AU633315B2 - Anaesthetic apparatus - Google Patents

Description

,,AU ST A LI 633315 P/00/011 Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: .Annlicp; r, Number: Lodged: PJ 3684 14th April 1989 Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art Name of Applicant: TO BE COMPLETED BY APPLICANT ULCO ENGINEEl rNG PTY. LIDIITED 25 SLOANE STREET PMARRICKVILLFE NSW 2204 Ad~dress of Applicant- Actual Inventor: Address for Sdrvico: EVANGELOS (ANDY) ROUSSOS of 134 RATM4SCATE AVENUE NORTH BONDI, NEW SOUTH W'..LES and LOVRO VIDAKOVIC of 22 NELSON ROAD, EARLWOOD, NEW SOUTH WALES HALFnRD CO.

49-51 YORK STREET SYDNEY NSW 2000 Complete Specification for the invention entitled: ANAESTHETIC APPARATUS The following statement is a full description of this lnver,',!on, including the best method of performing It known to me- (q 14699/78- L 1 4599l~- LPrinted hy C J TiiompsoN, Commonwealth (Jovc ment Printer, Canberra The pr'esent invention relates to the control of the supply of gaseous mixtures, such as oxygen-nitrous oxide mixtures in an anaesthetic apparatus.

When nitrous oxide is used as the anaesthetising gas a concurrent supply of oxygen is supplied and to ensure safe operating condition of the anesthetisinj gas the proportion of oxygen in the combined gas flow is required to be maintained at at least a minimum level, such as 25% of the combined oxygen-nitrous oxide flow.

In the prior art devices are known which either control the minimum oxygen concentration or provide an alarm when the concentration of oxygen falls below the specified minimum. Examples of these prior art devices are c-scribed in "The Anesthesia Mach.ne" by Clayton Petty, Churchill Livingston, Melbourne 1987, at pages 199- 203.

One prior art device comprises a pair of interconnected diaphragms which signal when the oxygen flow decreases to 30+5% of combined oxygen-nitrous oxide flow. This device merely provides an oxygen ratio monitor which functions best at oxygen flow rates between 700 ml/minute and 5 litres per minute wherea. i.t becomes inaccurate at flow rates below 700 ml/minute due to hysteresis of the diaphragm. This oxygen ratio monitor can be con'bined with a slave control valve so as to maintain the oxygen-nitrous oxide mixture at a minimum of 25-30% oxygen. When the oxygen pressure is proportionately higher than the nitrous oxide pressure the slavs valve opens and vice ,ersa. This system is also responsive to manual adjustment of the nitrous oxide flow to maintain the requisite minimum proportion of oxygen in the mixture.

This device cannot be used if any gas other than -3oxygen and nitrous oxide is used in the system. For example, it cannot be used where a combination of air, oxygen and nitrous oxide may be used.

A further prior art flow control device described in the above text is manufactured by Ohmeda, The BOC Group, Inc. as the Link 25 system. This system comprises a proportion limiting control system having a sprocket interconnecting rotary flow control valves for the oxygen and nitrous oxide. Each flow control valve has a sprocket secured to the needle valve stem.

A cable chain interconnects the two sprockets. At a orescribed minimum of 25% oxygen concentration the oxygen sprocket engages the collar of a needle valve stem and links the nitrous oxide and oxygen flow control valves. Independent adjustment of either the nitrous oxide or oxygen is possible but the link system automatically intercedes to maintain a minimum oxygen concentration. This system has been subject to a few mechanical problems in particular to having the needle valve jammed in the needle seat with attendant shearing of the needle valve tip when the valve is rotated too hard.

Similar prior art is described in U.S. patent 4,266,573 equivalent to Australian patent 520,324 in the name of Airco Inc. These patent specifications appear to describe a devi which is equivalent to that described in the preceeding paragraph.

The present invention seeks to overcome these disadvantages in the prior art and to provide a simpler and more efficient alternative.

In accordance with one broad form of the invention there is provided a control arrangemenit for an anaesthetic apparatus for providing a mixture of a first gas and a second gas of selected proportions, said control arrangement having at least a first rotatable valve control to vary the mixture of the first gas and the second gas, the rotary motion of said at least first rotatable valve control being converted into translational motion providing an opening or closing action of first and second valve closure members controlii-j espective the fiow of said first gas and said seco .d gas, means biasing each of said valve r'iosure members open, and means for actuating said first and second valve closure members in a g-ven ratio, said actuating means being controlled by said first rotatable valve control such that the percentage of said first gas by volume in the mixture provided by said anaesthetic apparatus is maintained at at least a predetermined minimum percentage. Preferably the first gas is oxygen, the second gas is nitrous oxide and the predetermined percentages are 75% nitrous oxide arid 25% oxygen.

In one embodiment of the invention the actuating means comprise first and second lever means between separate valve controls and the closure members, and the valve closure members are needle valves. The second lever means can operate the second needle valve while the first lever means controls the operation of both said first and second needle valves activating said first and second needle valves proportionately to maintain said at least predetermined percentage.

Embodiments of the inv,'ntion will now be described with respect to the following figures in which: Figure 1 is a general schematic of an anaesthetic apparatus embodying the present invention; Figure 2 is a schematic of a first embodiment of the 1 01 1 UVANOMM flow control arrangement according to the invention; Figure 3 is a schematic of a second embodiment of the flow control arrangement according to the invention; Figure 4 is a schematic of the embodiment of Figure 2 showing the gas flow paths; and Figure 5 is a schematic in elevation of the n-trous oxide valve of Figur s 2-4.

Figure 1 shows a general anaesthetic apparatus The apparatus 10 includes absorber 12, gas connection unit 14 having pressure monitoring gauge- 16, vaporiser 20 and flowmeters 21, 22. These elements of the apparatus are affixed to a wheeled frame for flexibility and mobility. Flowmeters 22 are provided to monitor the flow of each gas of either a two gas or a three gas system. A two gas system (as shown) would comprise nitrous oxide and oxygen while a three gas system would comprise oxygen, air aud nilrous oxide.

The flowmeters 22 enable the anaest.heologist to monitor the flow of the respective gases and in particular to ensure that sufficient percentage oxygen is supplied to provide a breathable life supporting mixture.

The flow of the respective gases is controlled by rotary knobs 24, 26. The gases are combined after passage through the flowmeters 21, 22 and piped passed vaporiser 20 where anaesthetic agent can be introduced. The mixture is then supplied via piping 28 to outlet tube The present invention provides means controlling the oxygen and nitrous oxide flows such that a minimum of by volume of oxygen is provided in an oxygen/nitrous oxide gas mixture. This oxygen/nitrous oxide gas control arrangement according to the invention is shown in Figures In Figure 2 an oxygen control valve 32 and a nitrous oxide control valve 34 each include respectively a control knob 36, 38 activating a screw threaded shaft 42 fixed to the wall of the flowmeter 21, 22 by nut 46, 48, while at the end of the shaft 40, 42 distal from the knob 36, 38 ball bearing 50, 52 is held in place by O-ring seal 54, 56.

The ball bearings 50, 52 press upon levers 58, which pivot respectively about axes 62, 64. Ball bearings 50, 52 provide low friction contact between shafts 40, 42 and levers 58, 60. Alternatively, the shafts 40, 42 may engage the levers 5 60 directly or via low friction intermediate members such as nylon bushings. These levers 58 and 60 in turn press on needle valves 66 and 68. In particular, lever 58 presses on both needle valves 66 and 68, while lever only presses on needle valve 68. These needle valves 66 and 68 are identical in structure and, as shown in expanded form for the nitrous oxide valve 34, will be described with respect thereto.

Needle valve 68 comprises valve seat 70 and needle valve member 72. Needle valve member 72 has a needle tip 74 to engage the aperture 76 in the valve seat Attached to the needle tip 74 is the main body of the needle valve member 72 having a shoulder 78 to accommodate spring 80 which biases the needle valve 72 away from the valve seat 70. An O-ring seal 82 is provided in a waisted portion of the needle valve member 72 to provide sealing against the body of the valve (not numbered). A bearing 84 sits in a cavity -7- 86 of the valve member 72. Movement of the lever 58i presses on bearing 84 which in turn conveys this motion into translation of the needle tip 74 to vary the size of the aperture 76 and thus the flow of gas through the valve 32, 34. The flow for the respective valves 32, 34 enters via couplings 88, 90 and exits via channels (see Figure 4) to be combined with other elements of the anaesthetic apparatus As shown in Figure 2, lever 60 only activates valve 34 while lever 58 activategs both valve 32 and valve 34.

The opposed feces of the levers 58 and 60 have chamfered or rounded edges 92 to enable independent operation. The position of bearing 84 for oxygen valve 32 is a distance X from pivot axis 62 while the tip of lever 58 is positioned a distance Y from bearing 84. The length of X and Y are chosen to provide the minimum predetermined oxygen concentration. Thus the ratio X:Y when equal to 1:3 provides a predetermined 25% concentration of oxygen in the nitrous oxide-oxygen mixture.

The operation of the control arrangement will now be described with respect to Figure 2. With valves 32 and 34 initially closed that is with needle tips 74 blocking their respective apertures 76, the nitrous oxide knob 38 is turned. Lever 60 rotates counterclockwise as seen in Figure 2 under action of spring 80. Lever 58 which also rests against bearing 84 of valve 34 prevents opening of valve 34 until knob 36 is turned to release the lever 58. Once this is done lever 58 rotates clockwise as seen in Figure 2 opening valve 32 to allow oxygen to pass while simultaneously opening valve 34. The dimensions X, Y of the lever 58 ensure that for every movement of the free end of lever 58 at chamfered end 92 thereof the motion at bearing 84 of valve 32 is one quarter of that movement. Thus whenever the nitrous oxide valve is activated the oxygen valve is simultaneously constrained to supply oxygen at least at the required percentage. In addition the oxygen valve 32 can be activated on its own to increase the flow of oxygen above the predetermined concentration. While turning knob 38 merely allows the nitrous oxide to vary up to but not exceed a maximum concentration 75%) of the mixture. Conversely if for any reason the oxygen valve is shut this simultaneously shuts the nitrous oxide valve while at all intermediate flow values maintaining the predetermined concentration of oxygern.

A variation of the invention is shown in Figure 3. In this embodiment all elements of the control arrangement are as described with respect to Figure 2 except for the levers 58, 60. As shown levers 158, 160 are provided with interleaved tongues 100 and 102 respectively. This arrangement provides an interlocked operation of the two valves otherwise equivalent to the set up as described above with respect to Figure 2.

As shown schematically in Figures 2 and 3 gas control arrangements of the above type are often supplied with a further valve 110 which is used for the control of an air supply. The supply of the oxygen, nitrous oxide and air may be controlled with a multi circuit selector 180 (as shown in Figure This selector 180 normally allows a selection of a mixture of air and oxygen, in position 182, or a mixture of nitrous oxide and oxygen, in position 184, to be supplied. As shown, the selector 180 is in the position 184 for the supply of a mixture of nitrous oxide and oxygen.

Nitrous oxide is supplied to valve 34 via coupling oxygen to valve 32 by coupling 88 and air to valve 110 by coupling 193. The flow of a gas through its respecive valve will now be described with respe"' to the nitrous oxide valve 34.

As valve 34 opens gas is admitted to passage 186 which in turn divides into passageways 188 and 190.

Passageway 190 leads to exit orifice 192 connected, see Figure 5, to the !ear of flowmeter 22 via mounting 200 having non-return valve 210.

Passageway 188 leads to the glass column comprising the indicator of the flowi'l-ter 22 equally via a mounting 200 having a non-return valve 210. Valve(s) 210 prevent(s) gas from flowing back if the nitrous oxide valve is left open.

Though the above description of gas flow has been limited to that of the nitrous oxide valve 34, the oxygen or air valves 32, 110 are to be understood to comprise similar details.

It is also contemplated that in place of the dual lever arrangement shown in Figures 2 and 3 a single lever arrangement controlling both valves may be provided. This control arrangement in our experience is sensitive to th- nominal gas pressure from the gas supply which even after regulation suffers from fluctuations in p -ssure. This can be reduced by providing a second stage of pressure regulation. The arrangement shown in Figure 2 can provide control of the percentagu oxygen in a mixture of oxygen and nitrous oxide in the range 25-30%.

In the anaesthetic apparatus 10 shown in Figure 1 and as well known in the art the gas mixture is supplied via tube 30 to a valving arrangement 191 on top of absorber 12. On inhalation the mixture is passed to mask 195 via tubing 194 while exhaled gas from mask 195 returns via tubing 196 back to absorber 12 where carbon dioxide is removed. The scrubbed residual gas is then stored in bladder 1/7 to reduce the volume of make-up gas required for subsequent inhalation.

The valves including the levers, knobs and other ancillary parts ar:e mar'e of any suitable material well known for such uso in tlis art.

Though the invention has been described above with respect to preferred embodiments of the invention it is to be understood that variations thereon are contemplated within the knowledge of a person skilled in the art. In particular the control arrangement can be appli',d to any situation requiring a given mixture of two or more gases (or fluids in general) to be provided.

Claims (5)

1. 2. A control arrangement as claimed in claim 1 wherein said first gas is oxygen, said second gas is nitrous oxide and said predetermined percentage is
2. 3. A control arrangement as claimed in claim 2 w'ierein said actuating means comprise a first lever means hinged at one end and located between said first rotatable valve control and said valve closure members actuating said first and second valve closure members proportionally to maintain said predetermined percentage. 12
3. 4. A control arrangement as claimed in claim 2, further including a second rotatable valve control ana wherein said actuating means comprise first lever means hinged at one end actuating said first and second valve closure members in direct proportion to said predetermined percentage, and a second lever means hinged at one end actuating said second valve closure member independently of said first lever means, said first and second rotatable valve controls controlling respectively operation of said first and second lever means, each lever being between its associated rotatable valve control and valve closure member, whereby operation of said second rotatable valve control cannot open said second valve closure member without. activation of said first rotatable valve control. A control arrangement as claimed in claim 2 further including a second rotatable valve -ontrol, and wherein said actuating means comprise fi a. ind second hinged lever means, said first and second lever means actuating respectively said first and second valve closure members in direct proportion to said predetermined percentage, said first and second rotatable valve controls controlling respectively operation of said first and second lever means, each lever being between its associated rotatable valve control and valve closure member, and said first lever means overlies said second lever means whereby operation of said second rotatable valve control cannot open said 3econd valve closure member without activation of said Fitrst rotatable valve control. 13
4. 6. A control arrangement for an anaesthetic apparatus substantially as herein described with reference to Figures 2, 4 and
5. 7. A control arrangement for an anaestheti, apparatus substantially as herein describeu with reference to Figure 3. Dated this 19th day of November, 1992 ULCO ENGINEERING PTY. LIMITED By their Patert Attorneys HALFORD CO.