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610 Anesthesia Concepts > Vent and Airway > Flashcards

Vent and Airway Flashcards

1
Q

What is compliance a ratio of? What does it measure?

A

ratio of change of V to change of P. It measures distensibility

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2
Q

What is a good way to determine baseline compliance of your patient’s lungs?

A

you can feel it when you use the reservoir bag to ventilate the patient

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3
Q

what is measured as the ratio of change in driving pressure to change to change in flow rate?

A

resistance; think Ohm’s Law: flow= (change in pressure/resistance) t/f: resistance= (change in pressure/flow rate)

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4
Q

What is expiratory flow time?

A

time b/w beginning and end of expiratory flow; how long it takes to exhale

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5
Q

What is expiratory pause time?

A

time from end of expiratory flow to start of inspiratory flow

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6
Q

What is inspiratory flow time?

A

time b/w beginning and end of inspiratory flow

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7
Q

where are you more likely to have underinflated alveoli? What do you use?

A

zone 3/ dependent areas; use PEEP

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8
Q

What is inspiratory pause time? What is another name for this?

A

portion of inspiratory phase time during which the lung is held inflated in a fixed pressure or volume. aka “sigh”

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9
Q

What is the I:E expressed in? What is normal?

A

seconds; 1:2

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10
Q

What does the volume parameter of the vent measure?

A

measure of the TV delivered by ventilator to patient

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11
Q

What is volume measured in?

A

liters for MV

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12
Q

What is the equation for TV in a normal person?

A

5ml per kg of ideal body weight

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13
Q

What is the equation for TV in a ventilated patient?

A

6-8ml/kg; or 10-15ml/kg depending on who you ask.

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14
Q

why do you see bigger volumes when the patient is ventilated?

A

going from physiologic to nonphysiologic way of breathing; with PP ventilation, cant expand the lung as well so you need bigger volumes

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15
Q

What is the definition of pressure in relation to vents?

A

impedance to flow

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16
Q

What causes impedance?

A

breathing circuit; patient’s airway and lungs

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17
Q

What is backpressure generated as a result of?

A

airway resistance (asthma attack), lung-thorax compliance; breathing circuit

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18
Q

What is pressure measured in?

A

cmH2O, mmHg, kPa

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19
Q

what is back pressure?

A

the pressure coming back to you

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20
Q

What is flow rate?

A

rate at which gas volume is delivered to patient

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21
Q

Where does flow rate span?

A

from patient connection of breathing system to the patient

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22
Q

What is flow rate expressed in?

A

L/sec or L/min

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23
Q

What will constant flow deliver?

A

a constant inspiratory gas flow regardless of a/w circuit pressure

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24
Q

How are vents characterized? Why

A

by inspiratory flow; because expiration is always passive

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25
Q

What does a vent w/ non constant flow deliver?

A

consistently varying flow w/ each inspiratory cycle

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26
Q

What does a constant pressure generator flow deliver?

A

maintains constant pressure irrespective of flow during inspiratoin

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27
Q

With constant pressure generator, when does flow stop?

A

when airway pressure equals set inspiratory pressure

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28
Q

How does anesthesia vent provide ventilation? What are the phases?

A 
PP ventilation
inspiration
transition btw I & E
expiration
transition btw E & I
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29
Q

What are different types of vents?

A

time cycle, volume cycle, pressure cycle

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30
Q

Is gas involved in a piston driven ventilator? What is required?

A

no, electricity

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31
Q

What type of machines require O2 and power to work?

A

compressible

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32
Q

What is the difference btw the air that drives an ICU vent and the air that drives an anesthesia vent?

A

ICU vent: air that goes in is what goes to the patient; no bellows
anesthesia vent: air that goes in is to drive bellows and is separate from the O2 that goes to the patient (which is mixed w/ NO & anesthetic gases)

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33
Q

Are cycling mechanism vents new or old technology?

A

older

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34
Q

How does a time cycled vent work?

A

vent goes to expiratory phase of breath after a specific, predetermined time interval has passed from time of inspiration

TV is a product of the set inspiratory time and inspiratory flow rate

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35
Q

How does a volume cycle vent work?

A

terminates inspiration after a predetermined TV is delivered

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36
Q

What type of vents are most adult vents? What do they have to avoid barotrauma?

A

volume cycled; second limiit on inspiratory pressure

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37
Q

A % of TV is lost in v-cycled ventilation d/t what? How much?

A

compliance of the system; usually about 4-5ml cmH2O

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38
Q

How does a pressure cycled vent work? What may vary?

A

cycle into expiratory phase when a/w pressure reaches predetermined level

TV and inspiratory time may vary

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39
Q

How does a flow cycled vent work?

A

pressure and flow sensors allow the vent to monitor inspiratory flow at a preselected fixed inspiratory pressure

when flow hits this predetermined level the vent cycles from I to E

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40
Q

What determines movement of the bellows?

A

expiration

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41
Q

Ascending bellows expand in what direction and when?

A

up; on exhalation

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42
Q

Why aren’t descending bellows used anymore?

A

if there was a problem ventilating you couldn’t tell because bellows would still fall

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43
Q

What is the air inside the bellows? What is the air outside the bellows

A

inside: gas that patient will receive; mixed w/ NO and anesthetics
outside: O2 being used to drive the movement of the bellows

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44
Q

During __________the driving gas of the bellows enters the chamber and increases pressure.
What does this increase in pressure cause?

A

inspiratory phase; ventilator relief valve closes (no gas can escape through scavenger); bellow are compressed and gas inside is delivered to patient

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45
Q

What valve on the vent is analagous to the APL valve?

A

pressure relief valve

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46
Q

During expiration, the driving gas ______________the chamber and the pressure in the bellows and the pilot drop to ____________

A

exits; 0

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47
Q

On expiration, does the vent pressure valve open or close? What kind of valve is it?

A

open; ball type

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48
Q

What happens to exhaled gas before it is sucked up by scavenger? Why?

A

exhaled gas fills bellows; pressure valve creates 2-3cmH2O of back pressure only

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49
Q

When does scavenging occur?

A

only when bellows is filled completely

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50
Q

The relief valve is only open during ______________ and any _____________ occurs at this point.

A

expiration; scavenging

51
Q

What determines how much gas is driven in to compress bellows?

A

set TV (bellows size doesn’t change w/ different patient populations)

52
Q

What kind of bellows does a piston vent have?

A

no bellows!

53
Q

After turning the vent on, what is the first selection you must make?

A

mode: IMV, pressure control, etc

54
Q

What are some advantages to piston vents?

A

quiet; no PEEP, greater precision in delivering TVs, less bulky, lack of O2 requirements means less concern if pipeline source is disrupted

55
Q

Why is some PEEP required on bellows vents?

A

2-3cm H2O required d/t bellows spill vavlve

56
Q

What is big disadvantage to piston vents? What monitor is important in detecting this?

A

can entrain air and continue to deliver TVs w/ hypoxic mixture; O2 analyzer

57
Q

What are some disadvantages to piston vents that may not apply to new practitioners?

A

quiet; loss of familiar visual clues from seeing bellows

58
Q

How does the inspiratory pause or sigh work?

A

flow of drive gas stops but pressure in bellows chamber stays the same

59
Q

What happens to the volume of gas going to the patient during the sigh?

A

it is held in patient’s lungs until exhalation occurs

60
Q

For the sigh, where is the time for this pause taken from?

A

time of expiration

61
Q

What does it mean if you have T1 of 25%?

A

you will spend 25% more time at end of inspiration than you normally would

62
Q

If your I:E is 1:2 and your pause time is 25% how much time are you spending in inspiration, expiration and pause? (inspiration is 2 sec, expiration is 4sec)

A

I=2sec; E=3.5; pause=.5sec

63
Q

If you are using an inspiratory pause but want to keep I:E ratio at what it was before, what must you do?

A

turn the ratio back up after setting pause time

64
Q

What can an inspiratory pause be beneficial for?

A

keep alveoli open a bit longer; kind of like PEEP

65
Q

Do all vents have an I:E knob?

A

no, must enter in TV, rate and inspiratory flow and machine will figure ratio out

66
Q

What is the cardinal way of telling if you are ventilating a patient adequately?

A

end tidal CO2

67
Q

What is a normal end tidal CO2? Is it usually higher or lower than PaCO2?

A

35-45mmHg; usually lower

if your end tidal is 45, you need to make some adjustments because your PaCO2 is probably higher

68
Q

If you dont think you are ventilating the patient appropriately do you usually want to adjust the RR or the volume? Why?

A

change the RR; you want to prevent atelectasis so you want to keep alveoli open; t/f avoid decreasing volumes

69
Q

When would you choice to change volume instead of RR?

A

if peak pressure alarms are going off

70
Q

If patient’s RR is >15, what is probably the issue?

A

pain, give narcs

71
Q

For the vent settings, what is the TV set at? What is the formula for MV?

A

TV= 10-15ml/kg

MV=TV x RR

72
Q

How much is flow rate?

A

4-6x MV

73
Q

Do asthmatics usually require different I:E ratios?

A

yes, longer expiratory times

74
Q

How do you determine inspiratory time?

A

TV/flow rate (in seconds)

75
Q

How do you determine expiratory time?

A

1st: figure out how long each ventilation total time is (60/RR)
2nd: then subtract TI from total breath time

76
Q

What is going to affect the patient’s O2 content more: PO2 or Hb?

A

Hb

77
Q

What formula do you use to determine O2 content in blood?

A

CaO2= (Hb x SaO2 x 1.34) + (PaO2 x 0.003)

78
Q

What is the rule of thumb regarding FiO2 and SaO2?

A

If FiO2 goes up, so will SaO2

79
Q

Hypoventilation will reduce PaO2 unless what?

A

patient is breathing an enriched O2 mixture

80
Q

If you increase FiO2 by 10%, how much do you increase PaO2?

A

50mmHg; another way of figuring this out is: 5xFiO2=PaO2

81
Q

What does a low pressure alarm usually mean?

A

disconnection; a drop in peak circuit pressure is detected

82
Q

What is a subatmospheric alarm? What do you do for this?

A

not enough flows in bag; pressure is less than or equal to 10cmH2O; bag is sucked in
turn up your flows

83
Q

what is a sustained/continuing pressure alarm? What can cause it?

A

15cmH2O for >10seconds; kink in tubing or issue w/ patient

84
Q

What does a high peak pressure alarm detect?

A

excess pressure at 60cmH2O or what is set by practitioner

85
Q

When will the ventilator setting alarm go off?

A

vent is unable to deliver set desired MV; need to turn up inspiratory flow

86
Q

What monitor is the best for determining a disconnect?

A

end tidal CO2

87
Q

What is the most important monitor on the anesthesia machine? What should it be calibrated at?

A

O2 analyzer; 21%

88
Q

What is flow rate?

A

the rate at which the gas volume is being delivered to the patient

89
Q

What does a respirometer measure?

A

rate of respiration based on rate of exchange of O2/CO2

90
Q

Where on the vent should the respirometer be? Why?

A

expiratory limb; some of TV is always lost in the system: you want to measure after this happens

91
Q

What do you expect the exhaled Vt to be?

A

Vt set on vent + Vt fresh gas flow - Vt lost in system

92
Q

What part of the respirometer is always active while mechanically ventilating?

A

exhaled volume monitor; activated automatically once breaths are sensed

93
Q

What other things can the respirometer sense?

A

reverse flow; apnea (insufficient breath based on TV setting not achieved w/ in 30 sec); low minute volume

94
Q

What are more powerful and adaptive: ICU or anesthesia vents?

A

ICU

95
Q

What is the most common mode of ventilation in the OR?

A

volume controlled

96
Q

In volume controlled vents; what parameters are set by the provider? To what extent does patient effort play a role?

A

TV and RR; independent of patient effort

97
Q

With volume control ventilation, what is controlled on inspiration? If this parameter is to high or too low, what happens?

A

flow rate
too low: wont work
too high: will add a pause or cause high peak pressures

98
Q

What does the provider set w/ pressure controlled vent mode?

A

inspiratory pressure

99
Q

How does gas flow w/ pressure mode ventilation?

A

flow decreases as airway pressure rises and ceases when airway pressure = set peak inflation pressure

100
Q

T or F: TV is set a specific # in pressure control ventilation

A

false; it depends on rise time and set pressure

101
Q

When is pressure control ventilation used?

A

when pressures are expected to be high; good for neonates and premature babies or patient w/ LMA in and you don’t want air to go into stomach

102
Q

What is intermittent mandatory ventilation?

A

vent delivers mandatory breaths at preset rate

103
Q

Does IMV allow for spontaneous breaths?

A

yep

104
Q

With IMV, what does the vent have a secondary source of?

A

gas flow for spontaneous breaths

105
Q

Where does the secondary source of gas flow for IMV come from?

A

either continuous gas flow w/in circuit or demand valve that opens to allow gas to flow from a reservoir

106
Q

Is IMV an acceptable mode to wean patients off of vent?

A

yes; turn down the rate

107
Q

How is SIMV different from IMV?

A

it is synchronized w/ patient’s effort; prevents breath stacking

108
Q

What does SIMV time the mechanical breath with?

A

beginning of spontaneous effort

109
Q

When is SIMV good to use?

A

when waking up patient in OR

110
Q

What is the assist control mode of ventilation? What triggers the vent to deliver a predetermined TV in this mode?

A

intermittent mode of PP ventilation; patient’s inadequate inspiratory effort creates a sub-baseline pressure in the inspiratory limb

111
Q

If you are using AC ventilation and the pts effort is inadequate what happens?

A

the vent will augment breaths; it will increase RR to set rate if patient isnt breathing fast enough

112
Q

T/F: With AC ventilation only some of the patient’s breaths are augmented by the ventilator.

A

false; every breath is assisted

113
Q

With AC ventilation is it pressure or volume controlled?

A

can be either

114
Q

Describe pressure support ventilation

A

aid in normal breathing w/ predetermined level of positive airway pressure

115
Q

How is pressure support different from IMV?

A

pressure support keeps airway pressure constant throughout entire inspiratory period

116
Q

What is the goal of pressure support ventilation?

A

to increase pt’s spontaneous TV by delivering airway pressure to achieve volumes equal to 10-12ml/kg

117
Q

What can pressure support ventilation prevent or delay?

A

work of breathing; muscle fatigue

118
Q

What are some characteristics of high frequency ventilation?

A

low TVs: less than dead space; high RR (60-300bpm)

119
Q

What are the typical settings for high frequency ventilation?

A

rate: 100-200 bpm
IT: 33%
drive pressure: 15-30psi

120
Q

What is the goal of high frequency ventilation?

A

maintain pulmonary gas exchange at lower mean airway pressures

121
Q

In the OR, what is a prime example of why you would use high frequency ventilation?

A

lithroscopy; patient has stone that needs to be zapped and regular ventilation will move the stone

122
Q

What can you not do when doing high frequency ventilation (ie jet ventilation)?

A

use anesthetic gases; must use IV meds (propofol at high doses)

123
Q

What is another formula for determining PaO2?

A

PaO2=PiO2-PaCO2/R + F (F is usually negligible); R=0.8

610 Anesthesia Concepts (6 decks)

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