U.S. patent number 3,814,091 [Application Number 05/218,337] was granted by the patent office on 1974-06-04 for anesthesia rebreathing apparatus.
Invention is credited to Melvyn L. Henkin.
United States Patent |
3,814,091 |
Henkin |
June 4, 1974 |
ANESTHESIA REBREATHING APPARATUS
Abstract
A general anesthesia rebreathing system comprised of a
disposable portion easily coupled to and decoupled from a permanent
portion. The disposable portion includes conventional breathing
tubing for coupling a source of fresh gas, as from an anesthesia
machine, to a patient and in addition an overflow tube for coupling
the patient end of the system to an overflow (pop-off) valve,
preferably mounted on the machine and constituting part of the
permanent portion. The overflow tube entrance is located close to
the patient end of the system and in communication with the tubing
which conveys expired gas to a reservoir, such as a conventional
breathing bag, mounted at the machine end. The arrangement assures
that the patient's initially expired dead space gas is conveyed by
the tubing to the reservoir with subsequently expired alveolar gas
being exhausted through the overflow tube and pop-off valve.
Inventors: |
Henkin; Melvyn L. (Tarzana,
CA) |
Family
ID: |
22814702 |
Appl.
No.: |
05/218,337 |
Filed: |
January 17, 1972 |
Current U.S.
Class: |
128/202.22;
128/205.17; 128/205.28; 128/909 |
Current CPC
Class: |
A61M
16/0833 (20140204); A61M 16/104 (20130101); F16L
55/04 (20130101); Y10S 128/909 (20130101); Y02C
20/40 (20200801); A61M 16/0078 (20130101); Y02C
10/06 (20130101) |
Current International
Class: |
A61M
16/10 (20060101); F16L 55/04 (20060101); A61M
16/00 (20060101); A61m 017/00 () |
Field of
Search: |
;128/188,191,202,203,204,272,277,145,145.6,145.5,145.7,145.8,142.4,211,210,207
;251/557 ;116/67 ;137/557 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Recla; Henry J.
Attorney, Agent or Firm: Lindenberg, Freilich &
Wasserman
Claims
What is claimed is:
1. An anesthesia system for coupling a fresh gas supply means to a
patient's airway, said system including
elongated breathing tube means having an open first end adapted to
communicate with said airway and an open second end adapted to
communicate with said supply means, said breathing tube means
providing a flow path in the direction from said airway to said
supply means and from said supply means to said airway;
overflow valve means having an input port and an exhaust port;
means mounting said overflow valve means in close proximity to said
elongated breathing tube means second end; and
elongated overflow tube means, substantially co-extensive with said
breathing tube means, having an open first end in communication
with said breathing tube means in close proximity to the first end
thereof and an open second end coupled to said overflow valve means
input port, said overflow tube means providing a flow path in the
direction from said breathing tube means to said overflow valve
means.
2. The system of claim 1 including reservoir means having an
entrance opening; and
means for communicating said reservoir means entrance opening with
said breathing tube means second end.
3. The system of claim 2 including an overpressure relief means for
permitting gas flow therepast in response to a positive pressure
differential between first and second surfaces thereof; and
means exposing said overpressure relief means first surface to said
breathing tube means first end and said second surface to ambient
pressure.
4. The system of claim 2 including an overpressure relief means for
permitting gas flow therepast in response to a positive pressure
differential between first and second surfaces thereof;
means exposing said overpressure relief means first surface to the
pressure in said first or second tube means and said second surface
to ambient pressure;
said overpressure relief means including means for producing an
audible alarm in response to gas flow therepast.
5. The system of claim 2 including means responsive to the pressure
in said first tube means exceeding a threshold value for producing
an audible alarm.
6. The system of claim 2 including a face mask having a single
output port; and
a tubular elbow means coupling said mask output port to said first
breathing tube first end.
7. The system of claim 2 wherein said reservoir means includes a
first flexible wall defining a first chamber;
a second flexible wall defining a second chamber disposed so as to
include at least a portion of said first flexible wall; and
wherein
said reservoir entrance opening is formed in said first flexible
wall for communication with said first chamber; and
a second opening formed in said second flexible wall for
communication with said second chamber.
8. The system of claim 2 wherein said overflow valve means includes
valve element means normally seated to hermetically isolate said
input and exhaust ports and responsive to a positive pressure
exceeding a first threshold from said input to said exhaust side of
said valve element means for unseating said valve element means to
permit gas flow therepast.
9. The system of claim 8 wherein said overflow valve means includes
a control port; and
means responsive to the application of a positive pressure
exceeding a second threshold to said control port for seating said
valve element means independent of the pressure differential
between said input and exhaust sides of said valve element
means.
10. The system of claim 9 including means for selectively
communicating the pressure available at said overflow valve means
input port to said control port.
11. The system of claim 9 wherein said reservoir means includes a
closed flexible outer wall;
a flexible septum wall peripherally sealed to the interior of said
outer wall to define first and second hermetically isolated
chambers;
said entrance opening existing in said outer wall and communicating
with said first chamber;
a second opening existing in said outer wall and communicating with
said second chamber; and
means for selectively communicating the pressure available in said
second chamber to said control port.
12. The system of claim 2 wherein said reservoir means includes a
closed flexible outer wall;
a flexible septum wall peripherally sealed to the interior of said
outer wall to define first and second hermetically isolated
chambers;
said entrance opening existing in said outer wall and communicating
with said first chamber; and
a second opening existing in said outer wall and communicating with
said second chamber.
13. The system of claim 12 wherein at least a portion of said
reservoir means outer wall is transparent and wherein said septum
wall is visible therethrough.
14. The system of claim 2 including a closed section of elastic
tubing; and
means communicating the interior of said section of elastic tubing
with the interior of said breathing tube means.
15. The system of claim 20 wherein said section of elastic tubing
is concentrically mounted around the exterior of a portion of said
breathing tube means;
means sealing at least one end of said section of elastic tubing to
said breathing tube means; and wherein
said means communicating the interior of said section and the
interior of said breathing tube means comprises an opening defined
in said breathing tube means between the sealed ends of said
section.
16. The system of claim 15 including elastic band means mounted
around said section of elastic tubing with said opening in said
breathing tube means between said elastic band means and said one
sealed end for holding said section to said breathing tube means;
and
gas leakage means formed in said section on the side of said
elastic band means remote from said opening.
17. The system of claim 2 wherein said breathing tube means
includes first and second breathing tubes having open first and
second ends;
patient communications means defining a passageway there through
having first and second open ends;
means forming a gas flow path between the first ends of said first
and second breathing tube means and the first end of said
passageway; and
means for communicating the second end of said second breathing
tube means with said reservoir means entrance opening.
18. The system of claim 17 including a unidirectional expiratory
gas valve means operatively disposed between said passageway first
end and said first tube means first end for preventing gas flow in
said first tube means in a direction from the second to the first
end thereof; and
a unidirectional inspiratory gas valve means operatively disposed
between said second tube means second end and said reservoir means
entrance opening for preventing gas flow in said second tube means
in a direction from the first to the second end thereof.
19. The system of claim 18 including means responsive to the
pressure in said first or second tube means exceeding a threshold
value for producing an audible alarm.
20. The system of claim 18 including a canister having open first
and second ends respectively in communication with said inspiratory
gas valve means and said reservoir entrance opening, said canister
having CO.sub.2 absorber material therein.
21. The system of claim 18 including an overpressure relief means
for permitting gas flow therepast in response to a positive
pressure differential between first and second surfaces thereof;
and
means exposing said overpressure relief means first surface to said
passageway first end and said second surfaces to ambient
pressure.
22. The system of claim 18 including an overpressure relief means
for permitting gas flow therepast in response to a positive
pressure differential between first and second surfaces
thereof;
means exposing said overpressure relief means first surface to the
pressure in said first or second tube means and said second surface
to ambient pressure;
said overpressure relief means including means for producing an
audible alarm in response to gas flow therepast.
23. The system of claim 18 wherein said expiratory valve means
comprises a housing having an input port and a first output port
and including passage means extending therebetween;
a valve member;
valve seat means formed within said passage means; and
means mounting said valve member in said passage means adjacent
said valve seat means for permitting gas flow therepast only in
response to a positive pressure differential between said input and
said first output port.
24. The system of claim 8 wherein said expiratory valve means
housing includes a second output port in communication with said
first output port; and
means coupling said expiratory valve means second output port to
said overflow tube means first end.
25. The system of claim 23 including an overpressure relief means
for permitting gas flow therepast in response to a positive
pressure differential between first and second surfaces thereof;
and
means mounting said overpressure relief means in said expiratory
valve means housing with the first surface thereof exposed to said
input port and with the second surface thereof exposed to ambient
pressure.
26. The system of claim 17 wherein said patient communication means
comprises a face mask having a single output port; and wherein
said means forming a gas flow path includes Y-piece means having a
single input port and first and second paths respectively coupling
said input port to first and second output ports; and
a tubular elbow means coupling said mask output port to said
Y-piece means input port.
27. The system of claim 26 including an expiratory valve means
positioned in said Y-piece means first passage between said input
port and said first output port;
said expiratory valve means including;
a valve member;
valve seat means formed within said first passage; and
means mounting said valve member in said first passage adjacent
said valve seat means for permitting gas flow therepast only in
response to a positive pressure differential between said Y-piece
means input port and first output port.
28. The system of claim 27 wherein said Y-piece means includes a
third output port in communication with said first output port;
means coupling said third output port to said overflow tube means
first end;
an overpressure relief means for permitting gas flow in response to
a positive pressure differential between first and second surfaces
thereof; and
means mounting said overpressure relief means in said Y-piece means
with the first surface thereof exposed to said input port and with
the second surface thereof exposed to ambient pressure.
29. An anesthesia circuit useful in combination with
a source of fresh anesthesia gases and a gas overflow valve, having
input and exhaust ports, mounted proximate to said fresh gas
source, said circuit comprising:
elongated breathing tube means having an open second end adapted to
communicate with said fresh gas source and an open first end
adapted to communicate with a patient's airway, said breathing tube
means providing a flow path in the direction from said airway to
said fresh gas source and from said gas source to said airway;
and
an elongated overflow tube means of substantially the same length
as said breathing tube means, having an open first end in
communication with said breathing tube means proximate to the first
end thereof and an open second end adapted to communicate with said
overflow valve input port, said overflow tube means providing a
flow path in the direction from said breathing tube means to said
overflow valve.
30. The system of claim 29 including reservoir means having an
entrance opening; and
means for communicating said reservoir means entrance opening with
said breathing tube means second end.
31. The system of claim 30 wherein said reservoir means includes a
closed flexible outer wall;
a flexible septum wall peripherally sealed to the interior of said
outer wall to define first and second hermetically isolated
chambers;
said entrance opening existing in said outer wall and communicating
with said first chamber; and
a second opening existing in said outer wall and communicating with
said second chamber.
32. The system of claim 30 including a section of elastic tubing;
and
means communicating the interior of said section of elastic tubing
with the interior of said breathing tube means.
33. The system of claim 32 wherein said section of elastic tubing
is concentrically mounted around the exterior of a portion of said
breathing tube means;
means sealing at least one end of said section of elastic tubing to
said breathing tube means; and wherein
said means communicating the interior of said section and the
interior of said breathing tube means comprises an opening defined
in said breathing tube means between the sealed ends of said
section.
34. The system of claim 33 including elastic band means mounted
around said section of elastic tubing with said opening in said
breathing tube means between said elastic band means and said one
sealed end for holding said section to said breathing tube means;
and
gas leakage means formed in said section on the side of said
elastic band means remote from said opening for permitting gas
leakage therepast.
35. The system of claim 34 wherein said gas leakage means includes
means for producing an audible alarm in response to gas leakage
therepast.
36. The system of claim 30 wherein said breathing tube means
includes first and second breathing tubes having open first and
second ends;
patient communication means defining a passageway there through
having first and second open ends;
means forming a gas flow path between the first ends of said first
and second breathing tube means and the first end of said
passageway; and
means for communicating the second end of said second breathing
tube means with said reservoir means entrance opening.
37. The system of claim 36 including a unidirectional expiratory
gas valve means operatively disposed between said passageway first
end and said first tube means first end for preventing gas flow in
said first tube means in a direction from the second to the first
end thereof; and
a unidirectional inspiratory gas valve means operatively disposed
between said second tube means second end and said reservoir means
entrance opening for preventing gas flow in said second tube means
in a direction from the first to the second end thereof.
38. The system of claim 37 including a canister having open first
and second ends respectively in communication with said inspiratory
gas valve means and said reservoir entrance opening, said canister
having CO.sub.2 absorber material therein.
39. The system of claim 37 including an overpressure relief means
for permitting gas flow therepast in response to a positive
pressure differential between first and second surfaces thereof;
and
means exposing said overpressure relief means first surface to said
passageway first end and said second surface to ambient
pressure.
40. The system of claim 26 including an overpressure relief means
for permitting gas flow therepast in response to a positive
pressure differential between first and second surfaces
thereof;
means exposing said overpressure relief means first surface to the
pressure in said first or second tube means and said second surface
to ambient pressure;
said overpressure relief means including means for producing an
audible alarm in response to gas flow therepast.
41. The system of claim 37 wherein said expiratory valve means
comprises a housing having an input port and a first output port
and including passage means extending there between;
a valve member;
valve seat means formed within said passage means; and
means mounting said valve member in said passage means adjacent
said valve seat means for permitting gas flow therepast only in
response to a positive pressure differential between said input and
said first output port.
42. The system of claim 41 wherein said expiratory valve means
housing includes a second output port in communication with said
first output port; and
means coupling said expiratory valve means second output port to
said overflow tube means first end.
43. The system of claim 36 wherein said patient communication means
comprises a face mask having a single output port; and wherein
said means forming a gas flow path includes Y-piece means having a
single input port and first and second paths respectively coupling
said input port to first and second output ports; and
a tubular elbow means coupling said mask output port to said
Y-piece means input port.
44. The system of claim 43 including an expiratory valve means
positioned in said Y-piece means first passage between said input
port and said first output port;
said expiratory valve means including;
a valve member;
valve seat means formed within said first passage; and,
means mounting said valve member in said first passage adjacent
said valve seat means for permitting gas flow therepast only in
response to a positive pressure differential between said Y-piece
means input port and first output port.
45. The system of claim 44 wherein said Y-piece means includes a
third output port in communication with said first output port;
means coupling said third output port to said overflow tube means
first end;
an overpressure relief means for permitting gas flow in response to
a positive pressure differential between first and second surface
thereof; and,
means mounting said overpressure relief means in said Y-piece means
with the first surface thereof exposed to said input port and with
the second surface thereof exposed to ambient pressure.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to apparatus for administering
general anesthetics in the gaseous state and more particularly to
an anesthesia rebreathing system, comprised of a permanent portion
and a disposable portion:
The use of conventional general anesthesia administration apparatus
inherently involves the danger of cross contamination between
patients, sometimes with fatal results. Typically, such apparatus,
for example an anesthesia circle, is comprised of one way valve
controlled inspiratory and expiratory tubes communicating between
an anesthesia machine providing fresh gases, and a patient. The
inspiratory and expiratory tubes generally communicate with the
patient's lungs via a tubular Y-piece and a mask or endotrachael
tube. At the anesthesia machine end of the system, the expiratory
tube normally communicates with the upper end of a canister of
CO.sub.2 absorber material. The lower end of the canister is
coupled to the machine end of the inspiratory tube and to a gas
reservoir such as a breathing bag. The fresh gas input from the
anesthesia machine is usually coupled to the inspiratory tube close
to the breathing bag. On expiration, the patient's gas is channeled
through the one way valve in the expiratory tube to the CO.sub.2
absorber material. On inspiration, the patient's gases are pulled
through the inspiratory tube via the one way inspiratory valve,
from the breathing bag and fresh gas supply. A pop-off valve is
normally located proximate to the CO.sub.2 absorber canister for
exhausting expired gas.
It will, of course, be readily appreciated that in the utilization
of such anesthesia apparatus, various parts of the apparatus are
exposed to gas expired by the patient, who, if infected, will
transmit bacteria throughout these parts. It has been found that
cultures taken from such patient exposed parts will grow bacteria
after the apparatus has been subjected to such cleaning procedures
as are considered practical for each particular part of the
apparatus.
In recognition of the foregoing contamination problem, recent
attempts have been made to sufficiently reduce the cost of
anesthesia apparatus so that most of the patient exposed parts can
be discarded after a single use. Generally, these attempts have
merely involved fabricating conventional apparatus in an
inexpensive manner so that disposal is economically feasible. Such
attempts have not, however, been too successful because cost
reduction has not been sufficiently significant and because such
cost reduction has necessitated the introduction of performance
compromises which have often adversely affected the reliability and
ease of use of various parts, such as the pop-off valve.
Accordingly, one of the important objects of the present invention
is to provide an anesthesia rebreathing system comprised of a
disposable portion and a permanent portion configured so as to
minimize the structural complexity and cost of the disposable
portion, while assuring that the disposable portion includes all
elements which are likely to contaminate gas inhaled by a
patient.
SUMMARY OF THE INVENTION
The present invention is directed to an improved general anesthesia
administration system incorporating disposable circuit apparatus
for coupling a permanent system portion to a patient. In accordance
with a first embodiment of the invention, the circuit constitutes
what is generally referred to as a circle, including both
inspiratory and expiratory tubes. In accordance with a second
embodiment of the invention, the circuit utilizes a single tube
alternately used for inspiration and expiration. This second type
of circuit is often referred to as a Magill type circuit. In
accordance with the preferred embodiment of the invention, the
permanent system portion is designed so that it can be used
interchangeably with both circuit embodiments.
In accordance with an important aspect of the invention, both
circuit embodiments incorporate an overflow tube whose entrance
communicates with the tubing carrying expired gas, close to the
patient. The overflow tube exits at an overflow (pop-off) valve
which can thus be located close to the anesthesia machine whereat
it can be conveniently controlled by the attending anesthetist and
can, preferably, constitute part of the permanent system portion.
By locating the overflow tube entrance close to the patient, the
overflow tube is able to function to preferentially vent alveolar
gases, rich in CO.sub.2, through the pop-off valve, and to save
dead space and unbreathed gas, rich in O.sub.2, within the tubing
and reservoir for rebreathing. As a consequence, the maximum amount
of CO.sub.2 is vented, thus substantially eliminating the need to
use CO.sub.2 absorber material. The unidirectional flow in (away
from patient) and the length (i.e., approximately three feet) of
the overflow tube prevents the pop-off valve from contaminating gas
inspired by the patient.
Both circuit embodiments incorporated a reservoir having flexible
walls. Dead space gas initially expired by a patient is conveyed
through the breathing tube to the reservoir with subsequently
expired alveolar gas being conveyed through the overflow tube to
the pop-off valve. As a consequence of the pop-off valve
constituting part of the system permanent portion, a refined and
highly reliable pop-off valve mechanism can be afforded while still
minimizing the cost of the disposable circuit.
The reservoir wall is flexible so as to enable the patient's
breathing to be assisted by squeezing the reservoir. Squeezing can
be accomplished manually or with a mechanical ventilator. In
accordance with a preferred embodiment of the invention, the
reservoir is formed by a flexible outer wall having a flexible
septum mounted therein so as to define two isolated chambers. The
first chamber is intended to communicate with a mechanical
ventilator and the second chamber is intended to communicate with
the circuit tubing. As the ventilator pressurizes the first
chamber, the pressure is transmitted to the second chamber via the
flexible septum and thereby to the patient's airway without
contamination of either the mechanical ventilator by the patient or
the patient by the mechanical ventilator.
In accordance with a further feature of the invention, the pop-off
valve is preferably selectably operable in two different modes;
i.e., (1) as a variable orifice pressure relief valve or (2) as a
balanced valve which closes in response to a positive control
pressure, the mode being defined by the control pressure applied
which can be selectively derived by the anesthetist from different
sources dependent on the type of ventilation being employed; i.e.,
spontaneous, manually assisted, or mechanically controlled.
In accordance with a still further feature of the invention, a
section of elastic material is preferably incorporated in the
circuit tubing in communication with the pressure within the
tubing. The elastic section stretches as pressure builds up within
the circuit thereby preventing sudden step like increases in
pressure which could be injurious to a patient's lungs. Use of the
elastic section permits the use of inexpensive reservoirs having
inelastic walls of plastic, for example, instead of requiring
elastic wall, e.g., rubber, reservoirs which should otherwise be
used to prevent sudden pressure increases.
In accordance with a still further aspect of the invention, an
overpressure relief means is incorporated in the circuit,
preferably close to the patient end, to maximize protection of the
patient's lungs against accidental rupture due to overpressure
malfunction in the rest of the system. In a first embodiment, an
overpressure relief valve is formed within a housing common to the
expiratory valve and Y-piece tubing coupling the mask or
endotracheal tube to the breathing and overflow tubes. In a second
embodiment, the previously mentioned elastic section is sealed to
the breathing tube by an elastic band which stretches and leaks
when the pressure within the breathing tube becomes excessive.
In accordance with a still further aspect of a preferred embodiment
of the invention, an audible alarm means is incorporated in the
overpressure relief means for alerting the anesthetist when an
overpressure condition exists.
Although, the need for using CO.sub.2 absorber material is
substantially eliminated in systems in accordance with the
invention, in order to accommodate special circumstances and
preferences of individual anesthetists, a CO.sub.2 absorber
canister is provided which can be used in the circle system at the
option of the anesthetist. The canister is preferably constructed
so as to be easily inserted in series with, and just upstream from,
the inspiratory valve.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a perpsective view of a general anesthesia rebreathing
system embodiment in accordance with the present invention
illustrating both the disposable and permanent portions system;
FIG. 2 is an enlarged perspective view better illustrating the
disposable portion of the system of FIG. 1 and the interface
between the disposable and permanent portions;
FIG. 3 is a schematic flow diagram of an anesthesia circle system
in accordance with the invention;
FIG. 4 is a schematic flow diagram of a single tube (Magill type)
anesthesia circuit system in accordance with the invention;
FIG. 5 is a side view, partially broken away, illustrating in
detail the interface region of the system of FIG. 2 between the
disposable and permanent portions;
FIG. 6 is a plan view, partially broken away, illustrating the
interface region of the system shown in FIG. 5;
FIGS. 7A and 7B are sectional views taken substantially along the
plane 7--7 of FIG. 5 respectively illustrating two different
positions of the controller valve for coupling system pressure and
ventilator pressure to the pop-off valve control port;
FIG. 8 is a sectional view taken substantially along the plane 8--8
of FIG. 5 illustrating a third position of the controller
valve;
FIG. 9 is a sectional view taken substantially along the plane 9--9
of FIG. 5 illustrating the valve element in the controller valve
for varying the pop-off valve exhaust orifice;
FIG. 10 is a developed view illustrating the relationship between
the controller valve spool element and the pop-off valve exhaust
orifice;
FIG. 11 is a side elevational view illustrating both the
inspiratory valve structure and mounting unit for coupling the
disposable anesthesia circuit to the system permanent portion;
FIG. 12 is a perspective view of the mounting unit shown in FIG.
11;
FIG. 13 is a perspective view of the inspiratory valve structure
shown in FIG. 11;
FIG. 14 is a side elevational view partially broken away
illustrating the patient end of the circuit and more particularly a
preferred Y-piece embodiment containing the expiratory valve and
overpressure relief valve;
FIG. 15 is a sectional view taken substantially along the plane
15-15 of FIG. 14;
FIG. 16 is an enlarged sectional view taken substantially along the
plane 16-16 of FIG. 15 illustrating the details of an overpressure
relief valve;
FIG. 17 is a sectional view taken substantially along the plane
17-17 of FIG. 14;
FIG. 18 is a sectional view of a preferred form of reservoir in
accordance with the present invention for isolating a mechanical
ventilator from a patient's gas;
FIG. 19 is a sectional view taken substantially along the plane
19-19 of FIG. 18;
FIG. 20 is a side elevational view illustrating the manner in which
the reservoir of FIGS. 18 and 19 is structurally incorporated in
the system and further illustrating the incorporation of a canister
of CO.sub.2 absorber material between the reservoir and inspiratory
valve;
FIG. 21 is an enlarged vertical sectional view taken through the
CO.sub.2 absorber canister of FIG. 20;
FIG. 22 is a horizontal sectional view taken substantially along
the plane 22-22 of FIG. 21;
FIG. 23 is a perspective view similar to FIG. 2 except, however,
illustrating the utilization of an elastic section for the purpose
of preventing sudden pressure increases within the system;
FIG. 24 is a sectional view taken substantially along the plane
24-24 of FIG. 23;
FIG. 25 is a sectional view taken substantially along the plane
25--25 of FIG. 24;
FIG. 26 is a vertical sectional view similar to FIG. 24
illustrating a modified form of elastic section which functions to
provide overpressure relief;
FIG. 27 is a sectional view taken substantially along the plane
27--27 of FIG. 26.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Attention is now called to FIG. 1 which illustrates a general
anesthesia rebreathing system in accordance with the present
invention. Briefly, the rebreathing system as shown in FIG. 1
includes a substantially conventional anesthesia machine 10 which
enables the attending anesthetist to meter and mix appropriate
anesthetic agents which are then delivered to a supply hose 12 at
an appropriate pressure, up to 50 psig. The gases supplied through
hose 12 are then delivered through, what is generally referred to
as an anesthesia circuit 14, to the patient. The anesthesia circuit
14 functions to:
1. Carry the gases to the patient and communicate with the
patient's airway via a mask or endotrachael tube;
2. Serve as a reservoir between the varying flow in and out of the
patient and the constant rate of supply;
3. Eliminate excess gas from the system;
4. Reduce the inspired concentration of CO.sub.2 to acceptable
levels; and
5. Enable the patient's breathing to be assisted or controlled by
manual or mechanical means.
The machine 10 is normally provided with sleeves 15 for holding a
mounting arm 16 which functions as a support for the anesthesia
circuit and pressure gauge 18.
As has been previously pointed out herein, it is extremely
difficult and impractical to fully sterilize all patient exposed
parts of an anesthesia system after each use. As a consequence, it
has long been recognized that utilization of anesthesia equipment
presents a potential hazard of cross contamination between
patients. In recognition of this potential hazard, efforts have
been made in the prior art to fabricate the patient exposed parts
sufficiently inexpensively to make disposal after a single use
economically feasible. These attempts thus far have been only
moderately successful because the required cost reductions have
compromised performance and reliability. The present invention is
directed to an anesthesia system designed to minimize the
complexity and cost of the disposable portion while retaining
within the disposable portion all of the elements which are likely
to contaminate patient inspired gas. Briefly, in accordance with
the present invention, two embodiments of disposable anesthesia
circuits are disclosed which can interchangeably be easily coupled
to a common permanent system portion. The two anesthesia circuit
embodiments represent modifications of circuits commonly known as
(1) an anesthesia circle and (2) a single tube anesthesia circuit
(Magill type). In accordance with the present invention, the
permanent system portion is comprised of the machine 10 including
up to the free end of the mounting arm 16. The disposable portion
of the system mates easily via a quick disconnect coupling to the
free end of the mounting arm 16.
More particularly, with continuing reference to FIG. 2, the circuit
14 is coupled to the mounting arm 16 by a mounting unit 20 which
will be described in greater detail hereinafter. The mounting arm
16 has an overflow (commonly referred to as a "pop-off") valve 22
mounted near the free end thereof. As will be seen hereinafter, the
operational mode of the valve 22 is selectable by the anesthetist
by operation of a manual controller valve 24.
The mounting arm 16 and the elements fixed thereto, e.g., the
pop-off valve 22 constitute part of the permanent or reusable
portion of a system in accordance with the preferred embodiment of
the invention. The circuit 14 constitutes the disposable portion
and includes all of the hardware elements between the mounting unit
20 and the patient airway communication means, e.g., face mask 26.
Briefly, the mounting unit 20 quickly connects and disconnects to
the mounting arm 16 and provides gas flow paths therethrough to
carry the gas supplied by hose 12 through the circuit 14 to the
mask 26 and to carry CO.sub.2 rich gases expired by the patient to
the pop-off valve 22. The circuit illustrated in FIG. 2 constitutes
an anesthesia circle and the flow path therethrough will be
discussed in connection with FIG. 3. To facilitate identification
of elements, it is pointed out that the circuit 14 of FIG. 2
includes an inspiratory valve 28 which passes fresh gas supplied
from the hose 12 by the arm 16, through an inspiratory tube 30, to
a Y-piece 32 coupled to the mask 26. Also in communication with the
inlet side of the inspiratory valve 28 is a gas reservoir or
breathing bag 34.
The Y-piece 32 is also coupled to the inlet end of an expiratory
tube 36 which has an expiratory valve in series therewith (not
shown in FIG. 2). The outlet end of the expiratory tube 36 is
coupled to the mounting unit 20 and communicates with the inlet
side of the reservoir 34.
As will be better appreciated hereinafter, in accordance with a
significant aspect of the invention, the circuit includes an
overflow tube 38 extending from the Y-piece 32 back to the mounting
unit 20 where at it is in turn coupled to the input port of the
pop-off valve 22.
Attention is now called to FIGS. 3 and 4 which respectively
constitute schematic flow diagrams of two circuit embodiments in
accordance with the present invention; namely (1) an anesthesia
circle (FIG. 3) and (2) a single tube Magill type circuit (FIG. 4).
Prior to considering the gas flow paths through these two circuits,
it is important to recognize that the gas exhaled by a patient can
appropriately be considered to consist of dead space gas and
alveolar gas. The dead space gas enters only the mouth, nose, and
large passages in the lungs and does not interact with the blood
flowing through the lungs. Therefore, dead space gas leaves the
patient as it enters except for changes in temperature and
humidity. It gives up no oxygen (O.sub.2) or anesthetic agent and
takes up no carbon dioxide (CO.sub.2).
On the other hand, alveolar gas does interact with the blood of the
lung and it leaves the patient depleted in O.sub.2 and rich in
CO.sub.2. In an adult having a tidal volume of 500 cc, 150 cc is
normally dead space gas and 350 cc is normally alveolar gas. The
circuits for FIGS. 3 and 4 in accordance with the present invention
are configured so as to retain the dead space and unbreathed gases
within the system and preferentially vent the CO.sub.2 rich
alveolar gases through the pop-off valve 22. Thus, with a fresh gas
inflow above 4 liters per minute, the inspired CO.sub.2
concentration remains acceptably low without requiring the use of
CO.sub.2 absorber material within the system.
Attention is now specifically called to FIG. 3 which depicts the
flow paths through an anesthesia circle circuit embodiment in
accordance with the present invention. Dashed line 40 in FIG. 3
represents the interface between the disposable portion to the left
and the permanent portion to the right. Fresh gas is supplied
through tube 42 shown in FIG. 3 to the inlet side 43 of inspiratory
valve 28. The fresh gas enters via a small orifice (not shown) with
a high pressure drop across it thus preventing any flow to and
contamination of the permanent portion of the patient's expired
gas. The inlet side of inspiratory valve 28 also communicates with
the reservoir 34. The inspiratory valve permits gas flow
therethrough only in the direction indicated by the arrow shown at
the outlet side thereof, thus allowing gas to be inspired by a
patient from the inspiratory tube 30. Gas expired by the patient is
applied to the inlet side of expiratory valve 44. The outlet side
of expiratory valve 44 communicates with the previous mentioned
overflow tube 38 and expiratory tube 36. The other end of
expiratory tube 36 communicates at the anesthesia machine end of
the system with the reservoir 34. The machine end of the overflow
tube 38 communicates with the pop-off valve 22 constituting part of
the system permanent portion.
In the operation of the anesthesia circle of FIG. 3, fresh gas
flows into the circle via tube 42 and the inspiratory and
expiratory valves 28 and 44 keep the flow around the circle
undirectional. When the patient breathes in or the reservoir 34 is
squeezed, the inspiratory valve 28 opens, the expiratory valve 44
closes, and fresh gas and gas from the reservoir 34 and inspiratory
breathing tube 30 flow into the patient's airway via mask 26. When
the patient breathes out, either spontaneously or because the
pressure on the reservoir has been relaxed, the expiratory valve 44
opens and the inspiratory valve 28 closes and gas flows from the
patient to the expiratory breathing tube 36 into the reservoir 34.
At the same time, fresh gas enters via the fresh gas inlet 42 and
flows primarily into the reservoir.
At some point during expiration during spontaneous ventilation, the
reservoir 34 becomes full and the gas near the patient end of the
circuit starts flowing through the overlfow tube 38 and out the
pop-off valve 22, which during spontaneous ventilation, merely
functions as a variable orifice pressure relief valve with an
opening pressure of 1 cm of H.sub.2 O. This gas which is the last
to leave the patient is alveolar gas which is rich in CO.sub.2. The
dead space gas, exhaled by the patient prior to expiration of the
alveolar gas, is either further up the expiratory tube or in the
distensible reservoir when the alveolar gas is exhaled.
Operation during manually assisted ventilation, i.e., when
squeezing the reservoir, is similar to operation during spontaneous
ventilation. However, flow out of the overflow tube 38 occurs
during inspiration, i.e., when the reservoir is being squeezed, due
to the pressure in the system. An alternative and preferred method
of operation during manually assisted and controlled ventilation is
to automatically positively close the pop-off valve 22 during
inspiration when the reservoir is squeezed and permit it to open
during expiration. As will be seen hereinafter when the operation
of the pop-off valve is explained in connection with FIG. 5, an
operational mode for the pop-off valve can be selected by the
anesthetists such that when system pressure increases in response
to the reservoir being squeezed, the pop-off valve 22 is sealed
closed. Relaxation of the pressure on the reservoir 34 reduces the
pressure within the circuit so that on expiration by the patient,
the dead space gas will initially flow through the expiratory tube
and into the reservoir 34 with the subsequently expired alveolar
gas then flowing through the overflow tube 38 out the pop-off valve
22.
Thus, in summary, during spontaneous ventilation, the pop-off valve
preferably comprises merely a variable orifice pressure relief
valve which opens in response to pressure within the system. During
manually assisted or controlled ventilation, the pop-off valve
preferably seals closed in response to pressure within the system,
i.e., inspiration.
As will be seen hereinafter, the operational mode of the pop-off
valve 22 is determined by the pressure applied to a control port 47
thereof. This control pressure is selected by the anesthetist by
manual control of a three way controller valve 24. The valve 24
enables any one of three control pressures to be available at an
output port 49 for application to the pop-off valve control port 47
for determining the pop-off valve operational mode. Briefly, the
control input port 47 of the pop-off valve 22 can be exposed to
ambient pressure via valve 24 and tube 50. In this position of the
three way valve, the pop-off valve 22 will function merely as a
variable orifice pressure relief valve. During manually assisted or
controlled ventilation, in order that the pop-off valve seals
closed during inspiration, the valve 48 is positioned so as to
couple tube 52 to the pop-off valve control port 47 to apply system
pressure thereto. When using a mechanical ventilator, and the
preferred reservoir embodiment, to be discussed hereinafter in
connection with FIGS. 18-20, the pressure provided by the
ventilator can be coupled through tube 54 and valve 24 to the
pop-off valve control port 47 to again assure that the pop-off
valve 22 is closed when the system is being pressurized during
inspiration.
Attention is now called to FIG. 4 which represents a schematic flow
diagram of a single tube anesthesia circuit often referred to as a
Magill type circuit. A Magill type circuit is characterized by the
utilization of a single breathing tube 60 in lieu of the
inspiratory and expiratory breathing tubes 30 and 36 of a circle
system as shown in FIG. 3. Thus, gas flow through the breathing
tube 60 of FIG. 4 is alternately toward the patient on inspiration
and away from the patient on expiration. The Magill type circuit of
FIG. 4 does not require the utilization of the unidirectional
inspiratory and expiratory valves as is characteristic of the
circle system of FIG. 3.
During spontaneous ventilation, using the system of FIG. 4, as the
patient breathes in, he draws fresh gas from the inlet tube 60 and
the reservoir 64. On expiration, his initially expired gas,
constituting the dead space gas, will flow back through the
breathing tube 60 to the reservoir 64. As the reservoir 64 becomes
full, the subsequently expired alveolar gases will flow via the
overflow tube 66 to the permanent pop-off valve 22. As has been
previously pointed out, the permanent system portion can be used
interchangeably with both the circle and single tube circuits of
FIGS. 3 adn 4.
During spontaneous ventilation utilizing the circuit of FIG. 4, the
previously discussed pop-off valve 22 is operated in a variable
orifice pressure relief mode by applying ambient pressure from tube
50 via three way valve 24 to the control port 47 of the pop-off
valve. When ventilation is assisted or controlled by squeezing the
reservoir 64, it is necessary to operate the pop-off valve 22 so
that it seals closed in response to a pressure increase during
inspiration or otherwise CO.sub.2 rich gas will be retained within
the system and fresh gas will exit through the pop-off valve. This
operational mode is selected by applying either system pressure
from tube 52, via valve 24, to the pop-off valve control port 47 or
by applying ventilator pressure via tube 54 and valve 24 to the
control port 47.
Attention is now called to FIGS. 5 and 6 which illustrate the
structural details of the free end of the mounting arm 16 and the
mounting unit circuit portion 20 which couples to the arm 16.
The mounting arm 16 is provided with a nipple 70 extending from the
underside thereof for coupling to the previously mentioned fresh
gas supply hose 12. The nipple 70 communicates with a fresh gas
passageway 72 extending parallel to the elongation of the arm 16.
The passageway 72 opens at a front face 74 of the arm 16. An
angular recess 76 is formed in the passageway 72 near face 74 and
retains an O-ring 78 therein for sealing around a male tube member
of the mounting unit 20 adapted to project into the passageway
72.
In addition to the passageway 72, the mounting arm 16 includes a
passageway 80 which also opens at the front face 74 of the arm 16.
An annular recess 82 is formed in passageway 80 near face 74 and it
too retains an O-ring 84 for sealing around a male tube member of
mounting unit 20, to be discussed hereinafter.
As was indicated with reference to FIGS. 4 and 5, the three way
controller valve 24 functions to control the operational mode of
the pop-off valve 22. The controller valve 24 is manually operable
to selectively communicate any one of the three previously
mentioned control sources to a control port of pop-off valve 22. In
a first position, ambient pressure is applied to the control port,
in a second position circuit pressure is applied to the control
port and in a third position, ventilator pressure is applied to the
control port. As will be seen, means are provided for automatically
assuring that the pop-off valve output orifice is fully open when
either circuit or ventilator pressure is applied to the control
port, corresponding to the operational modes used during manually
assisted and controlled ventilation. On the other hand, when
applying ambient pressure to the control port primarily used during
spontaneous ventilation, means for varying the size of the pop-off
valve output orifice are automatically moved into appropriate
position.
With continuing reference to FIGS. 5 and 6, the pop-off valve 22
includes an input port 92 extending through externally threaded
nipple 93, an output port 94, and the previously mentioned control
port 47. The nipple 93 is threaded into the arm 16 and communicates
the input port 92 with the circuit pressure in passageway 80. The
output port 94 is coupled by a short tube 95 to an exhaust input
port 96 in the housing of controller valve 24. The control port 47
is coupled by a short tube 97 to previously mentioned port 49 of
the controller valve 24.
The pop-off valve 22 includes a housing comprised of upper portion
98 threaded into lower portion 99 which in turn is threaded into
nipple 93. A flexible diaphragm 100 is held around its
circumference between opposed surfaces of housing portions 98 and
99. Disc 101, bearing against the underside of the diaphragm, has a
rod 102 depending therefrom. The rod 102 extends through, in sealed
relationship, a fixed wall 103 and into a recess defined in boss
104 formed in valve leaf 105. A coil spring 106 is contained around
rod 102 between wall 103 and disc 101.
In the operation of the pop-off valve 22, when ambient pressure is
available on the upper surface of diaphragm 100, the spring 106,
will force the rod 102 to the position shown in FIG. 5, in which
its end is spaced from the bottom of the recess in boss 104 of
valve leaf 105. As a consequence, valve leaf 105 which normally
rests on and seals against knife edge 107 on nipple 93 will be
lifted when the pressure within passageway 80 exceeds a first
threshold, e.g., 1 cm of H.sub.2 O, to permit gas flow from
passageway 80 out through port 94.
On the other hand, when a positive pressure is applied to the upper
surface of diaphragm 100 (from the circuit or ventilator via the
controller valve 24, as will be discussed hereinafter), the
diaphragm 100 will be bowed downwardly to bottom rod 102 in the
recess in boss 104 thereby positively sealing valve leaf 105
against knife edge 107. It is pointed out that the active area of
diaphgram 100 is greater than the active area of valve leaf 105 and
as a consequence, the valve leaf 105 will be sealed closed when
equal pressures are applied through the control port 47 and input
port 92 and the pressure on the diaphragm exceeds a second
threshold, e.g., 5 cm of H.sub.2 o.
The controller valve 24 functions to enable an anesthetist to
selectively apply either ambient pressure, circuit pressure or
ventilator pressure to the control port 47 for operating the
pop-off valve in the aforedescribed manner. As will be seen, when
ambient pressure is applied, the controller valve 24 also enables
the anesthetist to vary the size and thus the flow rate out of the
pop-off valve output port 94. When circuit pressure or ventilator
pressure is applied, the output port 94 is left fully open.
The controller valve 24 comprises a spool valve having a housing
comprised of an upper portion 107' threaded onto a lower portion
108. Lower portion 108 has an externally threaded nipple 109
threaded into arm 16. Nipple 109 has a central bore therethrough
which communicates the exhaust input port 96 through arm 16 to
nipple 110. A system exhaust hose 111 is intended to be coupled
into nipple 110 for carrying exhausted gas away, preferably out of
the operating room, to prevent any adverse effect upon the
personnel present.
From what has previously been said, it should be recognized that
three different pressure sources (including ambient) are applied to
the input side of controller valve 24 for selective coupling by the
anesthetist to the port 49 for communication through tube 97 to the
pop-off valve control port 47. One of these three sources comprises
circuit pressure (corresponding to tube 52 in FIG. 3) which is
available through nipple 112 via a hose 113 from nipple 114 in
communication with passageway 80 through arm 16. A second of the
sources is derived from ventilator pressure (corresponding to tube
54 in FIG. 3) through nipple 115 and will be discussed in greater
detail in connection with the description of FIGS. 18-20.
Communication from either nipple 112 or nipple 115 to port 49 is
controlled by the position of a spool 116 mounted for rotation
within lower housing portion 108. Spool 116 has a shaft 117 coupled
thereto which in turn is connected to a knob 118 available for
manual rotation by the anesthetist. The inner surface of housing
portion 108 is provided with annular recesses 118 and 119 each of
which retains an O-ring 120. Spool 116 is provided with a slot 121
extending around a portion of the circumference thereof of
sufficient length to bridge the distance between nipples 112 and
115 and port 49. More particularly, with the spool rotated to the
position of FIG. 7A, slot 121 will communicate nipple 115 with port
49. When spool 116 is rotated to the position of FIG. 7B, slot 121
communicates nipple 112 with port 49. In order to facilitate the
anesthetists positioning of the spool, the knob 118 is preferably
provided with a pointer 122 which can be appropriately detented in
two positions.
In order to selectively communicate a third pressure source, i.e.,
ambient (corresponding to tube 50 of FIG. 3) with port 49 the spool
116 is provided with an additional slot 123 extending greater than
180.degree. around the circumference thereof. The slot 123 is
vertically displaced from the slot 121 but is still able to
communicate with port 49 (see FIG. 8) as a consequence of the
provision of vertical slot 124 in communication with port 49. Slot
123 communicates with ambient pressure via passageway 126 through
the spool 116, shaft 117 and knob 118. Inasmuch as it is necessary
to prevent communication between slots 121 and 123, the spool
circumferential surface and the lower housing portion inner surface
are correspondingly tapered and a spring 127 is provided around
shaft 117 to seat the spool in the tapered housing so that the
housing inner surface seals the slots.
As previously pointed out, it is desirable to enable the
anesthetist to variably control the flow out of the pop-off valve
exhaust port 94 when the pop-off valve is being operated in the
pressure relief mode to assure the maintenance of an adequate gas
supply within the circuit. On the other hand, when the pop-off
valve is being operated in the balanced mode it is desirable that
the pop-off valve exhaust be wide open. In order to accomplish
this, the spool is provided with a valve member 128 depending from
the lower end thereof and shaped so as to variably cover the port
96 as the knob 118 and spool 116 are rotated. The variable covering
of the port 96 can best be seen in the developed view of FIG. 10
which shows how the valve member 128 wipes across the port 96. Note
that the valve covers the port 96 only when slot 123 communicates
with port 49 and is remote from and has no effect on the port 96
when the slot 121 is in communication with port 49.
The front face 74 arm of the mounting arm 16 is provided with a
pair of forwardly projecting pins 130 each of which has an annular
groove 131 formed therein at the forward end thereof. These pins
130 are utilized to align and retain the mounting unit 20 relative
to the arm 16 so as to provide mechanical support and gas flow
communication therebetween.
Attention is now called to FIGS. 11 and 12 which better illustrate
the mounting unit 20. The mounting unit 20 comprises a structure
defining internal passageways and terminating in male nipples
adapted to communicate with female fittings on mating parts. More
particularly, the unit 20 defines a large vertical bore 132
terminating in male nipples 133 and 134 which preferably comprise
22 millimeter outer diameter tapered fittings. The nipple 134 is
intended to be received in the upper opening of the reservoir 34 as
represented in FIGS. 5 and 7. The nipple 133 is intended to project
into a correspondingly tapered fitting defined within the housing
of inspiratory valve 28 as is also represented in FIGS. 5 and 7.
Also in communication with the large bore 132 is nipple 136 which
is 22 millimeters in diameter. This fitting is intended to project
into the expiration breathing tube 36 as is represented in FIGS. 2,
5 and 6. Nipple 135, which also opens into large bore 132 is
adapted to project into and communicate with passageway 72, in arm
16, as shown in FIG. 6. The mounting unit 20 further includes a
nipple 138 which is adapted to project into and communicate with
the passageway 80 in the mounting arm 16. Nipple 138 communicates
with a passageway 140 extending straight through the mounting unit
20 and terminating in a nipple 142 intended to be coupled into
overflow tube 38 as represented in FIGS. 2 and 6.
The mounting unit 20 is provided with a pair of parallel channels
150 extending along the underside thereof as shown in FIG. 12. A
resilient finger 152 is formed in the mounting unit 20 immediately
adjacent the channel 150 for locking into the annular groove 131
formed on the pins 130 of mounting arm 16. That is, in order to
couple the disposable anesthesia circuit to the permanent mounting
arm, the channels 150 of the mounting unit 20 are placed on the
pins 130 and then the mounting unit 20 is pushed toward the front
face 74 of the mounting arm 16 until the resilient fingers 152 of
the mounting unit 20 lock into the annular grooves 131 on the pins
130. This action positions the nipples 135 and 138 of the mounting
unit 20 in the passageways 72 and 80 of the mounting arm 16 with
seals being achieved by O-rings 78 and 84.
Still referring to FIG. 5, the inspiratory valve 28 is a
unidirectional valve which permits gas flow upwards from the nipple
133 on mounting unit 20 through the inspiratory valve 28 and out
through the exhaust port within nipple 160. Inspiratory valve
nipple 160 is also preferably a 22 millimeter diameter fitting
adapted to receive the inspiratory tube 30 thereon as represented
in FIGS. 2 and 5.
The inspiratory valve 28 is comprised of a two piece housing
including a cover 162 and a lower portion 164. The lower portion
164 is provided with a cylindrical tapered wall 168 defining a
central opening into which the male nipple 133 is force fit as
shown in FIG. 5. A knife-edge 170 is formed on the upper edge of
wall 168 for cooperation with a valve leaf 172. A trough 174 formed
around wall 168 communicates with the exhaust port defined within
tapered nipple 160. In the operation of the inspiratory valve 28,
in response to a positive pressure differential from the lower to
the upper side of valve leaf 172, as seen in FIG. 5, the valve leaf
172 will be lifted so as to provide communication between the bore
132 of the mounting unit 20 and the exhaust port defined within
inspiratory valve nipple 160. The inspiratory valve cover 162 is
provided with a depending pin 176 which limits the movement of the
valve leaf 172. The edges of the cover 162 are adapted to be
received within an annular recess 178 formed in the lower portion
of the inspiratory valve housing in sealed relationship.
From the foregoing, the interface between the disposable anesthesia
circuit and the permanent portion at the machine end of the system
should be appreciated. The configuration of the disposable mounting
unit 20 is such that it can be easily and quickly connected and
disconnected from the permanent system portion as the permanent
portion is used with successive patients.
Attention is now called to FIGS. 14-17 which illustrate a preferred
Y-piece embodiment 32 to be employed in a system in accordance with
the present invention. The preferred Y-piece embodiment 32
functions to couple a mask elbow 200 or endotracheal tube adaptor
to the breathing tubes 30 and 36 and overflow tube 38. As shown in
FIG. 14, the mask elbow terminates in a 15 millimeter tapered
fitting adapted to seat in sealed relationship within the bore 202
defined at the entrance of the Y-piece 32. The Y-piece 32 defines a
curved passageway 204 terminating in a nipple 206 adapted to be
secured to the patient end of the inspiratory tube 30. The upper
portion of the Y-piece 32, as shown in FIG. 14, includes both the
expiratory valve and an overpressure relief means.
More particularly, the bore 202 of the Y-piece 32 communicates with
a chamber 208 through passageway 210. Chamber 208 is defined by
three solid walls 212, 214, and 216 and by a fourth wall
constituting a valve leaf 218. The valve leaf 218 has two pins 220
and 222 secured thereto which are received and retained within pin
wells 224 formed within the Y-piece housing. The face 226 of walls
212 and 214 is curved to define a valve seat surface. When the
valve leaf 218 is in its quiescent state, as represented in FIG.
15, it is slightly stressed in bowed relationship about an axis
through pins 220 and 222. As a consequence, the valve leaf 218
bears against and conforms to the valve seat surface 226. The valve
leaf 218 of course prevents gas flow from right to left in FIG. 15
since pressure on the right side of valve leaf 218 merely better
seats the valve leaf. On the other hand, in response to a positive
pressure differential from the left to the right side of valve leaf
218, as seen in FIG. 15 the valve leaf 218 bends about the axis
through pins 222 and 224 there by permitting gas flow around the
edges of the valve leaf. When the valve leaf 218 opens under
pressure, it communicates the chamber 208 with male nipples 230 and
232. As represented in FIG. 15, nipple 230 is intended to fit into
and seal with expiratory tube 36 and male nipple 232 is intended to
fit into and seal with overflow tube 38.
In accordance with a preferred embodiment of the invention, the
Y-piece 32 additionally includes an overpressure relief means 240
which thereby is located close to the patient and thus provides
maximum protection against lung rupture which could otherwise occur
due to overpressure malfunction in the system. The overpressure
relief means 240 communicates with member 208 and is comprised of a
cup shaped recess 244 formed in the outer surface of wall 216 (FIG.
16). Apertures 242 extend through the wall 216 from the cup shaped
recess 244 to the chamber 208. An elastic valve member 246 is
provided which includes a central shaft portion 248 which extends
through the wall 216 in the center of the cup shaped recess 244. A
small flange 250 is formed on one end of the shaft 248 and a larger
flange 252 is formed on the other end. A pull tab 253 extends
axially from the small flange 250 remote from the shaft 248. The
elastic valve member 246 is installed into the position shown in
FIG. 16 by pulling the tab 253 to the right through the central
opening in the cup portion 244. As a consequence of the external
surface 254 on the flange 250 being tapered and as a consequence of
the elastic qualities of the valve member, the flange 250 can be
pulled through the central hole to arrive at the position
illustrated in FIG. 16. In this position, the flange portion 252
will conform to the cup shape of the recess 244. When in the
quiescent condition shown in FIG. 16, the shaft 248 of the valve
member 246 will be under slight stress thereby pulling the valve
flange 252 tightly against the recess 244 and sealing the apertures
242. However, as the pressure in chamber 208 increases, it will
bear outwardly (toward the left in FIG. 16) against the valve
flange 252. This action will distort the shape of the valve flange
252 and stretch the shaft 248 thereby permitting flow through the
apertures 242 and relieving pressure from the chamber 208 and thus
from the entire circuit. As gas escapes through apertures 242 past
valve flange 252, it will produce an audible alarm as the flange
252 vibrates.
Attention is now called to FIGS. 18 and 19 which illustrate a
preferred reservoir embodiment in accordance with the present
invention. As has been previously mentioned herein, the reservoir
thus far referred to, can constitute a conventional single
compartment breathing bag. However, although such a bag might be
adequate for spontaneous and manually assisted ventilation, it
would not be satisfactory for controlled ventilation where the
reservoir is squeezed by a mechanical ventilator since the
ventilator would then be exposed to the patient's gas and would
constitute an avenue for cross-contamination between patients.
Accordingly, a reservoir 300 is provided, as illustrated in FIGS.
18-20, which isolates the ventilator from the patient's gas. The
reservoir 300 includes a pair of hermetically isolated chambers
which respectively communicate with the anesthesia circuit and the
ventilator. The reservoir 300 preferably is formed utilizing three
layers of vinyl sheeting 302, 304 and 306 which are welded to each
other and to fittings 308 and 310. The fitting 310 communicates
with a chamber 312 formed between sheets 302 and 304 and the
fitting 308 communicates with a chamber 314 formed between the
sheets 304 and 306. The fitting 308 is a 22 millimeter fitting
adapted to force fit onto tapered male nipple 132 of the mounting
unit 20 as represented in FIGS. 5 and 7. The fitting 310 is
provided with a terminal taper 311 intended to be force fit into
the end of a corrugated tube 320 which in turn is coupled to a
mechanical ventilator (not shown).
In the use of the ventilator isolator reservoir 300 of FIGS. 18-20,
the ventilator will periodically pressurize the chamber 312. The
pressure on the isolating septum sheet 304 will be transmitted to
the chamber 314 thereby producing a correlary pressure within the
inspiratory breathing tube 30. The outer sheets 302, 304, 306 of
the reservoir 300 of FIG. 18 and 19 should be thin, flexible and
inelastic. The exterior contour of the reservoir 300 is preferably
similar to the contour of conventional breathing bags so that the
"feel" is similar. The septum sheet 304 is preferably contoured
similar to sheets 302 and 306 so that it may sweep the entire
volume of reservoir 300 with minimal pressure differential across
the septum sheet. Preferably, the septum sheet 304 should be a
visible color and at least one outer sheet should be transparent so
that volume changes caused by movement of the septum sheet can be
readily observed by the attending anesthetist. By providing the
reservoir 300 with thin and flexible outer walls, it will function
as a conventional breathing bag during manually assisted
ventilation since it can be readily squeezed by the anesthetist and
the conventional feel will only be minimally modified by the
presence of the septum sheet 304.
It has previously been mentioned with respect to the operation of
the pop-off valve 22 that it is preferable, under conditions of
controlled ventilation, to make the pop-off valve responsive to
ventilator pressure. That is, it will be recalled that when the
system is pressurized by the ventilator during inspiration, it is
desirable to close the pop-off valve. It will further be recalled
that for this purpose, reference was made to a tube 54 in FIG. 2
coupled to the input side of the three way controller valve 24,
i.e., to nipple 115 in FIG. 6. In order to communicate the
ventilator pressure to the nipple 115, a nipple 322, in
communication with chamber 312, is provided within sheet 302 of
reservoir 300. One end of the tube 54 fits onto the nipple 322.
Alternately, pressure may be supplied to tube 54 from a side port
nipple on the tapered 22 millimeter male fitting 311 which connects
corrugated tube 320 to the ventilator chamber 312 of the reservoir
300.
It has been previously pointed out that utilization of the overflow
tube in the manner indicated to preferentially vent alveolar gases
eliminates the need to use CO.sub.2 absorber material under most
circumstances. However, it has also been recognized that special
circumstances (e.g., fresh gas inflow less than 4 liters per
minute) or personal preferences of the anesthetist may dictate that
CO.sub.2 absorber material be used. In accordance with a preferred
embodiment of the invention, a canister 350 (FIG. 20) is provided
for optional incorporation between the tapered male nipple 133 of
the mounting unit 20 and the tapered female opening in inspiratory
valve 28.
Reference is now directed to FIGS. 21 and 22 which illustrate the
details of the CO.sub.2 absorber material canister 350. The
canister 350 includes a cylindrical central portion 352 whose
bottom wall 354 is perforated at 356 around an unperforated central
portion 360. A fluid guide ring 361 is provided on the undersurface
of wall 354 around the central portion 360. A perforated plate 362
fits over and covers the cylindrical container 352. The plate 362
is held in place by a cover 364 having a depending flange 366 which
defines an inwardly projecting annular ring 368 adapted to lock
against outwardly projecting annular ring 370 on the central
portion 352. The cover 364 is provided with a tapered 22 millimeter
male fitting 372, identical to the fitting 130 on the mounting unit
20, and consequently receivable in the female opening defined in
the housing of the inspiratory valve 28.
An annular flange 374 is formed on the lower surface of the wall
354 as shown in FIG. 21. The outer surface of the flange 374 has an
outwardly projecting annular rim 376 adapted to mate with and lock
against an inwardly projecting annular rim 378 formed on a sump
collector unit 380. The sump collector unit 380 is comprised of a
housing defining a cylindrical female opening 382 for receiving the
tapered male fitting 130 of the mounting unit 20. A trough 384 is
formed around the fitting 382 and functions as a sump to collect
caustic fluids generated during operation and to prevent accidental
spillage or flow to the patient. As a consequence of making the
central portion of wall 354 solid, and by providing the fluid guide
ring 361, any caustic fluid generated will be directed into the
sump and not into the breathing system.
Although utilization of systems in accordance with the teachings of
the present invention to preferentially exhaust alveolar gas
virtually eliminates the need to use CO.sub.2 absorber material, it
has been shown that such material can be easily incorporated into
the system when desired. When CO.sub.2 absorber material is
employed, it is of course depleted at a very slow rate. It is
further pointed out that where desired, as in situations of long
duration surgery, two or more CO.sub.2 canisters of the type shown
in FIGS. 21 and 22 can be incorporated in series within the system
between the mounting unit 20 and the inspiratory valve 28.
In order to minimize the cost of the disposable portion of the
anesthesia system, it is preferable to construct the reservoir of
plastic material rather than rubber. However, since plastics are
inelastic, they permit rapid and excessive pressure build-up in the
patient's airway. In recognition of this hazard, respected
authorities have suggested that only rubber breathing bags be
utilized. The advantage of using a rubber breathing bag, as
contrasted with a bag of inelastic material, is that as the
pressure in the breathing circuit increases, the rubber bag
stretches and therefore the pressure increases less rapidly and
there is more time for the anesthetist to recognize and abort the
developing danger. Moreover, as a rubber bag increases in size, a
maximum pressure is reached beyond which greater distention results
in a decreasing pressure within the bag and by like reasoning
within the patient's airway. Proper design of the bag volume, wall
thickness, and material elasticity can assure that the peak
pressure is within a safe range.
Although the foregoing advantages of rubber breathing bags are
recognized, it has also been recognized that such bags are
relatively difficult and expensive to fabricate. In view of this,
attention is now called to FIGS. 23-25 which illustrates a
construction which permits utilization of inelastic material
breathing bags and yet which also retains the advantageous
characteristics of rubber breathing bags.
More particularly, as shown in FIGS. 23-25, a section of elastic
tubing 400 is mounted around one of the breathing tubes with the
ends of the elastic tube secured and sealed to the breathing tube
402 at 404 and 406. An opening 408 is formed within the breathing
tube 402 in order to communicate the inside of the elastic tube
section 400 with the interior of the breathing tube. As a
consequence of the foregoing construction, the elastic tube 400
will act as a balloon and by properly selecting the physical
parameters (length, material thickness and elasticity) the elastic
section will protect the patient in the same manner as an inelastic
breathing bag. However, the cost of the elastic section 400 plus a
plastic breathing bag is considerably less than the cost of an
elastic breathing bag. Moreover, with conventional anesthesia
layout, the elastic tube 400 is more likely to be located in a
position at which it can be observed by the attending
anesthetist.
In accordance with a further modification of the invention as shown
in FIGS. 26 and 27, the elastic tube 400 of FIG. 24 can be modified
to function as an overpressure relief means, thus constituting an
alternative to the incorporation of the overpressure relief means
within the Y-piece as shown in FIGS. 14-16. In order to incorporate
an over-pressure relief means within the elastic section 400, an
elastic band 410 is mounted around the section 400 between the
sealed ends 404 and 406 and the section 400 is slit at 412 between
the band 410 and one end. Preferably, some filler material 411 is
provided between corrugations beneath the band 410. As the pressure
within the breathing tube 402 increases, the tube 400 will stretch
and at a certain point stretch the elastic band 410 away from the
breathing tube so as to permit leakage beyond the band 410. The gas
leaked beyond the band 410 is then relieved through the slit 412.
Preferably, as the gas is relieved through the slit 412, the
material adjacent the slit acts as a reed and creates an audible
alarm to advise the anesthetist of the overpressure condition.
From the foregoing, it should be appreciated that a general
anesthesia rebreathing system has been disclosed herein comprised
of a disposable portion and a permanent portion and configured so
as to minimize the cost and complexity of the disposable portion,
while including therein all of the elements likely to produce cross
contamination.
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