U.S. patent number 3,593,710 [Application Number 04/793,932] was granted by the patent office on 1971-07-20 for anesthetic apparatus.
This patent grant is currently assigned to Chemetron Corporation. Invention is credited to Francis J. Eichelman, Andrew A. Kenny.
United States Patent |
3,593,710 |
Eichelman , et al. |
July 20, 1971 |
ANESTHETIC APPARATUS
Abstract
A closed reservoir charged with a supply of liquid anesthetic
material communicates via a conduit with a vaporizer chamber
through which a stream of gas flows. The reservoir is pressurized
by a pressure line communicating with the reservoir at a region
beneath the surface of the liquid, and a pressure head is
maintained independently of the level of the anesthetic material in
the reservoir. The rate of flow of liquid through the conduit to
the vaporizer chamber is controlled by regulating the pressure
within the pressure line relative to the pressure within the
pressure line relative to the pressure within the vaporizer
chamber. The reservoir may be formed by an anesthetic containing
bottle in sealing engagement with a support for the vaporizer to
provide a compact assembly.
Inventors: |
Eichelman; Francis J. (La
Grange Park, IL), Kenny; Andrew A. (Chicago, IL) |
Assignee: |
Chemetron Corporation (Chicago,
IL)
|
Family
ID: |
25161198 |
Appl.
No.: |
04/793,932 |
Filed: |
January 27, 1969 |
Current U.S.
Class: |
128/200.11;
128/203.25 |
Current CPC
Class: |
A61M
16/18 (20130101); A61M 16/0833 (20140204) |
Current International
Class: |
A61M
16/10 (20060101); A61M 16/18 (20060101); A61m
017/00 () |
Field of
Search: |
;128/188,186,187,189,204,193--196,197,173,173.1 ;251/113,114 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Mitchell; J. B.
Claims
What I claim as new and desire to be secured by Letters Patent of
the United States is:
1. Anesthetic vaporizer for adding anesthetic vapor to a stream of
gas in order to provide an anesthetizing gaseous mixture, said
vaporizer comprising:
means defining a passageway for the stream of gas;
said passageway defining means including a vaporizer chamber
through which the stream of gas flows;
a closed reservoir adapted to be charged with a supply of
anesthetic in the liquid state;
a conduit having one end disposed within said reservoir and having
another end communicating with said vaporizer chamber, said one end
terminating at a point below the normal operating level of the
liquid; and
means for pressurizing said reservoir for gradually evacuating the
supply of liquid from said reservoir into said vaporizer chamber
through said conduit at a rate independent of the level of liquid
in said reservoir;
said pressurizing means including a pressure line for introducing a
pressurized gas into said reservoir and communicating with said
reservoir at a region beneath the surface of the liquid anesthetic
contained therein.
2. The vaporizer of claim 1 further comprising adjustable means for
controlling the pressure differential between said region and the
interior of said vaporizer chamber, thereby to control the rate of
flow of liquid through said conduit.
3. The vaporizer of claim 2, said adjustable means comprising a
pressure regulator connected to said pressure line for regulating
the pressure at said region.
4. The vaporizer of claim 2, said adjustable means comprising a
pressure regulator communicating with said passageway defining
means for regulating the pressure within said vaporizer
chamber.
5. The vaporizer of claim 3, said adjustable means further
comprising an additional pressure regulator communicating with said
passageway defining means for regulating the pressure within said
vaporizer chamber.
6. The vaporizer of claim 1 further comprising a metering valve in
said conduit between said vaporizer and said closed reservoir for
varying the resistance to the flow of liquid anesthetic through
said conduit.
7. The vaporizer of claim 6 further comprising adjustable means for
controlling the pressure differential between said region and the
interior of said vaporizer chamber.
8. A liquid anesthetic vaporizing unit for adding anesthetic
material to a stream of gas comprising a container adapted to
contain a supply of liquid anesthetic material, a vaporizer
including wall means defining an evaporation chamber, a first
passage in said wall means for conducting the stream of gas into
said chamber, a second passage in said wall means for conducting
the stream of gas from said chamber, sealing means supported by
said wall means, a conduit having a first portion extending
outwardly from said wall means and having a second portion
communicating with said chamber for introducing anesthetic material
into said chamber said first portion terminating within said
chamber at a point below the normal operating level of the liquid,
means for holding said container against said sealing means with
the first portion of said conduit extending into said container, a
second conduit extending outwardly from said sealing means and
received within said container terminating at a point below the
normal operating level of the liquid, and means for introducing
pressurized gas into said second conduit for pressurizing the
region bounded by said container and said sealing means.
9. The unit of claim 8, further comprising means defining a bleed
passageway extending from said container to said chamber for
venting excess pressures from said container into said chamber.
10. Anesthetic vaporizer for adding anesthetic vapor to a stream of
gas in order to provide an anesthetizing gaseous mixture, said
vaporizer comprising:
a vaporizer chamber;
inlet and outlet passageways for conducting the stream of gas
through said vaporizer chamber;
a reservoir for holding a supply of liquid anesthetic material;
a conduit extending from said reservoir to said vaporizer chamber
for conducting liquid anesthetic to said vaporizer chamber for
evaporation into the stream of gas one end of said conduit
terminating below the normal operating level of the liquid;
a pressure line communicating with said reservoir for pressurizing
said reservoir thereby to force liquid anesthetic to flow through
said conduit one end of said pressure line terminating within said
reservoir at a point below the normal operating level of the
liquid; and
pressure regulating means connected to said outlet passageway for
controlling the pressure within said vaporizer chamber, thereby to
control the rate of flow of liquid anesthetic through said
conduit.
11. The anesthetic vaporizer of claim 10 further comprising an
additional pressure regulator connected to said pressure line for
controlling the pressure within said pressure line.
12. The anesthetic vaporizer of claim 11 further comprising a
pressure equalizing line extending between said vaporizer chamber
and said additional pressure regulator for compensating for
pressure variations within said vaporizer chamber.
13. A method of producing a mixture of a gas and the vapor of a
liquid anesthetic material from a reservoir comprising the steps
of:
passing a stream of gas through a vaporizing chamber communicating
with the reservoir through a conduit which terminates at one end
within said reservoir below the normal operating level of the
liquid; and
adding pressurized gas to said reservoir at a point below the
surface of the liquid anesthetic material contained therein in
order to force the liquid anesthetic material through said conduit
at a rate of flow substantially independent of the liquid
level.
14. The method of claim 13 further comprising controlling the
pressure difference between the pressure of said point and the
pressure at said vaporizing chamber in order to meter the flow
through said conduit.
15. The method of claim 13 wherein the step of controlling the
pressure difference includes the steps of regulating the pressure
of said pressurized gas, and regulating the pressure of said stream
of gas.
16. Apparatus for producing a mixture of anesthetic and gas
comprising a reservoir for a supply of anesthetic in liquid form, a
vaporizer chamber, first conduit means for passing a stream of gas
through said chamber, a liquid passageway for discharging liquid
anesthetic from said reservoir into said chamber for evaporation
into said stream of gas one end of said passageway terminating at a
point below the normal operating level of the liquid, second
conduit means for passing a stream of pressurized gas into said
reservoir for forcing said liquid anesthetic into said liquid
passage one end of said second conduit means terminating at a point
below the normal operating level of the liquid, and a control valve
assembly for controlling flow through said first and second
conduits means, said control valve assembly comprising a first
valve in said first conduit means, a second valve in said second
conduit means, and a single manually operated means for
simultaneously opening both said first and second valves.
17. The apparatus of claim 16, said valve assembly including a
valve bore, first and second seats in said bore, and a single valve
member movable in said bore having first and second valve seating
surfaces engageable with said first and second seats to close said
first and second valves.
18. The apparatus of claim 17, said first and second valve seating
surfaces being constructed and arranged with respect to said first
and second seats so that said first valve is a shutoff valve and
said second valve is a throttling valve.
Description
The present invention relates to anesthetic apparatus, and more
particularly to apparatus for introducing anesthetic vapor into a
gas stream for use in anesthetizing a patient.
In the process of inducing a state of anesthesia in a patient, the
patient is caused to inhale a mixture of a gas, such as oxygen, and
an anesthetic vapor. Several inhalation anesthetic materials are
currently used, including ether, halothane (available under the
trademark Fluothane), trichloroethylene, methoxyflurane (available
under the trademark Penthrane) and others. The desired
concentration of any given anesthetic vapor in oxygen or other gas
varies in dependence upon the particular patient, and may vary over
a considerable range as anesthesia is first induced and
subsequently maintained at a given stage. In addition, the range of
concentration varies for different materials. For example, the
concentration of ether in some cases may be as high as 8 percent or
more, while methoxyflurane may be administered at a concentration
as low as 0.2 percent.
Anesthetic materials are customarily available in the form of
volatile liquids, and various methods have been used for
evaporating the liquid anesthetic into a gas stream. Anesthetic
apparatus known heretofore has been subject to one or more
problems, including lack of accuracy in achieving the desired
concentration, particularly over the wide range of concentrations
necessary for use with different anesthetic materials, undue
complexity, expense, and inconvenience. One common method is to
bubble a stream of gas through a supply of liquid anesthetic to
produce a highly concentrated mixture. Subsequently the mixture is
diluted to achieve the desired concentration. One difficulty
encountered with this method arises in accurately attaining the
desired concentration since the rate of evaporation varies widely
with temperature and pressure conditions.
Other known methods involve the use of vaporizing apparatus through
which a stream of gas is passed. A metered amount of liquid
anesthetic is introduced into the vaporizing apparatus and
evaporates into the gas stream. The accuracy of this arrangement is
not highly dependent upon temperature and pressure conditions
because all of the liquid anesthetic introduced into the vaporizing
apparatus is intended to evaporate into the gas stream. However,
difficulties are encountered in accurately metering the amount of
liquid anesthetic which is introduced into the vaporizing
apparatus, and in maintaining a constant pressure head for forcing
the liquid anesthetic into the vaporizing apparatus. One example of
a system of this type may be found in U.S. Pat. No. 3,128,764
issued to Wilbur R. Koehn.
Accordingly, it is an object of the present invention to provide
improved anesthetic apparatus for providing a gas and anesthetic
mixture which can be controlled accurately over a wide range of
concentrations.
Another object is to provide improved anesthetic apparatus which is
simple and convenient to operate.
A further object is to provide improved apparatus for maintaining a
constant pressure head for evacuating anesthetic liquid from a
container at a rate independent of a changing liquid level.
Another object is to provide an apparatus in which the anesthetic
concentration can be varied over a wide range and controlled with
great accuracy.
Another object of the invention is to provide improved anesthetic
apparatus suitable for use with a wide variety of anesthetic
materials and for use in both closed and open systems.
In brief, anesthetic apparatus constructed in accordance with the
invention may include a vaporizer chamber through which flows a
stream of gas to which anesthetic vapor is to be added. An
anesthetic material in the liquid state is introduced into the
vaporizer chamber through a conduit from a closed reservoir charged
with a supply of anesthetic liquid. In accordance with an important
feature of the invention, pressure within the reservoir forces the
anesthetic through the conduit to the vaporizer chamber at a rate
which is independent of the level of anesthetic in the reservoir.
Accordingly, there is no requirement to maintain a constant level
in the reservoir as in many prior art systems. In order to
accomplish this result, the reservoir is pressurized by means of a
pressure line communicating with the reservoir at a region beneath
the surface of the anesthetic.
The rate at which liquid flows into the vaporizer chamber is
regulated accurately and conveniently by varying the pressure
differential existing between the vaporizer chamber and the
reservoir. In accordance with a feature of the invention, the
pressure differential may be controlled by regulating the pressure
of the pressure line communicating with the reservoir, or by
regulating the pressure within the vaporizer chamber, or both.
Another feature of the invention resides in the simplicity and
convenience of the vaporizer apparatus. In certain embodiments of
the invention, the closed reservoir containing the liquid
anesthetic comprises the bottle or container in which the liquid
anesthetic is supplied. The bottle is held in sealing relation to a
support member associated with the vaporizer, and both the pressure
line and the liquid conduit extend into the bottle to a point
beneath the surface of the liquid anesthetic contained in the
bottle. This arrangement, in addition to being extremely simple and
inexpensive, reduces the evaporation waste occurring with prior art
apparatus, and also makes it extremely simple to change quickly
from one anesthetic material to another.
The apparatus of the present invention may also include a novel
arrangement for maintaining an even pressure differential between
the vaporizer chamber and the regulator by controlling the
reservoir pressure in accordance with minor fluctuations within the
vaporizer chamber. In addition, a restricted bleed line may extend
between the reservoir and the vaporizer chamber to prevent the
buildup of excess pressure within the reservoir due to accelerated
evaporation of the liquid anesthetic contained therein. A
dual-purpose valve with a single control may be used to control the
admission of pressurized gas to the regulator, and also to regulate
the gas stream passing through the vaporizer chamber.
The above and many other objects and advantages of the present
invention will appear from the following detailed description of
certain embodiments of the invention taken with the accompanying
drawings, in which:
FIG. 1 is a diagrammatic and elevational view, partly in section,
of vaporizer apparatus constructed in accordance with the
invention;
FIG. 2 is a diagrammatic and elevational view, partly in section,
of an alternative embodiment of the invention;
FIG. 3 is a diagrammatic and elevational view, partly in section,
of another alternative embodiment of the invention;
FIG. 4 is a perspective view of a self-contained vaporizer unit
including the components illustrated in FIG. 3;
FIG. 5 is an exploded view of the unit of FIG. 4;
FIG. 6 is an enlarged sectional view taken along the line 6-6 of
FIG. 4; and
FIG. 7 is an elevational view of one side of the unit of FIG.
4.
Referring now to the drawings, and initially to FIG. 1, there is
illustrated a liquid anesthetic vaporizing unit generally
designated as 10 and constructed in accordance with the present
invention. In the main, the unit 10 includes a vaporizer chamber
designated as a whole by the reference numeral 12 and a closed
reservoir generally designated as 14. A stream of gas to which an
anesthetic vapor is to be added is conducted from a source of
pressurized gas through a shutoff valve 15 and through the
vaporizer chamber 12 by means of an inlet conduit 16 and an outlet
conduit 18 communicating with anesthetic mixture utilizing
apparatus which may, for example, be part of a closed or an open
anesthetic system. In an open system a gas, such as oxygen, is
passed through the vaporizer chamber 12 and mixed with a desired
concentration of anesthetic vapor, and is forwarded via the outlet
conduit 18 to patient breathing apparatus. In a closed system, the
gaseous mixture is recycled through a closed circuit in which
carbon dioxide is removed from the exhaled gas and additional
oxygen combined with anesthetic vapor is added to replenish the
flow.
In accordance with one important feature of the invention, liquid
anesthetic is forced to flow from the closed reservoir 14 through a
liquid carrying conduit 20 to the vaporizer chamber 12 at a rate
which is accurately controlled and is independent of the liquid
level in the reservoir 14. The reservoir 14 is initially charged
with a supply of anesthetic liquid and no effort is made to
maintain a constant level within the reservoir 14 as the liquid
anesthetic is used. In order to provide a flow of fluid through the
conduit 20 at a rate independent of the liquid level in the
reservoir 14, the reservoir 14 is pressurized by means of a
pressure line 22 having an end 22a communicating with the reservoir
preferably near the bottom so as to be beneath the surface of
liquid in the reservoir. Accordingly, for a given pressure in the
pressure line 22, the pressure head causing evacuation of the
liquid through the conduit 20 remains constant regardless of the
level of liquid in the reservoir 14, and without the necessity for
special control apparatus. This represents a substantial advance in
convenience and simplicity over prior art arrangements wherein
complicated and expensive apparatus was required to maintain a
constant anesthetic level in order to maintain a constant pressure
head for forcing liquid from the reservoir into the vaporizer.
More specifically, the pressure head at the lower end 20a of the
liquid conduit 20 is made up of two components. One component of
the pressure head is produced by the pressure of the vapor or gas
within the reservoir 14 above the surface of the liquid contained
therein. The other pressure component results from the weight of
the liquid within the reservoir 14 above the lower end 20a of the
conduit 20.
In prior art apparatus, attempts have been made to maintain a
constant pressure head by maintaining the liquid level in the
reservoir constant and by maintaining the pressure of the
atmosphere within the reservoir constant. This approach, however,
has required a complicated valving mechanism for maintaining a
constant liquid level. In contrast, the present invention provides
a simplified, less expensive and conveniently regulated arrangement
for maintaining a constant pressure head at the lower end of the
conduit 20.
In the arrangement of the present invention, the liquid level does
not remain constant and the component of the pressure head caused
by the liquid decreases as the liquid level falls. However, since
this component of the pressure head acts on the submerged pressure
line 22 as well as on the liquid conduit 20, the pressure of the
gas contained within the reservoir 14 increases and compensates for
the falling liquid level. Accordingly, the pressure head effective
at the end 20a of the conduit 20 remains constant for a given
pressure within the pressure line 22.
Although the lower ends 20a and 22a of the liquid conduit 20 and
pressure line 22 are illustrated in FIG. 1 at approximately the
same level, it will be obvious that they may be disposed at
different levels if desired. A constant effective pressure head
will be maintained as long as both the pressure line and the liquid
conduit terminate beneath the surface of the liquid.
As noted above, the apparatus of the present invention is capable
of providing accurately controlled anesthetic concentrations over a
wide range. The conduit 20 is preferably of capillary size and may
include a segment having an inner diameter in the neighborhood of
0.007 inch. The flow of liquid anesthetic through the conduit 20 is
governed by the rules of laminar flow, in accordance with which the
flow through the conduit 20 is proportional to the pressure
differential existing between the lower end 20a of the conduit and
an upper end 20b disposed within the vaporizer chamber 12. Since
the pressure at the lower end 20a of the conduit 20 is determined
by the pressure within the pressure line 22, the rate of flow of
liquid anesthetic into the vaporizing chamber 12 is proportional to
the pressure differential existing between the pressure line 22 and
the interior of the vaporizer chamber 12.
In accordance with a feature of the invention, the rate of flow of
liquid anesthetic through the conduit 20, and thus the percentage
concentration of anesthetic vapor in the stream of gas, is
accurately controlled over a broad range by controlling the
pressure within the reservoir 14 relative to the pressure within
the vaporizer 12. In the embodiment of the invention illustrated in
FIG. 1 this is accomplished by controlling the pressure existing
within the pressure line 22 by means of a pressure line regulator
generally designated as 24, and controlling the pressure within the
vaporizer chamber 12 by means of a back pressure regulator
generally designated as 26.
More specifically, the pressure line 22 communicates with the
outlet of a pressure regulated valve 28, the inlet of which is
connected to a source of pressurized gas by way of a shutoff valve
30. If desired a single source may be used both for the gas stream
entering the inlet conduit 16 and for supplying the regulator 24,
although separate sources are indicated in FIG. 1. The pressure
regulator 24 may be of any suitable type, and as illustrated
includes a diaphragm 32 acted upon by the pressure within the
pressure line 22 and coupled to the valve 28 by means of a linkage
34 for operating the valve to maintain a constant pressure within
the pressure line 22. The pressure acting upon the diaphragm 32 is
opposed by the force applied by a spring 36, and preferably the
spring tension is adjustable by means of a handle 38 with which the
constant pressure level to be maintained within the pressure line
22 may be varied.
The back pressure regulator 26 may be of any desired type, and is
illustrated as being similar in many respects to the pressure line
regulator 24. The gaseous mixture flowing from the vaporizer
chamber 12 passes via the outlet conduit 18 to the inlet of a
pressure regulated valve 40, the outlet of which is connected to
the anesthetic mixture utilizing apparatus. The valve 40 is
controlled by means of a linkage 42 and diaphragm 44 to maintain
the pressure at the inlet side of the valve 40, and thus the
pressure within the vaporizer chamber 12, at a constant level. The
pressure within the vaporizer chamber 12 is adjusted to a desired
level by means of a handle 46 controlling the tension of a spring
48 acting on the diaphragm 44.
Since the rate of flow of liquid anesthetic through the conduit 20
is determined by the pressure differential existing between the
pressure line 22 and the vaporizer chamber 12, the concentration of
the anesthetic in the gas stream can conveniently and accurately be
adjusted by means of the handles 38 and 46 of the pressure line
regulator and the back pressure regulator. It is possible with the
apparatus of the present invention to regulate the pressure
differential and thus the flow rate with either one of the
regulators 24 and 26, the other being omitted or combined with
other equipment. Alternatively, one of the regulators 24 and 26 may
be permanently set or factory adjusted at a selected level and the
other may be adjusted by the anesthesiologist. If desired, of
course, both of the regulators may be used. For example, one of the
regulators may be set at a selected level to give a certain range
of flow rates, and the other used for finer adjustments within the
selected range.
A pair of pressure responsive indicators 50 and 52 are connected
respectively to the pressure line 22 and the outlet conduit 18
communicating with the interior of the vaporizer chamber 12. The
readings of the indicators 50 and 52 indicate the pressure
differential existing between the pressure line 22 and the
vaporizer chamber 12, and thus the anesthetic concentration may be
computed from this pressure differential. Alternatively, the
indicators 50 and 52 may be provided with scales (not shown)
calibrated in terms of anesthetic concentration.
It will be appreciated that due to factors such as friction and
inertia associated with the elements of the back pressure regulator
26, minor pressure variations and fluctuations may exist within the
vaporizer chamber 12. Although these variations are of a minor and
transient character, it may be desirable to compensate for such
variations in order to provide an evenly regulated flow of liquid
from the reservoir 14 into the vaporizer chamber 12. In order to
accomplish this, a pressure equalizing line 53 extends from the
interior of the vaporizer chamber 12 to the dome portion of the
pressure line regulator 24. Pressure variations existing within the
vaporizer chamber 12 are communicated via the equalizing line 53 to
the reverse or dome side of the diaphragm 32 automatically to
control the valve 28 for maintaining a constant pressure
differential between the vaporizer chamber and the reservoir.
With some anesthetic material such as ether a problem may arise
when the reservoir 14 is exposed to light or temperature
variations. Under some conditions it is possible for the liquid
within the reservoir 14 to evaporate at an accelerated rate and for
the vapor pressure within the reservoir 14 to increase to an
undesirable level. Rather than controlling the external conditions
affecting the rate of evaporation, it may be preferable to provide
a restricted bleed line 54 extending from the upper portion of the
closed reservoir 14 to the interior of the vaporizer chamber 12.
This line has a very small interior diameter, and serves very
gradually to vent any excess pressures that may exist within the
reservoir 14 to the lower pressure region within the vaporizer
chamber 12. The line is small in size, and the limited flow of gas
therethrough may readily be compensated for through calibration of
the system.
Referring now to the construction of the vaporizer chamber 12, the
chamber includes a cylindrical wall member 56 defining an interior
chamber and preferably formed of transparent material such as glass
in order to permit viewing of the flow of anesthetic liquid from
the conduit 20. The upper end 20b of the conduit 20 is provided
with a drip guide 58 for causing the liquid to form droplets rather
than running down the outer surface of the conduit 20 and/or into
the line 54.
The upper and lower ends of the cylindrical wall 56 are closed by
body members 60 and 62. The upper body member 60 includes a pair of
passages 18a and 53a communicating respectively with the outlet
conduit 18 and the pressure equalizing line 53, and communicating
with the interior of the vaporizer chamber 12. Similarly, the lower
body member 62 includes a passageway 16a communicating with the
inlet conduit 16 and with the interior of the vaporizer chamber
12.
The vaporizer chamber 12 is divided into two regions by means of a
porous metal diffusion plate or baffle 64 supported within the
lower body section 62. The stream of gas entering through the inlet
conduit 16 passes through the diffusion plate 64 to reach the
outlet conduit 18. Liquid anesthetic emerging from the conduit 20
falls from the drip guide 58 onto the plate 64 and is completely
evaporated into the stream of gas moving through the plate 64.
With the vaporizing unit 10 of the present invention it is not
necessary to transfer the liquid anesthetic from its original
container to a separate reservoir. In addition to being convenient,
this arrangement prevents the evaporation loss, contamination, and
the like suffered with known equipment during transferral of liquid
anesthetic from one vessel to another. Since the liquid is kept in
its original container, the possibility of confusion as to what
type of anesthetic is being used is reduced.
In order to permit the original container or bottle 66 in which the
anesthetic is obtained to serve as the closed reservoir in the
system, the lower body member 62 supports a sealing member 68
having a lower surface against which the neck of the bottle 66
abuts. The bottle 66 is held in sealing engagement with the sealing
block 68 by means of a yoke 70 pivotally supported by the lower
body member 62 and a clamping bolt 72 engaging the bottom of the
bottle 66. Since the pressure line 22 and the conduit 20 extend
downwardly through the lower surface of the sealing block 68, the
unit 10 is assembled for operation merely by positioning the bottle
66 and clamping it in place.
One of the advantages of the apparatus of the present invention is
that it may be used with a high degree of accuracy over a wide
range of anesthetic vapor concentration levels. Accordingly, the
apparatus is well suited for use with a wide variety of different
anesthetic materials which may require concentrations falling in
widely varying ranges. However, if for precautionary reasons it is
desired to restrict the use of the unit 10 to one particular
anesthetic at one given time a suitable indexing means (not shown)
may be provided on the sealing member 68 so that the unit can
accept only one particular type of bottle associated with the one
selected anesthetic material.
Reviewing the operation of the liquid anesthetic vaporizing unit
10, initially there is no stream of gas flowing through the
vaporizer chamber 12 and the shutoff valves 15 and 30 are in the
off position. In order to prepare the unit for operation, a bottle
66 of a selected anesthetic material is mounted against the sealing
member 68 and clamped in place by the clamping bolt 72. The valve
15 is opened and the flow of gas through the vaporizer chamber 12
is begun. The shutoff valve 30 is opened and one or both of the
regulators 24 and 26 are adjusted by means of the adjusting handles
38 and 46 to provide a desired pressure differential between the
lower end 20a and the upper end 20b of the liquid conduit 20.
Pressurized gas from the source of pressurized gas flows through
the pressure line regulator 24, where its pressure is dropped to
the selected level, and then through the pressure line 22 and into
the closed reservoir 14. Pressure within the reservoir forces
liquid anesthetic material through the conduit 20 to the vaporizer
chamber 12 where it drips onto the diffusion plate 64.
Gas entering the vaporizer chamber 12 through the conduit 16 flows
through the plate 64 and is mixed with evaporating anesthetic. The
gaseous anesthetic mixture then flows through the outlet conduit 18
and through the back pressure regulator 26 to the utilizing
apparatus. The back pressure regulator maintains a selected
pressure level within the vaporizer chamber 12. As the liquid level
drops in the reservoir 14, the pressure differential between the
ends 20a and 20b of the conduit 20, as determined by the regulators
24 and 26, does not vary and the rate of flow of anesthetic remains
constant.
If it is desired to change anesthetics or replace the bottle 66,
the shutoff valve 30 is closed, and the pressure within the
reservoir 14 drops quickly due to provision of the bleed line 54 to
stop the flow of liquid through the conduit 20. Since the reservoir
14 is located below the chamber 12, there is no liquid flow in the
absence of pressure within the reservoir. In addition, when the
bottle 66 is removed the conduit 22 is rapidly purged of liquid by
the force of gravity.
In apparatus constructed in accordance with the present invention
it was found that the unit could be used with different types of
anesthetics, and that the concentration of anesthetic in the gas
stream could be controlled accurately over wide ranges. In addition
it was observed that the flow of anesthetic remained constant even
though the liquid level in the reservoir decreased due to the novel
arrangement for pressurizing the reservoir with a pressure line
terminating beneath the surface of the liquid.
For example, in one unit constructed in accordance with the
invention, the liquid conduit 20 included a capillary size segment
one-half inch in length and 0.0075 inch in diameter. The regulator
24 was adjusted so that the pressure within the line 22 was the
equivalent of 24 inches of water. An oxygen gas stream was passed
through the vaporizer at a rate of 1,000 cubic centimeters per
minute. The reservoir 14 was charged with a supply of liquid ether,
and the regulator 26 was adjusted to maintain the interior of the
vaporizer at a pressure equivalent to 15.2 inches of water. Liquid
ether flowed into the vaporizer at a rate equivalent to 66 cubic
centimeters of vapor per minute and was evaporated into the gas
stream to produce an anesthetic mixture of 6.6 percent ether vapor
in oxygen.
The unit was also capable of operation with other anesthetics and
at other concentrations. For example, the reservoir 14 was charged
with a supply of liquid halothane and the regulator 26 was adjusted
to maintain the interior of the vaporizer 12 at a pressure
equivalent to 11.8 inches of water, while the other variables
remained the same as in the previous example. Liquid halothane
flowed into the vaporizer at a rate equivalent to 28 cubic
centimeters per minute of vapor, and an anesthetic mixture of 2.8
percent of halothane vapor in oxygen was produced as the liquid
evaporated into the gas stream.
It should be understood that the above examples are set forth only
as an illustration of one embodiment of the invention. The specific
information included here should not be taken to limit the
invention, which is defined in the claims appended to the
specification.
Having reference now to FIG. 2, there is illustrated an anesthetic
vaporizing unit generally designated as 80 and comprising an
alternative embodiment of the present invention. The unit 80
includes a vaporizer chamber designated as a whole as 82 together
with a closed reservoir generally designated as 84. A stream of gas
to which an anesthetic vapor is to be added is conducted from a
source of pressurized gas, through a shutoff valve 86 and through a
conduit 88 to the vaporizer chamber 82 where an anesthetic vapor is
added to the gas stream. The anesthetic and gas mixture leaves the
vaporizer chamber 82 through a conduit 90 and is supplied to
suitable anesthetic mixture utilizing apparatus.
As with the unit 10 illustrated in FIG. 1 and described above,
liquid anesthetic is forced to flow from the closed reservoir 84
into a submerged lower end 92a of a liquid conduit 92 and to the
vaporizer chamber 82 at a rate of flow which is independent of the
level of liquid in the reservoir 84. In accordance with the
invention, the reservoir 84 is pressurized by means of a pressure
line 94 having a lower end 94a communicating with the reservoir at
a region beneath the surface of the anesthetic liquid in normal
operation.
Thus, as described in detail in connection with the embodiment of
FIG. 1, for a given constant pressure in the pressure line 22, the
pressure head causing evacuation of liquid through the liquid
conduit 92 remains constant regardless of the level of liquid in
the reservoir 84.
The embodiment of the invention illustrated in FIG. 2 differs from
the unit 10 described above in that the liquid conduit 92
communicates with the interior of the vaporizer chamber 82 by way
of a metering valve 96. Valve 96 includes an operating handle 98
with which the valve setting may be varied between several
different settings thereby to vary the resistance to the flow of
liquid from the reservoir 84 to the vaporizer 82. The valve 96 may
be of any known type such as a variable orifice valve, or a valve
of the type in which movement of the operating handle serves to
vary the effective length of a capillary size passageway.
In accordance with a feature of the invention the rate of flow of
anesthetic from the reservoir 84 to the vaporizer 82, and thus the
concentration of the gas anesthetic mixture, is controlled by
regulating the pressure differential existing between the reservoir
84 and the vaporizer 82 and/or by operating the metering valve 96
to vary the resistance to flow between the reservoir 84 and the
vaporizer 82. In the arrangement of FIG. 2, the unit 80 is
illustrated as used with anesthetic mixture utilizing apparatus of
a type which maintains the pressure within the vaporizer chamber 82
substantially constant, although a back pressure regulator similar
to the regulator 26 of FIG. 1 could be used if desired.
Accordingly, the pressure differential between the reservoir 84 and
the vaporizer 82 is varied by controlling the pressure in the
pressure line 94 with a pressure line regulator generally
designated as 100 and including a pressure regulated valve 102
having its inlet connected through a conduit 104 to the shutoff
valve 86, and having its outlet connected to the pressure line 94.
The valve 102 is controlled by a linkage 106 operated by a
diaphragm 108 acted upon by the pressure within the pressure line
94 in opposition to a spring 110, the tension of which is
adjustable by means of a handle 112.
Since the rate of flow of liquid anesthetic to the conduit 92, for
any particular setting of the metering valve 96, is proportional to
the pressure differential existing between the reservoir 84 and the
vaporizer 82, the rate of flow may be adjusted by operation of the
handle 112 to a setting which provides the desired constant
pressure within the pressure line 94. A pressure responsive
indicator 114 communicates with the pressure line 94 to provide a
pressure reading or, if desired, a direct reading of the pressure
differential existing between the reservoir 84 and the vaporizer
chamber 82.
Referring now more specifically to the construction of the
vaporizer chamber 82, this chamber may be constructed in any
suitable fashion and is illustrated as including a transparent
cylindrical wall 116 having its upper and lower ends closed by body
members 118 and 120. The body members are provided with suitable
passageways 88a, 90a and 92b communicating between the interior of
the vaporizer chamber and the conduits 88, 90 and 92
respectively.
In order to evaporate the liquid anesthetic reaching the vaporizer
chamber into the flowing gas stream a porous metal diffusion plate
or baffle 122 divides the vaporizer chamber 82 into two regions.
The stream of gas entering through the conduit 88 passes through
the plate 122 and through the conduit 90 to the anesthetic mixture
utilizing apparatus. Liquid anesthetic entering the vaporizer
chamber 82 from the conduit 92 falls onto the plate 122 and is
completely evaporated into the gas stream flowing through plate
122.
The liquid reservoir 84 of the unit 80 may be of any desired
construction and as illustrated includes a container 124 closed by
means of a sealing member 126 held against the container 124 by a
suitable clamp or other means (not shown). It should be appreciated
that if desired the unit 80 of FIG. 2, may include an arrangement
such as illustrated in the unit 10 of FIG. 1 wherein the reservoir
comprises the original container of the liquid anesthetic and
wherein the reservoir and the vaporizer chamber are combined in a
single unit. In addition, the unit 80 may be provided with a
restricted bleed conduit and with a pressure equalizing line
similar to the conduit 54 and line 53 of the unit illustrated in
FIG. 1.
In the operation of the unit 80, when it is desired to provide a
mixture of gas and anesthetic the shutoff valve 86 is opened so
that a stream of gas flows through the vaporizer chamber 82 and to
the anesthetic mixture utilizing apparatus. The reservoir 84 is
charged with a supply of anesthetic liquid, and the metering valve
96 as well as the pressure line regulator 100 are adjusted to
selected settings for producing the desired concentration of liquid
anesthetic in the gas stream. The liquid anesthetic is evacuated
from the reservoir 84 through the liquid conduit 92 and into the
vaporizer chamber 82 where the liquid evaporates completely into
the gas stream. The effective pressure head within the reservoir 84
causing the evacuation of the liquid remains constant as the liquid
level falls due to the fact that the reservoir is pressurized by
the pressure line 94 which terminates at a point beneath the
surface of the liquid.
Having reference now to FIGS. 3--7, there is illustrated a liquid
anesthetic vaporizing unit designated as a whole by the reference
numeral 140 and comprising a further embodiment of the present
invention. As best shown in FIG. 3, wherein the unit 140 is
illustrated in somewhat schematic form, the unit in general
includes a vaporizer chamber generally designated as 142 together
with a liquid anesthetic reservoir generally designated as 144. A
stream of gas to which an anesthetic vapor is to be added is
conducted from a source of pressurized gas through a conventional
shutoff valve 146 and through a conduit 148 and into the vaporizer
chamber 142. Within the vaporizer chamber, a liquid anesthetic is
vaporized and mixed with the stream of gas, and the mixture of gas
and an anesthetic is conducted to an anesthetic mixture utilizing
apparatus by way of a conduit 150.
As with the units described above in connection with FIGS. 1 and 2,
the unit 140 operates to supply a uniform anesthetic concentration
regardless of the level of liquid anesthetic in the reservoir 144.
Furthermore the concentration is accurately controlled and is
variable over a wide range. In addition, and in accordance with
further features of the invention, the unit is conveniently
arranged in a compact package with all controls and connections
readily accessible. Furthermore a single-manual control serves to
operate a novel dual-purpose valve to control both the admission of
pressurized gas to the reservoir and to control the volume of gas
flow into the vaporizer through conduit 148.
As best shown in FIGS. 4 and 5, the unit 140 shown schematically in
FIG. 3 comprises a compact assembly including a housing 152 with
the vaporizer chamber 142 and the liquid anesthetic reservoir 144
mounted in an accessible location on the exterior thereof. This
construction has the advantage that much of the apparatus is safely
enclosed within the housing 152, while the reservoir 144, chamber
142 and the necessary controls are readily accessible to an
operator.
Proceeding now to a more detailed description of the reservoir 144
and the vaporizer chamber 142, these elements are best illustrated
in FIG. 6. The vaporizer chamber comprises a somewhat bell-shaped
enclosure 154 preferably formed of glass or other transparent
material. The enclosure 154 is held in position over a base member
156 by a threaded clamp ring 158. The interior of the vaporizer
chamber enclosure 154 is sealed by a pair of sealing gaskets 160
and 162 held in compression by the clamp ring 158. The upper
portion of the vaporizer enclosure 154 is communicated with the
conduit 150 by means of a fitting 164 threadedly connected to an
elbow 166. A pair of seals 168 and 170 are held in compression
against the wall of the enclosure 154 by engagement between the
fitting 164 and the elbow 166.
In order to admit a stream of gas to the lower portion of the
vaporizer chamber from the conduit 148, the base member 156
includes a passageway 148a extending from the lower surface of the
base member 156 to the interior of the vaporizer chamber 142. A
porous metal diffusion plate or baffle 172 extends across the
vaporizer chamber 142 between the passageway 148a and the fitting
164 in order to accomplish the evaporation of liquid anesthetic
into the flowing gas stream. The baffle 172 is held in place by
means of a pressure ring 174 held in place by means of the seal
162.
In accordance with a feature of the present invention, the
reservoir 144 advantageously and conveniently comprises the
original container or bottle in which the liquid anesthetic is
supplied. As noted above, this arrangement greatly simplifies
handling and use of the anesthetic vaporizing unit. The bottle is
readily inserted into place on the unit 140 by threading the neck
of the bottle into an adapter member 176 which is in turn threaded
into an extension 156a of the base member 156. The lip of the
bottle is sealed by engagement with a sealing block or member 178
supporting an O-ring 180. It should be understood that various
adapter members 176 may be provided for mating with different types
of bottles containing different anesthetic materials. Thus the
vaporizer unit is universally adaptable, and the adapter member 176
serves to prevent the use of an anesthetic material other than the
material intended for use by the operator. In addition, since the
chamber 142 and the reservoir 144 are supported on the base member
156, a unitary, compact and easily handled subassembly is made
possible.
As is the case with the liquid anesthetic vaporizer units 10 and 80
described previously, evacuation of the liquid anesthetic material
contained within the reservoir 144 is accomplished by the
introduction of pressurized gas into the vaporizer chamber at a
level normally beneath the surface of the liquid. In this manner
the rate of flow, and thus the concentration, is maintained
independent of the level of liquid contained within the reservoir.
The pressurized gas is introduced into the reservoir through a
conduit 182, while liquid anesthetic material is discharged from
the reservoir vaporized chamber through a liquid capillary conduit
184. In accordance with a feature of the invention, the conduits
182 and 184 are part of a unitary assembly supported on the base
member 156 and designated as a whole by the reference numeral
186.
More specifically, and referring in particular to FIG. 6, the
pressurized gas conduit 182 communicates with a passageway 182a
formed within the base member 156. The upper end of the conduit 182
is attached to the base member 156, while its lower end is attached
to a fitting 188 having an outlet opening into the reservoir 144.
The liquid conduit 184 extends through a passageway 184a in the
base member 156 between the reservoir 144 and the vaporizer chamber
142. Within the reservoir 144, the liquid conduit 182, which is of
small, capillary size, is preferably protected by a jacket member
or tube 190 having its ends connected to the base member 156 and to
the fitting 188. Fluid is admitted to the lower end 184a of liquid
conduit 184 through a filter screen 192 held in place on fitting
188 by a threaded cap 194.
In order to protect the upper portion of the liquid conduit 184
within the vaporizer chamber 142, a jacket or tube 196 is provided
The lowermost end of jacket 196 is attached to a fitting 198
threaded into the base member 156 through the porous metal
diffusion plate 172. The uppermost end of the jacket 196 supports a
drip guide 200 for guiding liquid anesthetic material emerging from
the upper end 184b of the liquid conduit 184 outwardly of the
jacket 196 so that it descends onto the diffusion plate 172.
In order to prevent excess pressure buildup within the anesthetic
reservoir 144 due to evaporation of the liquid anesthetic, there is
provided a bleed passage from the reservoir 144 to the vaporizer
142. In the event of a pressure buildup, gas can flow from the
reservoir through a small hole 190a in the jacket 190 and into the
passage 184a in the base member 156. This gas is then vented into
the vaporizer chamber through a small passage 202 in the fitting
198.
When pressurized gas is admitted to the reservoir 144 through the
passageway 182a and the conduit 182, the reservoir becomes
pressurized and liquid anesthetic material is discharged from the
vaporizer through the filter screen 192 and the capillary conduit
184 into the vaporizer chamber 142 where it is deposited upon the
diffusion plate or baffle 172. A stream of gas to which anesthetic
gas is to be mixed enters the vaporizer chamber through the
passageway 148a and passes through the porous plate or baffle 172.
Liquid anesthetic material reaching the diffusion plate is
evaporated into the gas stream, and the anesthetic and gas mixture
is discharged from the vaporizer chamber 142 through the fitting
162, elbow 166 and conduit 150.
One aspect of the present invention resides in the convenient
manner in which the base member 156 together with the vaporizer
chamber 142 and the reservoir 144 can be quickly connected to and
detached from the housing 152. Referring now more particularly to
FIGS. 4 and 5, the housing includes a laterally extending support
arm 204 defining a recess 206 complementary in shape to the
projection 156a of the base member 156. This recess is flanked by a
pair of extensions 204a and 204b of the arm 204. In order to mount
the base member 156 together with the vaporizer chamber 142, the
base member 156 is merely dropped into place on the arm 204.
In order to make connections between the internal passageways 148a
and 182a of the base member 156, each passageway communicates with
a quick release nipple 208 and 210 respectively. The nipples 208
and 210 are slidingly received within recesses 212 and 214 formed
in the arm extensions 204a and 204b. The recesses 212 and 214 are
communicated by way of passageways 218 and 220 (FIG. 6)
respectively with the conduit 148 and a pressure line conduit 222
illustrated only in FIG. 3.
In order releasably to interconnect the conduit 150 with the
housing 152, the conduit 150 is connected to a slipfit connector
224 engageable with a nipple 226 (FIG. 5). Consequently, the entire
vaporizer assembly can readily be attached and detached from the
housing 152 at will.
Returning to FIG. 3, it can be seen that pressurized gas for
supplying the pressure line 222 is obtained from a source of
pressurized gas by way of the shutoff valve 146. A pressure
regulator generally designated as 228 serves to regulate the
pressure within the pressure line 222 and may if desired be of the
construction of the regulator 24 illustrated in more detail in FIG.
1. In addition, flow of pressurized gas through the pressure line
222 is controlled by a shutoff valve generally designated as 230.
In addition, the volume of flow of gas through the conduit 148 may
be regulated by means of throttling valve generally designated as
232.
In accordance with an important feature of the present invention,
the shutoff valve 230 in the pressure line 222 and the throttling
valve 232 in the conduit 148 are combined into a single-valve
assembly operable by means of a single-manual control. An important
advantage of this novel arrangement is that gas is admitted to the
vaporizer chamber at the time the reservoir is pressurized so that
the vaporizer cannot be flooded or subjected to excess liquid
anesthetic. More specifically, and as illustrated in FIG. 3, there
is provided a single dual-purpose valve generally designated as 234
including a central bore 237 defining a valve seat 238 for the
shutoff valve 230. In addition, the bore 237 receives an adjustable
threaded plug 240 defining a seat 242 for the throttling valve
232.
A valve member 244 is threaded into the opposite end of the bore
237 in order to control the opening and closing of both valves 230
and 232. The valve member 244 includes a first tapered valve
surface 244a engageable with seat 238 and a second tapered valve
surface 244b engageable with seat 242. An operating shaft 244c of
the valve body member 244 is adapted to be provided with an
operating handle 246 (FIG. 7) for moving the valve surfaces 244a
and 244b into and out of engagement with the seats 238 and 242. The
plug 240 is preferably adjusted so that when the valve 230 is fully
closed, the valve 232 is closed as well.
Upon rotation of the handle 246 to open valves 230 and 232, the
pressure line shutoff valve 230 opens rapidly to a fully open
position due to the relatively abrupt taper of surface 244a.
However, due to the relatively gradual taper of surface 244b, the
throttling valve 232 opens only gradually. Consequently, it is
possible for the single-operating handle 246 to control the
dual-purpose valve member for both the shutoff valve and the
throttling valve functions.
In accordance with a feature of the invention, the rate of flow of
anesthetic liquid through the liquid conduit 184, and thus the
concentration of the anesthetic mixture provided by the unit 140 is
controlled by controlling the pressure differential existing
between opposite ends of the liquid conduit 184. The pressure
regulator 228 controls the pressure of gas admitted to the
reservoir 144 through the pressure line 222. In a similar manner, a
back pressure regulator 248 controls the pressure existing within
the conduit 150, and thus the pressure within the vaporizer chamber
142 at the uppermost end of the liquid conduit 184. If desired, the
back pressure regulator 248 may be similar in construction to the
regulator 26 illustrated in detail in FIG. 1.
Control of the rate of flow of liquid anesthetic material through
the liquid conduit 184 is achieved through adjustment of one or
both of the pressure regulators 228 and 248. In the illustrated
embodiment of the invention, the back pressure regulator 248 is
normally adjusted by the operator to vary the flow rate and thus
the concentration, while the pressure line regulator 228 is
normally preadjusted or factory adjusted at a given level. In order
conveniently to adjust the rate of flow, an operating knob 250 for
the regulator 248 is positioned in an accessible position of the
face of the housing 152. The regulator 228 may be located behind a
removable plate 251 on a sidewall of the housing 152 (FIG. 7). A
differential pressure gauge 252 is connected between the pressure
line 222 and the conduit 150 (FIG. 3) and gives a pressure reading
proportional to the rate of flow through the liquid conduit 184.
Conveniently, this pressure gauge is located on the housing 152
above the adjustment knob 250. It should be understood that if
desired a flow indicator could be included in the system, for
example in the conduit 148 or the conduit 150, in accordance with
known practice.
Convenient attachment of the conduit 148 and the regulator 228 to a
conduit 254 (FIG. 3) leading to a source of pressurized gas by way
of the conventional shutoff valve 146 is made possible by a quick
release tube fitting 256 located on the face of the housing 152
(FIG. 7). The use of a single source of gas assures that the
vaporizer receives a gas flow whenever the reservoir is
pressurized. Connection of the back pressure regulator 248 by way
of a conduit 258 to a anesthetic mixture utilizing apparatus is
made possible by another tube fitting 260 on the housing 152.
The operation of the liquid anesthetic vaporizing unit 140 will be
apparent to those skilled in the art from the preceding detailed
description. Reviewing the operation, it is assumed initially that
the shutoff valve 146, the valve 230 and the valve 232 are all in
their closed positions and the unit 140 is not in operation. To
prepare the unit for operation, a bottle of a selected liquid
anesthetic is attached to the base member 156 by means of a mating
adapter 176. The vaporizer unit is connected to the housing 152 of
the unit 140 either before of after the bottle of anesthetic is
attached to the base member 156.
In order to begin operation, the shutoff valve 146 is opened to
admit pressurized gas to the unit 140 through the fitting 256 on
the face of housing 152. The operating handle 246 for the valves
230 and 232 is then opened in order to fully open the shutoff valve
230 and to open the throttling valve 232 in order that the flow
through the conduit 148 is at the desired rate. The back pressure
regulator 248 is adjusted through a manipulation of knob 250 until
the reading of gauge 252 indicates that the desired rate of flow of
liquid anesthetic is established.
Pressurized gas then flows from conduit 148 through the vaporizer
chamber and by way of conduit 150 through the back pressure
regulator 248 to the anesthetic mixture utilizing apparatus.
Simultaneously, pressure admitted to the reservoir by way of
conduit 222 pressurizes the reservoir and forces liquid anesthetic
material through the liquid conduit 184 into the reservoir chamber
where it is evaporated into the gas stream.
In a liquid anesthetic vaporizing unit similar to the unit 140 and
constructed in accordance with the present invention, it was found
that various anesthetic liquids such as ether, halothane,
trichloroethylene and methoxyflurane could be mixed with oxygen at
extremely accurate and widely variable concentration levels. It was
found that the rate of flow of the anesthetic material into the
vaporizer chamber could be accurately controlled, independently of
the liquid level, by control of the pressure drop between the
pressure line 222 and the conduit 150 as shown by the reading of
the pressure gauge 252. This pressure drop could readily be
controlled by adjustment of the regulator 248.
For example, it was found F.sub.the relationship of anesthetic flow
for various anesthetic liquids to pressure drop was approximately
represented by the following equations:
F.sub.e =-20+4.delta.P
F.sub.h =-21.5+1.7.delta.P
F.sub.t =-21+1.9.delta.P
F.sub.m =-6.75+0.78.delta.P
In these equations F.sub.e, F.sub.h, F.sub.t and F.sub.m represent
the flow of ether, halothane, trichloroethylene and methoxyflurane
respectively, expressed in cubic centimeters per minute of the
vapor, while .delta.P represents the pressure drop between the
pressure line conduit 222 and the outlet conduit 150 expressed in
inches of water. Since the flow through the conduit 184 is governed
by the rules of laminar flow, the flow is a substantially linear
function of the pressure drop within the operative range of
pressures which may be from about 15 to about 80 or more inches of
water.
It can thus be seen that the concentration of the anesthetic and
gas mixture can be accurately and conveniently controlled through a
wide range of concentrations simply by adjustment of the pressure
drop and the rate of gas flow through the vaporizer chamber. For
example, if ether is used and the valve 232 is adjusted to permit
oxygen to flow through the vaporizer chamber 142 at a rate of about
2,000 cubic centimeters per minute, while the pressure drop is
adjusted to about 45 inches of water, concentration of about 8
percent of ether in oxygen is obtained. In contrast, if
methoxyflurane is used and oxygen is conducted through the
vaporizer chamber at a rate of about 6,000 cubic centimeters per
minute, while the pressure drop is maintained at about 20 inches of
water, a concentration of about 0.34 percent is obtained.
It should be understood that these specific examples are included
as illustrative of one particular embodiment of the invention only,
and should not be taken to limit the scope of the invention.
While the present invention has been described in connection with
the details of particular embodiments thereof, various other
modifications and embodiments may be devised by those skilled in
the art. The present invention is not limited to the details of the
described embodiments except as included in the appended
claims.
* * * * *