VAPORIZERSVAPORIZERS Moderator

Dr.krishna Prasad M.D,

Assistant professor of Anaesthesiology

Dr.Sowbhagya lakshmi M.D,

Professor of Anaesthesiology

Speaker

Dr. Santhi latha PG

INTRODUCTIONINTRODUCTION

• This equipment to deliver the volatile anaesthestic agent in its gaseous form to the patient was felt right from time of first successful demonstration of ether anaesthesia by Dr.W.T.G. Morton in 1846

Developemnt of Vaporisers slowed down intially because of the ease of admininstartion of chloroform using a handkercheif.

Deaths under chloroform anaesthesia indiacated the relative danger of using the volatile agents without control

• Almost a century later,with the introduction of potent agents like halothane in mid 50’s the necessity to have precision vaporisers was felt and modern vaporisers came into existence.

Vaporizer is an instrument designed to facilitate the change of a liquid anaesthetic into its vapour in a controlled manner

Vapour :is gaseous phase an agent which is normally a liquid at room temprature and atmospheric pressure.

• Different vaporizers are present• Old Vaporizers- Boyle’s vaporizer for

ether(ether bottle) and trilene(trilene bottle)and Goldman vaporizer

• Newer Vaporizers-Fluotec3,4,5 and vapor 19.1:for halothane,isoflurane,and sevoflurane(type V only)

• Tech 6 :for desflurane

classificationclassification1. Methods of regulating output concentration

a. Variable bypassb. Measured flow

2. Method of vaporisationa. Flow overb. Bubble throughc. Injection

3. Temperature compensationa. Thermo-compensation

4. Specificitya. Agent specificb. Multiple agent

5. Resistancea. Plenumb. Low resistance

Method of regulating output Method of regulating output concentrationconcentration

There are two methods to regulate the output concentration.

• Variable Bypass

• Measured Flow.

Variable bypassVariable bypass

The total flow from the machine flows through the vaporiser. It is divided into two components.

One component flows through the vaporising chamber and the other component flows through the bypass chamber.

The flow through the vaporising chamber is controlled by the concentration setting on the dial and the by the thermo-compensation mechanism available in the vaporiser.

At the outlet of the vaporiser the flows mix and flow into the machine. This is called the variable bypass vaporiser.

Measured Flow:Measured Flow: The measured flow vaporiser needs two

flowmeters.One flowmeter is used to control the flow through the vaporiser and the other to control the diluent flow. Both the flows are mixed to give the final concentration. These vaporisers are usually provided with a nomogram/slide rule to calculate the flows according to the temperature and the total flow.

Method of vaporisationMethod of vaporisation

• Flow-over vaporisers

In flow over vaporiser the carrier gas over the surface of the liquid . The surface area for vaporisation can be increased by using wicks. The carrier gas may be directed using baffles such that the time and area contact are increased and thus the efficiency of the vaporiser.

Bubble through vaporisersBubble through vaporisers::

This type vaporiser the carrier gas is

allowed to bubble through the liquid. There is some means to break the gas into small bubbles thus increasing the surface area for vaporisation. Smaller the bubbles , larger will be the surface area. This method is commonly used in measured flow vaporisers.

Injection vaporisersInjection vaporisers

A known amount of liquid anaesthetic or pure vapour is injected into the gas stream to provide the desired concentration. These vaporisers use extensive electronics and injection methods to control concentration.

Temperature compensationTemperature compensation As a liquid is vaporized, energy is lost in the form of

heat and the temperature of the liquid decreases

In order to maintain a constant vapor out put, temperature of liquid should be maintained and this is temperature compensation and achieved by

a ) supply heat directly or indirectly (or)

b) Alteration of flow of carrier gas.

Supplied heatSupplied heat

Various methods use to maintain temperature of anaesthetic liquid

1. Use of large mass of copper in construction of vaporizer (high specific heat and thermal conductivity of copper thus it provides a physical means heat supply by rapid transfer).

2. Wicks in vaporizer are in direct contact with a metal part so that they can replace heat lost due to vaporizer.

3. Direct heating is done by providing hotwater bath jackets surrounding vaporising chamber or electric heater inside the chamber

Flow compensationFlow compensation Another means of compensating for the

decrease in vapor pressure from lowering of temperature is to increase the percentage of the carrier gas that is directed through vaporizing chamber. Most of variables by pass vaporizers automatically adjust flow by a thermostatic mechanism which opens and closes the point of exit of gas from vaporizing chamber

• At high temperatures the vapor pressure inside the vaporizing chamber is high.

• To compensate, the bimetallic

strip of the temperature-compensating valve leans to the right.

• This allows more flow through the bypass chamber and less flow through the vaporizing chamber.

• The net effect is a constant vaporizer output.

• In a cold operating room environment, the vapor pressure inside the vaporizing chamber decreases.

• To compensate, the bimetallic strip swings to the left, causing more flow to the vaporizing chamber and less to the bypass chamber.

• The net effect is a constant vaporizer output.

Specific aneaesthetic Specific aneaesthetic agentsagents

Agent specific: Some vaporizers manufacture for a particular anaesthetic agent and calibrated accordingly

• Multiple agent : thease vaporizer used with various anaesthetic agents and are universal or all-purpose vaporizers

Most of the modern vaporisers are agent specific so that the concentration delivered can be maintained.

ResistanceResistance

Most modern vaporisers have a high resistance and depend on compressed gas driven under pressure. These are called plenum type vaporisers.

Gray and Nunn Gray and Nunn classificationclassification

• 1.plenum vaporizer

• 2.inhalers or draw over vaporizer

• 3.simple vaporizers for use inside circle anaesthetic systemle example.Goldman vaporizers,Rowbotham vaporizer.

• Plenum vaporizer: In this sytem fresh air is forced into a chamber.thease vaporizers used with fresh gas flow from anaesthetic machines.examples are

1.Boyl’s vaporizer 2.copper kettle 3.fluotec mark2 4.fluotec mark3 5.halox vaporizer 6.pentec(methoxy flurane) 7.tritec(for trichloro ethylene) 8.enfluratec( enflurane)• The vaporizer have unidirectional gas flow and have

relatively high resistence to gas flow so they are nor suitable for use as draw over vaporizers or circle system

• Inhalers or draw over vaporizer. Thease vaporizers have a very low

resistence to gas flow .example.1.EMO Vaporizer

• 2.Emotril 3.tecota,4.oxford manufacture inhaler

Physical PrinciplesPhysical Principles• Knowledge of physics of heat and

vaporisation is essential to understanding of vaporizer

• Physical principles are 1.vapour pressure2.boiling point3.concentration of a gases4.latent heat of vaporisation5.specific heat6.Thermal conductivity

• Vapour Pressure:a volatile liquid inside the container that is closed to atmosphere.mollecule of liqiud break away from surface end enter space above forming vapour.

• If the container is kept at constant tepmrature a dynamic equalibrium is formed between liquid and vapour phases .sothat the number of mollecule in vapour phase remain constant.thease mollecules bombard the walls of container,creating pressure.this is called the saturated vapour pressure

Vapor pressure is dependent on only the temperature and nature of liquid

Boiling Point:

The boiling point of a liquid is that temperature at which the vapor pressure is equal to the atmospheric pressure

Agent Saturated vapour pressure at 20 C Boiling point

Halothane 243 50.2Enflurane 175 56.5Isoflurane 238 48.5Desflurane 664 23.5Sevoflurane 160 58.5

Agent Saturated vapour pressure at 20 C

Boiling point

Halothane 243 50.2

Enflurane 175 56.5

Isoflurane 238 48.5

Desflurane 664 23.5

Sevoflurane 160 58.5

Concentration of gases: Two methods are commonly used to express

the concentration of gas or vapor .

1. Parital pressure.

2. Volumes percent.

Partial pressurePartial pressure• A mixture of gases in a closed container will exert a pressure

on the walls of the container that will equal to the atmospheric pressure

• The part of the total pressure exerted by any one gas in the mixture is called the partial pressure of that gas

• The total pressure of the mixture is the sum of the partial pressures of the constituent gases .

• The partial pressure exerted by vapour of the liquid agent depends on temperature of that agent and unaffected by the total pressure above the liquid

• The highest partial pressure that can be exerted by a gas at given temperature is its vapour pressure

VOLUMES PERCENTVOLUMES PERCENT• The term volumespercent is defined as:the number of

units of volume of a gas in relationship to a total of 100 units of volume for the total gas mixture .

• Expresses the relative ratio of gas molecules in a mixture ,while partial pressure expresses an absolute value.

• Patient uptake and the level of anaesthesia are directly related to the partial pressure ,but only indirectly to volumes percent.

• While a certain partial pressure represents the same anesthetic potency under various barometric pressures, this is not the case with volumes percent.

• Partial pressure/total pressure=volumes percent

HEAT OF VAPORIZATIONHEAT OF VAPORIZATION::

• Heat of vaporization of a liquid is the number of calories necessary to convert 1g(1cc) of liquid into vapor. (The colder the liquid the greater quantity of heat needed to convert a given amount of liquid into vapor).

the lower the liquid temperature the greater the gradient and greater the flow of heat from the surroundings

• SPECIFIC HEAT:

The specific heat of a substance is defined as quantity of heat required to raise the temperature of 1 gm of substance 1 C (The higher specific heat , the more heat required to raise the temperature of a given quantity of that substance).

specific heat is important for choosing material to construct

Thermal Conductivity: Thermal conductivity is measure of speed with which heat flows through a substance. The higher the thermal conductivity the better substance conducts heat (low thermal conductivity of a substance is poor conductor and good insulator of heat).

Metal Specific heat Thermal conductivity

Copper 0.1 0.92

Aluminum 0.214 0.504

Glass 0.16 0.0025

Steel 0.107 0.115

Brass 0.0917 0.260

Air 0.0003 0.000057

Factors affecting vaporiser output:Factors affecting vaporiser output:

1. Amount of carrier gas passing through the vaporiser. Higher the volume of gas , higher the output.

2. Surface area for vaporisation. Higher the surface area will be the vaporisation. Wicks are added to increase the surface area of vaporisation.

3. Gas liquid interface: If the carrier gas is bubbled through the

liquid ,it is likely to be fully saturated when it leaves the vaporiser. If the gas passes well above the liquid, the amount of vapour carried will be less

4.Temperature of that liquid. If the liquid is allowed to cool, as the vaporisation proceeds the vapour outputs will comedown.

5. Boiling point of the liquid . Higher the boiling point, less will be the vapour output at room temperature.

6.Altered Barometric pressure.

7.Intermittent Back pressure

ALTERED BAROMETRIC PRESSURE:ALTERED BAROMETRIC PRESSURE:

• Anesthetic agents with low boiling points are more succeptible than agents with higher boiling points

Low atmospheric pressures:• High resistance path way offers low resistance,

increasing vapor output slightly (partial pressure), the effect will be greater (volumes percent)

High atmospheric pressures:• Change in density of gases cause more

resistance to flow through vaporizing chamber and a decrease in output (partial pressure, volume percent)

Effects of Intermittent Back PressureEffects 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. This back pressure may either increase (pumping effect) or decrease (pressurizing effect) the output of the vaporizer.

Pumping EffectPumping Effect

Factors affect the magnitude of the observed in vaporizer concentration

1. When there is less agent in the vaporising chamber.

2. When carrier gas flow is low.

3. When the pressure fluctuations are high and frequent

4. When the dial setting is low.

MechanismMechanism: in variable bypass vaporizer: in variable bypass vaporizer

In inspiratory phase there is compression of gas in

vaporizing chamber and bypass , the bypass has smaller volume than vaporizing chamber so more molecules go to vaporizing chamber , which picks up anaesthetic vapor .

In beginning of exhalation due to pressure fall gas flow suddenly from vaporizing chamber and bypass to outlet, also due to less resistance pressure drop in bypass is quick than vaporizing chamber and gas containing anaesthetic vapor flows into bypass from vaporizing chamber causing increase in vapor concentration.

Measured flow vaporizer:Measured flow vaporizer:

There is no bypass so there is other mechanism. When back pressure is applied , there is retrograde flow of gas so that diluted gas mixture is forced back into vaporizer, it picks up more vapor and increase in flow increases vapor concentration.

Minimize pumping effectMinimize pumping effect

Variable bypass vaporizer:1. Minimize size of vaporizing chamber or increase size

of bypass.2. Preventing extra gas flow to vaporizing chamber

from picking up anaesthetic vapor by.a) Long spiral or large diameter tuder leading to

vaporizing chamberb) Exclude wicks from area where in let tube joins the

vaporizing chamberc) Special alteration ; A pressurizing valve is inserted in

gas line distal to vaporizer.

Measured flow vaporizerMeasured flow vaporizer

1 . Decrease rise of vaporizing chamber.

2. Increase size of outlet tube.

3. Special alteration : incorporate relief valve at the outlet to limit the pressure or check valve.

Pressurizing effectPressurizing effect

Factors causing decrease vaporizer output are

a) High flow rates.

b) Large pressure fluctuation.

c) Low settings.

Mechanism:Mechanism:

Increase pressure in vaporizer will compress gas, so more molecules per cubic centimeter. The no of molecules of anaesthetic vapor in vaporizing chamber will not increase since it depends on saturated vapor pressure of anaesthetic and not an atmospheric pressure so it will decrease in vapor concentration in vaporizing chamber and outlet.

Interplay Between Pressurising Interplay Between Pressurising and pumping Effectsand pumping Effects

The changes in vaporiser output caused by the pumping effect usually are greater in magnitude than those associated with the pressurising effect. The pressurising effect is seen with high gas flows and the pumping effect, at low flows.

Carrier Gas Composition :

• When the carrier gas is quickly switched from 100% oxygen to 100% nitrous oxide, there is a rapid transient decrease in vaporizer output followed by a slow increase to a new steady-state value

• Nitrous oxide's being more soluble than oxygen in halogenated liquid.

• The quantity of gas leaving the vaporizing chamber is transiently diminished until the anesthetic liquid is totally saturated with nitrous oxide.

Each vaporiser system consists of the three parts. 1.Vaporizer:

The vaporizer includes the body that holds the liquid . The vaporizer also has a window to view the liquid level, a filler port, and a thermometer to measure the temperature within the vaporizer.

2. Flowmeter Assembly:

The flowmeter may be calibrated either for the flow of gas through the flowmeter or for the vapor flow.

3. ON-OFF Valve:

The ON-OFF valve’s function is to isolate the vaporizer.

Characteristics of the ideal Characteristics of the ideal vaporizersvaporizers

• Its performance is not affected by changes in fresh gas

flow, volume of liquid agent, ambient temp & pressure fluctuation due to the mode of respiration.

• Low resistance to flow• Lightweight with small liquid requirement.• Economy and safety in use with minimal servicing

requirements• Corrosion and solvent -resistant construction.

SPECFIC VAPOURIZERSSPECFIC VAPOURIZERS1.Goldman vapourizer1.Goldman vapourizer

Goldman vaporizer:A.C.KingGoldman vaporizer:A.C.King 1952-1962 1952-1962

• Classification : a. Variable by pass , flow over without wick , in or out of

system. b. No temperature compensation. c. Multiple agent. – halothane, trilene• Parts:• Glass bottle 50cc, 100cc capacity.• Metalic cap with a control lever , click stops at each

settings.• Concentration 0-0.5%-1%-1.5%-2% of Halothane.• Types:• Mark I - with 0-2% control knob.• Mark II - with 0-3% control knob.• Mark III - with 0-2.5% control knob.

It Can be used inside or outside circuit.

Outside-the-circuit:

Goldman vaporizer is mounted on the Boyle’s machine , proximal to the breathing circuit. Patient’s spontaneous ventilation acts as motive force.

Inside-the-circuit:Goldman vaporizer is mounted in the closed circuit with soda lime canister use in inspiratory or expiratory limb( at inlet or outlet of canister) To increase halothane concentration:

Wicks can be added (copper) to increase concentration up to 4%. Known as Young’s modification

2 Goldman vaporizers can be in series making adjustable concentrations. Known as Hall’s modification.

Disadvantages:Disadvantages:

• No wicks. No temperature compensation mechanism• Accidental tilt with portable Goldman vaporizer

pouring liquid anaesthetic agent directly from breathing circuit to pt’s respiratory tract leading to pulmonary oedema -> high risk of mortality

• Pumping / backpressure effect -> risk of delivering unknown high concentration than indicated during IPPV.

Copper kettle vaporizerCopper kettle vaporizer• Measured flow vaporizer,

bubble through, out of systems.

• Temperature compensated by supplied heat and manual flow alteration.

• Higher than the expected concentrations with IPPV

• Effect of intermittent back pressure are seen

• A check valve in the newer models.

Boyles bottle vaporizerBoyles bottle vaporizer• Variable bypass, flow over

without wick, out of system, bubble through

• No temperature compensation, not calibrated

• Ether, trilene, chloroform, halothane, methoxy flurane.

• Temperature is maintained by wiping bottle from outside

• All agents are colored to prevent wrong agent in wrong bottle.

• It consist of ether bottle,lever for on and off ,a U tube,and a plunger with hood over U tube.

• Ether bottle is calibrated up to 300ml.whe the plunger is brought down,the hood comes under the surface of liquid and the gas pass through liquid(bubble through) delivering high concentration

• Utube is made up of copper which acts as anticatalyst to prevent decompsition of ether.

EMO vaporizerEMO vaporizer• Variable bypass, flow over

with wick, in or out of system

• Temperature compensation by supplied heat and flow alteration

• Agent specific for Diethyl ether, halothane, chloroform, trichloroethylene

• Draw over with low resistance

• Compact, low cost, portable• Used for mass casualties

EMO (Epstein, Macintosh, Oxford) EMO (Epstein, Macintosh, Oxford)

TEC 2TEC 2

• Variable bypass, flow over with wick, out of system• Halothane, methoxyfluraneEvaluation:• First common concentration calibrated device• Not accurate below 4 lit/min

Maintenance:• Yearly return it to company for servicing• Vaporizer is drained every 2 weeks

TEC-3TEC-3• Classification : 1. variable bypass flow over with wick, out of system.2. Temperature compensation by automatic flow

alteration, concentration calibrated.3. Agent specific – Halothane,Enflurane,Isoflurane

• Models: Fluotec-3,Enfluratec-3,Fortec-3

These vaporizers are no longer being manufactured.

TEC-4TEC-4• Classification :

1. variable bypass flow over with wick, out of system.

2. Temperature compensation by automatic flow alteration, concentration calibrated.

3. Agent specific – Halothane,Enflurane,Isoflurane

• Models:

Fluotec-4,Enfluratec-4,Fortec-4

• Off position: fresh gas enters the inlet passes through the bypass to the outlet.

• On position: Fresh gas divided into two parts

• One part enters the vaporizing chamber, the chamber that surrounds the bypass chamber.

• It passes over the two concentric wicks along the side of the vaporizer

• The vaporized gas leaves through second chamber to the outlet

• The rest of gas flow through bypass chamber

• When the vapor cools, the temperature compensated device causes more gas to flow inside the vaporizing chamber

Tec 4Tec 4

TEC-5TEC-5

• Classification :

1. variable bypass flow over with wick, out of system.

2. Temperature compensation by automatic flow alteration, concentration calibrated.

3. Agent specific – Isotec-5,Fluotec-5,

Enfluratec-5,Sevotec-5

Tec 5Tec 5

TEC-6TEC-6

• Classification:

1. Concentration calibrated,injection,out of system.

2. Thermo compensation by supplied heat.

3. Agent specific – desflurane.

TEC - 6TEC - 6

Tec 7Tec 7

Drager Vapor19.1Drager Vapor19.1

Computer controlledComputer controlled(Aladin cassette)(Aladin cassette)

• Used in Ohmeda(S/5 ADU )

• Electronically controlled vaporizer

• Designed to deliver halothane, isoflurane, enflurane, sevoflurane, and desflurane.

Aladin cassettesAladin cassettes

Safety features of modern Safety features of modern vaporizersvaporizers

• Important safety features include:• Keyed fillers• Low filling port• Secured vaporizers(less ability to move them

about minimises tipping.)• Interlocks

• Conc.dail increases output in all when rotated

counterclockwise.

Filling the VaporizerFilling the Vaporizer• Vaporizers are agent specific – each vaporizer is

calibrated to deliver a set amount of a particular agent. • Filling a vaporizer with the incorrect agent will result in

too much or too little agent being delivered.• The vaporizer should be filled to the fill level marked on

the indicator window.• Vaporizers should not be filled while they are in use or

turned on.

• Vaporizers may be funnel filled or key filled.

• Keyed fillers have an adaptor that can only be inserted into the filler port of the corresponding vaporizer.

• The filler has a bottle specific collar to prevent it from being attached to the wrong bottle.

• The vaporizer, filler and bottle are all color coded to lessen the risk of cross filling.

Filling devicesFilling devices

Filling spout Keyed filling system Quik fil filling system

Quik Fil filling systemQuik Fil filling system

• Such devices are required by the F1161-88 standard, which states that the filling mechanism should be fitted with a permanently attached, standard, agent-specific, keyed filling device to prevent accidental filling with the wrong agent.

Maintainence of vaporizersMaintainence of vaporizers

• Tech5-exterior of vaporizer may be wiped with dampcloth.no other cleaning or disinfection should be attempted.

• The vaporizer be drained every 2 weeks• Every 3 years the vaporizer should be returned

to service center for complete disassembly,cleaning,inspection for damage and replacement of wornparts and calibration.

• Tech6: this vaporizer require inspection every year at an authorized service center.

• Tech 7: halothane vaporizer should be drained every 2 weeks when the level is low ,and liquid discarded if there are additives or stabilizing agents.

• Every 3 years inspection and output is checked.• Aladin vaporizer-cassette surface is cleaned with cloth

moistened in mild soap solution .cassette should be emptied before sending it into service center.

• Vapours 19.1,19.3-the vaporizer should be inspected by trained personal every 6months.and the wicks changed every 2 years

• Drager d vapour-inspected and serviced by skilled personal every year

Hazards:Hazards:

• Mis-filling : filing of wrong agent than is indicated.• Tipping : can occur when vaporizers are incorrectly

moved or switched as with older one (Goldman vaporizer – accidentally tilting). It is unlikely with vaporizers fixed to the machine in an upright position permanently.

- Tipping can be cause liquid anaesthetic agent to enter directly into the respiratory passage causing damage to alveoli – risk of mortality ++.

• Over-filling :

Risk of overdose. Liquid anaesthetic agent enters the bypass chamber and up to 10 times vapour concentration can be delivered. Risk of morbidity++.

• Leak:Leaking vaporizer makes the patient light – risk of tachycardia, arrhythmias due to inadequate anaesthesia. Leak can occur with glass bottles of ether/trilene vaporizer on Boyle’s apparatus. Leak can occur with loose filler cap or broken ‘O’ ring in it. Pumping effect (Hill and Lowe effect -1962): Intermittent backpressure with IPPV or O2 flushing can cause high vaporizer output concentrations than dial setting. This is called pumping effect. It can be minimized be one-way check valve at common gas outlet. Pressurizing effect (Cole’s effect):Cole found that the vaporizer output concentration was lower at high flow rates

Summary of vaporizer performanceSummary of vaporizer performance

Vaporizer performance can thus be affected by:

• Temperature.

• Flow rate of the gas flowing over it.

• Barometric pressure (minimal effect in clinical practice)

• Variable vaporizer working pressures (back pressure surges)

• Liquid levels within the vaporizer

• Movement and titling of vaporizers.

• Carrier gas composition.

• Stabilizers in the inhalational agent ( e.g. thymol)

conclusionconclusion

• Understanding of physics involved and the working mechanisms of vaporizer that are being used is important for proper usage and the maintenance of the equipment

“Vaporizers are sensitive , accurate, scientific instruments involved directly in critical life support. Treat them with great care.”

THANK “U”