1) Vaporizers are devices that convert liquid anesthetic agents into vapor and add a controlled amount of vapor to the breathing system. 2) There are various types of vaporizers that use different mechanisms for vaporization and temperature compensation. Common vaporizers include the TEC, Goldman, and Copper Kettle vaporizers. 3) Special desflurane vaporizers are required due to desflurane's high vapor pressure, as standard vaporizers could result in dangerously high concentrations being delivered to the patient.

1. VAPORIZERDr Aneesha Basnyat
Anesthesiology & Critical Care

2. OBJECTIVES
• Basic terminologies
• The working principles
• Various types of vaporizer
• How desflurane vaporizers are different from other common vaporizers
• Different variables affecting vaporizer output
• Effect of altitude

3. Vaporiser
A device which converts liquid to vapor is called a vaporiser

4. VAPORIZER
• Anesthetic agent delivery system orVapor delivery system
• 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.

5. VAPOR
• a gas state of a substance at a temperature where it can co-exist with its
liquid form
• “Gas below the critical temperature”

6. Critical temperature
• Highest temperature at which a substance can exist in both liquid and
gaseous state
• Above its critical temperature, any amount of pressure will NOT compress a
gas into liquid
• A gas below its critical temperature  vapor
• A gas above its critical temperature gas

7. Vapor pressure
• Pressure exerted by a vapor in thermodynamic equilibrium with its
condensed phases (solid or liquid) at a given temperature in a closed
system.
• The pressure exerted by the vapor when in equilibrium with the liquid
phase at constant temperature is called “saturated vapor pressure”.
• depends only on the liquid and Temperature, not affected by ambient
pressure.
• separate vaporizer for different anesthetic agents

8. Boiling point
• temperature at which the saturated vapor pressure = atmospheric
pressure and at which all the liquid agent changes to the vapor phase.
• The lower the atmospheric pressure, lower the boiling point (high
altitudes).

10. Gas Concentration
• Expressed by Partial pressure and volume percent
1. Partial pressure(Dalton’s Law)
“the total pressure of mixture of gases must equal to the sum of partial
pressure of all the component gases.”
The partial pressure depends only on the temperature of that agent.

11. 2.Volumes percent –
• number of units of volume of gas in relationship to a total of 100 units of
volume for the total gas mixture.
-it expresses the relative ratio of gas molecules(%) in a mixture where
as partial pressure (mm Hg) expresses an absolute value.
Vol percent = Partial pressure/Total pressure
• Anesthetic uptake and potency are related directly to partial pressure and
only indirectly to volumes percent.

12. Latent heat of vaporization
• amount of energy that is consumed for a given liquid as it is converted to a
vapor
• number of calories required to change 1gm or 1ml of liquid into vapor
without a temperature change.
• Liquid temperature decreases as vaporization proceeds.

13. Specific heat
• the number of calories required to increase the temperature of 1g or 1ml of
a substance by 1°C.
• Importance:
• to maintain a stable temperature.
• choosing the material to construct a vaporizer.

14. Thermal conductivity
• a measure of the speed with which heat flows through a substance.
• The higher the value, the better the substance conducts heat
• Cu > Al> brass> Steel >> Glass
• Thermostabilization - metals that have relatively higher thermal
conductivity to minimize temperature changes

15. Working principle

16. High vs Low concentration setting
high anaesthetic concentration low anaesthetic concentration

17. Dial at zero

18. Splitting ratio
• The ratio of bypass flow to flow to the vaporizing chamber
• depends on
• ratio of resistances in two pathways
• variable/adjustable orifice present at inlet/outlet
• concentration dial setting
• total flow to the vaporizer

19. CLASSIFICATION
1. Based on regulating output concentration
• Variable bypass
• Measured flow
• Electronic vaporizers
2. Based on method of vaporization
• Flow over
• Bubble through
• Injection
3. Based on location of the vaporizer
• VOC
• VIC
4. Based on method of temperature Compensation
• Mechanical thermocompensation
• Supplied heat
• Computerized thermocompensation
5. Based on agent specificity
• Agent specific
• Multiple agent
6. Based on resistance
• Plenum
• Low resistance (Draw over)

20. Concentration calibrated vaporizers
• Most common
• calibrated by agent concentration expressed in percentage of vapor output
• Direct reading / Dial controlled / Automatic plenum / Percentage type /Tec
type vaporizers.
• 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.

21. Variable bypass vaporiser
• Vapor pressure of most anesthetic agents greater than their partial pressure at
room temperature
• clinically useful concentrations accomplished by SPLITTING the gas flow that
passes through the vaporizer

22. Measured flow vaporiser
• The vaporizer heats the anesthetic agent to a temperature above its boiling
point (so it behaves as gas) and this is then metered into the fresh gas flow.
• A measured flow is sent by a separate oxygen flow meter to pass to the
vaporizer with the output being at SVP for the anesthetic agent.
• In order to dilute this otherwise lethal concentration, output from that
flowmeter is combined with gas passing form the main flowmeter
• Operator has to set the flow to the vaporizer and bypass with separate
flowmeters
• Respective flows have to be calculated for each agent for a given temp
and vapour output

24. Electronic vaporisers
• 2 types:
• 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.

25. Depending on the method of vaporisation
Flow over
• a stream of carrier gas passes
over the surface of the liquid.
• Most commonly used.
• baffles or spiral tracks:
increases surface area 
efficiency of vaporization
increased
• Wicks: capillary action.
Bubble through
• the carrier gas is bubbled through
the volatile liquid, further increasing
the gas-liquid interface.
Injection:
• 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.

26. Temperaturecompensation
• thermocompensation
• supplied heat

27. A) mechanical thermocompensation
• altering the splitting ratio using thermal element.
B) supplied heat
• An electric heater
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.

30. Different vaporizers

31. MORTON’S ETHER INHALER
Draw over, flow over with wicks
concentration not calibrated,
temperature not compensated,
specific
agent

32. OPEN DROP METHOD
Draw over, concentration not calibrated
Temperature not compensated
multiple agent.

33. EPSTIEN MACINTOSH OXFORD
(E.M.O.)
Draw Over, Concentration calibrated,Flow over,
Temperature compensated by water jacket and agent specific,
can be used any where.
ether, chloroform,
halothane and
trichloroethylene

34. GOLDMANS VAPORIZER
Plenum or Draw over type ,variable bypass, flow over,
temperature not compensated, concentration poorly calibrated,
multiple agent, both inside and outside circle
Maximum concentration never exceeds
2% irrespective of total gas flow

35. BOYLES BOTTLE
ether and trichloroethylene.
Plenum type, variable bypass, flow over or bubble through,
Concentration poorly calibrated, temperature not compensated,
agent specific, out of circle

36. Copper kettle vaporiser
• Described by Lucien Morris in 1952
• a measured flow of oxygen is allowed to bubble
through the anesthetic liquid
• Separate supply of oxygen form an extra
flowmeter
• flow of oxygen through the copper kettle and flow
of fresh gas should be calculated.
• If the fresh gas flow is reduced the sudden high
anesthetic concentration may be dangerously
delivered to the patient.

37. TEC - 2
Plenum type, concentration poorly
calibrated,
flow over with wicks,
temperature compensated,
out of circle and agent specific.
TEC - 3
Plenum type, variable by pass, flow
over with wicks, temperature
compensated, concentration calibrated,
out of circle, agent specific.

38. TEC - 4
Plenum type, variable bypass, flow over with wicks, temperature
compensated, concentration calibrated, out of circle, agent specific.
if it is accidentally inverted, the
liquid agent will not spill into the
bypass.

39. TEC 5
• Plenum type, concentration calibrated, variable
bypass,
flow over with wicks, out of circle, agent specific with
keyed filling.
• Bimetallic strip which acts as a thermostat.
• 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 output.

40. TEC - 7
Concentration calibrated, plenum type, Variable bypass,
Flow over with wicks, Temperature compensated,
out of circuit, agent specific
innovative non-spill system limits
movement of liquid agent if the vaporizer
is lifted or inverted.This protects its
internal components and helps to
maintain output within clinically
acceptable limits.

41. The Desflurane
Problem!
 The vapor pressure of desflurane is 669 mm Hg (3-4
times that of other similar agents)
 The boiling point of desflurane is 22.8 °C (room
temperature)

42. TEC – 6 DESFLURANE VAPORIZER
It is a electrically heated, dual circuit gas/vapor blender,
constant-temperature, agent specific and out-of-circuit vaporizer.

43. PRINCIPLE OF DESFLURANE VAPORIZER

44. PRINCIPLE OF DESFLURANE
VAPORIZER (Contd…)

45. TEC - 6

46. THE GE ALADIN CASSETTE VAPORIZER
It is a electronically controlled, variable bypass, constant-temperature,
multiple agent specific, and out-of-circuit vaporizer.
The agent is in a portable cassette that
is inserted into a slot in the anesthesia
machine.
The control dial is on the machine next
to where the cassette is placed. A
magnetic sensor identifies the cassette.

47. Others
• Drager vaporizer
• Penlon SigmaVaporiser
• Vapor 19.1, 19.3, 2000

48. Factors affecting vaporization
• Flow through the vaporizing chamber
• Efficiency of vaporization
• Temperature
• Gas flow rate
• Carrier gas composition
• Time
• Volatility
• Boiling point
• Area of contact with the liquid.

49. Effects of Altitude
• Clinical effect of volatile agents is determined by their partial pressure.
• SVP is unaffected by ambient pressure; thus, vaporiser output remains
unaffected.
• Change in the agent concentration in the delivered gas flow:
% 𝒐𝒇 𝒂𝒈𝒆𝒏𝒕 = % (𝒄𝒂𝒍) 𝒙 𝑷 (𝒄𝒂𝒍)/𝑷𝟏
P (cal) = pressure at an altitude when vaporizer is calibrated
P1 = pressure at given altitude

50. Example:
If we dialed an isoflurane vaporizer to 2% at atmospheric pressure, delivered
concentration = 2%
Partial pressure of isoflurane at 1 atm = 2% of 101.3kPa = 2.026 kPa
Now,
If we dialed the vaporizer to 2% at reduced atm pressure (50Kpa), delivered
concentration = % cal x P (cal)/ P1
= 2 x 101.3/50 = 4.052%
So the partial pressure of isoflurane = 4.052% of 50kPa = 2.026 kPa

51. • This doesn’t apply toTec 6 vaporizer (desflurane)
• Pressurised to 2 atm
• No compensation for ambient pressure
• Stable concentration regardless of ambient pressure
• Example: delivered concentration is 2% regardless of ambient
pressure
Sea level- partial pressure = 2% of 101.3kPa = 2.026 kPa
At 50Kpa- partial pressure = 2% of 50kPa = 1 kPa
Hence, dial setting must be increased to maintain partial
pressure of desflurane at altitude.

52. Effects of intermittent back pressure
• assisted/controlled ventilation the positive pressure
generated transmitted from the breathing system back to
machine and vaporizer.
• use of O2 flush valve
• increase in the anesthetic gas pressure  transmitted back to
the vaporizer  increase the final vapor output.
• most pronounced when there is less agent in the vaporizing
chamber, carrier gas flow is low, high and frequent pressure
fluctuations, low dial setting.

57. • 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.
• Pressurizing effect – with high gas flows  output decreased
(less significant)
• Pumping effect – with low gas flows  output increased

58. Pressurising effect

59. Modifications to minimize pumping effect
1. Alterations to the vaporizer: small chamber, increased bypass
area, long inlet tube, resistance at the outlet
2. Alterations to the anesthesia machine: unidirectional valve,
pressure relief valve

60. How much liquid agent does a
vaporizer use per hour?
• Ehrenwerth andEisenkraft
3 x Freshgasflow(L/min) xVolume%= mlliquidused per hr
• typically1mlofliquidvolatileagentyieldsabout200mlof vapor

61. Filling Systems
• Funnel filling system, Keyed filling system, Quick –Fil system, Easy-Fil
system, and Desflurane filling system.

62. Safety features of modern vaporizers
• Keyed filling system
• Low filling port
• Secured vaporizers (less ability to move them minimizes tipping)
• Interlock devices or vaporizer exclusion systems – prevent more than one
vaporizer from being turned ON at a time.

63. Hazards of modern vaporizers
• Incorrect agent
• Tipping
• Overfilling
• Reversed flow
• Leaks
• Physical damage
• Contaminants in the vaporizing
chamber
• Obstruction to fresh gas flow
due to problems in mounting
system
• Interlock malfunction
• Concentration dial in wrong
position

64. Conclusion
• 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.

65. References
• Dorsch and Dorsch
• International Anesthesia Research Society

66. THANKYOU