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Anesthesia Machine Flashcards

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1
Q

How are vaporizer and FM settings affected by altitude?

A

AT HIGHER ALTITUDE, VAPORIZER SETTINGS WILL BE HIGHER AND FGF WILL BE LOWER THAN AT SEA LEVEL TO MAINTAIN SAME SETTINGS

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2
Q

Graham’s Law of Diffusion

A

Rate of diffusion (velocity) = 1/square root (MW)

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3
Q

Density of Gases at Altitude

A

density of gases decreases

When higher flows set in FM, actual flow of gases will be higher than the set flows, as flow is inversely proportional to the square root of density as per Graham’s law.

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4
Q

Regulatory Body that Oversees AM

A

American Society for Testing and Materials
o Updated 2005, F1850: Standard Specification for Particular Requirements for Anesthesia Workstations and their Components

2000: Canadian Standards Assoc

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5
Q

Do veterinary AM have to meet any standards?

A

No

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6
Q

E Tank - oxygen

A

660L, 1900PSI
14#

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7
Q

E Tank - N2O

A

1590L, 745psi
14#

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8
Q

G Tank - N2O

A

13,800L, 745psi
97#

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9
Q

H tank - oxygen

A

6900L, 2200psi
119#

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10
Q

H tank - N2O

A

15,800L, 745psi
119#

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11
Q

Anesthesia Machine

A
  • Permits delivery of precise yet variable combination of inhalant anesthetic and oxygen
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12
Q

Common Components

A

FROGS
FM
Regulator
vapOrizer
Gas supply
Scavenge

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13
Q

What is an anesthesia workstation?

A

machine + vaporizer(s) + ventilator + breathing system + scavenging + monitors

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14
Q

Advantages of Ax WS?

A

–integration of monitoring/control functions, and alarms
–data display on single or multiple screens
–reduced external connections that reduce likelihood of misconnections disconnections or kinked connections
–Automatic system checks, built in safeguards in event of machine failure

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15
Q

Disadvantages of Ax WS?

A

–potential disruption of CMV/ gas delivery
–display failure
–electrical failure
–fires
–liquid spills
–Malfunction in way that anesthesia provider doesn’t recognize

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16
Q

High Pressure Components of Pneumatic System?

A

Up to 2200psi

Gas cylinders
Hanger yoke/Yolk blocks
High pressure hoses
Cylinder pressure gauge
Cylinder pressure regulator

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17
Q

Intermediate pressure components of a pneumatic system?

A

40-55psi

Pneumatic part of master switch
Pipeline inlet connections
Pipeline pressure indicators
Piping
Gas Power Outlet
Oxygen pressure failure devices
Oxygen flush
Additional pressure regulators (if present)
Flow Control valves

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18
Q

Low Pressure Components

A

<30cm H2O - bc pressure in this part transmitted directly to patient lungs

Flowmeters
Hypoxia Prevention Safety Devices
Unidirectional Valves
Pressure Relief Devices
Vaporizer
Conduit btw Vaporizer, Common Gas Outlet
Common Gas Outlet

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19
Q

Hanger Yokes

A

Fxn: orients, supports cylinder, gas tight seal, ensures unidirectional gas flow

At least one yoke for oxygen, one yoke for N2O +/- second yolk for oxygen

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20
Q

Parts of the Hanger Yoke

A

Body
Retaining Screw
Nipple
Index Pins
Washer
Filter
Check Valve Assembly

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21
Q

Hanger Yoke Body

A

principal framework supporting structure
* Swinging gate: distal part hinged, can be swung to side when mounting cylinder

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22
Q

Hanger Yoke Retaining Screw

A

tightens cylinder valve outlet against washer/nipple of cylinder
* Threaded into distal end of yoke
* Gas-tight seal

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23
Q

Hanger Yoke Index Pins

A

prevent attachment of incorrect cylinder
* Below nipple, holes into which pins are fitted must be of specific depth

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24
Q

Hanger Yoke Nipple

A

where gas enters the machine, fits port on cylinder valve
* Impossible to obtain tight seal with cylinder valve if damaged

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25
Q

Hanger Yoke Washer

A

seal between cylinder and yoke, placed around nipple
* Only one washer per cylinder
* In good condition, not broken or curled

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26
Q

Hanger Yoke Filter

A

Prevents particulate matter from entering machine
* Between cylinder and pressure regulator or cylinder and flow control valve

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27
Q

Hanger Yoke Check Valve Assembly

A

unidirectional flow of gas through yoke, esp if no tank on machine
* allows empty cylinder to be replaced with a full one without losing gas
* Prevents transfer of gas from high pressure cylinder to low pressure when both connected to double yoke/turned on
* Plunger: slides away from side when pressure greater

  • Cylinder pressure > machine pressure, plunger pushed right –> gas into machine
  • Machine pressure > cylinder pressure –> plunger moves left, blocks gas flow
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28
Q

Empty Yoke

A

use yoke plug/dummy
* In absence of yoke plug gas can flow retrograde through open flow control valve, out through yoke

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29
Q

What should avoid contaminating with grease/oil?

A

Cylinder valves, yokes = fire hazard

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30
Q

Cylinder Pressure Gauge is what time of tube?

A

Bourdon Tube

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31
Q

Bourdon Tube

A

Cylinder Pressure Gauge

coiled party blower  hollow metal tube bent into curve, sealed, linked to clock like mechanism with opposite end connected to gas source
* increased gas pressure: inside tube straightens
* decreased gas pressure: tube resumes curved shape
* Movement of sealed end transmitted to an indicator –> moves over calibrated scale (kPa, +/- PSI)

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32
Q

Scale for cylinder, pipeline, machine working pressures?

A

PSI or kPa

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33
Q

Breathing system pressures?

A

usually cm H2O

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34
Q

Cylinder regulators

A

–Allow maintenance of constant flow with changing of supply pressure
–Bring high pressures of gas cylinders down to more reasonable, safe working pressure (40-55psi)
* no regulator: provider constantly altering flow control valve to maintain constant flow through flow meter as pressure and cylinder decreased
* Prevent fluctuations in pressure as tank empties

Required for each gas supplied from cylinder

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35
Q

What regulators are adjustable vs what regulators set by manufacturer?

A

 Pipeline regulators = adjustable
 Machine regulators set by manufacturer

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36
Q

ASTM standards for pressure regulators

A

regulators on anesthesia machines to be set to preferentially use pipeline gases before using gas on the backup cylinder
* Ensure pipeline pressure set 5psi higher than machine’s regulator for reserve oxygen cylinder

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37
Q

Intermediate

A

o Accepts gas from pressure regulator/central pipeline to flush valve/flow meter on AM
 40-55PSI
 Multiple routes through intermediate area: flowmeter, flush valve, auxiliary

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38
Q

How does oxygen enter the immediate pressure portion of circuit?

A

o Oxygen enters via master switch  when off, pressure in intermediate system = 0
 Downstream of inlets for cylinder, pipeline supplies
 O2 flush = independent of switch

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39
Q

Pipeline Inlet Connections

A

entry pt of gasses from pipeline, Diameter Index Safety System (DISS) connections
 Unidirectional (check) valve: prevent reverse gas flow from machine to piping system
 Filter required: pore size <100m, can become clogged –> decreases gas flow

40
Q

Pipeline Pressure Gauge

A

50-55psi
 Indicator: pipeline side of check valve
* Machine side: would not give true indication of pipeline pressure unless cylinder valves closed
 If pressure from cylinder (open valve) > pipeline, gas drawn from cylinder
* Always close valve of attached cylinder when using pipeline

41
Q

Gas Power Outlet

A

o Gas power outlet: serve as source of driving gas for ax ventilator HALLOWELL
 Not found on machines with built-in ventilators

42
Q

Oxygen Pressure Failure Devices

A

alarm when oxygen pressure fallen to dangerous level

Mitigate depletion of oxygen supply, deliver 100% anesthetic agent

43
Q

Oxygen Failure Safety Device

A

shuts off or proportionally decreases, ultimately interrupts supply of N2O if oxygen supply pressure decreases
 Will also interrupt supply of other gases to their flow valves
 Depends on pressure, not flow

44
Q

Oxygen Supply Failure Alarm

A

<30PSI, medium priority alarm that cannot inactivate

Depends on pressure, not flow

Do not prevent ax gas from flowing if no O2 flow, delivery hypoxic mixture

45
Q

Oxygen Flush

A

directs high unmetered flow directly to common gas outlet from pipeline inlet or cylinder pressure regulator
 Independent of master switch, vaporizer

46
Q

O2 Flush FR, pressure

A

 Flow rate: 35-75L/min
 ~50psi

47
Q

MOA Oxygen Flush

A

button, stem connected to ball with ball in contact with a seat
* Button pressed: forced away from seat allowing oxygen to flow to outlet
* Spring opposing ball will close valve when button not pressed

48
Q

ASTM Standards for Oxygen Flush

A

front of machine, recessed (avoid accidental activation)

49
Q

Hazards Assoc with Oxygen Flush

A

accidental activation, leaking, sticking  delivery of oxygen-enriched mixture if using medical air, barotrauma
* Activation during inspiration by ventilator: delivery of high VT, +/- barotrauma
* Not a problem in ventilators that exclude FGF from circuit
* Avoid activating with NRB, low vol circuits (pediatric circle systems)

50
Q

Flow Adjustment Control

A

regulate flow of air, oxygen, other gases to flow indicators
 Two types: mechanical, electronic
 Only one control per gas, must be adjacent to/identifiable with associated FM

51
Q

Mechanical Flow Adjustment Control

A
  • Used with both mechanical, electronic FMs
  • Stem, seat: fine threads, stem only moves short distance when complete turn made
  • Control knob: O2 = largest, fluted profile, distinct look/feel from other gas control knobs
52
Q

Mechanical Flow Control Knob

A
  • O2 = largest, fluted profile, distinct look/feel from other gas control knobs
    o Counterclockwise increases flow
    o +/- shield or bar to prevent accidental movement
    o Should be turned off when not in use
53
Q

Mechanical Flow Adjustment Control

A

o Closed valve: pin at end of stem in seat –> occludes orifice, no gas flow
o Open valve (stem outward): opening btw pin, seat –> gas flows through valve; larger space, greater gas flow

Stops:
 Off: avoids damage to valve seat (why shouldn’t overturn to close)
 Maximum: prevents stem from becoming disengaged with body

54
Q

Problems with Flow Adjustment Control

A

control knob sensitive if worn or loose, stem/seat can block flow

55
Q

Electronic Flow Control

A
  • Knob turned clockwise to increase flow, solenoid valve
  • Air-ox or ox-N2O: One control regulates oxygen concentration, another controls total flow
  • Flow/pressure transducers, temperature sensors maintain accuracy
56
Q

Low Pressure

A

downstream of flow control devices, slight above atmospheric pressure, variable pressures

57
Q

Flowmeters

A

indicate rate of flow of gas passing through them
 Control rate of gas delivery to low pressure area of ax machine, determine FGF to ax circuit
 1 per gas on machine

Electronic or Mechanical

58
Q

Electronic FMs

A

representation of mechanical FM on screen, # representing flow

59
Q

Mechanical FMs

A

Flow past resistance is proportional to pressure

60
Q

Thorpe Tube

A

vertical glass (Pyrex) internally tapered tube with freely mobile indicator
o Narrowest portion at bottom

61
Q

Single Taper Thorpe Tube

A

opening gradually increases from bottom to top, different tubes for high and low flows

62
Q

Double Taper Thorpe Tube

A

two tapers inside same tube for fine, coarse flows; opening size increases more rapidly >1L/min

63
Q

MOA Thorpe Tube

A

Open control valve, gas enters bottom, elevates indicator, flows through annular opening btw indicator and tube, to outlet at top of tube

 Indicator floats where downward force caused by gravity = upward force caused by gas pressure at bottom of cylinder
 increased gas flow: # gas molecules hitting indicator increases, indicator rises, size of annular opening increases (tapered tube), more gas flows
 decreased gas flow: gravity causes indicator to lower

64
Q

What factors affect rate of flow through Thorpe Tube?

A
  1. Pressure drop across constriction
  2. Size of Annular Opening
  3. Physical Properties of Gas
  4. Temp/pressure
65
Q

Thorpe Tube: pressure drop across constriction

A

 As gas flows around indicator, frictional resistance btw indicator, tube wall –> loss of energy = pressure drop
 Pressure drop constant for all positions in tube, = weight of float/cross sectional area

66
Q

Thorpe Tube: Size of Annular Opening

A

Annular cross-sectional area varies while pressure drop across indicator remains constant for all positions in tube

Constant pressure flowmeters

Increased flow does not increase pressure drop, causes indicator to rise to higher position in tube –> greater flow area for gas

67
Q

Thorpe Tubes: low GF, narrow opening

A

Low gas flow through tube, narrow annular opening
* Longer, narrower constriction
* Laminar flow, HP – flow is function of gas viscosity

68
Q

Thorpe Tubes: high GF, larger annular opening

A
  • Shorter, wide constriction
  • Turbulent flow, Graham’s Law – flow function of gas density
69
Q

Thorpe Tubes: Temp, Pressure Calibration

A

Calibrated at atmospheric pressure (760 Torr), room temp 20*C

 Temp, pressure changes –> changes viscosity, density of gas, influence accuracy

 Calibration: flow at ambient pressure = flow indicated on scale calibrated at sea level * (density of gas at sea level/density of gas at ambient pressure)

70
Q

Hyperbaric Chamber Flow Rates/FMs

A

FM delivers less gas than indicated

71
Q

Lower barometric pressure/higher altitude

A

actual flow rate greater than that indicated
* Gas less dense
* Less atmospheric pressure, lower flow will raise ball so flow will be more than sea level

72
Q

Mechanical FM Assembly

A

tube through which gas flows, indicator, stop at top of tube, scale
* Empties into common manifold (mixing chamber) that delivers measured amt of gases into low pressure system

73
Q

Indicators: nonrotating float

A

o Reading: upper rim
o Gas flow keeps in center of tube if tube vertical

74
Q

Indicators: rotameters (rotating floats)

A

o Reading: upper rim

o Upper rim diameter larger than body with slanted grooves in rim, causes float to rotate when gases passes

o Visual indicator gas flowing, indicator not stuck in tube

o Prevents fluctuations, reduces where slashed hair, assists passage of small particles, reduces errors caused by friction between tube and indicator

75
Q

Indicator: Ball

A

o Reading: middle of ball
o Rib guides hold in center of tube
o Rotation = ball can move freely in tube, reading accurate

76
Q

Where is the greatest accuracy on a FM?

A

Middle of the tube

77
Q

Stop

A

at top of FM tube, prevents indicator from plugging outlet – damages tube
* Prevents indicator from ascending to point cannot be seen, difficult to ensure off

78
Q

FM Tube Arrangement

A
  • FMs for different gases = side by side
  • Meet at common manifold/mixing chamber
  • Can have two FMs for same gas: one for low, one for high flows
79
Q

If have two FMs for same gas…

A

o Arranged in series – total flow NOT sum, total flow = flow shown on higher flow tube
o One flow control meter for both tubes
o Gas from flow control valve first passes through tube calibrated up to 1L/min, then passes to second tube calibrated for higher flows

80
Q

If have multiple FMs…

A

o Oxygen FM always most downstream/next to manifold outlet so that leak upstream results in loss of other gas, not oxygen
o Placement of air vs N2O variable

81
Q

Auxiliary FM

A
  • Self-contained FM with own flow control valve, flow indicator, outlet
  • Short tube, max flow ~10L/min, barbed fitting on outlet
  • Used to supply oxygen to patient without turning on anesthesia machine
82
Q

Problems with FM

A

FM scale, tube, indicator = unit, cannot replace individual parts

Tube assembly calibrated for one gas cannot be used for different gas

Degree of inaccuracy that will occur depends on gases for which flow meters were intended
o If gases of similar densities/viscosities, difference in accuracy minimal

Use of wrong FM common with air, N2O bc no standard order

83
Q

Problems with FM Indicators

A

Damage caused by sudden projection to top of tube when cylinder opened or pipeline hose connected with flow control valve open,
o Worn by handling
o Dislodgement of stop, rests on top of indicator

84
Q

FM Leaks

A
  • Leak downstream of indicator, upstream of common manifold = lower than expected concentration of gas in fresh gas
85
Q

FM ASTM Standards

A

O2 knob must be uniquely shaped (fluted)
O2 knob must be the right most side of FM bank downstream of all gases (to prevent anoxic mixtures)
O2 always set downstream to avoid anoxic mixture

86
Q

Hypoxia Prevention Safety Devices

A

Mandatory Minimum Oxygen Flow
Minimum Oxygen Ratio

87
Q

Mandatory Minimum Oxygen Flow

A
  • Minimum flow of oxygen (50-250mL/min) before other gases will flow, set by manufacturer
  • +/- alarm
  • Does not in itself prevent hypoxic gas mixture from being delivered
88
Q

Minimum Oxygen Ratio

A

Protection against operator selected delivery of mixture of oxygen, N2O with oxygen concentration < 21% in fresh gas or inspired gas

Two types: mechanical, electric linkage

89
Q

Minimum Oxygen Ratio: Mechanical Linkage

A

14 tooth sprocket on and two O flow control valve, 29 tooth sprocket on oxygen control valve

If 25% oxygen concentration reached, pin on oxygen sprocket engages pin on oxygen flow control knob –> Couples turning of oxygen, and two oh valves to maintain minimum 25% oxygen

Allows for independent control of each gas as long as percentage of oxygen above minimum

90
Q

Minimum Oxygen Ratio: Mechanical Linkage if increase N2O flow below ratio…

A

O2 flow increased

91
Q

Minimum Oxygen Ratio: Mechanical Linkage if lower O2 flow too much…

A

N2O lowered proportionally

92
Q

Electric Linkage

A

o Provides minimum ratio of oxygen to N2O flow
o Electronic proportionally valve controls oxygen concentration in fresh gas, computer continuously calculated maximum allowable amount nitrous oxide flow given oxygen flow

93
Q

Unidirectional Valves

A

Can have PP transmitted back to machine from BS with controlled or assisted ventilation or with use of oxygen flush valve

Valve = located vaporizers, common gas outlet
* upstream of where oxygen flush joins fresh gas flow
* Valve will lessen pressure increase but not prevent it – gas continually flowing from flow meters

94
Q

Pressure Relief Devices

A

 Near common gas outlet to protect machine from high pressures
 valve opens to atmosphere, vents gas to atmosphere if preset pressure exceeded
 May limit ability of anesthesia machine to provide adequate pressure for jet ventilation

95
Q

Common Gas Outlet

A

AM –> BC

Receives all gases, vapors from machine - delivers mixture to BS at concentration, flow rate determined by vaporizer setting, flow rates

Common location for disconnection

Fresh gas supply tube, conveys gas to fresh gas inlet and breathing system attaches to common gas outlet

Outlet gas does not usually equal inhaled concentration when using rebreathing circuits – dilution of incoming gas with what is already in the patient circuit

96
Q

What size is the connection btw the common gas outlet and the breathing system?

A

15mm (???)

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