Patent 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.

Full Description:
CROSS-REFERENCE SECTION 
   This application is a divisional application of currently U.S. patent application Ser. No. 09/412,954, filed Oct. 5, 1999. 

   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&#39;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&#39;s hand grasping the flexible airway tube adjacent its junction with the mask in order to gently urge the mask into the patient&#39;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&#39;s laryngeal inlet and hence obstructing formation of a full enclosed airway to the patient&#39;s lungs. This, in turn, may result in anesthetic gases passing unnecessarily into the patient&#39;s oesophagus and in any matter regurgitated through the oesophagus entering the larynx and soiling the patient&#39;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&#39;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&#39;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 in  FIG. 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&#39;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&#39;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 of  FIG. 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 of  FIG. 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 of  FIG. 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 line  5 - 5  of  FIG. 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 in  FIG. 5 ; 
       FIG. 7  is a schematic view of the device in the plane of  FIG. 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 of  FIG. 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 in  FIG. 5 ; 
       FIG. 10  is a cross-sectional view of a second embodiment of the device of  FIG. 1  removed from the patient, the device being shown in the plane of  FIG. 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 in  FIG. 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-device  20  or in the body relative to the extreme outer or connector end of the LMA-device. “Proximal” is the opposite of “distal”. The term “lateral” refers to a location to the right or left sides of the body, relative to other locations. Alternatively, “lateral” means to one or other side of the mid-line, with respect to the major axis of the body, or to a device lying in the body&#39;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 the reference numeral  20  in  FIGS. 1 and 2 . The LMA-device  20 , in a deflated condition, is inserted into the throat  22  the upper surface of which is bounded by hard and soft palates  25 ,  27 . The LMA-device  20  is lodged in the pharynx  30  of the throat  22  at the base of the hypo-pharynx  32  where the throat divides into the trachea  35  (i.e., windpipe) and oesophagus  37 . A lower portion of the LMA-device  20  reaches to the base of the hypo-pharynx  32 . After the LMA-device  20  is so lodged in the pharynx  30  such that the lower portion of the LMA-device reaches the base of the hypo-pharynx  32 , the LMA-device is inflated. Disposed in the junction between the throat  22  and trachea  35  is the flexible epiglottis  40  (i.e., a lid-shaped structure) which forms the upper border of the larynx, entry through which is provided by the laryngeal inlet  45 . 
   Referring to  FIGS. 1 and 2 , and more particularly to  FIG. 3 , the laryngeal-mask airway device (LMA-device)  20  is shown comprising an airway tube  47 , installed through the mouth  50  of a patient. The LMA-device  20  further comprises a backplate  52  having an airway port  55  through which the airway tube  47  can establish a free externally accessible ventilation passage, via the patient&#39;s mouth  50  and throat  22 , and past the epiglottis  40  to the larynx. The backplate  52  is preferably of an elastomer such as silicone rubber and relatively stiff, for example, of 80 Shore durometer. 
   As further shown in  FIGS. 3 and 4 , the backplate  52  is surrounded by a main-cuff  55  comprising an inflatable ring which, when inflated, has the shape of a torus generated by an asymmetrical oval or ellipse having a wider proximal region  57  and narrower distal region  60 . The main-cuff  55  is circumferentially united to the backplate  52  in essentially a single plane. 
   An externally accessible cuff-tube  62  and cuff-port  65  on the main-cuff  55  are the means of supplying air to the main-cuff and of extracting air from (and therefore collapsing) the main-cuff for purposes of insertion in or removal from the patient. The check-valve  67  is disposed in the cuff-tube  62  for holding a given inflation or holding a given deflation of the main-cuff  55 . 
   In the installed position of  FIGS. 1 and 2 , the projecting but blunted distal region  60  of the main-cuff  55  is shaped to conform with the base of the hypo-pharynx  32  where it has established limited entry into the upper sphincteral region of the oesophagus  37 . The pharyngeal-side  70  of the backplate  52  is covered by a thin flexible panel  72 , as shown in  FIGS. 3 and 5 , which is peripherally bonded to a margin  75  on the posterior surface of the main-cuff  55 , to define an inflatable back-cushion  77  which assures referencing to the posterior wall of the pharynx  30  and thus is able to load the inflated main-cuff  55  forward for enhanced effectiveness of sealing engagement to the tissues surrounding the laryngeal inlet  45 . The inflated main-cuff  55 , thus-engaged to the laryngeal inlet  45 , orients a portion of the airway tube  47  including the distal-end  80  at an acute angle to a mid-line major plane  82  of the main-cuff  55  and in substantial alignment with the axis of the laryngeal inlet  45 , for direct airway communication only with the larynx. 
   The major plane  82  is a plane containing the major axis  85  of the main-cuff  55  extending between proximal and distal regions  57 ,  60 . The major plane  82  is disposed between, and parallel to, the anterior and posterior surfaces of the main-cuff  55 . Additionally, the major plane  82  is equidistant from the anterior and posterior surfaces of the main-cuff  55 . 
   More specifically, and with particular reference to  FIG. 5 , the toroidal-shaped main-cuff  55  is formed by first moulding it in an intermediate stage having opposing edges, each of which has an elliptical shape. The opposing edges of the main-cuff  55 , when in generally edge-to-edge relation, are welded together to form an internal seam  87 , as shown in  FIG. 5 . The seam  87  defines an oval contained in a plane which is parallel to the major plane  82 , corresponding to the internal surface of the main-cuff  55 . 
   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-cushion  77 , or auxiliary rear cushion, overlies the posterior surface of the backplate  52 , as shown in  FIGS. 3 and 5 . Construction of the back-cushion  77  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-cushion  77  may be via one or more ports in the main-cuff  55  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-cushion  77  may be via a separate inflating means, such as an inflation tube (not shown), similar to cuff-tube  62 , may be provided for the back-cushion so that the back-cushion  77  and main-cuff  55  are separately and independently inflatable and deflatable. 
   If the main-cuff  55  and back-cushion  77  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-port  65  such that each perforation communicates with a port between the interiors of the main-cuff and back-cushion  77 . Such a separate tube preserves a flowpath between the cuff-port  65  and back-cushion  77  if the main-cuff  55  is completely collapsed from deflation, thereby providing for further deflation of the back-cushion  77  via the cuff-port  65 . Alternatively, a channel (not shown) may be formed on the inner surface of the main-cuff  55  between the opening of the cuff-tube  62  into the main-cuff and at least one of the one or more ports between the interiors of the main-cuff and back-cushion  77 . Such a channel preserves a flowpath between the cuff-tube  62  and back-cushion  77  if the main-cuff  55  is completely collapsed from deflation. 
   The backplate  52  has a one-piece, integral spoon-shape including a bowl  90  and an external tube-joint  92  oriented proximally relative to the bowl, as shown in  FIGS. 5 and 6 . Opposite proximal sides of the bowl  90  are defined by a convex pharyngeal-side  95  and concave laryngeal-side  97 . The bowl  90  is relatively shallow in the anterior-posterior direction. The bowl  90  also has an elongate integral reinforcing distal rib  105 . 
   The proximal portion of the bowl  90  sandwiched between the pharyngeal- and laryngeal-sides  95 ,  97  abuts the posterior surface of the seam  87 , as shown in  FIG. 5 , to attach the backplate  52  to the main-cuff  55 . More specifically, the periphery of the proximal portion of the bowl  90  sandwiched between the pharyngeal- and laryngeal-sides  95 ,  97  is hermetically bonded to the inner periphery of the main-cuff  55  to establish separation between the laryngeal-chamber region  100  and pharyngeal region  102 . The seam  87  may also be inserted into a corresponding groove in the bowl  90 . Alternatively, the backplate  52  and main-cuff  55  may be extruded as a single, unitary piece. The periphery of the bowl  90  which abuts the inner periphery of the main-cuff  55  defines a bowl plane  106  which is parallel to the major plane  82  of the main-cuff  55 . 
   When the backplate  52  is attached to the main-cuff  55 , the distal rib  105  pierces the proximal surface of the distal region  60 . The edges of the main-cuff  55  in the distal region  60  surrounding the distal rib  105  are hermetically sealed to it such that the enclosure of the main-cuff is defined in part by the distal rib. The distal rib  105  extends through the interior of the main-cuff  55  to the distal surface of the distal region  60 . 
   The bowl  90  has a longitudinally elongated airway aperture  107  into which opens a backplate passage  110  extending through the tube-joint  92 . The airway aperture  107  has a major axis  111  which is contained in the sagittal plane  112 . 
   Two mask aperture bars (MABs)  115 ,  117  extend longitudinally and anteriorly of the airway aperture  107 , as shown in  FIG. 4 . The MABs  115 ,  117  are disposed on opposite sides of the sagittal plane  112  and symmetrical relative to the plane. The MABs  115 ,  117  each have a proximal end  120 ,  122  abutting the laryngeal-side  97  of the bowl  90  proximally of the airway aperture  107 . Additionally, the MABs  115 ,  117  each have a distal end  125 ,  127 , abutting the laryngeal-side  97  of the bowl  90  distally of the airway aperture. 
   The MABs  115 ,  117  may be defined by a portion of a continuous layer of elastomer, integral with the main-cuff  55 , which overlies the laryngeal-side  97 . The elastomer layer has an opening the periphery of which is outward of the airway aperture  107 . The opening is longitudinally traversed by the MABs  115 ,  117 . 
   The distal ends  125 ,  127  of the MABs  115 ,  117  are joined to the bowl  90  generally near the longitudinal mid-point of the laryngeal-side  97 , or distally of it. This results in each MAB  115 ,  117  forming an angle  118  with the bowl plane  106  which is less than the corresponding angle between the MAB P 1  of a prior LMA-device, as shown in  FIG. 8 . The relative shallowness of the bowl  90  in the anterior-posterior direction further results in the angle  118  being more acute. A preferred angular displacement of the angle  118  is between 7 and 12 degrees, and may preferably be 9 degrees. 
   The elongate tube-joint  92  is formed on the pharyngeal-side  95  and extends posteriorly and proximally relative to the bowl  90 . The tube-joint  92  has a proximal end  130  from which the backplate passage  110  extends to the airway aperture  107  in the laryngeal-side  97 . The backplate passage  110  has a longitudinal central axis  132  contained in the sagittal plane  112 . At the proximal end  130 , the backplate passage  110  has an elliptical cross section with a major axis  135  oriented in perpendicular relation to the sagittal plane  112 . The major axis  135  is therefore transverse to the major axis  111  of the airway aperture  107 . This differing orientation of the major axes  111 ,  132  of the backplate passage  110  is accomplished by a smooth transition in the cross-sectional shape of the backplate passage along its length. 
   The tube-joint  92 , and the central axis  132  of the backplate passage  110  are inclined posteriorly in the sagittal plane  112  relative to a plane containing the periphery of the bowl  90 . In the embodiment shown in  FIG. 5 , the inclination of the tube-joint  92  may be defined by a tube-joint axis  136  which is perpendicular to the cross-section of the proximal end  130  and which coincides with the central axis  132  at its intersection with the cross-section of the proximal end  130 . The inclination of the tube-joint  92  may be further defined by an angle  137  between the tube-joint axis  136  and bowl plane  106 . A preferred angular displacement of the angle  137  is between 5 and 10 degrees, and may preferably be 7 degrees. The inclination of the tube-joint  92 , defined by the angle  137 , is less than the corresponding angle defined by the inclination of a tube-joint P 2  of a prior-LMA, as shown in  FIG. 7 . 
   The anterior surface of the tube-joint  92  has an indentation  140 , as shown in  FIGS. 4 ,  5 ,  6  and  9 . As shown in  FIG. 5 , the indentation  140  is in the thick wall region of the tube-joint  92  resulting in the advantage of increasing the flexibility of the tube-joint. The indentation  140  may be occupied by the main-cuff  55  when the main-cuff is inflated. The indentation  140  may also be formed closer to the proximal end  130 , such as is shown in  FIG. 1 . Alternatively, the proximal portion of the indentation  140  may also be formed across the boundary between the tube-joint  92  and airway tube  47  such that portions of the indentation are both the airway tube and tube-joint. Also, the entire indentation  140  may be formed in the airway tube  47  adjacent to its connection to the tube-joint  92 . 
   The backplate  52 , main-cuff  55  and back-cushion  77  of LMA-devices  20  are generally manufactured by molding techniques from suitably soft and compliant rubber materials. The backplate  52  and inflatable main-cuff  55  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. The backplate  52  is formed to have a greater thickness than the walls of the main-cuff  55  to provide the LMA-device  20  with a degree of rigidity while still allowing it to have an overall soft and flexible nature. The main-cuff  55  has a thin-walled construction and the reinforcing distal rib  105  has an intermediate thickness and compliancy. 
   As shown in  FIGS. 4 and 5 , the portion of the airway tube  47  containing the distal end  80  is supported in the backplate passage  110  of the tube-joint  92  in communication with the airway aperture  107  in the laryngeal-side  97 . Such communication provides a flowpath between the airway tube  47  and laryngeal-chamber region  100 . The airway tube  47  is connected to the tube-joint  92  by welding using an adhesive or, alternatively, connected by high-pressure or temperature fusion. 
     FIG. 10  shows a second embodiment of the backplate  52   a . Parts in  FIG. 10  having corresponding parts in  FIGS. 5 and 6  have the same reference numeral with the addition of suffix a. The backplate  52   a  is similar to the backplate  52  illustrated in  FIGS. 5 and 6  except that the distal rib  105   a  of the backplate  52   a  is applied to the posterior surface of the distal region  60   a  of the main-cuff  55   a , as shown in  FIG. 10 . The distal rib  105   a  has a concave anterior surface corresponding to the adjoining convex posterior surface of the distal region  60   a  thereby limiting the radial clearance between the distal region and end  60   a ,  105   a . The distal rib  105   a  does not pierce the posterior surface of the distal region  60   a , in contrast to the embodiment shown in  FIG. 5 , and is therefore separated from the interior of the main-cuff  55   a . The distal rib  105   a  may be effectively constituted by a thickening of the posterior wall of the distal region  60   a  of the inflatable main-cuff  55   a  and, as shown, forms a distal extension of the bowl  90   a  of the backplate  52   a . The distal rib  105   a  has a downturned profile by being incorporated into the posterior surface of the main-cuff  55   a . The distal end of the distal rib  105   a  is spatulate. 
   Insertion of the LMA-device  20  into the patient&#39;s throat  22  is illustrated in  FIG. 1 , and is done preferably with the patient in a supine orientation and the head  142  of the patient tilted backwards and supported from below by the left hand  145  of the anaesthetist. The right index finger  147  and thumb  150  of the anesthetist gently grasps the flexible airway tube  47  of the LMA-device  20 . The right index finger  147  is located at the junction of the airway tube  47  and the main-cuff  55  to gently urge the LMA-device  29  with its down-turned deflated main-cuff into the patient&#39;s throat  22 . As shown in  FIG. 1 , the indentation  140  provides a locator for the right index finger  147  of the anaesthetist during insertion of the LMA-device  20  into the throat  22  of the patient. When the LMA-device  20  is properly positioned across the patient&#39;s laryngeal inlet  45 , the main-cuff  55  is gently inflated through cuff tube  62  to form an airway seal around the laryngeal inlet and establish a closed airway to the patient&#39;s lungs. The LMA-device  20  so positioned, with the main-cuff  55  fully inflated, is shown in  FIG. 2 . The thin-walled construction of the main-cuff  55  enables it, when inflated, to present to the tissues surrounding the laryngeal inlet  45  a softly compliant sealing surface. 
   As shown in  FIG. 1 , the distal region  60  of the fully deflated main-cuff  55  is the leading end of the LMA-device  20  when inserting the LMA-device into the patient&#39;s throat  22 . Careful insertion of the LMA-device  20  into the patient&#39;s throat  22  is required to prevent the distal region  60  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 reinforcing distal rib  105  within the distal region  60  of the inflatable main-cuff  55 . The intermediate thickness and compliancy of the reinforcing distal rib  105  allows it to follow the contours of the posterior surface of the inflated main-cuff  55 , thereby to urge the deflated main-cuff into the desired downturned orientation and to enable the LMA-device  20  present a distal end to the tissues of the throat  22  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 in  FIGS. 3 and 4 , the distal rib  105  is not readily visible when the main-cuff  55  is either deflated or inflated since it is contained within the distal region  60 . 
   In the embodiment shown in  FIG. 10 , the downturned profile the distal rib  105   a  helps to facilitate adoption by the main-cuff  55   a  of the desired downturned orientation when it is fully deflated. The distal rib  105   a  may not be readily visible because it may appear to blend in with the posterior wall of the distal region  60 . The spatulate of the distal portion of the distal rib  105   a  does not present any sharp edges or corners to the throat  22  the patient during insertion of the LMA-device  20  which is desirable as striking of the throat  22  by sharp edges or corners is normally to be avoided. 
   The acute angle  118  between the MABs  115 ,  117  and the bowl plane  106  results in the MABs presenting a substantially less gradient to the patient&#39;s epiglottis  40  than the MABs P 1  of a prior-LMA, as shown in  FIG. 8 . The MABs  115 ,  117  provide a ramp up which the epiglottis  40  slides when the backplate  52  and the attached main-cuff  55  enter the pharynx  30 . If the MABs are sufficiently posterior of the epiglottis  40 , e.g., MAB P 1 , such sliding contact may result in the proximal end of the epiglottis  40  folding over posteriorly such that it becomes sandwiched between the base of the epiglottis and the MABs possibly obstructing the airway aperture  107 . The likelihood of such posterior folding over of the epiglottis  40  is substantially reduced by the MABs  115 ,  117  because the A-P clearance between the MABs  115 ,  117  and laryngeal-side  97  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 the MABs  115 ,  117  and laryngeal-side  97 , which in turn provides increased A-P clearance between the epiglottis  40  and airway aperture  107  contained in the laryngeal-side. 
   When the main-cuff  55  and backplate  52  are installed in the pharynx  30  such that main-cuff is sealed against the tissues surrounding the patient&#39;s laryngeal inlet  45 , the reduced angle  137  between the tube-joint axis  136  and bowl plane  106 , relative to the corresponding force resulting from tube-joint P 2 , reduces the force exerted by the tube-joint  92  and airway tube  47  against the posterior surface of the throat  22 . Any force against the tissues of the throat  22  should normally be limited. 
   The reduction in the force exerted by the tube-joint  92  and airway tube  47  against the posterior surface of the throat  22  may result in a reduction in the reaction force of the main-cuff  55  against the tissues surrounding the patient&#39;s laryngeal inlet  45  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-cushion  77  which gently urges the backplate  52  and main-cuff  55  anteriorly against the tissues surrounding the patient&#39;s laryngeal inlet  45  in order to reinforce the seal between the inflated main-cuff and the tissues. 
   Additionally, the inflatable back-cushion  77  presents a more softly compliant surface to the posterior surface of the patient&#39;s throat  22 . Also, the back-cushion  77  enables the main-cuff  55  to be inflated at a lower pressure, i.e., typically 60 cm H 2 O, as compared to the inflation pressure required of the main-cuff if the LMA-device  20  does not include a back-cushion  77 . Reducing the inflation pressure of the main-cuff  55  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.

Technology Classification (CPC): 0