Archive for the ‘Vaporisers’ Category

The Afya ether vaporiser.

There now follows the description of an anaesthetic system made by the German firm of DRAGER, along the same lines as the Penlon E.M.O vaporiser.
I was unable to get any comprehensive maintenance instructions out of the firm despite a polite letter in German, written by my brother who lives in Berlin,  the reply to which was also in German which took me a great deal of time to translate.
In essence, they said that it was too complicated for anyone to service but themselves.
This sort of comment is not very helpful and is an insult to intelligent technicians who, with the proper information and tools, can do most things.
As a result, I have done the best I can for you by copying the description and instructions for use manual.
Where it does not alter the meaning I have left words and lines out to shorten things a bit.
First here is the address of Drager:
Dragerwerk A. G. Lubeck,
Postfach 1339.
Moislinger allee 53/55,
D 2400, Lubeck 1.
West Germany.

Section 1.
General, Intended use.

Modern operating techniques place stringent demands on anaesthesia which are met by the types of compressed gas-operated anaesthetic apparatus in general use in hospitals today.
There are however many areas and situations where it is either impossible or difficult and unreliable to have a supply of anaesthetic gas (N2O) and oxygen in steel cylinders.
As a result, a call was made for anaesthetic apparatus which makes it possible by using a mixture of Ether and air to perform inhalation anaesthesia in all areas of surgery.
This call led to Dragerwerk A.G. developing the AFYA anaesthesia system, (Afya is the Swahili word for health).
It is designed in accordance with the modular principle and permits optimum use either in a fixed situation like a hospital or mobile use.
The heart of the module is the ether vaporiser CATO 12, which, like the associated breathing accessories, operates on the semi-open principle using the draw over method.
In view of the fact that the system has, to all intents and purposes, no dead space, the ether concentrations (adjustable in Vol.%) can be matched in all phases of anaesthesia to the clinical indications and requirements.
If oxygen is available, the appropriate fittings can be used to enrich the mixture of ether and air with oxygen.
Whatever the combination, the system makes it possible at any point during anaesthesia to switch from spontaneous breathing to assisted or controlled manual ventilation without any settings having to be altered.
Naturally, such ventilation can also be performed without anaesthesia.
For mobile use, the vaporiser and necessary accessories can be put in a metal case for safe transportation.

Fig 1 shows the modules together with the transportation case.


The shown parts are listed below:
1. Light alloy transportation case.
2. CATO 12 ether vaporiser.
3. Connecting valve.
4. Corrugated tube 1m long, 22 mm diameter.
5. Corrugated tube 1m long, 13 mm diameter.
6. Connection port for respiratory bag.
7. Respiratory bag, large.
8. Respiratory bag, small.
9. Anaesthesia respiration valve for adults and children.
10. Anaesthesia respiration valve PAEDI for new-born babies and infants.
11. Connection piece for PAEDI valve.
12. Face masks for adults and children, 3 sizes.
13. Rendell-Baker masks for infants and new born babies, 4 sizes.
14. Guedal mouth tubes, 8 sizes, 00 – 6.
15. Catheter connection, 21 sizes, 1. 5 – 13 mm diameter.
16. Drainage piece.
17. Intubation kit.
18. AMBU mini foot operated suction pump.
19. Tin with spare parts.

Section 2.
Ether vaporiser CATO 12.

Sub section 1.

Fig 2 shows a schematic section through the vaporiser. Figs 3 and 4 clearly illustrate the individual controls.



The vaporiser is provided with a water tank as a heat accumulator in order to offset the cold generated during vaporisation.
The ether concentration (infinitely variable between 2 and 20 vol. %) is set using the rotary knob 15 taking account of the temperature reading on the thermometer 9.

Sub section 2.
Preparation of the vaporiser for anaesthesia.

1. Unscrew lock nut 16 marked WATER and pour NOT MORE THAN 1. 5 litres using a
funnel. The water should be at approximately room temperature.
Close the filler port again.
In daily use it is not necessary to change the water, it can remain in the vaporiser for any
length of time.
The water need only be emptied prior to transportation.
This is accomplished using the drainage piece as shown in figure 5.

2. Unscrew ether filler screw 1 and pour in the ether through the funnel.

If ether is to be topped up during anaesthesia the rotary metering knob 15 and the on/off knob should be turned to 0 !

Approximate quantities required for filling:

Upon initial commissioning (wicks in vaporiser dry)  370ml (up to max)  240ml (up to min)

With continuous use (wicks soaked through) (between min and max. ) 270ml.

Screw filler back in place again.
The ether level can be continuously monitored during anaesthesia by way of the ether sight glass 2. The level must never exceed the max mark and should not drop below the min mark.

3. Move the on/off knob setting to 0.

Sub section 3.
Setting of Ether concentration.

1. Set on/off knob 4 to 1. the rotary metering knob 15 cannot be moved so long as this knob is in the ‘O’ position.

2. Read off temperature on built in thermometer 9.

3. Set desired ether concentration using rotary metering knob 15.                                             When making this setting, the chosen concentration (sloping curves on tapered scale 10) must be made to intersect with the temperature reading on the vertical scale. In the example given in Fig 6,the settings are as follows:

Temperature 20c, concentration 4 vol. %.

Fig 6.


Key to Figs 2 – 6.
1. Filler funnel with screw plug.
2. Ether sight glass.
3. Ether drain valve.
4. On/Off knob.
5. Water container.
6. Ether container.
7. Vaporiser chamber.
8. Wick fabric.
9. Thermometer.
10. Concentration adjustment scale.
11. Metering cone.
12. Bypass throttle.
13. Pressure compensation chamber.
14. Inlet connection to atmospheric air.
15. Rotary metering knob.
16. Lock nut ( water filler port ).
17. Threaded connection for breathing systems.

Sub section 4.
After use.

1. Turn rotary metering knob 15 in an anti-clockwise direction as far as the stop.

2. Set On/Off knob 4 to 0. This knob can only be moved when the rotary metering knob has been turned in an anti-clockwise direction as far as the stop. In the ‘O’ setting the pressure inside the vaporising chamber is relieved through as small hole.

3. At the end of each working day the residual liquid ether is removed via the drain valve.

3. Fig 4.


Residual ether should not be re-used. The ether soaked up by the vaporiser wicks can be removed by ventilating the vaporiser with the respiratory bag in the maximum setting (20 vol.%).
This should be done prior to lengthy stoppages.

4. The water is drained using the drainage piece.



After removing the lock nut 16, the drainage piece is inserted into the filler port and gently squeezed using two fingers. Briefly blowing once into the upward facing drainage piece is sufficient to cause the water to drain off through the tubing, (siphon principle).
The water must never be tipped out!

5. Procedure to be adopted should the device have been tilted.
If a CATO 12 filled with anaesthetic agent is tilted, liquid anaesthetic may get into the metering unit regardless of whether the device is switched On or Off (knob 4).
This may lead to either an excessive or insufficient concentration.
If a filled CATO 12 is inadvertently tilted more than 45 degrees, the device must be kept completely opened (i.e. concentration setting 20 vol.%) for at least 30 minutes, without gas flow and standing in a normal position. It must then be flushed as follows:

1. Approximately 20 strokes of the respiratory bag at a setting of 20 vol.%.

2. Approximately 50 strokes of the respiratory bag at a setting of 0 vol.% whereby the On/Off knob is in position 1.

3.Approximately 50 strokes of the respiratory bag at a setting of 0 vol.% whereby the On/Off knob is in position 0. After flushing, the CATO 12 is serviceable again. Up to a tilt of 45 degrees the concentration is not affected. If there is a danger of the device being tilted to a greater degree during transportation, the anaesthetic agent should be removed from the CATO12.

6. The CATO 12 ether vaporiser is a precision instrument. Any checks and repairs which may need to be required must only be performed at Dragerwerk A.G. or by its authorised field services.

Note, my comments.
The manual makes no comment on how often the unit should be checked, I should imagine that it would go on a long time (years) before anything needed doing to it.
As a guide you really need an anaesthetic gas tester to check the output about twice a year.
Deviations from the set figures found by the test should be reported to the anaesthetists, leave them to decide what to do, but get them to sign the service sheet if they want to continue to use it.

Section 3.
The breathing systems and their combination.

Sub section 1.

The CATO 12 ether vaporiser is designed such that accessories to meet the requirements of various usage modes can be connected. Thus every situation has its own tailor made anaesthetic apparatus.
The required combination can be put together and made ready for operation in a few minutes without the need for tools.
Disassembly likewise presents no problems. The various combination possibilities are shown in Figs 7 – 11, with the individual photographs being accompanied in each case by a schematic drawing.

Sub section 2.
Combination ‘A’  Figs 7 and 7a.

This set up is intended for outpatient use and permits the following applications at any desired place of use:
1. Ether – air anaesthesia in the semi-open system in accordance with the draw over method with spontaneous breathing.

2. With switching potential at any time from spontaneous breathing to assisted or controlled manual ventilation.

3. Assisted or controlled manual ventilation ( without ether ) for resuscitation purposes.
The dimensions and performance data of the anaesthesia respiration valve 4, the corrugated tubes 3 and 5 and the respiratory bag 7 are meant for adults and children.

Sub section 3
Combination B Figs 8 and 8a.

The principle and mode of use of this set up correspond to that of combination ‘A’, however the anaesthesia respiration valve 9 (paedi valve), the corrugated tubes 8 and 10 and the respiratory bag 11 are meant for infants and new-born babies.

Key to Figs 7 – 8a.


fig7 copy







1. CATO 12 ether vaporiser.
2. Connecting valve.
3. Corrugated tube, 1m long 22 mm dia.
4. Anaesthesia respiration valve.
5. Corrugated tube, 1m long 22 mm dia.
6. Connection port for respiratory bag.
7. Respiratory bag, large.
8. Corrugated tube, 1m long 13 mm dia.
9. PAEDI ventilation valve with 9a adapter.
10. Corrugated tube 1m long 13 mm dia.
11. Respiratory bag, small.

Sub Section 4
Combination C and D (figs 9 and 9a, 10 and 10a)

For stationary use in hospitals, it is appropriate to mount the CATO 12 ether vaporiser on the trolley made for the purpose and secure it in position using the central screw provided.
The breathing accessories and thus the fields of application are the same as those for combinations A and B.
If oxygen cylinders are available the quality of the anaesthesia can be significantly improved by enriching the ambient air sucked in by the patient (or the respiratory bag) with oxygen.
This is achieved most economically by way of the ancillary oxygen fixtures illustrated in Figs 9 and 10.
Pressure reducer 15 with flow control valve, flowmeter, safety valve, supply pressure gauge and second ( pressure ) outlet for bronchial aspiration.
Oxygen connection piece 12.
Oxygen reservoir tubing 13.
The O2 metering ( variable between 0 and 15 l.p.m. ) depends upon the patient’s minute volume and the O2 concentration considered suitable by the anaesthetist.

Key to figs 9 – 10a.

Fig 9


                                                                                                             Fig 9a


Fig 10


Fig 10a


1. CATO 12 ether vaporiser.
2. Connecting valve.
3. Corrugated tube, 1m long 22 mm dia.
4. Respiration valve.
5. Corrugated tube, 1m long 22 mm dia.
6. Connection port for respiratory valve.
7. Respiratory bag, large.
8. Corrugated tube, 1m long 13 mm dia.
9. PAEDI respiration valve with 9a adapter.
10. Corrugated tube, 1m long 13 mm dia.
11. Respiratory bag, small.
12. O2 connection piece.
13. O2 reservoir tube.
14. O2 connection tube.
15. O2 pressure reducer with flowmeter.
16. O2 cylinder.
17. Trolley.

Sub Section 5.
Combination E, ( Figs 11 and 11a ).                                                                                                                              Fig 11


Fig 11a


In the case of major and thus lengthy operations, monitoring of respiration/ventilation is extremely important.
For this purpose a number of optional accessories and measuring instruments can be supplied with and attached to the AFYA system.
They are all illustrated in Figs 11 and 11a and the individual breakdown is as follows:

Valve chamber ( item 18 in Fig 11a ).
This is screwed into the vaporiser in place of the connecting valve ( item 2 in Fig 7 ).
It contains the inspiratory valve 19, the expiratory valve 20 and under the expiratory valve, the expiratory valve control 18a, i.e. in another form the complete valve set contained in the respiration valve ( item 4 in Fig 7 ) or in the PAEDI valve.
The use of this valve chamber 18 makes it possible to prevent air exhaled by the patient from escaping in an uncontrolled manner into the open air, in that it is routed through the Y piece 22 and the second corrugated tube 3, into the measuring instruments 24 and 25 and only then via the expiratory control valve 18a into the open air.
It is thus possible to make use of measuring instruments and devices described in the following.

Drager Minute Volumeter ( item 25 in Fig 11 ).
This device is designed to measure and continually monitor the tidal volume.
It is screwed into position between the valve chamber 18 and the expiratory valve 20. With both spontaneous breathing and ventilation it measures each expiratory stroke, i.e. the tidal volume.
Monitoring the volume with the stop button for a period of 1 minute is a simple way of obtaining the minute volume.
My Note: I’m not sure what they mean by – monitoring with the stop button- but in any case  I think it means allowing the meter to register the breaths for 1 minute and taking a reading in litres at the end of that time.

Respiratory pressure gauge ( item 24 in fig 11 ).
This is likewise screwed into position between the valve chamber 18 and the expiratory valve 20 ( below the Volumeter ).
With every ventilatory stroke it indicated the inspiratory pressure in the breathing system.
The magnitude of the inspiratory pressure can be limited by using the pressure relief valve 21. The pressure gauge also makes it possible to detect whether the expiratory phase (which always takes place spontaneously) is continued as far as zero pressure.

Relief valve ( item 21 in Fig 11 ).
This is permanently attached to the valve chamber 18 and limits the level of respiratory pressure as desired. Settings between 10 and 40 mbar are possible.

Respiratory bellows ( item 23 in Fig 11 ).
These can be connected in place of the respiratory bag 7 or 11.
There permanent position on the trolley coupled with the unambiguous upward and downward movement makes easy manual ventilation in many cases. Ventilation is effected only with the fresh gas mixture sucked in via the O2 connection piece 12.
There is no re-breathing of the exhaled gas; the gas exhaled escapes via the expiratory control valve 18a into the open air.

Key to Figs 11 and 11a.
1. CATO 12 ether vaporiser.
3. Corrugated tubes 1m long 22 dia.
5. Corrugated tube 1m long 22 dia.
6. Connection port for respiratory bag.
7. Respiratory bag large.
11. Respiratory bag small.
12. O2 connection piece.
13. O2 reservoir tube.
14. O2 connection tube.
15. O2 pressure reducer with flowmeter.
16. O2 cylinder.
17. Trolley.
18. Valve chamber with
18a. Expiratory control valve
19. Inspiratory valve.
20. Expiratory valve.
21. Relief valve.
22. Y piece.
23. Respiratory bellows.
24. Respiratory pressure gauge.
25. Minute volumeter.
26. Anaesthesia timer/sphygmomanometer.
27. Sucker.
28. Connecting are for item 26.

Section 4.
Further accessories

Sub – section 1.
Anaesthesia timer ( item 26 Fig 11 )

During anaesthesia the timer makes all time dependent measurements easy.
1. Normal time measurement.
2. Stopwatch function: 1 revolution = 30 secs.
3. Pulse rate measurement.
4. Respiratory rate measurement.
This timer has an 8-day clock.

Sub – section 2.
Sphygmomanometer ( item 26 in Fig 11 ).

This is an aneroid type to which any cuff may be connected.

Sub – Section 3.                                                                                                                                         Sucker. ( item 27 Fig 11 ).

The sucker is a valuable supplement to the anaesthesia apparatus.
It is, however, reliant on the oxygen cylinders since it operates on the injector principle.
The generated maximum vacuum is – 6m WG (-0.6 bar), with an oxygen consumption of 6 l.p.m.

Sub – Section 4.
Ambu Foot operated sucker ( item 18 Fig 1 ).

The Ambu foot operated sucker is valuable whenever compressed oxygen or other vacuum is not available.
It is thus part of the AFYA transportation case. ( this is made by the Danish firm of AMBU who make a lot of resuscitation equipment ).

Section 5.
Notes on caring for the system.

Sub – Section 1.
Ether vaporiser CATO 12.

The CATO 12 is described in detail in section 2. It requires no maintenance other that external cleaning with a damp cloth and if necessary a disinfectant.

Sub – Section 2.
Connecting valve.

The connecting valve 2 can be easily disassembled without the need for tools.
All the parts can be washed in the usual manner and if necessary disinfected by immersing then in an appropriate liquid disinfectant.
The disc valve is made of high grade, surface ground porcelain and will not be effected by chemicals, though it can be broken if badly handled.
Care should be taken during cleaning to ensure that the valve seat is not damaged as leaks will occur.

Sub – Section 3.
Valve chamber ( item 18 in Fig 11a ).

The valve chamber contains not only the relief valve 21 but also the expiratory control valve 18a. The latter can be disassembled without tools for cleaning, washing and if necessary cold sterilising and then re – assembled.
The valve chamber itself together with the permanently attached relief valve should be properly rinsed and if necessary subjected to cold sterilising.
Before installing the expiratory control valve all parts should be properly dried otherwise they may stick.

Sub – Section 4.
Inspiratory valve and expiratory valve ( item 19, 20 in Fig 11 ).
The inspiratory and expiratory valves are similar to the connecting valve. See sub 2 for details.

Sub – Section 5.
Anaesthesia respiration valve ( item 4 Fig 7 ).
Fig 12 shows the disassemble valve.

Fig 12


These components should always be cleaned after use (and at least at the end of the working day) in warm soapy water and then disinfected in a liquid disinfectant.
If there is a risk of cross infection they can be boiled.
When cleaning, care should be taken to ensure that the small spring loaded inspiratory valve in the centre of the main diaphragm is not damaged.
Only assemble the respiration valve when all parts are dry.
When performing assembly work take particular care to ensure that the parts are installed in the sequence and position shown.

Sub section 6.                                                                                                                                           Paedi respiration valve (Item 9 in fig8)

The Paedi respiration valve is a practice proven product manufactured by Ambu international.

Sub section 7.                                                                                                                                           Tubes, masks and respiratory bags.

These are made from high grade anti static rubber. At the end of the day they should be cleaned with warm soapy water and then disinfected. They should be stored in a dark well ventilated and cool spot.

Sub – Section 8
Minute Volumeter 3000 ( item 25 Fig 11 ).
This requires a certain amount of care if it is to always function reliably.
It must be cleaned at the end of each working day.

To do so, allow hot water from the tap to run through from top to bottom, it can then be briefly centrifuged and dried on a Drager Volumeter drying unit.
My Comments: this method of drying sounds rather complicated to me, they do say that you can use a hair dryer to do it, if you do take care not to get it to hot, hold the unit in your hand and allow the hot air to blow through, if you find your hand getting to hot the hair dryer is to close.
If necessary it can be sterilised at 120C  in any super heated steam steriliser using standard procedures. Such sterilisation is performed subsequent to the cleaning procedure described above. In such cases drying can be despised with.

The bearings should be re-lubricated after 30-steam sterilisations, or every three months.
My comments: They say to use the lubrication set provided, when that has run out try to get some watch oil from a watch repair shop.
They also say that any repairs can only be done by Drager, not having seen the inside (or outside) of one I can’t say if this is true or not. However, at a guess, I would treat it like the Wrights respirometers written about in another section, or take it to a local watch repair man.
Sub – Section 9.
Respiratory pressure gauge ( item 24 Fig 11 ).

Clean with a damp cloth from time to time, if there is a danger of infection it can be steam sterilised like the Volumeter.
You must allow it to cool to room temperature before use.
Prior to use check the zero setting and adjust if necessary using the knurled adjusting ring.

Sub – Section 10.
Anaesthesia timer ( item 26 Fig 11 ).
This should require very little maintenance, if you are not happy about doing watch type repairs take it to a local watch repair shop.

Sub – Section 11.
Sphygmomanometer. ( item 26 Fig 11 ).

Repair as the aneroid sphygmomanometer described else where. Do not steam sterilise.

Sub – Section 12.
Pressure reducer. ( item 15 Fig 9 – 11 ).

The pressure reducer with blow off valve, flow control valve, flowmeter and pressure gauge (for displaying cylinder contents) requires no maintenance other than an occasional wipe with a damp cloth. Before changing cylinders the sealing ring is to be checked and replaced if damaged.

After some years they may need attention for leaks, Drager say to send them back to them, I would try to buy the parts and do it yourself.
Check the seal from time to time.

Sub – Section 13.
Sucker ( item 27 Fig 11 ).
When using the sucker care is to be taken to ensure that the secretions collector does not become over full.
The overflow of secretions to the injector is prevented by the float valve ( ping pong ball ) in the sealing cap of the collector.
At the end of the working day or in the event of acute danger of infection after each patient, those parts coming into contact with the secretions should be cleaned and disinfected.
The collector is to be properly rinsed and disinfected cold, i.e. in a liquid disinfectant.
If necessary it can be sterilised in super heated steam (observe temperature indicated on collector).
The same also applies to the secretions sight glass (glass tube at the patient end of secretions suction hose), the secretion aspiration hose itself and the sealing cap.
The ping pong ball can only be cold sterilised.

My Note: if the ping pong ball gets squashed but not punctured, they can sometimes be made round again by holding them in warm to hot water.

Sub section 14. Ambu foot pump.
I have written of this in another article.

Here is a list of spare parts and their numbers:
Cato 12 ether vaporiser
Sealing ring M 18789.

Connecting valve
Set of sealing rings (5). M 22155.
Set of valve discs (3) M 23249.
Set of transparent caps (5) M 22171.

Anaesthesia respiration valve.
Sealing ring. M 11345.
Diaphragm. M 11023.
Valve diaphragm. M 11140.

Valve chamber.
Diaphragm. M 18679.
Sealing ring. M 9257.

Inspiratory and expiratory valve.
Set of sealing rings (5)
Set of Valve discs (3).
Set of transparent caps (5).
numbers as for Connecting valve see above.

Respiratory pressure gauge and Volumeter.
Sealing ring. M 9257.
Sucker Sealing cap. M 22884.
Set of ping pong balls (3). M 22147.(or buy them in a local sports shop).
Set of caps (5) (under ping pong ball).M 20003.

Secretions jar. M 20091.
Set of secretion sight glasses (5). M 22150.

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The chances are you will never see one of these, they came set up for Ether, Trilene and Halothane.

The Boyle bottle ether vaporiser has two controls. The lever to the left of the picture, on the upstream side of the vaporiser, permits a proportion of the gas from the flowmeters to be ducted through the vaporiser or to bypass it. The control is uncalibrated but has extreme markings of ‘OFF’ and ‘ON’ and permits continuous proportional adjustment. The rod at the top of the vaporiser, known as the ‘plunger’, controls the extent to which the incoming gas is delivered to the liquid ether. Within the vaporiser bottle, it terminates in a cap that advances over the up-turned u-shaped gas inlet tube. In use, the lever is progressively rotated from OFF until it is fully ON. The plunger, initially fully raised, is progressively lowered. Gas is directed to pass more closely over the liquid ether surface and is ultimately bubbled through the liquid ether. This is the maximum setting possible. The rate of vaporisation causes rapid cooling so that the vapour concentration begins to diminish. The cooling can be delayed by filling the accessory water bath with water at room temperature. Without the water bath, the bottle will chill until frost forms on the glass to the level of the liquid ether. Depth of anaesthesia is judged clinically. The ‘U’ shaped inlet tube within the vaporiser and the cap of the plunger are made from un-plated copper. This is considered to protect the ether from degradation.



Below is an exploded diagram of the various parts.


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If you have a phone with a camera, take photos as you go to remind yourself where parts go.

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I am not sure who wrote this little piece, but thanks.

Photographs by me.

An anaesthetic vaporiser is a device generally attached to an anaesthetic machine which delivers a given concentration of a volatile anaesthetic agent.

Anaesthetic vaporiser
The design of these devices takes account of varying ambient temperature, fresh gas flow and agent vapour pressure

Historical vaporisers
Historically, ether (the first volatile agent) was first used by John Snow’s inhaler (1847) but was superseded by the use of chloroform (1848). Ether then slowly made a revival (1862–1872) with regular use via Kurt Schimmelbusch’s “mask”, a narcosis mask for dripping liquid ether. Now obsolete, it was a mask constructed of wire, and covered with cloth.
Pressure and demand from dental surgeons for a more reliable method of administrating ether helped modernise its delivery. In 1877, Clover invented an ether inhaler with a water jacket, and by the late 1899 alternatives to ether came to the fore, mainly due to the introduction of spinal anaesthesia. Subsequently, this resulted in the decline of ether (1930–1956) use due to the introduction of cyclopropane, trichloroethylene, and halothane.                                                                                                 By the 1980s, the anaesthetic vaporiser had evolved considerably; subsequent modifications lead to a raft of additional safety features such as temperature compensation, a bimetallic strip, temperature-adjusted splitting ratio and anti-spill measures.

Modern vaporisers
There are generally two types of vaporisers: plenum and draw over. Both have distinct advantages and disadvantages. A third type of vaporiser is exclusively used for the agent desflurane.

Plenum vaporisers
The plenum vaporiser is driven by positive pressure from the anaesthetic machine and is usually mounted on the machine. The performance of the vaporiser does not change regardless of whether the patient is breathing spontaneously or is mechanically ventilated. The internal resistance of the vaporiser is usually high, but because the supply pressure is constant the vaporiser can be accurately calibrated to deliver a precise concentration of volatile anaesthetic vapour over a wide range of fresh gas flows.                                                                                                                                                                                                     The plenum vaporiser is an elegant device which works reliably, without external power, for many hundreds of hours of continuous use, and requires very little maintenance.
The plenum vaporiser works by accurately splitting the incoming gas into two streams. One of these streams passes straight through the vaporiser in the bypass channel. The other is diverted into the vaporising chamber. Gas in the vaporising chamber becomes fully saturated with volatile anaesthetic vapour. This gas is then mixed with the gas in the bypass channel before leaving the vaporiser.

The performance of the plenum vaporiser depends extensively on the saturated vapour pressure of the volatile agent. This is unique to each agent, so it follows that each agent must only be used in its own specific vaporiser. Several safety systems, such as the Fraser-Sweatman system, have been devised so that filling a plenum vaporiser with the wrong agent is extremely difficult. A mixture of two agents in a vaporiser could result in unpredictable performance from the vaporiser.
Saturated vapour pressure for any one agent varies with temperature, and plenum vaporisers are designed to operate within a specific temperature range. They have several features designed to compensate for temperature changes (especially cooling by evaporation). They often have a metal jacket weighing about 5kg, which equilibrates with the temperature in the room and provides a source of heat. In addition, the entrance to the vaporising chamber is controlled by a bimetallic strip, which admits more gas to the chamber as it cools, to compensate for the loss of efficiency of evaporation.
The first temperature-compensated plenum vaporiser was the Cyprane ‘FluoTEC’ Halothane vaporiser, released onto the market shortly after Halothane was introduced into clinical practice in 1956.

Draw over vaporisers
The draw over vaporiser is driven by negative pressure developed by the patient, and must therefore have a low resistance to gas flow. Its performance depends on the minute volume of the patient: its output drops with increasing minute ventilation.
The design of the draw over vaporiser is much more simple: in general it is a simple glass reservoir mounted in the breathing attachment. Draw over vaporisers may be used with any liquid volatile agent (including older agents such as diethyl ether or chloroform, although it would be dangerous to use desflurane). Because the performance of the vaporiser is so variable, accurate calibration is impossible. However, many designs have a lever which adjusts the amount of fresh gas which enters the vaporising chamber.
The draw over vaporiser may be mounted either way round, and may be used in circuits where re-breathing takes place, or inside the circle breathing attachment.
Draw over vaporisers typically have no temperature compensating features. With prolonged use, the liquid agent may cool to the point where condensation and even frost may form on the outside of the reservoir. This cooling impairs the efficiency of the vaporiser. One way of minimising this effect is to place the vaporiser in a bowl of water.
The relative inefficiency of the draw over vaporiser contributes to its safety. A more efficient design would produce too much anaesthetic vapour.                                                                                                                                                                               The output concentration from a draw over vaporiser may greatly exceed that produced by a plenum vaporiser, especially at low flows. For the safest use, the concentration of anaesthetic vapour in the breathing attachment should be continuously monitored.
Despite its drawbacks, the draw over vaporiser is cheap to manufacture and easy to use. In addition, its portable design means that it can be used in the field or in veterinary anaesthesia.

Dual-circuit gas-vapour blender
The third category of vaporiser (a dual-circuit gas-vapour blender) was created specifically for the agent desflurane. Desflurane boils at 23.5C, which is very close to room temperature. This means that at normal operating temperatures, the saturated vapour pressure of desflurane changes greatly with only small fluctuations in temperature. This means that the features of a normal plenum vaporiser are not sufficient to ensure an accurate concentration of desflurane. Additionally, on a very warm day, all the desflurane would boil, and very high (potentially lethal) concentrations of desflurane might reach the patient.
A desflurane vaporiser (e.g. the TEC 6 produced by Datex-Ohmeda) is heated to 39C and pressurised to 200kPa (and therefore requires electrical power). It is mounted on the anaesthetic machine in the same way as a plenum vaporiser, but its function is quite different. It evaporates a chamber containing desflurane using heat, and injects small amounts of pure desflurane vapour into the fresh gas flow. A transducer senses the fresh gas flow.
A warm-up period is required after switching on. The desflurane vaporiser will fail if mains power is lost. Alarms sound if the vaporiser is nearly empty. An electronic display indicates the level of desflurane in the vaporiser.
The expense and complexity of the desflurane vaporiser have contributed to the relative lack of popularity of desflurane, although in recent years it is gaining in popularity.

A selection of early vaporisers.

An early ether vaporiser made by Coxiter.


A slightly later Boyle’s Trilene vaporiser.

More or less gas was directed down the wide bore metal tube you can see in the glass bottle. The vertical chrome rod with the flat top could be moved up and down by the anaesthetist, on the other end is the wide bore tube where the gas comes out of the bottom of it, if you push the tube right down under the Trilene fluid level you got a higher anaesthetic concentration, the more you lifted the end of the wide bore tube to the surface of the liquid or out of it the lower the concentration given.


Next we have the Emotril.


The one below is the Medrex halothane vaporiser made by Airmed.


The Cardiff inhaler for Penthrane, this was made by Cyprane.


The Cyprane portable ether draw over vaporiser


Cyprane MkIII halothane vaporiser


Penlon’s EMO ether vaporiser.


Penlon’s OMV vaporiser’s, OMV 50 tri-services (L), OMV 30 (R) both draw over vaporisers.



Goldman’s vaporiser.

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