US20090007920A1 - Laryngeal mask airway device - Google Patents

Abstract

A modified laryngeal mask airway device (LMA-device) is provided with means to improve ease of insertion, reliability of function and higher seal pressure (i.e., cuff pressure ratio). The LMA-device includes an indented section of the airway tube to offer locating means and purchase for the inserting finger, and extended mask aperture bars to increase the effective ventilating area of the mask and reduce the possibility of epiglottis displacement occasioned by mask insertion. The LMA-device further includes a modification of the airway tube angle of attachment to the mask, and provision of a posterior or back-cushion covering the entire posterior surface of the mask.

Description

CROSS-REFERENCE SECTION
• This application is a continuation application of currently pending U.S. patent application Ser. No. 11/193,525, filed Jul. 29, 2005, which is a divisional application of U.S. patent application Ser. No. 09/412,954, filed Oct. 5, 1999, now U.S. Pat. No. 7,156,100.
BACKGROUND OF THE INVENTION
• This invention relates to laryngeal mask airway devices (LMA-devices) which are artificial airway devices permitting spontaneous or artificial ventilation of the lungs of a patient.
• LMA-devices are described in UK Patents Nos. 2,111,394 and 2,205,499. Such devices 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.
• The insertion of such a LMA-device into the throat of the patient is, in the great majority of cases an entirely straightforward procedure which can be carried out successfully following readily understandable training.FIG. 1 illustrates a preferable situation for the insertion of an LMA-device into a patient's throat. The inflatable cuff surrounding the bowl of the mask is fully deflated and correctly oriented and aligned for passage through the back of the mouth and into the throat. The semi-rigid bowl of the mask is supported by the anesthetist's hand grasping the flexible airway tube adjacent its junction with the mask in order to gently urge the mask into the patient's throat.
• Circumstances do, however, occasionally arise during insertion leading to undesirable positioning of the device and/or undesirable forces being applied to the device and/or to the patient. One of the most common of such circumstances is that the leading end of the device, i.e., the distal end of the fully deflated inflatable cuff formation, becomes folded over on itself presenting the more rigid distal end of the mask to catch the inside the throat and subject the patient to undesirable forces. Alternatively, or additionally, the folded over distal end of the cuff will obstruct correct and full inflation of the cuff thereby obstructing the creation of a full seal around the patient's laryngeal inlet and hence obstructing formation of a full enclosed airway to the patient's lungs. This, in turn, may result in anesthetic gases passing unnecessarily into the patient's oesophagus and in any matter regurgitated through the oesophagus entering the larynx and soiling the patient's trachea and lungs.
SUMMARY OF THE INVENTION
• The present invention seeks to eliminate the disadvantages associated with such undesirable insertion by minimizing the risk of the deflated cuff formation becoming folding over on itself during the insertion procedure. This is achieved by incorporating into the cuff at its distal end a reinforcing rib which serves to stiffen the leading end of the LMA-device during the course of the procedure for its insertion.
• In accordance with the invention, there is provided a laryngeal mask airway device comprising a flexible airway tube and a mask attached to one end of the airway tube, the mask having a generally elliptical periphery provided with an inflatable cuff which surrounds the hollow interior of the mask into which the airway tube opens, the device including a reinforcing rib incorporated into the distal end of the inflatable cuff.
• In a preferred aspect, the mask structure or backplate which is of a more rigid material than that of the soft and inflatable cuff formation has its back extended to the distal end of the cuff, in order to form the reinforcing rib.
• The LMA-device of the invention incorporating such a reinforcing rib has a number of advantages over and above that for which it was specifically devised. Thus, not only does the reinforcing rib largely eliminate the likelihood of the distal end of the deflated cuff formation folding over on itself during insertion of the LMA-device into the patient's throat, but also the cuff is easier to deflate preferably since the reinforcing rib will urge the deflating cuff into the desired orientation. Since the cuff in its deflated state may adopt an upturned or down turned orientation, the reinforcing rib will urge the deflated cuff into the down turned position desirable for insertion into the patient. Further, in addition to the rib being stiffer than the deflated cuff, it will preferably also be more compliant than the material of the bowl of the mask and the stiffness gradient formed by the rib and the mask will assist in the insertion of the device and substantially reduce the likelihood of any hard or angular edges of the bowl of the mask being presented which may subject the patient's throat to undesirable forces. Additionally, the rib will substantially reduce the promontory previously formed by the distal end of the mask structure, rendering the LMA-device substantially self-inserting when it is properly deflated.
• As shown inFIG. 1, insertion of the LMA-device requires use of the index finger to ensure correct placement of the LMA-device in the base of the throat. However, the index finger may slip from its intended position on the airway tube at the proximal end of the inflatable cuff, due to the presence of slippery secretions in the patient's mouth and/or the application of lubricant to assist smooth passage of the LMA-device.
• In accordance with a preferred aspect of the invention, an indentation is provided on the airway tube or backplate at the intended location of finger contact to assist in locating and stabilizing the finger and to reduce the possibility of finger slippage. The indentation is situation on the surface of the airway tube adjacent its junction with the tube-joint, or on the tube-joint itself, and beneath the cuff formation surrounding the backplate. The airway tube usually has a thicker wall at this point, i.e., near the distal end of the airway tube, to form a smooth joint with the tube-joint, and the extra thickness enables the indentation to be accommodated without weakening the airway tube at this location. The tube-joint may also have a thicker wall at this point. Indeed, the indentation serves the additional useful purpose of improving the flexibility of the airway tube or tube-joint at this point. The indentation serves not only to prevent sideways slippage of the finger from the airway tube or tube-joint, but also to minimize the possibility of forward slippage and undesirable contact between the finger and the inflatable cuff, for example by the fingernail.
• An additional difficulty which may occur during attempts to insert the LMA-device is that the patient's epiglottis (which protects the entrance to the glottis or larynx) may be pushed downwards or anteriorly as the LMA-device is inserted fully into the throat. Indeed, this occurs in about 40% of cases and can sometimes obstruct breathing. A conventional LMA-device has the interior of the mask which in use surrounds the glottis, communicating with the interior of the airway tube through an aperture which is traversed by two bars, known as mask aperture bars (MABs). The MABs function as a ramp up which the epiglottis slides as the mask is inserted and are intended to hold the epiglottis away from the mask floor when the LMA-device is in its correct operating location. Additionally, the MABs serve to prevent the epiglottis from obstructing the narrow entrance of the airway tube. Generally, the MABs successfully perform this function but occasionally obstruction may occur if the epiglottis is down folded, e.g., anteriorly, or if the mask is not sufficiently advanced into place.
• In accordance with a preferred aspect of the invention, the aperture by which the interior of the airway tube opens into the mask is elongated and the MABs are extended to traverse the length of that aperture. By elongating the aperture to half the bowl of the mask, the range of positions of the LMA-device compatible with a clear airway is greatly increased and the angle of ramp up which the epiglottis must slide is reduced, both of which make the epiglottis less likely to be down-folded during insertion of the LMA-device.
BRIEF DESCRIPTION OF THE DRAWINGS
• In the drawings:
• FIG. 1 is a perspective view of the laryngeal-mask airway device of the present invention being inserted into the throat of a patient;
• FIG. 2 is a side view of the device ofFIG. 1 inserted into sealed engagement with the tissue surrounding the laryngeal inlet of the patient;
• FIG. 3 is a posterior perspective view of the device ofFIG. 1 removed from the patient, the proximal portions of the airway and inflation tubes being broken away, the back-cushion being cut-away;
• FIG. 4 is an anterior plan view of the device ofFIG. 1 removed from the patient, the proximal portions of the airway and inflation tubes being broken away, the indentation on the backplate being shown as hidden;
• FIG. 5 is a cross-sectional view of the device in the plane indicated by line5-5 ofFIG. 4, the proximal portions of the airway and inflation tubes being broken away;
• FIG. 6 is an anterior plan view of the backplate removed from the device shown inFIG. 5;
• FIG. 7 is a schematic view of the device in the plane ofFIG. 5 showing the present invention, in solid lines, and an airway tube and adjoining portion of the backplate of a prior laryngeal-mask airway device, in broken lines, the proximal portions of the airway and inflation tubes being broken away;
• FIG. 8 is a cross-sectional view of the device in the plane ofFIG. 5 showing one of the mask aperture bars of the present invention, in solid lines, and one of the mask aperture bars of a prior laryngeal-mask airway device, in broken lines, the proximal portions of the airway and inflation tubes being broken away;
• FIG. 9 is a lateral view of the backplate removed from the device shown inFIG. 5;
• FIG. 10 is a cross-sectional view of a second embodiment of the device ofFIG. 1 removed from the patient, the device being shown in the plane ofFIG. 5, the proximal portions of the airway and inflation tubes being broken away; and
• FIG. 11 is an anterior plan view of the backplate removed from the device shown inFIG. 10.
• 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 thethroat22 the upper surface of which is bounded by hard andsoft palates25,27. The LMA-device20 is lodged in thepharynx30 of thethroat22 at the base of the hypo-pharynx32 where the throat divides into the trachea35 (i.e., windpipe) andoesophagus37. A lower portion of the LMA-device20 reaches to the base of the hypo-pharynx32. After the LMA-device20 is so lodged in thepharynx30 such that the lower portion of the LMA-device reaches the base of the hypo-pharynx32, the LMA-device is inflated. Disposed in the junction between thethroat22 andtrachea35 is the flexible epiglottis40 (i.e., a lid-shaped structure) which forms the upper border of the larynx, entry through which is provided by the laryngeal inlet45.
• Referring toFIGS. 1 and 2, and more particularly toFIG. 3, the laryngeal-mask airway device (LMA-device)20 is shown comprising anairway tube47, installed through the mouth50 of a patient. The LMA-device20 further comprises abackplate52 having anairway port55 through which theairway tube47 can establish a free externally accessible ventilation passage, via the patient's mouth50 andthroat22, and past the epiglottis40 to the larynx. Thebackplate52 is preferably of an elastomer such as silicone rubber and relatively stiff, for example, of 80 Shore durometer.
• As further shown inFIGS. 3 and 4, thebackplate52 is surrounded by a main-cuff55 comprising an inflatable ring which, when inflated, has the shape of a torus generated by an asymmetrical oval or ellipse having a widerproximal region57 and narrowerdistal region60. The main-cuff55 is circumferentially united to thebackplate52 in essentially a single plane.
• An externally accessible cuff-tube62 and cuff-port65 on the main-cuff55 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-valve67 is disposed in the cuff-tube62 for holding a given inflation or holding a given deflation of the main-cuff55.
• In the installed position ofFIGS. 1 and 2, the projecting but blunteddistal region60 of the main-cuff55 is shaped to conform with the base of the hypo-pharynx32 where it has established limited entry into the upper sphincteral region of theoesophagus37. The pharyngeal-side70 of thebackplate52 is covered by a thinflexible panel72, as shown inFIGS. 3 and 5, which is peripherally bonded to amargin75 on the posterior surface of the main-cuff55, to define an inflatable back-cushion77 which assures referencing to the posterior wall of thepharynx30 and thus is able to load the inflated main-cuff55 forward for enhanced effectiveness of sealing engagement to the tissues surrounding the laryngeal inlet45. The inflated main-cuff55, thus-engaged to the laryngeal inlet45, orients a portion of theairway tube47 including the distal-end80 at an acute angle to a mid-linemajor plane82 of the main-cuff55 and in substantial alignment with the axis of the laryngeal inlet45, for direct airway communication only with the larynx.
• Themajor plane82 is a plane containing themajor axis85 of the main-cuff55 extending between proximal anddistal regions57,60. Themajor plane82 is disposed between, and parallel to, the anterior and posterior surfaces of the main-cuff55. Additionally, themajor plane82 is equidistant from the anterior and posterior surfaces of the main-cuff55.
• More specifically, and with particular reference toFIG. 5, the toroidal-shaped main-cuff55 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-cuff55, when in generally edge-to-edge relation, are welded together to form aninternal seam87, as shown inFIG. 5. Theseam87 defines an oval contained in a plane which is parallel to themajor plane82, corresponding to the internal surface of the main-cuff55.
• 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.
• The back-cushion77, or auxiliary rear cushion, overlies the posterior surface of thebackplate52, as shown inFIGS. 3 and 5. Construction of the back-cushion77 is described in U.S. Pat. No. 5,355,879, the contents of which are hereby incorporated by reference herein.
• Inflation-air supply to the back-cushion77 may be via one or more ports in the main-cuff55 which provide communication between the interiors of the main-cuff and back-cushion so that both are inflated and deflated together. Alternatively, inflation-air supply to the back-cushion77 may be via a separate inflating means, such as an inflation tube (not shown), similar to cuff-tube62, may be provided for the back-cushion so that the back-cushion77 and main-cuff55 are separately and independently inflatable and deflatable.
• If the main-cuff55 and back-cushion77 are inflated and deflated together, communication between the main-cuff and back-cushion may be facilitated by a separate tube (not shown), preferably with multiple perforations along its length, contained within the main-cuff in communication with the cuff-port65 such that each perforation communicates with a port between the interiors of the main-cuff and back-cushion77. Such a separate tube preserves a flowpath between the cuff-port65 and back-cushion77 if the main-cuff55 is completely collapsed from deflation, thereby providing for further deflation of the back-cushion77 via the cuff-port65. Alternatively, a channel (not shown) may be formed on the inner surface of the main-cuff55 between the opening of the cuff-tube62 into the main-cuff and at least one of the one or more ports between the interiors of the main-cuff and back-cushion77. Such a channel preserves a flowpath between the cuff-tube62 and back-cushion77 if the main-cuff55 is completely collapsed from deflation.
• Thebackplate52 has a one-piece, integral spoon-shape including abowl90 and an external tube-joint92 oriented proximally relative to the bowl, as shown inFIGS. 5 and 6. Opposite proximal sides of thebowl90 are defined by a convex pharyngeal-side95 and concave laryngeal-side97. Thebowl90 is relatively shallow in the anterior-posterior direction. Thebowl90 also has an elongate integral reinforcingdistal rib105.
• The proximal portion of thebowl90 sandwiched between the pharyngeal- and laryngeal-sides95,97 abuts the posterior surface of theseam87, as shown inFIG. 5, to attach thebackplate52 to the main-cuff55. More specifically, the periphery of the proximal portion of thebowl90 sandwiched between the pharyngeal- and laryngeal-sides95,97 is hermetically bonded to the inner periphery of the main-cuff55 to establish separation between the laryngeal-chamber region100 andpharyngeal region102. Theseam87 may also be inserted into a corresponding groove in thebowl90. Alternatively, thebackplate52 and main-cuff55 may be extruded as a single, unitary piece. The periphery of thebowl90 which abuts the inner periphery of the main-cuff55 defines abowl plane106 which is parallel to themajor plane82 of the main-cuff55.
• When thebackplate52 is attached to the main-cuff55, thedistal rib105 pierces the proximal surface of thedistal region60. The edges of the main-cuff55 in thedistal region60 surrounding thedistal rib105 are hermetically sealed to it such that the enclosure of the main-cuff is defined in part by the distal rib. Thedistal rib105 extends through the interior of the main-cuff55 to the distal surface of thedistal region60.
• Thebowl90 has a longitudinallyelongated airway aperture107 into which opens abackplate passage110 extending through the tube-joint92. Theairway aperture107 has amajor axis111 which is contained in thesagittal plane112.
• Two mask aperture bars (MABs)115,117 extend longitudinally and anteriorly of theairway aperture107, as shown inFIG. 4. TheMABs115,117 are disposed on opposite sides of thesagittal plane112 and symmetrical relative to the plane. TheMABs115,117 each have aproximal end120,122 abutting the laryngeal-side97 of thebowl90 proximally of theairway aperture107. Additionally, theMABs115,117 each have adistal end125,127, abutting the laryngeal-side97 of thebowl90 distally of the airway aperture.
• TheMABs115,177 may be defined by a portion of a continuous layer of elastomer, integral with the main-cuff55, which overlies the laryngeal-side97. The elastomer layer has an opening the periphery of which is outward of theairway aperture107. The opening is longitudinally traversed by theMABs115,117.
• The distal ends125,127 of theMABs115,117 are joined to thebowl90 generally near the longitudinal mid-point of the laryngeal-side97, or distally of it. This results in eachMAB115,117 forming anangle118 with thebowl plane106 which is less than the corresponding angle between the MAB P1 of a prior LMA-device, as shown inFIG. 8. The relatively shallowness of thebowl90 in the anterior-posterior direction further results in theangle118 being more acute. A preferred angular displacement of theangle118 is between 7 and 12 degrees, and may preferably be 9 degrees.
• The elongate tube-joint92 is formed on the pharyngeal-side95 and extends posteriorly and proximally relative to thebowl90. The tube-joint92 has aproximal end130 from which thebackplate passage110 extends to theairway aperture107 in the laryngeal-side97. Thebackplate passage110 has a longitudinalcentral axis132 contained in thesagittal plane112. At theproximal end130, thebackplate passage110 has an elliptical cross section with amajor axis135 oriented in perpendicular relation to thesagittal plane112. Themajor axis135 is therefore transverse to themajor axis111 of theairway aperture107. This differing orientation of themajor axes111,132 of thebackplate passage110 is accomplished by a smooth transition in the cross-sectional shape of the backplate passage along its length.
• The tube-joint92, and thecentral axis132 of thebackplate passage110 are inclined posteriorly in thesagittal plane112 relative to a plane containing the periphery of thebowl90. In the embodiment shown inFIG. 5, the inclination of the tube-joint92 may be defined by a tube-joint axis136 which is perpendicular to the cross-section of theproximal end130 and which coincides with thecentral axis132 at its intersection with the cross-section of theproximal end130. The inclination of the tube-joint92 may be further defined by anangle137 between the tube-joint axis136 andbowl plane106. A preferred angular displacement of theangle137 is between 5 and 10 degrees, and may preferably be 7 degrees. The inclination of the tube-joint92, defined by theangle137, is less than the corresponding angle defined by the inclination of a tube-joint P2 of a prior-LMA, as shown inFIG. 7.
• The anterior surface of the tube-joint92 has anindentation140, as shown inFIGS. 4,5,6 and9. As shown inFIG. 5, theindentation140 is in the thick wall region of the tube-joint92 resulting in the advantage of increasing the flexibility of the tube-joint. Theindentation140 may be occupied by the main-cuff55 when the main-cuff is inflated, as shown inFIG. 5. Theindentation140 may also be formed closer to theproximal end130, such as is shown inFIG. 1. Alternatively, the proximal portion of theindentation140 may be formed across the boundary between the tube-joint92 andairway tube47 such that portions of the indentation are in both the airway tube and tube-joint. Also, theentire indentation140 may be formed in theairway tube47 adjacent to its connection to the tube-joint92.
• Thebackplate52, main-cuff55 and back-cushion77 of LMA-devices20 are generally manufactured by molding techniques from suitably soft and compliant rubber materials. Thebackplate52 and inflatable main-cuff55 may be formed as a one piece molding by molds and molding techniques such as are described, for example, in U.S. Pat. No. 5,305,743, the contents of which are hereby incorporated herein. Thebackplate52 is formed to have a greater thickness than the walls of the main-cuff55 to provide the LMA-device20 with a degree of rigidity while still allowing it to have an overall soft and flexible nature. The main-cuff55 has a thin-walled construction and the reinforcingdistal rib105 has an intermediate thickness and compliancy.
• As shown inFIGS. 4 and 5, the portion of theairway tube47 containing thedistal end80 is supported in thebackplate passage110 of the tube-joint92 in communication with theairway aperture107 in the laryngeal-side97. Such communication provides a flowpath between theairway tube47 and laryngeal-chamber region100. Theairway tube47 is connected to the tube-joint92 by welding using an adhesive or, alternatively, connected by high-pressure or temperature fusion.
• FIG. 10 shows a second embodiment of thebackplate52a. Parts inFIG. 10 having corresponding parts inFIGS. 5 and 6 have the same reference numeral with the addition of suffix a. Thebackplate52ais similar to thebackplate52 illustrated inFIGS. 5 and 6 except that the distal rib105aof thebackplate52ais applied to the posterior surface of thedistal region60aof the main-cuff55a, as shown inFIG. 10. The distal rib105ahas a concave anterior surface corresponding to the adjoining convex posterior surface of thedistal region60athereby limiting the radial clearance between the distal region and end60a,105a. The distal rib105adoes not pierce the posterior surface of thedistal region60a, in contrast to the embodiment shown inFIG. 5, and is therefore separated from the interior of the main-cuff55a. The distal rib105amay be effectively constituted by a thickening of the posterior wall of thedistal region60aof the inflatable main-cuff55aand, as shown, forms a distal extension of thebowl90aof thebackplate52a. The distal rib105ahas a downturned profile by being incorporated into the posterior surface of the main-cuff55a. The distal end of the distal rib105ais spatulate.
• Insertion of the LMA-device20 into the patient'sthroat22 is illustrated inFIG. 1, and is done preferably with the patient in a supine orientation and the head142 of the patient tilted backwards and supported from below by the left hand145 of the anaesthetist. The right index finger147 and thumb150 of the anesthetist gently grasps theflexible airway tube47 of the LMA-device20. The right index finger147 is located at the junction of theairway tube47 and the main-cuff55 to gently urge the LMA-device29 with its down-turned deflated main-cuff into the patient'sthroat22. As shown inFIG. 1, theindentation140 provides a locator for the right index finger147 of the anaesthetist during insertion of the LMA-device20 into thethroat22 of the patient. When the LMA-device20 is properly positioned across the patient's laryngeal inlet45, the main-cuff55 is gently inflated throughcuff tube62 to form an airway seal around the laryngeal inlet and establish a closed airway to the patient's lungs. The LMA-device20 so positioned, with the main-cuff55 fully inflated, is shown inFIG. 2. The thin-walled construction of the main-cuff55 enables it, when inflated, to present to the tissues surrounding the laryngeal inlet45 a softly compliant sealing surface.
• As shown inFIG. 1, thedistal region60 of the fully deflated main-cuff55 is the leading end of the LMA-device20 when inserting the LMA-device into the patient'sthroat22. Careful insertion of the LMA-device20 into the patient'sthroat22 is required to prevent thedistal region60 from folding over onto itself because the distal region is formed of a soft and flexible material which facilitates such folding over. Such folding over is obstructed by the reinforcingdistal rib105 within thedistal region60 of the inflatable main-cuff55. The intermediate thickness and compliancy of the reinforcingdistal rib105 allows it to follow the contours of the posterior surface of the inflated main-cuff55, thereby to urge the deflated main-cuff into the desired downturned orientation and to enable the LMA-device20 present a distal end to the tissues of thethroat22 which is sufficiently pliable to avoid undesirable contact with the throat during its insertion but sufficiently rigid to prevent it from being readily folded over on itself during such a procedure. As shown inFIGS. 3 and 4, thedistal rib105 is not readily visible when the main-cuff55 is either deflated or inflated since it is contained within thedistal region60.
• In the embodiment shown inFIG. 10, the downturned profile the distal rib105ahelps to facilitate adoption by the main-cuff55aof the desired downturned orientation when it is fully deflated. The distal rib105amay not be readily visible because it may appear to blend in with the posterior wall of thedistal region60. The spatulate of the distal portion of the distal rib105adoes not present any sharp edges or corners to thethroat22 the patient during insertion of the LMA-device20 which is desirable as striking of thethroat22 by sharp edges or corners is normally to be avoided.
• Theacute angle118 between theMABs115,117 and thebowl plane106 results in the MABs presenting a substantially less gradient to the patient's epiglottis40 than the MABs P1 of a prior-LMA, as shown inFIG. 8. TheMABs115,117 provide a ramp up which the epiglottis40 slides when thebackplate52 and the attached main-cuff55 enter thepharynx30. If the MABs are sufficiently posterior of the epiglottis40, e.g., MAB P1, such sliding contact may result in the proximal end of the epiglottis40 folding over posteriorly such that it becomes sandwiched between the base of the epiglottis and the MABs possibly obstructing theairway aperture107. The likelihood of such posterior folding over of the epiglottis40 is substantially reduced by theMABs115,117 because the A-P clearance between theMABs115,117 and laryngeal-side97 is increased thereby anteriorly propping the epiglottis to limit further anterior displacement necessary to accommodate the posterior folding. Further reduction in the likelihood of an obstruction is provided by the increased A-P clearance between theMABs115,117 and laryngeal-side97, which in turn provides increased A-P clearance between the epiglottis40 andairway aperture107 contained in the laryngeal-side.
• When the main-cuff55 andbackplate52 are installed in thepharynx30 such that main-cuff is sealed against the tissues surrounding the patient's laryngeal inlet45, the reducedangle137 between the tube-joint axis136 andbowl plane106, relative to the corresponding force resulting from tube-joint P2, reduces the force exerted by the tube-joint92 andairway tube47 against the posterior surface of thethroat22. Any force against the tissues of thethroat22 should normally be limited.
• The reduction in the force exerted by the tube-joint92 andairway tube47 against the posterior surface of thethroat22 may result in a reduction in the reaction force of the main-cuff55 against the tissues surrounding the patient's laryngeal inlet45 which, in turn, may reduce the tightness of the seal between the main-cuff and tissues. Any such reduction in the seal is compensated for the inflatable back-cushion77 which gently urges thebackplate52 and main-cuff55 anteriorly against the tissues surrounding the patient's laryngeal inlet45 in order to reinforce the seal between the inflated main-cuff and the tissues.
• Additionally, the inflatable back-cushion77 presents a more softly complaint surface to the posterior surface of the patient'sthroat22. Also, the back-cushion77 enables the main-cuff55 to be inflated at a lower pressure, i.e., typically 60 cm H₂O, as compared to the inflation pressure required of the main-cuff if the LMA-device20 does not include a back-cushion77. Reducing the inflation pressure of the main-cuff55 enables a reduced wall thickness of the main-cuff.
• 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 backplate for a laryngeal-mask airway device, said backplate comprising a bowl having a transversely concave laryngeal-side and a convex pharyngeal-side, said backplate being bonded to a periphery of a main-cuff establishing separation between a laryngeal-chamber region and a pharyngeal region,

said backplate further comprising an external tube-joint, said tube-joint being formed on said pharyngeal-side and extending from said pharyngeal-side into said pharyngeal region, said tube-joint further including a passageway for communication between said pharyngeal and laryngeal-chamber regions, said device having an anterior outer surface defining an anterior-facing indentation proximate the tube joint, the indentation being accessible by a finger of a person when the person is inserting the device into a patient.

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