US20120145160A1 - Laryngeal mask airway device - Google Patents

Abstract

The invention relates to a laryngeal mask airway device (1) for insertion into a patient to provide an airway passage to the patient's glottic opening, the device (1) comprising an airway tube (2), a mask (3) attached to the airway tube (2), the mask (3) comprising a body (4) having a distal end (5) and a proximal end (6), a peripheral inflatable cuff (7), and defining an outlet (8) for gas, the mask (3) being connected to the airway tube (2) for gaseous communication between the tube (2) and the mask, the distal end of the mask being ventrally displaced, relative to the proximal end.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 11/915,557, filed on Nov. 26, 2007, which claims priority to a PCT Application No. PCT/GB2006/001908, filed on May 24, 2006, which also claims the benefit to priority of United Kingdom Patent Application No. 0510951.7, filed on May 27, 2005, the disclosures of which are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
• 1. Field of the invention
• The present invention relates to a laryngeal mask airway device.
• 2. Description of Related Art Including Information Disclosed under 37 C.F.R. 1.97 and 1.98
• The laryngeal mask airway device is a well known device that is useful for establishing airways in unconscious patients. U.S. Pat. No. 4,509,514 is one of the many publications that describe laryngeal mask airway devices. Such devices have been in use for many years and offer an alternative to the older, even better known endotracheal tube. For at least seventy years, endotracheal tubes comprising a long slender tube with an inflatable balloon disposed at the tube's distal end have been used for establishing airways in unconscious patients. In operation, the endotracheal tube's distal end is inserted through the mouth of the patient, past the patient's trachea. Once so positioned, the balloon is inflated so as to form a seal with the interior lining of the trachea. After this seal is established, positive pressure may be applied to the tube's proximal end to ventilate the patient's lungs. Also, the seal between the balloon and the inner lining of the trachea protects the lungs from aspiration (e.g., the seal prevents material regurgitated from the stomach from being aspirated into the patient's lungs).
• Although they have been enormously successful, endotracheal tubes suffer from several major disadvantages. The principal disadvantage of the endotracheal tube relates to the difficulty of properly inserting the tube. Inserting an endotracheal tube into a patient is a procedure that requires a high degree of skill. Also, even for skilled practitioners, insertion of an endotracheal tube is sometimes difficult or not possible. In many instances, the difficulty of inserting endotracheal tubes has tragically led to the death of a patient because it was not possible to establish an airway in the patient with sufficient rapidity. Also, inserting an endotracheal tube normally requires manipulation of the patient's head and neck and further requires the patient's jaw to be forcibly opened widely. These necessary manipulations make it difficult, or undesirable, to insert an endotracheal tube into a patient who may be suffering from a neck injury.
• In contrast to the endotracheal tube, it is relatively easy to insert a laryngeal mask airway device into a patient and thereby establish an airway. Also, the laryngeal mask airway device is a “forgiving” device in that even if it is inserted improperly, it still tends to establish an airway. Accordingly, the laryngeal mask airway device is often thought of as a “life saving” device. Also, the laryngeal mask airway device may be inserted with only relatively minor manipulation of the patient's head, neck and jaw. Further, the laryngeal mask airway device provides ventilation of the patient's lungs without requiring contact with the sensitive inner lining of the trachea and the size of the airway established is typically significantly larger than the size of the airway established with an endotracheal tube. Also, the laryngeal mask airway device does not interfere with coughing to the same extent as endotracheal tubes. Largely due to these advantages, the laryngeal mask airway device has enjoyed increasing popularity in recent years.
• U.S. Pat. Nos. 5,303,697 and 6,079,409 describe examples of prior art devices that may be referred to as “intubating laryngeal mask airway devices.” The intubating device has the added advantage that it is useful for facilitating insertion of an endotracheal tube. After an intubating laryngeal mask airway device has been located in the patient, the device can act as a guide for a subsequently inserted endotracheal tube. Use of the laryngeal mask airway device in this fashion facilitates what is commonly known as “blind insertion” of the endotracheal tube. Only minor movements of the patient's head, neck and jaw are required to insert the intubating laryngeal mask airway device, and once the device has been located in the patient, the endotracheal tube may be inserted with virtually no additional movements of the patient. This stands in contrast to the relatively large motions of the patient's head, neck and jaw that would be required if the endotracheal tube were inserted without the assistance of the intubating laryngeal mask airway device. Furthermore, these devices permit single-handed insertion from any user position without moving the head and neck of the patient from a neutral position, and can also be put in place without inserting fingers in the patient's mouth. Finally, it is believed that they are unique in being devices which are airway devices in their own right, enabling ventilatory control and patient oxygenation to be continuous during intubation attempts, thereby lessening the likelihood of desaturation.
• Artificial airway devices of the character indicated, are exemplified by the disclosures of U.S. Pat. No. 4,509,514; U.S. Pat. No. 5,249,571; U.S. Pat. No. 5,282,464; U.S. Pat. No. 5,297,547; U.S. Pat. No. 5,303,697; and by the disclosure of the UK Patent 2,205,499. Such devices with additional provision for gastric-discharge drainage are exemplified by U.S. Pat. No. 4,995,388 (FIGS. 7 to 10); U.S. Pat. No. 5,241,956; and U.S. Pat. No. 5,355,879.
• In general, laryngeal mask airway devices aim to provide an airway tube of such cross-section as to assure more than ample ventilation of the lungs, and the designs with provision for gastric drainage have been characterized by relatively complex internal connections and cross-sections calculated to serve in difficult situations where substantial solids could be present in a gastric discharge. As a result, the provision of a gastric discharge opening at the distal end of the mask applicable for direct service of the hypopharynx has resulted in a tendency for such masks to become bulky and unduly stiff, thus making for difficulty in properly inserting the mask. Moreover, undue bulk and stiffness run contrary to the requirement for distal flexibility for tracking the posterior curvature of the patient's throat on insertion, in such manner as to reliably avoid traumatic encounter with the epiglottis and other natural structures of the pharynx.
• A number of problems have been experienced with all of these prior types of device. For example, some prior devices seek to prevent occlusion of the airway outlet by parts of the patient's anatomy, such as the epiglottis, by the provision of bars and the like across the outlet. Although such devices function well in most cases, they can make manufacturing more complex, and can affect the performance of devices in use. This is especially so in devices formed from relatively rigid materials, like PVC, as opposed to the more traditional Liquid Silicon Rubber (LSR).
• In general, devices formed from materials such as PVC are attractive because they are cheaper to make, and can be offered economically as “single-use” devices. However, there are material differences in PVC and PVC adhesives, such as increased durometer hardness as compared to LSR, which affect how the devices perform in use. For example, it has been observed that for a given volume of air, an LSR cuff will expand to a larger size than a comparable PVC cuff. This superior elasticity allows the LSR cuff to provide an anatomically superior seal with reduced mucosal pressure. To close the performance gap, the PVC cuff must be of reduced wall thickness. However, a PVC cuff of reduced wall thickness, deflated and prepared for insertion, will suffer from poor flexural response as the transfer of insertion force through the airway tube to cuff distal tip cannot be adequately absorbed. The cuff assembly must deflate to a thickness that preserves flexural performance i.e. resists epiglottic downfolding, but inflate so that a cuff wall thickness of less than or equal to 0.4 mm creates a satisfactory seal. And where mask backplates are formed from PVC, as well as cuffs, the fact that the increased durometer hardness of PVC is inversely proportional to flexural performance (hysterisis) means that the flexural performance of the device in terms of reaction, response and recovery on deformation is inferior to a comparable LSR device.
• The above described problems are particularly acute in devices which incorporate an oesophageal drain. As mentioned above, in any such device regardless of the material from which it is formed, adding an oesophageal drain in itself adds greatly to complexity of manufacture and can also affect the performance of devices, in terms of ease of insertion, seal formation and prevention of insufflation. These problems can be exacerbated still further if PVC or similarly performing materials are used. For example, the skilled worker will appreciate that in terms of manufacture, the need to provide a drain tube which is sealed from the airway, and which must pass through the inflatable cuff poses a particularly difficult problem. In terms of effects on functionality, the provision of a drain tube can cause unacceptable stiffening of the mask tip area and occlusion/restriction of the airway passage.
BRIEF SUMMARY OF THE INVENTION
• According to the invention there is provided a laryngeal mask airway device for insertion into a patient to provide an airway passage to the patient's glottic opening, the device comprising an airway tube, a mask attached to the airway tube, the mask comprising a body having a distal end and a proximal end, a peripheral inflatable cuff, and defining an outlet for gas, the mask being connected to the airway tube for gaseous communication between the tube and the mask, the distal end of the mask being ventrally displaced, relative to the proximal end. It has been surprisingly found that a ventral displacement of the tip makes insertion of the mask much easier because the tip is presented at an optimum angle as it tracks around the curvature of the airway anatomy.
• It is preferred that the extent of distal displacement is from about 5 mm to about 20 mm, and it is most preferred that the extent of distal displacement is about 10 mm. This has been found to be the optimum range. It has been found that if the extent of displacement is too great, the device will not lie in the correct position at its maximum extent of insertion.
• It is preferred that the body describes a substantially convex curve, from the proximal to distal end. It is further preferred that the mask body comprises a plate, the plate having a dorsal side and a ventral side, the dorsal side being substantially smooth and having a convex curvature across its width. It is also preferred that the dorsal surface of the airway tube corresponds in curvature to the curvature across the width of the plate. All of these expedients assist in making insertion of the mask easier.
• The airway tube preferably comprises a relatively more rigid material than the mask body. Both the airway tube and the mask body preferably comprise a plastics material.
• The device may further including an oesophageal drain tube, and the oesophageal drain tube may be disposed on the ventral side of the body, in order to maintain a smooth profile on the dorsal side, to make insertion easier.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention will further be described by way of example and with reference to the following drawings, in which,
• FIG. 1 is a dorsal three quarter perspective view of a device according to the invention;
• FIG. 2 is a right side view of the device ofFIG. 1;
• FIG. 3 is a dorsal view of the device ofFIG. 1;
• FIG. 4 is a ventral view of the device ofFIG. 1;
• FIG. 4ais a ventral view of a further embodiment of device according to the invention;
• FIG. 5 is an end view, looking from the proximal towards the distal end of the device ofFIG. 1;
• FIG. 6 is an end view, looking from the distal towards the proximal end of the mask of the device ofFIG. 1;
• FIG. 7 is an enlarged view of the mask of the device ofFIG. 1;
• FIG. 8 is a dorsal view of the device ofFIG. 4a;
• FIG. 9 is a longitudinal sectional view along line Y-Y inFIG. 8;
• FIG. 10 is a side view, enlarged, of the device ofFIG. 4a;
• FIGS. 11A to 11K are transverse sectional views along lines A-A to K-K inFIG. 10;
• FIG. 12 is an exploded dorsal perspective view of a device according to the invention;
• FIG. 13 is an exploded ventral perspective view of a device according to the invention;
• FIG. 14 is a dorsal three quarter perspective view of a device according to the invention;
• FIG. 15 is a right side view of the device ofFIG. 14;
• FIG. 16 is a dorsal view of the device ofFIG. 14;
• FIG. 17 is a ventral view of the device ofFIG. 14;
• FIG. 18 is an end view, looking from the proximal towards the distal end of the mask of the device ofFIG. 14;
• FIG. 19 is an end view, looking from the distal towards the proximal end of the mask of the device ofFIG. 14;
• FIG. 20 is a dorsal three quarter perspective view of the device ofFIG. 14;
• FIG. 21 is a view of section CC-CC inFIG. 20;
• FIG. 22 is a view of section VC-VC inFIG. 17;
• FIG. 23 is a proximal end view of a part of the device ofFIG. 14; and
• FIG. 24 is a distal end view of a part of the device ofFIG. 14.
DETAILED DESCRIPTION OF THE INVENTION
• Referring now to the drawings, there is illustrated a laryngealmask airway device1 for insertion into a patient to provide an airway passage to the patient's glottic opening, thedevice1 comprising anairway tube2, a mask3 attached to theairway tube2, the mask3 comprising abody4 having a distal end5 and a proximal end6, a peripheralinflatable cuff7, and defining an outlet8 for gas, the mask3 being connected to theairway tube2 for gaseous communication between thetube2 and the mask, the distal end of the mask being ventrally displaced, relative to the proximal end.
• In this embodiment thedevice1 further comprises anoesophageal drain10, thedrain10 comprising aconduit11 extending from anopening12 at the distal end5 to a drain outlet13 disposed to the outside of the patient when thedevice1 is in place, wherein theconduit11 is formed integrally in the material of thebody4.
• As can be seen from the drawings, thedevice1, in terms of overall appearance is somewhat similar to prior art devices, in that it consists of the basic parts which make up most if not all laryngeal mask airway devices, i.e. anairway tube2 and mask3 which includes abody part4, and acuff7.
• For the purposes of description it is appropriate to assign reference names to areas of thedevice1 and accordingly with reference toFIGS. 2 to 6, thedevice1 has adorsal side14, aventral side15, a proximal end16 (in a sense that this is the end nearest the user rather than the patient) adistal end17 and right and leftsides18 and19.
• Referring firstly to theairway tube2, in the illustrated embodiments the tube comprises a relatively rigid PVC material such as a shore 90A Colorite PVC moulded into an appropriately anatomically curved shape. Thetube2 has some flexibility such that if it is bent it will return to its original shape. Although it is resiliently deformable in this way, it is sufficiently rigid to enable it to assist in insertion of thedevice1 into a patient, acting as a handle and guide. In this embodiment theairway tube2 does not have a circular cross-section as in many prior devices, but instead is compressed in the dorsal/ventral direction which assists in correct insertion of thedevice1, helps prevent kinking, and assists in comfortable positioning for the patient as the shape generally mimics the shape of the natural airway. In this embodiment eachside18,19 of theairway tube2 includes a groove orchannel20 extending for most of the tube's length from the proximal to distal ends. Thesegrooves20 further assist in preventing crushing or kinking of theairway tube2. Internally thegrooves20 form ridges along the inner surfaces of thesides18 and19.
• Referring now toFIG. 13, which shows an exploded view of thedevice1, it can be seen that theairway tube2 includes a flareddistal end22 withsurfaces22adisposed to allow for attachment of thetube2 to the mask3, conveniently by over moulding of the mask3 onto theairway tube2. Thus, theairway tube2 itself can form a pre-mould used in formation of thedevice1, which substantially simplifies manufacturing. Of particular note is the airway tube's dorsal mould surface23 (FIG. 13). Thissurface23 is located at the flareddistal end22, and takes the form of a flat land extending between the outer dorsal surface2aand the inner dorsal surface2b(FIG. 24) of the dorsal wall2c.It includes optional through holes2dto allow the over moulded backplate4 to lock onto thetube2, as will be described later on. This feature helps ensure a secure connection between the different materials making up theairway tube2 and mask3.
• A further feature of theairway2 is theoesophageal drain tube41. Thisdrain tube41 is located withinairway tube2, extending centrally through it from one end to the other, and in this embodiment it is disposed in contact with the inner surface2aof the dorsal wall2bof theairway tube2, and bounded on each side by raised, smooth walls (not shown) which form a shallow channel through which it runs.
• The proximal end of theairway tube2 is provided with aconnector42, for connection of thedevice1 to a gas supply and drain (not shown) as shown for example inFIGS. 12 and 13 and in section inFIG. 9. Theconnector42 comprises aconnector body43, anoptional bite block44 and aconnector plug45. Theconnector body43 andbite block44 correspond in shape and dimension with the internal shape of the proximal end of theairway tube2 such that they fit inside it. Theconnector body43 has a perpendicularly extendingperipheral flange46 which extends at one point on its circumference into atab47.Connector plug45 attaches toconnector body43 by adhesive or other suitable means applied toflange46. Theconnector plug45 comprises major andminor bores48,49 which both lead into acommon atrium50 at the distal end of theconnector plug45 where it attaches to theconnector body43.Drain tube41 extends into and throughminor bore49, such that the bore of theairway tube2 and the bore of thedrain tube41 are separated from one another.
• Turning now to the mask3, the mask3 consists of two parts, abody part4 often referred to as a back plate, and aperipheral cuff7.
• Theback plate4 is formed in these embodiments by moulding from a shore 50A Vythene PVC+PU. This material is substantially softer and more deformable than the material ofairway tube2.
• Referring now toFIG. 23, theback plate4 comprises a generally oval moulding when viewed from the dorsal or ventral directions, having a smoothdorsal surface24, a formedventral surface24a(FIG. 17), a proximal joining portion24b,and adistal tip61.
• Thedorsal surface24 has a convex curvature from one side to the other, corresponding to the curvature of the dorsal surface of theairway tube2, and longitudinally, thedorsal surface24 is also curved, having a curvature beginning at the joining portion24band extending with constant rate of curvature toward thedistal tip61. As a result thetip61 is ventrally biased relative to the distal end of the airway tube, in the assembleddevice1, the extent of displacement of thedistal tip61 being approximately20 mm or10 degrees, in order to produce a curvature in the mask that is suited to the anatomy of the patient. This is shown schematically at X inFIG. 2. On insertion, this displacement of thetip61 assists the mask in “turning the corner” in the insertion path.
• When viewed from the ventral side, the integrally moulded structures of theback plate4 can best be seen (FIGS.4,7,12,17). The precise shape of theventral side24aof the back plate is illustrated particularly in the sectional views shown inFIGS. 11A to 11K and in the enlarged perspective view inFIG. 7. Referring to the exploded view shown inFIG. 12, the convex curvature of thedorsal surface24 of theback plate4 is mirrored in a corresponding concave curvature on the ventral side. Thus, theventral surface24aforms a shallow, elongate channel tapering towards thedistal tip61. The channel is bounded bywalls26. Thewalls26 have correspondingly shaped, longitudinally extending convex outer surfaces25. Eachwall26 extends longitudinally substantially the entire length of theback plate4 from the proximal joining portion24btowards thedistal tip61. Eachwall26 also has a convexinner surface28, but rather than terminating at an angle normal to the channel floor, the curve of eachwall26 is continued, the walls curving back over the channel and terminating in inwardly extending webs27 (FIGS. 7 and 11). Theinner surfaces28 of theside walls26 curve down to form the floor of the channel but do not meet, because the base or floor of the channel is bisected by a longitudinally extending, integrally moulded conduit which is anoesophageal drain tube11 extending along it for its entire length from joining portion24btodistal tip61. Thus, it can be seen that the channel has three longitudinally extending conduits on its inner surface, the two openouter conduits28awhich are minor gas conduits in the assembleddevice1, and thecentral drain tube11, which forms a septum there between.
• Referring now in greater detail to thedrain tube11, it will be seen that thetube11 has a sufficient diameter such that its upper wall section11a,i.e. the wall section furthest from the floor of the channel, is on a similar level with the inwardly extendingwebs27 of theside walls26. Furthermore, the upper wall section11aitself also has outwardly extendingwebs30, which taper toward, but do not meet, the correspondingly tapered edges of thewebs27. Thus, the upper surface11bof the upper wall section11aof thedrain tube11, and thewebs27,30, together define asurface11cshown schematically by a dotted line inFIG. 11), below the level of which run all threeconduits11,28a.
• Referring now particularly toFIG. 7, it can be seen that although thedrain tube11 extends the full length of theback plate4 from its proximal joining portion24btodistal tip61, theconduits28ado not extend the full length of theback plate4, but instead terminate about half way along its length. Thefloors31 of theconduits28acurve gently upwards as they extend towards thedistal tip61 of theback plate4 until they terminate at a level approximately equal to the level of thewebs27 and30. In the embodiment shown inFIG. 4a, these areas are hollowed out to form depressions31b.
• As illustrated inFIG. 12 andFIGS. 21 to 23,drain tube11 extends todistal tip61, terminating in anopening12. Thus, an end section11eof thedrain tube11 protrudes past the end ofback plate4. This end section11eis provided with dorsal webbing11awhich extends to either side of it, and around it to form a hood orpocket36awhich encloses the end section11earound its circumference. The hood orpocket36ais attached to the distal end of thedrain tube11 around thecircumference12aof opening12 (FIG. 22). This hood orpocket36ais integrally formed in the material of theback plate4 atdistal tip61. It completely surrounds and extends from the circumference of thedrain tube opening12 and the joint therebetween is smooth. As illustrated, the ventral extent of the hood is more limited than the dorsal extent, the dorsal extent being to about midway back towards the proximal end of theback plate4. Referring to sectional views A-A and B-B inFIG. 11, it can be seen that thedrain tube11 is supported on its right and left sides, and on its dorsal surface, by perpendicularly extendingwebs62. Thesewebs62 are integrally formed, and extend back from theopening12 to the point where the end section11emeets the extent of theback plate4. In the illustrated embodiment thedorsal webs62 extend substantially perpendicularly from the drain tube, but in a preferred embodiment, they may extend to one side or the other, at an angle of less than 90 degrees.
• The second part of the mask3 is theperipheral cuff7. Thecuff7 is in this embodiment blow moulded PVC and takes the form of a generally elliptical inflatable ring having a central aperture7a,a relatively deeper proximal end37 with aninflation port38 and a relatively shallower distal end7btapering to a “wedge”profile39. As will be appreciated, particularly from the exploded views shown inFIGS. 12 and 13, thecuff7 is integrally formed in one piece. The wedge profile is provided such that the ratio of dorsal to ventral side surface areas favours the dorsal side. Thus, when deflated the distal end7bof thecuff7 will curl with bias from dorsal to ventral side.
• In the assembleddevice1,drain tube41 is inserted intoairway tube2, such that it protrudes fromproximal end16. Theconnector42 is attached to theairway tube2 by inserting theconnector body43 andbite block44 intoproximal end16. The parts are an interference fit and can be secured by adhesive.Plug45 is attached toconnector body43 viaflange46, such thatdrain tube41 passes intominor bore49, terminating at or adjacent its mouth. Thus it will be seen that the minor bore49 is solely in fluid communication withdrain tube41, and themajor bore48 is solely in fluid communication with the interior ofairway tube2.
• Airway tube2 is attached to theback plate4 conveniently by overmoulding theback plate4 onto the already formedtube2. Thus, the joining portion24bof theback plate4 is moulded onto the dorsal arc of the airway tube2 (FIG. 13). Secure attachment is facilitated by thesurfaces22a,23 which provide an increased surface area onto which the moulding occurs, and through-holes2d,into which back plate material can flow.Drain tube41 is connected in fluid tight manner to integrally mouldeddrain11, as demonstrated by arrow Z (FIG. 13).
• Thecuff7 is bonded to theback plate4 as illustrated inFIGS. 12 and 13 by inserting the wedge shaped distal end7bof thecuff7 into the hood orpocket36aat thedistal tip61 of theback plate4 such that thewedge surface39 mates with the inner surface36bof thehood36a, and sections of the inner periphery of thecuff7 mate with convexouter surfaces25 ofback plate walls26. Thecuff7 is bonded into the hood such that the space between the hood and the cuff is airtight and in this embodiment the cuff is provided with a “pinch off”40 (FIGS. 21 and 22) putting thecuff7 andhood36ainto fluid communication so that the air space in the hood can also be inflated, in addition to thecuff7 itself However thecuff7 pinch off does not extend the entire distance towards the distal tip of the cuff to prevent the pressure of inflation occluding theopening12. The proximal dorsal surface of the cuff is bonded to the ventral arc of thedistal end22 of theairway tube2. Thus, it will be appreciated that unlike in previous devices incorporating oesophageal drains, in the invention thedrain11 does not pierce thecuff7, making manufacturing simpler. Furthermore, in prior devices in which the drain pierces the cuff, the cuff must be securely attached around the circumference of the drain tube at the distal tip. Such a secure attachment, for example with adhesive, can make the tip hard, and prevent the drain tube collapsing in the deflated, flattened device, which is highly desirable to enable the mask to pass easily around the curvature of the anatomy. In addition, the acute curvature of a drain tube to cuff joint would be highly susceptible to cracking In the invention, these problems are avoided because thedrain tube11 is integrally moulded with thehood36a,which in effect forms a second or minor cuff at the distal tip.
• As will be appreciated, the airway of thedevice1, which is the conduit through which gas is passed to the patient, is provided by the bore ofairway tube2, which terminates at flareddistal end22. Flareddistal end22 defines, along withback plate4 andcuff7, outlet8 for gas passing fromtube2 into mask3. Outlet8 includes three routes by which gas may pass into the mask, namely a main gas conduit8a(FIG. 6), and twominor gas conduits28a.
• In use, the deflateddevice1 is inserted into a patient in the usual manner with devices of this type. As noted above, the relative rigidity of theairway tube2 allows a user to grip it and use it to guide thedevice1 into the patient, whilst the relatively softer, more compliant material of the back plate means that the mask will more readily deform to negotiate the insertion path without causing damage to the anatomy, and will return to its optimum shape to ensure that a good seal is achieved at the furthest extent of insertion. The ventral displacement of thedistal tip61 relative to the join between theback plate4 andairway tube2 further enhances ease of insertion, because thedistal tip61 is thereby presented at the optimum angle to negotiate the “bend” in the insertion path. In devices formed from relatively rigid materials such as PVC, as opposed to the often used LSR these features are particularly important in easing insertion and providing for an enhanced seal.
• Referring now to the features of the moulded backplate4, it will be seen that by providingdrain tube11 integrally moulded in the material of theback plate4, problems of mask stiffness and difficulty of manufacture in prior designs caused by the presence of a separate drain tube bonded in place with adhesive can be mitigated.
• Moreover, with theback plate4 of the invention, the combination of the centrally locateddrain tube11 andminor gas conduits28aassist in solving the problem of occlusion of the airway by parts of the patient's anatomy. Theminor gas conduits28acan be thought of as “nostrils” through which gas may continue to pass into the patient even if the main outlet8abecomes occluded by, for example the patient's epiglottis, as the epiglottis will rest upon the septum provided by thedrain tube11. As illustrated particularly inFIGS. 11I and 11J thewebs27,30 form a partial closure over theconduits28a,to assist in preventing structures such as the epiglottis from falling into and blocking theconduits28a,and also to make theback plate4 more resistant to lateral compression. It will be appreciated that in this embodiment, thedrain11 forms a convenient septum between theconduits28a,however, in devices with no oesophageal drain, a solid septum could simply be formed in the material of the back plate by moulding. In addition, a larger number ofconduits28acould be provided.
• Thus, it can be seen that the above described embodiments address the problems of prior art devices in novel and inventive ways.

Claims (9)

1. A laryngeal mask airway device for insertion into a patient to provide an airway passage to the patient's glottic opening, the device comprising an airway tube, a mask attached to the airway tube, the mask comprising a body having a distal end and a proximal end, a peripheral inflatable cuff, and defining an outlet for gas, the mask being connected to the airway tube for gaseous communication between the tube and the mask, the distal end of the mask being ventrally displaced, relative to the proximal end.

2. A device according toclaim 1, wherein the extent of distal displacement is from about 5 mm to about 20 mm.

3. A device according toclaim 2, wherein the extent of distal displacement is about 10 mm.

4. A device according to any precedingclaim 1, the body describing a substantially convex curve, from the proximal to distal end.

5. A device according to any precedingclaim 1, the mask body comprising a plate, the plate having a dorsal side and a ventral side, the dorsal side being substantially smooth and having a convex curvature across its width.

6. A device according toclaim 5, the airway tube having a dorsal surface, the dorsal surface of the airway tube corresponding in curvature to the curvature across the width of the plate.

7. A device according to any precedingclaim 1, the airway tube comprising a relatively more rigid material than the mask body.

8. A device according to any precedingclaim 1, further including an oesophageal drain tube.

9. A device according toclaim 8, the oesophageal drain tube being disposed on the ventral side of the body.

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