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BACKGROUND OF THE INVENTION
This invention relates to improved delivery of topical local anaesthetic
agents to an airway.
Adverse physiological response to laryngoscopy and intubation remains a
significant problem of airway manipulation, both during anaesthesia and
other diagnostic procedures. Tactile stimulation of receptors in the
pharynx, hypopharynx, vocal cords and tracheal mucosa results in reflex
gagging, coughing, bucking and laryngospasm as well as release of
catecholamine (adrenaline and nor-adrenaline) and direct reflex
sympathetic stimulation of the heart.
Clinical manifestations, other than the obvious motor responses, include a
rise in pulse rate and blood pressure. These changes can be marked and are
usually well tolerated by young healthy patients. However, in the elderly,
premature neonates, or patients with cardiac or neurological disease,
these haemodynamic changes, with concomitant increase in myocardial work
and a decrease in cardiac output, can be critical and overcome the ability
of a patient to compensate for existing disease.
Sensory block of the upper airway with an aerosolized, topical anaesthetic
such as lidocaine, is possible using an ultrasonic nebulizer, an IPPB
device or a compressed gas-powered jet nebulizer, and is clinically
effective in blunting these responses. See, for instance, Christoforidis
et al, Chest, 59 (6): 629-633 (1971); Vuckovic et al, Anesth. Analg., 59
(10): 803-804 (1980); Korttila et al, Acta Anaesth. Scanda. 25: 161-165
(1981); Kirkpatrick et al, Am. Rev. Respir. Dis., 136:447-449 (1987);
Isaac et al, Anaesthesia, 45:46-48 (1990); and Foster et al, Am. Rev.
Respir. Dis., 146:520-522 (1992). However, variable dosage loss due to an
unsatisfactory delivery method, is disadvantageous. Therefore, there
remains a need for an improved method of delivering a topical anaesthetic
to a patient's airway.
Moreover, this prior art delivery technique is primarily reserved for
procedures in awake patients as it requires patient cooperation, in
particular active breathing, and is time consuming. Therefore, there
remains a need for an improved method of delivering a topical anaesthetic
to the upper airway of an unconscious or uncooperative patient without
necessitating direct vision achieved by laryngoscopy.
Topical lidocaine spray currently available from ASTRA as "Xylocaine
Endotracheal Aerosol" requires direct application under vision best
achieved at laryngoscopy. The laryngoscopy is disadvantageously performed
without prior airway topicalization, and intubation carried out at the
time of laryngoscopy occurs too soon after the anaesthetic agent is
applied for significant benefit to be achieved. The large droplet size of
the current aerosol has been implicated in inducing airway irritation and
even laryngospasm. Any technique such as spraying the trachea and vocal
cords at laryngoscopy, that increases the duration and number of
manipulations of the procedure has been shown to increase the stress
response.
The Laryngojet technique of instilling liquid lidocaine directly into the
trachea just before intubation does have small beneficial effect by
blunting the early tracheal response to the tube, but has no effect on the
initial response to laryngoscopy and intubation. Bronchodilator aerosol
has been administered via the breathing circuit, to a mechanically
ventilated patient intubated with an endotracheal tube.
General anaesthetic and induction agent dosages are limited by their
adverse effects and must be titrated to a patient's individual
requirements in order to achieve the correct depth of anaesthesia without
haemodynamic compromise. Titration of the dose and timing of the airway,
manipulation, in particular of an intubation, are necessary. A reliable,
simple and reproducible method of blocking/blunting the physiological
response to intubation would simplify anaesthetic induction and
intubation.
Intubating a patient with an anaesthetized airway requires a significantly
lighter plane of anaesthesia. The intubation could possibly be achieved
safely and reliably under light general anaesthesia without muscle
relaxation. Therefore, a method providing for reliable and rapid sensory
block of the upper airway, would benefit this aspect of anaesthesia. Such
a method would be especially advantageous if it could be used to provide
reliable sensory block of the upper airway without direct vision achieved
by laryngoscopy.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide improved
delivery of a topical anaesthetic to a patient's airway.
It is a further object to provide improved delivery of a topical
anaesthetic to the upper airway of an unconscious or uncooperative
patient.
It is a still further object to provide reliable sensory block of the upper
airway without direct vision achieved by laryngoscopy.
It is an even further object to rapidly produce effective topical airway
anaesthesia.
Additional objects, advantages and novel features of the present invention
are set forth in the description that follows, and in part will become
apparent to those skilled in the art upon examination of the following
description or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and attained by means of
instrumentalities and combinations particularly pointed out in the
appended claims.
To achieve the foregoing objects and in accordance with the purpose of the
present invention, as embodied and broadly described herein, there is
provided a reliable and rapid method for passively providing topical
airway anaesthesia. In accordance with the method of this invention, an
anaesthetic suitable for topical airway anaesthesia and a suitable
aerosol-forming propellant, are provided in a canister adapted to release
the anaesthetic in aerosolized form, and disposed within a housing
provided with a lid member. Also in accordance with the method, an
oropharyngeal airway is inserted into the mouth of a patient according to
current standard practice. Thereafter, the anaesthetic in aerosolized form
is released from the canister into the oropharyngeal airway, and thence
into anaesthetizing contact with the patient's oropharyngeal cavity, by
exerting pressure upon the lid member of the housing. The lid member may
be transparent in which case the canister may be viewed through the lid
member.
A preferred aerosol delivery device for carrying out the method includes a
nozzle having an exit orifice adapted for fluid communication with the
oropharyngeal airway. Accordingly, the nozzle may be positioned into fluid
communication with the oropharyngeal airway. After release of the
anesthetic from the canister into the oropharyngeal airway, the nozzle may
be separated from fluid communication with the oropharyngeal airway. The
preferred delivery device may also include a valve stem seat of unique
cross-sectional size and/or shape, and the canister may likewise include a
valve stem of complementary cross-sectional size and/or shape.
In the drawing and in the detailed description of the invention that
follows, there is shown and essentially described only a preferred
embodiment of this invention, simply by way of illustration of the best
mode contemplated of carrying out this invention. As will be realized,
this invention is capable of other and different embodiments, and its
several details are capable of modification in various respects, all
without departing from the invention. Accordingly, the drawing and the
detailed description are to be regarded as illustrative in nature, and not
as restrictive.
BRIEF DESCRIPTION OF THE DRAWING
Reference is now made to the accompanying drawing, which forms a part of
the specification of the present invention.
FIG. 1 is a perspective view of a preferred embodiment of an apparatus
useful for carrying out the present invention;
FIG. 2 is a detailed cross-sectional view of the aerosol delivery device of
FIG. 1, taken substantially along the longitudinal axis thereof;
FIG. 3 is an enlarged, cross-sectional view taken substantially along line
3--3 of FIG. 2;
FIG. 4 is a perspective view of the nozzle the aerosol delivery device of
FIG. 1;
FIG. 5 is a partial section taken substantially along line 5--5 of FIG. 1;
FIG. 6 is a cross section of the lid member similar to FIG. 2, but shown in
a moved position; and
FIG. 7 is a cross section taken substantially along line 7--7 in FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
As explained above, the present invention passively provides topical airway
anaesthesia. In other words, active breathing of a patient is not
necessary. Thus, this invention may beneficially be used on both
unconscious and awake patients.
Advantageously, this invention may be used to provide reliable sensory
block of the upper airway without direct vision of the anesthesiologist.
Beneficially, this invention will facilitate smooth induction of
anaesthesia by blunting the stress response to intubation. Intubation is
routinely performed soon after induction, prior to surgery. A lighter
plane of anaesthesia to achieve intubation may result and the need for
muscle relaxation may be obviated, thus simplifying this critical period
during general anaesthesia.
Superficial sensory block is rapid, typically onsetting within 5 to 30
seconds, with the block becoming more profound over a few minutes and
affecting the pressure receptors deeper in the airway mucosal surface. By
comparison, a nebulized mist of aerosolized lidocaine, actively breathed,
typically takes about ten to fifteen minutes to achieve delivery of the
dose requirement with only about 20% of the drug dose delivered to the
patient.
Referring to the drawing, a preferred embodiment of an apparatus 10 for
carrying out the present invention is shown. With reference particularly
to FIG. 1, an aerosol canister 12 containing a suitable topical
anaesthetic and propellant, is shown in fluid communication with an
oropharyngeal airway 14, depicted as disposed within the oropharyngeal
cavity of a patient who is lying down.
As can be understood from the Figure, an oropharyngeal airway extends from
the lips to the pharynx, and has a curved shape that fits over the tongue
and an orifice 16 that "looks" straight at the larynx and trachea.
Accordingly, an oropharyngeal airway may be advantageously used for
administration of an anaesthetic to the upper airway, that is, the
epiglottis, hypopharynx, larynx and trachea, and may be used for sensory
block without direct vision of the anesthesiologist.
An anaesthetic useful in this invention is suitable for topical airway
anaesthesia. A preferred topical anaesthetic is lidocaine. Any other local
anaesthetic agent may be used.
An appropriate concentration of the anaesthetic within canister 12, depends
upon the topical anaesthetic selected. In the case of lidocaine, about
1-10 wt. % lidocaine will typically be selected, providing about 5 to 20
mg per metered dose. For neonates, an appropriate concentration will
produce a smaller dose, that is, about 1 to 5 mg of aerosolized lidocaine
per metered dose.
By the term "aerosolized" is meant for purposes of this invention, being in
the form of minute droplets having typically an average particle size on
the order of 6 to 25 microns. Thus, an aerosolized topical anaesthetic
having an average particle size of about 16 microns can be expected to be
effective for passive topical anaesthesia from the back of the throat to
the primary bronchus. By comparison, a large droplet spray having an
average particle size in excess of about 50 to 100 microns, would not be
useful in the present invention.
The dosage of the aerosolized anaesthetic to be administered, generally
depends upon the patient's weight. Improved delivery with reduced
"rain-out" may result in reduced dosage requirements from conventional
levels of 2 to 5 mg/Kg. The effective dose of aerosolized lidocaine
delivered in accordance with the present invention, may thus range from
about 0.5 to 2 mg/Kg.
Aerosol propellants are well known. A suitable aerosol propellant will be
non-toxic and compatible with the topical anaesthetic selected. Well known
aerosol propellants include freon propellants and mixtures of freon
propellants such as Freon 12 and Freon 114.
Referring to FIG. 2, a casing or housing 20 of an aerosol delivery device
22 defines a recess 24 in which aerosol canister 12 is disposed, and
includes a valve stem seat 26 provided with an aperture 28 that
communicates with an exit orifice 30 of the delivery device. The exit
orifice is designed for fluid communication with entrance 18, indicated in
FIGS. 1 and 5, to airway 14.
Canister 12, generally constructed as is conventional in the aerosol art,
has a tubular valve stem or spray head 34. The valve stem is seated within
valve stem seat 26, and has an outlet orifice 36 situated for directing an
aerosol discharge through aperture 28. Pressing the valve stem inwardly of
the canister causes a metered dose of aerosolized anaesthetic to be
released from a pre-filled metering chamber (not shown) and to issue from
the canister orifice.
With reference to FIG. 3, the valve stem 34 of of a topical
anaesthetic-containing canister may be provided with a unique exterior
shape, for instance a triangular cross-sectional shape, and the valve stem
seat provided with a complementary configuration. In this way, use of the
delivery device may be restricted to a topical anaesthetic. Also, this
indexed system would prevent adult strength canisters having a valve stem
incompatible in exterior shape with a valve stem seat of a neonatal/
paediatric aerosol delivery device, from being used in the
neonatal/paediatric delivery device and resulting in potential drug
overdose.
Referring to FIGS. 2 and 4, a nozzle 40, beneficially held in place by, and
removably detachable from, a threaded tip 42 of casing 20, terminates in
the exit orifice of the aerosol delivery device. External threads 46 on
tip 42, which is conveniently generally circular, and internal threads 48
of nozzle 40 provide for the attachment and detachment. Tip 42 may have a
radiused surface 51 inclined toward aperture 28 to assist cleaning.
If desired, the external nozzle threads could be omitted and the nozzle
friction fit into place over or inside tip 42, or the nozzle could be an
integral, nonremovable part of casing 20. Removability of the nozzle
beneficially permits selection of a nozzle of appropriate size and shape
as later described, disposal of a nozzle after use, and makes any cleaning
of the casing easier.
Within the perimeter of tip 42 and surrounding aperture 28, one or more
openings 50 may be formed in the casing. Openings 50 may facilitate
aerosol delivery by allowing entrainment of air with the expelled aerosol.
Advantageously, as shown in FIG. 1, the nozzle is shaped to direct the
expelled aerosol at an angle with respect to a main or longitudinal axis C
of the casing, so as to facilitate operator use in not requiring direct
alignment. Likewise, openings 50 may be disposed at an angle with respect
to longitudinal axis C to beneficially direct entrained air flow.
With particular reference to FIG. 5, exit orifice 30 of the aerosol
delivery device is advantageously provided with a size and shape suitable
for fluid communication with entrance 18 to airway 14. To this end, a
generally oval shape of an appropriate size that permits insertion of the
exit orifice within the entrance to the airway, may be selected.
Beneficially, a sealing, snug fit of the nozzle exit orifice within the
airway entrance may be provided to prevent positive pressure emanating
from the patient, causing dosage loss. The nozzle may taper to a decreased
cross-sectional area to allow a tight fit to a range of airway sizes.
Referring particularly to FIG. 6, the canister may be beneficially closed,
but not sealed, within the aerosol delivery device by cooperative fit of a
movable lid member 53 with casing 20. For this purpose, a canister insert
end 52 of the casing may be flared outwardly to accommodate a peripheral
wall portion 54 of lid 53, which is positioned over and around an end 56
of the canister. In this manner, peripheral wall portion 54 may be
slidingly fitted interior of outwardly flared end 52 of the casing, but
yet air flow between wall portion 54 and the casing, to openings 50 may be
provided for.
With reference to FIG. 7, posts 62 projecting from wall portion 54
advantageously are in snapengagement with slots 64 in outwardly flared end
52 to prevent the lid from separating from the casing. Elongated slots 64
are provided with a suitable length for the desired travel of posts 62
within the slots, and also may provide for air flow to openings 50.
The casing beneficially includes a handle 70 to be used in conjunction with
lid 53, which has an upper surface advantageously generally dome-shaped or
rounded for comfort, for facile, one-handed operation of an aerosol
delivery device in accordance with the present invention. If desired, the
handle may encircle the exterior of the casing, and the lid could likewise
be provided with a handle. Conveniently, handle 70 is located near flared
out end 52 of the casing.
Beneficially, the canister may be designed to have distinct colors to
indicate metered dose strength, differentiating adult from
neonatal/paediatric canisters. Consistent with this, lid 50 may be made of
transparent material so that the canister may be viewed without removal of
the lid.
Administration of an aerosolized topical anaesthetic through airway 14,
beneficially provides for reliable and rapid topical anaesthesia of the
upper airway, passively and without direct vision of the anesthesiologist.
After sensory block, airway 14 may be removed, and various airway
manipulations such as endotracheal tube intubation and laryngoscopy,
performed without adverse physiological response attributable to airway
manipulation. By comparison, I have found that "Xylocaine Endotracheal
Aerosol" released into airway 14 does not provide the desired topical
anaesthesia, apparently due to failure to exit from airway 14.
Having described the invention in detail and by reference to a preferred
embodiment for carrying out the method thereof, it will be apparent that
modifications and variations are possible without departing from the scope
of the invention defined in the appended claims. Several variants or
modifications have been briefly mentioned for purposes of illustration.
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