PHARYNGEAL AIRWAYThis invention relates to a pharyngeal airway, which may be a nasopharyngeal airway or an oropharyngeal airway, for maintaining a clear passage for air and anaesthetic gas to the laryngeal orifice of a patient during anaesthesia.
When a person falls asleep muscle tone is lost, and when the person is lying on his or her back, the tongue tends to fall backwards in the mouth and vibrate against the palate to cause snoring. During anaesthesia the loss of jaw muscle tone causes the tongue to flop further backwards and obstruct the air flow through the nose and nasopharynx. In addition, the epiglottis falls posteriorly, like a flap, to obstruct the laryngeal orifice. To overcome this it is customary to elevate the lower jaw, and with it the tongue, pulling both in an anterior direction towards the ceiling (i.e. with the patient on his/her back), whilst administering anaesthetic gases using a conventional face mask.
Because this effort occupies at least one, and sometimes both, of the anaesthetist's hands, it is difficult or impossible for the anaesthetist to tend to other matters. Furthermore, after a few minutes the effort becomes tiring, with the result that efficiency decreases and the patient's natural airway may be compromised.
Devices have been proposed for fixing the face mask on the patient's head in such a way as to assist the anaesthetist in holding up the jaw in order to keep the patient's airway open, but none are satisfactory.
A tubular airway for insertion through a patient's mouth is also known having a hinged distal end portion which can be pivoted by means of a lever operated linkage extending through the airway to lift the base of the tongue forwards and thereby hold open the patient's oropharyngeal passage. However, this device is relatively complex, both in construction and in operation, and is accordingly rather expensive to be used as a readily disposable item. It is also rather bulky.
In addition, endotracheal tubes are known for providing an air passage through a patient's mouth and directly into the trachea, the tube having an inflatable cuff adjacent its distal end for forming a seal with the inside wall of the trachea. However, in contrast to a pharyngeal airway which is intended for use only with patients who are capable of breathing spontaneously, endotracheal tubes are generally only used with patients who are not breathing spontaneously. Furthermore, considerable care must be exercised in their insertion since the distal end must be inserted past the epiglottis and into the trachea, and it is generally necessary to be able to view the distal end during the insertion in order to avoid damaging the larynx.
According to the invention there is provided a pharyngeal airway for insertion through the nose or mouth of a patient to establish and maintain an air passage to the laryngeal orifice, the airway comprising a flexible tube extending continuously along the length of the airway and means near the distal end of the tube for applying a force between the posterior wall of the oropharynx and the base of the tongue, preferably by acting directly between the posterior wall and the base of the tongue, to push the tongue away from the posterior wall of the oropharynx and lift the epiglottis clear of the laryngeal orifice.
Preferably the means for applying a force between the posterior wall of the oropharynx and the base of the tongue comprises an inflatable member attached to the tube near its distal end, and the airway includes means for conducting air to the inflatable member to inflate the member.
The inflatable member may be a flexible sleeve or cuff surrounding the tube and sealed at each of its ends to the tube in an airtight manner, for example by heat welding or bonding using a suitable solvent or adhesive.
Preferably the cuff has a length of from 30 mm to 50 mm, and adopts a substantially circular cross-section having a diameter of from 20 mm to 30 mm when inflated in unconstrained surroundings. The cuff is preferably spaced 20 mm to 30 mm from the distal end of the tube.
Generally the cuff will be of an elastic material and ideally will surround the tube as closely as possible depending on the material and the size of the cuff when inflated. Any suitable elastomeric material may be used, but usually the cuff will be made of a sufficiently plasticised PVC, particularly when the tube itself is made of a more rigid, but still flexible, PVC. As will be appreciated, the tube should be sufficiently soft and flexible to facilitate insertion without damaging the tissues of the pharyngeal passage, yet strong enough not to collapse when the cuff is inflated to push the tongue forwards and lodge the airway in position.
The means for conducting air to the inflatable member may comprise a pipe which extends along the tube, preferably inside the tube, and which communicates with the interior of the member. When the inflatable member is in the form of a cuff surrounding the tube, it will be particularly convenient for the air conducting means to comprise a capillary duct disposed within the wall of the tube and communicating with the interior of the cuff through an opening in the wall of the tube, and a pipe for connection to a source of air for inflating the cuff, the pipe communicating with the capillary duct at a position upstream from the cuff towards the proximal end of the tube.
As will be appreciated, since the pharyngeal airway is intended for patients who are breathing spontaneously, the primary function of the inflated cuff or other member is to push the tongue forwards and to hold the airway in position, not to form a seal with the surrounding tissues of the oropharynx. Indeed, since the inflated cuff will usually have a generally circular cross-section whereas the section of the oropharynx in the region of the cuff is non-circular, the cuff will not form a complete seal.
This has the advantage that while the inflated cuff will considerably reduce the unwanted escape of anaesthetic gases delivered to the patient through the tube of the airway, it will nevertheless permit some fluid flow around the sides thereof should the patient vomit while under the anaesthetic.
Preferably the tube of the airway is provided with means at a predetermined distance from the distal end of the tube to indicate when the tube has been inserted to the correct position. This indicator means may take the form of a marker or a radially outwardly projecting stop flange positioned so that it will lie adjacent the entrance to the patient's nose or mouth when the tube is correctly inserted.
Furthermore, the tube is preferably shaped so as to facilitate its insertion and mounting on a patient. For example, the distal end portion of the tube may be provided with a slight curvature, and the tube may have aU-shaped bend at a position upstream from the distal end portion and the indicator means (when provided), theU-shaped bend curving in a direction away from the distal end portion. In addition,the tube may bend outwards at the proximal end of the U-shaped bend to provide a straight proximal end portion of the tube for attachment to the patient's forehead. This provides a convenient location for the connection of anaesthetic breathing apparatus to the airway, for example by means of a suitable adaptor fitted in the proximal end of the tube.
The pharyngeal airway in accordance with the invention is thus capable of providing a simple, self-retaining device which can be inserted into position in the pharynx easily and safely through the nose or mouth of a patient, depending on whether the device is constructed as a naso pharyngeal or oropharyngeal airway, and which enables a safe anaesthetic passage to be maintained for long periods without the need for the anaesthetist to hold up the patient's jaw. This of course keeps the anaesthetist's hands free so that the anaesthetic can be administered and monitored safely and efficiently.In addition, since the anaesthetic breathing apparatus will preferably be connected to the proximal end of the airway tube in the region of the patient's forehead, it will be possible to perform operations on the face and mouth in areas to which surgical access would have been impossible using a conventional anaesthetic face mask and which would otherwise require the use of an endotracheal tube.
One embodiment of a pharyngeal airway in accordance with the invention designed for use as a nasopharyngeal airway will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:Figure 1 is a side view of the airway showing the cuff in an inflated condition;Figure 2 is an axial section through a distal end portion of the airway tube in a straightened condition and with the cuff deflated;Figure 3 is a diagram illustrating how the tongue and epiglottis can fall backwards to block a patient's air passage under anaesthesia; and,Figure 4 is a diagram similar to that of Figure 3 but illustrating how the airway of Figure 1 is used.
The nasopharyngeal airway shown in Figure 1 comprises a shaped, continuous tube 1 formed from a length of flexible extruded PVC tubing having a longitudinally extending capillary duct 2 (see Figure 2) within the wall of the tubing.
The tube 1 has a distal end 3 which is bevelled and has its outer edges radiussed to avoid damaging body tissues when the tube is inserted into position through the nasopharynx of a patient, and a proximal end 4 fitted with an adaptor 5 for the connection of an anaesthetic breathing apparatus. Between its distal and proximal ends, the tube 1 has a gently curved distal end portion 6 leading through a short straight portion 7 to a relatively tight U-shaped bend 8 curving outwardly with respect to the distal end portion 6 to a further short straight portion 9 which in turn leads through a short outwardly curved portion 10 to a straight proximal end portion 11 as shown.It will of course be appreciated that although the tube 1 is formed to the shape shown and will naturally adopt this shape when unconstrained, the tube nevertheless remains flexible and is readily deformable as necessary.
Surrounding the tube 1 near its distal end 3 is a thin elastic sleeve or cuff 12 of PVC or other suitable elastomeric material, the cuff 12 being heat welded to the tube 1 around the circumference thereof at each end 13,14 of the cuff in order to form a sealed enclosure within the cuff which communicates with the capillary duct 2 of the tube 1 through a notch 15 cut in the wall of the tube. At a position upstream from the cuff 12, approximately at the junction between the straight portion 7 and the U-shaped bend 8, the wall of the tube 1 is provided with a further notch 16 which opens into the capillary duct 2, and one end of a small diameter, flexible pipe 17 is inserted in a substantially sealed manner into the duct 2 through the notch 16.The other end of the pipe 17 is fitted with an adaptor 18 for the connection of means, such as a syringe pump, for supplying air through the pipe 17 and the duct 2 to inflate the cuff 12. As shown, the adaptor 18 is fitted with an inflatable pilot balloon 19 which inflates when the cuff 12 is inflated to indicate that the cuff is fully inflated. The capillary duct 2 is occluded at both the distal and proximal ends of the tube, although it is perhaps not essential to occlude it at the proximal end since the tight insertion of the pipe 17 in the notch 16 will in fact prevent the escape of air from the proximal end.
In use, the distal end 3 of the airway tube 1 is inserted, with the cuff 12 in a deflated condition, through the nose and nasopharyngeal passage 21 of a patient until a marker 20 provided on the tube just downstream (i.e. towards the distal end) from the notch 16 and the U-shaped bend 8 lies adjacent the entrance to the patient's nose. The marker 20 is located with respect to the distal end 3 of the tube so that when the marker is in this position the distal end 3 lies in the oropharynx 22 upstream of the laryngeal orifice 23, and with the cuffed region 12 of the tube sandwiched between the base of the tongue 24 and the posterior wall of the oropharynx. Outwardly of the nose, the U-shaped bend 8 of the tube 1 curves round the end of the nose so that the proximal end portion 11 of the tube lies adjacent the patient's forehead, where it can be taped securely in position.
A syringe containing sufficient air to inflate the cuff to the required extent is then connected to the adaptor 18 of the pipe 17 (not shown in Figure 4), and the air is injected to inflate the cuff 12 as shown in Figure 4. On inflation of the cuff 12 the tongue 24 is pushed forwards away from the posterior wall of the oropharynx (i.e from the position shown in Figure 3 to the position shown inFigure 4), thus raising the epiglottis 25 clear of the laryngeal orifice 23, and holding the distal end of the tube securely in position.
The anaesthet.ic breathing apparatus is then connected to the adaptor 5 at the proximal end of the tube 1, and administration of the anaesthetic can proceed. As described earlier, the inflated cuff 12 does not fully seal the pharyngeal passage 22, but it does nevertheless considerably reduce the unwanted escape of anaesthetic gases delivered through the tube 1.
When the airway is to be withdrawn, the breathing apparatus is disconnected from the adaptor 5 and the syringe pump is retracted to deflate the cuff 12 so that the tube 1 can then be withdrawn from the nose.
The dimensions of the nasopharyngeal airway shown inFigure 1 may of course be varied to suit different sizes of patient. For example, for small patients the tube 1 preferably has an internal diameter of 6 mm, and the arcuately curved distal end portion 6 preferably has a length of about 115 mm and subtends an angle of between 0 450 and 46 at its centre of curvature. The distance C from the tip of the distal end 3 to the cuff 12 is preferably 22.25 + 1.5 mm, and from the tip of the distal end to the marker 20 the distance is preferably 135 + 2 mm.
For large patients, however, the internal diameter of the tube 1 will preferably be 7 mm, and the length of the curved distal end portion 6 will be about 135 mm and will subtend an angle between 530 and 540 at its centre of curvature. The distance C from the tip of the distal end to the cuff will preferably be 24 + 1.5 mm, and the distance from the tip to the marker 20 will preferably be 155 + 2 mm.
Other dimensions of the airway, whether for large or small patients, are preferably as follows. The straight portion 7 preferably has a length of 27 + 2 mm, theU-shaped bend 8 preferably covers a 1750 arc with a radius of curvature (to the axis of the tube) of 22 + 2 mm, the straight portion 9 preferably has a length of about 12 mm, the bend 10 preferably covers an arc of 60 + 50 with a radius of 20 + 2 mm, and the straight proximal end portion 11 preferably has a length of 66 + 5 mm.
As explained earlier, the airway in accordance with the invention may also be designed to be used as an oropharyngeal airway. In this case the general shape and principles of construction utilised in the nasopharyngeal airway described above will be incorporated in the oropharyngeal airway, but the preferred dimensions may be modified to suit the slightly different mode of use.