Principles of vaporizers and older vaporizers

Report
Presented by: Dr Rashmi
Moderator: Dr Kartik Syal
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1847:
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1952:
◦ John Snow (1813-1858)
◦ described the relationship between temperature
and the saturation of ether vapor
◦ first major milestone in the attempt to control the
strength of anesthetic vapor administered to
patients
◦ Dr. Lucien E. Morris (1914-2011)
◦ Copper Kettle vaporizer
◦ first system to permit very fine control over the
concentration of volatile anesthetics
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A vaporizer is an instrument designed to facilitate the
change of a liquid anaesthetic agent into a vapor and
add a controlled amount of this vapor to the gas flow
to the patient.
known and reproducible concentration of anaesthetic
vapour delivered in a safe and reliable manner
A vapour is the gaseous phase of an agent which is
normally a liquid at room temperature and
atmospheric pressure.
May be expressed as
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VOLUME % :- it’s the concentration of gas in a
mixture. / no of units of volume of gas in 100 units of
vol of total gas mixture
PARTIAL PRESSURE :- In a mixture of gases the
pressure exerted by each gas is the same as that which
it would exert if it alone occupied the container
Method of regulating output concentration
1. Concentration calibrated (variable-bypass)- direct
type
2. Measured flow - indirect type
Method of vaporization
1. Flow over
2. Bubble Through
3. Injection
Temperature compensation
1. Thermo-compensation
2. Supplied heat
Specificity
Agent specific
Multiple agent
Resistance
1. Plenum
2. draw over
VIC / VOC
Total flow from the machine split by a variable resistance
proportionating valve
◦ One part (usually major): through bypass chamber &
◦ Other
(usually small): through vaporizing chamber
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agent concentration controlled by dial calibrated in volumes
percent
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ratio of the bypass gas to gas going to the
vaporizing chamber
depends on:
Resistance of the two pathways,
depends on the variable orifice of the inlet/outlet.
Temperature of the liquid/carrier gas.
Flow rate of gases
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separate, independent stream of vapour carrying gas,
added to the fresh flow
To calculate the vaporizer output, to know
Vapor pressure of the agent
The atmospheric pressure
The total flow of gases
The flow of the vaporizer
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Eg: Ohmeda Tec 6, sp for Desflurane, copper kettle
Method of vaporization:
Flow over Vaporizers : carrier gas flows over the
liquid agent, saturated with vapor.
Bubble through Vaporizers : carrier gas is bubbled
through the liquid agent
 Injection Vaporizers : known amount of liquid
agent or pure vapor injected into the gas stream to
provide the desired concentration.
TEMPERATURE COMPENSATION
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maintain a constant output
compensation for fluctuations in temperature
 Cooling affects vapour concentration.
 Mech:
Alteration in the splitting ratio (automatic
compensation)
Eg. Bimettalic strip in tec vaporizer
 Supplied heat – tec 6 (electrically heated)
 copper metal
 Ether filled copper bellows ex Penlon vaporisers
TEMPERATURE UNCOMPENSATED: boyle’s bottle, goldman etc
TEMPERATURE BUFFERING hot water jacket/ heat sink (ex
OMV)
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On cooling, bimetallic strip bends,moves away
reduces the resistance to flow=more flow into
vaporizing chamber
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SPECIFIC AGENT
use with one specific agent.
Must be labeled
Use of other agents may give incorrect
concentration, may damage vaporizer, harmful
byproducts.
MULTIPLE AGENT :Rarely in use, not advised.
Ex OMV, EMO, Copper kettle
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VOC = Vaporizer-outof-system
localized
btwn
flowmeter and CGO
Oxygen
from
the
flowmeter enters the
vaporizer
prior
to
entering the breathing
circuit.
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VIC = Vaporizer-insystem
Oxygen enters the
breathing circuit from
the flowmeter
either in circle , at
CGO, inhalers i.e in
breathing sytem – gas is
drawn through it by pts
breathing
spontaneously.
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Comparison of the two on basis of
RESISTANCE
DETERMINANTS OF VAPORIZER OUTPUT
CAPABILITY OF THE VAPORIZER
resistance :- VOS Need not hv low resistance as gas flow can be
supplied at any necessary pressure.
VIS Must have low resistance because pt breathes through them
Determinants of vaporizer output :vaporizer output -conc of vapor at outlet of vaporizer. (vo)
vaporizer conc :- conc delivered by vaporizer when fresh gas
containing no vapour passess through it . (vc)
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in VOC both VO & VC are equal
in VIS , BOTH the VC & VO are likely to differ..the VO will be
influenced by MV, uptake of agent, FGF to system and arrangement
of system ..with Low FGF, VO may rise to dangerous levels.
CAPABILITY OF VAPORIZER :- maximum concentration that can
be delivered at highest setting of conc dial..
VIS/ VOS used in non rebreathing system must have a high
capability as no more anesthetic will be added to gas going to pt.
but in circle system vaporizer, its not capable of delivering high
conc, because the gas may circulate through it many times, each
time picking up added vapors.
RESISTANCE
 PLENUM ( Latin = fullness )
 Driven by positive pressure ventilation
 internal resistance is high (22 cmH2O), accurately
caliberated
 Accurate at low flows also
 Eg. Boyle bottle, copper kettle, TEC vaporizers
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DRAW OVER
Carrier gas drawn through the vaporizer either by the patient’s own
respiratory efforts, or by a self-inflating bag or manual bellows
operate at less than, or at ambient pressure
Intermittent flow, varying with different phases of inspiration, ceasing in
expiration.
low internal resistance
may be used in a non rebreathing DRAW-OVER APPARTUS,
CIRCLE ABSORBER SYSTEM.
Eg. Goldman bottle, EMO
or in
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ADVANTAGES
Simplicity of concept and
assembly, with inherent
safety
No need for pressurised gas
supply, regulators and flow
meters
Minimum FiO2~21%
Robust, reliable, easily
serviced equipment
Low cost (purchase and
maintenance)
Portable, suitable for field
anaesthesia
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DISADVANTAGES
Decreasing familiarity with
the technique and
equipment
Filling systems not agent
specific (potential
advantage)
Basic temperature
compensation, affecting
performance at extremes
Less easy to observe
spontaneous ventilation
with self inflating bag
Cumbersome in paediatric
use, unless lightweight
tubing is available
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flow through the vaporizing chamber.
surface area of the liquid gas interface.
temperature
time
gas flow rate
carrier gas composition
boiling point
ambient pressure :-atmospheric, intermittent back pressure
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Low pressure: vaporizing chamber offers less resistance,
slight increase in vapor output occurs.
Deliver higher conc in vol. % but same Partial pressure
High pressure: INCREASES the Density of gas, More
resistance to flow of gas through the vaporizing chamber,
Decreased vapor output (Volume Percent)
Less Effect on partial pressure
ether may boil at room temp at low atm pressure.
Also at high pressure, liqiud agent may be pushed back into
the vaporiser inlet
avoided by maintaining a low flow of oxygen or filling the
vaporiser after increase in pressure.
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should theoretically deliver a constant partial
pressure of anesthetic if the ratio of gas flow
through the vaporizer to bypass the flow remains
the same.
For classical plenum vapourisers, the percentage
output increases roughly in proportion to the fall
in barometric pressure, but a smaller partial
pressure increase.
TEC 6 Desflurane vapouriser behaves differently.
The percentage delivered constant, so partial
pressure FALLS in proportion to the fall in
atmospheric pressure. The dial setting should be
turned up to compensate
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The increase in vaporizer output concentration due to
pulsatile back pressure developed in the breathing
system.
more fresh gas gets compressed into vaporising chamber
 seen especially when
-> carrier gas flow is low
-> agent in vaporizing chamber is low
-> dial setting is low
-> pressure fluctuations are high & frequent.
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keep VC (vaporising chamber)& BC (bypass channel) of
equal size/ VC small size.
Add long spiral or large diameter tube to lead to the
vaporizer chamber
add check valve, increase resistance to gas flow through V.C.
Exclude wicks from the area where the inlet tube joins the
vaporizing chamber.
Longer Outlet tube
Limit pressure transmitted to vaporizer to <10KPa above
normal working pressure, conc not to increase > 20%.
Increased constant pressure in vaporizer chamber
leads to decreased output
 Mostly seen when
-> High flow
-> Large pressure fluctuations
-> Low dial settings
The changes in vaporizer output caused by the
pumping effect usually are greater in magnitude
that those associated with the pressurizing effect
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INCORRECT AGENT
 Low output or high output
 Rx : Gas allowed to flow through it until no agent
detected in the outflow, labelling correctly.
RESISTANCE
TIPPING
 Liquid
from
the
vaporizing
Chamber→
bypass/outlet→ high output
 Drained before moving
OVERFILLING
 safety mechanisms: design of the filling port, agent
specific filling systems
 During filling dial to be off
FOAMING
 possibility of liquid agent getting into the outlet.
 Seen in bubble through vaporiser for methoxyflurane.
 foaming due to silicone grease, (used as a lubricant) or
solution used to test for leaks.
REVERSED FLOW
• Inlet male & outlet female
• Increased output
 CONCENTRATION DIAL IN WRONG POSITION
 CONTAMINANTS IN VAPORIZING CHAMBER
 PHYSICAL DAMAGE
 OBSTRUCTION TO FRESH GAS FLOW
 INTERLOCK MALFUNCTION
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Boyle’s bottle
Copper kettle
EMO (epstein, macintosh, oxford) vaporiser
Goldman vaporiser
OMV (oxford miniature vaporiser)
Cyprane
Vernitrol
others
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Useful in remote locations like military use, as
portable and simple to use (ex EMO)
Some peripheral setups still use goldman
vaporiser
Draw over vapouriser (2 OMVs with
sevoflurane) can be used in Paediatric circuit
Addition of OMV with ventilator in treatment
of severe asthma (Nagappan et al 2006)
Parts:
(1) vaporizing bottle 300 mL
(2) Metal top incorporating controls
(3) Lever, plunger which is chrome
plated (copper in case of Boyle ether
bottle and absent in halothane bottle)
(4) Stopper & Retaining chain
 Concentration calibrated, plenum
type
 Flowover or bubble through
 Not temperature compensated
 Multiple agents
 Vaporizer outside circuit
 With this bottle, the maximal
ether concentration would be
about 50% at 20 degrees C.
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Developed in 1930’s: modified by
Morris in 1952
measured flow (indirect type)
temperature compensated
bubble through, plenum type
agents – chloroform, ether ,
halothane
a separate supply of oxygen
from extra flowmeter passes
through the vaporizer.
Oxygen broken into minute
bubbles by sintered bronze
large mass of copper and
attachment to machine, sufficient
reservoir for heat
Disadv: high vap conc if FGF dec
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Measured flow
Bubble through
Out of system
Temperature compensated
(supplied heat)
Multiple agent
Body made of silicone
bronze, may contain upto
600 cc of liquid agent.
When used for halothane,
drained
periodically
to
prevent buildup of thymol,
ether and trichlorethylene
should not be allowed to
stand for long.
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originally designed for use with dental anaesthetic apparatus
Concentration caliberated
flow over with no wicks
multiple agents – halothane, chloroform
neither temperature and level compensated nor accurately
calibrated.
halothane concentration usually low (hence safe), output is
mainly influenced by gas flow rate.
VOC / VIC
small glass bottle with metal top, inlet- outlet , contol lever at
top is used to alter vapor output , capacity of 20ml , max
concentration delivered 2 % , (higher if splashing, spraying of
agent, if wick is used, or 2 vaporizers in series.)
3 models of goldman vaporizer are : MARK 1:- self locking in off position
 MARK 2 :- differs from mark 1 in size & shape of
opening in the ports & is provided with click stops at
each setting
 mark 1 and 2 both have three divisions btwn the on &
off positions.
 MARK 3 :- has one less division.
KOMESAROFF
 Similar to the Goldman but with gradations on the
glass bowl indicating volume
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Modification of Goldman
vaporizer (has wire wick
gauge)
simple flow-over type
not temp compensated
capacity of 35 ml
multiple agent
max concentration up to
3.1 % with 4L/ min flow
rate.
vapor
strength
is
controlled by means of
lever stopcock.
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Introduced by Epstein, Macintosh,
Mendelssohn in 1966.
Vaporizer inside/outside circuit
Variables bypass
Flow over with steel wicks (cleaned
with ether)
Not Temperature compensated (heat
sink= heat buffering)
multiple agent, detachable scales
(adv)
Halothane, trilene ,methoxyflurane
,ether, isoflurane.
particularly versatile, can be used to
vaporize a number of agents with
only the dial scale being changed.
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Original models contained 20mls of volatile agent, more modern
ones 50mls.
not temp compensated but basic thermal buffering in the form of a
small glycol (anti-freeze) reservoir within a metal heat sink.
reduced vapor output at lower temperatures, maximum output 24% with halothane between 0-30OC.
Made from stainless steel, resistant to corrosion.
Metal mesh wicks increase the output (halothane use, clogged with
thymol)
Using two OMVs with a drawover system appears to be a feasible
technique for the induction and maintenance of sevoflurane
anaesthesia, thus enabling wider use of sevoflurane in field
anesthesia. (study by Liu et al in 2000)
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Concentration caliberated
Flowover with wicks
Temp compensated (metal bellows with freon vapor)
Multiple agents- ether, chloroform, trilene, halothane
Dia:23 cm; Ht : 24 cm
Wt(ether) : 6 kg; (halothane) : 12 kg
0 – 20% graduations
40 ml ether when full
Inlet for air
Control lever with transit lock
Indicator to denote level of anaesthesia
Temp indicator (max eff 15-30 C)
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Water jacket : 1250 cc
Mark I: aluminium water jacket
Mark II/III/IV: stainless steel jacket
Used with OMV for spont resp
OMV filled with halothane for smooth
induction , maintained with ether in EMO
EMOTRIL (Epstein, Macintosh, Oxford Trilene inhaler)
 Introduced in 1949.
A draw over Trilene vaporizer
giving 0.35 and 0.5% Trilene in air, temperature
compensated, designed for unsupervised use by
midwives for pain relief during labor.
BRYCE-SMITH INDUCTION UNIT (BSIU)
 no longer manufactured.
 useful to facilitate induction when using the EMO
ether vaporizer
 simple no-controls vaporizer
 delivers 3 - 4 mls of halothane to precede, and assist
induction with, ether.
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device for trilene inhalation originally from
the Queen Victoria Hospital.
Maternity patients would hold the device and
inhale an air-trilene mixture.
The collar of the device could be rotated to
vary the concentration from about 0.22% to
0.54%. The collar can be locked.
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Designed in Sydney by Dr
Thomas Small, in the
mid
1930's,
for
the
provision
of
analgesia
during labour.
The
ether
container
consists of a chrome plated
brass drum which holds
270mls.
The control on top varies
the ether concentration.
Valves ensure unidirectional
flow,
and
a
separate
expiratory valve is on the
face mask mounting.
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Diamedica Draw-Over
Vaporizer (DDV) has
been developed as an
alternative
to
the
Oxford
Miniature
Vaporizer (OMV)
can function as drawover or plenum
larger
reservoir,
tendency
towards
greater
accuracy
during
IPPV
and
improved consistency
of output.
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Ohmeda Universal PAC drawover apparatus, a
modification of an earlier series of vapourspecific vaporizers
Caliberated, temperature compensated, flow over
Oxygen may be added but not necessary
clinical usage with isoflurane and enflurane
Tends to over-deliver vapour, esp at low flows
and at high temperatures
clinical performance during spontaneous and
positive pressure ventilation satisfactory
robust construction, relatively large capacity and
thermocompensation make it suitable for field or
military anaesthesia.
Cole halothane vaporiser
Ether bypass

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