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Vaporizers anand ram final

principles of vaporizers

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Vaporizers anand ram final

  2. 2. Definition • Vapour: – A gaseous phase of a substance that is liquid at room temperature and atmospheric pressure. • Vapouriser: – Instrument designed to change a liquid anesthetic agent into its vapour and to add a controlled amount of this vapour to fresh gas flow.
  3. 3. PHYSICS • Vapour pressure: – Pressure exerted by the molecules of vapour on the walls of the container. • Saturated vapour pressure: – Maximum vapour pressure at particular temperature. – At constant temperature, a dynamic equilibrium is formed between the liquid and vapor phase so that the number of molecules in the vapor phase remains constant. – Represented by density of dots above liquid
  4. 4. Vapor pressure changes with varying temperature
  5. 5. Vapour pressure of common anaesthetic agents Gas Vapour press. TORR (20 0C) Halothane 243 Enflurane 175 Isoflurane 238 Desflurane 669 Sevoflurane 157
  6. 6. Critical temperature: That temperature, above which a substance can not be liquified however much pressure is applied
  7. 7. • Boiling Point: – The temperature(of a liquid) at which its vapour pressure is equal to the atmospheric pressure. – The lower the atmospheric pressure, the lower the boiling point.
  8. 8. BOILING POINTS • Halothane - 50.2 C • Enflurane - 56.5 C • Isoflurane - 48.5 C • Desflurane - 22.8 C • Sevoflurane - 58.6 C
  9. 9. • VAPORIZER OUTPUT: refers to the concentration of vapor at the outlet of vaporizer. • VAPORIZERS CONCENTRATION :denotes the concentration delivered by a vaporizer when fresh gas containing no vapor flows through it. – Out of system vaporizer: output = conc. – In system vaporizer : output >conc. (expired gases contain some agent )
  10. 10. VAPORIZERS CAPABILITY • Refers to the maximum concentration that can be delivered by a vaporizer at the highest setting of the concentration dial. • Eg: sevoflurane has a higher MAC than isoflurane. So needs vaporizer with a higher capability (max 8%) than isoflurane (max 5%).
  11. 11. VAPORIZERS EFFICIENCY • Ability of a vaporizer to saturate the carrier gas passing into the vaporizing chamber at the temperature of the liquid. Increased by a)Wicks b)baffles or spiral tracks c)longer vaporizing chamber (inc. surface area for vaporization).
  12. 12. GAS CONCENTRATION • TWO METHODS USED TO EXPRESS : – partial pressure – volumes percent A. Partial pressure: – The part of the total pressure due to any one gas in the mixture is called as the partial pressure of that gas. – Depends only on temperature of the agent.
  13. 13. Contd…. B. Volumes percent : – The number of units of volume of a gas in relation to a total of 100 units of volume for the total gas mixture. – Partial pressure /total pressure = vol.percent
  14. 14. Partial pressure Volume percent Absolute value Relative ratio Patient uptake and depth of anesthesia are directly related. Indirectly related At a given partial pressure , anesthetic agent will have same potency under various barometric pressures. Not so.
  15. 15. Heat of vaporization • The number of calories necessary to convert 1g of liquid (or 1ml) into a vapor. • Liquid temperature decreases as vaporization proceeds. • So the heat flows from the surroundings into the liquid to compensate for the lost heat. • IMPORTANCE :If the lost heat is not compensated , there will be decrease in agent delivered.
  16. 16. Specific Heat • Is the quantity of heat required to raise the temperature of 1g of the substance by 1 C. – IMP : The higher the specific heat ,the more heat that is required to raise the temperature of a given substance. – Choice of material of vaporiser should have high specific heat as this provide a more stable temperature. – Amount of heat that must be supplied to a liquid anesthetic to maintain a stable temperature is known. (heat is lost during vaporization)
  17. 17. Thermal conductivity • Is a measure of the speed with which heat flows through a substance. • To construct a vaporizer,a substance with high thermal conductivity is used. – Eg. Copper,bronze. • Importance: heat lost during vaporization can be rapidly supplied if the substance has high thermal conductivity.
  18. 18. HISTORY • First vaporizer was developed by Lucein Morris, named as copper kettle vaporizer. • Shu-Hsun Ngai Proposed the incorporation of thermometer in vaporizers.
  22. 22. Copper kettle and vernitrol If vapor pressure and temperature of anesthetic liquid is known,concentration of inhaled anesthetic is calculated. DISADV: NOT TEMPERATURE COMPENSATED.
  23. 23. TECOTA VAPORIZER (temperature compensated trichloroethylene air) BI METALLIC STRIP made of brass and nickel-steel alloy with different coefficients of expansions.
  24. 24. Vaporizers and standards • ASTM anesthesia work station standard contains the following provisions regarding vaporizers : • 1)The effect of variations in ambient temperature and pressure ,tilting,back pressure,and input flow rate and gas mixture composition on vaporizer performance must be stated in the accompanying documents.
  25. 25. WITH OUT A BACK PRESSURE • 2)The average delivered concentration from the vaporizer shall not deviate from the set value by more than ±20% or ±5 % of the maximum setting ,which ever is greater , without back pressure.
  26. 26. WITH BACK PRESSURE • 3)The average delivered concentration from the vaporizer shall not deviate from the set value by more than +30% or -20% or by more than +7.5% or -5% of the maximum setting ,which ever is greater ,with pressure fluctuations at the common gas outlet of 2Kpa with a total gas flow of 2L/min or 5Kpa with a total gas flow of 8L/min.
  27. 27. – A system that prevents gas from passing through the vaporizing chamber or reservoir of one vaporizer and then through that of another must be provided. – The output of the vaporizer shall be less than 0.05% in the OFF or zero position ,if the zero position is also the OFF position. – All vaporizer control knobs must open COUNTER CLOCK WISE. – Either the maximum and minimum filling levels or the actual usable volume and capacity shall be displayed.
  29. 29. DORSCH AND DORSCH CLASSIFICATION • I.)METHOD OF REGULATING OUTPUT: • a) Variable by pass: ether bottle,TEC • b) Measured flow: copper-kettle,vernitrol. • II.)METHOD OF VAPORIZATION : • a)Flow over: – 1. with wick – TEC – 2.with out wick - goldman bottle
  30. 30. • b.)Bubble through :copper kettle • c)flow over bubble through : ether bottle depending on position of plunger. • d)Injection :TEC 6 (desflurane) III.TEMPERATURE COMPENSATED : a)Thermo compensated: 1)By altered flow –TEC 2)By supplied heat –copper kettle 3)Both –EMO (epstein mc intosh oxford) b)Non compensated : ether bottle.
  31. 31. • IV) SPECIFICITY : – Agent specific :TEC – multi agent : Goldmanbottle. • V)RESISTANCE : – plenum(high resistance) : TEC – Draw over (low resistance) :goldman bottle,EMO. • VI)LOCATION : – In circuit : (VIC) – E.M.O, Goldman – out of circuit (VOC) -TEC.
  32. 32. Recent • A.Concentration calibration 1.variable bypass 2.Measured flow 3.electronic • B.Vaporization methods 1.Flow over 2.Injection • C.Temperature compensation 1.Mechanical 2.Supplied heat 3.Computerized
  33. 33. Variable bypass vaporizer a.)Has an inlet and outlet. b.)Fresh gas flows through bypass chamber and vaporizing chamber. c.)Concentration of anesthetic agent delivered depends on amount of gas flowing through the vaporizing chamber.
  34. 34. Contd…. • The total flow of gas arriving from the anesthesia machine flow meters is split between variable bypass and the vaporizing chamber containing the anesthetic agent. • The ratio of these two flows, the Splitting ratio depends on the anesthetic agent, temperature, and chosen vapor concentration set to be delivered to the patient circuit.
  35. 35. Measued Flow Vaporizer • A measured flow of oxygen is selected on a separate flowmeter to pass to the vaporizer, from which vapor emerges at its SVP. This flow is then diluted by an additional measured flow of gases from flowmeters on the anesthesia machine.
  36. 36. FACTORS AFFECTING THE VAPORIZER OUTPUT • A.)Flow rate. • B.)Barometric Pressure • C.)Temperature. • D.)Intermittent back pressure. • E.)Carrier gas composition.
  37. 37. Effect OF Flow rates • At low flowrate:(<250 ml/min) – The anesthetic agent delivered is less than the dial setting at low flow rates because of insufficient turbulence generated to upwardly displace vapor molecules. • At extremely high flow rates: (15L/min) – the output is less than the dial setting, due to incomplete mixing and failure to saturate the carrier gas.
  38. 38. Effect of Barometric Pressure •Vaporizers calibrated at standard (Sea level) atmospheric pressure •Low boiling point, High SVP agents are more susceptible to barometric pressure changes.
  39. 39. Low atmospheric pressure  CONC CALIBERATED VAPORIZERS. - Deliver same partial pressure [IMPORTANT FOR ANAES. DEPTH SO CLINICAL EFFECT UNCHANGED]. - Small deviations in performance due to altered splitting ratio. -Deliver higher concentration if measured in vol% • MEASURED FLOW VAPOURIZERS. - Partial pressure increase and Vol% increased even more.
  40. 40. High atmospheric pressure. • CONC. CALIBERATED VAPOURIZERS. Increased density of gas  Increased resistance through vaporizing chamber  Decreased vap. output (In both PP and Vol%) At 2 ATM. - Conc in VOL. % Is half - Effect on PP is less • MEASURED FLOW VAPOURIZERS. Decreased conc in both PP and Vol %
  41. 41. Effect of Temperature • As vaporization continues, the temperature in vaporizing chamber decreases as heat is lost during the process of vaporization. • So vapor pressure of anesthetic agent decreases and output decreases. • So to prevent this fresh gas flow rate is increased into the vaporizing chamber by an expanding rod or a bi metallic strip.
  42. 42. Vapor out put decreases
  43. 43. Expanding Metal rod
  44. 44. Bi metalic strip
  45. 45. Cont… • Wicks are placed in direct contact with the metal wall of the vaporizer to help replace heat used for vaporization. • Vaporizers are constructed with metals having relatively high specific heat and high thermal conductivity to minimize heat loss.
  46. 46. Effects of intermittent back pressure • When assissted or controlled ventilation is used,the positive pressure generated during inspiration is transmitted back to the machine and vaporizers. • Back pressure may either • Increase vapor output-PUMPING EFFECT • Decrease vapor output- PRESSURIZING EFFECT
  47. 47. Pumping Effect • Concentrations delivered by vaporizers increase during ventilation than used with free flow to atmosphere. • Change is more pronouced when – less agent in vaporizing chamber – low carrier gas flow – pressure fluctuations are high and frequent. – dial setting is low.
  48. 48. MECHANISM
  49. 49. INSPIRATION Pressure in bypass and vaporizing chambers increase. As bypass has smaller volume than vaporizing chamber more gas enters vaporizing chamber.
  50. 50. Increased vaporization Extra gas entering vaporizing chamber collects the anesthetic vapour
  51. 51. EXPIRATION When bag is released, the compressed gas expands in all directions.
  52. 52. Some of the rapidly expanding vapor containing anesthetic agent enters the inlet and cross over into the bypass channel .
  53. 53. This vapor in bypass chamber adds to that of vapor coming from vaporizing chamber and increases the final anesthetic conc. Delivered. (pumping effect).
  54. 54. MODIFICATIONS TO MINIMIZE THE PUMPING EFFECT 1.) long inlet tube: The extra gas can not enter the bypass channel as inlet tube is long.
  55. 55. 2.) Increase in the internal resistance of vaporizer resists changes due to back pressure ventilation.
  56. 56. 3.)One way valve. Allows the flow of gas in one direction only and prevents the reverse direction.
  57. 57. PRESSURIZING EFFECT Increased pressure is applied to the vaporizer outlet. Compress carrier gas ,so that there will be more molecules/ml. The no of anesthetic vapor molecules will not increase.(as this depends on vapor pressure of anesthetic). Net effect is decrease in conc of anesthetic delivered.
  58. 58. EFFECT OF BACK PRESSURE. PUMPING EFFECT  Higher conc than indicated on dial delivered. - inc. by : - Large pressure fluctuations - Low dial setting - Low flow rate PRESSURING EFFECT  Lower conc than indicated on dial delivered. - Inc by : - Large pressure fluctuations - Low dial setting - High flow rate
  59. 59. Effect of Carrier Gas Composition • Vaporizer output may be affected with change of 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 • As Nitrous oxide's being more soluble than oxygen in halogenated liquid. • So the quantity of gas leaving the vaporizing chamber is transiently diminished until the anesthetic liquid is totally saturated with nitrous oxide.
  60. 60. Factors affecting steady state • A)viscosity and density of carrier gas. • B) solubility of carrier gas in the anesthetic liquid. • C) flow splitting characteristics of the specific vaporizer. • D) concentration control dial setting.
  61. 61. Tec 6 • Electrically heated,pressurized device specially designed for Desflurane. • ??deflurane needs special vaporizer • 1)HIGH VAPOR PRESSURE: • Has vapor pressure 3 to 4 times that of others. • So at, same flow rate, the amount of desflurane delivered is DANGEROUSLY HIGH.
  62. 62. Contd… • 2) LACK OF AN EXTERNAL HEAT SOURCE: – MAC of desflurane is high. – So ,rate of vaporization in a vaporizer is high and leads to excessive cooling of the vaporizer. This causes reduced output. – In the absence of an external heat source,the temperature compensation is almost impossible.
  63. 63. Two independent gas circuits. Vapor originates in the desflurane sump which is electrically heated and thermostatically controlled to 39C Fixed restrictor
  64. 64. The differential pressure transducer conveys the pressure difference b/w the fresh gas circuit and the vapor circuit to the control electronics system, which regulates the pressure control valve.
  65. 65. Steady state Differential pressure transducer Fixed resistance
  66. 66. Signals Pushes diaphragm upwards. Pressure Control valve Increased fresh gas flow
  67. 67. Differential pressure transducer in Increasd vapor flow Neutral position
  69. 69. Goldman Vaporizer • Conc. calibrated  Flow over (Without wicks) • No temp compensation • Agent non specific (Halothane, ether, trilene) • In & Out of system
  70. 70. Boyles Bottle • Variable bypass (Conc calibrated) • Flow over wicks • Out of system • No temp compensation • Muliple agent (Ether, trilene, Halothane)
  71. 71. E.M.O (EPSTEIN MACINTOSH OXFORD VAPORIZER) • Draw over inhaler • Variable bypass • Flow over wicks • Temp compensation by supplied heat & flow alteration • Agent specific
  72. 72. OXFORD MINIATURE VAPOURIZER • Draw over and plenum • Thermo-stabilized • Concentration calibrated • Agent non –specific. • (Halothane, trilene, methoxyflurane)
  73. 73. TEC 2 Agent-specific for Halothane, variable bypass, flow over with wicks, low resistance, temperature compensated with bimetallic strip in vapour path, non-tippable, no interlocks, non-keyed filler. Volume 750ml.
  74. 74. • DISADV : • Not accurate below 4l/min. • Nitrous oxide affects out put. • Subject to pressurizing and pumping effect. • Filling tap is at side – chance of over fill.
  75. 75. TEC 3 Conc-calibrated, flow over with wick, automatic thermo-compensation. Bimetallic temp-sensitive element that is located concentrically within bypass chamber. Volume decreased to 250ml Vaporising chamber at high pressure (overcomes the resistance to flow of relatively dense saturated vapor even at low flow rates.)
  76. 76. Contd… Adv over tec 2 : • Accurate with lower dial settings. Nitrous oxide has little effect on output. • Between off and 0.5% ,dial setting, output is less affected by fresh gas flow. • Sudden increase or decrease in FGF ,back pressure,O2 flush has negligible effect on vapour output. • Filling and draining is at bottom- so over fill is avoided.
  77. 77. • Dis adv: small amounts of leaks in bypass in OFF position. • Can be rotated beyond off position, resulting in delivery of vapour. • Tipping upto 90 degrees has no affect.But beyond 90 degrees causes increase in out put.
  78. 78. Tec 4 The release button to the left must be depressed before the vaporizer can be turned on. Safety interlock system for ensuring a ,single vaporiser use only at any time. Internal baffle system to prevent contamination of the bypass chamber on tilting. Dis adv: difficulty in operation one handed.
  79. 79. TEC 5 One handed dial control and more obvious OFF position. Helical intermittent positive pressure assembly to minimize effects of positive pressure ventilation. Capacity increased from 125 to 300 ml.
  80. 80. Tec 6 Is described as a dual gas blender. Tec 6 can deliver an accurate concentration of desflurane, between 1% and18% at a flow rates from 0.2 to 10 litres/min at 21c
  81. 81. TEC 7: an improved version of the TEC 5 was introduced in July 2002 by Datex-Ohmeda with minor modifications 1. "Easy-fil" filler mechanism 2. New ergonomics and design 3. Planned factory service free 4. Improved sight glass design
  82. 82. ALADIN VAPORIZER 2 parts. a). Electronic control system in anesthesia machine b). A portable cassette containing agent. The flow at the out let is controlled by the CENTRAL PROCESSING UNIT in the anesthesia machine.
  83. 83. • The Aladin Cassette can be handled or stored in any position. Automatic record keeping and gas usage calculation • Electronic control of desired agent concentration . .Provides agent setting data for automatic record Keeping and fresh gas flow data. • Gas usage data provides a unique tool for low flow
  84. 84. DRAGER 19.1 similar to tec 4,5 vaporizers. The interlock on Dräger machines continues to function if any vaporizers are removed. There is no outlet check valve- the tortuous inlet arrangement protects from the pumping effect. No anti-spill mechanism. Should not be tipped more than 45.
  85. 85. Drager 19.1
  86. 86. Drager 2000 : • Is one of two tippable vaporizers (ADUcassettes are the other). • The dial must first be rotated to a "T" setting ("transport" or "tip") which is beyond zero (clockwise). •Tortous in let protects against pumping effect.
  87. 87. Filling devices • Funnel fill system • Keyed fill system • Quik- fil system • Easy-fil system
  88. 88. FUNNEL FILL Vaporizers may be filled by a conventional funnel-fill mechanism, in which the liquid anesthetic is simply poured into a funnel in the vaporizer. Complication is filling with wrong agent.
  89. 89. KEYED FILL In this system, an agent-specific filler tube is used, one end of which slots into a fitting on the vaporizer, and the other end slots into a collar on the bottle of anesthetic. The fitting on the vaporizer and the collar on the bottle are specific to each agent.
  90. 90. QUIK FIL : The bottle has a permanently attached, agent-specific filling device that has three ridges that fit into slots in the filler.
  91. 91. EASY FIL : A color coded bottle adaptor is attatched to bottle and then fitted into the vaporizer. A drain plug is there for draining vaporizer.
  92. 92. Hazards of a vaporizer • a)In correct agent • b)Tipping • c)over filling • d)reversal of flow • e)leaks
  93. 93. a)In correct agent: minimized by agent specific filling devices, color coding, agent monitors.
  94. 94. Contd… b)TIPPING: lead to delivery of very high concentrations of vapor. Prevented by – 1.Mounting vaporizers on manifold. – 2.draining vaporizer before being moved. c) OVER FILLING : – Liquid agent enter the fresh gas line, leading to high concentrations. – Prevented by low level filling port, indicator glass.
  95. 95. D )REVERSAL OF FLOW : output is increased.prevented by indicator arrows. E) LEAKS : lead to wastage of agent, OT pollution,delivery of wrong concentrations. prevented by NEGATIVE PRESSURE CHECK TEST
  96. 96. Thank you