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Copy of vaporizers


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Copy of vaporizers

  1. 1. VAPORIZERS <ul><li>DR. AVADHESH PRATAP </li></ul><ul><li>RESIDENT </li></ul><ul><li>DEPARTMENT OF ANAESTHESIOLOGY </li></ul><ul><li>AND CRITICAL CARE </li></ul><ul><li>N.S.C.B. MEDICAL COLLEGE JABALPUR (M.P.) </li></ul>
  2. 2. WHY WE NEED A VAPORIZER <ul><li>Most volatile agents exist as liquid at room temperature and atm. pressure . </li></ul><ul><li>Vaporizers convert this liquid form to vapor phase and add a certain amount of this vapor to anaesthetic circuit </li></ul><ul><li>In precisely determined concentration over a wide range of temp, pressure and carrier gas flow rates </li></ul>
  3. 3. PHYSICS RELATED TO VAPORIZERS ? <ul><li>What is vapor ? </li></ul><ul><li>What is vapor pressure ? </li></ul><ul><li>What is a vaporizers ? </li></ul>
  4. 4. DEFINITIONS <ul><li>Vapor is the gaseous phase of a substance which is normally a liquid at room temp. and atm. pressure. Eg. water vapor is the vapor form of water </li></ul><ul><li>Gas is substance which exists only in the gaseous state at room temp. and amt. pressure. </li></ul>
  5. 5. WHAT IS CRITICAL TEMPERATURE ? <ul><li>For any substance there is a max. temp. at which it can be compressed so as to convert it from a gas to a liquid. This is known as the critical temp. and above this temp. no amount of compression will liquefy it. </li></ul><ul><li>Under this condition the substance is a gas. </li></ul><ul><li>Below that critical temp it is a vapor. </li></ul>
  6. 7. WHAT IS VAPOR PRESSURE <ul><li>This vapor exerts a pressure on its surroundings – Vapor pressure . </li></ul><ul><li>Vapor pressure depends only on the temp. and liquid. </li></ul><ul><li>Vapor pressure of an agent determines how much of vapor will be formed from 1 ml of the liquid. </li></ul><ul><li>Since different anaesthestic agents have different vapor pressures the need separate vaporizers. </li></ul>
  8. 9. <ul><ul><ul><li>For a particular liquid at a particular temp. there occurs an equilibrium at which the number of molecules leaving the liquid equals the number reentering </li></ul></ul></ul><ul><ul><ul><li>It is the maximum VP at a particular temp. Increases rapidly as boiling point approaches. </li></ul></ul></ul>
  9. 10. BOILING POINT ?
  10. 11. <ul><li>Go on increasing the temp. </li></ul><ul><li>The V.P. will increase. </li></ul><ul><li>At a point it equals the atm pressure </li></ul><ul><li>B.P. OF A LIQUID IS THE TEMPERATURE AT WHICH ITS VAPOR PRESSURE IS EQUAL TO THE ATM PRESSURE </li></ul><ul><li>Low atm pressure - > Low B.P. </li></ul><ul><li>High SVP -> Low B.P. (Means very volatile) </li></ul>
  11. 12. CONCENTRATION OF VAPOR <ul><li>May be expressed as </li></ul><ul><li>VOLUME % </li></ul><ul><li>OR </li></ul><ul><li>PARTIAL PRESSURE </li></ul>
  12. 13. PARTIAL PRESSURE <ul><li>A mixture of gases in a closed container will exert a pressure on the walls of the container. The part of the pressure exerted by any one gas in the mixture is called its partial pressure </li></ul><ul><li>Depends only on the temperature and nature of liquid </li></ul><ul><li>The highest partial pressure that can be exerted by a gas at a given temperature is its vapor pressure it is an absolute value. </li></ul><ul><li>UPTAKE & DEPT. OF ANAE. α PP. </li></ul>
  13. 14. VOLUMES PERCENT <ul><li>No of units of volume of a gas in relation to a total of 100 units of volume for the total gas mixture </li></ul><ul><li>It expresses the relative ratio of gas molecules in a mixture. </li></ul><ul><li>Most commonly used. </li></ul><ul><li>PARTIAL PRESSURE/TOTAL PRESSURE = VOLUMES PERCENT/100 </li></ul>
  14. 15. LATENT HEAT OF VAPORIZATION ? <ul><li>The number of calories required to convert 1gm of liquid into a vapor or number of calories required to convert 1 ml of liquid into a vapor. </li></ul><ul><li>In a vaporizer as the liquid agent vaporizes -> heat is lost -> temp. drops -> V.P. drops -> less volume of agent is available for the carrier gas to take away -> decreases output </li></ul>
  15. 16. SPECIFIC HEAT ? <ul><li>It is the amount of heat required to raise the temp of 1gm or 1ml of a substance through 1 degree 0 C </li></ul><ul><li>Significance </li></ul><ul><li>LIQUID ANAESTHETIC AGENT – Should have a low specific heat so as to facilitate vaporization </li></ul><ul><li>VAPORISER CONSTRUCTION MATERIAL- Should have high specific heat; acts as a heat sink; provides a more stable temp. </li></ul>
  16. 17. THERMAL CAPACITY <ul><li>SPECIFIC HEAT x MASS </li></ul><ul><li>Amount of heat stored in the vaporizer body </li></ul><ul><li>A vaporizer constructed from a substance with high thermal capacity -> temp. changes more slowly and so preferred </li></ul>
  17. 18. THEMAL CONDUCTIVITY <ul><li>Speed with which heat flows through a substance; Cu > Al> brass> Steel >> Glass. </li></ul><ul><li>Higher the thermal conductivity, better the substance conducts heat. </li></ul><ul><li>Significance </li></ul><ul><li>Vap. Constructor material should be able to conduct heat from surroundings to contained liquid. </li></ul><ul><li>Cu has a moderate sp. Heat and high thermal conductivity – use for construction of vaporizers </li></ul><ul><li>More recently use bronze stainless steel </li></ul>
  18. 19. THERMOSTABILIZATION ? <ul><li>Utilization of some means to minimize temp. changes. </li></ul><ul><li>Construct vaporizers of materials with high thermal conductivity and specific heat to minimize temp. changes when in use. </li></ul><ul><li>Heavy metal parts act as a heat reservoir. </li></ul><ul><li>Wicks to be in contact with the metal part so that heat loss due to vaporization is quickly replaced. </li></ul>
  19. 20. GAS LAWS <ul><li>Boyles law: V α 1/p (at constant temperature ) </li></ul><ul><li>Charle’s law: V α T (at constant pressure ) </li></ul><ul><li>DALTON’S LAW OF PARTIAL PRESSURES </li></ul><ul><li>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 </li></ul>
  20. 21. AVOGADRO’S HYPOTHESIS <ul><li>Equal volumes of gases at the same temperature and pressure contain equal number of molecules. </li></ul><ul><li>This no. is 6.023 x 10 23 </li></ul><ul><li>This much no. of particles of any gas at STP will occupy 22.4 Ls </li></ul>
  21. 22. WHAT IS MAC ? <ul><li>Typically expressed as vol. % or alveolar gas at 1 atm Eg. MAC of </li></ul><ul><li>halothane - 0.75 </li></ul><ul><li>enflurane - 1.68 </li></ul><ul><li>isoflurane - 1.2 </li></ul><ul><li>desflurane - 6.0 </li></ul><ul><li>sevoflurane - 2.0 </li></ul>
  22. 23. WHAT IS MAPP ? <ul><li>Minimum alveolar partial pressure ( MAPP) </li></ul><ul><li>Expresses MAC in terms of PP (Pmac1) </li></ul><ul><li>MAC of hal is 0.75 </li></ul><ul><li>pp of hal for 1 MAC is </li></ul><ul><li>0.75/100x760 = 5.7 mm Hg </li></ul><ul><li>Pmac1 of des for is </li></ul><ul><li>6/100x760 = 45.6 mm Hg </li></ul>
  23. 24. WHAT IS A VAPORIZER ? <ul><li>A vaporizer is an instrument designed to facilitate the change of a liquid anaesthetic agent into a vapor </li></ul><ul><li>And </li></ul><ul><li>Add a controlled amount of this vapor to the FGF </li></ul><ul><li>The SVP of most inhalation agents is MUCH more that is required to produce anesthesia i.e. 32% vs 0.75 or 243 mm Hg vs 5.7 mm Hg for halothane </li></ul><ul><li>Need to dilute this vapor with the carrier gas and deliver a controlled amount of this vapor to the patient </li></ul>
  24. 25. <ul><li>What amount of vapor produced by 1 gram of its liquid agent ? </li></ul><ul><li>1 mole of a gas weighs 1 gram molecular weight. </li></ul><ul><li>The molecular weight of isoflurane is 185 </li></ul><ul><li>Therefore, 1 mole of isoflurane vapor weighs 185 g </li></ul><ul><li>As per avogadro’s hypothesis 1 mole of a substance = 22.4 liters of gas </li></ul><ul><li>22.4 L of isoflurane vapour weighs 185 g </li></ul>
  25. 26. <ul><li> density of isoflurane vapor is 185/22.4 = 8.25 g/litre </li></ul><ul><li> 1 gram = 1000/8.25 ml of vapor </li></ul><ul><li>Density of lsoflurane liquid is 1.5 g/ml </li></ul><ul><li> 1 gram = 1/1.5 ml of liquid </li></ul><ul><li>1/1.5 ml of liquid = 1000/8.25 ml of vapor </li></ul><ul><li>1 ml of liquid = 1000/8.25 x 1.5 = 180 ml. </li></ul><ul><li>For most modern agents, </li></ul><ul><li>1 ml of liquid volatile agent yields about 200 ml of vapor </li></ul>
  26. 27. <ul><li>How much liquid agent does a vaporizer use per hour ? </li></ul><ul><li>The amount of vapor used per min. = </li></ul><ul><li>FGF x time x concentration setting </li></ul><ul><li>For e.g., to deliver 1% isoflurane at FGF of 2 litres per min for 60 mins. One would need 1/100 x 2000 ml x 60 min = 1200 ml of isoflurane vapor </li></ul><ul><li>This woul correspon to 1200/180 = 6.7 ml of liquid isoflurane </li></ul><ul><li>Another formula which can be used with most agents is </li></ul><ul><li>3 x Fresh gas glow (FGF) (L/min)x volume % ml liquid used per hour </li></ul>
  29. 30. METHOD OF VAPORIZATION <ul><li>FLOW OVER </li></ul><ul><li>BUBBLE THROUGH </li></ul><ul><li>INJECTION </li></ul><ul><li>SIMPLE </li></ul>
  31. 32. SPECIFICITY <ul><li>AGENT SPECIFIC </li></ul><ul><li>MULTIPLE AGENTS </li></ul>
  32. 33. POSITION <ul><li>VAPORIZER INSIDE CIRCUIT </li></ul><ul><li>VAPORIZER OUTSIDE CIRCUIT </li></ul>
  33. 34. RESISTANCE <ul><li>PLENUM </li></ul><ul><li>LOW RESISTANCE/DRAW OVER </li></ul>
  34. 35. BASIC DESIGN
  35. 36. METHOD OF REGULATING OUTPUT CONSENTRATION <ul><li>CONCENTRATION CALIBRATED </li></ul><ul><li>Total flow form the machine passes through the vaporizer. This is split by a variable resistance proportionationg valve into two: </li></ul><ul><li>One part ( usually major ) flows through the bypass chamber & the other ( usually small ) through the vaporizing chamber. </li></ul>
  36. 37. CONCENTRATION CALIBRATED <ul><li>AGENT CONCENTRATION IS CONTROLLED BY A DIAL CALIBRATED IN VOLUMES PERCENT </li></ul><ul><li>Depends on resistance of the 2 pathways (controlled by conc. Control dial & thermocomp. vol.) </li></ul><ul><li>Volume vapourised – typically 200 ml vapour per ml of liquid Anaesthetic </li></ul>
  39. 40. SPLITTING RATIO <ul><li>The ratio of the bypass gas to the gas going to the vaporizing chamber is called the SPLITTING RATIO . Splitting ratio depends on : </li></ul><ul><li>The resistance of the two pathways, which inturn depends on the variable orifice of the inlet/outlet. </li></ul><ul><li>Temperature of the liquid/carrier gas. </li></ul><ul><li>Flow rate of gases </li></ul>
  40. 41. MEASURED FLOW VAPORIZERS <ul><li>The vaporizer heats the anesthetic agent to a temperature above its boiling point (so it behaves as gas) and this is then metered into the fresh gas flow. </li></ul><ul><li>A measured flow is sent by a separate oxygen flow meter to pass to the vaporizer with the output being at SVP for the anesthetic agent. </li></ul><ul><li>In order to dilute this otherwise lethal concentration, outpur from that flowmeter is combined with gas passing form the main flowmeter </li></ul>
  41. 42. <ul><li>Operator has to set the flow to the vaporizer and bypass with separate flowmeters </li></ul><ul><li>This means that respective flows have to be calculated for each agent for a given temp and vapour output </li></ul><ul><li>To calculate the vaporizer output, one must know the - Vapor pressure of the agent </li></ul><ul><li>- The atmospheric pressure </li></ul><ul><li>- The total flow of gases </li></ul><ul><li>- The flow of the vaporizer </li></ul>MEASURED FLOW VAPORIZERS
  42. 43. CALCULATIONS FOR OUTPUT IN MEASURED FOW VAPORISERS <ul><ul><li>Set 100 ml/min flow of carrier gas (oxygen) from dedicated flowmeter </li></ul></ul><ul><ul><li>SVP of hal in vap. Chamber is 243 mmHg </li></ul></ul><ul><ul><li>Hal forms 243/760 x 100 = 32% of gas mixture </li></ul></ul><ul><ul><li>Carrier gas will occupy the rest of the vol. i.e. 100-32=68% </li></ul></ul><ul><ul><li>This 68% is occupied by 100ml/min carrier gas </li></ul></ul><ul><ul><li>And 32% hal will be = 100/68x32=47 ml </li></ul></ul>
  43. 44. <ul><ul><li>Gas exiting is 147 ml with 47 ml hal vapor </li></ul></ul><ul><ul><li>To get a mixture containing 1% hal this 47 ml should be diluted in 4700 ml </li></ul></ul><ul><ul><li>Required carrier gas is 4700-147=4553 ml </li></ul></ul><ul><ul><li>If set 100 ml measured flow to vaporiser usually set 5 l/min flow of carrier gas to get 1% halothane </li></ul></ul><ul><ul><li>Ratio of gas through vaporiser: main gas flow is 100:4600=1:46 </li></ul></ul><ul><ul><li>% concentration of agent = 100 x vaporizer output of anaesthetic/total flow </li></ul></ul>CALCULATIONS FOR OUTPUT IN MEASURED FOW VAPORISERS
  44. 45. VAPORIZATION METHODS <ul><ul><li>FLOW OVER </li></ul></ul><ul><ul><li>Here the carrier gas passes over the surface of a liquid </li></ul></ul><ul><ul><li>Surface area of vaporization can be increased by using wicks. </li></ul></ul>
  45. 46. FLOW OVER
  46. 47. <ul><li>Due to capillary action, the anaesthetic agent rises into the wicks. This dramatically increases the surface area of anaesthetic agent exposed to the fresh gas and thereby improves the efficiency of vaporization. </li></ul><ul><li>Carrier gas can be directed using baffles or spiral tracks that lengthen the gas pathways over the liquid. This increases the time and area of contact . </li></ul>FLOW OVER
  48. 49. <ul><li>Carrier gas is allowed to bubble through the liquid. </li></ul><ul><li>Smaller the bubble, larger will be the surface area. </li></ul><ul><li>Methods to break the gas into small bubbles are agitation & splashing. </li></ul><ul><li>Factors influencing the vaporizer output: </li></ul><ul><li>Size of the bubble, </li></ul><ul><li>Depth of liquid, </li></ul><ul><li>- Bubbling speed (Velocity of carrier gas flow) </li></ul>BUBBLE THROUGH
  49. 50. INJECTION VAPORIZERS <ul><li>A known amount of liquid agent or pure vapor is injected into the gas stream to provide the desired concentration </li></ul><ul><li>Eg. TEC 6 desflurane vaporizer (it is more ideally classified as a gas-vapor blender) </li></ul>
  50. 51. TEMPERATURE COMPENSATION <ul><li>To maintain a constant output from the vaporizer, mechanisms to compensate for the fluctuations in temperature are to be employed </li></ul><ul><li>Alteration in the splitting ratio (automatic compensation </li></ul><ul><li>Eg. Bimetallic strip in tec vaporizers, ether filled bellows in penlon vaporizers, EMO </li></ul><ul><li>Computer control – electronic vaporizers </li></ul><ul><li>Supplied heat – tec 6 (electrically heated) </li></ul>
  52. 53. THERMOCOMPENSATION <ul><li>Most variable bypass vaporizers compensate for changes in vapor pressure by altering the splitting ratio. </li></ul><ul><li>Done by using a thermosensitive element (BIMETALLIC STRIP) incorporated in the vaporizing chamber or bypass chamber. </li></ul><ul><li>So, the splitting of gas is controlled by 2 valves: </li></ul><ul><li>(1) the dial we set (splitting valve) </li></ul><ul><li>(2) the temperature compensating valve. </li></ul>
  53. 54. THERMOCOMPENSATION <ul><li>In a bimetallic strip, two metals with very different coefficients of thermal expansion are fixed together. </li></ul>
  54. 55. THERMOCOPENSATION <ul><li>When the temp. of the vaporizing chamber drops, the bimetallic strip bends and moves away. This reduces the resistance to flow and thus more flow occurs into the vaporizing chamber </li></ul>
  55. 56. SUPPLIED HEAT <ul><li>An electric heater can be used to supply heat to a vaporizer and maintain it at a constant temperature </li></ul><ul><li>Eg. Tec 6 </li></ul>
  56. 57. RESISTANCE <ul><li>PLENUM ( Latin = fullness) </li></ul><ul><li>Vaporizers with high resistance which depend on compressed gas driven under pressure are called plenum vaporizers. </li></ul><ul><li>Eg. Boyle bottle, copper kettle, TEC vaporizers </li></ul>
  57. 58. <ul><li>DRAW OVER </li></ul><ul><li>Carrier gas is drawn through the vaporizer either by the patient’s own respiratory efforts, or by a self-inflating bag or manual bellows </li></ul><ul><li>Drawover systems operate at less than, or at ambient pressure </li></ul><ul><li>Flow through the system is intermittent, varying with different phases of inspiration, and ceasing in expiration. </li></ul>RESISTANCE
  58. 59. <ul><li>DRAW OVER </li></ul><ul><li>Have a low internal resistance to gas flow </li></ul><ul><li>So that they may be used within the breathing circuit, the gas flow being driven through them by the patient’s breathing. </li></ul><ul><li>They may be used in a non rebreathing DROW-OVER APPARTUS, or as IN-CIRCUIT VAPORZERS in a CIRCLE ABSORBER SYSTEM. </li></ul><ul><li>Eg. Goldman bottle, EMO </li></ul>
  59. 60. FACTORS AFFECTING VAPORIZER OUTPUT <ul><li>1. FLOW THROUGH THE VAPORIZING CHAMBER: Varying the proportion of gas passing through the vaporizing chamber and bypass chamber </li></ul><ul><li>2. SURFACE AREA OF THE LIQUID GAS INTERFACE: Greater the surface area, more will be the vaporization. </li></ul><ul><li>Bubble through > flow over </li></ul>
  60. 61. FACTORS AFFECTING VAPORIZER OUTPUT <ul><li>3. TEMPERATURE: as temperature increase, output increase </li></ul><ul><li>4. TIME: Output concentration tend to fall over time </li></ul><ul><li>5. GAS FLOW RATE: (A) At high flowrates, the gas leaving vaporization chamber is less saturated </li></ul><ul><li>(B) Alters the total flow that passes through the vaporization chamber </li></ul>
  61. 62. <ul><li>6. CARRIER GAS COMPOSITION: </li></ul><ul><li>(a) Changes in viscosity & density may affect the proportion of the total flow passing through the vaporization chamber </li></ul><ul><li>(b) N 2 O dissolves in the flow, thus altering the effective volume passing through the vaporization chamber </li></ul><ul><li>7. BOILING POINT: Higher the boiling point, less will be the vapor output </li></ul>FACTORS AFFECTING VAPORIZER OUTPUT
  62. 63. <ul><li>8. AMBIENT PRESSURE: </li></ul><ul><li>- SVP is solely a function of temp. so if ambient pressure is reduced, the constant SVP becomes a greater proportion of the total pressure </li></ul><ul><li>-> output increases. </li></ul><ul><li>- Agents with low boiling points are more susceptible to the influence of ambient pressure </li></ul>FACTORS AFFECTING VAPORIZER OUTPUT
  63. 64. EFFECT OF LOW ATMOSPHERIC PRESSURE <ul><li>CONCENTRATION CALIBRATED </li></ul><ul><li>High resistance pathway through the vaporizing chamber offers less resistance, under hypobaric conditions and so a slight increase in vapor output occurs. </li></ul><ul><li>Deliver higher conc. if measured in vol. % but deliver same PP so clinically affect unchanged </li></ul><ul><li>C  P  =CP or C  =CP/P  </li></ul><ul><li>At 0.5 atm. C  =Cx1/.5=2% </li></ul>
  64. 65. EFFECT OF LOW ATMOSPHERIC PRESSURE <ul><li>MEASURED FLOW </li></ul><ul><li>Here the delivered partial pressure & volume percent increases. </li></ul><ul><li>Amount of increase depends on the barometric pressure & the vapor pressure of the agent. </li></ul><ul><li>Closer the vapor pressure is to barometric pressure, greater the effect. </li></ul>
  65. 66. <ul><li>CONCENTRATION CALIBRATED </li></ul><ul><li>ATM PRESSURE </li></ul><ul><li>INCREASES -> Density of gas </li></ul><ul><li>CHANGES -> More resistance to flow of gas through the vaporizing chamber </li></ul><ul><li>-> Decreased vapor O/P (Partial Pressure & Volume Percent) </li></ul><ul><li>Effect on partial pressure is less dramatic </li></ul>EFFECT OF HIGH ATMOSPHERIC PRESSURE
  66. 67. <ul><li>MEASURED FLOW </li></ul><ul><li>Lower concentration in terms of PP/Volume percent </li></ul>EFFECT OF HIGH ATMOSPHERIC PRESSURE
  67. 68. EFFECT OF INTERMITTENT BACK PRESSURE <ul><li>When assisted or controlled ventilation is used, the positive pressure generated during inspiration is transmitted from the breathing system back to the machine & some way may be transmitted to the vaporizers. </li></ul><ul><li>Also seen with the use of oxygen flush </li></ul>
  68. 69. PUMPING EFFECT <ul><li>The increase in vaporizer output concentration due to back pressure </li></ul>
  69. 70. PUMPING EFFECT <ul><li>When the bag is squeezed, pressure is transmitted back into both, the “by pass” channel and also to the vaporizing chamber. The fresh gas tries to move forward and gets compressed both in the ‘by pass’ channel and the vaporizing chamber. However, the vaporizing chamber volume is much larger than the ‘by pass’ channel volume, an thus, more fresh gas gets compressed into it than into the ‘by pass’ channel. </li></ul>
  70. 71. PUMPING EFFECT <ul><li>This extra fresh gas that enters the vaporizing chamber collects anaesthetic vapor </li></ul>
  71. 72. PUMPING EFFECT <ul><li>When the positive pressure is suddenly released (expiration) the previously compressed gases now suddenly expands in all direction. </li></ul><ul><li>Some of the rapidly expanding gas (containing vapor) enter the inlet of the vaporizer and cross over into the ‘by pass’ channel </li></ul>
  72. 73. PUMPING EFFECT <ul><li>Normally, a vaporizer ‘by pass’ channel does not have vapor. So his vapor due the pumping effect’ is additional. When this ‘by pass’ vapor flows across to the exit, it meets the vapor from the vaporizing chamber. The addition of the ‘by pass’ vapor to the vapor from the vaporizing chamber raises the final concentration of anaesthetic delivered. i.e. the ‘pumping effect’ increases the delivered concentration of anaesthetic agent. </li></ul>
  73. 74. PUMPING EFFECT <ul><li>SEEN ESPECIALLY WHEN </li></ul><ul><li>-> CARRIER GAS IS LOW </li></ul><ul><li>-> AGENT IN VAPORIZING CHAMBER IS LOW </li></ul><ul><li>-> DIAL SETTING IS LOW </li></ul><ul><li>-> PRESSURE FLUCTUATIONS ARE HIGH & FREQUENT. </li></ul>
  74. 75. PUMPING EFFECT <ul><li>MECHANISM IN MEASURED FLOW: </li></ul><ul><li>Gas flow to these vaporizers become saturated with vapor & is joined by gas from other flowmeter, which dilutes its concentration. </li></ul><ul><li>When back pressure is applied, there is retrograde flow of gas so that the diluted gas mixture is forced back into the vaporizer, because this gas is not saturated, it will then pick up anesthetic vapor, the final concentration will be higher </li></ul>
  75. 76. MODIFICATIONS TO MINIMIZE PUMPING EFFECT <ul><li>Keep the vaporizing chamber small </li></ul><ul><li>Or </li></ul><ul><li>Increasing the size of the bypass chamber. </li></ul>
  76. 77. MODIFICATIONS TO MINIMIZE PUMPING EFFECT <ul><li>Add long spiral or large diameter tube to lead to the vaporizer chamber. The extra gas forced into this tube & subsequently returned to the bypass does not reach the vaporizing chamber </li></ul>
  77. 78. <ul><li>Increase resistance to gas flow through the vaporizer </li></ul>MODIFICATIONS TO MINIMIZE PUMPING EFFECT
  78. 79. <ul><li>Check valve to prevent backward flow of gas </li></ul>MODIFICATIONS TO MINIMIZE PUMPING EFFECT
  79. 80. <ul><li>Exclude wicks from the area where the inlet tube joins the vaporizing chamber. </li></ul><ul><li>Outlet tube may be made longer so that further back before picking up anesthetic vapor. </li></ul><ul><li>Connections of oxygen flush valve line to the common gas outlet be designed to minimize pressure fluctuations that may produce a pumping effect </li></ul><ul><li>Limit pressure transmitted to vaporizer to <10KPa above normal working pressure, conc not to increase > 20% </li></ul>MODIFICATIONS TO MINIMIZE PUMPING EFFECT
  80. 81. PRESSURIZING EFFECT <ul><li>The output of some vaporizer used in conjunction with automatic ventilator has been found to be lower than during free flow to atmosphere. </li></ul><ul><li>Mostly seen when </li></ul><ul><li>-> High flow </li></ul><ul><li>-> Large pressure fluctuations </li></ul><ul><li>-> Low dial settings </li></ul>
  82. 83. <ul><li>No of mol.s of the agent picked by carrier gas α density of vapor mol.s in vaporizing chamber α vapor pressure </li></ul><ul><li>Increased pressure in vaporizer chamber compress carrier gas -> more mol.s/mL-> no of mols of the anesthetic agent same ->o/p  </li></ul><ul><li>The changes in vaporizer O/P caused by the pumping effect usually are greater in magnitude that those associated with the pressurizing effect </li></ul>PRESSURIZING EFFECT
  83. 84. 1988 ASTM MACHINE STANDARDS FOR VAPORIZERS <ul><li>The effects 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. </li></ul><ul><li>The average delivered concentration from the vaporizer shall not deviated from the set value by more than ± 20% or ± 5% of the maximum setting whichever is greater without back pressure. </li></ul>
  84. 85. <ul><li>The average delivered concentration from the vaporizer shall not deviate from the set value by more that + 30% or – 20% or by more than + 7.5% or – 5% of the max. setting whichever is greater, with pressure fluctuations at the common gas outlet of 2 kPa with a total gas flow of 2 L/minute or 5 kPa with a total gas flow of 8 L/minute </li></ul><ul><li>A system that prevents gas from passing through the vaporizing chamber or reservoir of one vaporizer and the through that of another must be provided </li></ul><ul><li>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. </li></ul>
  85. 86. <ul><li>All vaporizer control knobs must open counterclockwise </li></ul><ul><li>Either the max. and min. filling levels or the actual usable volume and capacity shall be displayed </li></ul><ul><li>The vaporizer must be designed so that it cannot be overfilled when in the normal operating position. </li></ul><ul><li>Vaporizer unsuitable for use in the breathing system must have noninterchangeable proprietary or 23 mm fittings. Conical fittings of 15 mm and 22 mm cannot be used. When 23 mm fittings are used the inlet must be male and the outlet female . The direction of gas flow must be marked. </li></ul>
  86. 87. <ul><li>10. Vaporizers suitable for use in the breathing system must have standard 22-mm fittings or screwthreaded, weight-bearing fittings with the inlet female and the outlet male . The direction of gas flow must be indicated by arrows and the vaporizer marked “for use in the breathing system. </li></ul>
  88. 89. <ul><li>A vaporizer designed for a single agent be fitted with a permanently attached agent specific device to prevent accidental filling with a wrong agent. </li></ul><ul><li>They prevent accidental filling with the wrong agent. </li></ul><ul><li>Reduce air pollution. </li></ul><ul><li>Vaporization chamber </li></ul><ul><li>TYPES </li></ul><ul><li>KEYED FILLING SYSTEM </li></ul><ul><li>SCREW CAPPED FILLING SYSTEM </li></ul><ul><li>PIN SAFETY SYSTEM </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  89. 90. <ul><li>BOTTLE COLLAR </li></ul><ul><li>Attached at the neck of the bottle. </li></ul><ul><li>2 projections, one thicker than the other are there. </li></ul><ul><li>This mates with the corresponding indentations on the bottle adaptor </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  91. 92. <ul><li>BOTTLE ADAPTOR </li></ul><ul><li>AT ONE END IS </li></ul><ul><li>The bottle connector with a screw thread to match the thread on the bottle </li></ul><ul><li>Skirt that extends beyond the screw threads </li></ul><ul><li>Slots that match the projections on the bottle collar </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  92. 93. <ul><li>AT THE OTHER END IS </li></ul><ul><li>The male adaptor that fits into the vaporizer filler receptacle. </li></ul><ul><li>A short length of plastic tubing with 2 inner tubes connects the ends. </li></ul><ul><li>The tube allows the bottle to be held higher or lower than the vaporizer. </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  93. 94. <ul><li>MALE ADAPTER </li></ul><ul><li>Has a groove on one side to prevent the probe from being placed in the incorrect vaporizer </li></ul><ul><li>2 holes on the other side </li></ul><ul><li>LARGER -> for agent to leave/enter </li></ul><ul><li>SMALLER -> for air </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  94. 95. <ul><li>FILLER RECEPTACLE </li></ul><ul><li>(Filler socket/vaporizer filler unit/fill & drain system) </li></ul><ul><li>Must permit the insertion of the intended bottle </li></ul><ul><li>Must have a means of tightening the male adapter, to from a tight seal. </li></ul><ul><li>Must have a means of sealing (plug) the adaptor when bottle adaptor not inserted. </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  95. 96. <ul><li>FILLER RECEPTACLE </li></ul><ul><li>Single port for filling & drainage. </li></ul><ul><li>A valve attached to a knob at the top controls the opening into the vaporizer </li></ul><ul><li>A ball valve in the airline occludes the air port after the vap is filled to prevent overfilling & flooding of airline with the agent. </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  96. 97. <ul><li>FILLING </li></ul><ul><li>Cap of bottle removed </li></ul><ul><li>Adapter screwed to the collar </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  97. 98. <ul><li>FILLING </li></ul><ul><li>Vaporizer turned off </li></ul><ul><li>Plug removed </li></ul><ul><li>Bottle with adapter inserted such that the grooves match; (tube bent such that bottle is below inlet) </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  98. 99. <ul><li>FILLING </li></ul><ul><li>Retaining screw tight </li></ul><ul><li>Fill valve (vent) opened </li></ul><ul><li>Bottle held high </li></ul><ul><li>Air from the vaporizer displaced by the liquid moves through the other tube and enters the air space inside the bottle </li></ul><ul><li>Gentle up and down motion may help </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  100. 101. <ul><li>DRAINING </li></ul><ul><li>Adapter attached to bottle -> filler plug removed -> male adaptor inserted -> retaining screw tightened -> bottle held below the receptacle -> drain valve opened -> drained -> screw loosened -> adaptor removed -> filler plug inserted </li></ul>AGENT SPECIFIC FILLING SYSTEMS
  101. 102. <ul><li>Difficulty in filling </li></ul><ul><li>Misalignment of adaptor in filler receptacle </li></ul><ul><li>Adaptor not sealing at the bottle end </li></ul><ul><li>Leak in the bottle adaptor </li></ul><ul><li>Air bubbles. </li></ul><ul><li>Lost bottle adaptor </li></ul><ul><li>Failure of keyed system </li></ul><ul><li>Liquid leaks </li></ul>AGENT SPECIFIC FILLING SYSTEMS PROBLEMS
  102. 103. <ul><li>10. VAPORIZER TIPPING </li></ul><ul><li>If filler receptacle on vaporizer extends beyond the base -> it cannot be set upright on a flat surface -> this can cause tipping prevented by setting the vaporizer receptacle at the edge of the surface or a ring can be fitted at the base that extends below the projection of the filler reeptacle </li></ul><ul><li>POOR DRAINAGE </li></ul><ul><li>BROKEN INNER TUBE </li></ul>AGENT SPECIFIC FILLING SYSTEMS PROBLEMS
  103. 104. LOCATION <ul><li>Between the flowmenters & common gas outlet </li></ul><ul><li>Between the common gas outlet & breathing system </li></ul><ul><li>In-system vaporizers </li></ul>
  104. 105. HAZARDS <ul><li>INCORRECT AGENT </li></ul><ul><li>Low output or high output </li></ul><ul><li>Misplacing desflurane dangerous </li></ul><ul><li>Gas allowed to flow through it until no agent detected in the outflow </li></ul>
  105. 106. <ul><li>TIPPING </li></ul><ul><li>Liquid from vaporizing </li></ul><ul><li>Chamber->bypass/outlet->high output </li></ul><ul><li>Drained before moving </li></ul><ul><li>OVERFILLING </li></ul><ul><li>In majority, the design of the filling port and agent specific filling systems prevent this </li></ul><ul><li>During filling do not : </li></ul><ul><li>Turn the dail ON/Unscrew the bottle adaptor </li></ul>HAZARDS
  106. 107. <ul><li>REVERSED FLOW </li></ul><ul><li>Inlet male & outlet female </li></ul><ul><li>Increased output </li></ul><ul><li>CONCENTRATION DIAL IN WRONG POSITION </li></ul><ul><li>CONTAMINATS IN VAPORIZING CAHMBER </li></ul><ul><li>PHYSICAL DAMAGE </li></ul><ul><li>OBSTRUCTION TO FRESH GAS FLOW </li></ul><ul><li>INTERLOCK MALFUNCTION </li></ul>HAZARDS
  107. 108. INTERLOCK DEVICES <ul><li>Applied to control dial of vaporizer so that only one vaporizer can be turned on at a time </li></ul><ul><li>Ensure that </li></ul><ul><li>- Only 1 vap. is turned on at a time </li></ul><ul><li>Gas only enters that which is ON at that time </li></ul><ul><li>Trace vapor output is minimized when OFF </li></ul><ul><li>Vap.s are locked onto gas circuit hence correctly seated </li></ul>
  108. 109. INTERLOCK DEVICES <ul><li>Selector valve </li></ul><ul><li>Selectatec system </li></ul><ul><li>Back bar devices </li></ul><ul><li>Ohio switch </li></ul><ul><li>Drager lock </li></ul>
  109. 110. ORDER OF VAPORIZERS <ul><li>Less potent - upstream </li></ul><ul><li>More potent - downstream </li></ul><ul><li>If equipotent </li></ul><ul><li>Low VP - upstream </li></ul><ul><li>High VP - downstream </li></ul><ul><li>Also </li></ul><ul><li>If explosive - downstream </li></ul><ul><li>Trilene - downstream </li></ul><ul><li>Easy to clean - downstream </li></ul>
  111. 112. EVOLUTION OF VAPORIZERS <ul><li>MORTONS ETHER INHALER </li></ul><ul><li>1846, OCT 16 </li></ul>
  115. 116. OPEN DROP MASK
  116. 117. OPEN DROP MASK
  117. 118. OGSTON INHALER
  118. 119. BOYLES BOTTLE <ul><li>Parts: (1) vaporizing bottle 300 mL (2) Metal top incorporating controls (3) Lever, plunger which is chrome plated (4) Stopper & Retaining chain </li></ul><ul><li>Concentration calibrated </li></ul><ul><li>Flowover or bubble through </li></ul><ul><li>Not temperature compensated </li></ul><ul><li>Multiple agents </li></ul><ul><li>Vaporizer outside circuit </li></ul>
  119. 120. OXFORD MINIATURE VAPORIZER (OMV) <ul><li>Variables bypass </li></ul><ul><li>Flowover with steel wicks </li></ul><ul><li>Temperature compensated </li></ul><ul><li>For use by multiple agents </li></ul><ul><li>Vaporizer outside circuit </li></ul><ul><li>Halothane trilene methoxyflura ne ether isoflurane </li></ul>
  127. 128. ROWBOTHOM VAPORIZER <ul><li>Modification of Goldman vaporizer </li></ul>
  130. 131. TEC VAPORIZERS <ul><li>CLASIFICATION (TEC I-V) </li></ul><ul><li>Variable bypass </li></ul><ul><li>Flow over with wick </li></ul><ul><li>Out of system </li></ul><ul><li>Temp. compensated by automatic flow alteration </li></ul><ul><li>Conc. calibrated. </li></ul><ul><li>Agent specific </li></ul>
  131. 132. TEC 5 <ul><li>CONSTRUCTION </li></ul><ul><li>Top control dial </li></ul><ul><li>Locking lever and release button </li></ul><ul><li>Sight glass-bottom right </li></ul><ul><li>Keyed filling device </li></ul><ul><li>Filling draining port </li></ul><ul><li>Locking lever to secure filler block </li></ul><ul><li>Small lever at base allows liquid to be added or drained </li></ul><ul><li>Screw cap with drain plug </li></ul>
  132. 133. TEC 5
  133. 134. TEC 5
  134. 135. TEC 5 <ul><li>INTERNAL BAFFLE SYSTEMS </li></ul><ul><li>EVALUATION </li></ul><ul><li>Greater accuracy at FGF of 5L/min and dial <3% </li></ul><ul><li>More pumping effect than tec 4 </li></ul><ul><li>Accuracy max. 15-35 degree Celsius </li></ul>
  135. 136. TEC 5 <ul><li>INTERNAL STRUCTURE </li></ul><ul><li>Internal baffle system </li></ul><ul><li>VC lies within the bypass which lies along side of the vap. </li></ul><ul><li>Bimetallic strip in the base </li></ul><ul><li>Before reaching VC - helical IPPV assembly - spiral wick </li></ul>
  136. 137. TEC 5
  137. 138. TEC 5 <ul><li>EVALUATION </li></ul><ul><li>Accurate at FGF 5Lpm & dial settings <3% </li></ul><ul><li>Improved key filler </li></ul><ul><li>Easier mech - to switch on rotary valve & lock with one hand </li></ul><ul><li>HAZARDS </li></ul><ul><li>Pumping effect > tec 4 </li></ul><ul><li>Large liquid loss if filling part is opened </li></ul><ul><li>Overfilling – bottle adaptor loose, vaporizer ON </li></ul><ul><li>Reverse flow increases output </li></ul>
  138. 139. TEC 6 <ul><li>CLASSIFICATION </li></ul><ul><li>Conc calibrated </li></ul><ul><li>Injection </li></ul><ul><li>Thermocompensation </li></ul><ul><li>by supplied heat </li></ul><ul><li>Or </li></ul><ul><li>Electrically heated dual </li></ul><ul><li>circuit gas-vapor blender </li></ul>
  139. 140. TEC 6 <ul><li>INT. STRUCTURE </li></ul><ul><li>Electronically powered and controlled </li></ul><ul><li>Des heated to 39 0 by to heater in the base </li></ul><ul><li>VP 1300mmHg in sump </li></ul><ul><li>FGF restricted at fixed orifice, sensed by differential pressure transducer and adjusts resistor R1(differential pressure transducer) </li></ul><ul><li>Control dial adjusts 2 nd resistor R2 (adjusted by control dial) </li></ul>
  140. 141. TEC 6 <ul><li>EFFECT OF BAROMETRIC PRESSURE </li></ul><ul><li>Works at absolute pressure-It maintains a constant output in terms of vol% but pp varies if atm pr decreases-output in pp is also decreased </li></ul><ul><li>Reqd. dial setting =dial setting x 760/ambient pressure </li></ul><ul><li>Effect of carrier gas; addition of N2O – less viscosity – decrease vapor output </li></ul><ul><li>Mounting – for rt - side of machine </li></ul><ul><li>Bottle; has a spring valve to prevent escape of agent </li></ul>
  141. 142. TEC 7 <ul><li>Accurate through clinical flow range </li></ul><ul><li>Easy turning dial to allow left and right hand operation </li></ul><ul><li>Smaller graduation for accuracy </li></ul><ul><li>3 filling options </li></ul><ul><li>Datex ohmeda easy fil </li></ul><ul><li>Funnel fil </li></ul><ul><li>Easy fil (for sevolurane) </li></ul><ul><li>Non spill system </li></ul><ul><li>Prismatic sight glass </li></ul>
  142. 143. ALADIN VAPORIZER <ul><li>ALADIN CASSETTE </li></ul><ul><li>Classification </li></ul><ul><li>Conc calibrated </li></ul><ul><li>Flowover </li></ul><ul><li>Automatic thermocompensation </li></ul><ul><li>Use with datex – Engstrom AS/3 ADU </li></ul>
  146. 147. THANK YOU…