U.S. patent number 3,901,230 [Application Number 05/465,817] was granted by the patent office on 1975-08-26 for anesthesia rebreathing apparatus including improved reservoir means.
Invention is credited to Melvyn L. Henkin.
United States Patent |
3,901,230 |
Henkin |
August 26, 1975 |
Anesthesia rebreathing apparatus including improved reservoir
means
Abstract
Apparatus useful in a general anesthesia rebreathing system
comprised of a disposable portion easily coupled to and decoupled
from a permanent portion. The disposable portion includes 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. 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. The reservoir comprises one chamber of an assembly including
two hermetically isolated chambers. The second chamber communicates
through a selector valve means with either (1) a flexible container
which can be squeezed by an attending anesthetist or (2) a
mechanical ventilator. The pop-off valve is operable in two
different modes, i.e. (1) as a manually controlled variable orifice
for spontaneous ventilation and (2) as an automatically controlled
valve responding to a positive control pressure for manually
assisted or mechanically controlled ventilation. The control
pressure is obtained from the second chamber of the reservoir
assembly.
Inventors: |
Henkin; Melvyn L. (Tarzana,
CA) |
Family
ID: |
26912807 |
Appl.
No.: |
05/465,817 |
Filed: |
May 1, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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218337 |
Jan 17, 1972 |
3814091 |
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Current U.S.
Class: |
128/205.17;
128/205.15; 128/909; 128/910 |
Current CPC
Class: |
F16L
55/04 (20130101); A61M 16/104 (20130101); Y10S
128/91 (20130101); Y10S 128/909 (20130101); A61M
16/0833 (20140204); A61M 16/0078 (20130101) |
Current International
Class: |
A61M
16/10 (20060101); F16L 55/04 (20060101); A61M
16/00 (20060101); A61m 016/00 () |
Field of
Search: |
;128/188,202,203,191,204,272,277,145,145.6,145.5,145.7,145.8,142.4,211,210,207 |
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,
Rosen & Fernandez
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent
application Ser. No. 218,337, filed Jan. 17, 1972, now patent No.
3,814,091 by Melvyn L. Henkin.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
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 and
including 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;
means mounting said overflow valve means in close proximity to said
elongated breathing tube means second end;
elongated overflow tube means, substantially coextensive 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;
a reservoir assembly including outer wall means enclosing a volume
and inner wall means partitioning said volume into first and second
hermetically isolated chambers, said inner wall means being
flexible for transmitting pressures between said chambers;
means for communicating said first chamber with said breathing tube
means second end;
said overflow valve means including 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;
means for selectively communicating the pressure in said second
chamber to said control port;
container means having a flexible wall capable of being manually
squeezed to increase the pressure therein; and
means for communicating the pressure in said container means to
said reservoir assembly second chamber.
2. The system of claim 1 wherein said means for communicating the
pressure in said container means to said second chamber includes a
manual valve means having first and second input ports and on an
output port;
means coupling said output port to said second chamber;
means coupling said container means to said first input port;
and
means adapted to couple said second input port to a mechanical
ventilator.
3. The system of claim 1 wherein said reservoir assembly outer wall
means is rigid.
4. The system of claim 1 including an opening in said reservoir
assembly outer wall; and
lid means adapted to fit over and seal said opening, said lid means
including a fitting extending into said volume and a flexible bag
detachably sealed to said fitting.
5. The system claim 1 wherein said means for selectively
communicating said second chamber to said control port includes a
controller means having selectable first and second input ports and
an output port;
means coupling said controller means output port to said control
port;
means coupling said second chamber to said controller means first
input port; and
means exposing said controller means second input port to ambient
pressure.
6. The system of claim 1 wherein said breathing tube means includes
first and second breathing tubes having open first and second
ends;
patient communication means defining a passageway therethrough
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 assembly first chamber.
7. Anesthesia rebreathing apparatus useful in combination with a
source of fresh anesthesia gases, said apparatus comprising:
a gas overflow valve, having input and exhaust ports, mounted
proximate to said fresh gas source;
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;
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 in communication 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;
a reservoir assembly including outer wall means enclosing a volume
and inner wall means partitioning said volume into first and second
hermetically isolated chambers, said inner wall means being
flexible for transmitting pressures between said chambers;
container means having a flexible wall capable of being manually
squeezed to increase the pressure therein;
means for communicating the pressure in said container means to
said reservoir assembly second chamber; and
means for communicating said first chamber with said breathing tube
means second end.
8. The apparatus of claim 7 wherein said reservoir assembly outer
wall means is rigid.
9. The apparatus of claim 7 wherein said means for communicating
said first chamber with said breathing tube means second end
includes a fitting extending into said volume through said
reservoir assembly outer wall means; and wherein
said inner wall means comprises a flexible bag detachably sealed to
said fitting.
10. The apparatus of claim 7 wherein said breathing tube means
includes first and second breathing tubes having open first and
second ends;
patient communication means defining a passageway therethrough
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 assembly first chamber.
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.
The parent (Ser. No. 218,337) of this continuation-in-part
application discloses an anesthesia rebreathing system comprised of
a disposable circuit apparatus 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. In the first embodiment disclosed in the parent
application, the circuit constitutes what is generally referred to
as a circle, including both inspiratory and expiratory tubes. In
the second embodiment disclosed in the parent application, the
circuit utilizes a single tube alternately used for inspiration and
expiration. 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 is located close to the anesthesia machine
where it can be conveniently controlled by the attending
anesthetist. By locating the overflow tube entrance close to the
patient, the overflow tube functions to preferentially vent
alveolar gases, rich in CO.sub.2, through the pop-off valve and
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 substantialy eliminating the
need to use CO.sub.2 absorber material.
Both circuit embodiments in the parent application incorporate a
reservoir having flexible walls and arranged such that 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.
The pop-off valve is disclosed as being operable in two different
modes, i.e. (1) as a manually controlled variable orifice for
spontaneous ventilation and (2) as an automatically controlled
valve responding to a positive control pressure for manually
assisted or mechanically controlled ventilation. The source of
control pressure is selectable by the attending anesthetist such
that the pop-off valve is sealed closed in response to (1) pressure
within the circuit for manually assisted ventilation and to (2)
pressure produced by a mechanical ventilator for mechanically
controlled ventilation.
SUMMARY OF THE INVENTION
In accordance with the present invention, a reservoir assembly is
provided comprised of two hermetically isolated chambers with the
first chamber being defined by flexible walls subjected to the
pressure within the second chamber. The second chamber selectively
communicates with either a breathing bag which can be squeezed by
an attending anesthetist for manually assisted ventilation or a
mechanical ventilator for mechanically controlled ventilation. The
pop-off valve control pressure is derived from the second chamber
regardless of whether ventilation is manually assisted or
mechanically controlled. By always deriving the pop-off valve
control pressure from the reservoir assembly second chamber rather
than directly from the circuit, the following advantages are
achieved:
1. The possibility of a high pressure in the circuit sealing the
pop-off valve and creating an unsafe pressure condition is
avoided;
2. The possiblity of cross-contamination is further reduced;
and
3. The pop-off valve control mechanism can be more simply and
inexpensively constructed since it need only respond to two, rather
than three, control pressures.
In accordance with the preferred embodiment of the invention, the
reservoir assembly is comprised of a rigid container in which an
inexpensive and disposable plastic or latex bag is mounted in
communication with the circuit. The interior of the container
outside of the plastic bag is pressurized by either a mechanical
ventilator or a conventional breathing bag which can be manually
squeezed by the anesthetist.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a general anesthesia rebreathing
system disclosed in the parent application;
FIG. 2 is an enlarged perspective view better illustrating the
disposable portion of the system of FIG. 1;
FIG. 3 is a schematic flow diagram of an anesthesia circle system
in accordance with the teachings of the parent application;
FIG. 4 is a schematic flow diagram of a single tube (Magill type)
anesthesia circuit system in accordance with the teachings of the
parent application;
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 the different
positions of the controller valve for coupling system pressure and
ventilator pressure to the pop-off valve control ports;
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 as disclosed in the parent application;
FIG. 11 is a sectional view of one type of reservoir assembly
disclosed in the parent application for isolating a mechanical
ventilator from a patient's gas;
FIG. 12 is a sectional view taken substantially along the plane
12--12 of FIG. 11;
FIG. 13 is a side elevational view illustrating the manner in which
the reservoir assembly of FIGS. 11 and 12 is structurally
incorporated in the system and further illustrating the
incorporation of a canister of CO.sub.2 absorber material between
the reservoir assembly and inspiratory valve;
FIG. 14 is a schematic flow diagram of an anesthesia circle system
similar to that shown in FIG. 3 but modified in accordance with the
teachings of the present invention;
FIG. 15 is a schematic flow diagram of a single tube (Magill type)
anethesia circuit system similar to that shown in FIG. 4 but
modified in accordance with the teachings of the present
invention;
FIG. 16 is a perspective disassembled view of a preferred reservoir
assembly embodiment in accordance with the present invention;
and
FIG. 17 is a side sectional view of the preferred reservoir
assembly embodiment of FIG. 16.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Prior to describing the apparatus illustrated in the figures, it is
pointed out that FIGS. 1-10 hereof are identical to the
corresponding figures of the parent application. Further, FIGS.
11-13 hereof are identical to FIGS. 18-20 of the parent
application. FIGS. 14-17 hereof illustrate the improvements in
accordance with the present invention.
Attention is now called to FIG. 1 which illustrates a general
anesthesia rebreathing system as disclosed in the parent
application. 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 is well known, 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 parent application discloses 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, 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 oulet end of the expiratory tube 36 is
coupled to the mounting unit 20 and communicates with the inlet
side of the reservoir 34. The circuit further includes an overflow
tube 38 extending from the Y-piece 32 back to the mounting unit 20
where 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 invention disclosed in the parent application;
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 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 the anesthesia circle circuit embodiment. 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
by 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
unidirectional. 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 overflow 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
anesthetist 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. 11-13, 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 and 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 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 previoulsy
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
diaphragm 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 presssure 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. 11-13.
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 106 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
anesthetist's 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 (correpsonding 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 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.
11-13, 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 utlizing 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 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. 11-13,
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 corollary pressure within the
inspiratory breathing tube 30. The outer sheets 302, 304, 306 of
the reservoir 300 of FIGS. 11 and 12 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. Thus, a canister 350 (FIG. 13)
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.
As previously mentioned, the apparatus illustrated in FIGS. 1-13
hereof is disclosed in applicant's parent application. Attention is
now called to FIGS. 14 and 15 which schematically illustrate the
improved anesthesia rebreathing systems in accordance with the
present invention. It will be recognized that FIG. 14 illustrates
an anesthesia circle system similar to that previously discussed in
connection with FIG. 3 and FIG. 15 illustrates a single tube
anesthesia circuit system similar to that previously discussed in
connection with FIG. 4. Elements in FIGS. 14 and 15 corresponding
to elements in FIGS. 3 and 4 are identified by the same designation
numerals preceded by the digit "5". Thus, for example, the overflow
tube 38 of FIG. 3 is designated by the numerals 538 in FIG. 14.
Elements in FIGS. 14 and 15 which do not have an identical
counterpart in FIGS. 3 and 4 will be identified by a designating
numeral beginning with "4".
The embodiment of FIG. 14 requires utilization of a two chamber
reservoir assembly 400, for example of the type illustrated in
FIGS. 11-13, or preferably, of the type to be discussed hereinafter
in connection with FIG. 16. The reservoir assembly 400 is comprised
of an outer wall means 402 defining a certain volume and an inner
wall means 404 disposed therein to partition the volume into first
and second hermetically isolated chambers 406 and 408. The inner
wall means 404 is flexible so as to enable pressure levels to be
transferred therethrough as has been previously mentioned with
respect to the structure of FIGS. 11-13. The first chamber 406
communicates with the breathing tubes at the second end thereof.
The second chamber 408 opens into a fitting 410 which can
selectively communicate through tubing 411 and selector valve means
412 either with a squeezable container 414 or a mechanical
ventilator 416.
Prior to considering the operation of the system as represented in
FIG. 14, it is important to note that the embodiment of FIG. 14
differs from the embodiment of FIG. 3 by the absence of tube 52
which, it will be recalled, couples breathing circuit pressure to
one input port of the controller 24 in FIG. 3.
It will further be recalled that in the system of FIG. 3, the
anesthetist can manually operate the controller 24 to select any of
three sources to apply to the control port of pop-off valve 22.
That is, for spontaneous ventilation, ambient pressure is applied
to the control port of pop-off valve 22 via tube 50. For manually
assisted ventilation, system pressure available through tube 52 is
applied to the pop-off valve control port. For mechanically
controlled ventilation, mechanical ventilator pressure available
through tube 54 is applied to the pop-off valve control port.
In accordance with the present invention, tube 52 of FIG. 3 is
eliminated and the pop-off valve controller, for both manually
assisted and mechanically controlled ventilation, applies the
pressure from the second chamber 408 of the reservoir assembly 400
to the pop-off valve control port. Thus, the pop-off controller
(524 in FIG. 14) need only comprise a two input port device rather
than the three input port device represented in FIGS. 4-9. Thus,
for simplicity, the controller 524 of FIG. 14 can be considered as
being identical in construction to the controller 24 illustrated in
FIGS. 5-9 except that the port 112 is sealed closed.
The operation of the system of FIG. 14 is identical to the
operation of the system of FIG. 3 for spontaneous ventilation. For
manually assisted ventilation, the attending anesthetist will
operate the two position valve 412 to communicate the second
chamber 408 of the reservoir assembly 400 with the interior of the
container 414. The container 414 can comprise a conventional
breathing bag which can be squeezed by the anesthetist. A source of
working gas 418 is coupled through a valve 420 to the fitting 410
to enable the anesthetist to fill the volume of the second chamber
408, container 414 and communicating tubes therebetween. With these
volumes filled, the anesthetist can now periodiclly squeeze the
container 414. As the container 414 is squeezed, the pressure is
increased in the second chamber 408. The increase in pressure is
communicated through the wall 404 to the first chamber 406 to open
the inspiratory valve 528 and permit gas flow to the patient via
breathing tube 530. In addition, the increased pressure in the
second chamber 408 is communicated via tube 554 to the controller
524 to seal the pop-off valve 522. When the anesthetist relaxes the
pressure on the container 414, the inspiratory valve 528 closes,
the expiratory valve 544 opens, and the pressure is also relieved
from the pop-off valve thereby enabling the patient's expired
alveolar gases to flow through overflow tube 538 and out of the
pop-off valve 522.
In the mechanically controlled mode of ventilation, the anesthetist
will switch the position of the manually controlled two position
valve 412 to couple the mechanical ventilator 416 to the reservoir
assembly second chamber 408. The mechanical ventilator 416 will
then periodically increase the pressure in chamber 408 in a manner
directly analogous to that produced by the anesthetist in squeezing
the container 414 during the manually assisted mode.
Thus, it should be appreciated that although the system of FIG. 14
operates similarly to the system of FIG. 3 in the spontaneous and
mechanically controlled ventilation modes, it represents a
significant improvement thereover in that it avoids the necessity
of employing tube 52 of FIG. 3 to couple system pressure to the
pop-off valve controller. Elimination of tube 52 of FIG. 3 yields
several advantages:
1. It avoids the possibility of a high pressure in the breathing
tubes sealing the pop-off valve so as to create a physiologically
unsafe condition;
2. It avoids exposing the controller to the patient's gases and
thereby eliminates a remote possibility of cross-contamination;
and
3. It enables the utilization of structurally simpler two input
port controller as contrasted with the three input port controller
required in the embodiment of FIG. 3.
Attention is now called to FIG. 15 which illustrates a single tube
rebreathing system of the type represented in FIG. 4 which has been
modified in the same manner as was the system of FIG. 3. That is,
it will be noted that the system of FIG. 15 differs from the system
of FIG. 4 by elimination of tube 52 of FIG. 4. The operation of the
system of FIG. 15 is identical to that described in connection with
FIG. 4 except that during the manually assisted ventilation mode,
the attending anesthetist will squeeze container 414 rather than
container 64 as represented in FIG. 4.
Attention is now called to FIGS. 16 and 17 which illustrate a
preferred embodiment of the reservoir assembly 400 schematically
illustrated in FIGS. 14 and 15. From the operational description of
the system of FIGS. 14 and 15, it should be recognized that during
manually assisted ventilation, the attending anesthetist squeezes
container 414 to periodically increase the pressure within the
second chamber 408 of the reservoir 400. These periodic pressure
increases are communicated from chamber 408 to chamber 406 through
the wall 404. It is important to note that the anesthetist need not
squeeze the reservoir 400.
In recognition of the foregoing, a preferred reservoir assembly, as
represented in FIGS. 16 and 17, is provided comprised of a rigid
container 430. The container is preferably cylindrical and defines
top and bottom walls 432 and 434 and a circumferential wall 436.
The walls 432, 434 and 436 envelop a fixed volume 438. Top wall 432
defines an opening 440 surrounded by an upstanding flange 442
preferably supporting O-ring 443. Openings 444 and 446 are formed
in wall 436, in communication with fittings 448 and 450, for
coupling to the tubes 554 and 411 illustrated in FIG. 14.
The portion of the reservoir assembly of FIGS. 16 and 17 thus far
described constitutes part of the permanent system hardware since
it is not exposed to the patient's gas. The disposable portion 460
of the reservoir assembly for use with the container 430 includes a
lid 462 configured so as to fit over the flange 442 to seal the
opening 440. A tubular fitting 464 is formed in the lid 462 and at
its lower end opens into a bag 466. The upper end of fitting 464 is
intended to be coupled to the second end of the breathing tube 536
(FIG. 14) proximate to the inspiratory valve 528.
It should be recognized from the structural configuration described
that the bag 466 defines the first chamber discussed in FIG. 14 and
the volume within the container 430 outside of the bag 466 defines
the second chamber. In the use of the reservoir assembly, only the
disposable portion 460 is exposed to the patient's gas.
Accordingly, by disposing of the portion 460 after each use, the
possibility of cross-contamination via the reservoir assembly is
eliminated. It should further be recognized that the disposable
portion 460 can be very inexpensively formed of plastic material,
for example.
From the foregoing, it should be appreciated that an improved
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 within the disposable portion
all of the elements likely to produce cross-contamination.
* * * * *