Abstract:
An intubating LMA construction features a rigid airway tube wherein curvature in a single plane establishes essentially an arcuate path of angular extent in the preferred range of 130°, plus or minus 5°, which I have found to be in substantial anatomical conformance with the adult human&#39;s airway path, between a proximal end of the arc at substantial register with the longitudinal midpoint of the hard palate, and a distal end that faces and is at short offset from the glottic aperture, it being understood that my findings apply to suitably quantified allowance for variations in patient-head anatomy, as is for example customary for different sizes of LMA devices, each of which is adapted to serve one of five selected patient-size ranges. The proximal end of the rigid tube is suitably a short straight portion which is tangentially and integrally related to the proximal end of the arc. And the distal end of the arc is fitted with flexible mask structure of preferably elastomeric material such as silicone rubber, wherein an internal ramp formation within the mask structure assures a limited but important measure of further and stabilized guidance of an ET which has emerged from the distal end of the rigid tube, such that unguided displacement of the ET (i.e., beyond the ramp) is oriented to target safe entry of the ET into the glottic opening.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention pertains to endotracheal-device placement in a patient requiring assured airway access, for breathing or anaesthetic purposes, for example, after the patient has lost consciousness with resulting compromise to the air passages, which can be life-threatening, if the airway access is not quickly and assuredly accomplished.  
           [0002]    Endotracheal intubation using a laryngoscope is a relatively skilled procedure and inevitably involves distortion of the anatomy in order to bring the glottis into the line of sight. In addition, an endotracheal tube (ET) is designed for ease of passage when the anatomy is thus distorted; thus, curvature of the ET does not correspond with the contours of the relaxed anatomy of the patient&#39;s upper airway. Because it is not always possible or desirable to distort the anatomy, the so-called “difficult” airway remains an important cause of mortality and morbidity in anaesthesia, in spite of a plethora of intubating aids and difficult-airway algorithms.  
           [0003]    The laryngeal mask (LMA) has found a place in this arena, but suffers from the disadvantage that its airway tube is too long and narrow to act as an acceptable conduit for intubation, in that it cannot be removed easily from the ET, once intubation has been accomplished. In addition, the mask-aperture bars (MAB) of an LMA may obstruct or deflect ET passage. Nevertheless, the LMA has the advantage that ventilation can usually be maintained, whether or not the patient can be intubated. Examples of LMA devices in prior-art patents are to be found in U.S. Pat. Nos. 4,509,514; 4,995,388; 5,241,956; 5,303,697*, 5,355,879; 5,477,851* (now Reissue patent Re. No. 35,531*); and also in pending U.S. application Ser. No. 08/826,563, filed Apr. 4, 1997*. Of these patent disclosures, those just identified by asterisk (*) deal in one way or another with various structural improvements to facilitate use of an LMA as an aid to intubation.  
           [0004]    U.S. Pat. No. 5,303,697 discloses use of an intubating LMA featuring a rigid stainless-steel airway tube with an inflatable mask at its distal end. The point of the invention was to adopt as thin as possible tube-wall thickness, for purposes of accommodating a range of ET diameters, and to enable manipulation of the placement of the distal mask. The two embodiments of this patent show curvature of the rigid tube to be of differing arcuate extent, namely, either (i) a right angle or (ii) somewhat less than a right angle; and my experience in working with either of these configurations is that distortion of the anatomy was needed, e.g., by the anesthesiologist lifting the patient&#39;s neck and extending the head to seek an accommodating non-neutral* variation of spine curvature in the neck region, in order to achieve suitable conditions for LMA placement and intubation through the LMA. Such manoeuvering has at least the disadvantages of (a) requiring full mobility of the bones of the neck, and (b) inviting neurological damage if the patient has sustained a neck injury.  
           [0005]    Brief Statement of the Invention  
           [0006]    It is an object of the invention to provide an improved LMA construction, with specific applicability to intubation of a patient with an ET or other device.  
           [0007]    Specific objects are to achieve the above object with an improved construction that features a rigid airway tube which accommodates natural anatomical curvature and:  
           [0008]    (i) in which the need for head and neck manipulation can be avoided, during mask insertion and placement and during intubation;  
           [0009]    (ii) in which the need for distortion of the anterior pharyngeal anatomy by a laryngoscope can be avoided;  
           [0010]    (iii) in which the intubating laryngeal mask, as a unit, can be self-retaining at an anatomically correct installed position, with minimum local stress on any part of adjacently contacted anatomy;  
           [0011]    (iv) in which the larynx can be “masked” by the LMA device without requiring finger-insertion into a patient&#39;s mouth;  
           [0012]    (v) in which the intubation guide is easily removable without head/neck manipulation or distortion of anterior or posterior anatomical structure;  
           [0013]    (vi) in which a more anatomically appropriate ET can be accommodated; and  
           [0014]    (vii) in which an intermediate airway is available, prior to or during intubation attempts, or following extubation under deep anaesthesia.  
           [0015]    The invention achieves the foregoing objectives and other advances in an intubating LMA construction which features a rigid airway tube wherein curvature in a single plane establishes essentially an arcuate path of angular extent in the range of 100° to 145°, a preference being indicated for the range 125° to 135° which I have found to represent normal anatomy in a neutral position; more specifically, I have found the range 125° to 135° to be in substantial anatomical conformance with the airway path of the adult human. The rigid tube extends between a proximal end of the arc—at substantial register with the longitudinal midpoint of the hard palate, and a distal end that faces and is at short offset from the glottic aperture, it being understood that my findings apply to suitably quantified allowance for variations in patient-head anatomy, as is for example customary for different sizes of LMA devices. The proximal end of the rigid tube is suitably a short straight portion which is tangentially and integrally related to the proximal end of the arc. And the distal end of the arc is fitted with flexible mask structure of preferably elastomeric material such as silicone rubber, wherein an internal ramp formation within the mask structure assures a limited but important measure of further and stabilized guidance of an ET which has emerged from the distal end of the rigid tube, such that unguided displacement of the ET (i.e., beyond the ramp) is oriented to target safe entry of the ET into the glottic opening. Stated in other words, the included angle of ET guidance by the preferred embodiment of the invention is approximately 130°, plus or minus 5°, between (a) the “launch” direction of an ET emerging from ramp guidance and (b) the orientation axis of the straight proximal-end portion of the rigid tube. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The invention will be described in detail for preferred embodiments, in conjunction with the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 is a simplified fragmentary view in side elevation and in partial section, taken in the vertical plane of symmetry, showing an intubating laryngeal mask of the invention, in schematically suggestive context of relevant-features of a patient&#39;s head/neck anatomy;  
         [0018]    [0018]FIG. 2 is a view similar to FIG. 1, to show relevant ET structure that has been guided by the device of FIG. 1; and  
         [0019]    [0019]FIG. 3 is a schematic sectional view taken at the distal end of ramp structure, provided at the distal end of ET guidance by the device of FIGS. 1 and 2, the section being taken in a plane normal to the path of ET guidance, to show ramp stabilization of the ET; and  
         [0020]    [0020]FIG. 4 is a simplified view similar to FIG. 1 to show a modification. 
     
    
     DETAILED DESCRIPTION  
       [0021]    In FIG. 1, an intubating laryngeal-mask (ILM) device  10  of the invention is shown installed in and self-retained by relevant features of a patient&#39;s oral anatomy. An anatomically curved rigid tube portion  11  of device  10  is suitably of bent stainless-steel tubing which may be of 13-mm minimum internal diameter, in order to accept insertion of a cuffed 8-mm endotracheal tube (ET). The curved portion  11  is suitably conformed to a circular arc a of preferably 130°±5°, extending from a proximal limit  12  of tube curvature to a distal limit  13  of tube curvature, the curvature being along a central axis  14  of airway passage and in a first (or vertical) geometric plane of symmetry; the maximum or outer radius R 1  of tube ( 11 ) curvature is suitably 41.5 mm, for use by a large fraction of the adult population, for whom the minimum or inner radius R 2  of curvature is about 27 mm.  
         [0022]    At the proximal limit  12  of curved portion  11 , a straight proximal end portion  15  is an integrally formed part of the same tubing, having tangential connection to the proximal end of the arc at location  12 , which is in register with substantially the longitudinal mid-point of the patient&#39;s hard palate, labeled HP in the drawing. The outer radius R 1  of curved portion  11  is shown to substantially conform to concave curvature of the patient&#39;s soft palate (SP), as also labeled in the drawing; and the inner radius R 2  of curved portion  11  will be understood to conform to convex curvature of the back of the patient&#39;s tongue (not shown).  
         [0023]    At the distal end  13  of the curved portion  11  of the rigid tube, the central axis  14  of the airway path determined by the tube is directed toward the laryngeal inlet and is in the above-noted first or vertical plane of symmetry, said distal-end limit being at the upper region of the pharynx and at considerable offset from the intended target of ET entry into the glottic aperture, but laryngeal-mask structure  20  carried by the distal end of the rigid tube is internally configured to extend and laterally stabilize the guidance of an inserted ET, for greater assurance of the targeted entry.  
         [0024]    The laryngeal-mask structure  20  is of flexibly yieldable elastomeric material, wherein relative thickness determines the relative stiffness or weakness of compliant deformability. Basically, structure  20  comprises a relatively stiff backing plate formation  21  having an inlet-air counterbore formation (shown, but not marked) of arcuately curved extent δ which accounts for telescopic reception and bonding of mask structure  20  to the distal end of tube  11 . As shown, the arcuate extent δ of telescopic fit is 20° to 25°, which is sufficient to assure a circumferentially sealed fit and also to fully provide enclosure of a truncated radially inner-end portion of the rigid tube, the truncation being identified  22  in the drawing.  
         [0025]    As with prior laryngeal masks, the backing plate will be understood to terminate in a generally elliptical rim of attachment to a peripherally continuous and softly compliant ring formation which, in the preferred form shown is an inflatable ring  23  having means  24  of control connection for air-inflation/deflation purposes. The elliptical rim and ring  23  will be further understood (a) to have lateral symmetry about the vertical plane of symmetry and (b) to lie generally in a second geometric plane  25  which is normal to the first or vertical plane.  
         [0026]    Within the backing plate  21 , the airway passage of the rigid tube  11  is seen to be effectively extended by a ramp formation  26  of V-section and of progressively increasing depth, beginning at substantially tangential relation to the adjacent end of the tube bore at the outer radial limit (R 1 ) of rigid tube curvature; by reason of its sectional symmetry about the above-noted first geometric plane of symmetry, ramp formation  26  will be seen to serve the dual purpose of stabilizing an ET in the course of its insertional advance beyond the distal end of tube  11 , while at the same time providing a substantially shortened offset distance for otherwise unsupported projection of the distal end of an ET, beyond the distal end of ramp formation  26 , for better-controlled targeting of ET entry into the glottic opening. FIG. 3 schematically illustrates stabilizing support for an insertionally advancing ET, wherein the Vee of ramp  26  is seen to provide side walls  26 ′ which symmetrically diverge from the central plane of symmetry, the included angle of Vee spread between the walls of ramp formation  26  being suitably in the range 150° to 165°.  
         [0027]    The thus-extended advancing guidance of ET insertion is also seen in the drawing to involve ET encounter with a compliantly and effectively hinged tongue formation  27  which may be an integral formation of backing plate  21 , but which has been shown with a different direction of cross-hatching, for better identification of parts in the drawing. Tongue formation  27  will be understood to have lateral symmetry about the first geometric plane of symmetry and to be of lateral extent which is less than the bore diameter of tube  11 , thus permitting free airway communication to the glottis and through device  10 , once ring  23  has been inflated to develop a seal around the laryngeal inlet. However, the compliant hinging of tongue  27  at  28 , on an effective hinge axis in plane  25  and perpendicular to the first geometric plane, enables an advancing ET to drive tongue  27  (clockwise, in the sense of the drawing) for deflecting the patient&#39;s epiglottis  30  out of the path of the ET as it advances toward the targeted glottic opening.  
         [0028]    It will be seen that in general terms, the fact of ET clearance within the inside diameter of the rigid airway tube necessarily means that at exit from the rigid tube, the ET may be at minor misalignment with resepct to the orientation of the central axis  14  at the distal or exit end of the rigid tube; however, the existence and action of the described ramp  26  are such not only to assure ET-centering between opposed ramp walls  26 , but also to effect such a ramped deflection of the ET (at ET exit from the ramp) as to substantially offset, minimalize, or correct for the minor misalignment noted at ET exit from the distal end of rigid tube  10 . Thus, at launch from the exit end of the ramp, the ET can be more assuredly projected for targeted entry into the glottic opening.  
         [0029]    Description of the device of FIG. 1 is completed by identification of a rigid handle  35 , secured to the externally projecting proximal end portion  15  of the rigid airway tube  10 ; handle  35  (preferably sufficiently malleable to enable a technician to adjust handle orientation to suit his individual preference) serves for manual manipulation of tube  10  and its distal mask structure  20 ; and it will be understood that the open proximal end of portion  15  is adapted by means of an inwardly tapered contour  15 ′ to fit standard ventilating or anaesthetizing equipment for accessing the patient&#39;s lungs, as needed. Further preference is indicated for an elastomeric cladding or coating of tube  10 , as suggested by cross-hatching  36  in FIG. 1.  
         [0030]    In use, the device  10  is grasped via handle  35 , and the inflatable ring  25  is deflated to define a suitably flexible lip which will smoothly adapt to the patient&#39;s airway, as device  10  is being inserted. Once the flexible lip enters the mouth, it naturally and flexibly adapts to hard-palate and soft-palate curvatures on its way to the pharynx, and the truncation  22  of the distal end of the rigid tube enables flexed compression of the mask/tube junction for ease of passage through a narrowed inter-dental gap. In the course of such insertion, it will be appreciated that manipulation of the straight proximal end  15  undergoes a bodily angular displacement (clockwise, in the sense of FIG. 1) about the center C of arcuate portion  11 , as said portion  11  is sensed to be in very substantial conformance with the patient&#39;s oral anatomy, all the way to the pharynx, thus positioning the distal orientation of tube- 11  exit in near-register with the glottic opening. The limit of such angular displacement occurs when the straight proximal end  15  abuts upper tooth structure, e.g., the patient&#39;s incisors ( 33 ). This event will be recognized as a stop whereby to know that insertion has been completed as far as needed, and ring  23  may be immediately inflated, to establish a peripherally sealed adaptation at and surrounding the laryngeal inlet, with ramp ( 26 ) oriented for immediate insertion of an ET device, it being noted that, once ring  23  has been inflated to establish its seal to and around the laryngeal inlet, airway access to the patient&#39;s lungs has been provided. On exit from ramp ( 26 ) guidance, further displacement of the ET device encounters the compliantly hinged tongue  27 , to assure that the epiglottis is lifted out of possible encounter with the advancing ET device, as seen in FIG. 2 for the ET device  32 . When the ET device has entered the glottic opening, it can pass the vocal cords and be sealed by inflation of its cuff, as is customary.  
         [0031]    After the ET has been sealed in its installed position, the ET can accommodate all patient-ventilating/anaesthetizing purposes. In some clinical circumstances, the intubating laryngeal mask (ILM) can be left in place during the procedure. When the patient has had all use that is needed for the ET, and after its seal cuff has been deflated, ET removal is then a simple matter of extraction via the guide passage established by mask  20 . After ET extraction, the device of FIGS. 1 and 2 may then resume its patient-ventilating function, with the hinged tongue  27  compliantly returning to its position of FIG. 1, whereby to avoid epiglottis blocking of the airway; and a resumed intermediate airway can be established for patient ventilation. This procedure may be appropriate when extubation is judged to be best performed while the patient is still under deep anaesthesia. However it is also possible and sometimes desirable to remove the ILM while the ET remains in place. In this case, the ET cuff remains inflated and the ILM cuff is deflated prior to removing the device, following the same circular arc as is followed for insertion. To prevent accidental ET dislodgement, the ET is meanwhile held in place by counterpressure supplied by a short flexible rod abutting against the outer end of the ET as the metal tube is slid over it.  
         [0032]    It has been indicated above that, for most cases, a single rigid tube  10  may well serve patients for whom different elastomeric distal-mask components may be fitted, thus serving patients having different oral-cavity geometries and proportions. In some cases, however, and in particular for a patient who can be readily recognized as having an unusually long neck, it is recommended to follow the described rigid-tube configuration of FIGS.  1  to  3 , subject to a single modifying departure, at the tube location at which a tangent to the convex outer profile of the tube is locally parallel to (or near-parallel to) the alignment of the patient&#39;s vertebrae. Such a condition is illustrated in FIG. 4, wherein the arcuate extent a of rigid tube  10  is seen to have been divided into a first and larger proximal arc α 1  about a first center C 1 , and a second and shorter distal arc α 2  about a second center C 2 . Radius of curvature is the same for both arcs α 1  and α 2 , and the centers C 1  and C 2  are on a geometric alignment that is essentially parallel to the alignment of locally adjacent vertebrae. Thus, a straight section  37  is effectively aligned essentially parallel to the alignment of adjacent vertebrae, and this straight section  37  is integrally and tangentially united with the adjacent ends of the arcs α 1  and α 2 . In FIG. 4, all other structural features of FIGS. 1 and 2 apply, as described above.  
         [0033]    It is noted that the laryngeal opening into and through which the described intubating laryngeal mask provides guided entry is a relatively tolerant anatomical feature for the human adult, in that in terms of a geometric direction suggested by downward extension of line  12  in FIGS. 1 and 2, there is a span between an upper limit established by the epiglottis and a lower limit associated with arytenoid cartilages, wherein said span may extend, typically approximately 20-mm, for target acceptance by the laryngeal opening of an ET launched from the described mask structure. What is accomplished by the structure of FIG. 4 is a predetermined (illustratively 10-mm) further downward offset of the ET-launch point, for the case of a person having a recognized longer-than-usual neck, it being understood that such recognition can be readily deduced from external observation of the patient&#39;s “Adam&#39;s apple” in relation the patient&#39;s maxillary structure.  
         [0034]    The described intubating laryngeal-mask devices will be seen to meet all stated objects. Mask removal follows deflation of ring  20 , followed by an extraction manoeuver wherein the straight proximal portion undergoes counterclockwise bodily displacement about the center C. As long as the patient has first been supported in supine position, as with a suitable pillow to assure a “neutral” orientation of the upper region of his spine (i.e., adjacent regions of his head, neck and body), there is no need to manipulate the spine, i.e., the patient&#39;s head with respect to his body, either in the course of mask insertion/removal or in the course of ET insertion/removal, thus assuring minimum risk to a patient whose spine has been injured, and thus also removing the major cause of difficulty in intubation of the trachea when immobility of the neck makes it difficult to use a laryngoscope to locate the glottis.  
         [0035]    A significant feature of the present invention is the fact that a single manufactured size of the rigid airway tube  10 , of bent tubing having a minimum inner diameter of 13-mm, with its arcuate extent in the range 130° plus or minus 5°, and at a minimum outer radius (R 1 =41.5 mm) about a common center (C), can be assembled with a selected one of three standardized distally fitted LMA inflatable-mask sizes, namely, a selected one of the sizes 3, 4 and 5 which have become standardized on the following basis:  
         [0036]    Size 3, for children and small adults, weighing in the range 30 to 50 kg;  
         [0037]    Size 4, for adults weighing in the range 50 to 70 kg; and  
         [0038]    Size 5, for adults weighing more than 70 kg.  
         [0039]    From the point of view of manufacturing economy, this circumstance portends satisfying anatomy requirements of the vast majority of patient&#39;s requiring intubation, all using the same size rigid tubing, but fitted with different selected distal inflatable mask sizes, selected from the indicated grouping.  
         [0040]    It is also possible that similar economies of rigid airway tube ( 10 ) construction can be achieved for remaining standardized LMA sizes, namely, sizes 1, 1.5, 2, and 2.5.