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Fall 2013 Anesthesia Concepts > Anesthesia Ventilators > Flashcards

Anesthesia Ventilators Flashcards

1
Q

What is compliance?

A

Compliance is the ratio of change in volume to change in pressure. It is a measure of distensibility. delta V to delta P.

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2
Q

What is resistance?

A

The ratio of change in driving pressure to change in flow rate. delta P: delta Q

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3
Q

What is expiratory flow time?

A

The time between the beginning and end of expiratory flow.

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4
Q

What is expiratory pause time?

A

The time from end of expiratory flow to start of inspiratory flow.

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5
Q

What is inspiratory flow time?

A

The time between the beginning and end of inspiratory flow.

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6
Q

What is inspiratory pause time?

A

The portion of the inspiratory phase time during which the lung is held inflated in a fixed pressure or volume.

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7
Q

Time, in ventilation, is divided into _________ and _________ periods.

A

inspiratory and expiratory

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8
Q

Time is expressed in _________

A

seconds

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9
Q

What is the I:E ratio?

A

The relationship of inspiratory time to expiratory time

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10
Q

What is volume?

A

The measure of tidal volume delivered by the ventilator to the patient.

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11
Q

Volume is expressed in:

A

mL

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12
Q

For minute ventilation (MV), volume is expressed in:

A

Liters

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13
Q

Pressure is:

A

the impedence to gas flow rate

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14
Q

Impedence is encountered in:

A

the patient’s breathing circuit, the patient’s airways and lungs.

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15
Q

Pressure is the amount of backpressure generated as a result of:

A

airway resistance and lung-thorax compliance

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16
Q

Pressure can be expressed in three terms, they are:

A

cmH2O, mmHg, or kPa

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17
Q

What is flow rate?

A

The rate at which the gas volume is delivered to the patient.

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18
Q

Flow rate is measured from:

A

from the patient connection of the breathing system to the patient.

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19
Q

Flow rate refers to:

A

the volume change over time

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20
Q

Flow rate is expressed in:

A

L/sec or L/min

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21
Q

Constant flow delivers a constant inspiratory pressure regardless of:

A

airway circuit pressure

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22
Q

Describe constant flow when delivered by a high pressure gas source.

A

5-50 psi of pressure allows inspiratory flow to remain constant despite changes in airway resistance or compliance.

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23
Q

Describe constant flow when a low pressure (Venturi) gas source is used.

A

Flow varies to some degree with airway pressure.

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24
Q

Describe non-constant flow.

A

Non constant flow consistently varies with each cycle.

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25
Q

What are constant pressure generators?

A

THey maintain a constant airway pressure throughout inspiration irrespective of inspiratory gas flow. Gas flow ceases when airway pressure equals the set inspiratory pressure.

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26
Q

Ventilators work by_________ __________ ventilation.

A

positive pressure

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27
Q

Each ventilator cycle is divided into 4 phases, they are:

A

Inspiration, Transition from inspiration to expiration, Expiration, and transition from expiration to inspiration.

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28
Q

How are vents classified?

A

By their method of cycling.

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29
Q

Name the 3 methods of ventilator cycling

A

Time cycled, Volume cycled, Pressure cycled.

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30
Q

Are vents classified by their inspiratory or expiratory characteristics?

A

By their inspiratory characteristics

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31
Q

Why are we mostly concerned with how vents perform on inspiration?

A

Expiration is a passive process, it depends more on airway resistance and lung compliance. We control the inspiratory part.

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32
Q

Describe time-cycled ventilation

A

Cycle to the expiratory phase once a predetermined interval elapses from the start of ventilation. Tidal volume is a product of the set inspiratory time and inspiratory flow rate.

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33
Q

Describe volume cycled ventilation.

A

Terminates inspiration when a preselected tidal volume is delivered. Most adult vents are V-cycled but have a second limit on inspiratory pressure to guard against barotrauma.

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34
Q

In volume cycled ventilation is the total Tidal Volume always delivered?

A

No, a percentage of TV is always lost to the compliance of the system. Usually about 4-5cc per cmH2O of pressure.

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35
Q

Describe pressure cycled ventilation.

A

Cycle into the expiratory phase when airway pressure reaches a predetermined level. Tidal volume and inspiratory time vary.

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36
Q

Decribe flow cycled ventilation.

A

Have pressure and flow sensors that allow the vent to monitor inspiratory flow at a preselected fixed inspiratory pressure. When this flow reaches a predetermined level, the vent cycles from inspiration to expiration.

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37
Q

What are the 3 different power sources for anesthesia vents?

A
  1. compressed gas-gas only 2. piston-powered only 3. compressbile bellows-gas and power.
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38
Q

What are the 2 different drive mechanisms for anesthesia vents?

A
  1. double circuit-bellows compressed by driving gas and pneumatically driven 2. piston-bellows compressed by electricity.
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39
Q

How are bellows classified?

A

Teh direction of bellows movement during Expiration determines this classification. They are either ascending or descending.

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40
Q

How do ascending bellows work?

A

Bellows rise from bottom on expiration

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41
Q

How do descending bellows work?

A

They descend from the top during expiration.

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42
Q

Which type of bellows is also called “standing” bellows?

A

Ascending

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43
Q

Which type of bellows is also called “hanging” bellows?

A

Descending bellows

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44
Q

Will we see hanging bellows in practice today?

A

No, they were deemed unsafe and could give false affirmation of patient respiration if they fell on their own when pressure falls surrounding the bellows.

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45
Q

Which type of bellows is this

A

Ascending or standing

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46
Q

Which type of bellows are depicted in this picture?

A

Descending or hanging

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47
Q

The cycling mechanism is found in older machines. Most of the anesthesia vents currently are:

A

time-cycled, electronically controlled with a volume-limiting aspect.

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48
Q

The bellows separate the _______ gas from the __________.

A

driving gas from the patient gas circuit.

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49
Q

What happens in the chamber surrounding the bellows during the inspiratory phase?

A

The driving gas enters the chamber and increases pressure.

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50
Q

The increase in pressure in the chamber that surrounds the bellows causes what 2 things to occur?

A
  1. The ventilator relief valve closes so no gas can escape to the scavenger 2. THe bellows are then compressed and the gases in the bellows are delivered to the patient (analogous to you squeezing the bag)
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51
Q

During expiration, what happens to the drive gas in the bellows chamber?

A

It exits

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52
Q

What happens to the ventilator relief valve of the bellows during exhalation?

A

The ball-type ventilator-relief valve opens when the drive gas pressure drops to zero. .

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53
Q

When, during the exhalation does scavenging occur from the bellows?

A

Exhaled pt. gas fills the bellows before any scavenging occurs, because teh valve ball produces 2-3 cm H2O back pressure. Scavenging will only occur when the bellows is filled completely.

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54
Q

The relief valve is only open during __________, and any scavenging occurs at this point.

A

expiration

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55
Q

The traditional vents use a driving gas to power the bellows but the piston vents use:

A

The newer piston vents use electricity to power the vent.

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56
Q

The ventilator is __________ controlled and _________ driven.

A

electronically controlled and pneumatically driven.

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57
Q

What are the 3 ventilator modes on the anesthesia vent?

A

Volume controlled (VCV), SIMV, and Pressure Controlled (PCV)

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58
Q

What are the advantages of the piston ventilator?

A

It is quiet. It has no PEEP. Greater precision in delivered tidal volume. Measuring compliance and leaks with a transducer near the piston, electricity is the driving force of the piston.

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59
Q

Is there PEEP on the older bellows model vent?

A

Yes, there is a mandatory 2-3cm H2O due to the design of the ventilator spill valve.

60
Q

How is there greater precision of delivered tidal volume in the piston vent?

A

due to compliance and leak compensation, fresh gas decoupling, and the rigid piston design.

61
Q

Why is measuring compliance and leaks with a transducer in the piston better than the older vents?

A

It eliminates the need for a costly, bulky sensor close to the patient’s airway.

62
Q

Why is advantageous to have electricity powering the piston vent as opposed to oxygen?

A

If the oxygen pipeline were to fail you would have to rely on oxygen from the emergency cylinder. In the piston, mechanical ventilation can continue without exhausting the cylinder supply simply to drive the bellows.

63
Q

What are some disadvantages to piston ventilators?

A

You lose that familiar visible behavior of a standing bellows during disconnectes, or when the patient is breathing over and above the ventilator settings. It is quiet so it is less easy to hear regular cycling. And it can entrain air and continue to deliver tidal volumes with less oxygen concentration. There is also a potential for NEEP.

64
Q

What is NEEP?

A

It is negative end expiratory pressure. If this occurs you will actually pull fluid into the patients lungs.

65
Q

What is the inspiratory pause/sigh?

A

The pause in an increase in the inhalation time by 25%. The flow of drive gas stops, the gas pressure in the bellows housing system stays the same, the volume of gas to the patient is held in teh pt’s lungs until exhalation begins.

66
Q

This waveform represents inspiration (with or without) a pause?

A

without

67
Q

This waveform represents inspiration (with or without) a pause?

A

With

68
Q

How much tidal volume should we give the patient?

A

10-15 ml/kg

69
Q

What is the normal range for RR we should give to our patients?

A

8-12

70
Q

How do you calculate Minute Ventilation?

A

MV= TV x RR

71
Q

How do you calculate flow rate?

A

Flow rate is about 4-6x the minute ventilation.

72
Q

What is the normal physiologic I:E ratio?

A

1:2

73
Q

How do you calculate the time it takes to inspire? (TI)

A

Tidal volume (mL) divided by flow rate (mL/min) x 60sec.

74
Q

How do you calculate the time it takes for expiration? (TE)

A

Figure out the total time for each ventilation for 1 minute cycle. ex. total 60 sec divided by 12 breaths/60seconds = 5 seconds. Then subtract your inspiration time, so 5-1 =4. This would leave an I:E ratio of 1:4

75
Q

What is the formula for calculating the oxygen concentration of blood (O2/100mL)?

A

(Hgb x %sat x 1.39 mL O2) + (PaO2 x 0.0031 mL O2)

76
Q

One gram of pure Hgb combines with how many mL of O2?

A

1.39 mL

77
Q

For each mmHg of PO2, there is _____ O2/ 100mL of blood.

A

0.0031

78
Q

A normal arterial blood with a PO2 of 100mmHg contains ___ mL of Oxygen.

A

0.3

79
Q

Calculate the oxygen concentration of blood in a patient with a Hgb of 10, Sat of 99% and PaO2 of 100.

A

(Hgb x sat x 1.39 mL O2) + (PaO2 x 0.0031 mL O2) = (10 x .99 x 1.39) + (100 x 0.0031)= 13.76 + 0.31 = 14.07 mL O2/ 100mL

80
Q

When titrating O2, each time you increase the FiO2 by 10%, you increase PaO2 by ‘__________ mmHg.

A

50

81
Q

Rule of thumb when titrating O2 is: If you increase FiO2 _____________

A

you increase SaO2

82
Q

Hypoventilation reduces PaO2 except when?

A

Except when the patient breathes an enriched O2 mixture.

83
Q

If you FiO2 at 21% is 100mmHg, what is it at 30%, 40%, and 50%?

A

Remember, each 10% increase in FiO2 yields an increase in PaO2 by 50mmHg. So 30% = 150mmHg and 40% would = 200mmHg and 50% = 250mmHg.

84
Q

What is the formula for calculating PaO2?

A

PaO2= PIO2 - PaCO2/ R+F where R is the extraction ratio (0.8) and F is the correction factor (small or negligible)

85
Q

What triggers the low pressure or disconnect alarm?

A

a drop in circuit pressure

86
Q

What triggers the sub atmospheric pressure alarm?

A

pressure of < or = to -10 cm H20

87
Q

What triggers the sustained/ continuing pressure alarm?

A

-15 cm H2O for more than 10 seconds

88
Q

What triggers the high peak pressure alarm?

A

excess pressure in the system. Activated at 60cm H2O or set by practitioner

89
Q

What triggers the low oxygen supply alarm?

A

Low oxygen supply.

90
Q

What triggers the ventilator setting alarm?

A

The ven’ts ability to deliver the desired set Minute Ventilation.

91
Q

What is the best monitor for detecting disconnect?

A

ETCO2

92
Q

What is the most important monitor on the machine?

A

The O2 analyzer (calibrate at 21%)

93
Q

Which monitor measures the accuracy of our vent settings and the peak airway pressure?

A

The respirometer

94
Q

What is the very best monitor we have?

A

Vigilance

95
Q

What is the respirometer?

A

An exhaled volume monitor. Clips onto the expiratory limb. It is a tranducer cartridge and tidal volume sensor clip. It converts gas flow into electricle pulses. The sensor clip snaps onto the transducer cartridge.

96
Q

What is the exhaled tidal volume you expect to measure?

A

Vt= Vt (from vent) + Vt (fresh gas flow) - Vt (lost in system)

97
Q

The respirometer will activate the reverse flow alarm when?

A

If flow is going back toward the patient from the expiratory limb

98
Q

The respirometer will trigger the apnea alarm when?

A

If a sufficient breath, based on the Vt settings, is not achieved within 30 seconds.

99
Q

The respirometer will trigger a low minute volume alarm when?

A

the minute volume is low.

100
Q

Which is more powerful, the ICU vent or the anesthesia vent?

A

The ICU vent. they have greater inspiratory pressure and tidal volumes.

101
Q

Does the ICU vent have a CO2 absorber?

A

no

102
Q

Which supports more modes of ventilation, the ICU vent or the anesthesia vent?

A

ICU vent

103
Q

Is there a driving gas in the ICU vent?

A

No, the gas supplied in the ICU vent directly ventilates the patient.

104
Q

Does the driving gas in the anesthesia machine ever reach the patient?

A

No.

105
Q

What is the driving gas used in the anesthesia machine?

A

100% O2 in old machines, a combination of O2/ air in newer machines.

106
Q

Do the ICU and anesthesia vents both have bellows?

A

The ICU vent does not have bellows. Bellows are essential in the anesthesia vents except for in the piston type.

107
Q

What is the most common vent mode used in the OR?

A

Volume Control

108
Q

In which mode of ventilation is a preset TV delivered?

A

Volume Controlled.

109
Q

In Volume Controlled ventilation, which two parameters are set by the practitioner?

A

The TV and RR. These will be independent of pt. effort.

110
Q

How does volume controlled ventilation work?

A

It is time initiated, volume limited, cycled by volume or time. depending on the machine type.

111
Q

The flow rate if fixed in Volume Controlled ventilation. But if the flow rate were to low what would happen? too high?

A

Low- it won’t work. High- it will add a pause or it can cause high peak pressures.

112
Q

In which mode of ventilation does the operator set the inspiratory pressure?

A

Pressure controlled.

113
Q

How does pressure controlled ventilation work?

A

Gas flow decreases as airway pressure rises and ceases when airway pressure equals the set peak inflation pressure.

114
Q

Is TV fixed in pressure controlled ventilation?

A

No. It depends on rise time and set pressure.

115
Q

Unlike ICU vents, increasing inspiratory rate shortens ________ and _________.

A

time and volume

116
Q

When would you use pressure controlled ventilation?

A

In situations where airway pressures may be high. Useful in neonates and premature infants.

117
Q

Which mode (of our 3 anesthesia modes) of ventilation gives mandatory breaths at a preset rate?

A

IMV

118
Q

Does IMV allow for spontaneous breaths?

A

Yes, it will allow unassisted spontaneous breaths.

119
Q

Where does the gas come from for the spontaneous breath?

A

The vent has secondary source of gas flow for the spontaneous breath. Either continuous gas flow within the circuit or a demand valve that opens to allow gas to flow from a reservoir.

120
Q

Which vent mode is a good weaning mode?

A

IMV is used to wean patients off the vent. The rate is gradually decreased.

121
Q

What is the difference between SIMV and IMV?

A

SIMV is synched with the patient’s effort. The pt. breathes spontaneously and at a predetermined interval the spontaneous breath is assisted by the machine. It times the mechanical breath with the beginning of spontaneous effort. It’s good for waking up pt. in the OR.

122
Q

Describe a trigger breath, like in SIMV mode.

A

If the patient has the ability to initiate a breath but lacks the abilty to maintain a rate or tidal volume there is a small trigger window that senses the patient’s efforts and supplies the required TV and rate.

123
Q

What is assist control?

A

An intermittent mode of positive pressure ventilation. The pt’s inspiratory effort causes a sub-baseline pressure in the inspiratory limb of the vent circuit that then triggers the vent to deliver a predetermined TV.

124
Q

In AC mode, if the pt.’s rate drops below a preset minimum rate the machine does what?

A

takes over with controlled vent mode.

125
Q

In AC, are all of the pt. breaths assisted?

A

Yes, all breaths to the pt. are a full assisted ventilator breath.

126
Q

Is AC pressure controlled or volume controlled?

A

Can be either.

127
Q

Which mode of ventilation aids normal breathing with a predetermined level of positive airway pressure?

A

Pressure Support

128
Q

Pressure support is similar to SIMV except that:

A

airway pressure is held constant over the inspiratory period.

129
Q

What is the objective of pressure support ventilation?

A

to increase the pt’s spontaneous TV by delivering airway pressure to achieve volumes equal to 10-12 mL/kg. PS decreases the work of breathing and delays muscle fatigue.

130
Q

Describe high frequency ventilation.

A

Low tidal volumes (less than dead space) with a high rate (60-300 bpm). It uses typical settings and has a drive pressure of 15-30psi. The goal is to maintain pulmonary gas exchange at lower mean airway pressures.

131
Q

What is one quick way we can make a general judgement of compliance in the pt. lung?

A

When we deliver a breath via the reservoir bag we can feel how easily or not it flows in.

132
Q

Considering PEEP, which zone of the lung is more prone to collapse, the Apex or the Base in the absense of PEEP?

A

zone 3, at the base

133
Q

What might you need to do to the I:E ratio in a patient with a very compliant lung, ex. emphysema?

A

You might need to create a longer expiratory time.

134
Q

Would an obese patient require a different TV than a pt. of normal weight?

A

Yes, once they are paralyzed and the dead weight of their chest is crushing down on their thorax, they may need more volume to inflate.

135
Q

What is the tidal volume given in ICU vs. in anesthesia?

A

In ICU we gave 4-6 mL/ kg of ideal body weight but in anesthesia we need higher tidal volumes so around 10mL/kg is about right.

136
Q

The amount of impedence or backpressure is the amount of pressure we have to overcome to get a breath into the patient. What are 6 potential sources of backpressure?

A
  1. pt. lungs/airways 2. the breathing circuit (although the corrugated tubing helps decrease this) 3.Compliance of pt lungs 4. The chest wall/ musculature 5. What’s going on in the lung tissue itself 6. After a muscle relaxant and weight of chest is crushing down.
137
Q

The amount of volume I’m getting into the patient as a function of time is known as the __________

A

Flow rate

138
Q

In time cycled ventilation we set the I:E ratio and the vent determines the?

A

tidal volume

139
Q

An inspiratory sigh can be compared to:

A

a poor man’s PEEP. The pause after inspiration takes away from the exhalation time, leaving a little volume in the alveoli.

140
Q

What is the maximun inspiratory pressure?

A

30-35 cmH2O

141
Q

If peak pressures are high, which would you dial down first, TV or RR?

A

RR. In anesthesia you want to keep your tidal volume so you can recruit as many alveoli as you can.

142
Q

Normal ETCO2 is?

A

35-45. We try not to let it go above 40.

143
Q

Letting the pt. breathe on their own is good in the OR because a RR > 15 is a good indicator of?

A

Your patient is feeling pain

144
Q

Any time you get an alarm you should start at the _________ and work your way back to the machine.

A

Patient

145
Q

Which vent mode would be ideal if you were ventilating through an LMA?

A

Pressure controlled. You don’t want a pressure of more than 15-20 going into the pt.’s stomach.

146
Q

If a patient in IMV is waking up, they could start stacking breaths. A good mode to switch them to at this point is?

A

SIMV

147
Q

What’s one adult case in which you would use high frequency ventilation (jet vent or oscillator) as opposed to regular ventilation.

A

LIthotripsy of Kidney stones. When the pt. takes a breath it moves the stone, so the pt. must go on a jet neb. However you cannot give anesthetic through a jet neb so it’s a total IV anesthesia.

Fall 2013 Anesthesia Concepts (8 decks)

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