– A gaseous phase of a substance that is liquid at room
temperature and atmospheric pressure.
– Instrument designed to change a liquid anesthetic
agent into its vapour and to add a controlled amount
of this vapour to fresh gas flow.
• Vapour pressure:
– Pressure exerted by the molecules of vapour on the walls of the
• Saturated vapour pressure:
– Maximum vapour pressure at particular temperature.
– At constant temperature, a dynamic equilibrium is formed between
the liquid and vapor phase so that the number of molecules in the
vapor phase remains constant.
– Represented by density of dots above liquid
Vapor pressure changes with varying
Vapour pressure of common
Gas Vapour press. TORR (20 0C)
That temperature, above which a substance can not be
liquified however much pressure is applied
• Boiling Point:
– The temperature(of a liquid) at which its vapour
pressure is equal to the atmospheric pressure.
– The lower the atmospheric pressure, the lower the
• Halothane - 50.2 C
• Enflurane - 56.5 C
• Isoflurane - 48.5 C
• Desflurane - 22.8 C
• Sevoflurane - 58.6 C
• VAPORIZER OUTPUT: refers to the
concentration of vapor at the outlet of vaporizer.
• VAPORIZERS CONCENTRATION :denotes
the concentration delivered by a vaporizer when
fresh gas containing no vapor flows through it.
– Out of system vaporizer: output = conc.
– In system vaporizer : output >conc. (expired gases
contain some agent )
• Refers to the maximum concentration that can be
delivered by a vaporizer at the highest setting of
the concentration dial.
• Eg: sevoflurane has a higher MAC than
isoflurane. So needs vaporizer with a higher
capability (max 8%) than isoflurane (max 5%).
• Ability of a vaporizer to saturate the carrier gas
passing into the vaporizing chamber at the
temperature of the liquid.
Increased by a)Wicks
b)baffles or spiral tracks
c)longer vaporizing chamber
(inc. surface area for vaporization).
• TWO METHODS USED TO EXPRESS :
– partial pressure
– volumes percent
A. Partial pressure:
– The part of the total pressure due to any one gas in
the mixture is called as the partial pressure of that
– Depends only on temperature of the agent.
B. Volumes percent :
– The number of units of volume of a gas in relation to
a total of 100 units of volume for the total gas
– Partial pressure /total pressure = vol.percent
Partial pressure Volume percent
Absolute value Relative ratio
Patient uptake and depth of
anesthesia are directly related.
At a given partial pressure ,
anesthetic agent will have same
potency under various
Heat of vaporization
• The number of calories necessary to convert 1g of liquid
(or 1ml) into a vapor.
• Liquid temperature decreases as vaporization proceeds.
• So the heat flows from the surroundings into the liquid to
compensate for the lost heat.
• IMPORTANCE :If the lost heat is not compensated ,
there will be decrease in agent delivered.
• Is the quantity of heat required to raise the temperature of
1g of the substance by 1 C.
– IMP : The higher the specific heat ,the more heat that is
required to raise the temperature of a given substance.
– Choice of material of vaporiser should have high
specific heat as this provide a more stable temperature.
– Amount of heat that must be supplied to a liquid
anesthetic to maintain a stable temperature is known.
(heat is lost during vaporization)
• Is a measure of the speed with which heat flows through a
• To construct a vaporizer,a substance with high thermal
conductivity is used.
– Eg. Copper,bronze.
• Importance: heat lost during vaporization can be rapidly
supplied if the substance has high thermal conductivity.
• First vaporizer was developed by Lucein Morris, named as
copper kettle vaporizer.
• Shu-Hsun Ngai Proposed the incorporation of
thermometer in vaporizers.
Copper kettle and vernitrol
If vapor pressure and temperature of anesthetic
liquid is known,concentration of inhaled
anesthetic is calculated.
NOT TEMPERATURE COMPENSATED.
BI METALLIC STRIP
made of brass and
nickel-steel alloy with
different coefficients of
Vaporizers and standards
• ASTM anesthesia work station standard contains
the following provisions regarding vaporizers :
• 1)The effect of variations in ambient temperature
and pressure ,tilting,back pressure,and input flow
rate and gas mixture composition on vaporizer
performance must be stated in the accompanying
WITH OUT A BACK PRESSURE
• 2)The average delivered concentration from
the vaporizer shall not deviate from the set
value by more than ±20% or ±5 % of the
maximum setting ,which ever is greater ,
without back pressure.
WITH BACK PRESSURE
• 3)The average delivered concentration from the
vaporizer shall not deviate from the set value by more
than +30% or -20% or by more than +7.5% or -5% of
the maximum setting ,which ever is greater ,with
pressure fluctuations at the common gas outlet of 2Kpa
with a total gas flow of 2L/min or 5Kpa with a total gas
flow of 8L/min.
– A system that prevents gas from passing through the vaporizing
chamber or reservoir of one vaporizer and then through that of
another must be provided.
– The output of the vaporizer shall be less than 0.05% in the OFF
or zero position ,if the zero position is also the OFF position.
– All vaporizer control knobs must open COUNTER CLOCK
– Either the maximum and minimum filling levels or the actual
usable volume and capacity shall be displayed.
• FIXED DESIRED CONC. (EQUAL TO CONC.
ON DIAL SETTING)
• INDEPENDENT OF TEMPERATURE ,
FLOW RATE AND CARRIER GAS
• NO EFFECT OF BACK PRESSURE
• EASY TO MAINTAIN AND CLEAN
• AGENT SPECIFIC
DORSCH AND DORSCH
• I.)METHOD OF REGULATING OUTPUT:
• a) Variable by pass: ether bottle,TEC
• b) Measured flow: copper-kettle,vernitrol.
• II.)METHOD OF VAPORIZATION :
• a)Flow over:
– 1. with wick – TEC
– 2.with out wick - goldman bottle
• b.)Bubble through :copper kettle
• c)flow over bubble through : ether bottle depending on position of
• d)Injection :TEC 6 (desflurane)
III.TEMPERATURE COMPENSATED :
1)By altered flow –TEC
2)By supplied heat –copper kettle
3)Both –EMO (epstein mc intosh oxford)
b)Non compensated : ether bottle.
• IV) SPECIFICITY :
– Agent specific :TEC
– multi agent : Goldmanbottle.
• V)RESISTANCE :
– plenum(high resistance) : TEC
– Draw over (low resistance) :goldman bottle,EMO.
• VI)LOCATION :
– In circuit : (VIC) – E.M.O, Goldman
– out of circuit (VOC) -TEC.
Variable bypass vaporizer
a.)Has an inlet and outlet.
b.)Fresh gas flows through
bypass chamber and
c.)Concentration of anesthetic
agent delivered depends on
amount of gas flowing
through the vaporizing
• The total flow of gas arriving from the anesthesia machine
flow meters is split between variable bypass and the
vaporizing chamber containing the anesthetic agent.
• The ratio of these two flows, the Splitting ratio depends on
the anesthetic agent, temperature, and chosen vapor
concentration set to be delivered to the patient circuit.
Measued Flow Vaporizer
• A measured flow of oxygen is selected on a separate
flowmeter to pass to the vaporizer, from which vapor
emerges at its SVP. This flow is then diluted by an
additional measured flow of gases from flowmeters
on the anesthesia machine.
FACTORS AFFECTING THE
• A.)Flow rate.
• B.)Barometric Pressure
• D.)Intermittent back pressure.
• E.)Carrier gas composition.
Effect OF Flow rates
• At low flowrate:(<250 ml/min)
– The anesthetic agent delivered is less than the dial setting at low
flow rates because of insufficient turbulence generated to
upwardly displace vapor molecules.
• At extremely high flow rates: (15L/min)
– the output is less than the dial setting, due to incomplete mixing
and failure to saturate the carrier gas.
Effect of Barometric Pressure
•Vaporizers calibrated at standard (Sea level)
•Low boiling point, High SVP agents are more
susceptible to barometric pressure changes.
Low atmospheric pressure
CONC CALIBERATED VAPORIZERS.
- Deliver same partial pressure [IMPORTANT FOR ANAES. DEPTH SO
CLINICAL EFFECT UNCHANGED].
- Small deviations in performance due to altered splitting ratio.
-Deliver higher concentration if measured in vol%
• MEASURED FLOW VAPOURIZERS.
- Partial pressure increase and Vol% increased even more.
High atmospheric pressure.
• CONC. CALIBERATED VAPOURIZERS.
Increased density of gas Increased resistance through
vaporizing chamber Decreased vap. output (In both PP and
Vol%) At 2 ATM.
- Conc in VOL. % Is half
- Effect on PP is less
• MEASURED FLOW VAPOURIZERS.
Decreased conc in both PP and Vol %
Effect of Temperature
• As vaporization continues, the temperature in vaporizing
chamber decreases as heat is lost during the process of
• So vapor pressure of anesthetic agent decreases and
• So to prevent this fresh gas flow rate is increased into the
vaporizing chamber by an expanding rod or a bi metallic
• Wicks are placed in direct
contact with the metal wall of
the vaporizer to help replace
heat used for vaporization.
• Vaporizers are constructed
with metals having relatively
high specific heat and high
thermal conductivity to
minimize heat loss.
Effects of intermittent back pressure
• When assissted or controlled ventilation is used,the
positive pressure generated during inspiration is
transmitted back to the machine and vaporizers.
• Back pressure may either
• Increase vapor output-PUMPING EFFECT
• Decrease vapor output- PRESSURIZING EFFECT
• Concentrations delivered by vaporizers increase
during ventilation than used with free flow to
• Change is more pronouced when
– less agent in vaporizing chamber
– low carrier gas flow
– pressure fluctuations are high and frequent.
– dial setting is low.
Pressure in bypass and
As bypass has smaller
volume than vaporizing
chamber more gas enters
Extra gas entering
When bag is
expands in all
Some of the rapidly
enters the inlet and
cross over into the
bypass channel .
This vapor in bypass
chamber adds to that
of vapor coming from
and increases the
final anesthetic conc.
MODIFICATIONS TO MINIMIZE THE PUMPING
1.) long inlet
The extra gas can
not enter the bypass
channel as inlet tube
2.) Increase in the
due to back
Allows the flow of
gas in one direction
only and prevents
Increased pressure is applied to
the vaporizer outlet.
Compress carrier gas ,so that
there will be more molecules/ml.
The no of anesthetic vapor
molecules will not increase.(as
this depends on vapor pressure of
Net effect is decrease in conc of
EFFECT OF BACK PRESSURE.
Higher conc than indicated
on dial delivered.
- inc. by :
- Large pressure fluctuations
- Low dial setting
- Low flow rate
Lower conc than indicated
on dial delivered.
- Inc by :
- Large pressure fluctuations
- Low dial setting
- High flow rate
Effect of Carrier Gas Composition
• Vaporizer output may be affected with change of
carrier gas composition
• When the carrier gas is quickly switched from
100% oxygen to 100% nitrous oxide, there is a
rapid transient decrease in vaporizer output
followed by a slow increase to a new steady-state
• As Nitrous oxide's being more soluble than oxygen
in halogenated liquid.
• So the quantity of gas leaving the vaporizing
chamber is transiently diminished until the
anesthetic liquid is totally saturated with nitrous
Factors affecting steady state
• A)viscosity and density of carrier gas.
• B) solubility of carrier gas in the anesthetic liquid.
• C) flow splitting characteristics of the specific
• D) concentration control dial setting.
• Electrically heated,pressurized device specially
designed for Desflurane.
• ??deflurane needs special vaporizer
• 1)HIGH VAPOR PRESSURE:
• Has vapor pressure 3 to 4 times that of others.
• So at, same flow rate, the amount of desflurane
delivered is DANGEROUSLY HIGH.
• 2) LACK OF AN EXTERNAL HEAT
– MAC of desflurane is high.
– So ,rate of vaporization in a vaporizer is high and
leads to excessive cooling of the vaporizer. This
causes reduced output.
– In the absence of an external heat source,the
temperature compensation is almost impossible.
Two independent gas
Vapor originates in the
which is electrically
controlled to 39C
The differential pressure
transducer conveys the
pressure difference b/w
the fresh gas circuit and
the vapor circuit to the
system, which regulates
the pressure control
Differential pressure transducer
Signals Pushes diaphragm upwards.
Increased fresh gas flow
Differential pressure transducer in
Increasd vapor flow Neutral position
• Conc. calibrated Flow over
• No temp compensation
• Agent non specific (Halothane,
• In & Out of system
• Variable bypass (Conc
• Flow over wicks
• Out of system
• No temp compensation
• Muliple agent (Ether,
(EPSTEIN MACINTOSH OXFORD VAPORIZER)
• Draw over inhaler
• Variable bypass
• Flow over wicks
• Temp compensation by
supplied heat & flow
• Agent specific
OXFORD MINIATURE VAPOURIZER
• Draw over and plenum
• Concentration calibrated
• Agent non –specific.
• (Halothane, trilene,
Agent-specific for Halothane,
variable bypass, flow over with
wicks, low resistance,
temperature compensated with
bimetallic strip in vapour path,
non-tippable, no interlocks,
• DISADV :
• Not accurate below 4l/min.
• Nitrous oxide affects out put.
• Subject to pressurizing and pumping effect.
• Filling tap is at side – chance of over fill.
Conc-calibrated, flow over with wick,
Bimetallic temp-sensitive element that is
located concentrically within bypass
Volume decreased to 250ml
Vaporising chamber at high pressure
(overcomes the resistance to flow of
relatively dense saturated vapor even at
low flow rates.)
Adv over tec 2 :
• Accurate with lower dial settings. Nitrous oxide has little effect
• Between off and 0.5% ,dial setting, output is less affected by
fresh gas flow.
• Sudden increase or decrease in FGF ,back pressure,O2 flush has
negligible effect on vapour output.
• Filling and draining is at bottom- so over fill is avoided.
• Dis adv: small amounts of leaks in bypass in OFF
• Can be rotated beyond off position, resulting in
delivery of vapour.
• Tipping upto 90 degrees has no affect.But beyond 90
degrees causes increase in out put.
The release button to the left
must be depressed before the
vaporizer can be turned on.
Safety interlock system for
ensuring a ,single vaporiser
use only at any time.
Internal baffle system to
prevent contamination of the
bypass chamber on tilting.
Dis adv: difficulty in operation
One handed dial control and
more obvious OFF position.
Helical intermittent positive
pressure assembly to
minimize effects of positive
Capacity increased from 125
to 300 ml.
Is described as a dual gas
Tec 6 can deliver an
accurate concentration of
desflurane, between 1%
and18% at a flow rates
from 0.2 to 10 litres/min
an improved version of the TEC
5 was introduced in July
2002 by Datex-Ohmeda
with minor modifications
1. "Easy-fil" filler mechanism
2. New ergonomics and
3. Planned factory service
4. Improved sight glass
a). Electronic control system
in anesthesia machine
b). A portable cassette
The flow at the out let is
controlled by the CENTRAL
PROCESSING UNIT in the
• The Aladin Cassette can be handled or
Automatic record keeping and gas
• Electronic control of desired agent
.Provides agent setting data for
Keeping and fresh gas flow data.
• Gas usage data provides a unique tool
for low flow
similar to tec 4,5 vaporizers.
The interlock on Dräger machines
continues to function if any vaporizers
There is no outlet check valve- the
tortuous inlet arrangement protects
from the pumping effect.
No anti-spill mechanism.
Should not be tipped more than 45.
Drager 2000 :
• Is one of two tippable
vaporizers (ADUcassettes are
• The dial must first be rotated
to a "T" setting ("transport" or
"tip") which is beyond zero
•Tortous in let protects against
• Funnel fill system
• Keyed fill system
• Quik- fil system
• Easy-fil system
Vaporizers may be filled
by a conventional funnel-fill
mechanism, in which
the liquid anesthetic is
simply poured into a
funnel in the vaporizer.
Complication is filling
with wrong agent.
In this system, an agent-specific
filler tube is used, one end of
which slots into a fitting on the
vaporizer, and the other end
slots into a collar on the bottle
of anesthetic. The fitting on the
vaporizer and the collar on the
bottle are specific to each
QUIK FIL :
The bottle has a
device that has three
ridges that fit into slots
in the filler.
EASY FIL :
A color coded bottle
adaptor is attatched to
bottle and then fitted into
A drain plug is there for
Hazards of a vaporizer
• a)In correct agent
• c)over filling
• d)reversal of flow
a)In correct agent: minimized by agent specific filling
devices, color coding, agent monitors.
b)TIPPING: lead to delivery of very high
concentrations of vapor. Prevented by
– 1.Mounting vaporizers on manifold.
– 2.draining vaporizer before being moved.
c) OVER FILLING :
– Liquid agent enter the fresh gas line, leading to high
– Prevented by low level filling port, indicator glass.
D )REVERSAL OF FLOW :
output is increased.prevented
by indicator arrows.
E) LEAKS : lead to
wastage of agent, OT
pollution,delivery of wrong