4. Anesthetic Equipment

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  • Placement of an endotracheal tube bypasses the oral and nasal cavities, pharynx, and larynx.
  • Figures A, C, and D are Murphy tubes; Figure B is a Cole tube.
  • Figure 4-2 shows the variety of materials. Figure 4-3 F shows scale. Table 8-2 lists common sizes used in common species.
  • Endotracheal tube parts. A, Valve with syringe attached. B, Pilot balloon. C, Machine end. D, Connector. E, Tie. F, Measurement of length from the patient end (cm). G, Measurement of internal diameter (mm). H, Inflated cuff. I, Patient end. J, Murphy eye.
  • The size 5 blade for a small animal is large; the size 0 blade is small.
  • Laryngoscope handles and blades. A, Size 4 Miller blade. B, Size 4 McIntosh blade. C, Size 2 Miller blade. D, Size 1 McIntosh blade. E, Laryngoscope handle with size 00 Miller blade in unlocked position. F, Laryngoscope handle with size 3 McIntosh blade in locked position (note that the light turns on when the blade is locked).
  • Masks can be used on a fully conscious patient, a sedated patient, or an anesthetized patient that cannot be intubated. Without an endotracheal tube, brachycephalic breeds are prone to tracheal obstruction during anesthesia. Procedure 8-4 describes mask induction.
  • Chamber induction is described in Procedure 8-5.
  • Anesthetic machines come in a wide variety of brands, ages, sizes, and sophistication. New machines can cost as little as $2000 to as much as more than $100,000. Underlying similar machine design and principles of operation, is an inherent complexity that must be understood.
  • Anesthetic machines can also be used to deliver pure oxygen to a critically ill patient. The vaporizer is turned off for this procedure.
  • The most common configuration of an anesthetic machine is one with a precision vaporizer and a rebreathing circuit. Patients under 2.5-3.0 kg use a machine with a precision vaporizer and a nonrebreathing circuit.
  • In some instances H tanks are used as the primary supply and E tanks are used as a secondary supply. In other cases, E tanks are used for both primary and secondary supply. H tanks are usually stored remotely with tubes connecting them to oxygen supply outlets throughout the hospital/clinic.
  • Threaded connector, pressure-reducing valve, tank pressure gauge, line pressure gauge, and knurled knob are labeled on this figure.
  • This figure shows the different yoke attachment holes on the two tanks that will prevent the wrong type of gas cylinder from accidentally being attached to a specific yoke.
  • See Figure 4-17.
  • Not all machines will have a line pressure gauge. See Figure 4-17.
  • Some machines will have two flowmeters for oxygen. One provides a coarse adjustment (>1 L/min) and the other provides a fine adjustment (<1 L/min). At this point there is still no anesthetic agent in the oxygen.
  • If the meter reads zero the patient is not receiving any oxygen.
  • No anesthetic agent can leave the vaporizer unless it is mixed with the carrier gas. If the flowmeter is not turned on, no oxygen will flow and no anesthetic will be delivered to the patient.
  • Where the vaporizer is placed is determined by the resistance of gas flow through the vaporizer. Gas flow around the breathing circuit is driven by the normal breathing force of the patient.
  • Most modern precision vaporizers are temperature, flow, and pressure compensated.
  • Start with the lower end of the range if the patient has been premedicated.
  • The breathing circuit may be part of the anesthetic machine (rebreathing system) or it may be a separate unit (non-rebreathing system).
  • The breathing circuit may be part of the anesthetic machine (rebreathing system) or it may be a separate unit (non-rebreathing system).
  • The valves may also be used to check for proper placement of the ET tube. The valves will not open and close despite normal breathing patterns in the patient.
  • The valve is controlled to be used from fully open to fully closed, or any amount in between.
  • The ideal rebreathing bag will hold at least 60 mL/kg patient body weight.
  • The water produced humidifies the air returned to the patient. Using depleted granules will result in carbon dioxide being returned to the patient. Depleted granules are hard, brittle, and change color from white to off-white or violet. Replace granules after 6-8 hours of use or when ½ to 1/3 of the granules have changed color. To prevent adverse reactions, use granules compatible with the anesthetic agent being used.
  • Excessive pressure may cause dyspnea, lung damage, or pneumothorax.
  • Negative pressure can develop when the machine is incorrectly assembled, when a scavenging system is exerting excessive suction, when the oxygen flow rate is too low, or when the tank runs out of oxygen.
  • Figure 4-40 shows these configurations. Class A, modified A, modified D, E, and F are the most commonly used in veterinary medicine.
  • Rebreathing system recommended for patients weighing >7 kg unless it is fitted with pediatric hoses, lightweight and nonstick unidirectional valves. Non-rebreathing system recommended for patients weighing <2.5-3 kg. Closed systems are the most economical because of very low gas flow rates; non-rebreathing systems are the least economical. Anesthetic depth changes more quickly in a non-rebreathing system. Rebreathing systems allow the patient to breath warm, moist air. Closed rebreathing systems release the least amount of waste anesthetic gas.
  • Box 4-4 provides recommended flow rates. Box 4-5 gives examples of flow rate calculations. Tables 4-3 and 4-4 are quick look-up charts for rebreathing and non-rebreathing systems.
  • Bag, breathing tubes, and Y-piece: wash with mild, soapy disinfectant (chlorhexadine gluconate) and rinse thoroughly.
  • 4. Anesthetic Equipment

    1. 1. Anesthetic Equipment The purpose, function, use, and maintenance of machines and equipment used to administer inhalation anesthetics Chapter 4
    2. 2. Endotracheal Tubes (ET Tubes) <ul><li>Flexible tube placed in the trachea </li></ul><ul><li>Delivers anesthetic gases directly from the anesthetic machine to the lungs </li></ul><ul><li>Advantages </li></ul><ul><ul><li>Open airway </li></ul></ul><ul><ul><li>Less anatomical dead space </li></ul></ul><ul><ul><li>Precision administration of anesthetic agent </li></ul></ul><ul><ul><li>Prevents pulmonary aspiration </li></ul></ul><ul><ul><li>Responds to respiratory emergencies </li></ul></ul><ul><ul><li>Monitors respirations </li></ul></ul>
    3. 3. Types of Endotracheal Tubes <ul><li>Murphy tubes </li></ul><ul><ul><li>Beveled end and side holes </li></ul></ul><ul><ul><li>Possible cuff </li></ul></ul><ul><li>Cole tubes </li></ul><ul><ul><li>No side hole or cuff </li></ul></ul><ul><ul><li>Abrupt decrease in diameter of the tube </li></ul></ul><ul><ul><li>Used in birds and reptiles </li></ul></ul>
    4. 4. Types of Endotracheal Tubes (Cont’d)
    5. 5. Properties of Endotracheal Tubes <ul><li>Materials </li></ul><ul><ul><li>Polyvinyl chloride: clear and stiffer </li></ul></ul><ul><ul><li>Red rubber: flexible and less traumatic, absorbent, and may kink or collapse </li></ul></ul><ul><ul><li>Silicone: pliable, strong, less irritating, resist collapse </li></ul></ul><ul><li>Length </li></ul><ul><ul><li>Standard lengths </li></ul></ul><ul><ul><li>Scale marks distance from patient end (centimeters) </li></ul></ul><ul><li>Size </li></ul><ul><ul><li>Measured by internal diameter (ID) </li></ul></ul><ul><ul><li>Range from 1 mm to 30 mm </li></ul></ul>
    6. 6. Parts of the Endotracheal Tube <ul><li>Patient end </li></ul><ul><li>Machine end </li></ul><ul><li>Connector </li></ul><ul><li>Cuff </li></ul><ul><li>Pilot balloon and valve </li></ul>
    7. 7. Parts of the Endotracheal Tube (Cont’d)
    8. 8. Laryngoscope <ul><li>Used to increase the visibility of the larynx while placing an ET tube </li></ul><ul><li>Parts </li></ul><ul><ul><li>Handle containing batteries </li></ul></ul><ul><ul><li>Blade to depress tongue and epiglottis </li></ul></ul><ul><ul><li>Light source to illuminate the throat </li></ul></ul><ul><li>Sizes </li></ul><ul><ul><li>Small animal 0 to 5; large animal up to 18-inch blade </li></ul></ul><ul><li>Types </li></ul><ul><ul><li>Miller blades </li></ul></ul><ul><ul><li>McIntosh blades </li></ul></ul>
    9. 9. Laryngoscopes (Cont’d)
    10. 10. Masks <ul><li>Cone-shaped devices used to administer oxygen and anesthetic gases to nonintubated patients </li></ul><ul><li>Used for induction and maintenance of anesthesia in very small animals </li></ul><ul><li>Plastic or rubber </li></ul><ul><li>Variety of diameters and lengths </li></ul><ul><li>Rubber gasket </li></ul>
    11. 11. Anesthetic Mask
    12. 12. Anesthetic Chambers <ul><li>Clear, aquarium-like boxes used to induce general anesthesia </li></ul><ul><li>Used in feral, vicious, or intractable animals to reduce stress </li></ul><ul><li>Acrylic or Perspex </li></ul><ul><li>Removable top with two ports </li></ul><ul><li>Cannot monitor patient closely </li></ul>
    13. 13. Anesthetic Chamber (Cont’d)
    14. 14. Anesthetic Machines <ul><li>Used to deliver precise amounts of oxygen and volatile anesthetic under controlled conditions </li></ul>
    15. 15. Principles of Operation of Anesthetic Machines <ul><li>Carrier gas: oxygen or nitrous oxide </li></ul><ul><li>Liquid inhalant anesthetic: to be vaporized </li></ul><ul><li>Mixed gases delivered to patient </li></ul><ul><li>Exhaled gases removed from patient: scavenging system or recirculated </li></ul>
    16. 16. Components of the Anesthetic Machine <ul><li>Compressed gas supply </li></ul><ul><li>Anesthetic vaporizer (precision or nonprecision; VOC or VIC) </li></ul><ul><li>Breathing circuit (rebreathing or nonrebreathing) </li></ul><ul><li>Scavenging system </li></ul>
    17. 17. Components of the Anesthetic Machine (Cont’d)
    18. 18. Components of the Anesthetic Machine (Cont’d)
    19. 19. Compressed Gas Supply <ul><li>Oxygen </li></ul><ul><ul><li>Used to increase inspired air to at least 30% oxygen </li></ul></ul><ul><ul><li>Level necessary to maintain cellular metabolism under anesthesia </li></ul></ul><ul><ul><li>Used to carry vaporized anesthetic to patient </li></ul></ul><ul><li>Cylinders (tanks) </li></ul><ul><ul><li>Contain large volume of gas under high pressure </li></ul></ul><ul><ul><li>E tanks (small), attached directly to anesthetic machine </li></ul></ul><ul><ul><li>H tanks (large), attached remotely to anesthetic machine </li></ul></ul>
    20. 20. Compressed Gas Supply (Cont’d) <ul><li>Control valve (outlet port) </li></ul><ul><ul><li>Located on top of the tank </li></ul></ul><ul><ul><li>Left loose (open), right tight (closed) </li></ul></ul><ul><li>Pressure-reducing valve </li></ul><ul><ul><li>Reduces outgoing pressure to a usable level </li></ul></ul>
    21. 21. Compressed Gas Cylinders
    22. 22. Size H Compressed Gas Cylinder
    23. 23. Safety Issues with Compressed Gas <ul><li>Combustibility </li></ul><ul><li>Yoke attachment </li></ul><ul><li>High-pressure release </li></ul><ul><li>Storage </li></ul><ul><li>Color coding </li></ul><ul><ul><li>Oxygen: green (United States) or white (Canada and Europe) </li></ul></ul><ul><ul><li>Nitrous oxide: blue </li></ul></ul><ul><ul><li>Medical air: yellow (United States) or white and black (Canada and Europe) </li></ul></ul><ul><ul><li>Carbon dioxide: gray </li></ul></ul>
    24. 24. Carbon Dioxide and Oxygen Tanks
    25. 25. Tank Pressure Gauge <ul><li>Indicates the pressure of gas remaining in a compressed gas cylinder </li></ul><ul><ul><li>Measured in pounds per square inch (psi) (United States) or kilopascals (kPa) (Canada and Europe) </li></ul></ul><ul><li>Determine the number of liters remaining in a tank </li></ul><ul><li>Label tanks: full, in service, or empty </li></ul><ul><li>Keep backup full tank on the machine </li></ul>
    26. 26. Labeling Cylinders
    27. 27. Pressure-Reducing Valve (Pressure Regulator) <ul><li>Reduces gas pressure to a constant 40-50 psi (275-345 kPa) </li></ul><ul><li>Color coded </li></ul>
    28. 28. Line Pressure Gauge <ul><li>Indicates pressure in the gas line between the pressure-reducing valve and flowmeter </li></ul><ul><li>Should read 40-50 psi after the oxygen tank is opened </li></ul><ul><li>After turning the tank off, use the oxygen flush valve to evacuate line pressure until the gauge reads 0 psi. </li></ul>
    29. 29. Flowmeter <ul><li>Indicates gas flow expressed in liters per minute (L/min) </li></ul><ul><li>Reduces pressure of gas to 15 psi (~100 kPa) </li></ul><ul><li>Specific for each type of gas </li></ul><ul><li>Flow rate is controlled by anesthetist </li></ul>
    30. 30. Flowmeters (Cont’d)
    31. 31. Oxygen Flush Valve <ul><li>Delivers a short, large burst of pure oxygen directly into the rebreathing circuit or common gas outlet </li></ul><ul><li>Bypasses vaporizer and flowmeter </li></ul><ul><li>Used to refill breathing bag, to deliver pure oxygen to a patient, or to dilute the anesthetic gas remaining in the circuit at the end of anesthesia </li></ul>
    32. 32. Vaporizer Inlet Port <ul><li>Where carrier gas (usually oxygen) enters a vaporizer from the flowmeter </li></ul>
    33. 33. Anesthetic Vaporizer <ul><li>Converts liquid anesthetic agent to a gaseous state </li></ul><ul><li>Adds a controlled amount of vaporized agent to the carrier gas </li></ul><ul><li>Gas mixture leaves vaporizer through the outlet port </li></ul><ul><li>Mixture is known as fresh gas and enters the breathing circuit </li></ul><ul><li>Variable-bypass, flow-over vaporizers </li></ul>
    34. 34. Types of Anesthetic Vaporizers <ul><li>Nonprecision vaporizer </li></ul><ul><ul><li>Used to deliver low vapor pressure anesthetics </li></ul></ul><ul><ul><li>Rarely used </li></ul></ul><ul><li>Precision vaporizers </li></ul><ul><ul><li>Used to deliver a precise amount of anesthetic to the patient </li></ul></ul><ul><ul><li>Expressed as a percent of total gases leaving the vaporizer </li></ul></ul><ul><ul><li>Used to deliver high-vapor pressure anesthetics </li></ul></ul><ul><ul><li>Anesthetist controlled </li></ul></ul>
    35. 35. VOC vs. VIC Vaporizers <ul><li>VOC = Vaporizer-out-of-circuit </li></ul><ul><ul><li>Not localized within the breathing circuit </li></ul></ul><ul><ul><li>Oxygen from the flowmeter enters the vaporizer prior to entering the breathing circuit </li></ul></ul><ul><ul><li>Precision vaporizers </li></ul></ul><ul><ul><li>High resistance gas flow </li></ul></ul><ul><li>VIC = Vaporizer-in-circuit </li></ul><ul><ul><li>Oxygen enters the breathing circuit from the flowmeter </li></ul></ul><ul><ul><li>Exhaled gases pass through the vaporizer </li></ul></ul><ul><ul><li>Nonprecision vaporizers </li></ul></ul><ul><ul><li>Low-resistance gas flow </li></ul></ul>
    36. 36. Factors That Affect Vaporizer Output <ul><li>Vaporizer setting </li></ul><ul><ul><li>The primary determinant of output in both compensated and noncompensated vaporizers </li></ul></ul><ul><ul><li>Controlled by anesthetist </li></ul></ul><ul><li>Carrier gas flow influences the concentration of anesthetic in breathing circuit in both compensated and noncompensated vaporizers </li></ul>
    37. 37. Factors That Affect Vaporizer Output (Cont’d) <ul><li>Factors that affect output of noncompensated vaporizers </li></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><ul><li>Ambient room temperature </li></ul></ul></ul><ul><ul><ul><li>Temperature of carrier gas </li></ul></ul></ul><ul><ul><li>Carrier gas flow rate </li></ul></ul><ul><ul><li>Respiratory rate and depth (nonprecision only) </li></ul></ul><ul><ul><li>Back pressure </li></ul></ul><ul><ul><ul><li>Due to manual ventilation or activation of oxygen flush valve </li></ul></ul></ul>
    38. 38. Use of Vaporizers <ul><li>Specific-use vaporizers are color coded </li></ul><ul><ul><li>Isoflurane = purple </li></ul></ul><ul><ul><li>Sevoflurane = yellow </li></ul></ul><ul><ul><li>Halothane = red </li></ul></ul><ul><ul><li>Desflurane = blue </li></ul></ul><ul><li>Induction and maintenance rates </li></ul><ul><ul><li>Isoflurane = 3-5% induction; 1.5-2.5% maintenance </li></ul></ul><ul><ul><li>Sevoflurane = 4-6% induction; 2-4.5% maintenance </li></ul></ul><ul><ul><li>Desflurane = 10-15% induction; 8-12% maintenance </li></ul></ul>
    39. 39. Precision Vaporizer
    40. 40. Safety with Vaporizers <ul><li>Leakage </li></ul><ul><li>Human exposure </li></ul><ul><li>After using a non-rebreathing circuit, always be sure to reattach the connector of the rebreathing circuit to the outlet port or common gas outlet </li></ul>
    41. 41. Vaporizer Outlet Port and Common Gas Outlet <ul><li>Vaporizer outlet port </li></ul><ul><ul><li>Oxygen/anesthetic exits the vaporizer </li></ul></ul><ul><ul><li>Connected to the common gas outlet or directly into the breathing circuit </li></ul></ul><ul><li>Common gas outlet </li></ul><ul><ul><li>Fresh gas outlet </li></ul></ul><ul><ul><li>Connected to the vaporizer outlet port and breathing circuit </li></ul></ul>
    42. 42. Fresh Gas Inlet <ul><li>Where carrier and anesthetic gases enter the breathing circuit </li></ul><ul><li>Connected to the vaporizer outlet port or common gas outlet </li></ul>
    43. 43. Breathing Circuit <ul><li>Carries anesthetic and oxygen from the fresh gas inlet to the patient </li></ul><ul><li>Conveys expired gases away from the patient </li></ul><ul><li>Rebreathing or non-rebreathing </li></ul>
    44. 44. Rebreathing System <ul><li>Circle systems </li></ul><ul><li>Used on all but very small animals </li></ul><ul><li>Carbon dioxide removed from exhaled air </li></ul><ul><li>Exhaled air is inhaled again with added oxygen and anesthetic </li></ul>
    45. 45. Rebreathing System (Cont’d) <ul><li>Air flow: Inhalation unidirectional valve -> Inhalation tube -> Animal -> Exhalation tube -> Exhalation unidirectional valve -> Carbon dioxide absorber canister -> past reservoir bag -> Pop-off valve -> Pressure manometer -> Inhalation unidirectional valve </li></ul>
    46. 46. Rebreathing System (Cont’d) <ul><li>Closed rebreathing system </li></ul><ul><ul><li>Total system </li></ul></ul><ul><ul><li>Pop-off valve is nearly or completely closed and oxygen flow is low </li></ul></ul><ul><ul><li>Used mostly in large animal anesthesia </li></ul></ul><ul><li>Semiclosed rebreathing system </li></ul><ul><ul><li>Partial system </li></ul></ul><ul><ul><li>Pop-off valve is open and oxygen flow is high </li></ul></ul><ul><ul><li>Excess air is released into scavenging system </li></ul></ul><ul><ul><li>Most common configuration </li></ul></ul>
    47. 47. Breathing Systems
    48. 48. Parts of a Rebreathing System <ul><li>Unidirectional valves </li></ul><ul><li>Reservoir bag </li></ul><ul><li>Pop-off (pressure relief) valve </li></ul><ul><li>Carbon dioxide absorber canister </li></ul><ul><li>Air intake valve </li></ul><ul><li>Pressure manometer </li></ul><ul><li>Corrugated breathing tubes </li></ul><ul><li>Y-piece </li></ul>
    49. 49. Parts of a Rebreathing System (Cont’d)
    50. 50. Unidirectional Valves <ul><li>Control the direction of gas flow </li></ul><ul><li>Inspiratory (inhalation) </li></ul><ul><li>Expiratory (exhalation) </li></ul><ul><li>Open and close as patient breathes </li></ul><ul><li>Monitor respiratory rate and depth </li></ul>
    51. 51. Pop-off Valve <ul><li>Also known as the exhaust valve, adjustable pressure limiting valve, or overflow valve </li></ul><ul><ul><li>Allows excess carrier and anesthetic gases to exit the breathing circuit and enter the scavenging system </li></ul></ul><ul><ul><li>Prevents excessive pressure or volume of gases in the circuit </li></ul></ul><ul><li>Closed when manually ventilating a patient </li></ul><ul><li>Controlled by anesthetist </li></ul>
    52. 52. Pop-off Valve (Cont’d)
    53. 53. Reservoir Bag (Rebreathing Bag) <ul><li>Flexible air storage reservoir </li></ul><ul><li>Indicator of respiratory rate and depth </li></ul><ul><li>Confirms proper endotracheal tube placement </li></ul><ul><li>Allows delivery of anesthetic gases or pure oxygen to patient </li></ul><ul><ul><li>Manual ventilation or “bagging” </li></ul></ul><ul><li>Various sizes: 500 mL to 30 L </li></ul><ul><li>Controlled by anesthetist </li></ul>
    54. 54. Reservoir Bags
    55. 55. Manual Ventilation (Bagging) <ul><li>Minimize atelectasis </li></ul><ul><ul><li>Ventilate every 5-10 minutes </li></ul></ul><ul><li>Force fresh gas into alveoli to normalize gas exchange </li></ul><ul><li>Normalize respiratory rate </li></ul>
    56. 56. Carbon Dioxide Absorber Canister <ul><li>Contains absorbent granules </li></ul><ul><ul><li>Primary absorbent ingredient: calcium hydroxide </li></ul></ul><ul><ul><li>Also: water, sodium hydroxide, potassium hydroxide, calcium chloride, calcium sulfate </li></ul></ul><ul><li>Granules react with carbon dioxide to form calcium carbonate </li></ul><ul><li>Heat and water produced </li></ul><ul><li>Becomes more acidic with more use </li></ul><ul><li>Granules must be replaced when depleted </li></ul>
    57. 57. Carbon Dioxide Absorber Canister (Cont’d)
    58. 58. Pressure Manometer <ul><li>Indicates the pressure of gases within the breathing circuit </li></ul><ul><ul><li>Expressed as centimeters of water (cm H 2 O), millimeters of mercury (mm Hg), or kPa </li></ul></ul><ul><li>Used when manually ventilating (bagging) the patient to prevent excessive pressure in the lungs </li></ul><ul><li>Monitored by the anesthetist </li></ul>
    59. 59. Pressure Manometer (Cont’d)
    60. 60. Air Intake Valve <ul><li>Negative pressure relief valve </li></ul><ul><li>Admits room air into the circuit if negative pressure is detected in the breathing circuit </li></ul><ul><ul><li>May be separate or incorporated into inspiratory unidirectional valve or pop-off valve </li></ul></ul><ul><li>Negative pressure is indicated by a collapsed reservoir bag </li></ul><ul><li>Patient will develop hypoxemia </li></ul>
    61. 61. Breathing Tubes and Y-Piece <ul><li>Breathing tubes </li></ul><ul><ul><li>Corrugated breathing tubes or inspiratory and expiratory breathing tubes </li></ul></ul><ul><ul><li>Carry anesthetic gases to and from the patient </li></ul></ul><ul><ul><li>Connected to unidirectional valve and Y-piece </li></ul></ul><ul><ul><li>Three sizes: 50 mm, 22 mm, and 15 mm in diameter </li></ul></ul><ul><li>Y-piece </li></ul><ul><ul><li>Connects breathing tubes </li></ul></ul><ul><ul><li>Connects to mask or endotracheal tube </li></ul></ul>
    62. 62. Breathing Tubes
    63. 63. Non-rebreathing Systems <ul><li>Semiopen system </li></ul><ul><ul><li>Used in very small patients (<2.5 kg) </li></ul></ul><ul><ul><li>Little exhaled gas is returned to the patient </li></ul></ul><ul><ul><li>Exhaled gas is evacuated by the scavenging system </li></ul></ul><ul><ul><li>Fresh gas is routed to the patient directly from the vaporizer </li></ul></ul><ul><ul><li>No carbon dioxide absorber canister, pressure manometer, or unidirectional valves </li></ul></ul><ul><ul><li>Several configurations are available </li></ul></ul><ul><li>Components : Endotracheal tube connector, fresh gas inlet, reservoir bag, overflow valve, scavenger tube, and scavenger system </li></ul>
    64. 64. Configurations of Nonrebreathing Circuits <ul><li>Bain coaxial circuit (modified Mapleson D system) </li></ul><ul><li>Ayres T-Piece (Mapleson E system) </li></ul><ul><li>Magill circuit (Mapleson A system) </li></ul><ul><li>Lack circuit (modified Mapleson A system) </li></ul><ul><li>Jackson-Rees circuit (Mapleson F system) </li></ul><ul><li>Norman mask elbow (Mapleson F system) </li></ul>
    65. 65. Operation of an Anesthetic Machine <ul><li>Daily inspection </li></ul><ul><ul><li>Oxygen and liquid anesthetic levels </li></ul></ul><ul><ul><li>Leaks </li></ul></ul><ul><ul><li>Pop-off valve or overflow valve </li></ul></ul><ul><li>Machine choice is based on patient body weight </li></ul><ul><ul><li>Small animal machine <150 kg </li></ul></ul><ul><ul><li>Large animal machine  150 kg </li></ul></ul><ul><li>Choose rebreathing system </li></ul>
    66. 66. Choice of Breathing System <ul><li>Primarily based on patient size </li></ul><ul><li>Also based on </li></ul><ul><ul><li>Cost </li></ul></ul><ul><ul><li>Control of anesthetic depth </li></ul></ul><ul><ul><li>Conservation of heat and moisture </li></ul></ul><ul><ul><li>Production of waste gas </li></ul></ul><ul><li>Choice of breathing system will determine </li></ul><ul><ul><li>Type of equipment required </li></ul></ul><ul><ul><li>Position of pop-off valve </li></ul></ul><ul><ul><li>Carrier gas flow rates </li></ul></ul>
    67. 67. Carrier Gas Flow Rates <ul><li>Calculating gas flow rate </li></ul><ul><ul><li>Patient body weight </li></ul></ul><ul><ul><li>Tidal volume (V T ) 10 mL/kg/min </li></ul></ul><ul><ul><li>Respiratory minute volume (RMV) = V T × respiratory rate (~20 bpm) </li></ul></ul><ul><ul><li>Type of breathing system </li></ul></ul><ul><ul><li>Expected period of anesthesia </li></ul></ul>
    68. 68. Mask or Chamber Induction Flow Rates <ul><li>High flow rates required </li></ul><ul><li>Mask: ~30 times V T for dogs, cats, neonate large animals, pigs (1-5 L/min) </li></ul><ul><li>Chamber: 5 L/min for small animals </li></ul>
    69. 69. Flow Rates in a Semiclosed Rebreathing System <ul><li>After induction with injectable agent: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine) </li></ul><ul><li>When making changes in anesthetic depth: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine) </li></ul><ul><li>During maintenance: 20-40 mL/kg/min (SA machine) and 3-5 L/min (LA machine) </li></ul><ul><li>During recovery: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine) </li></ul>
    70. 70. Flow Rates in a Closed Rebreathing System <ul><li>Normally used during maintenance only </li></ul><ul><li>Oxygen flow must equal oxygen requirements of the patient </li></ul><ul><li>Minimum requirement = 5-10 mL/kg/min </li></ul>
    71. 71. Safety Concerns with a Closed Rebreathing System <ul><li>Carbon dioxide accumulation </li></ul><ul><li>Increased pressure in anesthetic circuit </li></ul>
    72. 72. Flow Rates in a Non-rebreathing System <ul><li>Require high flow rates per unit body weight during all periods </li></ul><ul><li>Rates are based on patient body weight and Mapleson classification of circuit </li></ul><ul><li>Usually used on patients weighing <7 kg </li></ul>
    73. 73. Care and Maintenance of Anesthetic Equipment <ul><li>Compressed gas cylinders </li></ul><ul><ul><li>Inspected and maintained by company that owns them </li></ul></ul><ul><ul><li>Silicone or Teflon-based lubricants safe for difficult tank valves </li></ul></ul><ul><li>Tank and line pressure gauges, pressure manometer, and oxygen flush valve </li></ul><ul><ul><li>Require no regular maintenance </li></ul></ul><ul><li>Pressure-reducing valve adjusted to 40-50 psi </li></ul><ul><li>Flowmeters require no regular maintenance </li></ul><ul><ul><li>Check accuracy occasionally </li></ul></ul>
    74. 74. Care and Maintenance of Anesthetic Equipment (Cont’d) <ul><li>Vaporizer </li></ul><ul><ul><li>Serviced and maintained by manufacturer or service professional </li></ul></ul><ul><li>Vaporizer inlet port, outlet port, common gas outlet, and fresh gas inlet </li></ul><ul><ul><li>Check and replace hoses as necessary </li></ul></ul><ul><ul><li>Routine low-pressure leak tests </li></ul></ul>
    75. 75. Care and Maintenance of Anesthetic Equipment (Cont’d) <ul><li>Unidirectional valves </li></ul><ul><ul><li>Disassemble, clean, inspect </li></ul></ul><ul><ul><li>Prevent water vapor, mucus, and dust buildup </li></ul></ul><ul><ul><li>Check integrity of the valves </li></ul></ul><ul><li>Pop-off valve </li></ul><ul><ul><li>Check for proper operation and adjust as necessary </li></ul></ul><ul><ul><li>Daily and during an anesthetic procedure </li></ul></ul>
    76. 76. Care and Maintenance of Anesthetic Equipment (Cont’d) <ul><li>Reservoir bag, breathing tubes, and Y-piece </li></ul><ul><ul><li>Remove and clean after each procedure </li></ul></ul><ul><ul><li>Prevents patient-to-patient transfer </li></ul></ul><ul><ul><li>Hang to dry </li></ul></ul><ul><ul><li>Check integrity of each part before use </li></ul></ul><ul><li>Carbon dioxide absorber canister </li></ul><ul><ul><li>Change granules and clean canister as per guidelines </li></ul></ul><ul><ul><li>Wear gloves and a mask when handling granules </li></ul></ul><ul><ul><li>Check integrity of each part before use </li></ul></ul>
    77. 77. Disinfecting Anesthetic Equipment <ul><li>Endotracheal tubes, laryngoscope blades, face masks </li></ul><ul><li>To prevent spread of disease from patient to patient </li></ul><ul><li>Wash with disinfectant, rinse, dry, reassemble </li></ul><ul><li>Check integrity of each part before use </li></ul>
    78. 78. Disinfecting Anesthetic Equipment (Cont’d) <ul><li>Disinfectants </li></ul><ul><ul><li>Chlorhexidine gluconate: not 100% effective </li></ul></ul><ul><ul><li>Glutaraldehyde solutions (2%): short shelf life, toxic, absorbed </li></ul></ul><ul><ul><li>Ethylene oxide gas: special equipment needed, toxic, absorbed </li></ul></ul><ul><ul><li>Steam under pressure (autoclave): damages rubber surfaces </li></ul></ul><ul><li>Discard damaged equipment </li></ul>

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