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Anesthesia Machine


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Anesthesia Machine

  3. 3. October 16, 1846  Triumph <ul><li>Morton brought “ Letheon” to the operating theater at Harvard. </li></ul><ul><li>Gilbert Abbott had a jaw tumor. </li></ul><ul><li>“ Gentlemen, this is no humbug!”  J.C. Warren </li></ul>Copyright © 2003 American Society of Anesthesiologists. All rights reserved.
  4. 4. Success of Ether <ul><li>Why was ether so successful? </li></ul><ul><ul><li>Morton’s demonstration was public and dramatic (called it Letheon and had it colored green, inhaler device). Later admitted it was simple ether. </li></ul></ul><ul><ul><li>Easy to prepare </li></ul></ul><ul><ul><li>Easy to store in bottles (unlike nitrous oxide) </li></ul></ul><ul><ul><li>Good physical properties; volatility enabled inhalation </li></ul></ul><ul><ul><li>Low concentrations meant patients didn’t become hypoxic </li></ul></ul><ul><ul><li>Very little cardiopulmonary depression </li></ul></ul><ul><ul><li>Slow induction … safety margin for new learners </li></ul></ul><ul><ul><li>Easy to administer (towel soaked in ether; later, drop inhalers) </li></ul></ul>Photo: Hugh Smith, Courtesy of Wood-Library Museum, Park Ridge, Illinois Copyright © 2003 American Society of Anesthesiologists. All rights reserved.
  5. 5. Control of the Airway <ul><li>Early anesthesia: No definitive airway control </li></ul><ul><ul><li>Mask anesthesia, inhalers, drop mask techniques were all equally capable of producing an unconscious patient but offered no airway protection or control against apnea or emesis. </li></ul></ul><ul><li>1877: Joseph Clover describes jaw-thrust technique for opening airway. Performs surgical airway with metal canula (first cricothyrotomy by anesthesia provider). </li></ul><ul><li>Frederick Hewitt developed a device for preventing the tongue from obstructing the airway in the unconscious patient. He called this device the “air-way restorer.” Device was a direct precursor to modern oral airways. </li></ul>Copyright © 2003 American Society of Anesthesiologists. All rights reserved.
  6. 6. Anesthesia Machine
  7. 7. OBJECTIVES <ul><li>Become familiar with the basic design of an anesthetic machine </li></ul><ul><li>Become familiar with the design and functioning of anesthetic vaporizers . </li></ul><ul><li>Become familiar with the design and functioning of the more commonly used breathing circuits </li></ul>
  8. 8. CONSIDERATIONS <ul><li>ANESTHETIC CONCENTRATION CONTROL </li></ul><ul><li>BUILD UP OF CARBON DIOXIDE </li></ul><ul><li>CONSUMPTION OF OXYGEN </li></ul><ul><li>ATMOSPHERIC POLLUTION </li></ul><ul><li>SIZE </li></ul><ul><li>AIRWAY CONTROL </li></ul>
  9. 9. Inhaled Anesthetic Delivery Systems <ul><li>Anesthesia machine </li></ul><ul><li>Vaporizers </li></ul><ul><li>Anesthetic breathing circuit </li></ul><ul><li>Ventilator </li></ul><ul><li>Scavenging system </li></ul>
  10. 10. Vaporizers
  11. 11. Generic Anesthetic Machine <ul><li>The pressures within the anesthesia machine can be divided into three circuits </li></ul><ul><ul><li>High - pressure </li></ul></ul><ul><ul><li>Intermediate - pressure </li></ul></ul><ul><ul><li>Low - pressure circuit </li></ul></ul>
  12. 12. Gas supply Pipeline Cylinder
  13. 13. Pipeline supply <ul><li>primary gas source for the anesthesia machine </li></ul><ul><li>oxygen, nitrous oxide, and air </li></ul><ul><li>&quot;normal working pressure&quot; 50 psi </li></ul><ul><li>DISS ( diameter index safety system ) </li></ul>
  14. 14. Gas Management Systems
  15. 15. Medical gases <ul><li>O 2 , and medical compressed air (5 bar) used for life support and respiratory therapy . </li></ul><ul><li>N 2 O is an analgesic gas used in anesthesia machine . </li></ul><ul><li>Vacuum (technically not gas), negative pressure to to do suction </li></ul><ul><li>AGSS (Anesthesia Gas Scavenging System), to take out N 2 O and filter it before being outdoors. </li></ul><ul><li>Compressed air (8 bar) or Nitrogen , to operate pneumatic surgical tools . </li></ul><ul><li>CO 2 used for insufflations . </li></ul><ul><li>Xenon new inert gas </li></ul>CO2 xeno n O 2 C ompress ed air (5 bar) N 2 O (Nitrous oxide ) Vacuum Compressed air (8 bar) or Nitrogen AGSS
  16. 16. Medical Gas pipeline system <ul><li>A pipeline system is a system that includes: </li></ul><ul><ul><li>The pipeline network , </li></ul></ul><ul><ul><li>The control unit and </li></ul></ul><ul><ul><li>The terminal units where the medical gases or anesthetic gas scavenging disposal systems may be required. </li></ul></ul>
  17. 17. Medical gas pipeline components <ul><li>Air compressor </li></ul><ul><li>Vacuum systems </li></ul><ul><li>Medical gas outlets </li></ul><ul><li>Alarms </li></ul><ul><li>Manifolds </li></ul><ul><li>Zone valves & Zone valves boxes </li></ul><ul><li>Wall and floor mounting systems </li></ul><ul><li>Rails for flexible equipment movement and utilize floor space </li></ul>
  18. 18. Medical gas pipeline diagram
  19. 19. Oxygen Supplying System <ul><li>Oxygen may be supplied as follows: </li></ul><ul><ul><li>Gas in cylinders </li></ul></ul><ul><ul><li>Cryogenic liquid in mobile vessels or stationary vessels </li></ul></ul>
  20. 20. 1. Gas in Cylinders <ul><li>A cylinder manifold system shall have two banks (groups) of cylinders or cylinder bundles </li></ul><ul><li>The banks alternately supply the pipeline, </li></ul><ul><li>Each bank having its cylinders connected to a common header with a separate manifold pressure regulator . </li></ul><ul><li>The secondary bank comes into operation automatically when content of the primary bank becomes exhausted. </li></ul>
  21. 21. 2. Cryogenic liquid Systems <ul><li>Cryogenic tanks systems hold liquefied cryogenic gases (oxygen, nitrogen, argon, hydrogen or helium) and dispense these gases in the form of a liquid or gas as required by the customer. </li></ul><ul><li>Cryogenic tanks pressure vessels manufactured with an inner and outer vessel to hold cryogenic liquefied gases that have condensation points less than -150 ºC . </li></ul>Cryogenic Tank
  22. 22. Cryogenic design <ul><li>Designed to minimize or eliminate loss by: </li></ul><ul><ul><li>Heat conduction: tanks are supported only on the top and bottom (to limit amount of contact between the inner and outer vessels) </li></ul></ul><ul><ul><li>Heat convection through fluids: use of vacuum between the inner and outer vessel of the cryogenic tank. (No fluid). </li></ul></ul><ul><ul><li>Heat radiation from heated source to other surfaces: use alternate wraps of foil and fiberglass or pearlite to prevent heat travel by radiation. </li></ul></ul>
  23. 23. <ul><li>Pressure regulators </li></ul><ul><li>Pressure relief valve </li></ul>Oxygen system components
  24. 24. 1. Pressure Regulators <ul><li>There are two types of regulators </li></ul><ul><ul><li>Operating pressure regulator: there are two operating regulators; one on every bank manifold </li></ul></ul><ul><ul><li>Line pressure regulator </li></ul></ul><ul><ul><ul><li>There are one or two line regulators on every manifold. </li></ul></ul></ul><ul><ul><ul><li>Function : to maintain a constant pressure at maximum flow rate of the system. </li></ul></ul></ul>
  25. 25. 2. Pressure Relief Valve <ul><li>Pressure relief valves are installed downstream of all pressure regulators </li></ul><ul><li>Valves set at no more than 50% above the pressure regulator setting . </li></ul><ul><li>Function : Fully relieving the pressure at the set point in case failure of regulator. </li></ul><ul><li>All pressure relief valves have piping connections to allow release of to outside facility. </li></ul>
  26. 26.
  27. 27. Pipeline
  28. 28. Cylinder supply <ul><li>reserve E cylinders </li></ul><ul><li>Color - coded </li></ul><ul><li>Pin Index Safety System ( PISS ) </li></ul><ul><li>high - pressure cylinder source </li></ul><ul><li>pressure regulator </li></ul><ul><ul><li>oxygen 2200 psig to 45 psig </li></ul></ul><ul><ul><li>nitrous oxide 745 psig to 45 psig </li></ul></ul>
  29. 29. Medical gas cylinders with plastic wrapping intact
  30. 30. Oxygen cylinder valve and pin index
  31. 31. Nitrous cylinder valve and pin index
  32. 32. Carbon dioxide cylinder valve and pin index
  33. 33. Anesthetic machine cylinder yoke
  34. 34. Color coding of medical gas cylinders and their pressure when full Body color Shoulder color Pressure,kPa (at room temp) Oxygen Black White 13 700 Nitrous oxide Blue Blue 4400 Carbon dioxide Grey Grey 5000 Air Grey White/black quarters 13 700 Entonox Blue White/blue quarters 13 700 Oxygen/helium Black White/brown quarters 13 700
  35. 35. Diagram showing the index positions of a cylinder valve. Oxygen: 2 & 5 Nitrous oxide: 3 & 5 Air: 1 & 5 CO 2 : 1 & 6
  36. 36. A cylinder yoke and pin index system. Note that a Bodok seal is in position
  37. 37. New cylinder valve which allows manual opening and closing
  38. 38. A Bodok seal
  39. 39. Inserting a remote probe into its matching wall- mounted outlet socket
  40. 40. Outlet sockets mounted in a retractable ceiling unit
  41. 41. Color-coded hoses with NIST fittings attached to an anesthetic machine
  42. 42. A oxygen cylinder manifold
  43. 43. A vacuum-insulated evaporator
  44. 44. Schematic diagram of a liquid oxygen supply system
  45. 46. Pressure Relief Valves – Heidbrink valve An anesthetic machine may contain a pressure valve operating at 35 kPa, situated on the back bar of the machine between the vaporizers and the breathing system. Modern ventilators may contain a pressure relief valve set at 7 kPa Anesthetic scavenging systems operate at pressures of 0.2 – 0.3 kPa
  46. 47. A pressure relief valve
  47. 48. <ul><li>Pressure reducing valves </li></ul><ul><li>(Pressure Regulators) </li></ul><ul><li>Pressure regulators have two important functions in anesthetic machines: </li></ul><ul><li>They reduce high pressures of compressed gases to to manageable levels (acting as pressure-reducing valves). </li></ul><ul><li>They minimize fluctuations in the pressure within an anesthetic machine, which would necessitate frequent manipulations of flowmeter controls </li></ul>
  48. 49. A simple pressure-reducing valve p a P A =
  49. 50. <ul><li>Pressure reducing valves </li></ul><ul><li>(Pressure Regulators) </li></ul><ul><li>Modern anesthetic machines operate at pressure of 3-4 bar ( usually 4 bar in the UK) 50-60 PST </li></ul><ul><li>Hospital pipeline supplies also operate at a pressure of a 4 bar and therefore pressure regulators are not required between a hospital pipeline supply and an anesthetic machine . </li></ul>
  50. 52. Needle valve
  51. 54. Mechanism of action of a flowmeter
  52. 55. As the bobbin rises from A to B, the clearance increases (from X to Y)
  53. 56. Different types of bobbins 1. ball, 2. non-rotating, 3. skirted, 4. non-shirted
  54. 57. Safety Devices for Oxygen Supply Pressure Failure <ul><li>Oxygen Supply Failure Alarm </li></ul><ul><ul><li>oxygen supply pressure decreases to 30 psig </li></ul></ul><ul><ul><li>activated within 5 seconds </li></ul></ul><ul><li>Second - Stage Pressure Regulator for Oxygen </li></ul><ul><ul><li>set at between 12 and 19 psig </li></ul></ul><ul><ul><li>supplies a constant pressure to the oxygen flow control valve </li></ul></ul>
  55. 58. Safety Devices for Oxygen Supply Pressure Failure <ul><li>Fail - Safe Valves </li></ul><ul><ul><li>Pressure sensor's shut - off valve </li></ul></ul><ul><ul><li>Oxygen failure protection device ( OFPD ) </li></ul></ul>
  56. 59. Pressure sensor's shut - off valve A, The valve is open because the oxygen supply pressure is greater than the threshold value of 20 psig. B, The valve is closed because of inadequate oxygen pressure
  57. 60. The oxygen failure protection device ( OFPD ) OFPD responds proportionally to changes in oxygen supply pressure
  58. 61. Flow Meter Assemblies
  59. 62. VAPORIZER Function: <ul><li>to provide a means for anesthetic vapor to be combined with the carrier gas in a controlled manner. </li></ul>
  61. 64. Flowmeter Patient VARIABLE BYPASS
  62. 65. Flowmeter Patient
  63. 66. Flowmeter Patient
  64. 67. <ul><li>Vaporizers </li></ul><ul><li>Vaporizers may be classified into 2 types: </li></ul><ul><li>Drawover vaporizers </li></ul><ul><ul><ul><ul><li>Subatmospheric pressure created by patient inspiration </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Least resistance to flow </li></ul></ul></ul></ul><ul><li>Plenum System </li></ul><ul><li>Gases are forced through by pressure of FGF </li></ul>
  65. 68. Principle of the draw-over vaporizer
  66. 69. Oxford miniature vaporizer (OMV)
  67. 70. The Goldman drawer vaporizer
  68. 71. The EMO (Epstein and Macintosh of Oxford) drawover ether vaporizer
  69. 72. Principle of the plenum vaporizer
  70. 73. The Boyle’s bottle
  71. 74. Halothane vaporizer at 20 0 C illustrating principle of action
  72. 75. <ul><li>Concentration Of Vapor Depends On </li></ul><ul><li>The saturated vapor pressure </li></ul><ul><li>The temperature </li></ul><ul><li>The splitting ratio </li></ul><ul><li>The surface area </li></ul><ul><li>Duration of use </li></ul><ul><li>The flow characteristics </li></ul>
  73. 76. Relationship between vapor pressure and temperature for different anesthetic agents
  74. 77. A simple type of vaporizer
  75. 78. Generic variable bypass vaporizer
  76. 79. Simplified schematic of the Ohmeda Tec 4 vaporizer
  77. 80. North American Drager Vapor 19.1 vaporizer
  78. 81. Tec Mk 5 vaporizers mounted on the back of an anesthetic machine
  79. 82. Agent-specific, color coded, keyed filling devices
  80. 83. The Tec Mk 6 vaporizer
  81. 84. Tec 6 desflurane vaporizer
  82. 85. <ul><li>Modern anesthetic vaporizers problems are overcome by: </li></ul><ul><li>Maintenance of full saturation </li></ul><ul><li>Large surface area </li></ul><ul><li>Use of wicks </li></ul><ul><li>Gas travels through a concentric helix </li></ul><ul><li>To bubble gas through liquid anesthetic </li></ul><ul><li>Copper kettle </li></ul><ul><li>A sintered disc </li></ul><ul><li>Halox vaporizer </li></ul>
  83. 86. <ul><li>Temperature Compensation </li></ul><ul><li>Increased splitting ratio </li></ul><ul><li>A bimetallic strip </li></ul><ul><li>A bellows mechanism </li></ul><ul><li>A metal rod </li></ul>
  84. 87. Techniques to achieve full saturation of the gas in the vaporizer chamber. (A) use of wicks, (B) use of small bubbles from sintered glass or metal (A) (B)
  85. 88. Partial control of the temperature in the vaporizer by the use of a metal casing and a heat reservoir
  86. 89. <ul><li>Temperature controlled valves </li></ul><ul><li>Bimetallic strip </li></ul><ul><li>bellows </li></ul><ul><li>metal rod </li></ul>(A) (C) (B)
  87. 90. The effect of a hyperbaric pressure of a 200 kPa on the performance of a halothane vaporizer
  88. 91. Negative Pressure Leak Test
  89. 92. Negative Pressure Bulb is in Drawer If not, Page your Anes Tech
  90. 93. Anesthesia Apparatus Checkout Recommendations
  91. 94. EMERGENCY VENTILATION EQUIPMENT <ul><li>1 . Verify Backup Ventilation Equipment Is Available and Functioning </li></ul>
  92. 95. HIGH - PRESSURE SYSTEM <ul><li>2 . Check Oxygen Cylinder Supply </li></ul><ul><ul><li>Open O 2 cylinder and verify that it is at least half full ( about 1000 psi ). </li></ul></ul><ul><ul><li>Close cylinder. </li></ul></ul><ul><li>3. Check Central Pipeline Supplies </li></ul><ul><ul><li>Check that hoses are connected and that pipeline gauges read about 50 psi </li></ul></ul>
  93. 96. LOW - PRESSURE SYSTEM <ul><li>4 . Check Initial Status of the Low - Pressure System </li></ul><ul><ul><li>Close flow control valves, and turn vaporizers off . </li></ul></ul><ul><ul><li>Check the fill level, and tighten the vaporizers' filler caps </li></ul></ul>
  94. 97. LOW - PRESSURE SYSTEM <ul><li>5 . Perform a Leak Check of the Machine's Low - Pressure System </li></ul><ul><ul><li>Verify that the machine master switch and flow control valves are OFF . </li></ul></ul><ul><ul><li>Attach a suction bulb to the common (fresh) gas outlet. </li></ul></ul><ul><ul><li>Squeeze the bulb repeatedly until fully collapsed . </li></ul></ul><ul><ul><li>Verify bulb stays fully collapsed for at least 10 seconds. </li></ul></ul><ul><ul><li>Open one vaporizer at a time, and repeat steps c and d above . </li></ul></ul><ul><ul><li>Remove the suction bulb, and reconnect the frésh gas hose. </li></ul></ul>
  95. 98. LOW - PRESSURE SYSTEM <ul><li>6. Turn on the Machine's Master Switch and All Other Necessary Electrical Equipment . </li></ul><ul><li>7 . Test Flow Meters </li></ul><ul><ul><li>Adjust flow of all gases through their full range, checking for smooth operation of floats and undamaged flow tubes . </li></ul></ul><ul><ul><li>Attempt to create a hypoxic O 2 /N 2 O mixture, and verify correct changes in the flow and/or alarms. </li></ul></ul>
  96. 99. SCAVENGING SYSTEM <ul><li>8 . Adjust and Check the Scavenging System </li></ul><ul><ul><li>Ensure proper connections between the scavenging system and both the adjustable pressure limiting ( APL ) ( pop - off ) valve and the ventilator's relief valve . </li></ul></ul><ul><ul><li>Adjust the waste gas vacuum (if possible). </li></ul></ul><ul><ul><li>Fully open the APL valve and occlude the Y - piece . </li></ul></ul><ul><ul><li>With minimum O 2 flow, allow the scavenger reservoir bag to collapse completely, and verify that the absorber pressure gauge reads about zero. </li></ul></ul><ul><ul><li>With the O 2 flush activated, allow the scavenger reservoir bag to distend fully, and then verify that absorber pressure gauge reads <10 cm H 2 O . </li></ul></ul>
  97. 100. BREATHING SYSTEM <ul><li>9 . Calibrate the O 2 Monitor </li></ul><ul><ul><li>Ensure the monitor reads 21% in room air . </li></ul></ul><ul><ul><li>Verify that the low O 2 alarm is enabled and functioning. </li></ul></ul><ul><ul><li>Reinstall the sensor in the circuit, and flush the breathing system with O 2 . </li></ul></ul><ul><ul><li>Verify that monitor now reads greater than 90% </li></ul></ul>
  98. 101. BREATHING SYSTEM <ul><li>10 . Check Initial Status of Breathing System </li></ul><ul><ul><li>Set the selector switch to Bag mode . </li></ul></ul><ul><ul><li>Check that the breathing circuit is complete, undamaged, and unobstructed. </li></ul></ul><ul><ul><li>Verify that the carbon dioxide absorbent is adequate . </li></ul></ul><ul><ul><li>Install the breathing circuit accessory equipment (e.g., humidifier, PEEP valve) to be used during the case. </li></ul></ul>
  99. 102. BREATHING SYSTEM <ul><li>11 . Perform a Leak Check of the Breathing System </li></ul><ul><ul><li>Set all gas flows to zero ( or minimum ). </li></ul></ul><ul><ul><li>Close the APL (pop-off) valve, and occlude the Y-piece. </li></ul></ul><ul><ul><li>Pressurize the breathing system to about 30 cm H 2 O with an O 2 flush . </li></ul></ul><ul><ul><li>Ensure that pressure remains fixed for at least 10 seconds. </li></ul></ul><ul><ul><li>Open the APL ( pop - off ) valve, and ensure that the pressure decreases . </li></ul></ul>
  100. 103. MANUAL AND AUTOMATIC VENTILATION SYSTEMS <ul><li>12 . Test the Ventilation Systems and Unidirectional Valves </li></ul><ul><ul><li>Place a second breathing bag on the Y - piece . </li></ul></ul><ul><ul><li>Set appropriate ventilator parameters for the next patient. </li></ul></ul><ul><ul><li>Switch to automatic ventilation mode ( i . e . , Ventilator ). </li></ul></ul><ul><ul><li>Turn the ventilator ON, and fill the bellows and breathing bag with an O 2 flush. </li></ul></ul><ul><ul><li>Set the O 2 flow to minimum and other gas flows to zero . </li></ul></ul><ul><ul><li>Verify that the bellows deliver an appropriate tidal volume during inspiration and that the bellows fill completely during expiration. </li></ul></ul>
  101. 104. MANUAL AND AUTOMATIC VENTILATION SYSTEMS <ul><li>12 . Test the Ventilation Systems and Unidirectional Valves </li></ul><ul><ul><li>Set the fresh gas flow to about 5 L / min . </li></ul></ul><ul><ul><li>Verify that the ventilator's bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration. </li></ul></ul><ul><ul><li>Check for proper action of unidirectional valves . </li></ul></ul><ul><ul><li>Exercise breathing circuit accessories to ensure proper function. </li></ul></ul><ul><ul><li>Turn the ventilator off, and switch to manual ventilation mode ( i . e . , Bag / APL ). </li></ul></ul><ul><ul><li>Ventilate manually, and ensure inflation and deflation of artificial lungs and appropriate feel of system resistance and compliance. </li></ul></ul><ul><ul><li>Remove second breathing bag from the Y - piece . </li></ul></ul>
  102. 105. MONITORS <ul><li>13 . Check, Calibrate, and / or Set Alarm Limits of all Monitors </li></ul><ul><ul><li>Capnometer </li></ul></ul><ul><ul><li>Oxygen analyzer </li></ul></ul><ul><ul><li>Pressure monitor with alarms for high and low airway pressure </li></ul></ul><ul><ul><li>Pulse oximeter </li></ul></ul><ul><ul><li>Respiratory volume monitor ( i . e . , spirometer ) </li></ul></ul>
  103. 106. Physical Principles of Conventional Flow Meters The clearance between the head of the float and the flow tube is known as the annular space . It can be considered an equivalent to a circular channel of the same cross - sectional area .
  104. 107. Physical Principles of Conventional Flow Meters viscosity (laminar flow) density ( turbulent flow )
  105. 108. Flow Meter Assemblies <ul><li>Flow Control Valve </li></ul><ul><li>Flow Meter Subassembly </li></ul><ul><ul><li>FLOW TUBES </li></ul></ul><ul><ul><ul><li>fine flow tube - 200 mL/min to 1 L/min </li></ul></ul></ul><ul><ul><ul><li>coarse flow tube – 1 L/min to between 10 and 12 L/min </li></ul></ul></ul><ul><ul><li>INDICATOR FLOATS AND FLOAT STOPS </li></ul></ul>
  106. 109. The flow meter sequence is a potential cause of hypoxia A and B, In the event of a flow meter leak, a potentially dangerous arrangement exists when nitrous oxide is located in the downstream position . C and D, The safest configuration exists when oxygen is located in the downstream position
  107. 110. An oxygen leak from the flow tube can produce a hypoxic mixture, regardless of the arrangement of the flow tubes
  108. 111. Proportioning Systems <ul><li>Prevent delivery of a hypoxic mixture </li></ul><ul><li>N 2 O and O 2 are interfaced mechanically or pneumatically </li></ul><ul><li>Minimum O 2 concentration at the common gas outlet is between 23% and 25% </li></ul>
  109. 112. N 2 O and O 2 flow control valves are identical. A 14-tooth sprocket is attached to the N 2 O flow control valve, and a 28-tooth sprocket is attached to the O 2 flow control valve. A chain links the sprockets. The combination of the mechanical and pneumatic aspects of the system yields the final oxygen concentration. The Datex-Ohmeda Link-25 proportioning system can be thought of as a system that increases oxygen flow when necessary to prevent delivery of a fresh gas mixture with an oxygen concentration of less than 25%
  110. 113. Oxygen Flush Valve
  111. 114. CARRIER GASES <ul><li>Oxygen </li></ul><ul><li>Nitrous Oxide </li></ul><ul><li>supplied in cylinders as a gas (oxygen) or liquid (nitrous oxide) under pressure </li></ul>
  112. 115. CYLINDER IDENTIFICATION <ul><li>Color </li></ul><ul><ul><li>Oxygen = Green (US) or White (everywhere else) </li></ul></ul><ul><ul><li>Nitrous oxide = Blue </li></ul></ul>
  113. 116. CYLINDER IDENTIFICATION <ul><li>Labels </li></ul>
  114. 117. CYLINDER IDENTIFCATION <ul><li>PIN Index Safety System </li></ul>
  115. 119. CYLINDER SIZES <ul><li>E Tanks </li></ul>
  116. 120. <ul><li>H tanks </li></ul><ul><li>Bulk Tanks </li></ul>
  117. 121. PIPELINES
  119. 125. PRESSURE GAUGE
  120. 126. CALCULATING VOLUMES* <ul><li>H tanks = 7000 litres at 2000 psi </li></ul><ul><li>E tanks = 700 litres at 2000 psi </li></ul><ul><li>QUESTION? </li></ul><ul><ul><li>HOW MANY LITRES IN AN E TANK READING 750 PSI? </li></ul></ul>
  122. 128. Oxygen Flush Valve <ul><li>Direct communication between the oxygen high - pressure circuit and the low - pressure circuit </li></ul><ul><li>Delivers 100% oxygen at a rate of 35 to 75 L / min to the breathing circuit </li></ul><ul><li>High pressure of 50 psig </li></ul>
  123. 129. Oxygen Flush Valve <ul><li>Several hazards </li></ul><ul><ul><li>Barotrauma </li></ul></ul><ul><ul><li>Awareness </li></ul></ul><ul><ul><ul><li>dilutes the inhaled anesthetic </li></ul></ul></ul>
  124. 130. VAPORIZERS <ul><li>Vapor Pressure </li></ul><ul><li>Latent Heat of Vaporization </li></ul><ul><ul><li>calories required to change 1 g of liquid into vapor without a temperature change </li></ul></ul><ul><li>Specific Heat </li></ul><ul><ul><li>calories required to increase the temperature of 1 g of a substance by 1°C. </li></ul></ul><ul><li>Thermal Conductivity </li></ul>
  125. 131. Vapor pressure versus temperature curves for desflurane, isoflurane, halothane, enflurane, and sevoflurane The vapor pressure curve for desflurane is steeper and shifted to higher vapor pressures compared with the curves for other contemporary inhaled anesthetics.
  126. 132. Variable - bypass vaporizer
  127. 133. Ohmeda Tec-type vaporizer. At high temperatures , the vapor pressure inside the vaporizing chamber is high. To compensate for the increased vapor pressure, the bimetallic strip of the temperature-compensating valve leans to the right, allowing more flow through the bypass chamber and less flow through the vaporizing chamber. The net effect is a constant vaporizer output. In a cold operating room environment , the vapor pressure inside the vaporizing chamber decreases. To compensate for the decreased vapor pressure, the bimetallic strip swings to the left, causing more flow through the vaporizing chamber and less through the bypass chamber. The net effect is a constant vaporizer output
  128. 134. North American Dräger Vapor 19.1 vaporizer. Automatic temperature-compensating mechanisms in bypass chambers maintain a constant vaporizer output with varying temperatures. An expansion element directs a greater proportion of gas flow through the bypass chamber as temperature increases.
  129. 135. Tec 6 desflurane vaporizer. The vaporizer has two independent gas circuits arranged in parallel. The fresh gas circuit is shown in red, and the vapor circuit is shown in white. The fresh gas from the flow meters enters at the fresh gas inlet, passes through a fixed restrictor (R1), and exits at the vaporizer gas outlet. The vapor circuit originates at the desflurane sump, which is electrically heated and thermostatically controlled to 39°C, a temperature well above desflurane's boiling point. The heated sump assembly serves as a reservoir of desflurane vapor. Downstream from the sump is the shut-off valve. After the vaporizer warms up, the shut-off valve fully opens when the concentration control valve is turned to the on position. A pressure-regulating valve located downstream from the shut-off valve downregulates the pressure. The operator controls desflurane output by adjusting the concentration control valve (R2), which is a variable restrictor
  130. 136. MEASURED FLOW
  133. 139. PRECISION VAPORIZER <ul><li>FLOW COMPENSATED </li></ul><ul><li>TEMPERATURE COMPENSATED </li></ul><ul><li>HIGH RESISTANCE </li></ul><ul><li>KNOWN CONCENTRATION </li></ul><ul><li>AGENT SPECIFIC </li></ul>
  136. 143. FLOWMETERS
  137. 145. FRESH GAS PORT
  141. 152. CONSIDERATIONS <ul><li>ANESTHETIC CONCENTRATION CONTROL </li></ul><ul><li>CONSUMPTION OF OXYGEN </li></ul><ul><li>BUILD UP OF CARBON DIOXIDE </li></ul><ul><li>ATMOSPHERIC POLLUTION </li></ul><ul><li>SIZE </li></ul><ul><li>AIRWAY CONTROL </li></ul>
  142. 153. Condensed water vapor Makes Ventilators fail Makes Gas Monitors fail Use a H eat and M oisture E xchanger
  143. 154. Wet dome valve - Ohmeda Mod 2
  144. 155. Wet dome valve - Aestiva
  145. 156. Fabius flow sensor gets wet, too
  146. 157. Wet ET tube, dry circuit
  147. 158. Datex-Ohmeda Edith ® is BWH present HME product
  148. 159. Gas Line Filters sometimes crack Save them if they do crack Page Anes Technician who will bring it to ORCSS Materials Management” to return to Manufacturer For analysis
  149. 160. Inhaled Anesthetic Delivery Systems
  150. 161. ANESTHETIC CIRCUITS <ul><li>Deliver oxygen and anesthetic gases to the patient </li></ul><ul><li>Eliminate carbon dioxide </li></ul><ul><ul><li>adequate inflow of fresh gas </li></ul></ul><ul><ul><li>carbon dioxide absorbent </li></ul></ul><ul><li>Semiclosed rebreathing circuits and the circle system. </li></ul>
  151. 162. Mapleson Systems
  152. 163. Mapleson Systems <ul><li>Factors influence carbon dioxide rebreathing </li></ul><ul><ul><li>the fresh gas inflow rate </li></ul></ul><ul><ul><li>the minute ventilation </li></ul></ul><ul><ul><li>the mode of ventilation (spontaneous or controlled), </li></ul></ul><ul><ul><li>the tidal volume </li></ul></ul><ul><ul><li>the respiratory rate </li></ul></ul><ul><ul><li>the inspiratory to expiratory ratio </li></ul></ul><ul><ul><li>the duration of the expiratory pause </li></ul></ul><ul><ul><li>the peak inspiratory flow rate </li></ul></ul><ul><ul><li>the volume of the reservoir tube </li></ul></ul><ul><ul><li>the volume of the breathing bag </li></ul></ul><ul><ul><li>ventilation by mask </li></ul></ul><ul><ul><li>ventilation through an endotracheal tube </li></ul></ul><ul><ul><li>the carbon dioxide sampling site. </li></ul></ul>
  153. 164. Mapleson Systems <ul><li>Prevention of rebreathing, during spontaneous ventilation: A > DFE > CB. </li></ul><ul><li>During controlled ventilation, DFE > BC > A </li></ul><ul><li>A, B, and C systems are rarely used today </li></ul>
  154. 165. The Bain circuit <ul><li>a modification of the Mapleson D system </li></ul><ul><li>spontaneous and controlled ventilation. </li></ul>
  155. 166. The Bain circuit <ul><li>Exhaled gases in the outer reservoir tubing add warmth to inspired fresh gases </li></ul><ul><li>unrecognized disconnection or kinking of the inner fresh gas hose </li></ul><ul><li>The fresh gas inflow rate necessary to prevent rebreathing is 2.5 times the minute ventilation </li></ul>
  156. 167. Components of the C ircle system APL, adjustable pressure limiting; B, reservoir bag; V, ventilator
  157. 168. Circle Breathing System <ul><li>A circle system can be semiopen, semiclosed, or closed, depending on the amount of fresh gas inflow </li></ul><ul><ul><li>Semiopen system has no rebreathing and requires a very high flow of fresh gas </li></ul></ul><ul><ul><li>Semiclosed system is associated with rebreathing of gases </li></ul></ul><ul><ul><li>Closed system is one in which the inflow gas exactly matches that being consumed by the patient </li></ul></ul>
  158. 169. Circle Breathing System <ul><li>Components of The circle system </li></ul><ul><li>(1) a fresh gas inflow source </li></ul><ul><li>(2) inspiratory and expiratory unidirectional valves </li></ul><ul><li>(3) inspiratory and expiratory corrugated tubes (4) a Y-piece connector </li></ul><ul><li>(5) an overflow or pop-off valve, referred to as the APL valve </li></ul><ul><li>(6) a reservoir bag </li></ul><ul><li>(7) a canister containing a carbon dioxide absorbent </li></ul>
  159. 170. Circle Breathing System <ul><li>Rules to prevent rebreathing of carbon dioxide in a traditional circle system </li></ul><ul><ul><li>Unidirectional valves must be located between the patient and the reservoir bag on the inspiratory and expiratory limbs of the circuit. </li></ul></ul><ul><ul><li>The fresh gas inflow cannot enter the circuit between the expiratory valve and the patient. </li></ul></ul><ul><ul><li>The overflow (pop-off) valve cannot be located between the patient and the inspiratory valve. </li></ul></ul>
  160. 171. Circle Breathing System <ul><li>Advantages </li></ul><ul><ul><li>stability of inspired gas concentrations, </li></ul></ul><ul><ul><li>conservation of respiratory moisture and heat, </li></ul></ul><ul><ul><li>prevention of operating room pollution </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>complex design </li></ul></ul>
  161. 172. ABSORPTION <ul><li>Lack of toxicity with common anesthetics, low resistance to airflow, low cost, ease of handling, and efficiency </li></ul><ul><li>3 formulations </li></ul><ul><ul><li>soda lime </li></ul></ul><ul><ul><li>Baralyme </li></ul></ul><ul><ul><li>calcium hydroxide lime (Amsorb) </li></ul></ul>
  162. 173. ABSORPTION <ul><li>Soda lime (most commonly used ) </li></ul><ul><ul><li>80% calcium hydroxide, 15% water, 4% sodium hydroxide, and 1% potassium hydroxide (an activator) </li></ul></ul><ul><ul><li>silica </li></ul></ul><ul><li>The equations </li></ul><ul><ul><li>1) CO2 + H2 O ⇔ H2 CO3 </li></ul></ul><ul><ul><li>2) H2 CO3 + 2NaOH (KOH) ⇔ Na2 CO3 (K2 CO3 ) + 2H2 O + Heat </li></ul></ul><ul><ul><li>3) Na2 CO3 (K2 CO3 ) + Ca(OH)2 ⇔ CaCO3 + 2NaOH (KOH) </li></ul></ul>
  163. 174. ABSORPTION <ul><li>Baralyme </li></ul><ul><ul><li>20% barium hydroxide and 80% calcium hydroxide </li></ul></ul><ul><li>Calcium hydroxide lime </li></ul><ul><ul><li>lack of sodium and potassium hydroxides </li></ul></ul><ul><ul><li>carbon monoxide and the nephrotoxic substance known as compound A </li></ul></ul>
  164. 175. ABSORPTION <ul><li>Absorptive Capacity </li></ul><ul><ul><li>soda lime is 26 L of carbon dioxide per 100 g of absorbent </li></ul></ul><ul><ul><li>calcium hydroxide lime has been reported at 10.2 L per 100 g of absorbent </li></ul></ul><ul><li>size of the absorptive granules </li></ul><ul><ul><li>surface area </li></ul></ul><ul><ul><li>air flow resistance </li></ul></ul>
  165. 176. ABSORPTION <ul><li>Indicators </li></ul><ul><ul><li>Ethyl violet :pH indicator added to soda lime and Baralyme </li></ul></ul><ul><ul><li>from colorless to violet when the pH of the absorbent decreases as a result of carbon dioxide absorption </li></ul></ul><ul><ul><li>Fluorescent lights can deactivate the dye </li></ul></ul>
  166. 177. ABSORPTION <ul><li>Sevoflurane interaction with carbon dioxide absorbents </li></ul><ul><ul><li>Compound A </li></ul></ul><ul><ul><ul><li>fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether </li></ul></ul></ul><ul><li>Factors </li></ul><ul><ul><li>low-flow or closed-circuit </li></ul></ul><ul><ul><li>concentrations of sevoflurane </li></ul></ul><ul><ul><li>higher absorbent temperatures </li></ul></ul><ul><ul><li>fresh absorbent </li></ul></ul><ul><ul><li>Baralyme dehydration increases the concentration of compound A, and soda lime dehydration decreases the concentration of compound A </li></ul></ul>
  167. 178. ABSORPTION <ul><li>Desiccated soda lime and Baralyme </li></ul><ul><ul><li>carbon monoxide </li></ul></ul><ul><ul><li>after disuse of an absorber for at least 2 days, especially over a weekend </li></ul></ul>
  168. 179. ABSORPTION <ul><li>Several factors appear to increase the production of CO and carboxyhemoglobin: </li></ul><ul><ul><li>Anesthetic agents (desflurane ≥ enflurane > isoflurane ≥ halothane = sevoflurane) </li></ul></ul><ul><ul><li>The absorbent dryness (completely dry absorbent produces more carbon monoxide than hydrated absorbent) </li></ul></ul><ul><ul><li>The type of absorbent (at a given water content, Baralyme produces more carbon monoxide than does soda lime) </li></ul></ul>
  169. 180. ABSORPTION <ul><li>Several factors appear to increase the production of CO and carboxyhemoglobin: </li></ul><ul><ul><li>The temperature (a higher temperature increases carbon monoxide production) </li></ul></ul><ul><ul><li>The anesthetic concentration (more carbon monoxide is produced from higher anesthetic concentrations) </li></ul></ul><ul><ul><li>Low fresh gas flow rates </li></ul></ul><ul><ul><li>Reduced animal size per 100 g of absorbent </li></ul></ul>
  170. 181. ABSORPTION <ul><li>Interventions have been suggested to reduce the incidence of carbon monoxide exposure </li></ul><ul><ul><li>Educating anesthesia personnel regarding the cause of carbon monoxide production </li></ul></ul><ul><ul><li>Turning off the anesthesia machine at the conclusion of the last case of the day to eliminate fresh gas flow, which dries the absorbent </li></ul></ul><ul><ul><li>Changing carbon dioxide absorbent if fresh gas was found flowing during the morning machine check </li></ul></ul>
  171. 182. ABSORPTION <ul><li>Interventions have been suggested to reduce the incidence of carbon monoxide exposure </li></ul><ul><ul><li>Rehydrating desiccated absorbent by adding water to the absorbent </li></ul></ul><ul><ul><li>Changing the chemical composition of soda lime (e.g., Dragersorb 800 plus, Sofnolime, Spherasorb) to reduce or eliminate potassium hydroxide </li></ul></ul><ul><ul><li>Using absorbent materials such as calcium hydroxide lime that are free of sodium and potassium hydroxides </li></ul></ul>
  172. 183. Inspiratory (A) and expiratory (B) phases of gas flow in a traditional circle system with an ascending bellows anesthesia ventilator. The bellows physically separates the driving-gas circuit from the patient's gas circuit. The driving-gas circuit is located outside the bellows, and the patient's gas circuit is inside the bellows. During the inspiratory phase (A), the driving gas enters the bellows chamber, causing the pressure within it to increase. This causes the ventilator's relief valve to close, preventing anesthetic gas from escaping into the scavenging system, and the bellows to compress, delivering the anesthetic gas within the bellows to the patient's lungs. During the expiratory phase (B), the driving gas exits the bellows chamber. The pressure within the bellows chamber and the pilot line declines to zero, causing the mushroom portion of the ventilator's relief valve to open. Gas exhaled by the patient fills the bellows before any scavenging occurs because a weighted ball is incorporated into the base of the ventilator's relief valve. Scavenging happens only during the expiratory phase, because the ventilator's relief valve is open only during expiration
  173. 184. Inspiratory (A) and expiratory (B) phases of gas flow in a Dräger-type circle system with a piston ventilator and fresh gas decoupling. NPR valve, negative-pressure relief valve.
  174. 185. SCAVENGING SYSTEMS <ul><li>The collection and the subsequent removal of vented gases from the operating room </li></ul><ul><li>Components </li></ul><ul><ul><li>(1) the gas-collecting assembly </li></ul></ul><ul><ul><li>(2) the transfer means </li></ul></ul><ul><ul><li>(3) the scavenging interface </li></ul></ul><ul><ul><li>(4) the gas-disposal assembly tubing </li></ul></ul><ul><ul><li>(5) an active or passive gas-disposal assembly </li></ul></ul>
  175. 186. Components of a scavenging system . APL valve, adjustable pressure limiting valve
  176. 187. Each of the two open scavenging interfaces requires an active disposal system. An open canister provides reservoir capacity. Gas enters the system at the top of the canister and travels through a narrow inner tube to the canister base. Gases are stored in the reservoir between breaths. Relief of positive and negative pressure is provided by holes in the top of the canister. A and B, The open interface shown in A differs somewhat from the one shown in B. The operator can regulate the vacuum by adjusting the vacuum control valve shown in B. APL, adjustable pressure limiting valve
  177. 188. Closed scavenging interfaces. Interface used with a passive disposal system (left). Interface used with an active system (right)
  178. 189. Avogadro’s Hypothesis Avogadro’s hypothesis states that the equal volumes of gases at the same temperature and pressure contain equal numbers of molecules
  179. 190. Avogadro’s number is the number of molecules in 1 g molecular weight of a substance and is equal to 6.022 x10 23
  180. 191. Under conditions of standard temperature and pressure, 1 g molecular weight of any gas occupies a volume of 22.4 litres (L)
  181. 192. N 2 O mol. Wt. 44 i.e 44 gm of N 2 O occupy 22.4 lit. gas at STP If full cylinders wt. Of N 2 O is 3 kg then it will yield 3 x 1000 x 22.4 44 = 1524 Lit of N 2 O at STP When the last drop of liquid N 2 0 is vaporized- 400L of gas still in cylinder L
  182. 193. Critical Temperature The critical temperature of a substance is the temperature above which that substance cannot be liquefied by pressure, irrespective of its magnitude .
  183. 194. <ul><li>Critical temperature of </li></ul><ul><li>Oxygen –118 0 C </li></ul><ul><li>Nitrogen –147 o C </li></ul><ul><li>Air –141 o C </li></ul><ul><li>Carbon dioxide 31 o C </li></ul><ul><li>Nitrous oxide 36.4 o C </li></ul><ul><li>Entonox - 5 to -8 (psuedocrit-temp) </li></ul>
  184. 195. The term adiabatic implies a change in the state of a gas without exchange of heat energy with its surroundings
  185. 196. Filling Ratio The degree of filling of a nitrous oxide cylinder is expressed as the mass of nitrous oxide in a cylinder divided by the mass of water that the cylinder could hold.Normally, a cylinder of nitrous oxide is filled to a ratio of 0.67. This should not be confused with the volume of liquid nitrous oxide in a cylinder .
  186. 197. A full cylinder of nitrous oxide at room temperature is filled to the point at which approximately 90% of the interior of the cylinder is occupied by liquid, the remaining 10% being occupied by gaseous nitrous oxide .
  187. 198. <ul><li>Entonox </li></ul><ul><li>Mixture of 50% oxygen and 50% nitrous oxide </li></ul><ul><li>Compressed into into cylinders containing gas at a pressure of 137 bar (2000 lb in -2 ) </li></ul><ul><li>The critical temperature of the mixture is -5 o C </li></ul>
  188. 199. The Entonox two-stage pressure demand regulator
  189. 200. Viscosity is defined as that property of a fluid that causes it to resist flow. The coefficient of viscosity (  ) is defined as : (  ) =force x velocity gradient area Flow Of Fluids
  190. 201. <ul><li>(  ) =force/area x velocity gradient </li></ul><ul><li>Fluids that obey this formula are referred to as Newtonian fluids </li></ul><ul><li>Some biological fluids are non – Newtonian </li></ul><ul><li>A prime example is blood . </li></ul><ul><li>Viscosity changes with the rate of flow of blood ,in stored blood, with time (blood thickens on storage) </li></ul><ul><li>Viscosity of liquids diminishes with increase in temperature </li></ul><ul><li>Viscosity of a gas increases with increase in temperature </li></ul>
  191. 202. Laminar Flow Laminar flow through a tube is smooth flow The linear velocity of axial flow may be twice the average linear velocity of flow In a tube, the factors determining flow are given by the Hagen – Poiseuille formula: Q =  Pr 4 8  l The Hagen – Poiseuille formula applies only to Newtonian fluids R = 8  l  r 4
  192. 203. In turbulent flow fluid no longer moves in orderly planes but swirls and eddies around in a haphazardly manner. Turbulent flow is affected by changes in density Turbulent Flow
  193. 204. The relationship between pressure and flow in a fluid is linear up to the critical point, above which flow becomes turbulent
  194. 205. The critical point or critical velocity at which the characteristics of flow change from laminar to turbulent Reynolds’ number =  r /   - linear velocity r - radius of the tube   - density and  - viscosity If Reynolds’ number exceeds 2000 , flow is likely to be turbulent, whereas a Reynolds’ number of less than 2000 is usually associated with laminar flow
  195. 206. <ul><li>Flow Of Fluids Through Orifices </li></ul><ul><li>In an orifice the diameter of fluid pathway exceeds the length. Flow rate of a fluid through an orifice is dependant upon: </li></ul><ul><li>The square root of the pressure difference across the orifice </li></ul><ul><li>The square root of the diameter of the orifice </li></ul><ul><li>The density of the fluid, as flow through an orifice inevitably involves some degree of turbulence </li></ul>
  196. 207. Resistance to gas flow through tracheal tubes of different internal diameter (ID)
  197. 208. <ul><li>Applications In Anesthetic Practice (turbulent) </li></ul><ul><li>In upper respiratory tract obstruction </li></ul><ul><li>Trachea </li></ul><ul><li>Aorta </li></ul><ul><li>Obstructive </li></ul><ul><li>Bends </li></ul><ul><li>F.B </li></ul><ul><li>DENSITY effect </li></ul><ul><li>The density of oxygen is 1.3 and that of helium is 0.16 (HELOX) </li></ul>
  198. 209. <ul><li>A sudden change in diameter , irregularity of the wall may be responsible for a change from laminar to turbulent flow. </li></ul><ul><li>Thus a tracheal and other breathing tubes must possess: </li></ul><ul><li>Smooth internal surfaces </li></ul><ul><li>Gradual bends </li></ul><ul><li>No constrictions </li></ul><ul><li>Large diameter </li></ul><ul><li>Short length </li></ul><ul><li>Resistance to breathing is much greater when a tracheal tube of small diameter is used </li></ul>Anesthetic breathing systems
  199. 210. The Injector The injector is frequently termed as Venturi , formulated by Bernoulli in 1778 some 60 years earlier than Venturi As fluid passes through a constriction, there is an increase in velocity of the fluid; beyond the constriction velocity decreases to the initial value.
  200. 211. The Bernoulli Principle
  201. 212. Fluid entrainment by a Venturi injector
  202. 213. A simple injector
  203. 214. Fixed performance mask with a range of Venturi devices
  204. 215. Color Delivered FiO 2 Fresh gas flow(l/min) Blue 24% 2 White 28% 4 Orange 31% 6 Yellow 35% 8 Red 40% 10 Green 60% 15 Entrainment ratio 100ax21b=30x required FiO 2 a+b=30
  205. 216. <ul><li>The Coanda Effect </li></ul><ul><li>Coanda Effect - gas flow through a tube, with two Venturis tends to cling either to one side of the tube or to the other </li></ul><ul><li>The principle has been used in anesthetic ventilators (termed fluidic ventilators) </li></ul><ul><li>The application of a small pressure distal to the restriction may enable gas flow to be switched from one side to another </li></ul>
  206. 217. The Coanda effect