CA2039075C - Anaesthetic vaporisers - Google Patents
Anaesthetic vaporisersInfo
- Publication number
- CA2039075C CA2039075C CA 2039075 CA2039075A CA2039075C CA 2039075 C CA2039075 C CA 2039075C CA 2039075 CA2039075 CA 2039075 CA 2039075 A CA2039075 A CA 2039075A CA 2039075 C CA2039075 C CA 2039075C
- Authority
- CA
- Canada
- Prior art keywords
- anaesthetic
- passage
- liquid
- chamber
- vaporising chamber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
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- Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)
- Respiratory Apparatuses And Protective Means (AREA)
- Nozzles (AREA)
Abstract
An anaesthetic vaporlser includes a passagevay 10, 30 for directing carrier gas through a fixed laminar restrictor 32 to a vaporising chamber 26. Liquid anaesthetic agent ls injected into the vaporising chamber 26 from a constant level tank 12 the output of vhich is controlled by a laminar control valve 28. Liquid anaesthetic agent flov is determined by the pressure of carrier gas in the passagevay 10, 30 and the setting of the liquid laminar control valve 28.
Description
90BllOUK/PG/ALF
1- ~Q~g~5 IMPROVEHENTS IN ANAEST~ETIC VAPORISERS
The present invention relates to anaesthetic vaporisers.
UK Patent No 1 224 478, describes an anaesthetic vaporiser of the by-pass type in vhich a carrier gas such as oxygen, air or nitrous oxide is initially divided on entry to the vaporiser between a first stream which is directed towards the sump or vaporising chamber of the vaporiser to entrain vapour from a volatile liquid anaesthetic contained therein; and a second by-pass stream, the first and second streams subsequently recombining prior to leaving the vaporiser for delivery to a patient.
This known vaporiser has been used successfully over a number of years for delivering anaesthetic agents such as halothane, trichloroethlene and ether derivatives including enflurane, fluoroxene, methoxyflurane and isoflurane. All the aforementioned anaesthetic agents have a boiling point at atmospheric pressure well above 40C.
However, a new anaesthetic agent has been developed namely 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane which has a boiling point at atmospheric pressure of between 20 and 25C. This physical characteristic of 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane renders existing anaesthetic vaporisers unsuitable for delivering said agent to a patient.
Conventional vaporisers of the by-pass type are unsuitable for this new anaesthetic agent in that its boiling point is approximately in the middle of a conventional vaporisers operating ambient temperature range of between 15C and 35C. ~hen the ambient temperature and hence the vaporiser temperature is above 25C heat is transferred to the anaesthetic agent and causes an amount of vapour to boil off such that heat lost by the latent heat of vaporisation is equal to the heat transferred to it.
90BllOUK/PG/ALF
_ 2 - 2~ ~9 ~5 It is an aim of the present invention to provide an anaesthetic vaporiser which is capable of deliving a predetermined concentration of an anaesthetic agent having a boiling point at normal atmospheric pressure of less than 30C to a patient.
According to the present invention, an anaesthetic vaporiser comprises inlet for carrier gas and an outlet for carrier gas and anaesthetic agent for delivery to a patient, a passageway from said inlet to a vaporising chamber and a passage from said vaporising chamber to the outlet, said passageway having located therein a laminar restrictor, and a constant level tank containing liquid anaesthetic agent, a second passage extending between said tank and the vaporising chamber, a laminar control valve being located in said second passage and means for transmitting the pressure in said passageway to the liquid in the liquid level tank to drive the liquid anaesthetic agent along the second passage for injection into the vaporising chamber.
An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying drawings in which:-Figure 1 is a diagrammatic sketch of an anaesthetic vaporiseraccording to the present invention; and Figure 2 is a diagrammatic sketch of a modification of the anaestheitc vaporiser as illustrated in Figure 1.
As shown in Figure 1, an anaesthetic vaporiser 1 has an inlet 2 for carrier gas and an outlet 4 for carrier gas and gaseous anaesthetic agent. Extending between the inlet 2 and the outlet 4 is a passage 6 in which is located a fixed laminar flow restrictor 8. The restrictor 8 exhibits laminar flow characteristics over its operating range.
90BllOUK/PGtALF
1- ~Q~g~5 IMPROVEHENTS IN ANAEST~ETIC VAPORISERS
The present invention relates to anaesthetic vaporisers.
UK Patent No 1 224 478, describes an anaesthetic vaporiser of the by-pass type in vhich a carrier gas such as oxygen, air or nitrous oxide is initially divided on entry to the vaporiser between a first stream which is directed towards the sump or vaporising chamber of the vaporiser to entrain vapour from a volatile liquid anaesthetic contained therein; and a second by-pass stream, the first and second streams subsequently recombining prior to leaving the vaporiser for delivery to a patient.
This known vaporiser has been used successfully over a number of years for delivering anaesthetic agents such as halothane, trichloroethlene and ether derivatives including enflurane, fluoroxene, methoxyflurane and isoflurane. All the aforementioned anaesthetic agents have a boiling point at atmospheric pressure well above 40C.
However, a new anaesthetic agent has been developed namely 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane which has a boiling point at atmospheric pressure of between 20 and 25C. This physical characteristic of 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane renders existing anaesthetic vaporisers unsuitable for delivering said agent to a patient.
Conventional vaporisers of the by-pass type are unsuitable for this new anaesthetic agent in that its boiling point is approximately in the middle of a conventional vaporisers operating ambient temperature range of between 15C and 35C. ~hen the ambient temperature and hence the vaporiser temperature is above 25C heat is transferred to the anaesthetic agent and causes an amount of vapour to boil off such that heat lost by the latent heat of vaporisation is equal to the heat transferred to it.
90BllOUK/PG/ALF
_ 2 - 2~ ~9 ~5 It is an aim of the present invention to provide an anaesthetic vaporiser which is capable of deliving a predetermined concentration of an anaesthetic agent having a boiling point at normal atmospheric pressure of less than 30C to a patient.
According to the present invention, an anaesthetic vaporiser comprises inlet for carrier gas and an outlet for carrier gas and anaesthetic agent for delivery to a patient, a passageway from said inlet to a vaporising chamber and a passage from said vaporising chamber to the outlet, said passageway having located therein a laminar restrictor, and a constant level tank containing liquid anaesthetic agent, a second passage extending between said tank and the vaporising chamber, a laminar control valve being located in said second passage and means for transmitting the pressure in said passageway to the liquid in the liquid level tank to drive the liquid anaesthetic agent along the second passage for injection into the vaporising chamber.
An embodiment of the invention will now be described, by way of example, reference being made to the Figures of the accompanying drawings in which:-Figure 1 is a diagrammatic sketch of an anaesthetic vaporiseraccording to the present invention; and Figure 2 is a diagrammatic sketch of a modification of the anaestheitc vaporiser as illustrated in Figure 1.
As shown in Figure 1, an anaesthetic vaporiser 1 has an inlet 2 for carrier gas and an outlet 4 for carrier gas and gaseous anaesthetic agent. Extending between the inlet 2 and the outlet 4 is a passage 6 in which is located a fixed laminar flow restrictor 8. The restrictor 8 exhibits laminar flow characteristics over its operating range.
90BllOUK/PGtALF
- 3 - ~ ~ ~9 Q75 Exending from the passage 6 from a location 9 upstream of the restrictor 8 ls a second passage 10 vhich communications ~ith a first chamber 14 of a constant level tank 12. The tank 12 includes a second chamber 16 ~hich is separated from the first chamber 14 by a diaphragm 18.
The second chamber 16 is connected via a passage 20 vith a liquid anaesthetic reservoir 22. A further passage 24 extends from the second chamber 16 to a vaporising chamber 26. In the passage 24 bet~een the tank 12 and the vaporising chamber 26 there is located a laminar control valve 28.
A passage 30 extends between the passage 10 and the vaporising chamber 26 and located in the passage 30 is a further fixed laminar restrictor 32. As will be explained, the passages 10, 30 form a passage~ay for a first stream of carrier gas to flo~ to~ards the vaporising chamber 26.
Extending from the vaporising chamber 26 to join the passage 6 adjacent the oulet 4 is a passage 34.
In use, fresh carrier gas is fed to the inlet 2 of the vaporiser 1 from a conventional flow metering bank delivering typically 0.2 to 15 litres per minute of air, oxygen or nitrous oxide in various proportions.
The carrier gas enters the vaporiser 1 and at location 9 is divided into a first stream ~hich passes initially along passage 10 and a second by-pass stream which passes along passage 6 through restrictor 8 towards the outlet 4. The proportion of the gas which enters the passages 6 and 10 is determined by the value of the restrictors 8, 32 ~hich have a fixed and linear (laminar) flow characteristic. The carrier gas in the first stream passes from passage 10 into passage 30 through restrictor 32 and into vaporising chamber 26. Vithin the vaporising chamber 26 volative liquid anaesthetic agent is injected into the vaporising chamber and evaporated into the carrier gas 90BllOUK/PG/ALF
_ 4 _ 2 0 3 q ~ 7 ~
stream. Carrier gas and anaesthetic agent vill then leave the vaporising chamber 26 along passage 34 and exit the vaporisor 1 at outlet 4.
It will be evident, that the pressure of the first stream in passages 10, 30 is reflected in the pressure existing in the first chamber 14 and this pressure is transferred across the diaphragm 18 in the constant level tank 12 to liquid contained vithin the second chamber 16. The temperature of the liquid in the tank 12 is kept sufficiently constant so that variations in temperature hence vapour pressure of the volatile anaesthetic agent are small compared vith the pressure of the first stream in passages 10, 30. The liquid level in the second chamber 16 is kept constant and at the same height as the point of injection in the vaporising chamber 26 so that no liquid head effects are superimposed on the pressure available to drive the liquid agent into the chamber 26. The liquid flow from the tank 12 along passage 24 is determined by the pressure in the first stream that is the pressure in passages 10, 30, and the setting of the laminar control valve 28 which is connected to a dial calibrated in percentage volume of drug in the delivered mixture. By use of the laminar characteristics of the fixed restrictors 8, 32 and the laminar control valve 28 the concentration of drug is independent of the carrier gas flow into the vaporiser 1.
~ith the embodiment illustrated in Figure 1, as previously stated, it is necessary to maintain the temperature of the liquid anaesthetic agent in the constant level tank 12 constant so that variations in vapour pressure are small compared vith the pressure in passages 10, 30.
In practice this is difficult to achieve particularly ~hen heating or cooling is possible vith the flov of liquid anaesthetic agent from the reservoir 22 to the tank 12. An alternative approach is illustrated in Figure 2 in vhich the passage 10 is interrupted by a balanced venting system 50.
90BllOUK/PG/ALF
- 5 - ~03~7~
If, for example, the pressure in chamber 14 increases above the pressure in passage 10 due to the heating of the liquid anaesthetic agent, the pressure in chamber a increases to the same value as in chamber 14. This will cause diaphragm c to move upwards (as shown) against the lower pressure in chamber d which is equal to the pressure in passage 10. Movement of the diaphragm c opens a valve b releasing pressure to atmosphere until the pressure imbalance ceases.
Conversely, if the pressure in chamber 14 falls relative to the pressure in passage lO a valve _ opens due to the imbalance in pressure between chambers f and h allowing gas to flow from the passage 10 into the chamber ~ until the imbalance is eliminated.
Means (not shown) is connected between the constant level tank 12 and the reservoir 22 for sensing the level of liquid anaesthetic in the chamber 16 and automatically feeding liquid anaesthetic from the reservoir to the chamber 16 when the liquid level drops below a predetermined level.
Anaesthetic agents such as halothane, enflurane and isoflurane are normally delivered in concentrations of approximately 5Z of the total flow of gas administered to a patient. However, the relatively new anaesthetic agent 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane has a much higher vapour delivery concentration up to, for example, 18Z of the total flow of gas administered to a patient. It is an advantage therefore that the laminar control valve 28 be associated with the liquid flow passage 24 rather than the usual line passing gaseous mixture of carrier gas and anaesthetic agent.
In a modification that portion of the passage 6 between the junction 9 and the point where the passage 34 joins the passage 6 can be deleted so that in effect all the carrier gas can be made to pass along the passageway 10, 30 into the vaporising chamber 26.
The second chamber 16 is connected via a passage 20 vith a liquid anaesthetic reservoir 22. A further passage 24 extends from the second chamber 16 to a vaporising chamber 26. In the passage 24 bet~een the tank 12 and the vaporising chamber 26 there is located a laminar control valve 28.
A passage 30 extends between the passage 10 and the vaporising chamber 26 and located in the passage 30 is a further fixed laminar restrictor 32. As will be explained, the passages 10, 30 form a passage~ay for a first stream of carrier gas to flo~ to~ards the vaporising chamber 26.
Extending from the vaporising chamber 26 to join the passage 6 adjacent the oulet 4 is a passage 34.
In use, fresh carrier gas is fed to the inlet 2 of the vaporiser 1 from a conventional flow metering bank delivering typically 0.2 to 15 litres per minute of air, oxygen or nitrous oxide in various proportions.
The carrier gas enters the vaporiser 1 and at location 9 is divided into a first stream ~hich passes initially along passage 10 and a second by-pass stream which passes along passage 6 through restrictor 8 towards the outlet 4. The proportion of the gas which enters the passages 6 and 10 is determined by the value of the restrictors 8, 32 ~hich have a fixed and linear (laminar) flow characteristic. The carrier gas in the first stream passes from passage 10 into passage 30 through restrictor 32 and into vaporising chamber 26. Vithin the vaporising chamber 26 volative liquid anaesthetic agent is injected into the vaporising chamber and evaporated into the carrier gas 90BllOUK/PG/ALF
_ 4 _ 2 0 3 q ~ 7 ~
stream. Carrier gas and anaesthetic agent vill then leave the vaporising chamber 26 along passage 34 and exit the vaporisor 1 at outlet 4.
It will be evident, that the pressure of the first stream in passages 10, 30 is reflected in the pressure existing in the first chamber 14 and this pressure is transferred across the diaphragm 18 in the constant level tank 12 to liquid contained vithin the second chamber 16. The temperature of the liquid in the tank 12 is kept sufficiently constant so that variations in temperature hence vapour pressure of the volatile anaesthetic agent are small compared vith the pressure of the first stream in passages 10, 30. The liquid level in the second chamber 16 is kept constant and at the same height as the point of injection in the vaporising chamber 26 so that no liquid head effects are superimposed on the pressure available to drive the liquid agent into the chamber 26. The liquid flow from the tank 12 along passage 24 is determined by the pressure in the first stream that is the pressure in passages 10, 30, and the setting of the laminar control valve 28 which is connected to a dial calibrated in percentage volume of drug in the delivered mixture. By use of the laminar characteristics of the fixed restrictors 8, 32 and the laminar control valve 28 the concentration of drug is independent of the carrier gas flow into the vaporiser 1.
~ith the embodiment illustrated in Figure 1, as previously stated, it is necessary to maintain the temperature of the liquid anaesthetic agent in the constant level tank 12 constant so that variations in vapour pressure are small compared vith the pressure in passages 10, 30.
In practice this is difficult to achieve particularly ~hen heating or cooling is possible vith the flov of liquid anaesthetic agent from the reservoir 22 to the tank 12. An alternative approach is illustrated in Figure 2 in vhich the passage 10 is interrupted by a balanced venting system 50.
90BllOUK/PG/ALF
- 5 - ~03~7~
If, for example, the pressure in chamber 14 increases above the pressure in passage 10 due to the heating of the liquid anaesthetic agent, the pressure in chamber a increases to the same value as in chamber 14. This will cause diaphragm c to move upwards (as shown) against the lower pressure in chamber d which is equal to the pressure in passage 10. Movement of the diaphragm c opens a valve b releasing pressure to atmosphere until the pressure imbalance ceases.
Conversely, if the pressure in chamber 14 falls relative to the pressure in passage lO a valve _ opens due to the imbalance in pressure between chambers f and h allowing gas to flow from the passage 10 into the chamber ~ until the imbalance is eliminated.
Means (not shown) is connected between the constant level tank 12 and the reservoir 22 for sensing the level of liquid anaesthetic in the chamber 16 and automatically feeding liquid anaesthetic from the reservoir to the chamber 16 when the liquid level drops below a predetermined level.
Anaesthetic agents such as halothane, enflurane and isoflurane are normally delivered in concentrations of approximately 5Z of the total flow of gas administered to a patient. However, the relatively new anaesthetic agent 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane has a much higher vapour delivery concentration up to, for example, 18Z of the total flow of gas administered to a patient. It is an advantage therefore that the laminar control valve 28 be associated with the liquid flow passage 24 rather than the usual line passing gaseous mixture of carrier gas and anaesthetic agent.
In a modification that portion of the passage 6 between the junction 9 and the point where the passage 34 joins the passage 6 can be deleted so that in effect all the carrier gas can be made to pass along the passageway 10, 30 into the vaporising chamber 26.
Claims (7)
1. An anesthetic vaporiser which comprises:
(a) a vaporising chamber, (b) an inlet for carrier gas, which is connected to the vaporising chamber by means of a passageway, (c) an outlet for carrier gas and anaesthetic agent for delivery to a patient, which is connected to the vaporising chamber by means of a first passage, (d) a laminar restrictor located in the passageway which connects the inlet to the vaporising chamber, (e) a constant level tank for containing liquid anaesthetic agent, which is connected to the vaporising chamber by means of a second passage, (f) a laminar control valve which is located in the said second passage, and (g) means for transmitting the pressure in the passageway to liquid in the constant level tank to drive the liquid along the second passage for injection into the vaporising chamber.
(a) a vaporising chamber, (b) an inlet for carrier gas, which is connected to the vaporising chamber by means of a passageway, (c) an outlet for carrier gas and anaesthetic agent for delivery to a patient, which is connected to the vaporising chamber by means of a first passage, (d) a laminar restrictor located in the passageway which connects the inlet to the vaporising chamber, (e) a constant level tank for containing liquid anaesthetic agent, which is connected to the vaporising chamber by means of a second passage, (f) a laminar control valve which is located in the said second passage, and (g) means for transmitting the pressure in the passageway to liquid in the constant level tank to drive the liquid along the second passage for injection into the vaporising chamber.
2. An anaesthetic vaporiser as claimed in claim 1, in which the constant level tank is arranged such that the level of the liquid anaesthetic agent within it is kept constant and at the same level as the point of injection of the liquid anaesthetic agent into the vaporising chamber.
3. An anaesthetic vaporiser as claimed in claim 2, which includes a liquid reservoir connected to the constant level tank for maintaining the level of liquid anaesthetic agent in the tank.
4. An anaesthetic vaporiser as claimed in any one of claims 1 to 3, in which the constant level tank includes two chambers divided by a flexible diaphragm, a first one of the chambers being in communication with the passageway, and the second chamber serving as a container for the liquid anaesthetic agent.
5. An anaesthetic vaporiser as claimed in any one of claims 1 to 3, which includes a third passage which connects the inlet directly to the outlet, and which has located within it a fixed laminar restrictor.
6. An anaesthetic vaporiser as claimed in any one of claims 1 to 3, which includes a balanced venting system which interrupts the passageway connecting the inlet and the vaporising chamber.
7. An anaesthetic vaporiser as claimed in any one of claims 1 to 3, in which the pressure transmitting means comprises a branch passage which connects the passageway to the constant level tank.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB909006777A GB9006777D0 (en) | 1990-03-27 | 1990-03-27 | Improvements in anaesthetic vaporisers |
| GB9006777.8 | 1990-03-27 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2039075A1 CA2039075A1 (en) | 1991-09-28 |
| CA2039075C true CA2039075C (en) | 1996-02-13 |
Family
ID=10673302
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2039075 Expired - Fee Related CA2039075C (en) | 1990-03-27 | 1991-03-26 | Anaesthetic vaporisers |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2039075C (en) |
| GB (1) | GB9006777D0 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105963843A (en) * | 2016-04-15 | 2016-09-28 | 杨建勇 | Intelligent anesthetic vaporizer |
-
1990
- 1990-03-27 GB GB909006777A patent/GB9006777D0/en active Pending
-
1991
- 1991-03-26 CA CA 2039075 patent/CA2039075C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2039075A1 (en) | 1991-09-28 |
| GB9006777D0 (en) | 1990-05-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |