What is a vapour ?
Vapour refers to a gas phase at a
temperature where the same substance
can also exist in liquid or solid
VAPORIZER= Anesthetic agent delivery system OR Vapor
A ‘vaporizer’ is a device that changes a liquid anesthetic agent
into its vapor and adds a controlled amount of that vapor to
the fresh gas flow or the breathing system.
All inhalational anesthetic agents are highly potent and toxic
Can not be given directly
It has to be given in small concentrations along with oxygen
and other carrying gases
Vapor pressure: The molecules from the liquid which
exists in gaseous phase are known collectively as ‘vapor’. This
vapor exerts a pressure on its surroundings which is known as
The pressure exerted by the vapor when in equilibrium with
the liquid phase at constant temperature is called “saturated
On applying heat, more molecules enter vapor phase-> raises
Passing a carrier gas over the liquid causes shift to vapor phase.
Vapor pressure depends only on the liquid and
TEMPERATURE, not affected by ambient pressure.
Boiling point: it is that temperature at which the saturated vapor
pressure is equal to the atmospheric pressure and at which all the
liquid agent changes to the vapor phase.
The lower the atm. pressure, lower the boiling point, for eg, at
The most volatile agents are those with the highest SVPs.
Concentration of Gases
Partial pressure(Dalton’s Law) According to this law, the total
pressure of mixture of gases must equal to the sum of partial
pressure of all the component gases.
The partial pressure exerted by the vapor of a liquid agent
depends only on the temperature of that agent. The highest partial
pressure that can be exerted by a gas at a given temperature is its
Volumes percent – it is the number of units of volume of gas in
relationship to a total of 100 units of volume for the total gas
The volume percent expresses the relative ratio of gas
molecules(%) in a mixture where as partial pressure (mm Hg)
expresses an absolute value.
Anesthetic uptake and potency are related directly to partial
pressure and only indirectly to volumes percent.
Latent heat of vaporization : The amount of energy that is
consumed for a given liquid as it is converted to a vapor is called
the ‘latent heat of vaporization’.
More precisely it is the number of calories required to change 1gm
or 1ml of liquid into vapor without a temperature change.
Latent heats of vaporization at 200 C for halothane, enflurane and
isoflurane are 35, 42 and 41 cal/g respectively.
Specific heat:Is the number of calories required to increase the temperature of
1g or 1ml of a substance by 10 C.
Water is the standard with specific heat of 1cal/g/ 0C or
The concept of specific heat is important
a) considering the amount of heat that must be supplied to a liquid
anesthetic to maintain a stable temperature when heat is lost
b) choosing the material to construct a vaporizer.
Thermal capacity is defined as product of specific heat and mass,
represents the amount of heat stored in the vaporizer body.
Vaporizer construction from a substance with high thermal
capacity will change temperature more slowly than one with low
Thermal conductivity:Is a measure of the speed with which heat flows through a
substance. The higher the value, the better the substance
Vaporizers are made up of metals that have relatively higher
thermal conductivity to minimize temperature changes when
vaporizer is in use, thus thermostabilization achieved.
Splitting ratio:The ratio of bypass flow to flow to the vaporizing chamber is
referred to as the "splitting ratio" and this ratio depends on
a)ratio of resistances in two pathways
variable/adjustable orifice present at inlet/outlet
concentration dial setting.
b)total flow to the vaporizer.
2.7% at 20
One implication in the above data is that concentration-
calibrated vaporizers are agent specific and therefore only the
particular anesthetic agent for which the vaporizer has been
designed and calibrated may be safely used.
For example, if an enflurane (Ethrane) vaporizer was set to deliver
1% agent but had been inadvertently filled with halothane (Fluothane)
the splitting ratio would be 46: 29, yielding an actual halothane
(Fluothane) vapor not of 1% but rather of 1.6%.
Based on method of regulating
Variable bypass vaporizer or concentration
Measured flow vaporizer
vaporizers / Variable bypass
Vaporizers calibrated by agent concentration
expressed in percentage of vapor output are
vaporizers/Direct reading/Dial controlled /
Automatic plenum/Percentage type/Tec type
Vaporizer output is controlled by single knob / dial
calibrated in Volumes percent.
Located between flowmeters and common gas outlet. Not
calibrated for high gas flows (O2 flush) and offers high
resistance, hence not suited for use in breathing system.
They are called Variable Bypass Vaporizers because clinically
useful concentrations accomplished by SPLITTING the gas flow
that passes through the vaporizer –
a part flows through the vaporizing chamber and the
remainder flows through the bypass to the vaporizer outlet, both
gas flows join downstream of the vaporizing chamber, where the
gas exits at the desired concentration.
A computer calculates the carrier gas flow that needs to
pass through vaporizing chamber to produce desired
concentration of anesthetic agent.
Withdraws a calculated amount of liquid agent and injects
into the breathing system / fresh gas flow.
The composition of the carrier gas affects vaporizer output (
VAPORIZER ABBERANCE ) in many concentration
Most vaporizers are calibrated using Oxygen as carrier gas.
Addition of nitrous oxide to carrier gas results in both
temporary (decrease output) and long lasting effect (increase
or decrease, depending on the construction of vaporizer).
Kettle type / flow metered / flowmeter controlled
Use a measured flow of carrier gas–oxygen, to pick up
No longer available for sale.
Depending on method of vaporization
1. Flow over
2. Bubble through
Depending on temperature compensation
By supplied heat
By flow interaction
a stream of carrier gas passes over the surface of the liquid.
Most commonly used.
Efficiency of vaporization enhanced by increasing the area of
carrier gas-liquid interface by
- using baffles or spiral tracks to lengthen the pathway of gas
- using wicks that have their bases in the liquid. The liquid
moves up the wick by capillary action.
B) bubble through:
the carrier gas is bubbled through the volatile liquid, further
increasing the gas-liquid interface.
vapor concentration controlled by injecting a known amount
of liquid anesthetic agent (from a reservoir in the vaporizer
or from the bottle of agent) into a known volume of gas.
As a liquid is vaporized, energy in the form of heat is lost. As
the temperature of the liquid decreases, so does the vapor
Two methods employed to maintain a constant vapor output
with fluctuations in liquid anesthetic temperature:
A) mechanical thermocompensation
By altering the splitting ratio so that the percentage of carrier
gas that is directed through the vaporizing chamber is
increased or decreased by the thermal element.
As the vaporizer cools the bypass flow is restricted
more carrier gas passes through the vaporizing chamber. The
opposite occurs if the vaporizer becomes too warm.
B) supplied heat
An electric heater used to supply heat to a vaporizer and
maintain it at a constant temperature.
C) computerized thermocompensation
The amount of agent injected into the breathing system or
fresh gas flow may be altered.
Computerized control of the amount of carrier gas that flows
through the vaporizing chamber.
Depending on the location
Outside the breathing system (VOC)
Inside the breathing system. (VIC)
Depending on the specificity
Plenum vaporizers: positive pressure applied
at the inlet of the vaporizer. Eg. Boyle vaporizers,
copper kettle, fluotec Mark 2 and 3.
Inhalers or draw over vaporizers: negative
pressure applied at the outlet. Eg. EMO vaporizer,
Oxford miniature inhaler, Tecota
Simple vaporizers Eg. Goldman, Rowbotham
Factors affecting vaporization of
Flow through the vaporizing chamber
Efficiency of vaporization
Gas flow rate
Carrier gas composition
Area of contact with the liquid.
Effects of altered barometric
Most vaporizers are calibrated at sea level (standard
atmospheric pressure). Anesthetic agents with low boiling
points are more susceptible to variations in barometric
ASTM machine standard requires that the effects of changes
in ambient pressure on vaporizer performance be stated in
High altitude (Hypobaric conditions)
Consider a variable bypass vaporiser for halothane is being used at an altitude of
10,000 feet above sea level.
Ambient pressure = 500 mmHg.
SVP of halothane = 243 mmHg
= 48.6% of atmospheric
pressure at that altitude.
Splitting ratio for a setting of 1% halothane in a variable bypass
vaporiser is 46:1.
Suppose a total fresh gas flow of 4,700 ml is on flow.
100 ml of this will pass through the vaporiser where halothane now
represents 48.6% of the atmosphere in the vaporising chamber.
= agent vapour(xml)
Carrier gas (y ml) + Agent vapour (X ml)
= X ml
100 + X
Solving this, X = 94.55 ml ≅ 95 ml
Thus, 95 ml of vapour + 100 ml of carrier gas
= 195 ml.
195 ml + 4,600 ml bypass flow
= total flow of 4795 ml,
= 1.98 % ≅ 2%.
Set concentration – 1%
Delivered concentration – 2%
Is this a worry?
2% of 500 mmHg ambient pressure (altitude of 10,000 feet) is 10 mmHg
1% of halothane at sea level is 7.6 mmHg.
BRAIN RECOGNISES PARTIAL PRESSURE!
10 mmHg = 1.3 times halothane at sea level.
The increase in the partial pressure is only 1.3 times.
High atmospheric pressure: this causes decrease in vaporizer
output in both partial pressure and volumes percent because
increased atmospheric pressure changes the density of gases
more resistance to flow through vaporizing chamber.
At 2 atm, the concentration in volume percent is halved
But clinically, anesthetic potency output expected for any
given vaporizer setting changes little, even though volumes
percent may be altered considerably.
Let us use the halothane vaporiser at 3 atmospheric pressures with a fresh gas flow
of 4,700 ml.
Let us use the halothane vaporizer at 3 atmospheric pressures with a fresh gas flow
of 4,700 ml.
If it is set at a dial concentration of 1%, since the splitting ratio is 46:1, 100 ml of the
fresh gases will flow through the vaporiser as a carrier gas flow.
Total pressure =
Agent vapour (x ml)
Carrier gas + Agent vapour
Agent vapour (x ml)
Total pressure =
Carrier gas + Agent vapour
A total of 112 ml from the vaporiser will join the bypass flow to make a
100 ml + x ml
total of 4712 ml to give a halothane concentration of 0.25%.
On solving the equation, x = 11.92 ml ≅ 12 ml
But, the partial pressure of halothane delivered would be 0.25% x 2280
mmHg = 5.7 mmHg.
This is 0.75 times the partial pressure achieved at sea level with a setting of 1%.
The partial pressure of halothane delivered would be 0.25% x 2280 mmHg = 5.7
This is 0.75 times the partial pressure achieved at sea level with a setting of
∴At 3 atmospheres, concentration of halothane vapour is 0.25%.
But, actual partial pressure is 0.75% of that at sea level.
Slightly Lower Partial Pressure
Low atmospheric pressure: a concentration calibrated vaporizer
increases output slightly under hypobaric conditions by altering the
splitting ratio. The high resistance pathway through vaporizing
chamber offers less resistance under such conditions.
It will deliver approximately the same partial pressure but increasing
concentrations measured as volume percent.
With measured flow vaporizer the delivered partial pressure
increases and volumes percent increases even more if the
surrounding pressure is lowered.
Effects of intermittent back
Pumping effect – increase the output
Pressurizing effect – decrease the output
Sources of back pressure
1. during assisted/controlled ventilation, the positive pressure
generated during inspiration is transmitted from the breathing
system back to machine and vaporizer.
2. use of O2 flush valve, the output from O2 flush enters the
circuit downstream of vaporizers and its activation produces
When resistance is applied to the outlet of the anesthetic
machine, as during assisted or controlled ventilation, there is an
increase in the anesthetic gas pressure which is transmitted back
to the vaporizer.
This adds to the vaporizer output to increase the final vapor
This change is most pronounced when there is less agent in the
vaporizing chamber, carrier gas flow is low, high and frequent
pressure fluctuations, low dial setting.
Pressurizing effect: the output of some vaporizers decreases
when there is back pressure. This effect is greater with high
flows, large pressure fluctuations and low vaporizer settings.
The changes in vaporizer output caused by the pumping
effect is usually greater in magnitude than those associated
with the pressurizing effect.
Pressurizing effect – with high gas flows
Pumping effect – with low gas flows
Effects of Rebreathing
Rebreathing causes a difference between the vaporizer
setting and the inspired concentration.
Only an agent analyser can provide an accurate value for the
inspired agent concentration.
Sequence of vaporizers
In modern anesthesia machines an interlocking system called the
SELECTATEC system incorporated so that only one vaporizer is in
use at a time.
If selectatec system is not installed the sequence of vaporizer
should be such that least potent agent must be placed upstream and
most potent agent last in the sequence.
How much liquid agent does a
vaporizer use per hour?
Ehrenwerth and Eisenkraft gives the formula
3 X Fresh gas flow(L/min) X Volume % = ml liquid used
This formula is based on the fact that typically 1 ml of liquid
volatile agent yields about 200ml of vapor
Features of ideal vaporizers
It should be simple, safe, satisfactory and more practical.
It should have low resistance to gas flow.
It should be temperature compensated for uniform
It should have flow stability and should permit a relatively
constant concentration at different flow rates of the carrier
It should permit precise, accurate, controllable and
predictable delivered concentration of the vapor to the
The performance of the vaporizer should not be affected by
changes in fresh gas flow, volume of liquid, ambient
temperature and pressure, decrease in temperature due to
vaporization and pressure fluctuation due to mode of
It should be light weight and small liquid requirement.
Construction should be corrosion and solvent resistant.
It should have good quality control.
The case of the vaporizer is usually made of copper which is a
good heat sink and it consists of bypass channel and vaporization
Boyle’s bottle:Mainly for ether and trichloroethylene.
Flow over or bubble through type.
No temperature compensation or calibration.
Multiple agent type.
Agitation of vaporizer and splashing may also increase the
concentration most probably due to a little warming of the liquid
Single vaporizer for use as draw over or within the closed
circuit system was designed by Goldman. It has no
Maximum concentration never exceeds 2% irrespective of
total gas flow.
It is a low efficiency vaporizer except during splashing
when over 5% of concentration of halothane can be
By incorporating a wick made of blotting paper or by
employing two vaporizers in series output may be
It was introduced by Epstein, Macintosh and Oxford in 1952
Variable bypass and flow over (with wick) type of vaporizer,
temperature compensated and may be used for vaporization of
ether, chloroform, halothane and trichloroethylene.
There is a thermocompensator small metal bellows containing a
liquid at the vaporising chamber outlet
Copper kettle vaporizer
Described by Lucien Morris in 1952
In this a measured flow of oxygen is allowed to bubble through the
Separate supply of oxygen form an extra flowmeter
Flow of oxygen through the copper kettle and flow of fresh gas should
If the fresh gas flow is reduced the sudden high anesthetic
concentration may be dangerously delivered to the patient.
It is a plenum vaporizer flow over with wicks. It is temperature
compensated by flow alteration and agent specific
Bimetallic strip for temperature compensation is present within the
The control knob is calibrated from off position to 4% in 0.5%
A pressuring valve has been designed to prevent pumping effect
Its of variable bypass and flow over type. Its both temperature and
flow compensated. Its used for halothane, isoflurane, enflurane and
Bimetallic strips provide temperature compensation.
It has a larger bypass. It is more reliable and accurate
The dial has 0.5% to 5% graduation with a lock.
The tube leading to vaporizer chamber is longer and wicks
have been removed from the area of vaporizer near the inlet.
Tipping leads to increased concentration and reversed flow
leads to increased output
Round in shape with
capacity of 150ml
Capacity is around 70ml
Effect of back
More compared to tec 2
Bimetallic strip Present in chamber
Present in the bypass
Its of variable bypass, flow over with wicks variety. Its is
temperature compensated and agent specific
This has similar features of Floutec3.
Added features are that if it is accidentally inverted, the
liquid agent will not spill into the bypass.
It incorporates an interlocking facility of push rod
mechanism, so that two vaporizer mounted side by side
are not turned on at the same time
The wick assembly is constituent of a hollow cloth tube held open by
a steel wire spiral, which is wound into a helix within the vaporizer.
Bimetallic strip which acts as a thermostat.
It has a keyed filling system.
Greatest accuracy is at gas flow of 5L/min, 150 C and 350C and dial
settings less than 3%.
At higher flow rates and at higher dial settings there is a decrease in
135ml when dry and 100ml
when wicks are wet
300ml when dry and 225ml
when wicks are wet
Present in centre of vaporizer Present at the base
Easier and simpler
It is concentration calibrated, gas vapor blender,
thermocompensation by supplied heat, agent specific and plenum
The concentration dial is at the top and is calibrated from 1% to
18%, in graduation of 1% upto 10% and 2% from 10% to 18%.
The filler port is in front and is designed that only a Desflurane
specific bottle can be inserted into it
The amber warm up LED indicator is connected to the main
The green operational LED is illuminated, indicating that the
vaporizer has reached its operational temperature.
The red no output LED flashes with an auditory alarm of
repetitive tones, if the vaporizer is not able to deliver the
Desflurane is heated at 390 C it produces a vapor at pressure of
A pressure reducing valve reduces these pressures with the help
of electronic transducers such that fresh gas flow and the
desflurane vapor are at same pressure
Output is linear with varying concentration settings and flow
These are used for halothane, enflurane, isoflurane and
There is a release button that must be pushed in before the
vaporizer can be turned on at the rear of the dial.
A locking lever connected to the control dial is provided so that
the vaporizer cannot be turned on until it is locked on the
manifold provided at the rear
Greater accuracy is fresh gas flow of 5l/min and dial setting
At higher flow rates and higher dial settings there is a
decrease in output.
The innovative non spin system in the Tec 7 vaporizer limits
the movement of liquid agent, if the vaporizer is tilted or
It is of variable bypass, flow over (with wicks), temperature
compensated and agent specific.
Output is independent of fresh gas flows in the range of 0.3
When vaporizer is turned on, gas partly enters the
vaporizing chamber and bypass channel.
Gas which is saturated later mixes with bypass gas and then pass on to
Temperature changes will be compensated by the bypass cone.
It is calibrated using air as the carrier gas
In cases of 100% O2 the output conc is 5-10% higher and in 30% and
70% N2O it is 5-10% lower.
Reversed flow has no effect on output
Only for Desflurane.
Concentration range 2% - 18%. Higher than 12% are in inverted
D-Vapor filling system (Saf-T-Fil System) is located on the front of
the vaporizer along with display and alarm indicators (LED).
The delivered desflurane concentration is determined by the
relationship b/w the bypass resistance and flow control
cone, which is determined by control dial setting.
Carrier gas composition will affect the vaporizer output,
calibrated using O2. The output reduced when air/N2O
Performance better at 18-300C.
Cellular phones should not be used within 10m of the
This is designed agents desflurane, isoflurane, sevoflurane,
halothane and enflurane.
Concentration calibrated, flow over and automatic
The agent is in a portable cassette that is inserted into a slot in the
The control dial is on the machine next to where the cassette is
placed. A magnetic sensor identifies the cassette.
The cassette is color coded and magnetically coded
Fresh gas enters the vaporizer and is split between the bypass
flow that is in the machine and the vaporizer chamber
Wicks in the chamber increase the surface area.
The flow at the outlet of the chamber is controlled by the central
processing unit (CPU) in the machine.
Penlon Sigma PPV
To dispense halothane, enflurane,isoflurane, sevoflurane.
The upper part of the vaporizer and concentration dial are colour
coded. To set a concentration, the dial is pushed in and rotated.
The filling device can be funnel fill / quick-fil / keyed filler. The
liquid level indicator has lines for the maximum and minimum
The direction of gas flow is marked on top.
Gas enters the vaporizer and is split into two streams. In
zero-lock position, the bypass remains open, but the
vaporizing chamber is isolated.
If the zero lock port is open, the gas flows through a spiral
tube into vaporizing chamber which contains stainless steel
wick. Gas saturated with vapor exits the chamber through
vapor control orifice whose size is determined by the control
dial, then joins the bypass gas and flows to the outlet.
Temperature compensation provided by liquid-filled expansion
bellows controlling a variable resistance valve in the bypass.
Accurate at 15-350C.
The output is high at low flows, higher temperature, with N2O &
reversed gas flow.
Calibrated every 3-6 months, major overhaul every 5 yrs. The
exterior is cleaned with a dry cloth.
Penlon Sigma Delta
For halothane, enflurane, isoflurane, sevoflurane.
Improved version of Penlon Sigma PPV.
Temperature compensation is by means of a Thermostat
in the bypass.
Calibrated with 100% oxygen. N2O and air in the
carrier gas will decrease the output.
Operating temperature 15-350C, FGF 0.2-15L/min. A
steady back pressure 10-15kPa reduce the vaporizer
Its flow direction sensitive. Output inaccurate if flow is
Hazards of Sigma Delta: may malfunction if exposed to
excessively high temperatures. The control dial should be at 0
and the vaporizer upright while filling and transport.
If transported in open position, the vaporizer must be flushed
with 5L/min flow of gas for atleast 10min before use.
If tipped or inverted during transport, control dial set to
maximum output and run at 5L/min for 10min prior to use.
Calibration done using suitable agent gas analyzer. Major
overhaul every 10 yrs.
Penlon Sigma Alpha
Electrically powered, for DESFLURANE.
Control dial is in the front, below which is the display screen that
shows Warm-up, Standby, Inuse, Battery in use messages.
Warmup takes approx 2min, no vapor output during that period.
The agent consumption mechanism allows the user to quantify the
volume of desflurane used for each case. Liquid desflurane flow is
measured by a liquid flow sensor.
Calibrated with pure O2.
Designed to use at temp 15-300C, flow range 0.5-12L/min
Hazards : excessive electronic noise caused by a device such
as electrosurgery unit may adversely interfere with vaporizer
- electromagnetic interference
Available for halothane, enflurane, isoflurane, sevoflurane.
Agent specific coloured label is on front below the
concentration dial which is pushed inwards and rotated
counterclockwise to set concentration. The dial should not
be set b/w zero and first setting.
Filling device: funnel fill, keyed filler, sevo can have
Gas enters the vaporizer and is split into two streams, one
passing through bypass, other through vaporizing chamber.
When vaporizer is turned ON, zero lock valve opens, & gas
passes through a spiral tube to minimize the effects of
intermittent positive pressure ventilation, then through
chamber that contains a main & a coil wick.
Gas saturated with vapor exits through vapor control valve
whose size determined by dial setting.
Temp compesation is provided by a mechanism with its base
in the vaporizing chamber, connected to variable bypass valve.
Calibrated using air. O2 will increase the output slightly.
Excessive output may occur if vaporizer is moved suddenly
during use. It should be drained prior to transport.
Changes in atmospheric pressure do not usually affect the
output, but altitudes greater than 1500m may require a
Exterior cleaned with clean, damp cloth. Halothane
vaporizers drained at regular intervals to prevent thymol
The vaporizing chamber is a simple reservoir of glass with or without the
means of temperature compensation.
There are two ways that gas flows through a vaporizer: push through and
Eg. Oxford Miniature Vaporizer (OMV) for halothane, enflurane,
It is designed for continuous flow rates b/w 3 and 8L/min or drawover
rates b/w 4 and 10L/min and ambient temperatures b/w 18 and 280 C.
Not recommended for use within closed system – rapid anesthetic
overdose may result, their performance will deteriorate with time
because water condenses on the wick.
There are a number of different filling systems available: Funnel
filling system, Keyed filling system, Quick –Fil system, Easy-Fil
system, and Desflurane filling system.
ASTM machine standard recommends that a vaporizer should be
designed for a single agent fitted with a permanently attached,
agent specific device to prevent accidental filling with the wrong
Funnel filling system
Vaporizer component – funnel and cap
Filling: the filler cap is removed by turning it
counterclockwise and agent is poured into the filling port.
This can be converted to an agent specific keyed filling
system by addition of an adaptor that screws into the
Bottle component – colour coded adaptor with screw thread
and skirt with slots that matches the projections on Bottle
Keyed filling system
Vaporizer component – vaporizer filler receptacle (filler socket
or block, vaporizer filler unit, fill and drain system) permits
only the intended bottle adaptor to be inserted.
There may be a single port for both filling and draining or two
ports, upper one for filling and lower for draining.
An air vent may be located on the vaporizer which must be
opened prior to filling to prevent air lock.
Bottle component – colour coded collar attached securely to
the neck. Colours:
Red – halothane
Yellow – sevoflurane
Purple – isoflurane
Orange – enflurane
Bottle adaptors (adaptor tubes or assemblies, tube adaptors,
filler tubes) are also colour coded. At one end is the connector
with screw thread and skirt which extends beyond. Other end
is the male connector that fits into the vaporizer filler
receptacle. A short length of plastic tubing with two inner
tubes connects the ends, allows the bottle to be held higher or
lower than the vaporizer
The male connector (key, probe, tube block, filler plug,
male adaptor) on the adaptor consists of a rectangular piece
of plastic with a groove on one side and two holes on another
surface. The groove is in different locations depending on the
agent to be used. The larger hole is for the agent to enter or
leave the vaporizer, the smaller hole is for air to leave the
Filling – bottle adaptor screwed onto the bottle. Vaporizer
turned off, the plug removed. The filler block is inserted,
retaining screw tightened, filler valve (vent) opened and the
bottle held higher than the filler receptacle so that liquid
enters the vaporizer.
Draining – the bottle is held below the vaporizer receptacle,
drain (spool) valve is opened.
Problems with keyed filling
Liquid can leak if the device that holds the keyed
component into vaporizer is not tight.
Vapor can leak out if the fill or drain valve is not closed.
Misalignment of the filling channel and the air channel
between the filler and vaporizer will make it difficult to fill
Quick-fil system is used for only Sevoflurane.
The vaporizer filler has a screw-on cap. Filler neck has 3
grooves that can accept only a special filler device, which
comes attached to the bottle.
The bottle has a permanently attached agent specific
filler device that has 3 ridges that fits into the slots in the
filler. A valve prevents liquid from draining when the
bottle is inverted but not inserted into the vaporizer.
Filling : the bottle is pushed into the vaporizer
component as far as it will go and held firmly in place.
This will open the valve and allow liquid agent to flow
into the vaporizer.
Draining : the drain attachment is fitted to the bottom to
which the bottle is inserted.
Easy-fil system : used in all Tec-7 vaporizers. The vaporizer has
a cap with a tool that is used to open and close the drain on the
filler. The filler channel has 2 keys (ridges) that fit into grooves
on the bottle adapter.
The bottle nozzle is inserted into the filler block, aligning the
adaptor grooves with projections in the filler block.
Adv: they are used for filling, draining and storage of anesthetic
agent. They also reduce air pollution and prevent water and
other contaminants entering the vaporizing chamber.
Desflurane filling system : the bottle has a crimped-on
adaptor that has a spring loaded valve that opens when the
bottle is pushed into the filling port on the vaporizer.
To fill the Tec 6 vaporizer, the bottle is fitted to the filler port
and pushed up against the spring, then rotated upward and held
in this position while filling. Once filled, the bottle is rotated
downward and removed from the vaporizer.
If the “O” ring on the bottle is damaged or missing, agent may
leak during filling.
Incorrect filling of vaporizer
They should neither be overfilled nor underfilled.
Tilting the vaporizer or the anesthetic machine may result in liquid
anesthetic reaching the anesthesia gas outlet causing lethal
concentration in the breathing system
To avoid the filling of vaporizer with a incorrect agent KEYED
FILLING devices are used
Vaporizer Mounting System
Permanent mounting and Detachable mounting
Permanent means it requires tools to remove or install a
Advantages are: vaporizers will not be dropped or abused,
leaks will be less
Disadvantages are that machines must have enough mounting
locations to accommodate all the vaporizers
Any location that does not have an attached vaporizer will
need to be protected to prevent gas leaks
Detachable means mounting system that allow the vaporizer to be
moved by the user without any tools.
The Selectatec system is the most widely used
Advantages - anesthesia machine can have fewer mounting
locations allowing a more compact machine, vaporizers can be
easily removed and replaced even during a case (malignant
Disadvantages - leaks, partial or complete obstruction to gas
flow and failure to deliver anesthetic vapor may occur.
Safety features of modern
Keyed filling system
Low filling port
Secured vaporizers (less ability to move them minimizes
Interlock devices or vaporizer exclusion systems – prevent
more than one vaporizer from being turned ON at a time.
Hazards of modern
Incorrect agent – if an agent of high potency or volatility
is used in a vaporizer intended for an agent of low potency or
volatility, a dangerously high concentration may be
delivered. The vaporizer must be completely drained and all
liquid discarded. Gas should be allowed to flow through it
until no agent can be detected in the outflow.
Tipping – liquid from the vaporizing chamber may get into
the bypass or outlet high concentration will be delivered
when the vaporizer is first used. Prevented by keeping the
vaporizer in off/travel position while movement.
Overfilling – liquid agent may enter the fresh gas line, and
lethal concentrations may be delivered, or no output due to
complete vaporizer failure. Agent specific filling devices
Reversed flow – increases output.
Leaks – affect fresh gas composition and flow, pollutes
- common causes of leak: failure to replace or
adequately tighten the filler cap, vent not closed or the
plug not replaced/ tightened in keyed filling system,
vaporizer not mounted properly, inlet / outlet
connection is loose/broken.
- with a leak in the vaporizer, the machine will often
function normally until the vaporizer is turned on. At
that point, FGF is lost through the leak.
Vapor leak into the fresh gas line – can cause a sensitised individual
to react to halogenated agent or trigger malignant hyperthermia.
Contaminants in the vaporizing chamber
Obstruction to fresh gas flow due to problems in mounting system
Concentration dial in wrong position
Disposing of liquid
By the use of an evaporator – the liquid is allowed to
evaporate and the vapor is removed by the vacuum system.
Inhalational anesthetic agent is an integral part of “balanced
anesthesia”. Hence its important to know functioning and the
working principle of “vaporizer”, the device intended to
deliver vapors of inhalational agent.
Dorsch and Dorsch