The Anesthesia Machine

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The Anesthesia Machine

• 
  

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R1 ???
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Introduction

• Modern anesthesia machines
• extremely sophisticated
• many safety features devices
• microprocessors
•         gt Anesthesia workstation
• ?? ??? ??? ?? ? ??? ??? ?? ?? ?? ??? ??? ?? ? ??
  3? ?? ??
• ??? ???? ????
• ?? ?? ??
•         -gt breathing circuit (single m/c source
  of injury)

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Overview

• Basic form for anes machine
• -gt gas supply??? medical gas ??
• -gt ??? ??? ??? ?? flow control?
• -gt ?????? ???? final gas mixture ??
• -gt gas? breathing circuit?? ??

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Gas supply

• Gas inlet oxygen, nitrous oxide, and air
• Pipeline inlets
• DISS(diameter-index safety system) color coded,
  noninterchangeable
• filter trap debris from the wall supply
• one-way check valve prevents retrograde flow
• Cylinder inlets
• Yoke assemblies pin index safety system
• ?? pipeline failure? back-up supply??? ??
• Bourdon pressure gauge cylinder pressure ??

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Flow control circuits(1)

• Pressure regulators
• ?? psig (ex.1??760mmHg7.25psig)
• Pipeline(50-55psig)? ??? ?? ?????
  cylinder(2200psig)? ??? ???? ?? flow control? ???
  
• pressure regulator? ?? cylinder gas pressure?
  flow valve ???
• 45-47 psig?? ??
• ?? ??(Datex-Ohmeda)? ?? two-stage pressure
  regulation? ?? pipeline? cylinder pressure? ??
  ????
• oxygen? 20psig?, N2O? 38psig? ????

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Flow control circuits(2)

• Oxygen supply failure protection devices
• Oxygen ?? flow control valve? ??
• N2O, air flow control valve? ???? ?? safety
  device? ?? ??? ?
• ??? ??? oxygen pressure? ??? ???? ?? gas flow?
  ????
• ????(20psig)? ?? gas valve? ??? ?
• ? oxygen supply failure? N2O ? hypoxic
  mixture? ??? ???
• ?? ???? oxygen supply low-pressure sensor? ?? gas
  whistle or electric alarm? ???? ? ??

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Flow control circuits(3)

• Flow valves and meters
• ???? ??? gas
• ? flow-control valve ??
• ? flowmeter
• ? ?? gas?? ?? ?
• ? active vaporizer? ????? ?? ???? ??
• ? machine's common gas outlet?? ??
• flow valve ??? gas line ? high-pressure circuit
• flow valve? common gas outlet ?? ? low-pressure
  circuit

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Flow control circuits(4)

• Flowmeter
• constant-pressure variable-orifice flowmeter
• Indicator ball, bobbin, float
• ???? ??? ??? low gas flow? float? ?????? ??? ??
  ??
• gas? tube's wall? ??? ??? ?? float? ????? ???? ??
  tube ??? ?? ?
• flowmeter malfuction ??
• dirt in the flow tube, vertical tube
• Misalignment
• sticking or concealment of a float at the top of
  a tube

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Flow control circuits(5)

• Flow valves and meters is designed to
• A. minimum oxygen flow
• ????? ?? ?? ? oxygen flow? ?? ?? 150mL/min ? ??
• B. oxygen/nitrous oxide ratio controller
• O2? N2O flow? ???? ?? O2??? 21-25? ??

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Flow control circuits(5)

• Vaporizers
• flowmeter? common gas outlet ??? ??
• ??? vaporizer? ????? interlocking or exclusion
  device??
• A. physics of vaporization
• gas molecule? ?? ??? vapor pressure ??(??? ????
  ???)
• vaporization? energy? ???? ?? liquid? ????? ???
• B. copper kettle
• measured-flow or flowmeter-controlled vaporizer?
  ???
• copper high specific heat, high thermal
  conductivity gt maintain a constant temperature
• carrier gas? vaporizer? ???? anesthetic liquid?
  ???? vapor? ??
• liquid anesthetic 1mL 200mL anesthetic vapor gt
  saturated gas? ???? ???? ?? ????? ?

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• halothane? vapor pr. 243mmHg
• copper kettle?? ?? 243/760 32

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Vaporizers

• C. modern conventional vaporizers
• agent specific, ??? flow ??? ???? ??? ?? ??
• variable-bypass vaporizer
• calibrated control knob? ??? gas flow? ????
  carrier gas? ??? vaporizing chamber? ???
• temperature compensation bi-metal? flow ??
• flow rate? ??? anesthetic concentration?? ??? ???
  
• Gas composition? ??(100O2-70N2O)? N2O? volatile
  agent? ??? ane concent.? ??? ?? ? ??
• agent-specific keyed filling port? ?? ?? agent?
  ??? ??
• pumping effect ?????? ????? ???? ?? ????? ???
  ???? ????? ??
• one-way check valve(vaporizer? O2 flush valve ???
  ??)? ??
• vaporizer? ?? ??? ??? compensate ??? ????

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Vaporizers

• D. Electronic vaporizer
• Desflurane
• High volatility ? ?? ??
• vaporization? cooling effect ?? ???? vaporizer??
  ???? ??
• vaporization? ?? ??? ??? ?? high fresh gas flow
  ??
• Desflurane vaporizer
• electrically heated to 39 C-gt 2??? vapor pressure
  ??
• Unlike a variable-bypass vaporizer
• ? no fresh gas flows through the desflurane
  sump
• pure desflurane vapor? vaporizer? ??? ?? fresh
  gas mixture? ??
• ??? ??? ?? ??? ????? ???, ??? partial pressure?
  ??
• -gt ?????? ?????? ???? ??? ????? ?

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Common(fresh) gas outlet

• Multiple gas inlet
• ?only on common gas outlet !
• Oxygen flush valve
• flowmeters and vaporizers bypassing
• ? common gas outlet? high O2 flow
  (35-55L/min) ??
• real potential of lung barotrauma
• ? Dont push it during ventilation!!

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The breathing circuit

• Circle system (m/c)
• Common gas outlet gas composition
• ? flowmeters vaporizers?
  ?? ??? ???? ??
• Breathing circuit
• ? ?? ???? anesthetic uptake
• ? minute ventilation
• ? total fresh gas flow
• ? volume of the breathing circuit
• ? gas leaks
•    gt induction and emergence?? high gas flow
  ???? ?? ?? ? ??
• ??? ????? ??? ?? ??????? ??
•      gt?? misconnects, disconnects, kinks,
  leaks ??? ??

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The breathing circuit
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Oxygen analyzers

• 3 type
• ?polarographic(Clark electrode)
• ?galvanic(fuel cell) external power source? ??
  ??
• ?paramagnetic
• ??? oxygen-permeable memb.? ??? electrolyte gel?
  sample gas? cathode anode electrodes? ???
  sensors ? ??
• ?? ????? ??? ??? ??? ???? ???? ??? ????? ?? ?? ?
  ?? ????? ???? ??? ? ??
• ?? O2 analyzer?? low-level alarm? ??
• ?? ??? inspiratory or expiratory limb ?? ???
  ??.(fresh gas line? ??) expiratory limb??
  inspiratory limb???? lower oxygen partial
  pressure? ??

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Oxygen analyzers

• 3 type
• ?polarographic(Clark electrode)
• ?galvanic(fuel cell)
• ?paramagnetic
• ?? oxygen-permeable memb.??? O2
  ?electrochemical sensor
• ? ????? ???, self-calibrating, no consumable
  part
• ????? ?? ?? ? ?? ????? ???? ??? ? ??
• ?? O2 analyzer?? low-level alarm? ??
• Location inspiratory or expiratory limb of
  brething system
• Humidity of expired gas not affect

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Spirometer

• Exhaled tidal volume ??
•  1) vane anemometer(or Wright respirometer)
• Expiratory limb In front of the expiratory valve
• Another variation volumeter or displacement
  meter
• Exhaled TV? ?? ?? ventilator setting? ??
• circuit leaks
• Disconnections
• ventilator malfunction
• Circuit?? ?? gas ?? ??? ???? ???? ?? ??
• long compliant breathing tube
• rapid respiratory rates
• high airway pressure
•      gt Y-piece?? ???? ??? ??? ?? ? ??

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Spirometer(2)

• 2) hot-wire anemometer
•  - electrically heated, fine platinum wire? gas
  flow ?? ??
•  - cooling effect? ????? ??? ??? ?? ??
•  - ?? reverse flow? ?? ??, ???? ???
• 3) ultrasonic flow sensor
•  - flow stream? turbulent eddies? ?? ?? gas flow?
  discontinuity? ??
•  - ?? no moving parts, independence from gas
  density

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Spirometer(3)

• 4) variable-orifice flowmeter
•  - inspiratory expiratory port? ?? ??? ???
  sensor? ??? ??? ?? flow pressure drop? ??
•  
• 5) pneumotachograph(fixed-orifice flowmeter)
•  - parallel bundle of small-diameter tubes in
  chamber(Fleisch pneumotachograph) or mesh screen?
  ????? ??? ??? ??? ?? ?? pressure drop? ??
•  - ????, ????? ?? ???? ? ???? ???
•      

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Circuit pressure

• Breathing circuit pressure
• airway pressure ??
•        gt Y connection???? ??? ?? ??
• Airway pressure ??? ??
• ? pulm. compliance ??       
• ? TV ??
• ? Obx in breathing circuit, tracheal tube, or
  Pt's airway
• Airway pressure ??? ??
• ? compliance ??     
• ? TV ?? 
• ? leak in the circuit

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Adjustable pressure-limiting valve

• Fully open during spontaneous ventilation
• Partially closed during manual or assisted bag
  ventilation
• Fully closed
• ? pressure? ?? ???
• ? pulm. Barotrauma,
• hemodynamic compromise ??
• ????? ?? ???? 70-80cmH2O? ??? ??? ?? ????

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Humidifier(1)

• Absolute humidity
• ? weight of water vapor in 1L of gas(mg/L)
• Relative humidity
• ? ratio of the actual mass of water present
  in a volume of gas at a particular temperature
• Gas? ?????? ???? ???? ??? ??
• ? but tracheal intubation, high fresh gas
  flow ?? bypass
• ???? dehydration of mucosa,
• altered ciliary function
• inspissation of secretions
• Atelectasis
• ventilation/perfusion mismatching ??

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Humidifier(2)

• A. Passive humidifier
•  - condenser humidifier or heat and moisture
  exchanger(HME)
•  - do not add heat or vapor
•  - ??? ??? ??? ??? ?? ??? ??
•  - dead space ?? , breathing circuit? ????
•  - HME? ??? ???? ???? ???? breathing circuit? ??
  ? ??
•  - effective filter ?? ?? ? bacterial or viral
  contamination ??

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Humidifier(3)
? passover humidifier ? wick humidifier ?
bubble-through humidifier ? vapor-phase
humidifier

• B. Active humidifier
• Heated humidifier? ???
• ? thermal lung injury  
• ? nosocomial infection 
• ? circuit disconnection  
• ? increased airway resistance 
• ? interference with flowmeter function
• ?? ???? hypothermia small tracheal tube? dried
  secretion? plugging ??
• filter??? ??

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Ventilators

• ?? ?? ??? ?? ICU?? ??? ventilator? ?? ??? ????
  ??? ?? ICU-type' ventilator? ??
• Overview
• proximal airway? alveoli ??? pressure gradient?
  ??? gas flow? ??
• ???? chest?? negative pressure ??
• ?? ventilator? upper airway? positive pressure?
  gas flow? ??

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Ventilators(1)

• Classification
• ? inspiration phase ??
• ? method of cycling from inspiration to
  expiration
• Power source
• Pneumatic
• Electronic
• Design
• Single circuit
• Double circuit
• Rotatory piston
• Liner piston

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Ventilators(1)

• A. inspiratory phase
• B. Transition phase from inspiration to
  expiration
• C. Expiratory phase
• D. Transition phase from expiration to
  inspiration

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Ventilators(2)

• A. inspiratory phase
• ? TV ??
• ? constant-pressure generators
• ? constant-flow generators
• ? nonconstant generators
• Pressure? gas flow rage ??
• half cycle of a sine wave? ?? flow pattern

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Ventilators(3)

• B. Transition phase from inspiration to
  expiration
• Termination of Inspiratory phase
• 1. preset limit of time (fixed duration)
• 2. set inspiratory pressure ??
• 3. predetermined tidal volume
• ? time-cycled ventilators
• ?lung compliance? ?? TV ? peak insp.
  pr. ??
• ? pressure-cycled ventilators
• ?Preset pressure? ???? ??? cycling ??
  ?? ???.
• ? volume-cycled ventilators
• ?inspiratory duration? pressure?
  ???? preset vol. ? ??

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Ventilators(4)

• C. Expiratory phase
• airway pr.? ??? ???? ??? PEEP ? ????
• Passive
• Flow out of lung
• ? airway resistance
• ? lung compliance? ?? ??

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Ventilators(5)

• D. Transition phase from expiration to
  inspiration
• Preset time interval?? change in pressure?
  ??
• ?volume-control mode
• ? set TV ventilatory rate IE ratio
• ? gas flow rate inspiratory time ??
• ?pressure-control mode
• ? set ventilator rate IE ratio? ??
  inspiratory time ??
• ? gas flow? inspiratory pressure? ???? ??? ??
  

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Ventilator circuit design

• A. Double-circuit system ventilators
• Bellows??? ???? TV ??
• Ventilator power outlet pressurized O2 or air
  (45-50psig)
• ? space between the plastic enclosure and
  the bellow
• Standing bellows(asending) circuit disconnect
  ?? ??
• Hanging bellows(descending) circuit disconnect
  ?? ??

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Ventilator circuit design

• B. Piston ventilators
• Bellow?? electrically driven piston?? ??
• ? very poor lung compliance
• ? very small Pt ??? TV ?? ??
• Piston? volume-controlled??? ??? ???,
  pressure-controlled??? ??? ????? ???
• Negative-pressure relief valve
• ??? ??? piston? downstroke?? ?? ?? ??

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Ventilator circuit design

• Bag/ventilator switch
• bag ? ventilator excluded, spontaneous/manual
  (bag) ventilation ??
• ventilator ? breathing bag APL valve
  excluded, ventilator ??
• spill valve ventilator ??? pressure-relief(pop-o
  ff) valve
• ??? pneumatically closed ? ventilator? positive
  prssure
• ??? ??

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Pressure and volume monitoring

• peak insp. pr. 
• The highest circuit pressure
• Indication of dynamic compliance
• plateau pressure
• Inspiratory pause? ??
• mirror of static compliance

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Ventilator alarms

•  disconnect alarm
• ? low peak inspiratory pressure
• ? low exhaled tidal volume
• ? low exhaled CO2
• ?? ???? ???? circuit ??? ? ???? ??? ??? ? ? ??
• ?? alarm
• high peak insp. pr.,
• high PEEP
• negative pr.
• low oxygen-supply pr.

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Problems associated
with anesthesia ventilators

• a. ventilator-fresh gas flow coupling
• ??? spill valve ???? common gas outlet? fresh gas
  flow? TV? ???
• Ex) fresh gas flow 6L/min, IE ratio 12(??33),
  respiratory rate 10?/min
• gt ? TV?? ventilator? output? 200ml? ???
          
•   
• ??? fresh gas flow? ???? TV, minute ventilation,
  peak inspiratory pressure? ??
• ?? ?? ?? airway pressure? exhaled TV? ???? ????,
  ??? fresh gas flow? ??? ?

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Problems associated
with anesthesia ventilators

• b. Excessive positive pressure
• Ventilator? ??? setting?? ???,
• fresh gas flow coupling
• ?? ? O2 flush ?? ?? ?? ??
• pulmonary barotrauma ? hemodynamic compromise ??

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Problems associated
with anesthesia ventilators

• c. tidal volume discrepancies
• ??
• breathing circuit compliance
• gas compression
• ventilator-fresh gas flow coupling
• leaks in the anesthesia machine, breathing
  circuit, patient's airway
• ?? ???? ?? spirometer? Y connector ??? ??

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Waste-gas scavengers

• NIOSH? ???
• ?N2O? 25ppm??, halogenated agent? 2ppm??
  (N2O??? 0.5ppm ??)
• APL valve? spill valve? ???? gas? hose (transfer
  tubing)? ???? scavenging interface? ???
• ? open interface ??? ???
• closed interface negative-
  positive-pressure relief valve ??
• ? passive scavenging recirculation ???
  ventilation duct ?? ??? ??
• active scavenging ??? vacuum system?? ??
• ??? 10-15L/min ?? ??

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Thanks for your attention
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