7/27/2019 Chapter 6. Vaporizers
1/111
Chapter 6
VaporizersP.122
Most of the inhalational anesthetic agents in use today are l iquids at atmospheric
pressure and room temperature and must be converted into vapors before they can
be used. A vaporizer (anesthetic agent or vapor delivery device) is a device that
changes a l iquid anesthetic agent into its vapor and adds a controlled amount of
that vapor to the fresh gas f low or the breathing system. Up to three vaporizers are
commonly attached to an anesthesia machine.
Physics
Vapo r P r e s s u r e
Figure 6.1Ashows a volat i le l iquid inside a container that is closed to atmosphere.
Molecules of l iquid break away from the surface and enter the space above, forming
a vapor. I f the container is kept at a constant temperature, a dynamic equil ibrium is
formed between the l iquid and vapor phases so that the number of molecules in the
vapor phase remains constant. These molecules bombard the walls of the
container, creating a pressure. This is called the saturated v apor pressure and is
represented by the density of dots above the l iquid.
I f heat is supplied to the container (Fig. 6.1B), the equil ibrium wil l be shif ted so
that more molecules enter the vapor phase and the v apor pressure wil l r ise. I f heat
is taken away from the system (Fig. 6.1C), more molecules wil l enter the l iquid
state, and the vapor pressure wil l be lower. I t is meaningless, therefore, to talk
about vapor pressure without specifying the temperature. Vapor pressures of some
anesthetic agents at 20C are shown in Table 6.1. Vapor pressure depends only on
the l iquid and the temperature. I t is not affected by ambient pressure within the
range of barometric p ressures encountered in anesthesia.
Bo i l i n g Po i n t
A l iqu id's bo il in g poin t is th e tempe rature at wh ic h its vapor pres sure is equal to th e
atmospheric pressure. The boiling point will be lower with lower atmospheric
pressure. Anesthetic agents with low boil ing p oints are more susceptible to
variat ions in barometric pressure than agents with higher boil ing points. The boil ing
points for some anesthetic agents are shown in Table 6.1 .
7/27/2019 Chapter 6. Vaporizers
2/111
P.123
View Figure
Figure 6.1Vapor pressure changes with varying
temperature. A:The liquid and vapor are in equilibrium. B:The application of heat causes the equilibrium to shift sothat more molecules enter the vapor phase, as illustrated bythe increased density of dots above the liquid. C:Loweringthe temperature causes a shift toward the liquid phase and adecrease in vapor pressure. D:Passing a carrier gas over theliquid shifts the equilibrium toward the vapor phase. Theheat of vaporization is supplied from the remaining liquid.This causes a drop in temperature.
Gas Con c e n t r a t i o n
Two methods are commonly used to express the concentrat ion of a gas or vapor:
Part ial pressure and volumes percent (vol %).
Partial Pressure
A mix ture of gases in a c losed conta ine r wi l l ex ert a p ressure on th e wa lls of the
container. The part of the total pressure due to any one gas in the mixture is called
the part ial pressure of that gas. The total pressure of the mixture is the sum of the
part ial pressures of the constituent gases. The part ial pressure exerted by the
vapor of a liquid agent depends only on the temperature of that agent and is
unaffected by the total pressure above the l iquid. The highest part ial pressure that
can be exerted by a gas at a given temperature is its vapor pressure.
TABLE 6.1 Properties of Common Anesthetic Agents
7/27/2019 Chapter 6. Vaporizers
3/111
Heat of
Vaporization
Specif ic Heat
of Liquid
Agent
Trade
Name
Boiling
Point
(C,
760
mm
Hg)
Vapor
Pressu
re
(torr,
20C)
Density
of Li qu i
(g/mL) cal/g cal/mL cal/mL cal/g
MACa
in O2
(%)
Haloth
ane
Fluot
hane
5
0.2
2
43
1.8
6(20
C)
35
(20C)
65
(20C)
0.
35
0.
19
0.
75
Enflur
ane
Ethra
ne
5
6.5
1
75
1.5
17(25
C)
42
(25C)
63
(25C)
1.
68
Isoflurane
Forane
48.
5
23
8
1.496
(25C)
41(25
C)
62(25
C)
1.1
5
Desflurane
Suprane
22.8
669
1.45
(20C)
6.4
Sevoflurane
Ultane
58.6
157
2.0
aMinimum anesthetic concentration.
Adapted with permission from Quasha AL, Eger EL, Tinker JH. Determinaion andapplications of MAC. Anesthesiology 1980;53:315334.
Volumes Percent
7/27/2019 Chapter 6. Vaporizers
4/111
The concentrat ion of a gas in a mixture can also be expressed as i ts percentage of
the total volume. Volumes percent is the number of units of volume of a gas in
relat ion to a total of 100 units of v olume for the total gas mixture. In a mixture ofgases, each constituent gas exerts the same proport ion of the total pressure as its
volume is of the total volume. Volumes percent expresses the relat ive rat io of gas
molecules in a mixture, whereas part ial pressure expresses an absolute value.
Part ial Pressure/Total pressure = Volumes percent
Al though ga s and vap or concen trations deliv ered by a vaporizer are usua lly
expressed in volumes percent, pat ient uptake and anesthetic depth are direct ly
related to
P.124
part ial pressure but only indirect ly to volumes percent. While a given part ial
pressure represents the same anesthetic potency under various barometric
pressures, this is not the case with volumes percent (1).
Heat o f Vapo r i z at i o n
I t takes energy for t he molecules in a l iquid to break away and enter the gaseous
phase. A l iquid's heat of vaporizat ion is the number of calories necessary to
convert 1 g of l iquid into a v apor. Heat of vaporization can also be expressed as
the number of calories necessary to convert 1 mL of l iquid into a vapor. The heats
of vaporizat ion of some anesthetic agents are shown in Table 6.1.
Liquid temperature decreases as vaporizat ion proceeds. As the temperature fal ls, a
gradient is created so that heat f lows from the surroundings into the l iquid. The
lower the liquid temperature, the greater the gradient and the greater the flow of
heat from the surroundings. Eventually, equil ibrium is es tablished so that the heat
lost to vaporizat ion is matched by the heat supplied from the surroundings. At this
point, the temperature ceases to d rop.
In Figure 6.1D, a f low of gas (carrier gas) is p assed through the container and
carries away molecules of vapor. This causes the equil ibrium to shif t so that more
molecules enter the vapor phase. Unless some means of supplying heat is
available, the l iquid wil l cool. As the temperature drops, so does the v apor pressure
of the l iquid, and fewer molecules wil l be picked up by the carrier gas so that there
is a decrease in concentrat ion in the gas f lowing out of the container.
Spec i f i c Hea t
7/27/2019 Chapter 6. Vaporizers
5/111
A substa nce's spec ifi c hea t is th e quanti ty of hea t re qui red to ra ise the te mpera tu re
of 1 g of the substance by 1C. The higher the specific heat, the more heat that is
required to raise the temperature of a g iven quantity of that substance. A sl ight lydif ferent def init ion of specif ic heat is the amount of heat required to raise the
temperature of 1 mL of the substance by 1C. Water is the standard with a specif ic
heat of 1 ca l/g/C or 1 cal/mL/C.
Specif ic heat is important when considering the amount of heat that must be
supplied to a l iquid anesthetic to maintain a stable temperature when heat is lost
during vaporizat ion. Specif ic heats for some anesthetic agents are given in Table
6.1.
Specif ic heat is also important for choosing the material to construct a v aporizer.
Temperature changes more gradually for materials with a high specif ic heat than for
those with a low specif ic heat.
The rm a l Con d u c t i v i t y
Another con side rati on in cho osin g ma terial f rom wh ich to construc t a vapo rizer is
thermal conductivity. This is a measure of the speed with which heat f lows through
a substance. The higher the thermal conductivity, the better the substance
conducts heat.
Thermostabil izat ion is achieved by construct ing a v aporizer of a metal with h igh
thermal conductivity (copper, bronze) to minimize temperature changes when the
vaporizer is in use. In a vaporizer containing a wick, i t is important that the wick be
in contact with a metal part so that heat lost as a result of vaporizat ion can be
quickly replaced.
Vaporizer Design
Con c e n t r a t io n Cal ib r a t i o n
Nearly all the vaporizers in use today in the United States are calibrated by agent
concentrat ion as expressed in percentage of vapor output. They are known as
concentrated-calibrated vaporizers .
They are also called direct-reading, dial-controlled, automatic plenum, percentage-
type , and tec-type vaporizers. Vaporizer output is controlled by a s ingle knob or
dial that is calibrated in volumes percent.
Concentrat ion-calibrated v aporizers are designed to be located between the
flowmeters and the common gas outlet on the anesthesia machine. They are not
designed to be used between the common gas outlet and the breathing system or in
7/27/2019 Chapter 6. Vaporizers
6/111
the breathing system, because they are not calibrated for the high gas f lows that
occur with the oxygen f lush in these locations and offer too much resistance.
Variable Bypass VaporizersThe vapor pressures of most anesthetic agents at room temperature are much
greater than the partial pressure required to produce anesthesia. To produce
clinically useful concentrat ions, a vaporizer dilutes saturated vapor. This can be
accomplished by split t ing the gas f low that p asses through the vaporizer (Fig. 6.2).
Some of the gas f lows through the vaporizing chamber (the part containing the
liquid anesthetic agent), and the remainder goes through a bypass to the v aporizer
outlet. Both gas f lows join downstream of the v aporizing chamber, where gas exits
the vaporizer at the desired concentrat ion.The rat io of bypass gas to gas going to the vaporizing chamber is called the
split t ing rat ioand depends on the ratio of resistances in the two pathways ( 2 ,3).
This in turn depends on the variable (adjustable) orif ice. This orif ice may be in the
inlet to the vaporizing chamber but is in
P.125
the outlet in most modern vaporizers. The split t ing rat io may also depend on the
total f low to the v aporizer.
View Figure
Figure 6.2Concentration-calibrated vaporizer. A:In theOFF position, all of the inflowing gas is directed throughthe bypass. B:In the ON position, gas flow is divided
between the bypass and the vaporizing chamber. In the
MAX position, all of the gas flow allowed by the vaporizergoes to the vaporizing chamber.
Electronic Vaporizers
7/27/2019 Chapter 6. Vaporizers
7/111
In an electronic vaporizer, the volume of carrier gas necessary to produce the
desired agent concentrat ion may be determined by a computer that calculates the
carrier gas f low that needs to pass through the vaporizing chamber in order toproduce the desired a nesthetic agent concentrat ion.
Another ty pe of elec tr on ic vapori ze r wi thdraws a calcul ated am ou nt of l iqui d ag en t
from the agent bott le and injects that l iquid into the breathing system or fresh gas
flow. The amount of l iquid that is injected is adjusted to achieve the desired
anesthetic agent c oncentrat ion.
Vapo r i z a t io n Me th o d s
Flow-over
In a f low-over vaporizer, a s tream of carrier gas passes over the surface of the
liquid. Increasing the area of the carrier gas-l iquid interface can enhance the
eff iciency of vaporizat ion. This can be done by using baff les or spiral tracks to
lengthen the gas pathway over the liquid. Another method is to employ wicks that
have their bases in the l iquid. The l iquid moves up the wick by capil lary act ion.
Most of the vaporizers used in anesthesia employ this v aporizat ion method.
Injection
Certain vaporizers control the vapor c oncentrat ion by inject ing a known amount of
l iquid anesthetic into a known volume of gas.
Tem pe r at u r e Com pen s a t io n
As a l iqu id is vapori zed, energy in the form of hea t is lo s t. As th e l iqu id tempera ture
decreases, so does the v apor pressure. Two methods have been employed to
maintain a constant vapor output with f luctuations in l iquid anesthetic temperature.
Mechanical Thermocompensation
Most concentrat ion-calibrated vaporizers compensate for c hanges in vapor p ressure
with temperature changes by altering the split t ing rat io so that the percentage ofcarrier gas that is directed through the v aporizing chamber is increased o r
decreased. As the vaporizer cools, the thermal element restr icts the bypass f low,
causing more carrier gas to pass through the vaporizing chamber. The opposite can
occur if the vaporizer becomes too warm.
Supplied Heat
An el ec tri c he ate r can be us ed to supp ly heat to a vap ori ze r and mai nta in i t at a
constant temperature.
7/27/2019 Chapter 6. Vaporizers
8/111
Computerized Thermocompensation
Thermocompensation may be accomplished by computer control. Two methods have
been used. The amount of agent injected into the breathing system or fresh gas
flow may be al tered. I f the vaporizer withdraws an amount of l iquid from a bott le
and injects it , the heat loss due to v aporization may not be important. The second
method is computerized control of the amount of carrier gas that f lows through the
vaporizing chamber.
Effects of Altered Barometric Pressure
Most vaporizers are calibrated at sea lev el (4). Because they are sometimes used
in hyperbaric chambers or at high alt i tudes where atmospheric pressure is low, it is
important to have some knowledge of how they
P.126
wil l perform when the barometric pressure is changed. The American Society of
Testing and Materials (ASTM) anesthesia workstat ion standard (5) requires that the
effects of changes in ambient pressure on vaporizer performance be stated in the
accompanying documents.
Effects of Intermittent Back Pressure
When assisted or con trolled venti lat ion is used, the posit ive pressure generated
during inspirat ion is transmitted from the breathing system back to the machine and
the vaporizers. Back pressure also occurs when the oxygen f lush is act ivated. Back
pressure may either i ncrease (pumping effect) or decrease (pressurizing effect) the
vaporizer output.
The ASTM anesthesia workstat ion standard (5) l im its the changes in concentrat ion
from intermittent back pressure. Manufacturers are required to state in operators'
manuals the extent to which back pressure affects a vaporizer's performance.
Pum p i n g E f f ec t
Factors
Studies have shown that c oncentrat ions delivered by so me vaporizers during
controlled or assisted venti lat ion are higher than when the vaporizer was used with
free f low to atmosphere (6 ). This change is most pronounced when there is less
agent in the v aporizing chamber, when carrier gas f low is low, when the pressure
f luctuations are high and frequent, and when the dial sett ing is low.
7/27/2019 Chapter 6. Vaporizers
9/111
View Figure
Figure 6.3The pumping effect in a concentration-calibratedvaporizer. (See text for details.) (FromHill DW. The design and calibration of vaporizers forvolatile anesthetic agents. Br J Anaesth 1968;40:656.)
Mechanisms
A pro posed me chanism for the pu mping ef fe ct in the concentr ation-c al ib rate d
variable-bypass vaporizers is shown in Figure 6.3AC. Figure 6.3Ashows the
vaporizer during exhalat ion. The relat ive resistances of the outlets from the bypass
and vaporizing chamber determine the f lows to each (items 3 and 4 in the f igure).
Figure 6.3Bshows inspirat ion. Posit ive pressure at point C prevents gas and v apor
outf low. Pressure is transmitted to points A and B. This results in gas being
compressed in the vaporizing chamber and bypass. Because the bypass has a
smaller volume than the vaporizing chamber, more gas enters the vaporizing
chamber so that the normal rat io between the f low to the v aporizing chamber and
that through the bypass is dis turbed. The result is an increased f low to the
vaporizing chamber, which then picks up addit ional anesthetic vapor.
Figure 6.3Cshows the situat ion just after the beginning of exhalat ion. The pressure
at point C falls rapidly, and gas f lows from the vaporizing chamber and the bypass
to the outlet. Because the bypass has less resistance than the vaporizing chamber
outlet, the pressure in the bypass fal ls more quickly than that in the vaporizing
chamber, and gas containing vapor f lows from the vaporizing chamber into the
bypass. Because the gas in the bypass (which dilutes the gas from the v aporizing
chamber) now carries vapor and the gas f lowing from
P.127
7/27/2019 Chapter 6. Vaporizers
10/111
the vaporizing chamber is st i l l sa turated, the concentrat ion in the v aporizer output
is inc reased.
Modifications to Minimize the Pumping Effect
A l t e r a t i o n s t o t h e V a p o r i z er
Because the increased output is related to the relat ive sizes of the space a bove the
liquid in the vaporizing chamber and the space in the bypass, keeping the
vaporizing chamber small or increasing the size of the bypass wil l decrease the
effects of back pressure (2). Another method is to employ a long, spiral or large-
diameter tube to lead to the vaporizing chamber (Fig. 6.3DF). The extra gas
forced into this tube and subsequently returned to the bypass does not reach the
vaporizing chamber. Another method is to exclude wicks from the area where the
inlet tube joins the vaporizing chamber. Finally, an overall increase in resistance to
gas f low through the vaporizer may be used.
A l t e r a t i o n s t o t h e A n e s t h e s i a Ma c h i n e
These devices (pressurizing valve, unidirect ional valve, and pressure relief device)
were discussed in Chapter 5. A check v alve near the machine outlet but upstream
of the junct ion with the oxygen f lush offers less protect ion from the pumping effect
than a check valve at the outlet of a v aporizer (7).
P re s su r i z i n g E f f e c t
Factors
The output of some vaporizers used in c onjunction with automatic venti lators has
been found to be lower than during f ree f low to atmosphere (8 ). The effect is
greater with high f lows, large pressure f luctuations, and low vaporizer sett ings.
Mechanisms
The explanation for the pressurizing effect is shown in Figure 6.4 . Figure 6.4A
shows a vaporizer f lowing free to atmosphere. The pressure in the v aporizing
chamber and the bypass is P. As gas f lows to the outlet, the pressure is reduced to
R. The number of molecules of anesthetic agent picked up by each mil l i l i ter of
carrier gas depends on the density of the anesthetic v apor molecules in the
vaporizing chamber. This, in turn, depends on the agent's vapor pressure. The
vapor pressure depends solely on the temperature and is not affected by alterat ions
in the atmospheric pressure.
7/27/2019 Chapter 6. Vaporizers
11/111
Figure 6.4Bshows the situat ion when an increased pressure is applied to the
vaporizer outlet and transmitted to the vaporizing chamber. The increased pressure
wil l compress the carrier gas so that there wil l be more molecules per mil l i l i ter. Thenumber of anesthetic vapor molecules in the vaporizing chamber wil l not be
increased, however, because this depends on the saturated vapor pressure of the
anesthetic and not on the pressure in the container. The net result is a decrease in
the concentrat ion of anesthetic in the vaporizing chamber and the vaporizer out let.
View Figure
Figure 6.4The pressurizing effect. An increase in pressure(p) causes an increase in pressure (p) inside the vaporizer.The vapor pressure of the volatile anesthetic is unaffected
by changes in the total pressure of the gas mixture above it.As a result, the concentration is reduced.
In t e r p l a y b e t w e en P r es s u r i z i n g a n d Pum p i n g E f f ec t s
The changes in vaporizer output caused by the pumping effect usually are greater
than those associated with the pressurizing effect. The pressurizing effect is seen
with high gas f lows and the pumping effect at low f lows.
Effects of Rebreathing
The vaporizer dial s ett ing ref lects the concentrat ion of inhalat ional agent delivered
to the breathing system. When the fresh gas f low is high, there may be l i t t le, i f any,
exhaled gas rebreathed, and the inspired concentrat ion should be close to the
vaporizer sett ing. As the fresh gas f low is lowered, exhaled gases contribute a
more signif icant port ion of the inspired gases. Rebreathing causes a dif ference
between the vaporizer sett ing and the inspired concentration. Also, i f minute
volume is
P.128
7/27/2019 Chapter 6. Vaporizers
12/111
increased, there wil l be more rebreathing and a greater effect. With signif icant
rebreathing, only an agent analyzer can provide an accurate value for the inspiredagent concentrat ion.
Vaporizers and Standards
An interna ti on al stan da rd cov ers vapori ze rs (9). The AS TM anesthesia workstat ion
standard (5) contains t he fol lowing provisions regarding vaporizers:
The effects of variations in ambient temperature and pressure, t ilt ing, back
pressure, and input f low rate and gas mixture c omposit ion on vaporizer
performance must be stated in the accompanying documents. The average delivered concentrat ion from the vaporizer shall not deviate
from the set value by more than 20% or 5% of the maximum sett ing,
whichever is greater, without back p ressure.
The average delivered concentrat ion 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 sett ing, whichever is greater, with pressure f luctuations at
the common gas outlet of 2 kPa with a total gas f low of 2 L/minute or 5 kPa
with a total gas f low of 8 L /minute.
A sys te m that prev ents gas from pas sin g thr oug h the vap ori zing cham be r 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
posit ion if the zero posit ion is also the OFF posit ion.
All vapo rizer contr ol knobs mus t open cou nte rcloc kwise .
Either the maximum and minimum f i l l ing levels or the actual usable volume
and capacity shall be displayed.
The vaporizer must be designed so that i t cannot be overf i l led when in the
normal operat ing posit ion.
Vaporizers unsuitable for use in the b reathing system must have
noninterchangeable proprietary or 23-mm f it t ings. Conical f i t t ings of 15 mm
and 22 mm c annot be used. When 23-mm fit t ings are used, the inlet of the
vaporizer must be male and the outlet female. The direct ion of gas f low must
be marked.
Vaporizers suitable for use in the breathing system must have standard 22-
mm fi t t ings or screw-threaded, weight-bearing f i t t ings with the inlet female
7/27/2019 Chapter 6. Vaporizers
13/111
and the outlet male. The direct ion of gas f low must be indicated by a rrows
and the vaporizer marked for use in the breathing system.
Concentration-calibrated Vaporizers
Tec 5
Tec 5 vaporizers are designed for use with halothane, enf lurane, isof lurane, and
sevoflurane.
Construction
Tec 5 vaporizers are shown in Figure 6.5 . The control dial is at the top. A release
button located at the rear of the dial must be pushed in before the vaporizer can beturned ON. At the rear is a locking lever that is connected to the control dial so that
the vaporizer cannot be turned ON unti l i t is locked on the manifold. At the bottom
right front is a sight g lass that shows the l iquid agent level in the vaporizing
chamber.
Tec 5 vaporizers are available with either of two f i l l ing devices. One is a keyed
system (Fig. 6.5). The f i l l ing/draining port is at the front of the vaporizer on the left
near the bottom. A locking lever to secure the f i l ler block is located on the left side
of the vaporizer. A small lever at the base allows l i quid to be added to or drained
from the vaporizer. The other f i l l ing device is a funnel f i l l that has a drain plug that
can be loosened to drain the vaporizer.
A schemat ic diag ram of a Tec 5 vaporizer is shown in Figure 6.6. The internal
baff le system is designed to keep l iquid from reaching the outlet i f the vaporizer is
t ipped or i nverted.
When the concentrat ion dial is in the zero posit ion, al l of the gas from the
flowmeters bypasses the vaporizer through the Select-a-tec bar (Fig. 6.74). When
the dial is turned past zero, inf lowing gas is split into two streams by the rotary
valve. One stream is directed to the vaporizing chamber, the other through thebypass.
Gas f lowing through the bypass f lows down one side of the vaporizer and past the
thermostat, which is a bimetall ic s tr ip in the base. As the temperature in the
vaporizer decreases, the thermostat permits less gas f low through the bypass so
that more gas passes through the vaporizing chamber. From the thermostat, gas
f lows up the other side of the vaporizer and near the outlet joins the gas that has
passed through the vaporizing chamber.
7/27/2019 Chapter 6. Vaporizers
14/111
The gas f lowing to t he vaporizing chamber f irst passes through the central part of
the rotary valve, after which i t is directed through a helical c hannel then past a
spiral wick that is in contact with the wick skirt , which dips into the l iquid agent.Gas with vapor leaves the vaporizing chamber via a channel in the concentrat ion
dial rotary valve and f lows to the outlet.
Evaluation
The manufacturer's performance curves are shown in Figure 6.7. Greatest accuracy
is at a fresh gas f low of
P.129
P.130
P.131
P.132
less than 5 L/minute and dial sett ings less than 3%. At higher f lows and higher dial
sett ings, there is a decrease in output (10).
View Figure
Figure 6.5Tec 5 vaporizers. The locking lever for the
filling device is on the lower left side of each vaporizer. Thelever for filling-draining is at the base, below the sightglass. To fill, the bottle adaptor is inserted into the port andclamped in place by pulling the locking lever down. The
bottle is then lifted up, and the filling-draining lever ispulled forward. When filling is completed, the filling-draining lever is returned to the closed position, the bottle islowered, the clamping lever is pushed upward, and the
bottle is removed. Draining of the vaporizer isaccomplished by using the same levers but by lowering the
bottle rather than lifting it. Behind each control dial is alocking lever in the locked position. (Courtesy of Ohmeda,a division of BOC Health Care, Inc.)
7/27/2019 Chapter 6. Vaporizers
15/111
View Figure
Figure 6.6Diagram of Tec 5 vaporizer in the ON position.(See text for details.) (Redrawn from a drawing furnished
by Ohmeda, a division of the BOC Health Care, Inc.)
View Figure
Figure 6.7Performances of four Tec 5 vaporizers.(Redrawn from drawings furnished by Ohmeda, a division
of the BOC Health Care, Inc.)
The greatest accuracy is between 15C and 35C. The thermostat does not respondto temperatures below 15C, and the output wil l be less than indicated on the dial.
If the temperature is above 35C, the output will be unpredictably high.
The Tec 5 is prone to increases in output from the pumping effect (11 ). Carrier gas
composit ion affects the output of the Tec 5 vaporizers. At low f lows, the ou tput is
less when air or ni trous oxide is used than when oxygen is the carrier gas. At high
f lows, a small increase in output wil l occur.
Hazards
7/27/2019 Chapter 6. Vaporizers
16/111
I f the locking lever is part ial ly loose or the f i l l ing port open, there wil l be a gas leak
(12,13,14,15 ). Liquid agent may be lost i f the vaporizer is fair ly ful l .
These vaporizers can be overf i l led if the bott le adaptor is loose and the control dialis in the ON posit ion (16,17 ,18 ). Tilt ing the vaporizer can result in overf i l l ing (19).
This wil l cause the vapor output to be e levated. Reversed f low through the
vaporizer results in increased output (20).
Maintenance
The exterior of the vaporizer may be wiped with a damp cloth. No other cleaning or
disinfect ion should be attempted.
The manufacturer recommends that i f the agent contains addit ives or stabil izing
agents, the vaporizer should be drained every 2 weeks or when the level is low. I fthere are no addit ives or s tabil izing agents, the v aporizer can be drained at less
frequent intervals. The vaporizer should be returned to a service center every 3
years. There may be some f lexibil i ty in the recommended service frequency when
agent analysis is used.
Tec 6
The Tec 6 vaporizer is designed for use only with desflurane (21,22 ,23 ).
Construction
The Tec 6 vaporizer is shown in Figure 6.8. I t is somewhat larger than the Tec 5
vaporizers. The concentration dial at the top is calibrated from 1% to 18% in
gradations of 1% up to 10% and 2% between 10% and 18%. A dial release at the
back of the dial must be depressed to turn the dial from the standby posit ion or to
dial concentrat ions over 12%. This release cannot be depressed unless the
operat ional l ight-emitting diode (LED) is i l luminated.
The f i l ler port is at the front on the left . I t is designed so that only a desflurane-
specif ic bott le can be i nserted into it . The power cord attachment and battery case
are on the bottom. The battery provides power for the alarms and l iquid crystallevel indicator during mains power fai lures. The power cord exits at the side. The
vaporizer casing is warm to the touch when it is connected to the electr ical supply,
which wil l cause s light heating of adjacent equipment (24 ). The drain plug is
located at the base. A special kit is required to drain the v aporizer.
7/27/2019 Chapter 6. Vaporizers
17/111
View Figure
Figure 6.8Tec 6 vaporizer. The filler port is at the bottomleft. At the bottom right are the liquid level indicator and thevisual signals for monitors of vaporizer function. A bottle ofdesflurane with the protection cap in place is to the left of thevaporizer. The locking lever behind the control dial is in theunlocked position. (Courtesy of Ohmeda, a division of BOC
Health Care, Inc.)
On the front lower r ight of the vaporizer is the display panel, which has visual
indicators for vaporizer funct ions (Fig. 6.8). With the exception of the t i l t condit ion,
there is a 10-second delay between detect ing a malfunct ion and alarm act ivat ion.
An aud itory ala rm is mo unte d behi nd th e upper part of the display pa nel. An au dio
OFF (mute) button is located above the display panel.
The amber warm-upLED indicates an init ial warm-up period after the v aporizer is
f irst connected to the mains power. Once warm-up is complete, the green
operationalLED is i l luminated, indicat ing that the vaporizer has reached its
operat ing temperature and the concentrat ion dial can be turned ON. A s hort tone
sounds at the transit ion from warm-up to operat ional.
The red no outputLED f lashes and an auditory alarm of repetit ive tones sounds if
the vaporizer is not able to deliver vapor. This can be caused by an agent level less
than 20 mL, t i l t ing t he vaporizer more than 10 degrees, power fai lure, or an internal
malfunct ion. Turning the concentrat ion dial to s tandby wil l mute this alarm and
il luminate the red l ight.
P.133
The amber low agentLED accompanied by an audible alarm is i l luminated if there
is less than 50 mL of agent in the vaporizer. This alarm can be audio paused
(muted) for 120 seconds. I f less than 20 mL remain i n the vaporizer, the no output
alarm is act ivated.
7/27/2019 Chapter 6. Vaporizers
18/111
The amber alarm battery lowLED il luminates to indicate that a new battery is
required. There is no auditory signal for this condit ion.
The l iquid level indicator has a l iquid crystal display (LCD) that indicates theamount of l iquid in the vaporizer between 50 and 425 mL. The LCDs are visible
whenever the vaporizer is powered. There are 20 bars. A single bar corresponds to
a volume of approximately 20 mL. An arrow on the side indicates the 250 mL ref i l l
mark. I f the level is below this mark, the vaporizer wil l accept a f ul l bott le (240 mL)
of desflurane.
View Figure
Figure 6.9Diagram of Tec 6 vaporizer. (1) agent, (2) levelsensor, (3) sump heaters, (4) electrical mains, (5) shut-off
valve, (6) agent pressure-regulating valve, (7) battery foralarms, (8) LCD level display, (9) alarm electronics, (10)
heater electronics, (11) control electronics, (12) alarmbattery low LED, (13) warm-up LED, (14) low agent LED,
(15) no output LED, (16) pressure transducer, (17) pressuremonitor, (18) heater in vapor manifold, (19) heater in valve
plate, (20) solenoid interlock, (21) variable resistor(controlled by rotary valve), (22) fixed restrictor, (23) tilt
switch, (24) operational LED. (See text for details.)(Redrawn from a diagram furnished by Ohmeda, a division
of BOC Health Care, Inc.)
When the unit is plugged in, the electronics go through a self-test. For 2 seconds,
the alarm sounds, and each LED and LCD il luminates. This self-test can be
repeated at any t ime by pressing the mute button for 4 seconds or more. Once the
vaporizer is plugged in, the power is always ON, and the sump heaters are
operat ional. Init ial ly, the vaporizer wil l take 5 to 10 minutes to reach operat ing
temperature.
The internal construct ion is shown in Fig. 6.9. Desflurane is heated to 39C
(102F), which is well above its boil ing point, by two heaters in the base. An
external heat source is needed, because the potency of desf lurane requires that
large amounts be vaporized. In addit ion, the desflurane boil ing point is near room
temperature and depending on ambient temperature would make the output
unpredictable. These factors make
P.134
7/27/2019 Chapter 6. Vaporizers
19/111
thermocompensation using the usual mechanical devices impossible. A transformer
and alternating current (AC) to direct current (DC) converter provide DC power forthe v aporizer.
The sump assembly holds the agent and includes the f i l l ing port, drain, heaters,
and agent level sensor. I t has a capacity of 425 mL. The temperature is monitored,
and the associated electronics act as a thermostat. Two heaters in the upper part of
the vaporizer prevent agent condensation where the warm vapor meets the cold gas
from the common manifold.
The l iquid agent level is sensed by a probe and sheath in the sump assembly.
These measure the capacitance by using the agent as a dielectr ic. The display is
on the front of the vaporizer.
When the proper temperature is reached, the green operat ional LED il luminates. A
signal from the control electronics operates the solenoid interlock, al lowing the dial
and rotary valve to be turned. When the dial and rotary valve are turned, the shut-
off valve opens.
Fresh gas f low enters the v aporizer and encounters a f ixed resistor that creates
back pressure. The higher the fresh gas f low, the greater the back pressure
generated. Electromechanical devices maintain the agent vapor pressure a t the
variable resistor in the rotary valve at the same level as the fresh gas pressure at
the fixed restrictor. This pressure balance between the desflurane and the diluent
f low compensates for changes in temperature, vapor pressure, or di luent f low rate.
The pressures are sensed by a transducer that sends a s ignal to the control
electronics, which in turn alters the agent pressure at the variable resistor by
opening or closing t he agent pressure-regulat ing valve to balance the pressures.
With this balance of pressures maintained, the concentrat ion delivered by the
vaporizer depends only on the ratio of fresh gas flow through the fixed restrictor
and agent vapor f low through the variable resistor, which depends on the
concentrat ion dial sett ing. When the concentrat ion dial is turned to a higher value,
resistance to desflurane f low decreases and the f low of desf lurane increases. With
an increase in di luent f low, the electronics wil l increase the f low in the desflurane
limb to ma intain the pressure balance. The vapor mixes with fresh gas just before
the latter exits the vaporizer.
The f i l l ing s ystem is discussed later in the chapter under Desflurane Fil l ing Sys tem
(see Fig. 6.73). The vaporizer can be f i l led while in use, but the f resh gas f low
should be less than 8 L/minute, the concentration dial set at no more than 8%, and
7/27/2019 Chapter 6. Vaporizers
20/111
the vaporizer should not be subjected to high back pressure. The vaporizer can be
fi l led while it is in its warm-up cycle.
EvaluationThe manufacturer's data are shown in Figure 6.10. The vaporizer is cal ibrated for
f lows from 0.2 to 10 L/minute. The output is almost l inear at the 3%, 7%, and 12%
sett ings, with sl ight ly lower outputs at f lows less than 5 L /minute and slight ly
greater outputs at higher f lows. The vaporizer is designed to be used at ambient
temperatures between 18C and 30C. Studies have shown that the output is within
15% of the dial sett ing. Tilt ing does not render the vaporizer inoperat ive or
dangerous to operate (25 ). Nitrous oxide in the carrier gas decreases the output
slight ly.
View Figure
Figure 6.10Performance of Tec 6 vaporizer, with oxygenas the carrier gas. (From a graph furnished by Ohmeda, adivision of BOC Health Care, Inc.)
Fluctuating back pressure does not signif icantly affect the Tec 6 vaporizer output.
Carrier gas composit ion affects vaporizer output (25,26,27,28). The output is
decreased with air or nitrous oxide as the carrier g as.
Electr icity consumption by the vaporizer is low (29). The battery must be replaced
annually.
Hazards
Vapor can leak into the fresh gas with the vaporizer turned OFF.
When f i l l ing the vaporizer, the bott le must be gripped t ight ly when it is rotated
downward. I f not gripped t ight ly, the bott le may be d ropped when it is released
under pressure at the lower posit ion.
7/27/2019 Chapter 6. Vaporizers
21/111
A cas e has bee n rep ort ed where a val ve pi ston in the attac hment s tuck in the
depressed posit ion, causing a large leak of fresh gas (30). Other vaporizers
mounted on the machine could not be turned ON.If the Tec 6 is used on an anesthesia machine that turns OFF the fresh gas f low
during inspirat ion (fresh gas decoupling; Chapter 12), the intermittent f low will
t r igger an alarm if the software to avoid this problem is not in place (31,32,33).
Cases of sparks and smoke around the connection between the mains power cord
and the socket have been
P.135
reported (34 ). This was believed to be the result of a loose plug.
The Tec 6 should be mounted on the far r ight-hand side on the back bar of the
anesthesia machine (35). In other positions, the power cord may interfere with the
vaporizer interlock mechanism for the other vaporizers (36,37).
Leaks have been reported with this vaporizer (38).
Two cases of cardiac arrest s econdary to a massive overdose caused by a
defect ive control valve have been reported (39).
Maintenance
This vaporizer requires servicing every year at an authorized center. The external
surface may be wiped by us ing a cloth sl ight ly dampened with a c leaning agent. No
other cleaning or disinfect ion should be attempted.
Tec 7
There are Tec 7 v aporizers fo r halothane, enf lurane, isof lurane, and sevoflurane.
Construction
A Tec 7 vapori zer is shown in Figure 6.11. On top is the concentrat ion control dial.
At the re ar of the dial is a re lea se bu tto n tha t mus t be pus he d in be fore the
vaporizer can be turned ON. At the rear is a locking lever that is connected to thecontrol dial so that the vaporizer cannot be turned ON unti l i t is locked on the
manifold. At the bottom right front of each vaporizer is a sight glass that indicates
the l iquid level in the vaporizing chamber.
7/27/2019 Chapter 6. Vaporizers
22/111
View Figure
Figure 6.11Tec 7 vaporizer with Easy-Fil system. Note thelocking lever behind the control dial. The interlock devicecan be seen near the back on the right of the vaporizer.(Courtesy of Datex-Ohmeda, a division of GeneralElectric.)
View Figure
Figure 6.12Back of Tec 7 vaporizer. The rectangle at thelower right is the identification label. At the top is thelocking lever. Note the interlock connectors at either side.
The back of the vaporizer is shown in Figure 6.12. A vaporizer identif icat ion label is
aff ixed to the back. An anesthesia system f it ted with a vaporizer identif icat ion unit
uses this label to identify the vaporizer.
Al though the re are a nu mber of improv ement s in th is vapo rizer com pare d wi th the
Tec 5, the schematic diagram of the Tec 7 vaporizer is essential ly the same as for
the Tec 5 (Fig. 6.6). Tec 7 v aporizers are available with three f i l l ing devices: a
funnel f i l ler, the Quik-Fil, or the Easy-Fil system (Fig. 6.11).
7/27/2019 Chapter 6. Vaporizers
23/111
Approx im ate ly 30 0 mL of l iqu id is ne ede d to f i ll a vaporiz er wi th dry wi cks.
Approx im ate ly 75 mL is reta in ed in the wicks when the vap ori ze r is drained.
P.136
Evaluation
The manufacturer's performance curves are similar to those of the Tec 5 (Fig. 6.7 ).
Greatest accuracy is at a fresh gas f low of 5 L/minute and dial sett ings less than
3%. At higher f lows and higher dial sett ings, there is a decrease in output below the
set value.
The greatest accuracy is between 15C and 35C. The thermostat does not respondto temperatures below 15C, and the output wil l be less than indicated on the dial.
If the temperature is above 35C, the output will be unpredictably high.
Changes in barometric changes are compensated for automatically. Fluctuating
back pressure can affect the vaporizer and increase the delivered concentration.
When air or nitrous oxide is part of the carrier gas, the output is lowered compared
with the output when oxygen is the carrier gas. The effect is g reatest during low
flow rates and low dial sett ings. The effect is greatest (up to 20% of sett ing) at low
flows when nitrous oxide is used.
If the anesthesia machine and vaporizer are out of service for a period of t ime
without gas f lowing, low concentrat ions of the agent may be detected at the
machine outlet immediately after the gas f low is turned ON. When the vaporizer is
turned ON after a period of nonuse, a high concentrat ion of agent may be delivered
for approximately 10 seconds.
Hazards
The Tec 7 v aporizers are intended to be operated in the upright posit ion. I f a
vaporizer is inverted, i t s hould be connected to a scavenging system, the dial set to
5%, and the vaporizer purged with carrier gas at 5 L/minute for 5 minutes.
7/27/2019 Chapter 6. Vaporizers
24/111
View Figure
Figure 6.13Aladin cassette vaporizer in place. The cassettefits into a recess on the front of the anesthesia machine. Itcan be removed by squeezing the handle. The concentrationdial is to the left of the cassette. The wheel on the left of thecassette is used to lock the keyed filler in place and open theinlet to the vaporizer. The liquid level indicator is at the
bottom near the center of the cassette. To its left is thekeyed filling receptacle.
The vaporizer could be overf i l led if i t is not f i l led in the upright posit ion. The dial
must not be turned ON during f i l l ing to prevent overf i l l ing.
Maintenance
The halothane vaporizer should be drained every 2 weeks when the level is low and
the l iquid discarded if there are addit ives or stabil izing agents. Other vaporizers
should be drained once a year. Three years from the date of purchase and every 6
months thereafter, the vaporizers should undergo a safety inspection and the
output checked.
The external surfaces can be cleaned with a moist cloth and neutral detergent. The
cleaning agent must not be allowed to accumulate in the f i l ler, the gas inlet, or
outlet ports or around the control dial.
A l a d i n Vapo r i z er
The Aladin vaporizer is d esigned for desf lurane, isof lurane, sevoflurane, halothane,
and e nflurane.
Construction
The vaporizer consists of two parts. T he electronic control mechanism is in the
anesthesia machine. The agent is in a portable cassette that is inserted into a slot
in the anesthesia machine.
The concentrat ion dial is on the anesthesia machine next to where the cassette is
placed (Fig. 6.13). A magnetic sensor identif ies the cassette. A g reen LED on the
front panel beside the agent wheel is used to indicate that the vaporizer is turned
7/27/2019 Chapter 6. Vaporizers
25/111
ON. On the display screen (Fig. 6.14), the agent is identif ied by name and color
code and the setting in numbers and on a triangular graph.
P.137
View Figure
Figure 6.14Display screen showing the agent and setting atthe bottom in the center. The agent is identified in text andcolor code. The setting is in numerals and a triangulargraph.
The cassette is shown in Figures 6.15 and 6.16 . I t is color coded for the agent that
it is designed to contain and is magnetically coded so that the machine can
automatically identify which cassette has been inserted. A handle on the front is
used to carry the cassette and to insert i t into and remove it from the machine.
There is a release on the inside of the handle that when squeezed releases the
cassette from the machine. I t can be transported and stored in any posi t ion.
The cassettes for halothane, enf lurane, and isof lurane have keyed f i l lers or the
Easy-f i l system. Sevoflurane cassettes may be equipped with either a keyed f i l ler or
the Quik-Fil system. A lock-and-f i l l wheel on the left locks the keyed f i l ler in place
and opens the air vent and l iquid f i l l ing channel. The desflurane cassette has a
f i l l ing system similar to the one on the Tec 6 vaporizer (Fig. 6.17). The l iquid level
indicator and the f i l l ing port are located on the front. The c assette holds up to 250
mL when full. When the ball in the s ight tube is at the bottom, the cassette contains
80 mL or less. The l iquid level may also be displayed on the machine. When only
10% of l iquid remains in the cassette, an alarm message appears.
The internal construct ion is shown in Figure 6.18. Fresh gas enters the v aporizer
and is split between the bypass f low that is in the machine and the vaporizing
7/27/2019 Chapter 6. Vaporizers
26/111
chamber. Sensors in the vaporizing chamber outlet and b ypass monitor the f low
through each. Wicks in the vaporizing chamber increase the surface area. A check
valve in the inlet to the v aporizing chamber protects against agent backf low into thebypass. The f low at the ou tlet of the vaporizing chamber is controlled by the central
processing unit (CPU) in the anesthesia machine. This receives information,
including the fresh gas composit ion, anesthetic agent, dial sett ing, temperature in
the rear of the cassette, and flow. This information is used to determine the ratio of
gas f low through the bypass and the vaporizing chamber. A m ixing chamber
stabil izes the output and reduces the effects of back pressure f luctuations.
Inside the vaporizing chamber, metal plates increase heat capacity, heat
conductivity, and vaporizing surface, al l of which improve temperature stabil i ty and
vaporizat ion. When cassette temperature decreases to less than 18C, a fan below
it is act ivated to facil i tate heat transfer to the vaporizer.
When the cassette is removed, two s pring-loaded valv es automatically close the
channels to and from the vaporizer. When the cassette is inserted into the machine,
these valves open to make the connections with the inflow and outflow channels. In
error situat ions, the
P.138
valves operate to cut off anesthetic agent delivery. A pressure relief v alve opens to
the scavenging l ine if a high pressure is detected in the cassette or the l iquid level
measuring device detects overf i l l ing.
View Figure
Figure 6.15Aladin cassette vaporizer. The handle is used totransport the vaporizer, which can be held in any position.Inside the handle is a release that when squeezed willrelease the cassette from the machine. The cassette is colorcoded for the agent contained.
7/27/2019 Chapter 6. Vaporizers
27/111
I f the cassette pressure is higher than the pressure distal to the cassette outf low,
the vaporizer starts to work as an injector.
A lo cking mechani sm ho lds th e cassette in th e slot on the mac h in e. Th e conn ec ti onis automatic when the cassette is pushed into posit ion. The cassette is unlocked by
squeezing the handle.
The control dial (Fig. 6.13) is turned to s et the concentrat ion. The sett ing is
displayed on the a nesthesia machine screen ( Fig. 6.14).
During f i l l ing, the cassette must be on a level surface or in i ts slot without being
locked. The keyed f i l ler is screwed f irmly onto the bott le and then inserted into the
f i l l ing port. The f i l ler is locked in place by turning the lock-and-f i l l wheel on the left
ful ly clockwise (Fig. 6.15). There wil l be a sl ight resistance when the f i l l ing port is
opened. The bott le is turned upside down. Liquid should then f low into the cassette.
When the vaporizer is f i l l ed, the bott le is rotated downward and the keyed f i l ler
released by turning the lock-and-f i l l wheel counterclockwise. The f i l ler is then
removed from the f i l l ing port.
View Figure
Figure 6.16Back of Aladin cassette vaporizer. A magneticidentification system is used by the anesthesia machine to
determine which cassette is in place.
7/27/2019 Chapter 6. Vaporizers
28/111
View Figure
Figure 6.17Aladin cassette vaporizer for desflurane.
Evaluation
The manufacturer indicates that the accuracy for al l agents is 10% of the sett ing
or 3% of the maximum dial sett ing (whichever is greater) with fresh gas f lows from
200 mL/minute to 8 L/minute. Figure 6.19shows variat ions in output with changes
in fresh gas composit ion. One study found that the output remained within 10% of
the dial concentrat ion with most commonly used fresh gas f lows (40 ). Desflurane
vaporizer accuracy was slight ly less and accuracy with all anesthetics d ecreased at
the extremes of fresh gas f low. The effects of sudden changes in fresh gas f low or
carrier gas composit ion, back pressure, and t ipping were minimal. I f the
temperature fal ls below 20 C or the fresh gas f low is over 8 L/minute, the vaporizer
may be unable to produce high concentrat ions and the messages insuff icient agent
and decreased f lowwil l appear on the m achine.
The delivered concentrat ion wil l increase with a decrease in am bient pressure.
Inaccurate output may occur brief ly i f the temperature of the l iquid agent added to
the cassette is considerably lower than the normal operat ing temperature.
Hazards
The cassette is f i t ted with an overf i l l protect ion mechanism. I f air is al lowed into the
agent bott le, this mechanism is deactivated. This may result in overf i l l ing and
anesthetic overdose.
Turning the vaporizer ON while f i l l ing may pressurize the cassette and cause l iquid
to leak at the f i l l ing port.
7/27/2019 Chapter 6. Vaporizers
29/111
P.139
View Figure
Figure 6.18Diagram of Aladin cassette vaporizer. (See text
for details.)
When the fresh gas f low is lowered, the one-way valv e that prevents backf low of
saturated vapor from the cassette toward the bypass channel may fail to close,
result ing in high delivered concentrat ions (41 ). This problem may be more
signif icant when desflurane is used.
Maintenance
The cassette surface can be cleaned with a cloth moistened in a mild soap solut ion.
The cassette should be emptied before sending it to a s ervice center.
Vap o r 19 .1 , 19 .3
The Vapor 19.1 v aporizors are designed for halothane, isof lurane, sevoflurane, and
enflurane.
Construction
The Vapor 19.1 is shown in Figure 6.20 . The 0 must be depressed before the
concentrat ion dial can be turned. A f i l l ing spout, sight glass, and drain are located
at the bottom.
The Vapor 19.1 is shown s chematically in Figure 6.21. In the OFF position, the
vaporizing chamber inlet and outlet are interconnected and vented to the outside.
This prevents anesthetic agent from leaking into the fresh gas. Fresh gas passes
7/27/2019 Chapter 6. Vaporizers
30/111
direct ly through the inlet port and ON-OFF switch to the outlet port without entering
the interior of the vaporizer (42).
In the ON posit ion, at dial sett ings above 0.2%, incoming gas is diverted past thebypass cone to the l ower vaporizing sect ion. Part of the fresh gas f lows through a
pressure compensator that is designed to prevent
P.140
pressure f luctuations upstream or downstream of the vaporizer from affect ing the
output. Part of the fresh gas then f lows to the vaporizing chamber, where it
becomes saturated. The gas that passes through the vaporizing chamber exits past
a control cone that is controlled by the concentrat ion dial. As the concentrat ion is
increased or decreased, the space between the cone and its housing increases or
decreases, al lowing more or l ess gas-containing agent to leave the vaporizing
chamber. The gas not f lowing to the vaporizing chamber is routed past the bypass
cone, where it mixes with gas from the vaporizing chamber and f lows to the
vaporizer output. The brass shell around the bypass cone contracts and expands
with changes in temperature. I f the vaporizing chamber cools, the shell wil l contract
and the bypass cone wil l move upward, reducing the f low through the bypass and
increasing the f low through the vaporizing chamber (42A ,43 ).
View Figure
Figure 6.19Output of Aladin cassette vaporizer withchanges in fresh gas composition. The electronic control
unit in the machine makes adjustments for changes in freshgas composition to maintain a steady output.
7/27/2019 Chapter 6. Vaporizers
31/111
View Figure
Figure 6.20Vapor 19.1 vaporizer. (Courtesy of NorthAmerican Drager.)
The 19.3 version of this vaporizer is similar to the 19.1 but has a mounting adapter
that wil l attach to a plug-in system. This is a quick release device similar to, but not
interchangeable with, the Select-a-tec mounting system.
Evaluation
The manufacturer's data for the Vapor 19.1 are shown in Figure 6.22 . Output is
independent of fresh gas f low in the range of 0.3 to 15 L/minute with lower dial
sett ings, but
P.141
with high gas f lows output fal ls. An accuracy of 10% can be expected between
10C and 40C. At temperatures outside this range, the vaporizer wil l be less
accurate. Investigat ions of Vapor 19.1 vaporizers for isof lurane, enf lurane,
sevoflurane, and halothane with high and low f lows found that they perform
accurately (44 ,45 ).
7/27/2019 Chapter 6. Vaporizers
32/111
View Figure
Figure 6.21Vapor 19.1 vaporizer in the ON position. (Seetext for details.) (Redrawn from a drawing furnished by
North American Drager.)
The Vapor 19.1 is calibrated by using air as the ca rrier gas. With 100% oxygen, the
delivered concentration is 4% to 10% higher than the set concentrat ion (44,46).
When operated with 30% oxygen and 70% nitrous oxide, the d elivered
concentrat ion is 5% to 10% lower. Changing from 66% nitrous oxide in oxygen to
100% oxygen results in an increase in output fol lowed by a decrease (47 ). I f helium
is in the carrier gas, the output does not vary by more than 10% (48 ,49 ).
When the vaporizer was exposed to pressures up to 4 atm, the output decreased
with increasing pressure but remained within 20% of sett ing (50 ).
Mounting the vaporizer on a moving trol ley or reversed f low through it has no effect
on output (20,51).
The Vapor 19.1 with a keyed f i l ler wil l not overf i l l , even when the vaporizer is in the
ON posit ion and the bott le adaptor is loosened (52 ).
Hazards
I f a f i l led Vapor 19.1 is t i l ted, l iquid agent may spil l into the control device whether
the vaporizer is turned ON or OFF. This can result in ei ther an increase or
decrease in delivered concentrat ion. I f the vaporizer is t ipped more than 45, i t
should be f lushed with a f low of 10 L/minute with the concentrat ion dial at the
highest sett ing for at least 20 minutes.
A cas e has bee n rep ort ed where a rubb er f ragme nt ob str uc te d the l iqu id lev el
indicator (53). This gave the appearance of a l iquid level although the vaporizer
was empty.
7/27/2019 Chapter 6. Vaporizers
33/111
When this vaporizer is equipped with a keyed f i l l ing device, a metal plug is used to
seal the f i l l ing port (Fig. 6.62). There is also a vent on the top of the f i l ler block. I f
the vent is not closed or the p lug is not securely placed in the key f i l ler, there wil lbe a s ignif icant gas leak when the vaporizer is turned ON. Unlike some other
vaporizers that f i l l below the l iquid level, there wil l not be an escape of l iquid
anesthetic.
Maintenance
The outer part of the vaporizer can be cleaned with a damp cloth soaked with
detergent. The manufacturer recommends that the halothane vaporizer be rinsed
with fresh halothane when the l iquid in the sight glass shows discolorat ion or
part icles.The vaporizer should be inspected by trained personnel every 6 months. The
vaporizing chamber should be cleaned and the wicks changed every 2 y ears.
Vapo r 2000
The Vapor 2000 is designed for isof lurane, sevoflurane, halothane, and enflurane.
Construction
Vapor 2000 vaporizers are shown in Figures 6.23 and 6.24. The 0 button on the
handwheel (control dial) must be depressed to turn the v aporizer ON. To the r ight
of the
P.142
OFF posit ion is the T (transport) posit ion. This is used when the vaporizer is to be
removed from the anesthesia machine. When the handwheel is turned to this
posit ion, the button locks in p lace.
7/27/2019 Chapter 6. Vaporizers
34/111
View Figure
Figure 6.22Output of Vapor 19.1 vaporizers at an ambienttemperature of 22C. (Redrawn from graphs furnished by
North American Drager.)
An adapte r at the back of th e vapori zer has hol es tha t matc h pi ns on the ane sthes ia
machine. The vaporizer is secured/released by turning the locking lever at the top.
A pin on the locking lev er mus t eng ag e a gro ov e in the top of th e hand wh ee l to
release the vaporizer. This can be done only when the handwheel is at the T
sett ing.There are two interlock s ystems to prevent more than one vaporizer being turned
ON at the same t ime. For sys tems in which the vaporizer is easily removable, there
is a s l ide lever that causes a shaft to engage a hole in the
P.143
unused vaporizer handwheel that then cannot be used (Figs. 6.23, 6.24). For
permanently mounted v aporizers, there is a rocker-style lever that engages a
groove in the back of the handwheel. I f one end is in this groove, the handwheel
cannot be rotated and the vaporizer cannot be used (see Figs. 6.77, 6.78).
7/27/2019 Chapter 6. Vaporizers
35/111
View Figure
Figure 6.23Vapor 2000 vaporizers. The left vaporizer has afunnel filler. The right vaporizer has a keyed filling system.
Note the locking levers at the top. An interlock mechanismis between the two vaporizers at the top. The lever is turnedtoward the vaporizer in use.
View Figure
Figure 6.24View of Vapor 2000 vaporizers from the top.The 0 button on the handwheel (control dial) must bedepressed to turn the vaporizer ON or to put it into thetransport position. To the right of this is the T (transport)mark. When the handwheel is turned to this position (leftvaporizer), the lever at the back of the vaporizer fits into the
groove on the top of the dial so that the dial cannot bemoved. The vaporizer can then be removed.
Three dif ferent f i l l ing systems are available. A simple funnel is available (Fig. 6.23,
left vaporizer). There is also a keyed f i l l ing device similar to that available on other
vaporizers (Fig. 6.23, r ight vaporizer). Sevoflurane vaporizers may have a Quik-Fil
system. A drain is located under the vaporizer. The Quik-Fil system has a drain
under the f i l ler. The drain valve is opened by insert ing a 2.5-mm Allen key and
turning it counterclockwise. The Quik-Fil system is discussed later in this chapter
(see Figs. 6.66 ,6.68 ,6.69)
The internal vaporizer construct ion is shown in Figures 6.25, 6.26, and 6.27. When
the vaporizer is turned OFF (Fig. 6.25), the inflowing gas passes through two
7/27/2019 Chapter 6. Vaporizers
36/111
bypasses. Part of the gas f lows around the f low control cone. Two isolat ion valves
(A and B ) separate the vaporizing chamber from the bypass gas stream. The
vaporizing chamber is vented to the outside through isolat ion valve A to preventpressure buildup, thus preventing a vapor surge when the vaporizer is turned ON.
When the handwheel is turned to the transport position (Fig. 6.26), isolat ion valves
A and B sea l th e ven t cha nn el as we l l as bot h chann el s to th e vap orizing cha mber.
Another isol ati on valv e (C) seals th e bypass cha nn el arou nd the conc entr ati on
cone.
When the handwheel is turned ON and set to a concentration greater than 0.2%
(Fig. 6.27), isolat ion valve C closes one bypass and isolat ion valves A and B are
opened, allowing a stream of gas to pass through the vaporizing chamber. The vent
is closed. The stream of gas that passes through the vaporizing chamber bypass
passes the temperature-compensation mechanism. As the v aporizer cools, the
bypass channel is narrowed and more gas passes through the v aporizing chamber.
The remainder of the gas passes through the vaporizing chamber. An elongated
channel to the v aporizing chamber
P.144
reduces the pumping effect. The v apor-saturated carrier gas then passes through
the isolat ion valve and past the f low c ontrol cone, where it joins the bypass gas and
flows to the vaporizer out let.
View Figure
Figure 6.25Vapor 2000 vaporizer in OFF position.(Redrawn from graphs furnished by Drager Medical.)
Evaluation
7/27/2019 Chapter 6. Vaporizers
37/111
The performance data supplied by the manufacturer are i l lustrated in Figures 6.28
to 6.31. Some variat ion in vaporizer output occurs, mostly at higher sett ings, higher
f lows, and temperature extremes. While the vaporizer c an compensate for coolingthat occurs as the vaporizer is used, after a certain running t ime, the v aporizer
stabil izes at a sl ight ly lower temperature and delivers concentrat ions that deviate
slight ly from the set value. Alt i tude changes between 700 and 1100 mbar wil l cause
only minor deviat ions in output.
The Vapor 2000 is c alibrated by using air. One hundred percent oxygen wil l cause
an increase in the output by a maximum of 10% but no more than 0.4 vol % (Fig.
6.32). A 30:70 rat io of oxygen and nitrous oxide wil l lower the output by the same
amount.
Hazards
The vaporizer must be upright and secured while being f i l led. Overf i l l ing can occur
if the vaporizer is t i l ted during f i l l ing. I f this happens, the vaporizer may deliver
concentrat ions that are too high or too low. I f the vaporizer is t i l ted more than 30,
anesthetic agent may escape into the fresh gas, causing a high concentrat ion to be
delivered.
The output is not def ined i n the area between 0% and 0.2%. The handwheel should
not be set in this area.
The vaporizer should not be left in the ON posit ion with no gas f low through it ,
because agent may accumulate in the anesthesia machine.
Leakage in the keyed f i l l ing system has been reported (54 ,55 ). This was thought to
be the result of using oversized f i l l ing adaptors that damaged the sealing
component or excessive pressure on the f i l l ing device lever that brought the lever
mechanism out of al ignment. When this problem occurs, there is a strong smell of
agent near the vaporizer and reduced or no output from the vaporizer. This problem
may be corrected on more recent versions of the vaporizer.
P.145
7/27/2019 Chapter 6. Vaporizers
38/111
View Figure
Figure 6.26Vapor 2000 vaporizer in transport position.(Redrawn courtesy of Drager Medical.)
View Figure
Figure 6.27Vapor 2000 vaporizer in ON position.(Redrawn courtesy of Drager Medical.)
P.146
7/27/2019 Chapter 6. Vaporizers
39/111
View Figure
Figure 6.28Performance of halothane Vapor 2000vaporizer. (Redrawn from graphs furnished by DragerMedical.)
P.147
View Figure
Figure 6.29Performance of enflurane Vapor 2000vaporizer. (Redrawn from graphs furnished by DragerMedical.)
7/27/2019 Chapter 6. Vaporizers
40/111
I f the connection between the f i l l ing adapter and the agent bott le is not leak t ight,
the vaporizer can be ove rf i l led and anesthetic agent vapor can escape.
If f low through the v aporizer is reversed, the delivered concentration wil l be
incorrect and often too high.
Maintenance
The external parts of the v aporizer can be wiped with a disposable cloth soaked
with cleaning s olut ion. Halogen-releasing compounds, strong organic acids, and
oxygen-releasing compounds are not suitable.
P.148
7/27/2019 Chapter 6. Vaporizers
41/111
View Figure
Figure 6.30Performance of isoflurane Vapor 2000vaporizer. (Redrawn from graphs furnished by DragerMedical.)
P.149
View Figure
Figure 6.31Performance of sevoflurane Vapor 2000
vaporizer. (Redrawn from graphs furnished by DragerMedical.)
7/27/2019 Chapter 6. Vaporizers
42/111
The vaporizer should be inspected every 6 months by trained service personnel.
The calibrat ion should be checked weekly if the concentrat ion is not continuously
monitored.
D rage r D -Vapo r
The Drager D-Vapor is only for desflurane.
Construction
The D-Vapor is shown in Figure 6.33. The power cable is connected to the
vaporizer at the rear. The control dial on the top is used to s witch the vaporizer ON
or OFF, put i t in the transport posit ion, and adjust the delivered agent
concentrat ion. Pushing the 0 button on the front of the dial a l lows the dial to be
rotated. The control dial locks in the zero (0) and transport (T) posit ions.
The concentrat ion range is 2% to 18%. Concentrat ions higher than 12% are shown
in inverted order. The 0 button on the control dial must be depressed to allow
access to this high concentrat ion range.
When the vaporizer must be removed from the anesthesia machine, the 0 button
is depressed, and the concentrat ion dial is moved to the T posit ion. This allows
the vaporizer to be transported in any posit ion. A locking lever at the rear of the
vaporizer is used to disengage the vaporizer from its mounting.
The D-Vapor f i l l ing system (Saf-T-Fil Sys tem) (Fig. 6.33) is l ocated on the front ofthe vaporizer. A sealing plug cl oses the f i l l ing system when the v aporizer is not
P.150
being f i l led. To f i l l the vaporizer, the button on the r ight side of the vaporizer is
depressed to allow the sealing plug to be removed. The desflurane bottle is
inserted into the f i l l ing mechanism. When it is locked in place, an audible cl ick is
heard. Pressing the bottle downward will allow the agent to fil l the vaporizer. When
the vaporizer is ful l , the bott le retracts, stopping the agent f low. After wait ing 2 to 3
seconds to allow all of the agent to enter the vaporizer, the button is depressed to
release the bott le from the f i l l ing device. The sealing cap is pressed into the f i l ler
unti l i t locks in place, as determined by an audible cl ick.
7/27/2019 Chapter 6. Vaporizers
43/111
View Figure
Figure 6.32Effect of carrier gas composition on output ofthe halothane Vapor 2000 vaporizer. (Redrawn from graphsfurnished by Drager Medical.)
The agent-level indicator is at the front on the r ight side. There are three horizontal
l ines. The top l ine indicates that the vaporizer is ful l . The second l ine, which is
near the bottom, indicates when one complete bott le of desf lurane (240 mL) wil l be
needed to f i l l the v aporizer. The bottom line indicates that there are only 30 mL of
agent remaining in the vaporizer. The vaporizer has a capacity of 300 mL.
The D-Vapor can be f i l led when the device is switched OFF (no power to the
vaporizer), during the heating phase, or during operat ion. I f f i l led during operat ion,
the f i l l ing process wil l be slower.
The display and alarm i ndicators are l ocated on the front of the vaporizer to the
left . For a high priority alarm, there is a red f lashing LED accompanied by two
groups of f ive t ones, each emitted for 10 seconds. For a medium priority alarm,
there is an amber flashing LED and one group of three tones emitted every 25
seconds. The indicat ion alarm is a c ontinuously glowing amber LED with a single
tone every 1 to 2 seconds.
There is a b utton and LED at the top and f ive LEDs below. Pushing the button audio
pauses (si lences) the alarms for 2 minutes and causes the amber LED to i l luminate.
The second LED is green and indicates that the vaporizer is operat ional. The third
LED is red and indicates no output. The fourth LED is a mber and indicates warm
up. The f if th LED is amber and indicates that the vaporizer needs to be ref i l led
(Fil l UP). The bottom LED is amber and indicates Battery. In the event of a
mains power fai lure, i t wil l bl ink. I f i t glows continually, the battery should be
7/27/2019 Chapter 6. Vaporizers
44/111
changed. I f there is an apparatus fault , al l of the LEDs blink. The reader is referred
to the user manual for further details.
I f no power is supplied to the vaporizer, there wil l be no i l luminated LEDs. Whenpower is supplied to the vaporizer, a self-test is automatically performed. All s ix
LEDs should l ight, and an audible alarm signal sounds. During the 5-minute heating
phase, the green operat ion LED f lashes. When the heating phase is complete, this
LED glows continuously, and an audible signal is e mitted.
P.151
The vaporizer is then ready for use. The vaporizer must be set to 0 at least every
24 hours for a total of 5 seconds. This wil l in it iate a self-test.
View Figure
Figure 6.33Drager D-Vapor. (Courtesy of DragerMedical.)
The D-Vapor has its own battery backup. I f the battery is not suff icient ly charged,
the amber LED glows. The backup battery wil l last only 5 m inutes. After 5 minutes,
the vaporizer is switched OFF, and an alarm sounds. I f power is restored in less
than 5 minutes, there will be no interruption in output.
The internal construct ion is shown in Figure 6.34. The reservoir containing the
liquid desflurane is heated to 40C and is at a constant pressure of 2 bar. This
allows the desflurane that leaves the reservoir to be a ful ly saturated vapor. A
shutoff valve prevents the reservoir from delivering vapor when the control dial is at
the zero sett ing, during the heating phase, or in the event of vaporizer fai lure.
7/27/2019 Chapter 6. Vaporizers
45/111
Fresh gas from the f lowmeters is conducted through the bypass and on to the
machine outlet. There is a f low resistance in the bypass that increases the p ressure
in the l ine and causes pressure to be applied to a diaphragm in the regulat ingsensor. This sensor causes the proport ioning valve to deliver as much saturated
desflurane vapor as is necessary to balance the pressures between the fresh gas
flow and the desflurane f low. The delivered desflurane concentration is determined
by the relat ionship between the bypass resistances and the f low control cone,
which is determined by the control d ial sett ing.
Evaluation
Carrier gas composit ion wil l affect vaporizer output. With air or nitrous oxide, the
delivered concentration is reduced in comparison to that delivered when the carriergas is oxygen. For air, the output is reduced approximately 10%. With a ni trous
oxide:oxygen in a 70:30 rat io as the carrier gas, the output is reduced approxi-
mately 20%.
Vaporizer performance is not substantial ly inf luenced by ambient temperature
f luctuations within the range of 18C to 30C.
The D-Vapor is calibrated in v olume percent. Since this calibrat ion is independent
of ambient pressure, the control dial sett ings need to be adjusted higher at higher
alt i tudes to achieve the s ame concentrat ion.
The output accuracy is related to the volume of gas that passes through the
vaporizer (Fig. 6.35). The desflurane concentrat ion is accurate for dial
concentrat ion and f lows i n the shaded areas of the graph. In the unshaded areas,
the output is lower than the sett ing.
Hazards
Cellular phones should not be used within 10 m of the vaporizer.
The D-Vapor is not designed to be used at an angle of more than 10 degrees. At
greater angles, an uncontrolled concentrat ion of vapor may result , connections to
the vaporizer may leak, and the level in the sight glass wil l no t be correct. This
could lead to overf i l l ing.
Maintenance
Continuous agent monitoring is recommended. In the absence of this, a weekly
check of v apor output is recommended. The manufacturer requires that the
vaporizer be inspected and serviced by skil led personnel at yearly intervals.
7/27/2019 Chapter 6. Vaporizers
46/111
Detergents must not be allowed to get under the control dial o r into the inlet for gas
f low or the f i l l ing system. Halogen-releasing compounds, strong organic acids, or
oxygen-releasing compounds should not be used to clean the vaporizer.
Pen l o n S i gm a PPV
The Penlon Sigma PP V v aporizer is designed to dispense halothane, enf lurane,
isof lurane, and s evoflurane.
Construction
The Penlon Sigma PPV vaporizer is shown in Figure 6.36 . The upper part of the
vaporizer and concentrat ion dial are c olor coded. To set a concentrat ion, the dial is
pushed in and rotated. The f i l l ing device can be either a funnel f i l l , Quik-Fil, or
keyed f i l ler. The l iquid level
P.152
indicator has l ines for t he minimum and maximum levels. The di rect ion of gas f low
is marked on the top.
View Figure
Figure 6.34Internal construction of Drager D-Vapor.
(Redrawn courtesy of Drager Medical.)
Internal vaporizer construct ion is s hown in Figure 6.37. Gas enters the vaporizer
and is split into two streams, one passing through the bypass and the other through
the vaporizing chamber. In the zero lock posit ion, the bypass remains open, but the
vaporizing chamber is isolated. I f the zero lock port is open, gas passes through a
spiral tube into the vaporizing chamber, which contains a s tainless-steel wick. Gas
saturated with vapor exits the vaporizing chamber through the vapor control orif ice.
7/27/2019 Chapter 6. Vaporizers
47/111
The size of this orif ice is controlled by the concentrat ion dial sett ing. Gas saturated
with vapor then joins the bypass gas and f lows to the outlet.
Temperature compensation is p rovided by a l iquid-f i l led expansion bellowscontroll ing a variable resistance valve in the bypass. As the v aporizing chamber
cools, the orif ice becomes smaller so that a greater proport ion of gas passes
through the vaporizing chamber.
Evaluation
The performance characterist ics supplied by the manufacturer are i l lustrated in
Figure 6.38. The vaporizer is accurate at temperatures from 15C to 35C. At
higher temperatures, output is increased. I f nitrous oxide is in the carrier gas, the
output wil l be sl ight ly higher. Air or helium in the carrier stream causes the outputto drop s light ly. Intermittent back pressure may result in a small increase in output.
Reversed gas flow results in increased output ( 20).
Hazards
I f the vaporizer is transported while f i l led, the control must be in the zero posit ion,
and at least 2 minutes should elapse with the vaporizer in a secure upright posit ion
before use. I f the vaporizer has been transported with the control in the open
posit ion, i t should be f lushed with gas at 4 L/minute for 2 minutes.
The concentrat ion dial must be in the zero posit ion during f i l l ing or d raining. Thevaporizer must be upright to avoid ov erf i l l ing. A vaporizer that has been overf i l led
should be withdrawn from use.
Overf i l l ing can occur if the vaporizer is turned ON and the bott le adaptor loosened
(56). A high output wil l then occur when the vaporizer is used.
P.153
7/27/2019 Chapter 6. Vaporizers
48/111
View Figure
Figure 6.35The desflurane concentration is accurate fordial settings and flows in the shaded areas of the graph. Inthe unshaded areas, the output is lower than the setting.(Redrawn from a graph furnished by Drager Medical.)
The key f i l ler port is c losed with a block that is shaped l ike the end of the keyed
fi l ler. I f the block is not replaced or the screw not t ightened, there wil l be a gas
leak when the vaporizer is turned ON. This wil l result in l oss of the gas that passes
through the vaporizing chamber, and l i t t le or no vapor wil l reach the breathing
system (57 ,58 ). Liquid agent wil l not be lost through a loose f i l ler block.
Maintenance
The vaporizer should be calibrated every 3 to 6 months, with a major overhaul
every 5 years. The exterior should be cleaned with a dry c loth. No l iquids, including
water, should be applied to the surface. The halothane vaporizer should be drained
periodically and the l iquid discarded to prevent thymol buildup.
Pen l o n S i gm a Del t a
The Sigma Delta vaporizer is used to dispense halothane, enf lurane, isof lurane,
and sevoflurane.
Construction
The Sigma Delta vaporizer is shown in Figure 6.39. The front has a color-coded
control dial that locks in the 0 posit ion. To use the vaporizer, the dial is pushed
inward and rotated counterclockwise to the desired concentration. When the control
dial is turned
P.154
7/27/2019 Chapter 6. Vaporizers
49/111
OFF, it wil l automatically spring outward to the locked posit ion.
View Figure
Figure 6.36PPV Sigma vaporizer with screw cap filler andback entry connections. (Courtesy of Penlon, Ltd.)
At the bottom is th e l iqu id le vel ind ica to r, wi th max imum an d minimum lev el marks.
Three dif ferent f i l l ing devices are available: funnel f i l l , keyed f i l l , and Quik-Fil. The
keyed f i l ler ut i l izes a plug that is held in place by using a sc rew on the side.
At the bas e of th e f i ll ing mec ha nism is a mea ns of dra in age . If a keyed fi l le r is
used, the same bott le adaptor that is used to f i l l the vaporizer is used to drain it .
For the Quik-Fil and funnel-f i l l mechanisms, a screw at the base of the f i l ler block
opens the drain. The f i l ler cap must be removed from the vaporizer to drain it . The
liquid can drain direct ly into the bott le for the funnel f i l l . For the Quik-Fil, a
receptacle is sl id over the base of the f i l ler m echanism and is used to catch the
liquid (see Figs. 6.68, 6.69).
7/27/2019 Chapter 6. Vaporizers
50/111
View Figure
Figure 6.37Diagram of PPV Sigma vaporizer. (See text fordetails.) (Redrawn from a drawing furnished by Penlon,Ltd.)
The vaporizer has a l iquid capacity of 250 mL. At the MIN mark, the volume wil l be
35 mL. Approximately 60 mL of l iquid wil l remain in the wick after the vaporizer is
drained.
The internal construct ion is shown in Figure 6.40. The vaporizing chamber contains
a wick. Temperature compensation is by means of a thermostat in the bypass. In
the zero posit ion, the bypass remains open, but the v aporizing chamber is isolated
from the gas flow.
Evaluation
The operating temperature range is 15C to 35C. The temperature-compensating
mechanism reacts slowly to room temperature changes and may need a minimum of
1 to 2 hours to compensate for a change in room temperature. The vaporizer is
designed to operate between fresh gas f lows of 0.2 and 15 L /minute. Graphs of
P.155
P.156
P.157
vaporizer output in relat ion to fresh gas f low and temperature are given in Figures
6.41 to 6.44.
7/27/2019 Chapter 6. Vaporizers
51/111
View Figure
Figure 6.38Performances of PPV Sigma vaporizers withoxygen as the carrier gas. (Redrawn from graphs furnished
by Penlon, Ltd.)
View Figure
Figure 6.39Sigma Delta vaporizers. Left:With keyedfiller. Right:With Quick-Fil. (Photo courtesy of PenlonCompany UK.)
Barometric pressure effects are not usually cl inically i mportant. A steady back
pressure of 10 to 15 kPa (100 to 150 cm H2O) wil l reduce the vaporizer output.
Intermittent back pressure may result in some changes in ou tput. The effect is
greatest at low vaporizer sett ings and low f low rates.
The vaporizer is calibrated with 100% oxygen. Nitrous oxide in the carrier gas wil l
produce a decrease in output. Air wil l reduce the vaporizer output by a m aximum of
5%. Helium in the fresh gas wil l result in low concentrat ions.
Hazards
7/27/2019 Chapter 6. Vaporizers
52/111
The Penlon Sigma Delta may m alfunct ion if exposed to excessively high
temperatures. This may affect the calibrat ion. The vaporizer should be s tored
between -20C and 50C.The vaporizer control dial should be a t zero, and the vaporizer should be upright
during f i l l ing. I f i t is not upright, there is a possibil i ty of overf i l l ing. An agent bott le
that is cracked or a f i l ler that is not t ight ly attached to the bott le or is broken should
not be used because overf i l l ing may occur or contaminated agent may enter the
vaporizer. An overf i l led vaporizer must be taken out of service and the
manufacturer consulted.
I f the vaporizer is transported while f i l led, the control dial should be in the 0
posit ion. The dial must remain in the 0 posit ion for at least 10 minutes after the
vaporizer is attached to the anesthesia machine. Anesthetic agent overdose can
occur if not enough t ime for any l iquid to drain into the normal posit ion has
elapsed. I f a v aporizer has been transported with the control dial in an open
posit ion, i t must be f lushed with a 5 L/minute f low of gas for at least 10 min