vaporizer and vaporiser

1
VAPORIZERS
Sunakshi bhatia SPMC bikaner
2
CONTENTS

1. What Is Vaporizer?
2. Ideal Vaporizer
3. Physics
4. Classification
5. Basic Functioning
6. Factors Affecting Vaporizer Performance
7. Hazards
8. Safety Features
9. Vaporizers Of Historical Importance

3

• WHAT IS VAPORIZER?
• Vaporizer is an instrument designed to facilitate
  the change of a liquid anesthetic into its vapor
  and add a controlled amount of this vapor to the
  flow of gases going to the patient.

4
IDEAL VAPORIZER

• Lightweight, robust and durable
• Easy to transport
• Corrosion and solvent resistant
• Leak proof
• Economical and safe to use
• minimal servicing
• Accurate over a wide range of
• FGF
• Liquid agent levels
• Ambient pressures
• Ambient temperatures
• Unaffected by
• Heat loss due to vaporization
• Pressure changes downstream of the vaporizer
• Tilting or tipping
• Compatible with vaporizer interlock systems.

5
PHYSICS

1. Critical temperature
2. Vapor and gas
3. Saturated vapor pressure
4. Boiling point
5. Latent heat of vaporization
6. Heat of vaporization
7. Thermal conductivity
8. Specific heat

6

• Critical temperature
• Temperature above which a substance in the
  gaseous phase cannot be condensed into a liquid,
  no matter how much pressure is applied.
• E.g. CT of oxygen is -119 centigrade

7

• A vapor is a substance that is in gaseous phase
  below its critical temperature. This means that
  the vapor can be condensed to a liquid or to a
  solid by increasing its pressure without reducing
  the temperature,
• e.g. water vapor is the vapor form of water.
• The term gas is used to describe a substance that
  is in the gaseous phase above its critical
  temperature
• e.g. nitrogen is a gas at room temperature and
  atmospheric pressure. Nitrous Oxide, Cyclopropane
  delivered in cylinders

8

• When a surface of a liquid is exposed to
  air/gas/vacuum? vapor
• The remaining liquid now has a lower than average
  kinetic energy and hence temperature of the
  liquid decreases along with the mass.
• Vapor exerts pressure on the walls ? vapor
  pressure which varies with temperature and nature
  of liquid.
• When the liquid and its vapor are in
  thermodynamic equilibrium, the vapor pressure is
  now called? saturated vapor pressure

9
Vapor pressure
Saturated Vapor pressure
10

• saturated vapor pressure
• SVP at 20 Centigrade
• Halothane243
• Isofurane238
• Sevofurane 159 (lowest)
• Desfurane669(highest) Most volatile
• If the temperature of a vaporliquid system is
  increased, the SVP increases.
• The vapor pressure of a liquid does not depend on
  the amount on the liquid in the container, be it
  one liter or thirty liters at the same
  temperature, both samples will have the same
  vapor pressure.

11

• Boiling point The temperature at which SVP
  becomes equal to atmospheric pressure and at
  which all the liquid agent changes to the vapor
  phase is known as its boiling point.
• Halothane243 50.2
• Isofurane238 48.5
• Sevofurane 159 (lowest) 58.6
• Desfurane669 (highest) Most volatile 22.8
• Changes with atmospheric pressure
• So lower the atmospheric pressure, lower will be
  the boiling point

12
Latent heat of vaporization the calories
required to convert 1 gram or 1 ml of a substance
from the liquid state to the vapor. For most of
agents 60 Cal/ml Important because as the
vapors form, liquid cools, so heat needs to be
provided continuously (Thermo compensation) Speci
fic heat-quantity of heat required to raise the
temperature of 1 g of the substance by 1
centigrade. Use - to find amount of heat to be
supplied to liquid - to find out best material
for vaporizes e.g. copper has high specific
heat(thermal buffering)
13
Thermal conductivity It is a measure of speed
with which heat flows through a substance.
Substances with a high thermal conductivity can
supply more heat to the liquid anesthetic in
them. Wood- least thermal conductivity. Materi
als with higher thermal conductivity are selected
for vaporizer. Thermal capacity Product of
specific heat and mass (amount of heat stored in
the vaporizer body).
14
Concentration of gas

• Expressed as Vol (v/v) or Partial pressure
• Vol it is ml/100 ml . It is a relative value
• Partial pressure is absolute value. For e.g.
• Partial pressure of 21 oxygen at
• 1 tm 760 mmhg --------160 mmhg
• 500mmhg ---------105 mmhg (cause of
  hypoxia)

15
Partial pressure

• 760 mmhg 15 PSI 1000cm H2O 100 Kpa (SI unit)
• Daltons law of partial pressure
• total pressure by a mixture of gases is equal to
  the sum of the partial pressures of each of the
  constituent gases.
• 21 oxygen exerts how much partial pressure at
  sea level?
• PxVol
• 760 x vol 760x21/100 159.6 mmhg.
• If the liquid is open to the air, then the vapor
  pressure is seen as a partial pressure along with
  the other constituents of the air.
• Uptake and anesthetic depth depends on partial
  pressure!!concentration dial is volume percent

16
In a bottle containing halothane, calculate the
of halothane above the liquid level ?

• SVP243mmhg
• atm760 mmhg
• Vol243/760x10032(caution!!)

17

• Vaporizers concentration Denotes the
  concentration delivered by a vaporizer when fresh
  gas containing no vapor passes through it.
• Significance
• In an out-of-system vaporizer, vaporizer output
  equals vaporizer concentration.
• In an in-system vaporizer, expired gases contain
  some volatile anesthetic, and therefore vaporizer
  output can exceed the vaporizer concentration.

18

• Vaporizers capability Refers to the maximum
  concentration that can be delivered by a
  vapourizer at the highest setting of the
  concentration dial.
• Vaporizer capability depends on the MAC of the
  agent.
• For example, Sevoflurane has a higher MAC than
  Isoflurane and therefore needs a vapourizer with
  a higher capability (maximum 8 in case of
  Sevoflurane as compared to 6 with Isoflurane)
• Halothane -5
• Isofurane-6

19

• Vaporizers efficiency
• Means the ability of a vaporizer to saturate the
  carrier gas passing into the vaporizing chamber
  at the temperature of the liquid.
• Vaporizer efficiency is increased by using wicks
  and longer vaporizing chambers to increase the
  surface area available for vaporization.

20
Calculate the amount of vapor produced by 1
gramof its liquid agent. How much liquid agent
does avaporizer use per hour?

• 1 mole of a gas weighs 1 gram molecular weight.
• The molecular weight of Isoflurane is 185.
• Therefore, 1 mole of Isoflurane vapour weighs 185
  g.
• As per Avogadros hypothesis,
• 1 mole of a substance 22.4 liters of gas
• 22.4 liters of isoflurane vapour weighs 185 g.
• Therefore, density of isoflurane vapour is
  185/22.4 8.25 g/L
• so 8.25 g in 1 L ie 1000ml,
• Therefore, 1 gram 1000/8.25 mL of vapour(A)

21

• Density of Isoflurane liquid is 1.5 g/mL.
• 1.5 g in 1 ml
• Therefore, 1 gram 1/1.5 mL of liquid (B)
• Since 1g1g so AB
• 1/1.5 mL of liquid 1000/8.25 mL of vapour
• 1mL of liquid 1000/8.25 1.5 180 mL vapour
• For most modern agents, 1 mL of liquid volatile
  agent yields
• about 200 mL vapor.

22
vapor used per minute fresh gas flow rate
time concentration setting For example, to
deliver 1 Isoflurane at FGF of 2 liters
per minute for 60 minutes, one would need 1/100
2000 mL 60 min 1200 mL of Isoflurane
vapor. This would correspond to 1200/180 6.7
mL of liquid isoflurane. So from this we can
calculate time for remaining inhalational agent
to finish.
23
How to calculate liquid vapour use ?(another
method) Ehren werth Eisenkraft formula (
1993) 3 x FGF ( Litres / min) x dial setting
v/v FGF 4 litres dial setting 3 ML of
liquid per hour 3x 4 x3 36 ml/ hr
24
CLASSIFICATION

• the Dorsch and Dorsch classification
• Method of regulating output
• Method of vaporization
• Temperature compensation
• Location
• Caliberation
• Specificity
• Resistance

25

• 1. Acc to Method of regulating output
  concentration
• Variable bypass(concentration caliberated) Ether
  bottle, TEC vaporizers
• Draw-over
• Plenum
• Both variable and measured flow-Alladin Cassette
• Measured flow Copper kettle, side-arm vernitrol
• Dual Circuit-gas/vapor blender, Tec6 Desflurane
  vaporizer
• Injection- Drager DIVA(component of Drager Zeus
  anaesthesia workstation, The Maquet 950 series
  vapourise

26

• 2.Method of vaporization
• Flow over
• --with wickTEC vaporizers
• --without wickGoldman bottle
• Bubble through Copper kettle which has sintered
  bronze disks to increase vaporization
• Flow-over or bubble-through Ether bottle,
  depending on the position of the plunger
• Injection Desflurane, Kion though Desflurane
  vapourizer has been described as an injector,
  it is more ideally classified as a gas-vapour
  blender.

27

• 3.Temperature compensation
• Thermo-compensated
• --By altered flowTEC vaporizers
• --By supplied heatcopper kettle
• --By both supplied heat and altered flow EMO
• Non compensated Ether bottle.
• 4.Location
• In circuit VIC EMO, Goldman bottle
• Out of circuit VOC TEC vaporizers.

28
Out-of-system vaporizers All measured flow
vaporizers are located out of the
breathing system and have a dedicated flow meter.
Plenum vaporizers (high-resistance) are also used
out of system. In-system vaporizers They are
those in which the patients inspiratory and
expiratory gases go through the vapourizer.
29
5.Calibration

• Calibration
• a. Uncaliberated
• controls not precise
• OpenWire mask, Napkin
• PlenumBoyles bottle
• b. Caliberated
• directreading, dialcontrolled, automatic
  plenum, percentagetype, and tectype vaporizers
• Electronically controlled aladdin casket

30

• 6.Specificity
• Agent specific TEC vaporizers
• Multi agent Goldman bottle.
• 7.Resistance
• Plenum ( high resistance) TEC vaporizers
• Draw over ( low resistance) Goldman bottle, EMO.

31

• Plenum vaporizers(Plenuma chamber in which there
  is high pressure)
• Driven by positive pressure from the machine.
• The performance of the vaporizer does not change
  regardless of whether the patient is breathing
  spontaneously or is mechanically ventilated.
• The internal resistance of the vaporizer is
  usually high, but because the supply pressure is
  constant the vaporizer can be accurately
  calibrated to deliver a precise concentration of
  volatile anesthetic vapor over a wide range of
  fresh gas flows.
• ADVANTAGE- which works reliably, without external
  power, for many hundreds of hours, and requires
  very little maintenance.
• .

32

• Works by splitting the incoming gas into two
  streams.
• Plenum vaporizer can only work one way round if
  it is connected in reverse, much larger volumes
  of gas enter the vaporizing chamber that can be
  toxic.
• Technically, although the dial of the vaporizer
  is calibrated in volume percent (e.g. 2), what
  it actually delivers is a partial pressure of
  anesthetic agent (e.g. 2kPa)
• The performance of the plenum vaporizer depends
  on the SVP of the agent. SVP is unique to each
  agent, so it follows that each agent must only be
  used in its own specific vaporizer and safety
  features are needed.
• They have several features designed to compensate
  for temperature changes like metal jacket,
  bimetallic strip

33

• Drawover vaporizers
• Driven by negative pressure by the patient, and
  must therefore have a low resistance and Its
  performance depends on the minute volume of the
  patient its output drops with increasing minute
  ventilation.
• Design is simpler a glass reservoir mounted in
  the breathing attachment.
• Drawover vaporizers may be used with any liquid
  volatile agent.
• Because the performance of the vaporizer is so
  variable, accurate calibration is impossible.
  However, many designs have a lever which adjusts
  the amount of fresh gas which enters the
  vaporizing chamber.
• May be mounted either way round(bi-directional).

34

• No temperature compensating features.
• The relative inefficiency of the Drawover
  vaporizer contributes to its safety. A more
  efficient design would produce too much
  anesthetic vapor.
• ADVANTAGE
• cheap to manufacture
• easy to use.
• Portable design means that it can be used in the
  field
• Example-G E O
• Goldman
• EMO
• OME

35
Point DRAW OVER PLENUM
Requirement Patients efforts Gas under positive pressure
Pressure produced Negative pressure by the patient, Downstream of vaporizer Positive pressure , Upstream of vaporizer
Allows Bidirectional flow Unidirectional flow
Flow rare Can be up to 60L/min so wide range of fresh gas flows. Depends on flow meter
Resistance to flow Low because pressure has to be produced by patient. high
Can be used as VOC or VIC Only VOC
performance depends on minute volume of the patient its output drops with increasing minute ventilation. does not change regardless of whether the patient is breathing spontaneously or is mechanically ventilated.
36
(No Transcript)
37
BASIC FUNCTIONING
38
Functioning Of Variable-Bypass Vaporizers

• Variable bypass vaporizers accept the total gas
  flow from the anesthesia machine and deliver the
  gas flow with a predictable concentration of
  vapor to the common gas outlet.
• The carrier gas flow entering the vapourizer is
  divided into 2 parts
• one part going through the bypass chamber(major
  part)
• the other part going through the vaporizing
  chamber where it is saturated with the vapor of
  the liquid anesthetic agent.

Control dial
39
E.g. Sevofurane How much sevofurene collected
vaporizing chamber? SVP/atmospheric
pressure157/760 x 100 21 21 is lethal. So
dilution is required
40

• SPLITTING RATIO
• The ratio of the carrier gas flows through bypass
  and vaporizing chambers is called the splitting
  ratio.

The splitting ratio is affected by the
concentration setting on the dial ,SVP and by the
temperature-compensating mechanism in the
vaporizer.
41

• Can vaporizers be interchanged?
• Different anesthetic agents have different
  saturated vapor pressures at a given temperature.
• Therefore, the partial pressure exerted by the
  vapor in a mixture of gases will be different.
• Hence, splitting ratios are agent-specific and
  vaporizers cannot be interchanged unless 2 vapors
  have the same vapor pressure.

42
Functioning Of A Measured-flow Vapourizer

• This type of vapourizer utilizes a measured flow
  of carrier gas, usually oxygen, to pick up
  anesthetic vapour.
• This vapourizer system consists of 3 parts
• vapourizer fitted with a thermometer
• flowmeter assembly
• vapourizer circuit control valve.(diagram)

43

• A measured amount of carrier gas flows through a
  flow meter and onto the vapourizer circuit
  control valve, which directs it to the
  vapourizer.
• The gas saturated with vapor is returned to the
  vapourizer circuit control valve, where it is
  diluted by the remaining fresh gas flow and goes
  to the patient.

44

• It is important to remember that
• The oxygen flowing through the vapourizer should
  be counted as additional to that going directly
  to the patient.
• The vapourizer should not be turned on until the
  flows on the other flow meters have been seta
  lethal concentration of agent may be delivered to
  the patient.

45
Problems of Design

• High flows of fresh gas going through the whole
  vaporiser can affect its output.
• The temperature of the vaporiser drops with use
  and this can affect its output.
• Some ventilators transmit a positive pressure
  back into vaporiser which can affect its output.

46
Problem Of Flows

• If FGF is high, the vaporization process cant
  keep up with excess coming into the vaporization
  chamber.
• As a result, relative to the high flow of FGF,
  the amount of agent vaporized is inadequate.
• So this means that at high flows, the basic
  vaporizer delivers less agent concentration than
  is set on the dial.

47

• 2.Method of vaporization
• Flow over
• --with wickTEC vaporizers
• --without wickGoldman bottle
• Bubble through Copper kettle which has sintered
  bronze disks to increase vaporization
• Flow-over or bubble-through Ether bottle,
  depending on the position of the plunger
• Injection Desflurane, Kion though Desflurane
  vapourizer has been described as an injector,
  it is more ideally classified as a gas-vapour
  blender.

48
Solution?

• Dip Wicks.
• Due to capillary action, the agent rises into the
  wicks.
• This increases the surface area of agent exposed
  to the fresh gas entering the vaporisation
  chamber and thereby improves the efficiency of
  vaporisation.

49

• Bubbles though
• Example-Copper Kettle use bubbles to increase the
  surface area for vaporization.
• In these, some of the FGF is bubbled through a
  disk made out of a special material (sintered
  disk) that is very porous.
• Sintered --produced by or subjected to sintering
  (the process of coalescing a powdered material
  into a solid or porous mass by means of heating
  without liquefaction).
• The disk is submerged into the agent and when
  fresh gas is sent through it, tiny bubbles form.
• The tiny bubbles of fresh gas have a very large
  total surface and thus become fully saturated
  with vapor effciently.

50
(No Transcript)
51
Factors affecting efficiency of vaporization in
a bubble-through vaporizer? 1. Size of the
bubbles The smaller the bubbles, the more are
the surface area available for equilibration. For
example, in the copper kettle, a sintered bronze
plate is used to break the gas flow into small
bubbles to increase efficiency of
vaporization. 2. Depth of the liquid The deeper
the liquid, the more is the time required for
bubbles to reach the surface, allowing more time
for equilibration. For example, in the ether
bottle, depressing the plunger below the level of
the liquid increases vaporization. 3. Velocity
of carrier gas flow The faster the flow of
bubbles, the less is the time available for
equilibration.
52
Problem Of Temperature

• For vaporisation to occur, the anesthetic
  molecules have to escape from the liquid state
  and become vapor.
• This process reduces the energy left in the
  remaining liquid.
• As more and more molecules escape, more and more
  energy is lost from the liquid.

53
Therefore, as the escaping molecules reduce the
energy left in the liquid, the temperature of the
liquid falls. The falling temperature (lowering
energy) of the liquid means that less molecules
are able to escape. i.e. as vaporisation
happens, the temperature of the liquid falls
causing less vaporisation.
54
Solution?

• Temperature compensation in vaporizers can be by
  
• Supplied heat
• Use of coppercopper kettle
• Water jacketEMO
• Electrically heatedTEC 6 vapourizer for
  Desflurane.
• Altered flow At lower temperatures, a higher
  percentage of carrier gas flows through the
  vapourizing chamber.
• Eg
• Bimetallic stripTEC vaporizers.
• automatic temperature compensating valve

55
Supplied heat

• In most vaporizers, heat is not actively given.
  That is, we dont electrically heat it
  (complicated and needs a power supply) and nor do
  we light a fire under it.
• Instead, we make it easy for the vaporizer to use
  heat from the surrounding air.
• The vaporizing chamber is generally surrounded by
  a lot of metal which helps to minimize the
  temperature drop by two ways.
• Firstly metal is a very good conductor of heat
  and therefore is able to efficiently transfer
  heat from the surrounding air into the anesthetic
  agent.

56
(No Transcript)
57

• Secondly, metal acts like a heat store. It
  absorbs heat (green arrows) till its
  temperature equals the temperature of the
  surrounding air.
• When the anaesthetic agent starts to cool, the
  metal now donates heat ( yellow arrows ) ,
  helping to minimise the temperature drop.
• However, the metal casing cannot give up heat
  indefinitely and after sometime, its temperature
  also drops.

58

• Altered flow
• Increase the flow of gas via the vaporising
  chamber (altering the splitting ratio).
• One could manually do this by measuring the
  temperature of the liquid with a thermometer and
  increasing the dial setting according to some
  kind of reference chart which is quite tedious as
  we have to do it all the time.
• Modern vaporisers have removed this hard work.
  When the liquid drops its temperature, the flow
  of gas through the vaporising chamber is
  automatically increased.
• This is accomplished by an automatic temperature
  compensating valve that influences how much flow
  goes via the vaporising chamber.

59

• The automatic temperature compensating valve uses
  the physical property that substances (e.g.
  metals and liquids ) become smaller when the
  temperature lowers.
• A metal rod (shown in black below) shortens as
  the temperature drops.
• Similarly, a liquid filled in collapsing bellows
  (shown in green below) becomes smaller in volume
  when cooled to a lower temperature.

60

• This property is used in the design of automatic
  temperature compensating valves in vaporisers.
• In the design that uses a metal rod, the rod
  offers some resistance to flow into the
  vaporising chamber.
• As the vaporiser cools, the rod becomes shorter,
  making the valve move away from the opening. This
  reduces the resistance to flow and thus more flow
  occurs into the vaporising chamber.

61

• Some vaporisers eg. EMO use the expansion or
  contraction property of a special liquid inside
  bellows (shown in green) to control the valve.
• As the temperature falls, the liquid in the
  bellows contracts into a smaller volume.
• This makes the bellows shrink, pulling the valve
  away and thereby increase flow.

62

• Another method uses a bi metallic strip.
• Different metals expand and contract to differing
  extents when exposed to temperature changes.
• In the example below, the green metal expands
  and contracts less than the red metal.

63

• In a bimetallic strip, two metals with very
  different degrees of thermal expansion (
  different coefficients of thermal expansion )
  are fixed together.
• In the example below, when the temperature drops,
  the green metal contracts much more than the
  red metal.
• Because they are fixed together, they cannot
  contract independently, like in the diagram
  above.
• Instead, the green metal tries to drag the
  red metal and causes the bimetallic strip to
  bend.

64

• This reduces the resistance to flow and thus more
  flow occurs into the vaporising chamber.

65
(No Transcript)
66
FACTORS AFFECTING VAPORIZER PERFORMANCE

• 1. SURFACE AREA OF THE LIQUID GAS INTERFACE
  Greater the surface area, more will be the
  vaporization. Incorporated with wicks, baffles,
  long vaporizing VC, channels
• Bubble through gt flow over
• 2. TEMPERATURE as temperature increase, output
  increase
• No change between 10 to 40 centigrade
• 3. TIME Output concentration tend to fall over
  time

67

• 4. FRESH GAS FLOW RATE
• At lt250 ml/min-VOC is less due to insufficient
  turbulance.
• At high flow ratesgt15L/min, the gas leaving
  vaporization chamber is less saturated ( gas
  spends less time in VC- output tend to fall
• 5. CARRIER GAS COMPOSITION Nitrous oxide is
  more soluble in liquid anaesthesic thus
  decreasing the effective volume passing throug
  Vaporising Chamber. So decrease vapour of agent.
• 6. AMBIENT PRESSURE
• - SVP is solely a function of temperature, so if
  ambient pressure is reduced, the constant SVP
  becomes a greater proportion of the total
  pressure -- output increases.

68

• 7. EFFECT OF REBREATHING
• causes a difference between the vaporizer
  setting and the inspired concentration with
  significant rebreathing.
• More the rebreathing , more will be vapor
  concentration.
• An agent analyzer is needed
• 8. BOILING POINT Higher boiling point, lesser
  output
• 9. INTERMITTENT BACK PRESSURE-
• positive pressure and oxygen flush can cause 2
  situations
• VOC increasesPumping effect
• VOC decreases Pressurizing effect

69
PUMPING EFFECT

• During the positive pressure, there is a pressure
  rise and during expiration, there is a sharp drop
  in pressure.
• These pressure changes can be transmitted back
  into the vaporiser and can affect the
  concentration of anaesthetic agent delivered.
• The effect of changing pressure affects the
  output of the vaporiser is called the pumping
  effect.

70

• When the bag is squeezed pressure is transmitted
  back into the vaporiser
• This back pressure is transmitted to both, the
  by pass channel and also to the vaporising
  chamber.
• This back pressure opposes the flow of the
  fresh gas in both the by pass channel and the
  vaporising chamber.
• The fresh gas entering the vaporiser tries to
  move forward and gets compressed both in the by
  pass channel and the vaporising chamber.
• However, the vaporising chamber volume is much
  larger than the by pass channel volume, and
  thus, more fresh gas gets compressed into it than
  into the by pass channel.
• This extra fresh gas that enters the vaporising
  chamber collects anaesthetic vapor.

71

• when the positive pressure is suddenly released
  (expiration).
• The previously compressed gases now suddenly
  expands in all directions.
• Some of the rapidly expanding gas (containing
  vapor) enter the inlet of the vaporiser and cross
  over into the by pass channel.

72

• Normally, a vaporiser by pass channel does not
  have vapor.
• So this vapor due the pumping effect is
  additional.
• When this by pass vapor flows across to the
  exit of the vaporiser, it meets the vapor from
  the vaporising chamber.
• The addition of the by pass vapor to the vapor
  from the vaporising chamber raises the final
  concentration of anaesthetic delivered.
• Thus pumping effect increases the delivered
  concentration of anaesthetic agent.

73
Solution?

• Tricks to reduce the pumping effect
• Long inlet tube
• Increased resistance
• One way valve

74

• LONG INLET TUBE
• The vaporiser inlet tube can be made longer.
• When the back pressure is suddenly released
  during expiration, as discussed before, the extra
  gas in the vaporising chamber will suddenly
  expand.
• However, due to the long inlet tubing, the extra
  gas containing vapor expands into the long inlet
  tube and doesnt reach the by pass channel.

75

• INCREASED RESISTANCE
• The vaporiser can be designed to have a high
  internal resistance to flow.
• This high resistance resists changes to flow
  caused by the intermittent back pressure of
  positive pressure ventilation.

76

• ONE WAY VALVE
• A one way valve or the unidirectional valve can
  be put between the vaporiser outlet and the
  ventilator / breathing system.
• In the diagram below, the one way valve is
  allowing gases to flow forwards.
• However, this valve prevents flow from occurring
  in the reverse direction.
• This reduces the transmission of back pressure
  to the vaporiser.

77
Pressurizing Effect

• Occurs when carrier gas is compressed in the
  vapourizing chamber due to high flow rate.
• So no of carrier gas molecule per unit volume is
  excessively more than no of vapor molecules.
• This results in a dilution of anesthetic in the
  vapourizing chamber and a decrease in vapourizer
  output.
• There is usually an interplay between the
  pressurizing and pumping effects.
• Changes in vapourizer output are more with the
  pumping effect and are of greater clinical
  significance.

78
(No Transcript)
79
PUMPING EFFECT PRESSURIZING EFFECT
Increase in vapourizer output Decrease in vapourizer output
More with Low flows, Low dial settings and When the level of liquid agent in the vapourizer is low More at high gas flows Low dial setting Large pressure fluctuations
More effect so is clinically significant Less effect so is clinically insignificant
80
VAPORIZERS OF HISTORICAL ImPORTANCE
81
Materials used in the constructing of
vaporizers Copper Aluminum MRI compatible
vaporisers Brass Steel Glass
82

• OPEN DROP METHOD
• Folded Handkerchief
• Schimmelbusch Mask with Bellamy Gardner Bottle
• Bellamy Gardener face mask
• Yankauer face mask
• Ochsner wire framed face mask
• Ogden Inhaler
• DRAW-OVER VAPORIZERS
• Flaggs Can
• Epstein Macintosh Oxford Ether Inhaler
• Oxford Miniature Vaporizer
• Goldman
• Rowbotham
• Triservice Apparatus
• PLENUM VAPORIZERS
• Boyles Ether Vaporizer
• Copper Kettle
• Siemens KION Vaporizer

83
Mortons ether inhaler

• WTG Mortan first publically demonstrated
• ether anesthesia on 16 October 1846
• Glass sphere with ether soaked sponge
• Patient inhaled through mouth piece
• Drawover type
• Problem-No means of regulating its output
  concentration or compensating for changes in
  temperature caused by vaporization of the liquid
  anesthetic and the ambient environment.

84
Schimmelbusch Mask

• The Schimmelbusch Mask is a wire frame mask used
  with a suitable drop bottle like the Bellamy
  Gardner bottle.
• It can be used for chloroform or a mixture.
• Draw over, non-temperature compensated,
  multi-agent.

GUTTER
HINGE
85
Bellamy Gardner Bottle
It was the most common drop bottle in use. Used
for open-drop method of anesthesia. The dropper
consists of a red rubber stopper with two metal
tubes. The longer tube dips into the liquid and
the shorter acts as an air vent allowing air to
enter the bottle.
86
(No Transcript)
87
Ogston Inhaler

• It is similar to the above masks with an upright
  wire cage around the periphery. This helps in
  reducing air dilution.
• Gamgee is wrapped around the cage to increase the
  concentration by decreasing air dilution.

GAMGEE cotton placed between gauge
88

• Yankauers face mask had mesh and removable
  spiral wire collar holding down a piece of gauze
  onto which agents such as ether or chloroform was
  applied.

• Bellamy Gardener face mask for inhaling ether had
  hinged wire mesh covered with double layer of
  wool fabric held in place by lever.
• Difference- no handle.

89
(No Transcript)
90
Modified Yankauer-Gwathemy Mask
Yankauer Mask
Yankauer-Gwathemy Mask
O2 Supply
91
Prevent air dillution
92
Flaggs Can

• Drawover,
• flowover without wicks,
• non-temperature compensated multiple agents.
• This is an improvised vaporizer designed for use
  in the field (a coffee jar may be used).
• Hazards of Flaggs can
• Tipping, leading to direct entry of ether into
  the tube and respiratory tract. If side holes
  were completely obstructed, hypoxic mixture will
  be delivered to the patient.

93
(No Transcript)
94
Boyles Ether Vaporizer(1920)
Cork connected to mental chain.
ETHER 300ml copper
TRILENE lt300 ml steel
95

• Plenum, flowover and/or bubble through,
  non-temperature compensated, multiple
  agentsether, trichloroethylene, chloroform,
  methoxyflurane and VOC.
• It is a glass bottle with a copper lid which
  contains a bypass channel, lever and plunger.
• Copper is an anticatalyst which prevents
  decomposition of ether.
• The U shaped inlet tube within the vaporizer
  and the cap of the plunger are made from unplated
  copper.

plunger
96
A. Off B.
Onflowover C. Plunger
depressed bubble through
97
(No Transcript)
98
Goldman (1959)

• Classification
• Drawover(low resistance)
• Variable bypss
• Flowover,
• Multiple agentshalothane, isoflurane,
• Non-calibrated,
• VIC/VOC.
• Capacity 30 mL
• Max 3 halothane

99

• Construction
• It consists of
• Small glass bowl.
• Bowl is attached to head which receives gas and
  divides gas between vaporizing chamber and by
  pass
• A control lever on the top is used to alter the
  vaporizer output and is turned counterclockwise
  to increase the concentration.

• DISADVANTGE-
• Non-temperature compensated(so warm towel is
  used)
• Shaking can increase concentration. So never
  carry a filled vaporizer.

100
Rowbotham

• Similar to Goldman but has high resistance
• modified with steel wire-gauze wick.

101
Oxford Miniature Vaporizer

• Classification
• Drawover
• flowover,
• non-temperature compensated
• multiple agentether, trilene, halothane
  (detachable scales for each).
• Capacity 30 mL

102

• ADVANTAGE-
• low resistance
• Steel wicks increase vaporizaton
• Has antifreeze
• Scales are detachable

103
Epstein Macintosh Oxford Ether Inhaler

• Classification
• 24cm
• OMVEM to be used in war field and can cause
  faster induction of ether.

23 cm
104
(No Transcript)
105
Copper Kettle

• Classification
• Plenum
• Measured flow
• Bubble through
• Non-temperature compensated but has heat sink
• VOC
• Multiple agents

106

• Principle
• A small precise volume of carrier gas is
  completely saturated with the anesthetic agent
  and a predetermined amount is added to the FGF.
• This differs from the percentage v/v of the
  total gas flow which is used in other vaporizers.
  
• Every time the FGF is changed the vaporizer
  setting has to be manually changed.
• This system requires continuous close attention
  and modification.

107
(No Transcript)
108
Tec(Temperature compensted) vaoporizer
Mordern vaporizer Properties- 1. Variable
bypass 2. Flow over with wick 3. Out of system 4.
Temperature compensated by automatic flow
alteration 5. Concentration calibrated 6. Agent
specific.
109
Knob instead of dial
inlet
outlet
Draining port
110
Thymol of halothane damages the bimetalic strip.
So from tec 3 inside bypass chamber
111
Colour coded
Dial instead of knob
112
Tec 2 was notorious for pumping effect and
tilting of 10 degrees
TEC 3
Tec 3 allows 90 degree
MAJOR ADV- prevents pumping effect
113
(No Transcript)
114
Needs both hands to activate same as tec 3
115
Because release button is on posterior side
116
Long inlet reduces pumping effect
Thermocompensatory mechanism is in close contact
with the liquid.
117
Quick fill and easy fill
118
Super six of Desfurane

1. In chemical structure 6 fluoride atoms
2. Oil gas partition coefficient -18
3. Blood gas partition cofficent-0.42
4. Brain blood partition coefficient - 1.2
5. SVP at 20 centigrade- 666
6. Boiling point -22.8
7. MAC-6
8. Vaporizer-Tec 6
9. Maximum dial setting -18
10. Interim stop -12
11. No of indicators- 6
12. Technique of induction-propofol then 6L/min FGF
    and change dial settings every 2 breaths by 1
    till 6 and maintain it at same for 6 minutes

119
Desflurane Vaporizer (Important question)

• Desflurane has a very low boiling point and even
  at room temperature, has an high vapor pressure.
• Also, for small changes in temperature, the vapor
  pressure of desflurane changes quite
  dramatically.
• I.e. desflurane is said to have a very steep
  Vapor Pressure versus Temperature curve.
• An operating room temperature is not perfectly
  constant.
• These physical properties creates a big headache
  for vaporiser designers.

120

• the standard vaporisers try to resist changes in
  temperature (e.g. by having thick metal
  construction).
• However, these mechanisms are not perfect and in
  practice small changes in vaporiser temperature
  still occur.
• This is not a big problem with anaesthetic agents
  such as Iso or Sevo which have a relatively less
  steep Vapor Pressure versus Temperature curves.
• With Des, with its steep curve, even these small
  temperature changes can cause large changes in
  vapor pressure which cannot be compensated for
  with simple devices such a bimetallic strip.
• So a whole new vaporiser design had to be made
• DUAL CIRCUIT GAS VAPOR BLENDER

121
Solution?

• precisely control the temperature.
• The heated vapor is then injected into the
  fresh gas flow.
• In this method, the fresh gas flow coming from
  the flow meters does not split into two streams.
• There is only one stream for the fresh gas flow,
  and into this stream, the anaesthetic agent is
  directly injected.

122

• There is a tank (sump) which contains desflurane
  which is electrically heated to a highly
  controlled constant temperature (approx. 400C).
• Because of the heat, the liquid Desflurane
  becomes gaseous Desflurane at a pressure of about
  two atmospheres (about 1500 mmHg or 200 kPa).

123

• The amount of Desflurane concentration in the
  fresh gas is controlled by the dial setting set.
• The dial moves a valve which varies the
  resistance to Desflurane flow from the tank to
  the fresh gas.
• If we want a higher concentration of Desflurane,
  the valve attached to the dial reduces the
  resistance to flow of Desflurane and more of it
  gets injected into the fresh gas.
• Conversely, if we want a lower concentration of
  Desflurane, the valve attached to the dial
  increases the resistance to flow and less of it
  gets injected into the fresh gas.

124
(No Transcript)
125

• If we increase the fresh gas flow, but didnt
  increase the injection rate, the emerging mixture
  will now be inaccurate, the concentration being
  lower than before. A similar thing might happen
  if we increase the rate of injectate without
  increasing FGF.
• The rate of Desflurane gas injection must be
  adjusted to match the fresh gas flow going
  through the vaporiser.

126
Solution?

• Manually adjust the dial setting to match the
  fresh gas flow. For low flows, we have to reduce
  the dial setting to reduce the rate of Desflurane
  injection, and for high fresh gas flows, we need
  to do the opposite.
• This would be really tedious in our modern times.
• Fortunately, the Desflurane vaporiser
  automatically adjusts the rate of injection of
  desflurane to match the flow rate, and thus keeps
  the delivered concentration constant.

127

• Flow meters deliver the fresh gas flow 1.
• The fresh gas travels through pipe 2.
• Note that, unlike other vaporisers, none of the
  fresh gas goes to the vaporising chamber 4.
• The vaporising chamber is electrically heated
  3.
• Using sensors for feedback, the temperature is
  kept very constant.
• The heating causes the Desflurane to become a gas
  under pressure 4 and this travels down pipe 5.

128

• The flow of Desflurane is resisted by two valves
  6,13.
• Valve 6 is the valve that we control when we
  set the dial to a particular concentration.
• When we increase the concentration setting, the
  valve 6 opens a bit and lowers the resistance,
  allowing more Desflurane to flow through.
• Valve 13 is an electronically controlled valve.

129

• Computer 12, the vaporisers brain, is able
  to also alter the flow of Desflurane by
  controlling valve 13. i.e. both we and the
  computer can adjust the desflurane injection
  rate.
• The Desflurane then goes via pipe 7 and meets
  the fresh gas at 8.
• The Desflurane mixes with the fresh gas 8 and a
  final concentration emerges from the exit of the
  vaporiser 9.

130

• How the vaporiser, keep the output concentration
  accurate, adjusts the Desflurane flow when the
  fresh gas flow changes?
• As explained before, the fresh gas flows in pipe
  2.
• This pipe has a fixed resistance 10 in its
  path.
• For the fresh gas flow to overcome this
  resistance 10, the pressure in pipe 2 rises.
• Higher the fresh gas flow in pipe 2, higher
  will be the pressure rise in pipe 2 since more
  flow has to occur through the same fixed
  resistance 10.

131

• Similarly, when the fresh gas flow is decreased,
  the lesser flow will find it easier to go through
  the fixed resistance and the pressure in pipe 2
  drops.
• It is important to remember that the pressure in
  pipe 2 is proportional to the fresh gas flow
  going through it.
• Higher the flow, higher is the pressure in pipe
  2.
• Lower the flow, lower is the pressure.

132

• Device 11 is called a differential pressure
  transducer.
• It has a diaphragm that on one side is exposed to
  the pressure in pipe 2 carrying fresh gas and
  the other side is exposed to the pressure in pipe
  5 carrying Desflurane.
• When the pressure is equal neutral position
• If one side of the diaphragm is at a higher
  pressure than the other side, the pressure
  difference makes the diaphragm move.
• It continuously keeps computer 12 informed
  about pressure difference information.

133

• For example, when the fresh gas flow is increased
  1.
• Increased fresh gas flow flows through pipe 2
  and meets fixed resistance 10.
• The increased flow through the fixed resistance
  10 makes the pressure in pipe 2 to rise and
  this pressure is experienced by differential
  pressure transducer 11.
• Since the Desflurane pressure in pipe 5 is now
  lower than the fresh gas pressure in pipe 2,
  the diaphragm in the differential pressure
  transducer 11 moves and a signal about the
  pressure difference is sent to the computer 12.

134

• The computer 12, acts on the information
  provided.
• It proceeds to increase the flow of Desflurane to
  inject into the increased fresh gas flow.
• It commands the electronically controlled valve
  13 to reduce the resistance to flow.
• As the valve 13 opens up and lowers the
  resistance, the Desflurane flow increases.

135

• The increased flow of Desflurane causes the
  pressure in pipe 5 to rise.
• This pressure rise pushes the diaphragm of the
  differential transducer back to its neutral
  position 11.
• The differential transducer 11 informs the
  computer 12 that the diaphragm is in the
  neutral position.
• The computer 12 is now stops further opening of
  valve 13 .
• Since the two flows are matched, the output
  concentration 9 does not change despite the
  increased fresh gas flow.

136
Is this necessary?
137

• Classification of desfurane vaporizer
• Concentration calibrated
• Thermocompensated (electrically supplied heat)
• Agent-specific
• Out-of circuit
• Plenum
• Gas-vapour blender.

138
(No Transcript)
139

• The various color-coded alarms are
• Amberwithout audible alarmwarmup,
• Amber along with audible alarmlow agent level
  below 50 mL
• Greenoperational status
• Redno outputdue to
• Low agent level less than 20 mL
• Power failure
• Malfunction
• Tilted vapourizer beyond 10 degrees
• A liquid crystal display (LCD) indicates the
  amount of liquid in the vapourizer
• Once the vapourizer is connected to an electrical
  source, the vapourizer sump gets heated to 39C.
• During this warm-up phase, the concentration dial
  is in standby mode and the vapourizer cannot be
  used.
• Once the proper temperature is achieved, the
  green light comes on indicating readiness for
  operation

140

• Hazards with desfurane vaporser
• Vapor may leak into the fresh gas when the
  vaporizer is off
• The bottle may be dropped when released under
  pressure
• If the machine uses fresh gas decoupling, special
  software needs to be installed
• The vaporizer should be placed such that its
  power cord does not cause problems with the
  seating and mounting of other vaporizers.

141
(No Transcript)
142
Draer 19.1
143
(No Transcript)
144
(No Transcript)
145
(No Transcript)
146
(No Transcript)
147
(No Transcript)
148
Electronic- automatic record keeping. Magnetic
coding for specificity Light weight
149
HAZARDS and SAFETY FEATURES IN VAPORISERS

• Incorrect concentration delivered
• Misfilling
• Tipping
• Leaks
• Overfilling
• No Output
• Reversal of flow

150
Incorrect concentration delivered

• HIGH CONC.

• LOW CONC.

• Liquid anesthetic in delivery tube
• Pumping effect
• Reversed flow
• Agitation

• Cooling of liquid
• Pressurizing effect
• Wicks covered with liquid
• Very low/high flows.

151
(No Transcript)
152
FILLING SYSTEMS in vaporisers

• These systems reduce the air pollution associated
  with filling and draining vaporizers.
• Types
• Screw Fill
• Key Fill Systems prone to mis-filling
• Easy-Fil
• Solution
• Quik-Fil
• Saf-T-Fil

153
(No Transcript)
154
Screw Fill

• The early plenum vaporizers had a filling port at
  the bottom, and a liquid level indicatorsight
  glass.
• The screw threaded stopper is unscrewed, agent
  filled and stopper replaced.
• Filling should stop when the level reaches the
  recommended maximum on the indicator.
• Hazards are filling the wrong agent, overfilling,
  and environmental pollution.

155
Key Fill Systems
The various parts are made to align and fit into
each other like a key in a lock. The design of
the projections and the slots they fit in are
unique for each individual agent.
B
A
Key fill system. A. Halothane B. Isoflurane C.
Isoflurane key filler with vaporizer
156

• In addition to the physical shapes being
  different, the key fillers are also color coded
• The Isoflurane bottle has notches in them
  arranged in a way that is specific for
  Isoflurane.
• The Isoflurane key filler has specific
  corresponding cuts where the notches of the
  bottle will fit. This makes sure that you cannot
  fix the wrong filler key into the wrong bottle.

157
Isoflurane filler (key) has a notch in a corner.
This fits perfectly with the filling hole in the
Isoflurane vaporiser. The filling hole has pin at
the corner over which the notch of the Isoflurane
filler key can pass over. Not possible to fill,
as halothane key has side notch and isoflurane
vaporizer has corner pin.
158
Easy-Fil

• The principle is similar to the key-fill system.
• It is easier to use.
• The port on the vaporizer has been modified with
  corresponding modification to the distal end of
  adaptor.
• The filler channel and the bottle adaptor have
  grooves and ridges which align with each other.
• Each agent has a unique combination.

159
Quik-Fil

• Sevoflurane bottles are sealed and an agent
  specific filling device is fitted permanently on
  to the neck with a tamper proof crimped metal
  seal.
• The bottle is opened and inverted onto the
  filling port.
• A valve opens when a slight pressure is applied
  on the bottle and the agent enters the vaporizer.
  
• This prevents spilling and minimizes pollution.

160
Saf-T-Fil

• It has a filler nozzle which fits into the filler
  port of TEC 6.
• It is crimped onto the neck of the bottle.
• The nozzle is pushed onto the spring loaded
  aperture of the port and the bottle is inverted.
• The contents enter the vaporizer. The LCD display
  indicates the level.
• When filling is complete the bottle is returned
  to the starting position and the spring then
  ejects the filler nozzle.
• Advantage---The vaporizer can be filled while in
  use.
• The bottle is pressurized as Desflurane can boil
  at the ambient temperatures encountered.
• If the vaporizer has been removed from the back
  bar and a tilt is present, overfilling can occur.
  
• The shut-off valve prevents the liquid from
  leaving the sump.

161
(No Transcript)
162
VAPORIZER MOUNTING SYSTEMS

• Permanent
• Detachable
• Select-a-tec system
• Dräger Medical mounting system

163
Permanent Mounting Vaporiser

• Require tools to remove or install a vaporizer on
  the anesthesia machine.
• Advantage- less physical damage to vaporizers and
  fewer leaks.
• Disadvantage-
• Inadequate number of mounting locations
  to accommodate all the vaporizers that are likely
  to be needed.
• If there is a malfunction and the
  vaporizer needs to be exchanged, it cannot be
  easily removed especially with a case underway.

164
Detachable Mounting Vaporiser

• Here the vaporizers can be mounted or removed
  without using tools.
• They are standard on most new anesthesia
  machines.
• The Select-a-tec system and a similar system from
  Dräger Medical are widely used.
• There is no interchangeability.
• Advantages
• More compact anesthesia machine as fewer mounting
  locations needed.
• Replacement is possible during a case.
• If malignant hyperthermia is a potential problem,
  the vaporizers can be removed altogether.

165

• Disadvantages
• Partial or complete obstruction to gas flow can
  occur due to misalignment
• Potential for leaks is high, a common leak source
  is an absent or damaged O-ring or if the locking
  lever is unlocked
• Awareness can occur if there is failure to
  deliver agent vapor to the fresh gas due to
  problems with the mounting system
• If something is pushed under the vaporizer enough
  so that it slightly lifts off the O-ring, a leak
  may result when the vaporizer is turned ON

166
(No Transcript)
167
Dräger Medical mounting system

• It has different dimensions.
• The Vapor 2000 vaporizer must be in the T
  (travel) position before it can be unlocked from
  the machine.
• This position isolates the vaporizing chamber and
  prevents liquid from passing into the bypass
  during the time that the vaporizer is not on the
  machine.

168
INTERLOCK DEVICES

• These are vaporizer exclusion systems which
  prevent more than one vaporizer from being turned
  on at the same time.
• These should be checked with the anesthesia
  apparatus checkout procedure.
• Examples
• Select-a-tec interlock system
• Dräger vapor exclusion system
• Dräger Interlock II system

169
Select-a-tec interlock system(let us delete this
topic)

• When the dial release on the Datex-Ohmeda/GE
  vaporizers is unlocked and the dial moved a pin
  moves two extension rods which project out and
  the concentration control dials of the
  neighboring vaporizers become inoperational

• Select-a-tec interlock system.
• When both vaporizers are off
• When the first vaporizer is turned on

170
Dräger vapor exclusion system

• The Dräger vaporizers have a vapor exclusion
  system which consists of notches on the back of
  the concentration control dials.
• If a vaporizer is turned on, a pin occupies the
  notch of the adjacent vaporizers rendering the
  dial inoperational.
• In this system, each vaporiser has two pins
  protruding out.
• When the vaporiser is in use, the pins protrude
  outwards.
• When the vaporiser is turned off, the pins
  retract back to where they were.
• On the other hand, if any of the pins are pushed
  in (i.e. by another vaporiser) this locks the
  vaporiser dial in the OFF position.
• When the pin is no longer pushed in, the dial
  once again becomes unlocked and can be turned.

OFF
ON
171
WHEN ONE IS ON, IT PUSHES THE OTHER PIN AND TURNS
IT OFF
172
Dräger Interlock II system

• In the Dräger Interlock II system the operator
  moves a rod to release the concentration control
  dial of the vaporizer to be used. This locks the
  dial of the other vaporizer in place

173
Sequence of Vaporizers

• Vaporizers should not be used simultaneously.
• Old anesthesia machines had up to three
  variable-bypass vaporizers arranged in series
  such that fresh gas from the flow meters passed
  through each vapourizer to reach the common gas
  outlet of the anesthesia machine.
• Without the use of an interlock, it was possible
  to turn on all vaporizers simultaneously.
• This could lead to
• Overdose of anaesthetic
• Vapour from one vapourizer could condense in the
  downstream vapourizer leading to contamination.

174

• Hence, the order in which they are mounted
  becomes important.
• If the vaporizers are placed downstream of the
  common gas outlet then the use of oxygen flush
  can deliver large quantities of inhaled
  anesthetic to the patient.
• The volatile anesthetics are added to the gas
  mixture downstream from the flow meters and
  proportioning system. Hence when using high
  concentration of low potency inhaled anesthetics
  (maximum dial setting for desflurane is 18) it
  is possible to create a hypoxic mixture when you
  give desflurane in air.

175

• If vaporizers are to be placed in series, the
  vapourizer for the more volatile agent should be
  placed upstream (i.e. further from the patient)
  from the vapourizer for the less volatile. If
  this point is neglected, condensation of the less
  volatile agent (which will have a higher boiling
  point) will occur in a cooler downstream
  vapourizer.
• Vaporizers with les