- V. Tejasree

VAPORIZERS

What is a vapor?

What is a gas?

What is vaporiser?

Vapor- gaseous state of a substance which at

room temperature and pressure is a liquid.

Gas- Is a substance which at room temperature

and pressure exists only in gaseous state

Vaporiser – is a device that changes a liquid

anesthetic agent into its vapor and adds a

controlled amount of that vapor to the fresh gas

flow or the breathing system.

Why do we need a

vaporizer?

Most volatile, potent inhaled agents exists as a

liquid at room temperature and atmospheric

pressure.

Vaporizers are needed them to convert the liquid-

form of the anesthetic to vapor phase and add a

certain amount of this vapor to the anesthetic

circuit.

History

1540- Valerius Cordus- Ether- sweet oil of vitriol

1800- Humphry Davy- Nitrous oxide

1842- William E.Clarke &Crawford W. Long

1844- Horace Wells

1844- E.R. Smilie

1846

William Thomas Green Morton- American dentist

16th october 1846 in Massachusetts General

hospital, boston.

1847

John snow

First specialist anesthetist

Snow ether inhaler

1862

Joseph thomas clover

British physician

Clover chloroform apparatus

1879 - Esmarch Open drop mask

1890 Schimmelbusch

regulator

Augustus George vernon

Harcourt

English chemist

1908

Omberdanne ether inhaler-

Louis omberdanne

French pediatrician

and plastic surgeon

1910 - Yankaeur mask

1912 - Gwathmey-Woolsey Nitrous

Oxide-Oxygen ether Apparatus

1920’s - Boyle’s bottle

Goldman vaporizer

Copper kettle vaporizer

Oxford Miniature Vaporizer

(OMV)

Halothane, enflurane, isflurane and sevoflurane

1952- Epstein Macintosh Oxford

vaporizer (EMO)

Physics related to vaporiser

Vapor pressure

Boiling point

Gas concentration

Partial pressure

Volumes percent

Latent heat of vaporisation

Specific heat

Thermal conductivity

Ideal Gas Law

Gases Behave Predictably.

This behavior is expressed by the:

IDEAL GAS LAW

PV= nrT

P= Pressure

V= Volume

n= number of moles of gas

r= ideal gas law constant

T= Temperature

Vapor pressure

When a liquid is enclosed in a container, the

molecules of the liquid break from the surface

and enter the space above forming a vapor.

These molecules bombard the walls of the

container creating a pressure called vapor

pressure.

Saturated vapor pressure- the pressure exerted

by the vapor when in equilibrium with the liquid

phase at constant temperature

Vapor pressure depends on liquid and

temperature. Independent of ambient pressure.

SVP Varies as a Function of Temperature

Boiling point

Boiling point of a liquid is defined as the

temperature at which vapor pressure equals

atmospheric pressure.

Lower the atmospheric pressure lower the boiling

point.

Agents with low boiling points are more

susceptible to variations in barometric pressure

than agents with higher boiling points

SVP BP

Sevoflurane: 160mmHg 58.6O C

Enflurane: 175mmHg 56.5O C

Isoflurane: 238mmHg 48.5O C

Halothane: 243mmHg 50.2O C

Desflurane: 660mmHg 22.8O C

Gas concentration

Gas concentration can be explained by 2

methods.

1) Partial pressure

2) Volumes percent

Partial pressure

pressure exerted by a gas in a mixture of gases

is the partial pressure of that gas.

Dalton’s lawof partial pressures-

Ptotal = P1+P2+P3…. Pn

The partial pressure of an vapor depends only on

temperature of that agent

The highest partial pressure of a gas is its vapor

pressure at a given temperature.

Volumes percent

Concentration of a gas in a mixture is expressed

as its percentage of total volume.

Number of units of volume of a gas in relation to a

total of 100 units of volume for the total gas

mixture.

Volumes percent expresses the relative ratio of a

gas molecules in a mixture.

Partial pressure expresses an absolute value.

Heat of vaporization

Number of calories required to convert 1gram of a

liquid into a vapor.

Number of calories required to conver 1ml of an

liquid into a vapor

Specific heat

Quantity of heat required to raise the temperature

of 1 gram of the substance by 1C

Amount of heat required to raise the temperature

of 1ml of liquid by 1C

Thermal conductivity

Measure of the speed with which heat flows

through a substance.

Higher the thermal conductivity the better the

substance conducts heat. z

Ideal vaporizer Delivers a fixed desired concentration of the agent

Equal to the concentration on dial setting

Independent of temperature

Independent of flow rate

Independent of carrier gas

No effect on back pressure

Easy to maintain

Easy to clean

Agent specific

Vaporizer Classification (Old)A. Method of Regulating Output Concentration

1. Concentration Calibrated (Variable-Bypass)

2. Measured Flow (Copper Kettle)

B. Method of Vaporization

1. Flow Over

2. Bubble Through

3. Injection

C. Temperature Compensation

1. Thermo Compensation

2. Supplied Heat

D. Specificity

1. Agent Specific

2. Multiple Agent

E. Resistance

1. Plenum

2. Low Resistance

Vaporizers Classification (New)A. Concentration Calibration

1.Variable Bypass Vaporizers

2. Electronic Vaporizers

B. Vaporization Methods

1. Flow Over

2. Injection

C. Temperature Compensation

1. Mechanical Thermo Compensation

2. Supplied Heat

3. Electronic Thermo Compensation

Vaporizer design

Regulating output concentrations

Concentration calibrated / variable bypass

vaporizer

Direct reading/ Dial controlled/ Automatic plenum/

Percentage type/ Tec-type vaporizers.

Output is controlled by a single knob or dial that is

calibrated in volumes percent

Located between flow meters and common gas

outlet.

Should not be between common gas outlet and

breathing systems or in the breathing system.

Concentrations are accomplished by splitting the

gas flow that passes through the vaporizer.

Splitting ratio It is the ratio of the resistance of the two pathways.

Ratio of the bypass gas to the gas going to the

vaporizing chamber.

gas going through the bypass

Splitting ratio = gas going through the

vaporizing chamber

It depends on-

a) Variable adjustable orifice of the inlet/outet

b) Total flow to the vaporizer

The clinically useful concentrations are

accomplished by splitting gas flows that passes

through the vaporizer.

Some of the gas flow through the vaporizing

chamber and the remainder goes through a

bypass to the vaporizer outlet.

Both gas flows join downstream of the vaporizing

chamber, where gas exits the vaporizer at desired

concentrations.

Electronic vaporizers

They are of 2 types –

a)A computer calculates the volume of carrier gas

necesssary to produce the desired agent

concentration that needs to pass through the

vaporizing chamber

b) Another type withdraws a calculated amount of

liquid agent from the agent bottle and injects the

liquid into breathing system or fresh gas flow.

The amount of liquid is adjusted to achieve the

desired agent concentrations.

Measured flows

The vaporizer heats the anesthetic agent to a

temperature above its boiling point and is then

metered into the fresh gas flow.

A measured flow is sent by a separate oxygen flow

meter to pass to the vaporizer with the output being

at saturated vapor pressure.

To dilute this concentration, output from the flow

meter is combined with gas passing from the main

flow meter.

Flow metered/ flowmeter controlled vaporizer

systems.

Copper – kettle/ Verni- trol and Metomatic

vaporizers.

Vaporization methods

FLOW OVER-

A stream of carrier gas passes over the surface of

the liquid.

Increasing the surface area of the carrier gas –

liquid interface enhances the efficiency.

Baffles / spiral tracks / wicks

Bubble through

The carrier gas is bubbled through the liquid

anesthetic agent.

A known amount of the liquid is then injected into

the fresh gas flow.

Boyle’s bottle

Sintered diffuser

Injection

Some vaporizers control the vapor concentrations

by injecting a known amount of liquid anesthetic

into a known volume of gas.

How much liquid agent does a vaporizer use per

hour?

Ehrenworth & Eisenkraft gave a formula-

3 x FGF(L/min) x vol% = ml liquid used per hour

Location of vaporizer

Plenum

Low resistance

Plenum

Latin- fullness

Vaporizers with resistance which depend on

compressed gas driven under pressure are

plenum vaporizers.

In these the internal resistance is high such that

the fresh gas flow should be above the

atmospheric pressure.

Low resistance

In these they have a low internal resistance to

gas flow. So these can be used within the

breathing circuit.

The carrier gas is drawn through the vaporizer

either by the patient’s own respiratory efforts or

by a self inflating bag or manual bellows.

they may be used in a

Non-rebreathing draw-over apparatus

In-circuit vaporizer

In a circle absorber system

Eg: goldman vaporizer, stephens vaporizer

Temperature compensation

3 methods are employed to maintain a constant

vapor output with fluctuations in liquid anesthetic

temperature.

a) Mechanical thermocompensation

b) Supplied heat

c) Computerized thermocompensation

Mechanical thermocompensation

The splitting ratio is altered so that the

percentage of carrier gas that is directed through

the vaporizing chamber is increased or

decreased thus compensating changes in vapor

pressure with temperature changes.

As vaporizer cools, the thermal element restricts

the bypass flow, causing more carrier gas to pass

through the vaporizing chamber, vice versa.

2 types of mechanical thermocompensation are

used.

1) Bimettalic strip

2) Invar rod

Bimettalic strip-

2 dissimilar metals or alloys are placed back to

back.

Due to different rates of expansion and

contraction with temperature- Device bends

It can be used to vary the degree of occlusion in

the aperture of the gas channel and thus alter the

flow of carrier gases through it.

Invar rod-

It is a metal alloy with a low coefficient of

expansion.

The bimettalic device consists of a central rod

made of invar, sitting inside a brass jacket, the

top part of which is attached to the roof of

vaporizing chamber.

As the liquid cools, the brass jacket contratcs

more than the invar which is pushed upwards into

the bypass restricting the flow of gas.

Supplied heat-

An electric heater can be used to supply heat to a

vaporizer and maintain it at desired constant

temperature.

Computerized Thermocompensation

It is accomplished by computer control

2 methods.

1) Amount of agent injected into the breathing

system or fresh g an amount of as flow may be

altered.

If the vaporizer withdraws an amount of liquid from

a bottle and inject it, the heat loss due to

vaporization may not be important.

2) The computerized control of the amount of

carrier gas flows through the vaporizing chamber.

Agent specificity

Agent specific

Multiple agent

Effects of intermittent back pressure

When assisted or controlled ventilation is used,

the positive pressure generated during inspiration

is transmitted from the breathing system back to

the machine and the vaporizers.

Back pressure may either

Increase the vaporizer output-Pumping effect

Or

Decrease the vaporizer output- Pressurizing

effect

Pumping effect

Factors effecting pumping effect

Less agent in vaporizing chamber

Carrier gas flow is low

Pressure fluctuations are high and frequent

Dial setting is low

Modifications

Small vaporizing chamber

Increasing size of bypass chamber

Employing a long spiral large diametered tube

leading to vaporizing chamber.

Exclude wicks where the inlet tube joins the

vaporizing chamber

One – way valve

Pressurizing effect

Factors

High flows

Large pressure fluctuations

Low vaporizer settings

Effects of rebreathing

Vaporizer dial setting reflects the concentration of

inhalational agent delivered to the system.

When FGF is high, exhaled gas is rebreathed, and

inspired concentration should be close to the

vaporizer setting

If FGF is low, exhaled gases contirbute a significant

proportion of inspired gases.

If minute volume is increased, more rebreathing and

greater effect.

Agent analyzer

Vaporizers and standards

The effects of variations in ambient temperature

and pressure, tilting, back pressure and input flow

rate and gas mixture composition on vaporizer

performance must be stated in accompanying

documents

The average delivered concentration from the

vaporizer shall not deviate from the set value by

more than 20% or 5% of the maximum setting,

whichever is greater, without back pressure.

The average delivered concentration from the

vaporizer shall not deviate from the set value by

more than 30% or 20% or by more than 7.5%0r -

5% of the maximum setting, whichever is greater,

with pressure fluctuations at the common gas

outlet of 2kPa with a total gas flow of 2L/min or

5kPa with a total gas flow of 8L/min

A system that prevents gas from passing through the

vaporizing chamber 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 position if the Zero position is

also the OFF position

All vaporizer control knobs must open

counterclockwise

Either the maximum and minimum fillling levels or

the actual usable volume and capacity shall be

displayed.

The vaporizer must be designed so that it cannot be overfilled when in normal operating position.

Vaporizers unsuitable for use in the breathing system must have non-interchangeable proprietary or 23mm fittings. Conical fittings of 15mm and 22mm cannot be used. When 23mm fittings are used, the inlet of the vaporizer must be male and the outlet female. The direction of the gas flow must be marked

Vaporizers suitable for use in the breathing

system must have standard 22mm fittings or

screw threaded, weight bearing fittings with the

inlet female and the outlet male. The direction of

gas flow must be indicated by arrows and the

vaporizer marked “for use in the breathing

system.”

Tec 5 Vaporizer

Classification: Concentration Calibrated

Flow Over with Wick

Out of System Location

Temperature Compensation by Automatic Flow Alteration

Agent Specific

Tec 6 Vaporizer

Classification:

Concentration Calibrated

Injection

Thermo Compensation by

Supplied Heat,

Electrically Heated,

Dual Circuit Gas Vapor Blender

Single Agent (Desflurane)

Tec 7 Vaporizer

Classification:

Same as Tec 4/5

Classification Datex-Ohmeda:

Tec4, Tec 5,

Aladin (can use De

Drager:

Vapor 19.n,

Vapor 2000

Copper Kettle,

Vernitrol

Datex-Ohmeda:

Tec 6 (Desflurane)

Splitting Ratio

(Carrier Gas Flow)

Variable-Bypass

(vaporizer determines carrier gas split)

Measured-flow (operator determines carrier gas split)

Dual-circuit (carrier gas is not split)

Method of Vaporization

Flow-over (including Aladin)

Bubble-through Gas/Vapor blender (heat produces vapor, which is injected into fresh gas flow)

Temperature Compensation

Automatic Manual (by changes in flow)

Thermo controlled (heated to 39C)

Calibration Calibrated to agent

Multiple agents Calibrated to agent

Datex-Ohmeda Aladin Sevo Vaporizer Cassette

Datex-Ohmeda Aladin Cassette

CPU(central processing unit) FBC (flow-measurement unit that measures flow through the bypass chamber) FVC P ((flow-measurement unit that measures flow through the vaporizing chamber) P(pressure sensor) / T (temperature sensor)

Datex-Ohmeda Aladin Isoflurane Vaporizer Cassette

Datex-Ohmeda Aladin Desflurane Vaporizer Cassette

Agent Specific Fillers

Fillers

Agent Specific Fillers

Isoflurane Filler Notch

Halothane Filler Notch

Isoflurane Filler Cap

Isoflurane Filler Cap

Isoflurane Filler Cap

Isoflurane Filler Cap

Interlock Mechanism

Interlock Mechanism

Interlock Mechanism

Interlock Mechanism

Thank you