection of the main-cuff40 is normally only reliably achieved if the total stiffness of the LMA-device20 is within certain predetermined limits.
• The main-cuff40 is preferably urged through thethroat32 by placement of either the operator's index finger or an insertion tool inserted into thestrap200 against theheel50, because the side-by-side airway tube22 and internal-drain tube115 are normally not sufficiently stiff to be used as a rod to direct the main-cuff through the throat.
• The main-cuff40 is preferably positioned in thethroat32 by inserting the a sufficient length of the index finger of the operator through theintroducer tool slot201 such that the finger is placed on themid-line groove102 of the tube-joint92 and the end of the finger abuts theheel50, as shown inFIG. 16. Inserting the finger through theintroducer tool slot201 enables the finger to be partly wedged into thestrap100 to secure the index finger to themid-line groove102. Placement of the index finger on themid-line groove102 of the tube-joint92 and against theheel50 assists in locating and stabilizing the finger against theproximal region42 of the main-cuff40. This reduces the risk of finger slippage from its intended position on thebackplate27 due to the presence of slippery secretions in themouth25 and/or the application of lubricant, to assist smooth passage of the LMA-device20 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, theproximal region42 of the main-cuff40 provides a fulcrum.
• An alternative and equally preferable way to position the main-cuff40 in thethroat32 is by an introducer tool (not shown) including a relatively rigid elongate member having a distal end adapted for removable keyed engagement with theheel50 andstrap200 adjacent to the tube-joint92 for insertional guidance of the main-cuff40. During such insertion, as with placement of the operator's finger against theheel50, theproximal region42 of the main-cuff40 provides a fulcrum. The introducer tool and LMA-device20 may both be included in a kit.
• Preferably, the deflated main-cuff40 andbackplate27 are sufficiently flexible that they do not overcome the resistance provided by thesoft palate195. The main-cuff40 andbackplate27 are preferably flexible similar to a palette knife such that, when the main-cuff and backplate are urged or tensed against thesoft palate195, thedistal region45 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-cuff40 to itself bend smoothly around (i.e., in the shape of) anarc196, as shown inFIG. 21, also similar to a palette knife.
• Further, the deflated main-cuff40 andbackplate27 resist kinking. Kinking results in the main-cuff40 andbackplate27, during their insertion through thethroat32, collapsing on thetongue202 rather than arching over it. To avoid kinking, a specific overall stiffness and long-axis gradation of stiffness in the delated main-cuff40 is required, which in turn depends on the shape of thebackplate27. The primary factors or considerations to be balanced when designing thebackplate27 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-cuff65, and (iii) minimal thickness in the anterior-posterior dimension to reduce overall resistance to flexure.
• The relative stiffness of theairway tube22, external-drain tube165 andbackplate27 facilitate piloting and guiding of the substantially flattened, deflated main-cuff40 to smoothly ride or track posterior contours of thethroat32 andpharynx197 and to assure that the deflated main-cuff enters and locates immediately above the upperoesophageal sphincter207 and adjacent to thelaryngeal inlet67, as shown inFIGS. 1 and 2.
• Additionally, thebackplate27, internal-drain tube115 and main-cuff40 are sufficiently flexible to allow anterior and posterior deflection of thedistal region45 in thesagittal plane97 when the main-cuff is fully deflated, as shown inFIG. 21. Such deflection further facilitates riding or tracking of thedistal region45 of the main-cuff40 over the posterior contours of thethroat32 by allowing the distal region to deflect as necessary to conform to protrusions or recesses in the posterior surface of the throat.
• The deflated main-cuff40 further enters into its correct position opposite thelaryngeal inlet67 without colliding with anterior structures such as the posterior surface of thetongue202,epiglottis35, orarytenoids205. Insertion of the deflated main-cuff40 is facilitated by forming the main-cuff40 and attaching it to thebackplate27 such that theseam85 abuts the backplate, as shown inFIGS. 12, 13 and14. As a result, when the main-cuff40 is fully deflated, the anterior surface of the main-cuff is uninterrupted by theseam85, i.e., the seam is buried between thebackplate27 and the deflated main-cuff. Accordingly, the likelihood is reduced of the anterior surface of the deflated main-cuff40 scraping or catching on the anatomical structures of thethroat32, such as theepiglottis35 andarytenoids205. Further disclosure of insertion of the deflated main-cuff40 through thethroat32 may be had by reference to U.S. Pat. No. 5,632,271, the entire disclosure of which is hereby incorporated by reference herein.
• When the LMA-device20 is fully inserted in thethroat32, the side-by-side airway tube22 and external-drain tube165 extend proximally from the tube-joint92 in contacting relation with thesoft palate195, and lie against thehard palate192, i.e., the roof of themouth25. Thetubes22,165 are spaced inwardly of the sides of thethroat32 to avoid damage to the lingual nerves. Thetubes22,165 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 themouth25 between the teeth.
• The bite-plate176 is positioned at the emergence of thetubes22,165 from themouth25 such that the bite-plate is disposed between the upper and lower teeth and the tubes. The teeth thereby directly contact the bite-plate176, rather than thetubes22,165, to provide protection to the tubes.
• When the main-cuff40 is correctly positioned, thedistal orifice123 of the internal-drain tube115 contacts the upperoesophageal sphincter207 and lies posterior to thecricoid cartilage210. The bevelleddistal region45 of the main-cuff40, including thedistal orifice123 of the internal-drain tube115, forms a wedge-shape of approximately 45 degrees when the main-cuff40 is deflated. This facilitates insertion of the main-cuff40 andbackplate27 behind thecricoid cartilage210 because such insertion requires the cricoid cartilage to be gently forced anteriorly to allow passage of the wedge-shapeddistal region45, including thedistal orifice123, behind it. Further disclosure of positioning the LMA-device20 may be had by reference to U.S. Pat. No. 5,241,956, the entire disclosure of which is hereby incorporated by reference.
• When the LMA-device20 is completely inserted, the main-cuff40 contacts the base of the hypo-pharynx212 with thedistal region45 being wedged into the upper opening of the upperoesophageal sphincter207, a constriction which is however much too small to permit the LMA-device20 to pass through it. Complete insertion of the LMA-device20 is thereby detected by the operator as a resistance to insertion of the main-cuff40 into the upperoesophageal sphincter207. The main-cuff40 is then inflated with sufficient air, via thetube55, to obtain a seal against the laryngo-pharyngeal perimeter. The LMA-device20, when completely inserted in thepharynx197, lies in thesagittal plane97.
• Inflation of the main-cuff40 causes expansion of thedistal region45 enabling it to lie against and adapt to thepharynx197 and hypo-pharynx212. Additionally, inflation of the main-cuff40 causes the gas or fluid to flow into the space enclosed by theflexible panel62 andbackplate27, for example, via one or more ports in the main-cuff, resulting in inflation of the back-cuff65. Inflation of the back-cuff65 initially causes engagement between theflexible panel62 and posterior surface of thepharynx197. Further inflation of the back-cuff65 urges the main-cuff40 anteriorly to press it against the tissue surrounding thelaryngeal inlet67. This tightens the sealing engagement between the main-cuff40 and the tissue surrounding thelaryngeal inlet67, 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 theoval portion87 of thebackplate27 and the anterior surface of the main-cuff40, permitting accommodation of the posteriorly bulging posterior surface of thecricoid cartilage210 which is located distally relative to thelaryngeal inlet67.
• If the back-cuff65 is overinflated, theoval portion87 may bulge anteriorly outward resulting in anterior displacement of the internal-drain tube115 relative to the main-cuff40, and loss of the advantageously increased anterior-posterior space between theoval portion87 and the anterior surface of the main-cuff40, described above. The anterior-posterior dimension a between the anterior tangency of the internal-drain tube115 and a plane containing the anterior surface of the main-cuff40, shown inFIG. 8, must not decrease below a minimum level since such may result in the internal-drain tube undesirably impinging against anatomical structures of thethroat32 normally present in the laryngeal-chamber region110. For example, if the main-cuff40 is a standard adult size and is inflated to 40 millimeters Hg (mercury), at a point b contained in thesagittal plane97 and located 40 millimeters distally from the distal end of theproximal region42 of the main-cuff40, shown inFIG. 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.
• The transversely arched profile, degree of hardness, and increased anterior-posterior thickness of the distal portion of theoval portion87 are all factors chosen to offer adequate resistance to such anterior bulging thereby limiting such resulting anterior displacement of the internal-drain tube115 near thedistal region45 of the main-cuff40 where the internal-drain tube is nearest to the anterior surface of the main-cuff.Fillets160,160aand tethered panel62a, shown inFIGS. 11 and 12, also limit anterior displacement of the internal-drain tube115 relative to the main-cuff40. Anterior-posterior dimension a, shown inFIG. 8, should be maintained above a minimum amount to avoid anterior displacement of thearytenoids205 which may obstruct flow of gases through thelarynx37, and to avoid anterior displacement of anatomical structures relative to the main-cuff40 which may reduce the tightness of the seal between the main-cuff and the tissues surrounding thelaryngeal inlet67. Additionally, thebackplate27 is preferably sufficiently flexible to deflect in the anterior-posterior direction during insertion into thethroat32 to follow its contours, e.g., to bend around thesoft palate195.
• Thebackplate27 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-cuff65. Theback cuff65 of the LMA-device20 causes pressure to be applied to theoval portion87 of thebackplate27, which may cause the oval portion to herniate anteriorly. Thebackplate27 must therefore be designed to resist such herniation, preferably to pressures within back-cuff65 of up to 100 centimeters of water. Techniques for preventing such herniation of thebackplate27 include arching thebackplate27 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 tongue202), and possibly also providing the backplate with a midline longitudinally running30 groove for accurately locating adhesive to weld to it theback cuff65. In addition, theback cuff65 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 thebackplate27.
• The anteriorly facing laryngeal-chamber region110 of the main-cuff40 is wider than the transverse distance between the edges of thelaryngeal inlet67 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-cuff40 is thus functionally a pharyngo-laryngeal mask airway forming an end-to-end seal against thelarynx37.
• FIGS. 23 and 24 illustrate a third embodiment of the LMA-device20c. Parts inFIGS. 23 and 24 having corresponding parts in FIGS.1 to22 have the same reference numeral with the addition of suffix c. The main-cuff40cmay have soft and yielding ridges (not shown) bilaterally disposed on the anteriorly-facingdistal region45cof 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-device20cexploits the triangular cross-section of the grooves of the pyriform fossae which are roofed over and isolated by the anterior surface of the main-cuff40cbilaterally. The entire length of the grooves of the pyriform fossae are covered by the main-cuff40csuch 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 valves215, such as a reed or duck-bill valve, in the anterior wall of the main-cuff40cfacing 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 valves215 may be duck-bill valves of the type sold by Accusil® Incorporated of Merriville, Ind., U.S.A.
• Attached to the interior surface of the anterior wall of the main-cuff40care respectivecylindrical housings217, shown inFIG. 24, each surrounding a respective one of the one-way valves215. Deflation of the main-cuff40cdraws its posterior wall toward thehousings217 and one-way valves215, eventually causing the posterior wall to seat on the open posterior ends of thehousings217, as illustrated by a portion of the posterior wall being shown in phantom line inFIG. 24 in dashed lines. Seating of the posterior wall of the main-cuff40 on the open posterior ends of thehousings217 hermetically seals the respective one-way valves215 from the remainder of the interior of the main-cuff. Each of the one-way valves215 thereby becomes isolated from the reduced pressure inside the main-cuff40c. This prevents the reduced pressure within the main-cuff40cfrom drawing gases external of the main-cuff in the vicinity of the one-way valves215 through the one-way valves into the main-cuff thereby enabling the reduced pressure inside the main-cuff to deflate it.
• In an alternative embodiment (not shown), one-way valves215 and their associatedhousings217 may be replaced by ports or apertures, the ends of which within the main-cuff40care 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-cuff40csuch 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-cuff40cto 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.
• The sealing efficacy of the main-cuff40 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.
• Theepiglottis35, a leaf-like structure which normally projects proximally and posteriorly, is supported against the anterior surface of the internal-drain tube115. The internal-drain tube115 thereby defines a stop to prevent theepiglottis35 from interfering with communication between theairway tube22, via theairway port30, and thelaryngeal inlet67. This creates adequate space in the laryngeal-chamber region110 posterior to theepiglottis35 for passage of gases between theairway port30 andlaryngeal inlet67.
• Such passage of gases between theairway port30 andlaryngeal inlet67 is mainly in the portion of the laryngeal-chamber region110 lateral of thesagittal plane97 and containing the airway port. If, however, theepiglottis35 slides laterally from its propped position against the internal-drain tube115 into the lateral portion of the laryngeal-chamber region110 containing theairway port30, 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 theairway port30 andlaryngeal inlet67 via the radial clearance between the internal-drain tube115 and well95, and through the portion of the laryngeal-chamber region110 laterally of thesagittal plane97 offset from theairway port30. An alternative circulation flowpath is thereby provided to permit adequate and free gas communication between theairway tube22 andlaryngeal inlet67, while simultaneously preventing obstruction to such gas flow by theepiglottis35. The contour of the laryngeal-side81 of thebackplate27 props the internal-drain tube115 away from the laryngeal-side to facilitate sufficient radial clearance between the internal-drain tube115 and well95 thereby to provide the adequate and free gas communication between theairway tube22 andlaryngeal inlet67.
• Theoval portion87 of thebackplate27 has a sufficiently large anterior-posterior depth to contain the internal-drain tube115 such that the drain tube does not bear against other laryngeal structures and interfere with gas flow.
• The well95 also provides a route for drainage of secretions from the trachea, which may enter the laryngeal-chamber region110 via thelaryngeal inlet67. Such secretions normally collect in the well95 since, when the LMA-device20 is fully installed and the patient is supine, the laryngeal-side81 of thebackplate27 faces upward. In the absence of the well95, such secretions would collect between the laryngeal-side81 of thebackplate27 and internal-drain tube115.
• The adequately-sized well95 is provided behind the internal-drain tube115 to allow gases or secretions to pass between the internal drain tube and thebackplate27. This improves drainage of secretions emerging from thetrachea36 and improves gas exchange if there is any obstruction due to theepiglottis35 falling into the laryngeal-chamber region110 close to the distal-end72 of theairway tube22 adjacent to theairway port30.
• Inflation of the main-cuff40 causes expansion of thedistal region45 including the anterior-facinglip127,lateral portions145,147, andposterior portion150 of the invaginated end, as shown inFIGS. 8 and 14. The hermetic seal between the obliquedistal orifice123 of the internal-drain tube115 and thedistal region45 of the main-cuff40 obstructs communication between the oesophagus57 and laryngeal-chamber region110. Accordingly, leakage, e.g., of contents from the oesophagus57 into the laryngeal-chamber region110, and via thelaryngeal inlet67 into the trachea is obstructed.
• The invagination and 45 degree angulation of the distal end of the main-cuff40 reduces the likelihood of leakage between thedistal orifice123 of the internal-drain tube115 and the laryngeal-chamber region110 of the main-cuff40 which may result from the expansion of the main-cuff being hampered at the narrowerdistal region45 and distal end by the presence of the distal orifice. Also, the angle formed by the main-cuff40 when deflated was sufficiently large to impede insertion of the LMA-device20 to its correct location in thepharynx197 opposite thelaryngeal inlet67. The desired insertion characteristics are obtained by invagination by 3.5 millimeters (size 4) of the wall of the main-cuff40 forming theanterior lip127 of thedistal orifice123 produced an increased expandable area around the distal orifice of the internal-drain tube115, improving the seal and, by drawing proximally only theanterior lip127, sufficiently sharpening the angle of the distal tip of the deflated main-cuff.
• The side-by-side bonded adjacency of theairway tube22 and external-drain tube165 conforms to the cross-sectional shape of themouth25 andthroat32 facilitating insertion into and displacement through the throat. The side-by-side adjacency of theairway tube22 and external-drain tube165 also reduces the likelihood of kinking when they bend.
• After positioning the main-cuff40 opposite thelaryngeal inlet67 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 theairway tube22.
• Theevacuation tube80 has the following functions:
• (i) theevacuation tube80 allows gases to be administered to the lungs through theairway tube22 under positive pressure without the risk of inflating the stomach, via the upperoesophageal sphincter207, since gases escaping from the laryngeal-chamber region110 between the main-cuff40 and the tissues surrounding thelaryngeal inlet67 into the hypo-pharynx212 will be ducted out through the evacuation tube instead of being forced through the upperoesophageal sphincter207 into theoesophagus57, the latter of which may occur with other know LMA-devices such as is disclosed in U.S. Pat. No. 4,509,514 which is hereby incorporated by reference herein;
• (ii) conversely, if there is no evidence of gases being ducted through theevacuation tube80 during positive pressure ventilation through theairway tube22, this indicates proper positioning of the main-cuff40 with its distal end of thedistal region45 pressed into the base of the hypo-pharynx212. Theevacuation tube80 thus provides monitoring of correct placement of the LMA-device20;
• (iii) In the event of unexpected regurgitation though the upperoesophageal sphincter207, gastric contents are likely to follow the path of least resistance and enter into theevacuation tube80 through theoblique orifice123 rather than thelarynx37 via thelaryngeal inlet67, 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
• (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 theevacuation tube80 provided the outer diameter of any such inserted device is less than the internal diameter of the evacuation tube.
• An additional drain tube (not shown) may also be inserted though theairway tube22 in a distal direction to emerge through theairway port30 adjacent to thewell95. A suction may be applied to such additional drain tube to remove secretions which may collect in thewell95. The different inner diameters of theairway tube22 and external-drain tube165 facilitate their respective identifications by the operator so to facilitate insertion into the proper tube of such additional drain-tubes or endoscope.
• The internal- and external-drain tubes115,165 have different external but the same internal diameters because the external-drain tube must be soft in order to bend around thetongue202 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 tube165 is too soft, however, it may kink unless it has a sufficient wall-thickness. Theairway tube22 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 theairway tube22, about 11 millimeters (for #4), is therefore applied to the outer diameter of the external-drain tube165. Thetubes22,165 therefore have the same or similar outer diameter, but for different reasons.
• The portion of the internal-drain tube115 contained in the laryngeal-chamber region110, 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 tube115 is the same as the inner diameter of the external-drain tube165 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 tube115 is less than the inner diameter of the external-drain tube165, 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.
• Conversely, if the inner diameter of the internal-drain tube115 is larger than the inner diameter of the external-drain tube165, 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 region110 (free space within the laryngeal-chamber region is precious). The additional internal cross-sectional area of the internal-drain tube115 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 tube165.
• Anatomical Structures
• Ary-epiglottic folds—wings of tissue joining thearytenoid cartilages205 to each side of theepiglottis35.
• Arytenoid Cartilages205—a pair of pyramid-shaped cartilages bordering the posterior rim of thelaryngeal inlet67.Arytenoid cartilages205 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 thearytenoid cartilages205 is the posterior crico-arytenoid muscle, which draws the vocal cords open to permit air to enter and leave the lungs.
• Cervical vertebrae—the neck bones, of which there are seven counting from above downwards. The sixth vertebral body lies opposite thecricoid cartilage210 and the distal tip of the LMA-device20 lies between the two when correctly inserted.
• Constrictor muscles—three cylinders of muscle stacked within each other like plastic cups surround the interior space of thepharynx197 and act sequentially to squeeze swallowed food into theoesophagus57. The lower pharyngeal constrictor muscle is the one which mostly wraps around the inserted LMA-device20. The lowest part of this muscle (most distal part) forms a complete ring and defines the upperoesophageal sphincter207, also known as the crico-pharyngeus muscle.
• Cricoid cartilage210—a ring of cartilage which acts as the container or chamber of thelarynx37.Cricoid cartilage210 is attached distally to the trachea or wind-pipe36. From the lateral sides of thecricoid cartilage210, the membrane forming the vocal cords stretches upwards and medially. Proximally, the thyroid cartilage surrounds thecricoid cartilage210 but overlaps it on either side postero-laterally. Posteriorly, the broad flat surface (lamina) of thecricoid cartilage210 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 thepharynx197, so when the LMA-device20 enters this area of the pharynx, the LMA-device20 must squeeze in between these two normally contiguous surfaces. Hence the need to make the deflated LMA-device20 form a suitable wedge-shape with sufficient resilience to slip in behind (posterior to) thecricoid210. The part of the internal-drain tube115 which is enclosed by thedistal region45 of main-cuff40 of the LMA-device20 lies immediately posterior to the mid-line ridge on the back of thecricoid cartilage210. Were the LMA-device20 to lie to one or other side, it might compress one or other of the vitally important posterior crico-arytenoid muscles.
• Circopharingeus muscle—same as upperesophageal sphincter207. Part of the inferior constrictor muscle of thepharynx197.
• Epiglottis35—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-device20 is inadequate, theepiglottis35 potentially causes obstruction, particularly if it is large and floppy as may be the case in elderly males. Theepiglottis35 may be downfolded over the laryngeal vestibule if the distal tip of main-cuff40 catches it and flips it downwards during insertion. Correct deflation and insertion of the LMA-device20 minimise this risk, as does a good design permitting the optimal wedge-shape of the deflated LMA-device.
• Oesophagus57—muscular tube which is normally closed, unlike thetrachea36 which lies immediately anterior to it. The muscular coat is thickened to form the upperoesophageal sphincter207 and lower oesophageal sphincter. Stimulating the upperoesophageal sphincter207 excessively by insertion of a bulky device or inflation of the LMA-device20 to too high a pressure may cause the upperoesophageal sphincter207 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-device20, the chest movement of inspiration may cause such a high negative pressure within the chest cavity that the thin-walled oesophagus57 is literally sucked open, encouraging fluids to be drawn up into it from the stomach. A correctly placed LMA-device20 with a hole in the distal end, e.g.,distal orifice123, communicating with the oesophagus57 may prevent this cycle of events from occurring, since it permits air to be drawn into the oesophagus from above.
• Glottis—the constriction of theairway tube22 which occurs in the region of the vocal cords. Thelarynx37 is the structure which surrounds and controls the movements and shape of the glottic opening.
• Hard Palate192—the dome shaped bony vault which arches over the upper surface of thetongue202. Thesoft palate195 is attached to it posteriorly and it stretches down to the dental arcades anteriorly and laterally. The anterior surface of thehard palate192 blends with the gums and is innervated with nerves which trigger deglutition. Hence the importance of stimulating the anterior surface of thehard palate192 when inserting the LMA-device20, 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 thehard palate192, stimulating the acceptance of the LMA-device20 by triggering deglutition reflexes rather than rejection of the LMA-device, e.g., triggering vomiting reflexes.
• Hyoid bone—a semicircular ring of bone vital to the mechanical 0.5 functions of swallowing, including opening of themouth25. The hyoid bone lies above, i.e., proximal to, the thyroid cartilage and is attached above to the base of thetongue202, 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-cuff40 of the LMA-device20 near theproximal region42 of the main-cuff40. The hypoglossal nerves pass near the inner ends of the hyoid bone, limiting the pressure which should be safely generated within the main-cuff40 and the lateral expansion permissible in any device inflated in this region of thepharynx197.
• Hypo-pharynx212—the region of thepharynx197 lying behind thelarynx37, and normally a closed sack at the level of thecricoid210. Adjacent to the base of hypo-pharynx212 is the closed upperoesophageal sphincter207. The hypo-pharynx212 is surrounded by the middle and lower constrictor muscles. Anteriorly, the distal region of the hypo-pharynx212 is bordered by the posterior surface of thecricoid cartilage210. Also anteriorly, the proximal region of the hypo-pharynx212 is bordered by the laryngeal vestibule.
• Inter-arytenoid muscle—the muscle joining the twoarytenoid cartilages205 posteriorly and transversely, and proximal to the upper border of thecricoid cartilage210. 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 region110 of the LMA-device20 must have adequate depth to avoid interfering with the inter-arytenoid muscle or with thearytenoid cartilages205 which lie immediately anterior to it. Bruising of the overlying mucosal surface is common with improper insertion of the LMA-device20.
• Larynx37—the apparatus responsible for protecting the entrance to the lungs from contamination and for vocalisation. The principle advantage of the LMA-device20 is that it permits thelarynx37 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.
• Laryngeal inlet67—the rim of tissue surrounding the vestibule of thelarynx37, consisting of the ary-epiglottic folds laterally, the tip of theepiglottis35 proximally, and thearytenoids205 and inter-arytenoid notch distally.
• Laryngeal vestibule—a pocket of space above the vocal cords bounded laterally by the quadrate membranes, proximally by theepiglottis35 and distally by the vocal cords. The distal tip of the LMA-device20 may lodge in the laryngeal vestibule if the tip does not pass posterior to thearytenoids205. 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 thelarynx37. This closure of the laryngeal vestibule is observed when the LMA-device20 is inserted prematurely.
• Posterior crico-arytenoid muscle—the most important muscle of thelarynx37 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 thecricoid cartilage210. The distal tip of the LMA-device20 presses against the cartilaginous ridge which separates the two muscles. Excessive pressure in the main-cuff40 might drive blood out of the muscle, depriving it of the necessary oxygen to function, though such a complication has yet to be reported.
• Pyriform fossae—gutters lying on either side of the entrance to thelarynx37, bounded medially by the ary-epiglottic folds and laterally by the membranes stretching between the thyroid horns and the hyoid bones.
• 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 theepiglottis35.
• Rima glottidis—the space between the vocal cords.
• Soft palate195—a muscular wedge of tissue extending posteriorly from the posterior edge of thehard palate192. The surfaces of thesoft palate195 converge to the mid-line posteriorly and distally to end in a mid-line triangular structure known as the uvula. Thesoft palate195 acts like a bridge arching across the space separating the nasal cavity from the rest of thepharynx197 and completely closes this gap during swallowing. Insertion of the LMA-device20 relies on the resistance offered by the oral surface of thesoft palate195 to distally guide the distal tip of LMA-device20. If the deflated LMA-device20 is too rigid, or incorrectly deflated, thesoft palate195 cannot guide it downwards, thereby impeding insertion of the LMA-device20 into thepharynx197.
• Thyroid cartilage—a shield-like structure whose lower border bilaterally overlaps thecricoid cartilage210. The thyroid cartilage has two posterior-directed horns, the lower of which articulates with the sides of thecricoid210, 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. Theepiglottis35 is attached to the anterior prominence of the thyroid, also known as the “Adam's Apple”, because it projects more sharply in males.
• Trachea36—the wind-pipe, connected directly to the lower rim of thecricoid cartilage210.
• Upperesophageal sphincter207—guards the entrance to theoesophagus57. The upperesophageal sphincter207 is normally closed, even when the LMA-device20 is in place and pressed into the upper surface of the upper esophageal sphincter. The upperesophageal sphincter207 can open to approximately 1.5.times.1.0 centimeters.
• Vocal cords—folds of tissue which represent the upper free borders of a membrane arising from thecricoid210, i.e., the crico-vocal membrane. The vocal cords vibrate, lengthen and shorten (for speech), adduct (to prevent soiling of the airway ortrachea36 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 thearytenoids205 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 thearytenoids205 together to close the vocal cords.
• 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.

Claims (1)

1. A laryngeal mask airway device comprising:

A. an inflatable cuff, the cuff defining an anterior side, a posterior side, a central aperture, and a midline, 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, the midline being equidistant from the posterior and anterior sides of the cuff;

B. a backplate attached to the cuff at the midline or between the midline and 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.

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