chapter 6. vaporizers

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 .


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


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


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


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


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


7/111

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.


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.


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


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.


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


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


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.


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.)


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


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.


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.


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


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


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.


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.


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).


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.


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


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


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.


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.


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.


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


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.


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 ).


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.


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.


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).


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


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


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


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


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.)


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


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.)


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.


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


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.


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.


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.


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


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


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).


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.


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


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

chapter 6. vaporizers

Documents