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Boards: Machines, Physics > Ventilators > Flashcards

Ventilators Flashcards

1
Q

Direction of Bellows

A

Based on how fill on expiration

Ascending: rise on exhalation, aka standing

Descending: drop on exhalation, aka hanging

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2
Q

Disadvantages of descending bellows

A

–Draw air out of patient’s airway during expiration DT weight on bottom of bellows
–Increases work of breathing to raise bellows during inhalation (SpV)
–Can also generate sub atmospheric pressure during early part of expiration if expiratory flow not impeded, low FGFs

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3
Q

Advantages of Ascending Bellows

A

Less WOB

Does provide 2-4cm H2O PEEP

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4
Q

Leaks - Descending Bellows

A

with leaks – air dilution as bellow expands, will not reach bottom

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5
Q

Leaks - Ascending Bellows

A

detect leaks in BC by failure to rise completely

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6
Q

Summary of Pneumatic Driving Mechanism

A

compressed gas (~45-50psi) flows into bellows canister –> compression of accordion bellows –> delivery of breath

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7
Q

Summary Of Piston

A

electronically driven piston compresses bellows

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8
Q

LA Ventilators: Drager, Narkovet E, Surgivet

A

Dual circuit
Volume limited
Time cycled (fluid in drager, electronics in Narkovet, Surgivet)
Pneumatically driven
Descending Bellows

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9
Q

LA Ventilators: Mallard

A

Dual circuit
Volume limited
Time cycled
Pneumatically driven
ASCENDING Bellows

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9
Q

LA Ventilators: Tafonius

A

Single Circuit
Volume Limited
Time, volume cycled (electronic)
Piston

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10
Q

LA Ventilators: JD Medical/Bird

A

Dual Circuit
Pressure Limited
Time Cycled
Pneumatically Driven
Descending bellows

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11
Q

SA Ventilators: Mallard, Hallowell, Omega, Surgivet

A

Dual
Volume Limited
–Omega 7000 has preset minute volume
–7800 preset VY
Time cycled (all electronic)
Pneumatically driven
Ascending bellows

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12
Q

SA Ventilators: Ohio, Drager

A

Dual
Volume Limited
Time cycled - both fluid circuits
Pneumatically driven
DESCENDING bellows

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13
Q

SA Ventilators: Vetronics

A

Single Circuit
Volume limited
Time, pressure, volume cycled
Piston

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14
Q

SA Ventilators: Engler

A

Pneumatic, pressure limited ventilator

No bellows, FM, RBB: acts like NRB (no CO2)

Delivers inhalant only during inspiration via VDG through vaporizer, inflates lungs via positive pneumatic pressure

RR, PIP, FR controlled by device

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15
Q

Barotrauma

A

injury resulting from high airway pressure

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16
Q

Compliance

A

ratio of change in vol to change in pressure
o Measure of distensibility, usually expressed in mL/cm H2O

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17
Q

Continuous positive airway pressure (CPAP)

A

airway pressure maintained above ambient, usually in reference to SpV

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18
Q

Exhaust valve

A

valve in vent with bellows that opens to allow driving gas to exit bellows housing

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19
Q

Expiratory Flow Time

A

time between beginning, end of expiratory flow

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20
Q

Expiratory pause time

A

time from end of expiration flow to start of inspiratory flow

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21
Q

Fresh Gas Compensation

A

means to prevent FGF from affecting VT by measuring actual VT, using information to determine delivered VT

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22
Q

Fresh gas decoupling

A

means to prevent FGF from affecting VT by isolating FGF so doesn’t enter breathing system during inspiration

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23
Q

Inspiratory Flow Time

A

period btw beginning, end inspiratory flow

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24
Q

Inspiratory Pause Time

A

portion of inspiratory phase time during which lungs held inflated at fixed pressure or volume – ie time during which inspiratory phase has zero flow

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25
Q

Inspiratory Phase Time

A

time btw start of insp flow, beginning of expiratory flow
o Sum of inspiratory flow, insp pause times

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26
Q

IE Ratio

A

ratio of inspiratory phase time to expiratory phase

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27
Q

Inspiratory Flow Rate

A

rate at which gas flows to patient expressed as vol per unit time

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28
Q

Inverse ratio ventilation

A

ventilation in which inspiratory phase time longer than expiratory phase time

Possible for negative CV effects

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29
Q

Minute Volume

A

sum of all VT within one minute

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30
Q

Peak Pressure

A

maximum pressure during inspiratory phase time

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31
Q

Plateau Pressure

A

resting pressure during inspiratory pause, airway pressure usually falls when inspiratory pause – lower pressure = plateau pressure

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32
Q

PEEP

A

airway pressure above ambient at end of exhalation, CMV

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33
Q

Resistance

A

ratio of change in driving pressure to change in FR, commonly expressed in cm H2O per second

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34
Q

Sigh

A

deliberate increase in VT for one or more breaths

Equivalent of ARM

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35
Q

Solenoid

A

component that controls pneumatic flow by means of electronic signal

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36
Q

Spill Valve

A

valve in ax vent that allows excess gases in BS to be sent to SS after bellows or piston has become fully filled during exhalation

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37
Q

VT

A

vol of gas entering or leaving patient during insp, exp phase time

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38
Q

Volutrauma

A

injury DT overexpansion of lungs

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39
Q

Work of Breathing

A

energy expended by patient +/- ventilator to move gas in/out of lungs
o Expressed as ratio of work to vol moved, joules per liter
o Includes work needed to overcome elastic, flow-resistance forces of both resp system, apparatus

40
Q

Purpose Ventilator

A

provide patient ventilation control; replaces reservoir bag and APL valve with bellows/piston chamber and spill valve

41
Q

Basic MOA Dual Circuit, Pneumatically Driven Ventilator

A

Bellows housed in pressure chamber: inside of bellows connected to BS

Bellows acts as interface btw BS, VDG
* Separates breathing system gas from driving gas
* Pressure of anesthesia provider’s hand replaced by driving gas pressure that compresses bellows

42
Q

Pneumatically Driven: Inspiration

A

driving gas delivered into space between bellows, housing
 Causes bellows to be compressed  gas flows into breathing system
 At same time, spill valve (which vents excess gases to scavenging system) and exhaust valve (which vents driving gas) closed

43
Q

Pneumatically Driven: Expiration

A

bellows re-expand as breathing system gases and fresh gas flow into it

Driving gas vented to atmosphere through exhaust valve

After bellows fully expanded, excess gas from BS vented to SS through spill valve

44
Q

Piston Driven MOA

A

Electronically driven piston, eliminates need for drive gas circuit

Reservoir bag not isolated from BS during exhalation phase of automatic ventilation
* RB acts to modulate pressure increases in system

45
Q

Piston: Inspiration

A

piston forces gases into breathing system
* Bag isolated from the breathing system
* Bag collects FGF entering BS
* Some ventilators: bag can be seen to expand, contract with respiration even though piston actually ventilating patient (eg Fabius)

46
Q

Major Control Variable for Ventilators

A

Volume limited: Deliver set volume to patient regardless of airway pressure, stops when preset volume reached

Pressure limited: PIP determines ventilator’s action, regardless of VT
–variable based on compliance/resistance, insp flow rate, leaks, insp time, location of pressure sensor

47
Q

Power Source

A

What is required to operate mechanical ventilator: compressed gas, electricity, both

Most modern ventilators: some electrical components regardless of what actually produces PPV

48
Q

Circuit Drive Mechanism

A

Compressed gas (pneumatically driven) or electronically driven mechanical device (piston)

Compressed gas ventilators: dual circuit – two gas circuits; one for ventilator, one for breathing circuit
 Single circuit ventilators: do not use gas to power ventilation

49
Q

Can ventilators be set as dual or single circuits?

A

Yes - Bird Mark, Penlon Nuffield

Can be combined with bellows canister system (bag in a box) to create dual circuit ventilator

Lack of physical barrier potentially allows mixing of gas from circuit used to power ventilator with gas from patient circuit
* FGF ensures that mixing of driving gas, circuit gas doesn’t cause rebreathing

50
Q

Cycling Mechanism

A

Most = timing

Electronic microprocessor or fluid logic (older ventilations)

51
Q

Electronic Microprocessors for Cycling Mechanism

A

open, close valves allowing gas to drive ventilator or activate movement of piston

52
Q

Fluid Logic Units

A

Use compressed gas normally at constant pressure to activate timing valves for inspiration and expiration
* Amt of gas needed to activate timing valves, hence inspiratory/expiratory times, can be altered by increased or decreased flow of gas into timing valve
* Valves open and closed by changes in gas pressure within timing valves
* Pressure used to produce predictable fluid timers

Related to Coanda effect

53
Q

Which ventilator(s) are pressure cycled?

A

Bird, Engler

 Timing of inspiration function of duration of time required to attain specific pressure within patient circuit during PPV
 Cycling duration modified by gas FRs driving ventilator, changes in patient lung compliance
 Inspiration continues until specific threshold achieved regardless of time required to achieve pressure

54
Q

Components of Single Circuit Ventilators

A

 Cylinder
 Piston
 Linear actuator
 Rolling diaphragms
 Positive/negative pressure relief valve

55
Q

Single Circuit Piston Ventilators: Advantages

A

Use electronically controlled pistons to compress gas in BC - eliminates need for second circuit (driving gas)
 More precise delivery of VT, not influenced by presence of compressible driving gas

More efficient in terms of gas: additional gas not required to drive ventilator

56
Q

MOA Single Circuit Ventilators

A

2 rolling diaphragms that seal piston to prevent mixing of ambient and patient circuit gas
* Lower: seals breathing gas below piston in BS
* Upper seals upper side of lower diaphragm from ambient air to create space between 2 diaphragms
* Vacuum applied to space, holds two diaphragms tightly against piston, cylinder walls

Piston moves downward, space below lower diaphragm decreases, forcing gas into patients lungs

At end of inspiration patient exhales piston rises

57
Q

Piston Driven Ventilators: Expiration

A

piston moves in response to measured airway pressure, measured at Y piece
* When airway pressure increases by .5 cmH2O, piston moved up enough to bring airway pressure back to 0
* Correction made Q5ms (200 times per second), ensures no resistance to exhalation

58
Q

Bird Mark, Penlon

A

Key about single circuit: patient gas and ventilator drive gas move within same continuous circuit

No physical barrier between ventilator drive gas, patient gas

Can turn into dual circuit by combining with bellows in a canister

59
Q

Circuits used with a Bird Mark or Penlon

A

Non rebreathing FR/NRB systems, prevent contamination of patient circuit with ventilator drive gas
 Best suited for smaller patients
 Possible to ventilate up to ~1000mL: efficiency of gas (oxygen, inhalant) consumption required markedly reduced

60
Q

Penlon Nuffield

A

long corrugated tube that acts as a ‘reservoir,’ replaces rebreathing bag

Reservoir tube responsible for both exhaled, VDG

Inspiration: Patient valve closes, forcing ventilator driving gas into reservoir tube - compressing circuit gas back toward patient

Expiratory pause: patient valve opens, allowing ventilator driving gas to exit system via spill valve as pressure within circuit drops back to 0
–Followed closely by expired gas via high FGF

61
Q

Penlon Nuffield - Key Points

A

–Must have adequate FGF to prevent rebreathing
–VT: volume of drive gas delivered by ventilator + volume of FGF entering circuit during inspiration

62
Q

Dual Circuit

A

Physical separation btw two circuits of gas via compliant bellows

Primary: continuous with patient circuit = bellows, spill valve

Second: driving gas used to compress bellows

63
Q

Dual Circuit: Inspiration

A

Drive gas allowed into bellows housing for a specific period of time, delivered at specified rate –> housing exhaust valve closed –> compression of bellows, closing of spill valve –> gas enters patient’s lungs

64
Q

Dual Circuit: Expiration

A

Expiration: driving gas discontinued, housing pressure/patient circuit pressure drop –> gas in bellows housing allowed to escape from exhaust valve –> passive patient exhalation into bellows

Spill valve reopens: FGF from patient circuit to escape - prevents pressure from building up within patient circuit

65
Q

Ascending/Standing Bellows

A

o Up during expiration
o Spill valves normally pose slight resistance to opening: slight PEEP (2-4cm H2O) in system to counteract tendency of bellows to collapse DT their weight, elastic nature
–Can be mitigated by application of slight vacuum to interior of bellows housing

Advantage: bellows will fail to expand fully, progressively collapse if leak in BS

66
Q

Descending/Hanging Bellows

A

o Down during expiration
o Descent during expiration = passive, facilitated by weight placed in dependent portion of the bellows
o Can cause slight negative pressure in bellows/BS: if leak or disconnect, weight of bellows will cause normal expansion –Extraneous gases drawn into BS via leak, negative pressure relief valve

Increased WOB

67
Q

Detecting a Leak with Hanging Bellows

A

gas in BS diluted by non-anesthetic gases, but all or some of inspiration lost through leak
 Difficult to visually assess leaks vs ascending

Essentially bellows that fall very slowly or do not fall completely before next inspiration occurs

68
Q

Bellows Housing

A

Clear plastic, direct observation of bellows movement

69
Q

Exhaust Valve

A

Communication between inside of bellows housing, external atmosphere on pneumatically driven ventilators

Inspiration exhaust valve closed: DG builds pressure within housing, bellows compress driving air into patient

Exhalation: exhaust valve opens, DG stops, pressure decreases, bellows reexpand

70
Q

Spill Valve

A

Replaces function of APL valve (closed during CMV)
Directs excess FG from BS into SS during exp pause

Insp: valve closed to prevent escape of gas into SS, allow PP to develop within circuit
 Standing bellows: spill valve has normal opening pressure of 2-4cm H2O to offset downward force created by weight of bellows, allows complete filling during exhalation
 Normally controlled pneumatically in ventilators using gas to compress bellows, open/closed electronically with piston

71
Q

VDG

A

DG supplied to ventilator normally under intermediate pressure, 35-55 PSI

DG = typically 100% oxygen
 Minimizes potential for decreased O2 concentration should leak develop between 2 ventilator circuits

72
Q

Control of VDG

A

Electronic

 Inspiratory time: Duration of time DG allowed in bellows housing
 Inspiratory Flow Rate: rate at which DG flows into bellows housing
 Expiratory Time: pause between inhalations

Manipulation of above 3 variables leads to control RR, VT, IE ratio

73
Q

How FGF Affects VT

A

Increasing FGF, prolonging inspiratory time = larger VT

Significant in very small patients: FGF 1L/min +17mL of gas to VT during inspiration

74
Q

How Compliance, Compression Volumes Affect VT

A

Increases in compliance of breathing system, decrease patient Vt - more of delivered gas volume expended expanding breathing components

  • Gas volume compressible when subjected to increasing pressure
75
Q

How Leaks Affect VT

A

Gas escapes through leaks = reduction of delivered VT

Side stream airway gas monitors aspirate small volume of gas from BS (50-250mL/min, 0.4-0.8mL/s)

76
Q

Alarms for Ventilators

A

No standard alarm configurations for veterinary anesthesia ventilators

Low driving gas pressure alarm: when DG pressure < 35psi
* Decrease in DG pressure below a certain level - possible decrease in delivered VT

77
Q

VT On Most Pneumatically Driven Ventilators

A

Tidal volume on most pneumatically driven ventilators limited by:
1. FR of gas entering bellows housing
2. duration of time gas is allowed to enter bellows

78
Q

VCV

A

preset VT

If inspiratory flow too low to provide set VT, bellows/piston will not complete excursion

If flow set at faster rate than needed to provide VT = inspiratory pause

Excessively high PIP if inspiratory FR too high

Inspiratory phase may be terminated before VT delivered if peak airway pressure reaches set pressure limit

79
Q

VCV - pressure waveform

A

Steadily increases during ventilation

80
Q

VCV - volume waveform

A

Identical each breath

81
Q

VCV - flow waveform

A

Square top appearance bc gas flow constant while waiting to achieve volume

82
Q

Delivery of VT with CVC

A

For given VT, pressure in BS determined by resistance, compliance of BS, patient

Adding PEEP decreases TV delivered
* Effect greater with small TV

83
Q

PCV

A

Operator sets inspiratory pressure at level above PEEP, vent quickly increases pressure to set level at start of inspiration –> maintains pressure until exhalation begins

84
Q

PCV: flow waveform

A

o Inspiratory flow gas highest at beginning of inspiration, then decreases

Increased resistance may change shape of flow vs time waveform = flatter, more square-shaped pattern
* DT VT delivery shifting to latter part of inspiration

Spikey

85
Q

PCV: volume waveform

A

TV not set/constant - fluctuates with changes in resistance/compliance, with patient-ventilator asynchrony

If resistance increases or compliance decreases, VT will decrease

86
Q

PCV: volume waveform

A

will change with each pressure bc based on thoracic compliance

87
Q

Synchronized Intermittent Mandatory Ventilation

A

Synchronizes ventilator-delivered breaths with patient’s spontaneous breaths

If patient inspiratory activity detected, ventilator synchronizes its mandatory breaths so set resp frequency achieved

Trigger time: ventilator checks whether airway pressure has dropped minimum amount below pressure measured at end of expiratory phase
 Drop not sensed –> vent delivers a breath

88
Q

Pressure Support

A

Augments patient’s spontaneously breathing by applying positive pressure to airway IRT patient initiated breaths

Pressure or flow initiated

Provider must set trigger sensitivity, inspiratory pressure
 Triggering sensitivity set so that will respond to inspiratory effort without auto cycling in response to artefactual changes in airway pressures

89
Q

Engler - features

A

o Non rebreathing circuit (unidirectional circuit)
o No bellows housing, no piston
o No canister for chemical CO2 absorbent
o Not intended for connection to other BS

Also no FM, RBB, no one way valves

90
Q

Engler - Requires

A
  1. precision vaporizer
  2. breathing hose
  3. O2 supply 50psi
  4. Scavenging system that functions as ax delivery system
91
Q

Engler - MOA

A

Ventilation drive gas moves through vaporizer, only delivers gas (and anesthetic) to patient during inspiration

Intermittent bursts of oxygen at high flow rates 2-60L/min - inflates lungs via positive pneumatic pressure

Oxygen 50 PSI for normal mode, 5 PSI for laboratory/low flow mode

Exhaled CO2 washed out via scavenge

92
Q

Engler - limitations

A

Concern about accuracy of vaporizer output from intermittent nature of carrier gas delivery to vaporizer - VDG moves through vaporizer

Gas FR required to produce VT required for larger patients may fall outside recommended flow rates for most vaporizers

93
Q

Engler - limitations

A

Concern about accuracy of vaporizer output from intermittent nature of carrier gas delivery to vaporizer - VDG moves through vaporizer

Gas FR required to produce VT required for larger patients may fall outside recommended flow rates for most vaporizers

94
Q

JD Medical’s LAV-2000, 3000 series LA ventilators

A

Combined with Bird: Dual-circuit, pressure-limited, time cycled, pneumatically controlled/driven with descending bellows configuration

When operating, Bird ventilator supplies gas to pressurize space btw bellows, bellows housing (canister) = force bellows in upward motion delivering gases from bellows, through interface hose, to BS

95
Q

Bird Ventilator - cycling mechanism

A

o Manometer, hand timer (push-pull mechanism) used to initiate/end respiration

pressure cycled ventilator unless push-pull manual cycling rod pulled out  time cycled

96
Q

Manual Resuscitators

A

o Compressible, self-expanding bag, bag-refill valve, NRB valve
o +/- attachment for oxygen

97
Q

Demand Valves

A

Deliver oxygen when patient begins to inspire creating slight negative pressure that activates gas delivery

Manual delivery via compression of activation button

Disconnected from ETT after inspiration, decrease resistance to exhalation

98
Q

Demand Valves Flow Rates

A

High inspiratory flow rate desirable in large animals
 Low inspiratory flows: excessively long inspiratory time in patients requiring large VT

Maximum flow rate of approximately 160L/min at 50PSI, low flow 40L/min

Hudson demand valve: 200L/min if oxygen supply pressure 50 PSI, >275L/min if 80PSI

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