Principles of vaporizers and older vaporizers

1. Principles of vaporizers and older vaporizers Presented by: Dr Rashmi Moderator: Dr KartikSyal

2. 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

3. INTRODUCTION • 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 anaestheticvapourdelivered 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.

4. Concentration of vapour 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

5. classification Method 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

6. Classification contd. Temperature compensation 1. Thermo-compensation 2. Supplied heat Specificity Agent specific Multiple agent Resistance 1. Plenum 2. draw over VIC / VOC

7. Basic design

8. Concentration caliberated 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

9. Dial with high concentration

10. Dial with low concentration

11. Splitting ratio • ratio of the bypass gas to gas going to the vaporizing chamber • depends on: • Resistanceof the two pathways, • depends on the variable orifice of the inlet/outlet. • Temperature of the liquid/carrier gas. • Flow rate of gases

12. MEASURED FLOW VAPORIZERS • separate, independent stream of vapour carrying gas, added to the fresh flow • To calculate the vaporizer output, toknow • Vapor pressure of the agent • The atmospheric pressure • The total flow of gases • The flow of the vaporizer • Eg: Ohmeda Tec 6, sp for Desflurane, copper kettle

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

14. Flow over

15. Bubble through

16. Classification contd 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 tecvaporizer • Supplied heat – tec 6 (electrically heated) • copper metal • Ether filled copper bellows ex Penlonvaporisers TEMPERATURE UNCOMPENSATED: boyle’s bottle, goldman etc TEMPERATURE BUFFERINGhot water jacket/ heat sink (ex OMV)

17. Automatic compensation • On cooling, bimetallic strip bends,moves away • reduces the resistance to flow=more flow into vaporizing chamber

18. Classification contd. 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

19. VOC = Vaporizer-out-of-system • localized btwnflowmeter 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.

20. 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 -concof vapor at outlet of vaporizer. (vo) vaporizer conc:- concdelivered by vaporizer when fresh gas containing no vapourpassess through it . (vc)

21. VIC 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.

22. Classification contd • RESISTANCE • PLENUM ( Latin = fullness ) • Driven by positive pressure ventilation • internal resistance is high (22 cmH2O), accuratelycaliberated • Accurate at low flows also • Eg. Boyle bottle, copper kettle, TEC vaporizers

23. 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 rebreathingDRAW-OVER APPARTUS, or inCIRCLE ABSORBER SYSTEM. • Eg. Goldman bottle, EMO

24. Drawoveranaesthesia • 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 • 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

25. FACTORS AFFECTING VAPORIZER OUTPUT • 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

26. Effect of atmospheric pressure • 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 vaporiserinlet • avoided by maintaining a low flow of oxygen or filling the vaporiser after increase in pressure.

27. 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 Desfluranevapouriser 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

28. Pumping effect • 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.

29. Minimising 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%.

30. Pressurizing 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

31. Pressurizing effect

32. hazards INCORRECT AGENT • Low output or high output • Rx : Gas allowed to flow through it until no agent detected in the outflow, labelling correctly. RESISTANCE TIPPING • Liquid from the vaporizing Chamber→ bypass/outlet→ high output • Drained before moving

33. Hazards contd. 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.

34. 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

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

36. Relevance 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 goldmanvaporiser • 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)

37. Boyle’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 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.

38. Copper kettle • 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 vapconc if FGF dec

39. Copper kettle : internal design

40. Vernitrol (based on copper kettle) • 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.

41. Goldman vaporiser (1959)

42. 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 % , (higherifsplashing, spraying of agent, if wick is used, or 2 vaporizers in series.)

43. 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

44. Rowbothamvaporiser • 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.

45. Oxford miniature 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.

46. OMV 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 sevofluraneanaesthesia, thus enabling wider use of sevoflurane in field anesthesia. (study by Liu et al in 2000)

47. Epstein macintosh oxford vaporiser (emo)

48. EMO contd. • 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)

49. EMO contd • Water jacket : 1250 cc • Mark I: aluminium water jacket • Mark II/III/IV: stainless steel jacket • Used with OMV for spontresp • OMV filled with halothane for smooth induction , maintained with ether in EMO

50. 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.