Principles of vaporizers and older vaporizers

Principles of vaporizers and older vaporizers

Presented by: Dr Rashmi Moderator: Dr Kartik Syal

The start 1847:

◦ John Snow (1813-1858)◦ described the relationship between temperature and

the saturation of ether vapor◦ first major milestone in the attempt to control the

strength of anesthetic vapor administered to patients 1952:

◦ Dr. Lucien E. Morris (1914-2011)◦ Copper Kettle vaporizer◦ first system to permit very fine control over the

concentration of volatile anesthetics

A vaporizer is an instrument designed to facilitate the change of a liquid anaesthetic agent into a vapor and add a controlled amount of this vapor to the gas flow to the patient.

known and reproducible concentration of anaesthetic vapour delivered in a safe and reliable manner

A vapour is the gaseous phase of an agent which is normally a liquid at room temperature and atmospheric pressure.

INTRODUCTION

May be expressed as VOLUME % :- it’s the concentration of gas in

a mixture. / no of units of volume of gas in 100 units of vol of total gas mixture

PARTIAL PRESSURE :- In a mixture of gases the pressure exerted by each gas is the same as that which it would exert if it alone occupied the container

Concentration of vapour

Method of regulating output concentration 1. Concentration calibrated (variable-

bypass)- direct type 2. Measured flow - indirect typeMethod of vaporization 1. Flow over 2. Bubble Through 3. Injection

classification

Temperature compensation 1. Thermo-compensation 2. Supplied heat Specificity

Agent specific Multiple agent Resistance 1. Plenum 2. draw over VIC / VOC

Classification contd.

Basic design

Total flow from the machine split by a variable resistance proportionating valve

◦ One part (usually major): through bypass chamber &

◦ Other (usually small): through vaporizing chamber

agent concentration controlled by dial calibrated in volumes percent

Concentration caliberated

Dial with high concentration

Dial with low concentration

ratio of the bypass gas to gas going to the vaporizing chamber

depends on:

Resistance of the two pathways, depends on the variable orifice of the inlet/outlet.

Temperature of the liquid/carrier gas.

Flow rate of gases

Splitting ratio

separate, independent stream of vapour carrying gas, added to the fresh flow

To calculate the vaporizer output, to know

Vapor pressure of the agentThe atmospheric pressureThe total flow of gases The flow of the vaporizer

Eg: Ohmeda Tec 6, sp for Desflurane, copper kettle

MEASURED FLOW VAPORIZERS

Method of vaporization:Flow over Vaporizers : carrier gas flows

over the liquid agent, saturated with vapor.

Bubble through Vaporizers : carrier gas is bubbled through the liquid agent

Injection Vaporizers : known amount of liquid agent or pure vapor injected into the gas stream to provide the desired concentration.

Classification contd

Flow over

Bubble through

TEMPERATURE COMPENSATION maintain a constant output compensation for fluctuations in temperature Cooling affects vapour concentration. Mech: Alteration in the splitting ratio (automatic

compensation) Eg. Bimettalic strip in tec vaporizer

Supplied heat – tec 6 (electrically heated) copper metal Ether filled copper bellows ex Penlon vaporisers TEMPERATURE UNCOMPENSATED: boyle’s bottle, goldman

etc TEMPERATURE BUFFERING hot water jacket/ heat sink (ex

OMV)

Classification contd

On cooling, bimetallic strip bends,moves away

reduces the resistance to flow=more flow into vaporizing chamber

Automatic compensation

SPECIFIC AGENT use with one specific agent. Must be labeled Use of other agents may give incorrect

concentration, may damage vaporizer, harmful byproducts.

MULTIPLE AGENT :- Rarely in use, not advised. Ex OMV, EMO, Copper kettle

Classification contd.

VOC = Vaporizer-out-of-system

localized btwn flowmeter and CGO

Oxygen from the flowmeter enters the vaporizer prior to entering the breathing circuit.

VIC = Vaporizer-in-system

Oxygen enters the breathing circuit from the flowmeter

either in circle , at CGO, inhalers i.e in breathing sytem – gas is drawn through it by pts breathing spontaneously.

Comparison of the two on basis of RESISTANCE DETERMINANTS OF VAPORIZER OUTPUT CAPABILITY OF THE VAPORIZER

resistance :- VOS Need not hv low resistance as gas flow can be supplied at any necessary pressure.

VIS Must have low resistance because pt breathes through them

Determinants of vaporizer output :- vaporizer output -conc of vapor at outlet of vaporizer. (vo) vaporizer conc :- conc delivered by vaporizer when fresh gas

containing no vapour passess through it . (vc)

in VOC both VO & VC are equal in VIS , BOTH the VC & VO are likely to differ..the VO will be

influenced by MV, uptake of agent, FGF to system and arrangement of system ..with Low FGF, VO may rise to dangerous levels.

CAPABILITY OF VAPORIZER :- maximum concentration that can be delivered at highest setting of conc dial..

VIS/ VOS used in non rebreathing system must have a high capability as no more anesthetic will be added to gas going to pt. but in circle system vaporizer, its not capable of delivering high conc, because the gas may circulate through it many times, each time picking up added vapors.

VIC and VOC

RESISTANCE PLENUM ( Latin = fullness ) Driven by positive pressure ventilation internal resistance is high (22 cmH2O),

accurately caliberated Accurate at low flows also Eg. Boyle bottle, copper kettle, TEC

vaporizers

Classification contd

DRAW OVER Carrier gas drawn through the vaporizer either by the

patient’s own respiratory efforts, or by a self-inflating bag or manual bellows

operate at less than, or at ambient pressure Intermittent flow, varying with different phases of

inspiration, ceasing in expiration. low internal resistance may be used in a non rebreathing DRAW-OVER APPARTUS,

or in CIRCLE ABSORBER SYSTEM. Eg. Goldman bottle, EMO

ADVANTAGES Simplicity of concept and

assembly, with inherent safety

No need for pressurised gas supply, regulators and flow meters

Minimum FiO2~21% Robust, reliable, easily

serviced equipment Low cost (purchase and

maintenance) Portable, suitable for field

anaesthesia

DISADVANTAGES Decreasing familiarity with

the technique and equipment Filling systems not agent

specific (potential advantage) Basic temperature

compensation, affecting performance at extremes

Less easy to observe spontaneous ventilation with self inflating bag

Cumbersome in paediatric use, unless lightweight tubing is available

Drawover anaesthesia

flow through the vaporizing chamber.

surface area of the liquid gas interface.

temperature time gas flow rate carrier gas composition boiling point ambient pressure :-atmospheric, intermittent back pressure

FACTORS AFFECTING VAPORIZER OUTPUT

Low pressure: vaporizing chamber offers less resistance, slight increase in vapor output occurs.

Deliver higher conc in vol. % but same Partial pressure

High pressure: INCREASES the Density of gas, More resistance to flow of gas through the vaporizing chamber, Decreased vapor output (Volume Percent)

Less Effect on partial pressure ether may boil at room temp at low atm pressure. Also at high pressure, liqiud agent may be

pushed back into the vaporiser inlet avoided by maintaining a low flow of oxygen or

filling the vaporiser after increase in pressure.

Effect of atmospheric pressure

should theoretically deliver a constant partial pressure of anesthetic if the ratio of gas flow through the vaporizer to bypass the flow remains the same.

For classical plenum vapourisers, the percentage output increases roughly in proportion to the fall in barometric pressure, but a smaller partial pressure increase.

TEC 6 Desflurane vapouriser behaves differently. The percentage delivered constant, so partial pressure FALLS in proportion to the fall in atmospheric pressure. The dial setting should be turned up to compensate

The increase in vaporizer output concentration due to pulsatile back pressure developed in the breathing system.

more fresh gas gets compressed into vaporising chamber

seen especially when-> carrier gas flow is low-> agent in vaporizing chamber is low-> dial setting is low-> pressure fluctuations are high & frequent.

Pumping effect

keep VC (vaporising chamber)& BC (bypass channel) of equal size/ VC small size.

Add long spiral or large diameter tube to lead to the vaporizer chamber

add check valve, increase resistance to gas flow through V.C.

Exclude wicks from the area where the inlet tube joins the vaporizing chamber.

Longer Outlet tube Limit pressure transmitted to vaporizer to <10KPa

above normal working pressure, conc not to increase > 20%.

Minimising pumping effect

Increased constant pressure in vaporizer chamber leads to decreased output

Mostly seen when-> High flow-> Large pressure fluctuations -> Low dial settings

The changes in vaporizer output caused by the pumping effect usually are greater in magnitude that those associated with the pressurizing effect

Pressurizing effect

Pressurizing effect

INCORRECT AGENT Low output or high output Rx : Gas allowed to flow through it until no

agent detected in the outflow, labelling correctly.

RESISTANCETIPPING Liquid from the vaporizing Chamber→

bypass/outlet→ high output Drained before moving

hazards

OVERFILLING safety mechanisms: design of the filling port,

agent specific filling systems During filling dial to be off

FOAMING possibility of liquid agent getting into the outlet. Seen in bubble through vaporiser for

methoxyflurane. foaming due to silicone grease, (used as a

lubricant) or solution used to test for leaks.

Hazards contd.

REVERSED FLOW • Inlet male & outlet female• Increased output CONCENTRATION DIAL IN WRONG

POSITION CONTAMINANTS IN VAPORIZING CHAMBER PHYSICAL DAMAGE OBSTRUCTION TO FRESH GAS FLOW INTERLOCK MALFUNCTION

Hazards contd.

Boyle’s bottle Copper kettle EMO (epstein, macintosh, oxford) vaporiser Goldman vaporiser OMV (oxford miniature vaporiser) Cyprane Vernitrol others

Older vaporizers

Useful in remote locations like military use, as portable and simple to use (ex EMO)

Some peripheral setups still use goldman vaporiser

Draw over vapouriser (2 OMVs with sevoflurane) can be used in Paediatric circuit

Addition of OMV with ventilator in treatment of severe asthma (Nagappan et al 2006)

Relevance of older vaporisers in present times

Parts:(1) vaporizing bottle 300 mL(2) Metal top incorporating

controls(3) Lever, plunger which is

chrome plated (copper in case of Boyle ether bottle and absent in halothane bottle)

(4) Stopper & Retaining chain Concentration calibrated,

plenum type Flowover or bubble through Not temperature

compensated Multiple agents Vaporizer outside circuit With this bottle, the maximal

ether concentration would be about 50% at 20 degrees C.

Boyle’s bottle (early 1920’s)

Developed in 1930’s: modified by Morris in 1952

measured flow (indirect type) temperature compensated bubble through, plenum type agents – chloroform, ether ,

halothane a separate supply of oxygen

from extra flowmeter passes through the vaporizer.

Oxygen broken into minute bubbles by sintered bronze

large mass of copper and attachment to machine, sufficient reservoir for heat

Disadv: high vap conc if FGF dec

Copper kettle

Copper kettle : internal design

Measured flow Bubble through Out of system Temperature compensated

(supplied heat) Multiple agent Body made of silicone

bronze, may contain upto 600 cc of liquid agent.

When used for halothane, drained periodically to prevent buildup of thymol, ether and trichlorethylene should not be allowed to stand for long.

Vernitrol (based on copper kettle)

Goldman vaporiser (1959)

originally designed for use with dental anaesthetic apparatus Concentration caliberated flow over with no wicks multiple agents – halothane, chloroform neither temperature and level compensated nor accurately

calibrated. halothane concentration usually low (hence safe), output is

mainly influenced by gas flow rate. VOC / VIC small glass bottle with metal top, inlet- outlet , contol lever

at top is used to alter vapor output , capacity of 20ml , max concentration delivered 2 % , (higher if splashing, spraying of agent, if wick is used, or 2 vaporizers in series.)

3 models of goldman vaporizer are :- MARK 1:- self locking in off position MARK 2 :- differs from mark 1 in size & shape of

opening in the ports & is provided with click stops at each setting

mark 1 and 2 both have three divisions btwn the on & off positions.

MARK 3 :- has one less division.KOMESAROFF Similar to the Goldman but with gradations on

the glass bowl indicating volume

Modification of Goldman vaporizer (has wire wick gauge)

simple flow-over type not temp compensated capacity of 35 ml multiple agent max concentration up to

3.1 % with 4L/ min flow rate.

vapor strength is controlled by means of lever stopcock.

Rowbotham vaporiser

Introduced by Epstein, Macintosh, Mendelssohn in 1966.

Vaporizer inside/outside circuit Variables bypass Flow over with steel wicks

(cleaned with ether) Not Temperature compensated

(heat sink= heat buffering) multiple agent, detachable scales

(adv) Halothane,

trilene ,methoxyflurane ,ether, isoflurane.

particularly versatile, can be used to vaporize a number of agents with only the dial scale being changed.

Oxford miniature vaporiser

Original models contained 20mls of volatile agent, more modern ones 50mls.

not temp compensated but basic thermal buffering in the form of a small glycol (anti-freeze) reservoir within a metal heat sink.

reduced vapor output at lower temperatures, maximum output 2-4% with halothane between 0-30OC.

Made from stainless steel, resistant to corrosion. Metal mesh wicks increase the output (halothane use, clogged

with thymol) Using two OMVs with a drawover system appears to be a feasible

technique for the induction and maintenance of sevoflurane anaesthesia, thus enabling wider use of sevoflurane in field anesthesia. (study by Liu et al in 2000)

OMV contd.

Epstein macintosh oxford vaporiser (emo)

Concentration caliberated Flowover with wicks Temp compensated (metal bellows with freon vapor) Multiple agents- ether, chloroform, trilene, halothane Dia:23 cm; Ht : 24 cm Wt(ether) : 6 kg; (halothane) : 12 kg 0 – 20% graduations 40 ml ether when full Inlet for air Control lever with transit lock Indicator to denote level of anaesthesia Temp indicator (max eff 15-30 C)

EMO contd.

Water jacket : 1250 cc Mark I: aluminium water jacket Mark II/III/IV: stainless steel jacket Used with OMV for spont resp OMV filled with halothane for smooth

induction , maintained with ether in EMO

EMO contd

EMOTRIL (Epstein, Macintosh, Oxford Trilene inhaler) Introduced in 1949. A draw over Trilene vaporizer

giving 0.35 and 0.5% Trilene in air, temperature compensated, designed for unsupervised use by midwives for pain relief during labor.

BRYCE-SMITH INDUCTION UNIT (BSIU) no longer manufactured. useful to facilitate induction when using the EMO

ether vaporizer simple no-controls vaporizer delivers 3 - 4 mls of halothane to precede, and assist

induction with, ether.

cyprane

device for trilene inhalation originally from the Queen Victoria Hospital.

Maternity patients would hold the device and inhale an air-trilene mixture.

The collar of the device could be rotated to vary the concentration from about 0.22% to 0.54%. The collar can be locked.

Designed in Sydney by Dr Thomas Small, in the mid 1930's, for the provision of analgesia during labour.

The ether container consists of a chrome plated brass drum which holds 270mls.

The control on top varies the ether concentration.

Valves ensure unidirectional flow, and a separate expiratory valve is on the face mask mounting.

Small’s self help ether apparatus

Diamedica Draw-Over Vaporizer (DDV) has been developed as an alternative to the Oxford Miniature Vaporizer (OMV)

can function as draw-over or plenum

larger reservoir, tendency towards greater accuracy during IPPV and improved consistency of output.

others

Ohmeda Universal PAC drawover apparatus, a modification of an earlier series of vapour-specific vaporizers

Caliberated, temperature compensated, flow over Oxygen may be added but not necessary clinical usage with isoflurane and enflurane Tends to over-deliver vapour, esp at low flows and at

high temperatures clinical performance during spontaneous and positive

pressure ventilation satisfactory robust construction, relatively large capacity and

thermocompensation make it suitable for field or military anaesthesia.

U PAC (universal portable anesthesia complete) drawover system

Others

Cole halothane vaporiser Ether bypass

Freedman inhaler for trilene

Then and now

Thankyou