principles of vaporizers

1. PRINCIPLES OF
VAPORISERS
DR.A.ANAND RAM
MODERATOR:DR.SAPNA

2. Definition
• Vapour:
– A gaseous phase of a substance that is liquid at room
temperature and atmospheric pressure.
• Vapouriser:
– Instrument designed to change a liquid anesthetic
agent into its vapour and to add a controlled amount
of this vapour to fresh gas flow.

3. PHYSICS
• Vapour pressure:
– Pressure exerted by the molecules of vapour on the walls of the
container.
• 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

4. Vapor pressure changes with varying
temperature

5. Vapour pressure of common
anaesthetic agents
Gas Vapour press. TORR (20 0C)
Halothane 243
Enflurane 175
Isoflurane 238
Desflurane 669
Sevoflurane 157

6. Critical temperature:
That temperature, above which a substance can not be
liquified however much pressure is applied

7. • 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
boiling point.

8. BOILING POINTS
• Halothane - 50.2 C
• Enflurane - 56.5 C
• Isoflurane - 48.5 C
• Desflurane - 22.8 C
• Sevoflurane - 58.6 C

9. • 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 )

10. VAPORIZERS CAPABILITY
• 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%).

11. VAPORIZERS EFFICIENCY
• 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).

12. GAS CONCENTRATION
• 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
gas.
– Depends only on temperature of the agent.

13. Contd….
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
mixture.
– Partial pressure /total pressure = vol.percent

14. Partial pressure Volume percent
Absolute value Relative ratio
Patient uptake and depth of
anesthesia are directly related.
Indirectly related
At a given partial pressure ,
anesthetic agent will have same
potency under various
barometric pressures.
Not so.

15. 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.

16. Specific Heat
• 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)

17. Thermal conductivity
• Is a measure of the speed with which heat flows through a
substance.
• 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.

18. HISTORY
• First vaporizer was developed by Lucein Morris, named as
copper kettle vaporizer.
• Shu-Hsun Ngai Proposed the incorporation of
thermometer in vaporizers.

19. MORRIS COPPER KETTLE
VAPORIZER

20. COPPER KETTLE
(FOREGGER COMPANY)

21. VERNITROL VAPORIZER
(OHIO MEDICAL PRODUCTS)

22. Copper kettle and vernitrol
If vapor pressure and temperature of anesthetic
liquid is known,concentration of inhaled
anesthetic is calculated.
DISADV:
NOT TEMPERATURE COMPENSATED.

23. TECOTA VAPORIZER
(temperature compensated
trichloroethylene air)
BI METALLIC STRIP
made of brass and
nickel-steel alloy with
different coefficients of
expansions.

24. 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
documents.

25. 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.

26. 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.

27. – 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
WISE.
– Either the maximum and minimum filling levels or the actual
usable volume and capacity shall be displayed.

28. IDEAL VAPOURIZER
• 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

29. DORSCH AND DORSCH
CLASSIFICATION
• 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

30. • b.)Bubble through :copper kettle
• c)flow over bubble through : ether bottle depending on position of
plunger.
• d)Injection :TEC 6 (desflurane)
III.TEMPERATURE COMPENSATED :
a)Thermo compensated:
1)By altered flow –TEC
2)By supplied heat –copper kettle
3)Both –EMO (epstein mc intosh oxford)
b)Non compensated : ether bottle.

31. • 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.

32. Recent
• A.Concentration calibration
1.variable bypass
2.Measured flow
3.electronic
• B.Vaporization methods
1.Flow over
2.Injection
• C.Temperature compensation
1.Mechanical
2.Supplied heat
3.Computerized

33. Variable bypass vaporizer
a.)Has an inlet and outlet.
b.)Fresh gas flows through
bypass chamber and
vaporizing chamber.
c.)Concentration of anesthetic
agent delivered depends on
amount of gas flowing
through the vaporizing
chamber.

35. Contd….
• 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.

36. 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.

37. FACTORS AFFECTING THE
VAPORIZER OUTPUT
• A.)Flow rate.
• B.)Barometric Pressure
• C.)Temperature.
• D.)Intermittent back pressure.
• E.)Carrier gas composition.

38. 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.

39. Effect of Barometric Pressure
•Vaporizers calibrated at standard (Sea level)
atmospheric pressure
•Low boiling point, High SVP agents are more
susceptible to barometric pressure changes.

40. 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.

41. 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 %

42. Effect of Temperature
• As vaporization continues, the temperature in vaporizing
chamber decreases as heat is lost during the process of
vaporization.
• So vapor pressure of anesthetic agent decreases and
output decreases.
• So to prevent this fresh gas flow rate is increased into the
vaporizing chamber by an expanding rod or a bi metallic
strip.

43. Vapor out put decreases

44. Expanding Metal rod

45. Bi metalic strip

46. Cont…
• 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.

47. 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

48. Pumping Effect
• Concentrations delivered by vaporizers increase
during ventilation than used with free flow to
atmosphere.
• Change is more pronouced when
– less agent in vaporizing chamber
– low carrier gas flow
– pressure fluctuations are high and frequent.
– dial setting is low.

49. MECHANISM

50. INSPIRATION
Pressure in bypass and
vaporizing chambers
increase.
As bypass has smaller
volume than vaporizing
chamber more gas enters
vaporizing chamber.

51. Increased
vaporization
Extra gas entering
vaporizing
chamber collects
the anesthetic
vapour

52. EXPIRATION
When bag is
released, the
compressed gas
expands in all
directions.

53. Some of the rapidly
expanding vapor
containing
anesthetic agent
enters the inlet and
cross over into the
bypass channel .

54. This vapor in bypass
chamber adds to that
of vapor coming from
vaporizing chamber
and increases the
final anesthetic conc.
Delivered. (pumping
effect).

55. MODIFICATIONS TO MINIMIZE THE PUMPING
EFFECT
1.) long inlet
tube:
The extra gas can
not enter the bypass
channel as inlet tube
is long.

56. 2.) Increase in the
internal resistance
of vaporizer
resists changes
due to back
pressure
ventilation.

57. 3.)One way
valve.
Allows the flow of
gas in one direction
only and prevents
the reverse
direction.

58. PRESSURIZING
EFFECT
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
anesthetic).
Net effect is decrease in conc of
anesthetic delivered.

59. EFFECT OF BACK PRESSURE.
PUMPING EFFECT
 Higher conc than indicated
on dial delivered.
- inc. by :
- Large pressure fluctuations
- Low dial setting
- Low flow rate
PRESSURING EFFECT
 Lower conc than indicated
on dial delivered.
- Inc by :
- Large pressure fluctuations
- Low dial setting
- High flow rate

60. 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
value
• 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
oxide.

61. 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
vaporizer.
• D) concentration control dial setting.

62. Tec 6
• 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.

63. Contd…
• 2) LACK OF AN EXTERNAL HEAT
SOURCE:
– 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.

64. Two independent gas
circuits.
Vapor originates in the
desflurane sump
which is electrically
heated and
thermostatically
controlled to 39C
Fixed restrictor

65. The differential pressure
transducer conveys the
pressure difference b/w
the fresh gas circuit and
the vapor circuit to the
control electronics
system, which regulates
the pressure control
valve.

66. Steady state
Differential pressure transducer
Fixed resistance

67. Signals Pushes diaphragm upwards.
Pressure
Control valve
Increased fresh gas flow

68. Differential pressure transducer in
Increasd vapor flow Neutral position

69. INDIVIDUAL VAPORIZERS….

70. Goldman Vaporizer
• Conc. calibrated  Flow over
(Without wicks)
• No temp compensation
• Agent non specific (Halothane,
ether, trilene)
• In & Out of system

71. Boyles Bottle
• Variable bypass (Conc
calibrated)
• Flow over wicks
• Out of system
• No temp compensation
• Muliple agent (Ether,
trilene, Halothane)

72. E.M.O
(EPSTEIN MACINTOSH OXFORD VAPORIZER)
• Draw over inhaler
• Variable bypass
• Flow over wicks
• Temp compensation by
supplied heat & flow
alteration
• Agent specific

73. OXFORD MINIATURE VAPOURIZER
• Draw over and plenum
• Thermo-stabilized
• Concentration calibrated
• Agent non –specific.
• (Halothane, trilene,
methoxyflurane)

74. TEC 2
Agent-specific for Halothane,
variable bypass, flow over with
wicks, low resistance,
temperature compensated with
bimetallic strip in vapour path,
non-tippable, no interlocks,
non-keyed filler.
Volume 750ml.

75. • 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.

76. TEC 3
Conc-calibrated, flow over with wick,
automatic thermo-compensation.
Bimetallic temp-sensitive element that is
located concentrically within bypass
chamber.
Volume decreased to 250ml
Vaporising chamber at high pressure
(overcomes the resistance to flow of
relatively dense saturated vapor even at
low flow rates.)

77. Contd…
Adv over tec 2 :
• Accurate with lower dial settings. Nitrous oxide has little effect
on output.
• 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.

78. • Dis adv: small amounts of leaks in bypass in OFF
position.
• 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.

79. Tec 4
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.

80. TEC 5
One handed dial control and
more obvious OFF position.
Helical intermittent positive
pressure assembly to
minimize effects of positive
pressure ventilation.
Capacity increased from 125
to 300 ml.

81. Tec 6
Is described as a dual gas
blender.
Tec 6 can deliver an
accurate concentration of
desflurane, between 1%
and18% at a flow rates
from 0.2 to 10 litres/min
at 21c

82. TEC 7:
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
design
3. Planned factory service
free
4. Improved sight glass
design

83. ALADIN
VAPORIZER
2 parts.
a). Electronic control system
in anesthesia machine
b). A portable cassette
containing agent.
The flow at the out let is
controlled by the CENTRAL
PROCESSING UNIT in the
anesthesia machine.

84. • The Aladin Cassette can be handled or
stored in
any position.
Automatic record keeping and gas
usage calculation
• Electronic control of desired agent
concentration .
.Provides agent setting data for
automatic record
Keeping and fresh gas flow data.
• Gas usage data provides a unique tool
for low flow

85. DRAGER 19.1
similar to tec 4,5 vaporizers.
The interlock on Dräger machines
continues to function if any vaporizers
are removed.
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.

86. Drager 19.1

87. Drager 2000 :
• Is one of two tippable
vaporizers (ADUcassettes are
the other).
• The dial must first be rotated
to a "T" setting ("transport" or
"tip") which is beyond zero
(clockwise).
•Tortous in let protects against
pumping effect.

89. Filling devices
• Funnel fill system
• Keyed fill system
• Quik- fil system
• Easy-fil system

90. FUNNEL FILL
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.

91. KEYED FILL
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
agent.

92. QUIK FIL :
The bottle has a
permanently attached,
agent-specific filling
device that has three
ridges that fit into slots
in the filler.

93. EASY FIL :
A color coded bottle
adaptor is attatched to
bottle and then fitted into
the vaporizer.
A drain plug is there for
draining vaporizer.

94. Hazards of a vaporizer
• a)In correct agent
• b)Tipping
• c)over filling
• d)reversal of flow
• e)leaks

95. a)In correct agent: minimized by agent specific filling
devices, color coding, agent monitors.

96. Contd…
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
concentrations.
– Prevented by low level filling port, indicator glass.

97. D )REVERSAL OF FLOW :
output is increased.prevented
by indicator arrows.
E) LEAKS : lead to
wastage of agent, OT
pollution,delivery of wrong
concentrations.
prevented by
NEGATIVE PRESSURE
CHECK TEST

98. Thank you