Prof. Mridul M. Panditrao

Professor, Head & In-Charge of ICU

Dean of Academic Affairs

Department of Anaesthesiology and Intensive Care

Adesh Institute of Medical Sciences and Research (AIMSR)

Adesh University

Bathinda, Punjab, India

PreviouslyConsultant

Department of Anesthesiology and Intensive Care

Rand Memorial Hospital

Freeport

Commonwealth of Bahamas

Presented as a Faculty lecture on

26th December 2014:10.45-11.30 AM

Declaration

Author declares his gratitude for being able to use some of the

graphics from various web based resources, inclusive of

Howequipmentworks

Anesthesiavaporization2000

Vaporizers

Wikipedia

Google search

Google Images etc………

INTRODUCTION

An essential & integral part of the anesthesia work station

Physics, construction, working principles and classification

A very complex/a tedious affair

The novices/younger generation of anesthesiologists

tend to relegate this aspect to realm of ‘mystery’ and avoidance

This is an attempt to demystify very important/neglected topic

Many a monographs have been written about them,

Still there is scope for describing them in an understandable manner.

Effort to simplify

“scientific principles and theoretical aspects”

To make concepts become much easier to understand.

INTRODUCTION:

Definitions

Colloquially, a vaporizer or vaporiser is a device

Used to vaporize the active ingredients of plant material, commonly cannabis,

tobacco, or other herbs or blends for the purpose of inhalation.

However, they can be used with pure chemicals when mixed with plant material

(e.g. tobacco-free nicotine)

INTRODUCTION: Definitions:

All the inhalational anesthetic agents

In a liquid state at standard room temperature & pressure.

Need to be transformed in to a form, can be inhaled : Vapor

The process of transforming the liquid in to a vapor is : Vaporization

Pure vapors of the modern anesthetic agents are extremely potent

Can have deleterious effects if administered in high concentration

INTRODUCTION: Definitions:

Accordingly, the vaporizer can also be defined as:

A vaporizer is a device that changes a liquid anesthetic

agent in to its vapor/ allows vaporization and adds a

controlled and predictable amount of that anesthetic

vapor to the fresh gas flow/ Carrier gas or the breathing

system for delivery of the subsequent admixture to the

patient

Basic design

Fresh Gas Flow (Carrier Gas) enters vaporizer

Splitting of Gas Flow

Some amount is allowed to enter the vaporizing chamber

Majority is allowed to bypass

Gas Saturated with vapor exits the chamber

Mixing with the bypassed gas takes place

Diluted Gas + Vapor mixture at the outlet

Finally delivered to the Patient

Historical aspects:

‘Inhalational Anesthesia’ tried by early ‘clinicians’ from time immemorial

Historical records ; use of “Soporific sponges” soaked in ‘medicinal elixirs’

Idea of using vaporization for sleep & pain relief well accepted

Actual use of easily ‘vaporizable substances’ came much later, in 18th

century

16th October 1846 to be exact

WTG Morton used his ‘ Letheon’ inhaler - Ether inhaler first time

to achieve surgical anesthesia, as a public demonstration, in the history of mankind.

Thus ether then chloroform again back to ether,

Led to evolution of various devices used for vaporization

of these liquids

Historical aspects:

The main ‘reviver’ of ether was Kurt Schimmelbusch and his ‘mask’

Contraption made with wires and layer of gauze pieces/used along with

‘open ether - drop by drop method’ for administration of ether.

“Yankauer’s mask” in 1904, Flagg’s can/ KEM Bottle,

More sophistication: Epstein Macintosh Oxford (EMO) vaporizer with Oxford

inflating bellows (OIB)

“Anesthesia Machine” was invented

Glass- “Boyle Bottles” for ether, chloroform and trichloroethylene,

Ethyl Chloride

Historical aspects:

With deeper insights into physical principles, properties and laws

Advances for development of more sophisticated devices

As a result Oxford Miniature Vaporizer (OMV), Copper Kettle

halogenated compounds like halothane/halogenated ethers

has produced the Tec series of vaporizers.

Presently available modern vaporizers

advanced in their construction

capable of delivering precise, predictable and calculated/ constant concentration of

the Volatile anesthetic agent.

Thus the humble beginning has evolved in to a

precision perfect and an analytical science.

Physical Principles:

Process of vaporization:

Constantly happening even in the atmosphere

Formation of water vapor.

Surface molecules of the liquid, coming in contact with air / any

gas

Carried off along with these gases, because of their higher kinetic

energy.

Gas carrying these :‘Carrier gas’.

Surface molecules of the liquid now existing in gaseous form :

‘vapor’

Physical principles:

Vapor pressure

They now behave more like gases, rather than original liquid

form

In this vapor state, they exert a certain, specific pressure on the

things surrounding them.

This pressure is called ‘Vapor pressure (VP)’

Pressure exerted by the molecules of vapors on the wall of container

VP increases with temperature/physical characteristics of

volatile anesthetic agent

Not affected by the ambient pressure

Physical principles:

Saturated vapor pressure

If vaporization is happening in a closed container or a chamber,

Then some of these molecules will bounce back till the equilibrium is

reached.

When the molecules leaving the liquid and reentering it become equal,

at that temperature and specific to the agent, this pressure is called

“Saturated Vapor Pressure” (SVP).

The most important factor governing vaporizer design is the saturated

vapor pressure (SVP) of the anesthetic.

SVP is a measure of the volatility of the liquid anesthetic in the carrier gas:

Anesthetics with a high SVP will require

a smaller proportion of the total gas flowing through the vaporizer

To pass through the vaporizing chamber to produce a given concentration

Surface area of the liquid

larger the surface area of the liquid coming in contact with the carrier gas

directly proportionately larger the number of molecules will come in contact

more rapidly they will escape from the liquid

Increasing the surface area for the carrier gas by the use of

Wicks

Series of Baffles

Bubbling the gas through the liquid volatile anesthetic

Volatility/Volatile nature of the liquid

directly proportional the relationship.

Physical principles:Factors involved in the process of vaporization

Physical principles:

Temperature:

Temperature plays multiple roles in the process of vaporization.

As liquid is heated up, more and more kinetic energy is generated

More and more chances of its surface molecules getting lost by the process

of vaporization.

As the heating up continues, the temperature in the liquid will increase

proportionately, till a certain point of temperature

Where the saturated vapor pressure will become equal to atmospheric

pressure.

So now not only the surface of the liquid but the bubbling through the entire

quantity of liquid is involved.

Bubbling is indicative of boiling of the liquid and the point of temperature is

called the boiling point of the liquid.

Boiling point

Defined as

The temperature point, where the equalization of the SVP is achieved with that of the atmospheric pressure

Halothane Enflurane Isoflurane Sevoflurane Desflurane

SVP at20c 243 175 240 168 664

MAC at 20c 0.75 1.68 1.15 1.7 approx. 6

Boiling point

at 20C

50.2 56.5 48.5 58.5 22.8

Physical principles:

Temperature: Heat of Vaporization:

The Number of calories required to vaporize 1 ml. of the liquid

Latent heat of vaporization

The Number of calories needed to convert 1 gram of liquid to vapor without atemperature change

Temperature of remaining liquid falls and may decrease rate of vaporization

Specific heat : The quantity of heat energy required to increase the temperature of a 1 gm.

of a substance/1 ml. of a liquid by 10 Celsius is called the Specific Heat of thesubstance/ liquid

Thermal conductivity

Measure of speed with which heat flows through a substance.

Are made of materials having high specific heat & high thermal conductivity.

It helps maintain a uniform temperature.

Heat of Vaporization & Specific heat

As the vaporization with carrier gases, continues, temperature

within the liquid gradually falls

As a result, slowly the heat from the surrounding is taken up to

continue the process of vaporization.

As the gradient between the heat being supplied Vs. the heat

being lost due to vaporization is gradually neutralized, an

equilibrium is reached.

At this temperature point no vaporization is possible any further,

until and unless, external heat is supplied.

How much of this heat energy is required will depend upon the

specific heat of the liquid.

.

Clinical importance :

Heat of Vaporization & Specific heat

Plus container in which vaporization is going on is also very

important.

More the specific heat of the material of the container :

Gradual and slower will be the change of temperature fall and

deceleration of the vaporization,

better the control in the hands of the clinician.

Copper being the most ideal metal with very high specific

heat,

is most commonly employed, somewhere or the other,

during the construction of the most of the modern vaporizers

Clinical importance :

Thermocompensation

Temperature compensation is achieved by

Heat transferred from surrounding metal (vaporizer)

&

With the help of valves which are controlled by

Bimetallic strip

single metal strip

Bellows

Here the aperture of the valve increases or decreases depending upon the temperature

Thereby regulating the flow of gas through the vaporizing chamber

Final Output:

Flow of the carrier gas:

As is true with surface area of the container, same

principle also applies here

Larger the flow, more and more gas will come in

contact with the surface of the liquid

more will be rate of vaporization.

Final Output: Concentration

Correlation between the

Pressure of the gas mixture and its final output

volume/ concentration:

The gas mixture (gas + vapor), in any container exerts

certain pressure on the container walls.

This pressure is the sum total of the individual partial

pressures of all the constituents of the mixture.

So the volume concentration in percentage of the vapor

can be calculated by

dividing the partial pressure of the vapor by total pressure

inside the container, Multiplied by 100

With employment of

Intermittent Positive Pressure

ventilation (IPPV)

Given manually or by

automatic ventilation,

Certain back pressure that

is produced

As the pressure in the

breathing system

increases,

it is transmitted back to

the vaporizer

compressing the gas

inside the chamber,

especially at the bypass.

During the conduct of general anesthesia

“Pumping effect”.

The outlet gas which was already saturated with the vapor along with expanding

additional gas has entered the vaporizing chamber, carries more vapor.

Both of these gases leave the outlet leading to, with more than the set

concentration being delivered to the patient.

This is called as “Pumping effect”.

Automatic ventilator with low flows and low dial setting,

especially when the lower quantity of the agent is available in the vaporizer.

With manual ventilation when the pressure changes are not even (Too frequent

variations, swinging between high and low pressures).

Corrective measures:

Logically decreasing the volume of vaporizing chamber.

Increasing the size of variable bypass

Adding an increased resistance at both the bypass as well as at

vaporizing chamber.

Adding a long spiral tube before gas can reach the vaporizing chamber,

leading to bypass thus preventing the gas from reaching back

Applying One way valve

“Pressurizing effect

As opposed to this, again during the automatic ventilation,

In some vaporizers, output decreases than what has been set

This is called as “Pressurizing effect”.

The factors here are opposite of that in pumping effect,

High flows, but lower dial settings and frequent pressure changes.

As the extra pressure at the outlet is applied, the pressure inside the vaporizing chamber is increased.

However the increased carrier gas pressure will not carry an additional vapor molecules

because the final concentration is mainly dependent upon the SVP of the anesthetic rather than, total pressure inside the chamber.

As a result dilution takes place leading to decreased final output concentration.

Level of liquid anesthetic.

In both pumping as well as pressurizing effects, lower levels of anesthetic is

one of the causes.

If too much is filled in the chamber, then area available for the contact will

be decreased.

Spilling of the liquid in to the bypass can actually increase the

output to dangerously high levels.

Stabilizers like Thymol known to decrease the available surface

area and also interfere in the intricate mechanism of the

vaporizer.

Mounting of the vaporizer. If vaporizer is tilted or not exactly

straight, can increase the output.

Other factors affect the performance/ final output

Classification:

Extensive Variations in terms of their

Construction

structure and

mechanism of their functionality,

Placement

Each of the vaporizers can fit into multiple parameters of classifications.

Classification:

The concentration achieved (Output Concentration)

Variable Bypass

Measured flow

The Method of vaporization employed

Flow-over

Bubble through

The specificity of the anesthetic agent used

Agent specific

Multiple agents

If the thermo-compensation is possible or not

The Location, in relation with the breathing system.

Outside the circuit

Inside the circuit.

Draw over/Bubble through Variable bypass

Variable bypass with dial control

Bubble through/measured flow

Another Classification

Another nomenclature for older vaporizers like

EMO, EMOTril, OMV, Copper Kettle and even in TEC series TEC 2, 3 and 4

Draw-over

The carrier gas was drawn over the liquid directly inside the vaporizer.

Sub atmospheric pressure is developed in gas stream distal to vaporizers either by patient or

mechanical means(EMO, Oxford Miniature Vaporizers)

Low in resistance to gas flow

Nowadays obsolete.

Plenum

Fresh gas is forced in to the vaporizing chamber (Plenum System)

Positive pressure is developed upstream of vaporizers,

All Tec type vaporizer and kettle type

High resistance to gas flow

Simple glass bottles: inside the circuit e.g. Goldman vaporizer.

Characteristics of ideal VAPORIZER

Performance not affected by changes in

FGF,

Volume of liquid agent

Ambient temperature & pressure

Decrease in temperature & pressure

Low resistance to flow

Light weight with small liquid requirement

Economical and safe to use

Corrosion and solvent-resistant

Features of modern vaporizer

Variable bypass Fresh gas splits into bypass gas and carrier gas

Flow overCarrier gas flows over the surface of the liquid volatile agent in the vaporizing

chamber

Temperature compensated Equipped with automatic devices that ensure steady vaporizer output over a

wide range of ambient temperatures

Agent-specificOnly calibrated for a single gas, usually with keyed fillers

Out of circuit

Operating principles of variable bypass vaporizers

Variable bypass vaporizers can be of the plenum or draw-over type

Splitting ratio

Between carrier and bypass depends on concentration control dial

Temperature compensated valve

Effect of flow rate- Variation is notable at extremes of flow rates

Output is constant over the range of flow from 250ml-15L/min.

Effect of ambient temp: Output is linear (uniform increase) from 20-350c

Automatic temp compensation devices

Wicks in contact with the walls of vaporizer replace heat used for vaporization

Metals of high specific heat and thermal conductivity

Effect of intermittent back pressure/ Pumping effect.

Long inlet tube to vaporizing chamber.

One way check valve at common gas outlet.

Equal vol. of bypass and vaporization chamber

Most vaporizers in current use: variable-bypass type and

concentration-calibrated

• Include the Ohmeda Tec series (except 6) the Drager Vapor 19.1

• The total gas from the anesthesia machine flow meters is split with some gas flowing into

the vaporizing chamber picking up anesthetic agent molecules,

• While a larger gas Flow bypasses the chamber completely

• Vaporizer outflow is based on the re- mixing of the two streams• Results in administration to the patient of the anesthetic concentration indicated on the

dial.

Safety features

Important safety features include:

Color specific (for each agent)

Keyed fillers bottles

Low filling port

Secured vaporizers Interlocks

less ability to move them about minimizes tipping

Only one vaporizer is turned on

Gas enters only the one which is on

Trace vapor output is minimized when the vaporizer is off

Vaporizers are locked into the gas circuit, thus ensuring they are seated correctly

Concentration dial increases output in all when rotated counterclockwise

(as seen from above

Hazards

Tipping

If tipped >45 degrees-liquid can obstruct the outlet valves

Treatment: Flush for 20-30 min at high flow rates with dial set at high

concentration

Overfilling May result in high output

Fill only up to max filling line

Fill only when the vaporizer is off

Leaks

Relatively common due to malposition or loose filler cap.

Not detected with standard checklist perform negative pressure check

Hazards

Misfilling

Vaporizers not equipped with keyed filling lead to misfilling

Contamination

It occurs by filling a vaporizer with contaminated anesthetic bottle.

Underfilling

Leads to decreased vaporizer output.

Simultaneous Inhaled Anesthetic Administration

Happened in old machines with no interlock system

Individual Vaporizers Monologues have been written about the individual

vaporizers, which is beyond

the scope of present

discussion, because of the

paucity of space However we shall be

discussing, salient features of

only the Tec 5, 6 and 7 and

Drager 19.3 and Aladin

cassette

for example: while describing TEC 5 vaporizer

Variable Bypass,

Flow over,

agent specific,

thermo-compensated

outside the circuit.

Comparative properties

The commonly used vaporizers are enumerated in the Table I.

Property TEC 4, Vapor 19n,

2000, Aladin

TEC 5 TEC 7 Vapor 19n Vapor 2000 D Vapor

TEC 6 Des.

Principle of

vaporization

Flow over, Flow over Flow over Flow over Flow over Gas-vapor blender

Carrier gas flow Variable bypass Variable bypass Variable bypass Variable bypass Variable bypass Dual circuit

Capacity mls.

With dry wicks

With wet wicks

135

100

300

225 225200

140

360

280

D-vapor 300

TEC 425

Thermo-

compensation

Automatic Automatic Automatic Automatic Automatic Thermostatically controlled

at

39 0C.

Position Out of circuit Out of circuit Out of circuit Out of circuit Out of circuit Out of circuit

specificity Agent-specific Agent-specific Agent-specific Agent-specific Agent-specific Agent-specific

Low flow suitability Not very good Good Very Good Good Very Good Very Good

Problems of Desflurane

Desflurane is much more volatile than all the other inhalationals.

Its boiling point is low -- only 22.80 C, so most of it gets evaporated at normal room temperatures

Vapor pressure of desflurane at 200 C is 664 mm Hg.

While that of enflurane, isoflurane, halothane are 172, 240, 244 MM Hg. respectively

At 1 atmosphere and 200 C , 100mL/min flow passing through vaporizing chamber would carry

735 mL/min. of desflurane

versus

29, 46 and 47 mL/min of enflurane, Isoflurane and halothane respectively.

Under these conditions to produce 1% of desflurane,

we need 73 L/min Fresh Gas Flow as

compared

to 5 L/min for other anesthetics, to pass through vaporizer

• In the above figure, note different vapor pressure-temperature relationships

between common volatile agents

• Recognize that desflurane falls outside the grouping

• Not surprisingly, special vaporizer is required for desflurane

Specifically designed to deliver desflurane

Described as a gas/vapor blender than as a vaporizer.

It is heated electrically to 350 C

Pressurized Device with a pressure of 1550 mmHg (2 atm)

Electronic monitors of vaporizer function

FGF does not enter vaporization chamber, instead

Desflurane vapor enters the path of FGF

Percentage control dial regulates flow of Desflurane into FGF

Dial calibration is from 1% to 18%

Provided with back up 9 volt battery

Datex-Ohmeda Tec 6 Vaporizers for Desflurane

Schematic diagram of the TEC 6 vaporizer.

Is an electrically heated,

thermostatically controlled,

constant-temperature,

pressurized,

electromechanically coupled,

dual-circuit,

gas-vapor blender.

The pressure in the vapor circuit is electronically regulated to equal the pressure in the

fresh gas circuit.

At a constant fresh gas flow rate, the operator regulates vapor flow by use of a

conventional concentration control dial.

When the fresh gas flow rate increases, the working pressure increases proportionally.

At a specific dial setting, at different fresh gas flow rates, vaporizer output is constant

because the amount of flow through each circuit is proportional.

The latest model of the TEC series

It delivers Isoflurane, Sevoflurane, Enflurane, and Halothane

efficiently

Easy-fil* is designed to simplify agent filling and help minimize agent leaks while filling

The Tec 7 Vaporizer is also available with Quik-Fil* (Sevoflurane only)

accommodates 225 mL of anesthetic agent.

Anesthesia delivery systems equipped with the Selectatec*

Non-spill system limits movement of liquid agent

if the vaporizer is tilted or inverted

helping to protect internal components.

TEC

7

Clinical Performance

Designed to provide consistent output

Throughout the clinical flow range from 200 mL/min to 15 L/min.

Large diameter control dial incorporating

fine graduations of 0.2% between 0 and 1%,

0.5% from 1% to 8%.

The dial for Sevoflurane is marked

in steps of 0.2% up to 1% v/v,

in steps of 1% between 1% and 8%.

Fine tune anesthetic delivery over the range of dial settings/flow

rates.

Aladin Cassette Vaporizer System

A Novel system

Single vaporizer capable of delivering 5 different anaesthetic agents

It is designed for use with Datex-Ohmeda S/5 ADU and similar

machines.

FGF is divided into bypass flow and liquid chamber flow

Liquid chamber flow conducted into agent specific, color coded

cassette in which volatile anesthetic is vaporized

Machine accepts only one cassette at a time

Magnetic Labeling

Conclusion

Quest for understanding vaporizers is never-

ending.

The more we try to learn them,

more developments and newer insights happen.

Very demanding and rapidly developing field.

It pays for every anesthesiologist to remain in

constant accompaniment with them.

Thank You!