ARTIFICIAL AIRWAY DEVICE
The present invention relates to an artificial airway device.
Artificial airway devices such as the laryngeal mask airway device are well known devices
useful for establishing airways in unconscious patients. In its most basic form a laryngeal
mask airway device consists of an airway tube and a mask carried at one end of the airway
tube, the mask having a peripheral formation often known as a "cuff which is capable of
conforming to and of fitting within, the actual and potential space behind the larynx of the
patient so as to form a seal around the laryngeal inlet. The cuff can be inflatable, and in most
variants it surrounds a hollow interior space or lumen of the mask, the at least one airway tube
opening into the lumen.U.S. Patent No. 4,509,514 is one of the many publications that
describe laryngeal mask airway devices such as this. 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 en 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).
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 laiyngeal 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. Patent 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 singlehanded
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 US
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 UK Patent 2,205.499.
Furthermore, devices with additional provision for gastric-discharge drainage are exemplified
by EP 0 794 807; 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 and commonly known as gastro-laryngeal masks. These masks make
provision for airway assurance to the patient who is at risk from vomiting or regurgitation of
stomach contents whilst unconscious. From a reading of these prior art documents it will be
appreciated that gastro-Iaryrigeal masks present numerous and often conflicting requirements
of design and manufacture to achieve designs that do not sacrifice any of the benefits of the
more simpler designs described above.
Thus, in general, laryngeal mask airway devices aim to provide an airway tube of such crosssection
as to assure more than ample ventilation of the lungs. 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. Undue bulk and stiffness run contrary to the requirement for
distal flexibility for tracking the posterior curvature of the patient's anatomy on insertion, in
such manner as to reliably avoid traumatic encounter. Moreover, manufacturing is made much
more difficult and costly and the risks of device failure may be increased.
Problems such as these can be especially acute 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 devices perform i 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 o equal to 0.4mm 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 (hysteresis)
means that the flexural performance of the device in terms of reaction, response and recovery
on deformation is inferior to a comparable LSR device.
A problem experienced in the early days of the laryngeal mask was crushing and even
puncture of the airway tube due to biting or abrasion by the patient ' s teeth. It will be
remembered that the airway tube passes out through the patient's mouth between the teeth,
usually iri line with the incisors. This problem was addressed by the present inventor by
providing an airway tube of flattened as opposed to circular section. Such an airway tube is
illustrated in the drawings accompanying this application. A flattened section tube is less
likely to contact the patient's teeth because it requires less clearance between the teeth and
can be made to provide the same or a greater cross-sectional area for gas flow as a circular
section tube.
A further expedient devised by the present inventor to prevent crushing and puncturing is the
bite block. Bite blocks are now commonly used in laryngeal masks of all types. A bite block
is a part of the device that is disposed to sit between the patient's teeth when the device is in
place that is designed to be resistant to crushing and puncturing by the teeth. A bite block can
be made by increasing the thickness of the wall of the airway tube, by forming the relevant
section of the tube from a harder material, and by adding a reinforcement inside and or
outside of the material of the airway tube. Although all of these expedients help prevent
crushing and puncturing of the tube, they also to a greater or lesser extent increase the
likelihood of damage to a patient's teeth by the device, particularly the airway tube, which can
be particularly traumatic to a patient. It is an object of the present invention to seek to mitigate
problems such as this.
According to the invention there is provided an artificial airway device to facilitate lung
ventilation of a patient, comprising an airway tube and a mask carried at one end of the
airway tube, the mask having a distal en and a proximal end and a peripheral formation
capable of forming a seal around the circumference of the laryngeal iniet, the peripheral
formation surrounding a hollow interior space or lumen of the mask and the bore of the
airway tube opening into the lumen of the mask, the airway tube including support means
uch that the cross sectional area of the bore is substantially maintained upon application of
pressure by the patient's teeth, whilst allowing local deformation of the tube at the point of
tooth contact. In this way, the invention provides a device that has an airway tube that is
resistant to crushing and puncture whilst also guarding against damage to a patient's teeth.
The support means may comprise an insert within the airway tube. The insert may comprise a
wall disposed to contact and support the airway tube, the wall including a cut away portion
disposed at a point that in use will be in line with the direction of biting of the patient's teeth.
As an alternative, the support means, may comprise an external sleeve of the airway tube. The
sleeve may comprise a wall disposed to contact and support the airway tube, the wall
including a cut away portion disposed at a point that in use will be in line with the direction of
biting of the patient's teeth.
The peripheral formation may be inflatable, such as for example an inflatable cuff.
It is preferred that the mask 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 invention will further be described by way of example and with reference to the
following drawings, in which,
Figure 1 is an underplan, or ventral view of a device according to the invention;
Figure 2 is an exploded view of a part of the device of Figure ;
Figure 3 is a perspective ventral view of the mask of the device of Figure 1;
Figure 4 is a front end view of the mask shown in Figure 3 in a first position;
Figure 5 is a front end view of the mask shown in Figure 3 in a second position;
Figure 6 is a side view of the device of Figure 1; and
Figure 7 is a plan, or dorsal view of the device of Figure 1.
Referring now to the drawings, there is illustrated an artificial airway device 1 to facilitate
lung ventilation of a patient, comprising an airway tube 2 and a mask 3 carried at one end of
the airway tube, the mask 3 having a distal end 4 and a proximal end 5 and a peripheral
formation 6 capable of forming a seal around the circumference of the laryngeal inlet, the
peripheral formation 6 surrounding a hollow interior space or lumen 7 of the mask 3 and the
bore of the airway tube 2 opening into the lumen 7 of the mask, the airway tube including
support means 44 such that the cross sectional area of the bore is substantially maintained
upon application of pressure by the patient's teeth, whilst allowing local deformation of the
tube at the point of tooth contact.
As can be seen from the drawings, the device 1, 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. an airway tube 2 and mask 3. The mask 3 includes two
components, a body part 1 often referred to as a backplate (shown in Figures 6 and 7), and a
peripheral tbrmation 6 which here takes the form of an inflatable cuff with an inflation line
12.
For the purposes of description it is convenient to assign reference names to areas of the
device 1 (as opposed to its constituent parts) and accordingly with reference to Figures 6 and
7. the device 1 has a dorsal side 14, a ventral side 15, a proximal end 16 (in a sense that this is
the end nearest the user rather than the patient) a distal end 7 and right and left sides 8 and
19.
Referring firstly to the airway tube 2, in the illustrated embodiment the tube 2 comprises a
relatively rigid PVC material such as a shore 90A Colorite PVC moulded into an
appropriately anatomically shaped curve. The tube 2 has some flexibility such that if it is bent
it will return to its original shape. Although it is resiliency deformable in this way, it is also
sufficiently rigid to enable it to assist in insertion of the device 1 into a patient, acting as a
handle and guide for positioning the mask. The airway tube 2 does not have a circular crosssection
as in many prior devices, but instead is compressed in the dorsal/ventral direction
which assists in correct insertion of the device 1, 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 each side 18, 19 of the airway tube 2 also includes a groove or
channel 20 extending for most of the tube's length from the proximal to distal ends. These
grooves 20 further assist in preventing crushing or kinking of the airway tube 2. Internally the
grooves 20 form ridges along the inner surfaces of the sides 18 and 19, but this not essential to
their operation.
A further feature of the airway tube 2 is oesophageal drain tube 41. This drain tube 4 1 is
located within airway tube 2, extending centrally through it from the proximal end to the
distal end, and in this embodiment it is disposed in contact with the inner surface of the dorsal
wall 2b of the airway tube 2, and bounded on each side by raised, smooth walls (not shown)
whieh form a shallow channel through which.it runs. At the proximal end of the airway tube
2, the drain tube 4 exits the airway tube 2 via branch 42a of a bifurcated connector 42, to
which a suction line may be attached. Bifurcated connector 42 also allows for connection of
the airway tube to a gas supply via branch 42b. Here it is formed from a relatively rigid
plastics material (when compared with the airway tube 2) to enable easy connection of air
lines and suction. Referring to Figure 2, connector 42 comprises a hollow somewhat flattened,
conical connector body 43 defining an atrium having branches 42a and 42b extending from its
narrower, proximal end. Conical body 43 includes a circumferential flange 42c from which
extends tab42d in a direction generally normal to the longitudinal axis of the connector.
Referring to Figure 2, an insert section 44 extends longitudinally from the distal end of the
conical body 43, forming a bite block which supports the tube 2 against crushing or
puncturing by the patient's teeth. The insert section 44 can be described as a tube, flattened in
the dorsal to ventral direction and having two sections of wall removed leaving gaps 44e and
"amis" 44a which extend distally long the tube 2. The insert section 44 corresponds in shape
arid dimension with the internal shape of the proximal end of the airway tube 2 such that it fits
snugly inside it, with curved arms 44a corresponding in profile to and thereby providing
support and rigidity to the sides of the airway tube. As a result of the removed wall sections
44e the support for the parts of the airway tube 2 adjacent the removed sections is reduced,
such that a relatively softer, deformable surface is provided, although overall support for the
tube 2 remains. In particular, it will be appreciated that supporting the sides of the airway tube
using correspondingly shaped arms 44a prevents crushing of the airway tube. A sleeve 45 of a
soft and compliant material is bonded in place around the outside of the airway tube 2,
covering the area into which the insert section 44 locates, and the thickness of the airway tube
wall at this point can be reduced to accommodate this such that the overall thickness at this
point 46 is not increased. Thus, it will be appreciated that this configuration provides a bite
block that not only supports the airway tube 2 at a point where the patient's teeth are normally
located when the device is in use, but also guards against damage to the teeth by virtue of the
less rigid parts. It will be appreciated that this form of connector can also be applied to airway
devices that do not include an oesophageal d in.
Turning now to the mask 3, the mask 3 consists of two parts, a body part 1 often referred to
as a back plate, and a peripheral cuff 6.
The back plate 1 is formed by moulding from a shore 50A Vythene PVC 4- PU. This
material is substantially softer and more deformable than the material o airway tube 2. The
back plate comprises a generally oval moulding when viewed from the dorsal or ventral
directions, having a smooth dorsal surface 24, and a formed ventral surface 24a (Figure 5).
The dorsal surface 24 has a convex curvature from one side to the other, corresponding to the
curvature of the dorsal surface of the airway tube 2, and longitudinally, the dorsal surface 24
is also curved, having a curvature beginning at the joining portion 24b and extending with
constant rate of curvature toward the distal tip. As a result the tip is ventrally biased relative to
the distal end of the airway tube, in the assembled device 1, the extent of displacement of the
distal tip being approximately 20mm or 10 degrees, in rder to produce a curvature in the
mask that is suited to the anatomy of the patient. On insertion, this displacement of the tip
assists the mask in "turning the corner" in the insertion path.
Backplate 11 includes an integrally moulded cylindrical drain tube 20 that extends from its
proximal to distal ends. At the proximal end, the drain tube 11 is dimensioned such that it can
be joined to the drain tube of the airway tube. At its distal end, the wall of the drain tube 20
has a cut away portion 21, and a smooth, turned over edge.
The second part of the mask 3 is the peripheral cuff 6. The cuff 6 is in this embodiment blow
moulded PVC and takes the form of a generally elliptical inflatable ring, a relatively deeper
proximal end 37 with an inflation port 38 and a relatively shallower distal end tapering to a
"wedge" profile 39. At the distal end the cuff is formed with a channel 22 in it is dorsal
surface, the channel being of an open C shape that runs in a proximal to distal direction to the
tip of the cuff. The cuff 6 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 end of the cuff 6 wi l curl with bias from dorsal to ventral side.
The cuff 6 is bonded to the backplate 1 such that the cut away section of the drain tube 20
extends over the channel 22 in the dorsal surface of the backplate , thereby forming a tube,
part of the wall of which is formed by the backplate and part by the cuff 6. The tube
terminates at or just before the distal extremity of the cuff, the smooth edge flaring to some
extent in a dorsal direction.
In use, the deflated device is inserted into a patient in the usual manner with devices of this
type. As noted above, the relative rigidity of the airway tube 2 allows a user to grip it and use
it to guide the device 1 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 the distal
tip relative to the join between the back plate 1 and airway tube 2 further enhances ease of
insertion, because the distal tip 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. Once in place, the support 44 prevents crushing and
puncturing of the airway tube 2 by the patient's teeth because the curved side walls of the
airway tube 2 are supported by the correspondingly curved a ra s 44a of the support 44.
However the tube 2 still guards against tooth damage because the cutaway gaps 44e allow
some deformation of the surface of the tube 2.
Claims
1. An artificial airway device to facilitate lung ventilation of a patient,
comprising an airway tube and a mask carried at one end of the airway tube,
the mask having a distal end and a proximal end and a peripheral formation
capable of forming a seal around the circumference of the laryngeal inlet, the
peripheral formation surrounding a hollow interior space or lumen of the
mask, the bore of the airway tube opening into the lumen of the mask, the
aii-way tube including support means such that the cross sectional area of the
bore is substantially maintained upon application of pressure by the patient's
teeth whilst allowing local deformation of the tube at the point of tooth
contact.
2. A device according to claim 1, the support means comprising an insert within
the airway tube.
3. A device according to claim 2, the insert including a wall disposed to contact
and support the airway tube^ the wall including a cut away portion disposed at
a point that in use will be in line with the direction of biting of the patient's
teeth.
4. A device according to claim 2, the insert including an external sleeve of the
airway tube, the sleeve comprising a wall disposed to contact and support the
airway tube, the wall including a cut away portion disposed at a point that in
use will be i line with the direction of biting of the patient's teeth.
5. A device according to any preceding claim, the peripheral formation
comprising an inflatable cuff.