4. The anesthesia machine Morgan anesthesia

1
4. The anesthesia machineMorgan anesthesia

• ??????? 1?
• ???

2
Introduction

• Modern anesthesia machines
• extremely sophisticated
• incorporating many built-in safety features
  devices
• breathing circuit, monitors, mechnical
  ventilator
• microprocessors (enhance, integrate monitor
  all components)
•         gt Anesthesia workstation
• ?? ??? ??? ?? ? ??? ??? ?? ?? ?? ??? ??? ?? ? ??
  3? ?? ?? ??? ???? ???? ?? ?? ??? ??
•         -gt breathing circuit was the most common
  single source of injury

3
Overview

• Basic form for anes machine gas supply???
  medical gas ??
• -gt ??? ??? ??? ?? flow control?
• -gt ?????? ???? final gas mixture ??
• -gt gas? breathing circuit?? ??
• Mechanical ventilator? spontaneous or manual(bag)
  ventilation? ?? ? ? ??

4
Gas supply

• gas inlet for 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
• oxygen(pneumatic) power outlet to drive the
  ventilator, an auxiliary oxygen flowmeter
• Cylinder inlets
• the yoke assemblies pin index safety system
•   index pins, washer, gas filter, check valve ??
  
• ?? pipeline failure? back-up supply??? ??
• Bourdon pressure gauge cylinder pressure ??
• gas pr. ???? flexible tube straightened -gtmove
  a needle pointer

5
Flow control circuits(1)

• Pressure regulators
• pipeline? ??? ?? ????? cylinder? ??? ??? ?? flow
  control? ???
• pressure regulator? ?? cylinder gas pressure?
  flow valve ??? 45-47 psig?? ??(29psig2040mmHg)
• high-pressure relief valve ???? ??? ???
  ???????? ?? ??(95-110 psig) ?? cylinder?
  regulator failure?
• ?? ??(Datex-Ohmeda)? ?? two-stage pressure
  regulation? ?? pipeline? cylinder pressure? ??
  ????
• oxygen? 20psig?, N2O? 38psig? ????
• oxygen/nitrous oxide flow linkage ? proper
  functioning? ??

6
Flow control circuits(2)

• Oxygen supply failure protection devices
• oxygen? ?? flow control valve? ?????, N2O, air?
  ?? gas? ??? flow control valve? ???? ?? safety
  device? ?? ??? ?
• ??? ??? oxygen pressure? ??? ???? ?? gas flow?
  ???? oxygen supply failure?? hypoxic mixture? ???
  ???
• ??? oxygen from common inlet pathway ? oxygen
  flow control valve? ???? ???, safety device,
  oxygen flush valve, ventilator power outlet? ???
  ???? ????? ???
• ?? ??(Datex-Ohmeda Excel)??? piloting pressure
  line? ?? ??(20psig)? ???? ?? ?? gas? valve? ??
• proportioning safety device (oxygen failure
  protection device or balance regulator) ???
  minimum oxygen pressure ???? N2O? ?? gas flow ??
• ?? ???? oxygen supply low-pressure sensor? ?? gas
  whistle or electric alarm? ???? ? ??

7
Flow control circuits(3)

• Flow valves and meters
• ???? ??? gas? flow-control valve? ???? flowmeter?
  ?? ?? gas?? ?? ? active vaporizer? ??? machine's
  common gas outlet?? ??
• flow valve?? proximal?? gas line? high-pressure
  circuit, flow valve? common gas outlet ???
  low-pressure circuit?? ?
• flow control valve? ? ?????? ??? needle valve? ??
  
• Stops in the full-off and full-on positions
  prevent valve damage

8
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
• oxygen flow meter???? gas? ? ??? ???? ?? oxygen
  flow meter? ?? ??? downstream? ????? ?(vaporizer
  ???)
• electronic flow control and measurement
• flow restrictor? ?? pressure drop? ?? ??

9
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? ??

10
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? ???? ???? ?? ????? ?

11

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

12
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 ??? ????

13
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 ?????? ?????? ???? ??? ????? ?

14
Common(fresh) gas outlet

•  multiple gas inlet, but only on common gas
  outlet
• adding new gas of fixed and known composition to
  the circle system
• oxygen flush valve
• the flowmeters and vaporizers? ?? common gas
  outlet? high flow(35-55L/min) of oxygen? ??
• real potential of lung barotrauma

15
The breathing circuit

• circle system? ?? ?? ??
• common gas outlet?? ??? gas composition?
  flowmeters vaporizers? ?? ??? ???? ??? ? ??? ??
  breathing circuit??? gas composition, ? volatile
  anesthetic concentration? ?? ??? ????
• ? ?? ???? anesthetic uptake
• ? minute ventilation
• ? total fresh gas flow
• ? volume of the breathing circuit
• ? gas leaks
•    gt induction and emergence?? high gas flow
  ???? ?? ?? ? ??
• ??? ????? ??? ?? ??????? ?? f4-23
•      gt?? misconnects, disconnects, kinks,
  leaks ??? ??

16
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? ??

17
Spirometer

• - exhaled tidal volume ??
•   1) vane anemometer(or Wright repirometer)
  f4-24a
• rotating vane of low mass in expiratory limb in
  front of the expiratory valve
• Another variation the volumeter or displacement
  meter ? ??? ?? gas? discrete quantities ? ?????
  ??? ?f4-24b
• exhaled TV? ??? ?? ventilator setting? ??? ????,
  circuit leaks, disconnections, or ventilator
  malfunction? ?? ?? ??
• long compliant breathing tube? rapid respiratory
  rates, high airway pressure? ??? circuit?? ?? gas
  ?? ??? ???? ???? ?? ??? ??
•      gt Y-piece?? ???? ??? ??? ?? ? ??

18
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

19
Spirometer(3)

• 4) variable-orifice flowmeter f4-24c
•  - inspiratory expiratory port? ?? ??? ???
  sensor? ??? ??? ?? pressure drop? ??
•  - ???? ??? sensor? heated humidified circuit??
  ??? ? ??? ???? ? ? ??
• 5) pneumotachograph(fixed-orifice flowmeter)
•  - parallel bundle of small-diameter tubes in
  chamber(Fleisch pneumotachograph) or mesh screen?
  ????? ??? ??? ??? ?? ?? pressure drop? ??
•  - ????, ????? ?? ???? ??? ????? ???
•      gt ?? ???? ??? Y connection? ??? Pitot
  tube ?? f-d

20
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

21
Adjustable pressure-limiting valve

• fully open during spontaneous ventilation
• partially closed during manual or assisted bas
  ventilation
• fully closed??? ?? pressure? ?? ??? pulm.
  barotrauma and/or hemodynamic compromise ??
• ????? ?? ???? 70-80cmH2O? ??? ??? ?? ????

22
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 to the maximum
  amount of water possible at a particular
  temperature
• (? 37 C 100 relative humidity absolute
  humidity 44mg/L, 21 C 100 humidity 18mg/L)
• gas? ?????? ???? ???? ??? ????? ??? tracheal
  intubation?? high fresh gas flow? ?? bypass ?
  
•      gt ???? dehydration of mucosa, altered
  ciliary function, inspissation of secretions,
  atelectasis, ventilation/perfusion mismatching ??

23
Humidifier(2)

• a. passive humidifier
•  - condenser humidifier or heat and moisture
  exchanger(HME) f4-25
•  - do not add heat or vapor
•  - ??? ??? ??? ??? ?? ??? ??
•  - dead space ?? ???? ???? rebreathing ?? ??
•  - HME? ??? ???? ???? ???? breathing circuit? ??
  ? ??
•  - effective filter??? ??

24
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??? ??

25
Ventilators

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

26
Ventilators(2)

• a. inspiratory phase
• ? constant-pressure generators
• ? constant-flow generators
• ? nonconstant generators
• half cycle of a sine wave? ?? flow pattern
• airway resistance??? lung compliance??? peak
  inspiratory pressure? ??? ?????, flow rate? ???
  ??

27
Ventilators(3)

• b. transition phase from inspiration to
  expiration
• inspiratory phase? ?? preset limit of time (fixed
  duration), set inspiratory pressure?? ??,
  predetermined tidal volume ?? ?? ??
• ? time-cycled ventilators
• lung compliance? ?? TV ? peak insp. pr. ??
• ? pressure-cycled ventilators
• Preset pressure? ???? ??? cycling ?? ?? ???.
• ? volume-cycled ventilators inspiratory
  duration and pressure? ???? preset vol. ? ??

28
Ventilators(4)

• c. expiratory phase
• Passive exhalation?? airway pr.? ??? ???? ???
  PEEP ? ????
• flow out? airway resistance? lung compliance? ??
  ??

29
Ventilators(5)

• d. transition phase from expiration to
  inspiration
• preset time interval?? change in pressure? ??
• ?volume-control mode??? set ventilatory rate
  IE ratio? ?? gas flow rate inspiratory time ??
  
• ?pressure-control mode??? inspiratory time? set
  ventilator rate IE ratio? ??, gas flow?
  constant inspiratory pressure? ???? ??? ??

30
Ventilator circuit design

• a. double-circuit system ventilators
• bellows??? TV ??
• a standing bellows
• bellows? anesthesia circuit?? breathing bag? ??
• ??? ?????? negative pr. ??? ?? ??? ??? bellow?
  collapse??? free breathing valve? ??

31
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?? ?? ?? ??

32
Ventilator circuit design

• c. spill valve
• ventilator??? circle system? APL valve? ?????
  ????? ?
• bag/ventilator switch ? ??? bag?? ???
  spontaneous vent. ? ???? ?
• spill valve ventilator ??? pressure-relief(pop-o
  ff) valve
• ??? pneumatically closed
• ??? ??

33
Pressure and volume monitoring

• peak insp. pr. 
• indication of dynamic compliance
• plateau pressure
• mirror of static compliance

34
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.

35
Problems associated with anesthesia ventilators

• a. ventilator-fresh gas flow coupling
• ????? spill valve? ???? common gas outlet?????
  fresh gas flow? TV? ???
• ?? ?? fresh gas flow 6L/min, IE ratio 12,
  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? ??? ?

36
Problems associated with anesthesia ventilators

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

37
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 ??? ??

38
Thanks for your attention
39
Waste-gas scavengers

• NIOSH? ??? OR?? 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 ?? ??

40
(No Transcript)
41
(No Transcript)
42
(No Transcript)