Vaporoizer
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This document discusses vaporizers used to deliver inhalational anesthetic agents. It begins by defining vapor and vaporizers. It then covers the basic physics of vaporization including vapor pressure, boiling point, latent heat of vaporization. It classifies vaporizers based on method of regulating outflow and temperature compensation. Factors affecting vaporizer output like gas flow, temperature and barometric pressure are discussed. The document also covers concepts like splitting ratio, pumping and pressurizing effects. It concludes with discussing the proper sequence of mounting multiple vaporizers.
Vaporoizer
- 1. Vaporizer Presenter: Dr. Tirtha Raj Bhandari 2nd year Resident Department of Anesthesiology PMWH, Thapathali NAMS
- 2. Objectives To understand the basic physic of vaporizer. To classify vaporizer Factors affecting vaporizer outflow To discuss briefly about different types of vaporizer Features of ideal vaporizer To discuss hazards of vaporizer
- 3. Vapor?? Vapor is a phase at a temperature at which both liquid and gaseous phase of a substance co-exist.(i.e. below critical temperature) Gas: It the the gaseous phase of substance, which cannot be liquified with the application of pressure.( i.e. above critical temperature)
- 4. Physics: Critical temperature That temperature, above which a substance can not be liquefied, on application of much higher pressure. CRITICAL TEMP : O2 is -118.4 0 C N2O is 36.5 0C CO2 is 310 C The pressure required to liquefy a gas at its critical temp is the CRITICAL PRESSURE
- 5. Vapor/Gas
- 6. Vaporizer?? Vaporizer: Vapor delivery system/anesthetic gas delivery system Anesthetic gas delivers in the vapor form by the vaporizer after mixing with the fresh gas flow or breathing system.
- 7. Why?? • Inhalational agents are highly toxic and potent substance. • Cannot be given directly. • It has to be given in small amount along with the oxygen(FGF), and other gases.
- 8. Physics Vapor Pressure: A pressure exerted by the vapor to its surroundings. Saturated Vapor pressure: A pressure exerted by vapor when it is in equilibrium with the liquid state under constant temperature. On applying heat more liquid will enter into vapor phase. Also on passing fresh gas also causes more liquid will enter into vapor phase. (Vapor pressure mainly depend upon the liquid and temperature not on the ambient pressure.)
- 9. Physics
- 10. Physics Boiling point: It is that temperature at which saturated vapor pressure becomes equal to atmospheric pressure, also at which all the liquid agent changes into vapor phase. The lower the atmospheric pressure lower will be the boiling point.(high altitude) Most anesthetic agents has high saturated vapor pressure.
- 11. Physics
- 12. Physics Latent heat of vaporization: It is the amount of heat/calories required to convert 1 ml liquid into vapor. It removes the heat from the liquid so that temp of remaining liquid falls. Specific heat capacity: Amount of heat required to raise temp of 1 gm/1ml substance through 1 degree C. Liquid anesthetic agent should have the low specific heat so that it can be easily changed into vapor phase.
- 13. Physics Thermal conductivity: Measures the speed with which heat flows through the substance. Define as amount of heat flows through unit area of a plate of unit thickness in unit time per degree of temperature gradient. Significance: Vaporizer constructor material should be able to conduct heat from the surroundings to contained liquid. Copper has moderate specific heat and high thermal conductivity , so used in making vaporizer. Thermal capacity: Amount of heat stored in the vaporizer body(specific heat*mass)
- 14. Thermo stabilization: Aim to minimize temperature change. Construct the vaporizer with the metal with high specific heat and high thermal conductivity. Wicks to be in contact with metal parts so that it will minimize heat loss due to vaporization. Thermo compensation: To maintain vaporizer output constant despite alteration in temperature. Alteration in splitting ration(automatic compensation)
- 16. Thermo compensation When the temperature of the vaporizing chamber falls the bimetallic strip blends and move away , which reduces the resistance to gas flow, the gas flow rate increases.
- 17. Physics Dalton’s law of partial pressure: P(total)=P1+P2+P3….... Splitting ratio: The ratio of bypass flow to flow to the vaporizing chamber is referred to as the "splitting ratio" . It depends on a) Ratio of resistance in two pathways b) Total flow to vaporizer
- 18. VOLUME % Commonly used It is the number of units of volume of a gas in relation to a total of 100 units of volume for the total gas mixture Is a relative ratio of gas molecules in a mixture vol % /100 = partial pressure/total pressure OR Vol % = pp/tp x 100
- 19. Splitting Ratio
- 20. Splitting of Gas
- 21. Classification Based on method of regulating outflow; a) Variable bypass vaporizer/ concentration calibrated b) Measured flow vaporizer
- 22. Variable bypass/ Concentration calibrated Vaporizers calibrated by agent concentration expressed in percentage of vapor output are known as Concentration calibrated vaporizers/Direct reading/Dial controlled / Automatic plenum/Percentage type/Tec type vaporizers. Vaporizer output controlled by simple knob/dial calibrated in volume percent. Located between flow meter and common gas outlet. Also called variable bypass because desired concentration is achieved by splitting the gas.
- 25. Electronic Vaporizer Two types a) A computer calculates the carrier gas flow that needs to pass through vaporizing chamber to produce desired concentration of anesthetic agent. b) Withdraws a calculated amount of liquid agent and injects into the breathing system / fresh gas flow.
- 26. Measured Flow Vaporizer • Kettle type / flow metered / flowmeter controlled vaporizer systems. • Use a measured flow of carrier gas–oxygen, to pick up anesthetic vapor. • No longer available for sale.
- 28. Copper kettle
- 29. Classification Depending on method of vaporization 1. Flow over 2. Bubble through 3. Injection Depending on temperature compensation • None, • By supplied heat • By flow interaction • Computerized compensation
- 30. CONTD Flow over: A stream of carrier gas passes over the surface of the liquid. Bubble through: the carrier gas is bubbled through the volatile liquid, further increasing the gas-liquid interface. Injection: vapor concentration controlled by injecting a known amount of liquid anesthetic agent (from a reservoir in the vaporizer or from the bottle of agent) into a known volume of gas.
- 31. Classification: Depending on the location: a) Outside the breathing system b) Inside breathing system Depending upon specificity; a)Agent specific b)Multiple agent
- 32. Classification • Plenum vaporizers: positive pressure applied at the inlet of the vaporizer. eg. Boyle vaporizers, copper kettle, fluotec Mark 2 and 3. • Inhalers or draw over vaporizers: negative pressure applied at the outlet. eg. EMO vaporizer, Oxford miniature inhaler, Tecota • Simple vaporizers eg. Goldman, Rowbotham vaporizer.
- 33. Factors affecting vaporization of liquids Flow through the vaporizing chamber Efficiency of vaporization Temperature Time Gas flow rate Carrier gas composition Volatility Area of contact with liquid
- 34. Effect of Barometric Pressure(high atm) Concentration calibrated: increase in atm pressure change in density of gas provides more resistance to flow of gas through the vaporizing chamber decreased vapor output( both partial pressure and volume percent). The effect in the partial pressure is less dramatic. Measured Flow: There will be lower concentration in terms of both partial pressure as well as volume percent.
- 35. Effect of Barometric Pressure(low-atm) Concentrated Calibrated: High resistance pathway through the vaporizing chamber offers less resistance under hypobaric condition, so that slight increase in vapor output occurs. Measured flow: Here the delivered partial pressure and volume percent increases. The amount of increase depends upon the barometric pressure and agent.
- 36. Effect of intermittent back pressure Pumping effects: Increase in output. Pressurizing effect: Decrease in output Sources of back pressure; 1)During assisted/ controlled ventilation the positive pressure generated during inspiration transmitted from the breathing system back to the machine and vaporizer. 2) Use of O2 flush valve, the output from O2 flush enters the circuit downstream of vaporizers and its activation produces high pressure.
- 37. Pumping Effect a) When resistance is applied to the outlet of the anesthetic machine, as during assisted or controlled ventilation, there will be increase in the anesthetic gas pressure, which finally transmitted back to vaporizer. b) This adds to the output and finally increases the vaporizer output. c) This change is more pronounced when there is less agent, low carrier gas flow and high and frequent pressure fluctuation, low dial settings.
- 38. Pumping Effect
- 39. Pumping Effect
- 40. Pumping Effect
- 41. Pumping Effect
- 42. Pumping Effect
- 43. Modifications to reduce the ‘pumping effect’ • Decrease size of vapor chamber • Increase size of bypass • Long spiral tube leading to the vapor chamber • Exclude wicks from the inlet
- 44. CONTD
- 45. Pressurizing effect a) the output of some vaporizers decreases when there is back pressure. This effect is greater with high flows, large pressure fluctuations and low vaporizer settings. b) The changes in vaporizer output caused by the pumping effect is usually greater in magnitude than those associated with the pressurizing effect. Pressurizing effect: with high gas flow Pumping effect: with low gas flow
- 48. Effect of Rebreathing • Rebreathing causes a difference between the vaporizer setting and the inspired concentration. • Only an agent analyzer can provide an accurate value for the inspired agent concentration.
- 49. Sequence of vaporizer(Vaporizer Mounting) • In modern anesthesia machines an interlocking system called the SELECTATEC system incorporated so that only one vaporizer is in use at a time. • If selectatec system is not installed the sequence of vaporizer should be such that least potent agent must be placed upstream and most potent agent last in the sequence. • Seletatec Back Bar • Mechanical locking system • Mechanical Inter-connecter
- 50. Order of Vaporizer Less potent – upstream More potent – downstream If equipotent low VP – upstream high VP – downstream If explosive – downstream
- 52. How much liquid agent does a vaporizer use per hour? Ehrenwerth and Eisenkraft gives the formula => 3 X Fresh gas flow(L/min) X Volume % = ml liquid used /hr This formula is based on the fact that typically 1 ml of liquid volatile agent yields about 200ml of vapor
- 54. Early Methods • Open Drop Method – Inhalation anes. By vaporization of a liquid placed drop by drop on gauze mask covering mouth and nose • Devices Used: • Schimmelbusch mask • Yankauer mask • Bellamy Gardner mask Fig: Yankauer mask
- 55. • Semi open • Frame Added to keep ether in an enclosed area ,permitting some degree of rebreathing • Eg: Ogston inhaler, Junkers chloroform apparatus , Flagg’s can
- 56. Semi-open Fig: Ogston mask with schimmelbusch frame
- 57. • EMO (Epstein Machintosh Oxford) vaporizer • OMV(Oxford Miniature vaporizer)
- 58. • Oxford Inflating Bellows (OIB) • Morton’s Ether Inhalar
- 59. Boyle’s Bottle • Mainly for ether and trichloroethylene • Flow over or bubble through type. • No temperature compensation or calibration
- 60. Goldman Vaporizer • Conc. calibrated, Flow- over • No temp compensation • Agent non specific (Halothane, ether, trilene) • In & Out of system • Max. conc never exceeds 2% irrespective of total gas flow
- 61. CONTD • Described by Lucein Morris in 1952. • Constructed of copper -High heat capacity - High thermal conductivity -High degree of accuracy
- 62. TEC 2 TEC 3
- 63. TEC 5 • One handed dial control and more obvious OFF position. • Helical intermittent positive pressure assembly to minimize effects of positive pressure ventilation. TEC 5
- 64. Desflurane vaporizer(Tec 6) The Tec 6 vaporizer electrically heated, thermostatically controlled, constant-temperature, pressurized, electromechanically coupled, dual circuit, gas/vapor blender. The pressure in the vapor circuit is electronically regulated to equal the pressure in the fresh gas circuit. At a constant fresh gas flow rate, the operator regulates vapor flow using a conventional concentration control dial. When the fresh gas flow rate increases, the working pressure increases proportionally. At a specific dial setting at different fresh gas flow rates, vaporizer output is constant because the amount of flow through each circuit is proportional
- 65. Desflurane-Tec 6 vaporizer Schematic diagramof TEC 6
- 67. TEC 7 • an improved version of the TEC 5 was introduced in July 2002 by Datex-Ohmeda with minor modifications • "Easy-fil" filler mechanism • Improved sight glass design
- 68. GE Datex Ohmeda Aladin Cassette Vaporizer • 2 parts: • Electronic control system in anesthesia machine • A portable cassette containing agent • Flow at the out let is controlled by the CPU in the anesthesia machine
- 69. Fig: Schematic of GE- Datex Ohmeda Aldin Cassette Vapor
- 70. Vaporizer-characteristics Fig: Vaporizer models & Characteristics
- 71. Drager 2000 • Tippable vaporizers • Transpot mode “T” • Tortous in-let protects against pumping effect
- 72. Features of Ideal Vaporizer a) It should be simple, safe, satisfactory and more practical. b) It should have low resistance to gas flow. c) It should be temperature compensation for uniform vaporization. d) It should have flow stability and should permit constant concentration of agent at the different carrier gas flow rate. e) It should permit precise, accurate, controllable and predictable delivered concentration of the vapor to the patient.
- 73. CONTD f) The performance of the vaporizer should not be affected by changes in fresh gas flow, volume of liquid, ambient temperature and pressure, decrease in temperature due to vaporization and pressure fluctuation due to mode of respiration. g) It should be light weight and small liquid requirement. h) Construction should be corrosion and solvent resistant. i) It should have good quality control. j) The case of the vaporizer is usually made of copper which is a good heat sink and it consists of bypass channel and vaporization chamber.
- 74. ASTM Standard (1)Vap must be capable of accepting15L/min and deliver predictable vapor conc. (2)effects of condns of use in manual (3)influence of temp/in flow rate so be stated (4)must be a system to isolate vaps from each other (5)controls to limit escape of vapor from vc so less than 0.1% is delivered in off (6)Knobs to turn counterclockwise to increase (7)Must have liquid level indicator visible from front (8)Cannot be overfilled
- 75. CONTD (9) must allow calibrated flows of O2 & N2O in ON & OFF and not discharge liquid through outlet when mounted (10) if unsuitable for use in breathing system, non interchangeable 23 mm fittings; inlet to be male, outlet to be female, direction of gas flow to be marked (11) if suitable for use in breathing system, standard 22 mm fittings ; inlet to be female, outlet male and direction to be marked.
- 76. Safety Features of Modern vaporizer a)Keyed filling system b)Low filling ports c)Secured vaporizer(less ability to move) d) Interlock devices or vaporizer exclusion systems – prevent more than one vaporizer from being turned ON at a time. e)Color coding system f)Single agent h)Interlocking i)Anti spill Protection designs j)Firmly attachment with vaporizer manifold
- 77. Filling agent color code
- 78. Filling devices • Funnel fill system • Keyed fill system • Quik- fill system (For Sevoflurane) • Easy-fill system (Tec 7 Vaporizers)
- 81. Quik Fill System
- 82. Easy Fill System
- 83. Hazards of Modern Vaporizer a) Incorrect agent – if an agent of high potency or volatility is used in a vaporizer intended for an agent of low potency or volatility, a dangerously high concentration may be delivered. The vaporizer must be completely drained and all liquid discarded. b) Tipping – liquid from the vaporizing chamber may get into the bypass or outlet high concentration will be delivered when the vaporizer is first used. Prevented by keeping the vaporizer in off/travel position while movement.
- 84. CONTD c) Overfilling – liquid agent may enter the fresh gas line, and lethal concentrations may be delivered, or no output due to complete vaporizer failure. Agent specific filling devices prevent overfilling. d) Reversed flow – increases output. e) Leaks – affect fresh gas composition and flow, pollutes OR environment. f) Interlock malfunction , Concentration dial in wrong position , physical damage, g) Contaminant in vaporizing chamber, obstruction in fresh gas flow.
- 85. Any Questions??
- 86. Summary • Vaporizer is special device for delivery of anesthetic gas. • Vapor is the gaseous form of liquid below critical temperature. • Its output is affected by so many factors. • Mounting of vaporizer should be systemic. • It should follow ASTM guidelines. • We should know hazards of vaporizer.
- 87. References • Miller’s anesthesia 8th edition • Dorsch and Dorsch
- 88. THANK YOU