Presentation on theme: "Principles of vaporizers and older vaporizers"— Presentation transcript:
1Principles of vaporizers and older vaporizers Presented by: Dr RashmiModerator: Dr Kartik Syal
2The start 1847: 1952: John Snow (1813-1858) described the relationship between temperature and the saturation of ether vaporfirst major milestone in the attempt to control the strength of anesthetic vapor administered to patients1952:Dr. Lucien E. Morris ( )Copper Kettle vaporizerfirst system to permit very fine control over the concentration of volatile anesthetics
3INTRODUCTIONA 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 mannerA vapour is the gaseous phase of an agent which is normally a liquid at room temperature and atmospheric pressure.
4Concentration of vapour May be expressed asVOLUME % :- it’s the concentration of gas in a mixture. / no of units of volume of gas in 100 units of vol of total gas mixturePARTIAL 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
5classificationMethod of regulating output concentration 1. Concentration calibrated (variable-bypass)- direct type 2. Measured flow - indirect type Method of vaporization 1. Flow over 2. Bubble Through 3. Injection
8Concentration caliberated Total flow from the machine split by a variable resistance proportionating valveOne part (usually major): through bypass chamber &Other (usually small): through vaporizing chamberagent concentration controlled by dial calibrated in volumes percent
11Splitting ratioratio of the bypass gas to gas going to the vaporizing chamberdepends 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
12MEASURED FLOW VAPORIZERS separate, independent stream of vapour carrying gas, added to the fresh flowTo calculate the vaporizer output, to knowVapor pressure of the agentThe atmospheric pressureThe total flow of gasesThe flow of the vaporizerEg: Ohmeda Tec 6, sp for Desflurane, copper kettle
13Classification contd 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 agentInjection Vaporizers : known amount of liquid agent or pure vapor injected into the gas stream to provide the desired concentration.
16Classification contd TEMPERATURE COMPENSATION maintain a constant outputcompensation for fluctuations in temperatureCooling affects vapour concentration.Mech: Alteration in the splitting ratio (automatic compensation)Eg. Bimettalic strip in tec vaporizerSupplied heat – tec 6 (electrically heated)copper metalEther filled copper bellows ex Penlon vaporisersTEMPERATURE UNCOMPENSATED: boyle’s bottle, goldman etcTEMPERATURE BUFFERING hot water jacket/ heat sink (ex OMV)
17Automatic compensation On cooling, bimetallic strip bends,moves awayreduces the resistance to flow=more flow into vaporizing chamber
18Classification contd. SPECIFIC AGENT use with one specific agent. Must be labeledUse of other agents may give incorrect concentration, may damage vaporizer, harmful byproducts.MULTIPLE AGENT :-Rarely in use, not advised.Ex OMV, EMO, Copper kettle
19VOC = Vaporizer-out-of-system localized btwn flowmeter and CGOOxygen from the flowmeter enters the vaporizer prior to entering the breathing circuit.VIC = Vaporizer-in-systemOxygen enters the breathing circuit from the flowmetereither in circle , at CGO, inhalers i.e in breathing sytem – gas is drawn through it by pts breathing spontaneously.
20Comparison of the two on basis of RESISTANCEDETERMINANTS OF VAPORIZER OUTPUTCAPABILITY OF THE VAPORIZERresistance :- 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 themDeterminants 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)
21VIC and VOC 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.
22Classification contd RESISTANCE PLENUM ( Latin = fullness ) Driven by positive pressure ventilationinternal resistance is high (22 cmH2O), accurately caliberatedAccurate at low flows alsoEg. Boyle bottle, copper kettle, TEC vaporizers
23DRAW OVERCarrier gas drawn through the vaporizer either by the patient’s own respiratory efforts, or by a self-inflating bag or manual bellowsoperate at less than, or at ambient pressureIntermittent flow, varying with different phases of inspiration, ceasing in expiration.low internal resistancemay be used in a non rebreathing DRAW-OVER APPARTUS, or in CIRCLE ABSORBER SYSTEM.Eg. Goldman bottle, EMO
24Drawover anaesthesia ADVANTAGES Simplicity of concept and assembly, with inherent safetyNo need for pressurised gas supply, regulators and flow metersMinimum FiO2~21%Robust, reliable, easily serviced equipmentLow cost (purchase and maintenance)Portable, suitable for field anaesthesiaDISADVANTAGESDecreasing familiarity with the technique and equipmentFilling systems not agent specific (potential advantage)Basic temperature compensation, affecting performance at extremesLess easy to observe spontaneous ventilation with self inflating bagCumbersome in paediatric use, unless lightweight tubing is available
25FACTORS AFFECTING VAPORIZER OUTPUT flow through the vaporizing chamber.surface area of the liquid gas interface.temperaturetimegas flow ratecarrier gas compositionboiling pointambient pressure :-atmospheric, intermittent back pressure
26Effect of atmospheric pressure Low pressure: vaporizing chamber offers less resistance, slight increase in vapor output occurs.Deliver higher conc in vol. % but same Partial pressureHigh 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 pressureether may boil at room temp at low atm pressure.Also at high pressure, liqiud agent may be pushed back into the vaporiser inletavoided by maintaining a low flow of oxygen or filling the vaporiser after increase in pressure.
27should 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
28Pumping effectThe increase in vaporizer output concentration due to pulsatile back pressure developed in the breathing system.more fresh gas gets compressed into vaporising chamberseen especially when-> carrier gas flow is low-> agent in vaporizing chamber is low-> dial setting is low-> pressure fluctuations are high & frequent.
29Minimising 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 chamberadd 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 tubeLimit pressure transmitted to vaporizer to <10KPa above normal working pressure, conc not to increase > 20%.
30Pressurizing effectIncreased constant pressure in vaporizer chamber leads to decreased outputMostly seen when-> High flow-> Large pressure fluctuations-> Low dial settingsThe changes in vaporizer output caused by the pumping effect usually are greater in magnitude that those associated with the pressurizing effect
32hazards INCORRECT AGENT RESISTANCE TIPPING Low output or high outputRx : Gas allowed to flow through it until no agent detected in the outflow, labelling correctly.RESISTANCETIPPINGLiquid from the vaporizing Chamber→ bypass/outlet→ high outputDrained before moving
33Hazards contd. OVERFILLING safety mechanisms: design of the filling port, agent specific filling systemsDuring filling dial to be offFOAMINGpossibility 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.
34Hazards contd. REVERSED FLOW Inlet male & outlet female Increased outputCONCENTRATION DIAL IN WRONG POSITIONCONTAMINANTS IN VAPORIZING CHAMBERPHYSICAL DAMAGEOBSTRUCTION TO FRESH GAS FLOWINTERLOCK MALFUNCTION
36Relevance of older vaporisers in present times Useful in remote locations like military use, as portable and simple to use (ex EMO)Some peripheral setups still use goldman vaporiserDraw over vapouriser (2 OMVs with sevoflurane) can be used in Paediatric circuitAddition of OMV with ventilator in treatment of severe asthma (Nagappan et al 2006)
37Boyle’s bottle (early 1920’s) 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 chainConcentration calibrated, plenum typeFlowover or bubble throughNot temperature compensatedMultiple agentsVaporizer outside circuitWith this bottle, the maximal ether concentration would be about 50% at 20 degrees C.
38Copper kettle Developed in 1930’s: modified by Morris in 1952 measured flow (indirect type)temperature compensatedbubble through, plenum typeagents – chloroform, ether , halothanea separate supply of oxygen from extra flowmeter passes through the vaporizer.Oxygen broken into minute bubbles by sintered bronzelarge mass of copper and attachment to machine, sufficient reservoir for heatDisadv: high vap conc if FGF dec
40Vernitrol (based on copper kettle) Measured flowBubble throughOut of systemTemperature compensated (supplied heat)Multiple agentBody 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.
42originally designed for use with dental anaesthetic apparatus Concentration caliberatedflow over with no wicksmultiple agents – halothane, chloroformneither temperature and level compensated nor accurately calibrated.halothane concentration usually low (hence safe), output is mainly influenced by gas flow rate.VOC / VICsmall 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.)
433 models of goldman vaporizer are :- MARK 1:- self locking in off positionMARK 2 :- differs from mark 1 in size & shape of opening in the ports & is provided with click stops at each settingmark 1 and 2 both have three divisions btwn the on & off positions.MARK 3 :- has one less division.KOMESAROFFSimilar to the Goldman but with gradations on the glass bowl indicating volume
44Rowbotham vaporiserModification of Goldman vaporizer (has wire wick gauge)simple flow-over typenot temp compensatedcapacity of 35 mlmultiple agentmax concentration up to 3.1 % with 4L/ min flow rate.vapor strength is controlled by means of lever stopcock.
45Oxford miniature vaporiser Introduced by Epstein, Macintosh, Mendelssohn in 1966.Vaporizer inside/outside circuitVariables bypassFlow 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.
46OMV contd.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)
48EMO contd. Concentration caliberated Flowover with wicks Temp compensated (metal bellows with freon vapor)Multiple agents- ether, chloroform, trilene, halothaneDia:23 cm; Ht : 24 cmWt(ether) : 6 kg; (halothane) : 12 kg0 – 20% graduations40 ml ether when fullInlet for airControl lever with transit lockIndicator to denote level of anaesthesiaTemp indicator (max eff C)
49EMO contd Water jacket : 1250 cc Mark I: aluminium water jacket Mark II/III/IV: stainless steel jacketUsed with OMV for spont respOMV filled with halothane for smooth induction , maintained with ether in EMO
50EMOTRIL (Epstein, Macintosh, Oxford Trilene inhaler) Introduced in 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 vaporizersimple no-controls vaporizerdelivers mls of halothane to precede, and assist induction with, ether.
52device 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.
53Small’s self help ether apparatus 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.
54othersDiamedica Draw-Over Vaporizer (DDV) has been developed as an alternative to the Oxford Miniature Vaporizer (OMV)can function as draw- over or plenumlarger reservoir, tendency towards greater accuracy during IPPV and improved consistency of output.
55U PAC (universal portable anesthesia complete) drawover system Ohmeda Universal PAC drawover apparatus, a modification of an earlier series of vapour- specific vaporizersCaliberated, temperature compensated, flow overOxygen may be added but not necessaryclinical usage with isoflurane and enfluraneTends to over-deliver vapour, esp at low flows and at high temperaturesclinical performance during spontaneous and positive pressure ventilation satisfactoryrobust construction, relatively large capacity and thermocompensation make it suitable for field or military anaesthesia.