Note: Descriptions are shown in the official language in which they were submitted.
3~
--2--
The present invention relates to gas-flow units which are adapted to be
mounted on gas-administration apparatus and in particular, to gas-flow units
such as vaporisers which are adapted to be mounted on apparatus for the
administration of gaseous anaesthetics or analgesics (which, for convenience,
will hereinafter be referred to collectively as "anaesthetics") or other
"medical" gases or gas mixtures such as oxygen or air.
For the purposes of this specification the term "gas-flow unit" is intended
to embrace any type of unit which is mountable on a gas-administration apparatusand adapted to receive a gas supply dur~ng the operation of the apparatus.
"Gas-flow units" therefore comprise, inter alia vaporisers, flow meters, gas
mixers, volume meters, ventilators, pressure gauges and absorbers.
In United Kingdom patent specification No. 1 385 670 there is described a
gas-administration apparatus on which one or more gas-flow units can be mounted
in a removable, plug-in fashion. A plug-in system of this nature simplifies theinstallation and removal of gas-flow units from the apparatus, so facilitating
maintenance and cleaning of the units, as also the replacement of a unit should
it fail during an operation. Furthermore, this system is of great value to the
anaesthetist in allowing him to change the unit(s), for example, vaporiser(s)
installed on a given anaesthesia apparatus both easily and quickly. In this
way the apparatus can readily be adapted for the administration of any one (or
more) of the wide range of volatile anaesthetic agents currently available, and
the anaesthetist can accordingly ensure that the correct agent is made availablefor the needs of every patient.
Known gas-flow units adapted for the aforesaid 'plug-in' type of system
usually include a locking mechanism or member which cooperates with a backbar
or rack of the anaesthesia apparatus to physically lock the unit in place when
installed. Operation of the lock may also be effective to pull the unit tightlyagainst seals provided around the cooperating ports which are provided on the
anaesthesia apparatus to effect the desired gas supply to the unit. However, it~,
1~3~ 3
--3--
is possible to install a known unit of this type and thereafter operate the
apparatus without the lock having been moved into its operative position. The
installed but unlocked gas-flow unit may thereby be inadvertently displaced or
in any event gas leakage may occur past the seals which have not been compressedby operation of the lock and which are therefore not fully effective.
According to the present invention, a gas-flow unit adapted to be mounted
on a gas-administration apparatus in a removable plug-in fashion, comprises
means for controlling the admission to the unit of gas from a supply provided bythe apparatus, a locking mechanism for cooperation with the apparatus to lock
the unit in place when mounted on the apparatus, and an interlock system in
whlch the manipulation of the control means into an operating position which
provides for the admission of gas from the apparatus to the unit is prevented
unless the locking mechanism has been moved into a position in which it is
adapted to lock the unit on the apparatus.
It is thereby ensured that the unit cannot be switched into the gas circuit
unless it is properly locked in place on the apparatus, and in the event of a
gas-flow unit being installed but not locked in place this will become
immediately apparent to the operator by his inability to manipulate the unit's
control means.
The ports of known 'plug-in' type anaesthesia apparatus which are adapted
to effect the supply of gas to the removable gas-flow units usually embody
spring-biased valve members which, when a cooperating gas-flow unit is not
installed, seal off the respective ports from communication with the atmosphere
but which, when a cooperating unit is installed, are moved away from the port-
closing position by abutment with actuating members of the unit to provide fluidcommunication between the ports and the unit. So long as the gas-flow unit
remains in place on the apparatus the corresponding port valves will be open,
even though the control means of the unit may be in the OFF position. Thus,
even though it is not intended that the gas-flow unit be switched into the gas
i3~3
--4--
circuit, residual gas or vapour which exists within the internal passages of theunit between the aforesaid ports and control means may find its way into the
circuit. Further, if the gas-flow unit is a vaporiser and its control means is
a valve wnich does not seal perfectly when in the OFF position, significant
amounts of unwanted vapour may be delivered into the circuit, unknown to the
anaesthetist.
Clearly, such a state of affairs is undesirable and in a preferred
embodiment of the invention, we seek to eliminate these problems.
In a preferred embodiment, the control means controls the admission to the
unit of gas from a supply provlded through one or more cooperating ports on the
apparatus, the or each port having a valve member normally urged into a positionin which it acts to close the respective port, and the unit including actuating
means forming part of the interlock system such that when the unit is mounted
on the apparatus, the actuat;ng means is effective to move the respective valve
member of the or each cooperating port away from the port closing position only
when the control means has been manipulated to its operating position.
It is common practice for an anaesthesia apparatus to have mounted on it
two separate vaporisers for delivering different volatile anaesthetic agents to
a carrier gas, so that the same basic anaesthesia apparatus can be used during
a series of surgical operations wherein the needs of different patients require
the use of the different agents. In such a case it is clearly undesirable to
run the risk of the two agents being delivered to a patient at the same time or
otherwise becoming mixed. Apart from the case of alternative vaporisers,
however, there may be other cases where it is desirable for an anaesthesia
apparatus or other gas-administration apparatus to include two or more
alternative units which again should not be used at the same time. For example,there can be mentioned an apparatus which incorporates two units, eg. flow
meters which are designed to operate with different ranges of gas flow rates or
apparatus which includes both a trichlorethylene vaporiser and a soda lime
1~;3~8
--5--
absorber for C02 (which an anaesthetist may wish to use during different
operations but which must not be used together as trichlorethylene can react
with soda lime to produce a toxic gas).
Known anaesthesia apparatus which provide for 'multiple choice' vaporisers
typically include the backbar or rack, previously mentioned, upon which the
vaporisers are mounted and which provides the necessary pipework or ducting to
enable each vaporiser to be connected into the gas clrcuit. In an effort to
prevent the possibility of cross-contamination of the different vapours it is
known to provide a selector valve whereby the carrier gas can only be supplied
to one selected vaporiser at any one time. This system has the disadvantage,
however, that two valves must be operated to bring any one vaporiser into the
circuit, ie~ the selector valve on the backbar and the control valve on the
vaporiser which permits the passage of the carrier gas through the vaporiser andcontrols the concentration of the vaporised agent delivered to the carrier gas.
Furthermore, this system can still permit a situation to arise where, through
incorrect manipulation of the valves, either the wrong agent, or the wrong
concentration of the correct agent, or no agent at all, is delivered to the
patient without the anaesthetist immediately being aware of the fact.
In the preferred embodiment of the invention we seek to eliminate or at
least reduce the problems associated with the use of a selector valve in a
'multiple choice' anaesthesia apparatus whilst still ensuring that only a
selected one of two or more alternative vaporisers can be connected into the gascircuit at any one time.
In the preferred embodiment, the interlock system includes at least one pin
extendible outwardly from the unit on manipulation of the control means to its
operating position to prevent the control means of a similar adjacent unit
mounted on the apparatus from being manipulated to its operating position.
An embodiment of the invention will now be described, by way of example,
reference being made to the Figures of the accompanying diagrammatic drawings,
--6--
in which:
Figure 1 is a schematic plan view of two alternative gas-flow units
(vaporisers) mounted on the backbar or an anaesthesia apparatus;
Figure 2 is a more detailed plan view of one of the vaporisers of Figure
1, with certain parts broken away;
Figure 3 is an elevation of the vaporiser of Figure 2, partly in vertical
section;
Figures 4, 5 and 6 are respectfve detail sectional views of the vaporiser
of Figures Z and 3; and
F~gures 7A and 7B are schematic illustrations of the porting arrangement
provided by the anaesthesia machine for each vaporiser, in two operative
condltions.
Referring to the drawings, in Figure 1 there is shown the back bar 1 of an
anaesthesia apparatus upon which two gas-flow units in the form of vaporisers 2
and 3 adapted to deliver different volatile anaesthetic agents, are mounted
side-by-side. The vaporisers are installed in a removable, plug-in fashion,
being located on the back bar by respective pairs of ports 4a,4b, upstanding
from the back bar and which are received in corresponding recesses 5 in the rearportions of the vaporisers (see also Figures 3 and 6).
Means are provided for locking each vaporiser in place on the back bar,
comprising a rotatable shaft 6 borne by the vaporiser and which extends into a
rec-ess 7 in the back bar when the vaporiser is lowered onto the ports 4a,4b. The
shaft has a profiled groove 6a (fig 5) which engages with a latching member 7a
in the recess 7 when the shaft is turned by a thumb-lever 8 through 90, from
the position indicated for the vaporiser 3 in Figure 1 to the position indicatedfor the vaporiser 2. Operation of the lock is effective to prevent the
vaporiser being displaced from the back bar and also serves to draw the rear
portion of the vaporiser tightly down against the backbar, thereby ensuring a
gas-tight fit against annular seals 9 provided around the bases of the ports 4a,
~L~L3~
--7--
4b. It is to be noted that the thumb-lever 8 of vaporiser 3 is shown in the
unlocked position in Figure 1 for the purposes of illustration only, as it is
intended that so long as a vaporiser remains in place on the back bar its lock
will be in operation. Indeed, as will be more fully described hereinafter, it
is impossible to switch such a vaporiser into the gas circuit unless it is
locked to the backbar.
Mounted on the top of each vaporiser is means for controlling the admission
to the vaporiser of gas including a concentration dial 10 linked to a rotary
plate or other suitable form of control valve located within the body of the
~a~ h
vaporiser. It i~ ~ss~mcd t~ a~t, vaporiser is of the by-pass type, as
described for example in United Kingdom patent specification No. 1 224 478,
having a vaporising chamber in the lower portion 11 of the unit (fig 3) and a
circuit by-passing the vaporising chamber. In use the carrier gas admitted to
the vaporiser splits into two flows, one passing through the vaporising chamber
and the other through the by-pass circuit, the two flows thereafter reuniting
before leaving the vaporiser. The detailed construction of the control valve
will not be described herein, but briefly its function is to vary the relative
proportions of the gas flows passing through the vaporising chamber and by-pass
circuit in response to movement of the dial 10, thereby varying the
concentration of vaporised anaesthetic agent in the outlet flow. The dial has agraduated scale to indicate the anaesthetic concentration set by the control
valve, and also indicates an OFF position in which the control valve shuts off
gas flow through the vaporiser.
Referring now to Figures 2 and 3, mounted beneath, and rotatable with, the
concentration dial 10 is an annular cam 12 having an inclined shoulder 12a
separating lower and upper flat steps 12b and 12c. Cooperating with this cam isa crank 13, borne centrally at 13a and its end portions 13b and 13c resting
respectively on the surface of the cam 12 and ~he surface of a vertically
reciprocable platform 14. The platform 14 is borne by a pair of spring-biased
~;3~i~41~
--8--
plungers 15 (of which one can be seen in fig 6) which urge the platform upwards
against crank portion 13c which in turn urges the crank portion i3b downwards
against the surface of cam 12. While the concentration dial 10 is in its OFF
position (and the control valve is therefore closed) the crank portion 13b can
rest upon the lower step 1 2b of the cam and the pl atform 14 is accordingly
allowed to rise to its upper position as shown in figure 3. When, however, the
concentration dial is moved (anti-clockwise) away from the OFF position to its
operating position to thereby open the control valve the crank portion 13b has
to rise up the shoulder 12a to the upper step 12c of the cam and in so doing thecrank is rotated to the posit;on indicated in figure 2, so that in turn the
crank porti on 1 3c pushes the pl atform 14 downwardly agal nst its spri ng bi as.
Depending from the rear of the platform 14 is a pln 16 reciprocable in a
bore 17. Intersecting bore 17 is a bore 18 within which are housed a pair of
pins l9a, l9b, spring-biased towards one another (see fig 4). So long as the
platform 14 remains in its upper position the pin 16 is held clear of the bore
18 and the pins l9a and l9b remain wholly within the same. When, ha~ever, the
platform is lowered by the action of turning dial 10 the pin 16 intrudes into
the bore 18 and displaces the pins l9a and l9b to either side. In this conditionthe distal ends of the pins extend through the opposite ends of the bore 18, as
shown in figures 1,2 and 4 for vaporiser 2.
Thus it is seen that whenever the control valve of a vaporiser as
described above is man1pulated into a position which provides for the admission
of gas to the vaporiser, the two pins l9a and l9b will extend, one to each side
of the unit. Returning to figure 1 it is seen that the dial ~O of vaporiser 2
has been moved away from the OFF position to its operating position to open the
associated control valve and accordingly its pins l9a, l9b are extended. If an
attempt were now to be made to turn the dial of vaporiser 3 (assuming that its
lock had already been operated), by virtue of the linkage comprising its cam 12,crank 13, platform 14 and pin 16 its own two pins l9a and l9b would likewise
1~3~9~13
g
have to extend. However, the path of rnovement of its pin l9a is blocked by the
pin lgb of vaporiser 2 and n~vement of its di al 10 is thereby prevented.
With this arrangement it will be understood that it is impossible to switch
more than sne of the vaporisers into the gas circuit at any one time, and the
above described interlock system provided by the pins l9a and l9b will, of
course, be equally effective between any two similar vaporisers (or other gas-
flow units having a similar mechanism) occupying either of the two mounting
stations defined by the pairs of backbar ports 4a and 4b.
As previously indicated, the vaporisers 2 and 3 each comprise a mechanism
for preventing operation of the vaporiser unless it is locked in position on theback bar 1. This mechanism will now be described with reference to figures 2
and 5.
Fast with the shaft 6, beneath the platform 14, is a circular plate 20
having two upstanding pins 21. When the shaft is rotated into the LOCK
position, these pins 21 underly respective holes 22 in the platform 14, so that
subsequent movement of the dial 10 such as to lower the platfon~ is unimpeded.
However, while the shaft 6 is in the UNLOCK position the pins 21 underly
unapertured portions of the platform. Consequently in this condition lowering
of the platform is prevented and the dlal 10 thereby cannot be turned away from
its OFF positi on.
A further feature of the illustrated embodiment is the means whereby the
backbar ports 4a,4b associated with either vaporiser are opened only when the
associated vaporiser control valve is opened. Figure 7 indicates the porting
arrangement at each back bar station. The ports 4a and 4b communicate with
respective bores 23a and 23b in the backbar, bore 23a being connected to an
inlet duct 24 from the carrier gas supply and bore 23b to an outlet duct 25.
The two bores are joined by a bore 26. A piston-like valve member 27 and stem
28 is provided in each bore 23a, 23b, each biased upwardly by a spring 29.
~3L3~! 9~3
-10-
Figure 7a shows the condition of the ports when no vaporiser is mounted at
that station or when ~ vaporiser is mounted but not switched on. In this
condition each port is closed and the inlet and outlet ducts 24 and 25 are
connected together through bore 26. ~hen a vaporiser is mounted at the station
and its control valve is opened, however, the attendant lowering of the platform1~ brings respective actuating means in the form of pins 30 (figs 3 and 6) down
onto the valve stems 28 to move the valve members 27 into the positions
indicated in figure 7b. In this condition port 4a is open to the inlet duct 24
and the port 4b is open to the outlet duct 25, the bore 26 being closed off.
From port 4a the carr~er gas enters the cooperating recess 5 of the vaporiser
and passes through a side bore (not shown) from the recess into the body of the
vaporiser to be split into two flows as hereinbefore described; (it will be
noted that in this condition the top opening Sa from the recess will be closed
by a seal 30a provided around the valve actuating pin 30). After the flows
reunite the carrier gas/vapour mixture is fed to the other recess 5 of the
vaporiser and thence passes through port 4b and into the outlet duct 25 of the
backbar.
From the above it wi11 be appreciated that while a vaporiser is mounted on
the back bar, unless and until its dial 10 is moved away from the OFF position
to open the associated control valve, the cooperating ports of the back bar are
closed and the vaporiser is completely isolated from the gas circuit. Should
any leakage of vapour from the vaporiser occur for any reason It can be vented
from the recesses 5 through their top openings 5a (the pins 30 being withdrawn
in this condition) and thence to the atmosphere through suitable further
openings provided for the purpose.
Furthermore, while the vaporiser at either station is not switched on the
corresponding ports 4a and 4b are by-passed by the carrier gas which enables a
series connection of the two stations to the carrier gas supply to be effected.
In other words, referring to figures 7a and 7b, the outlet duct 25 from the
~ 3~
-11-
illustrated station constitutes the inlet duct to the next station. By using a
series connection of this type instead of the parallel connection which is more
usual in anaesthesia machines providing for 'multiple choice' vaporisers, the
amount of 'dead' pipework in the back bar can be minimised, thereby reducing thehazards associated with the build-up of explosive vapours such as ether in such
pipework.
In a modification it is possible that the actuating pins 31 could be used
to operate valves or machanisms other than the valve members ~ which mechanisms
mlght, for example, provide a connection to an indicator or pressure gauge whichoperates only when the control means is moved to its operating position.
