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610 Anesthesia Concepts > Scavenging systems, capnography, CO2 absorption > Flashcards

Scavenging systems, capnography, CO2 absorption Flashcards

1
Q

What is the definition of scavenging?

A

collection of excess gases from equipment used in the admin of anesthesia or exhaled by patients.
removal of these gases to an appropriate place of discharge outside working environment

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2
Q

What is the NIOSH recommended level of anesthetic gas alone in the OR?

A

2ppm

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3
Q

What is NIOSH recommended level of nitrous in the OR?

A

25ppm

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4
Q

What is the NIOSH recommended level of volatile anesthetic and nitrous in the OR?

A

0.5ppm

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5
Q

What are the 5 basic components of the scavenging system?

A
  1. gas collection assembly
  2. transfer means
  3. scavenging interface
  4. gas disposal tubing
  5. gas disposal assembly
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6
Q

What is the role of the gas collecting assembly?

A

captures excess gases at the site of emission and delivers them to the transfer means tubing

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7
Q

What is the size of the outlet tubing for the gas collecting assembly?

A

usually 30mm male (19mm on older machines)

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8
Q

What is the importance of the size of outlet tubing?

A

size of connections are important so that it doesnt connect to other components of the breathing system

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9
Q

Describe the role of the transfer means component?

A

conveys gas from gas collecting assembly to interface

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10
Q

What are some other common names of the transfer means component?

A

exhaust tubing or hose and transfer system

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11
Q

Describe the transfer means tubing.

A

usually female fitting connectors on both ends; tubing is short w/ large diameter; must be kink resistant; must have different characteristics from breathing tubes (ie colored coded yellow and more stiff)

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12
Q

Why does the transfer means tubing need to be short w/ large diameter?

A

to carry high gas flow w/o significant increase in pressure

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13
Q

What is the role of the scavenging interface?

A

prevents pressure increases or decreases in scavenging system from being transmitted to the breathing system

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14
Q

What are some other common names for the scavenging interface?

A

balancing valve; balancing device

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15
Q

The scavenging interface limits ___________, immediately downstream of the _____________to between ______________ and ____________

A

pressure
gas collecting assembly
-0.5 to 0.5cmH2O

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16
Q

What is the size of the scavenging interface?

A

inlet 30mm male

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17
Q

Where should the scavenging interface be situated?

A

as close to the gas collecting assembly as possible

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18
Q

What are the 3 basic elements of the scavenging interface?

A
  1. positive pressure relief
  2. negative pressure relief
  3. reservoir capacity
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19
Q

What is the importance of the positive pressure relief?

A

protects patient and equipment in case of occlusion

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20
Q

What is the importance of the negative pressure relief?

A

limits subatmospheric pressure

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21
Q

What is the importance of the reservoir capacity?

A

matches the intermittent gas flow from gas collecting assembly to the continuous flow of the disposal system

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22
Q

What are the 2 types of scavenging interface?

A

open and closed

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23
Q

T/F: The open interface has valves

A

false; no valves; it is open to atmosphere via holes in reservoir; avoid build up of neg or pos pressure

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24
Q

What does the open interface require?

A

requires use of central vacuum system and reservoir (open canister; size should allow for high waste gas flows)

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25
Q

How does the open interface work?

A

gas enters system at top of canister and travels through narrower innertube to base

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26
Q

T/F: the vacuum control valve can be adjusted

A

true: varies the level of suction on the canister/reservoir; must be greater than or equal to excess gas flow rate to prevent OR pollution

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27
Q

The closed interface is broken down into what type of systems?

A

positive pressure relief only or positive pressure and negative pressure relief

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28
Q

How does the positive pressure only closed interface work?

A

single positive pressure relief valve opens when a max pressure is reached and passive disposal
no vacuum used and no reservoir needed

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29
Q

How does the positive pressure & negative pressure relief closed interface work?

A

has both +/- pressure relief vavles w/ reservoir bag and gas is vented to the atmosphere when pressure exceeds 5cmH2O

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30
Q

for the closed interface w/ +/- pressure: what happens if the pressure falls below -0.5cm H2O?

A

room air is entrained

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31
Q

what happens if the primary negative pressure relief valve becomes occluded?

A

a backup negative pressure relief valve opens at -1.8cm H2O

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32
Q

What is the function of the gas disposal tubing?

A

it connects the scavenging interface to the disposal assembly

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33
Q

T/F: the gas disposal system should be long and thin?

A

false: short and wide because its a passive part of the system

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34
Q

How can you prevent the accidental occlusion/kinking of the disposal tubing?

A

by running the tubing overhead

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35
Q

What is the gas disposal assembly?

A

consists of components used to remove wastes from the OR

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36
Q

The gas disposal assembly is broken down into 2 types: what are the major differences?

A

active: mechanical flow inducing device that moves gases (produces neg pressure in disposal system; must have neg relief)
passive: pressure raised above atmospheric by patient exhalation, manual squeezing, or ventilator (needs pos pressure

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37
Q

What 3 ways does the passive system evacuate the waste gases?

A
  1. open window
  2. pipe passing thru outside wall
  3. extractor fan vented to outside air
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38
Q

What are the adv/disadv to passive system of gas disposal assembly?

A

adv: inexpensive, simple to operate
disadv: impractical in some buildings

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39
Q

How does the active system of gas disposal assembly function?

A

these systems connect the exhaust of the breathing system to hospital vacuum system via interface controlled needle valve

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40
Q

What are the adv/disadv of the active gas disposal assembly?

A

adv: convenient in large hospitals where many machines are used in diff locations
disadv: vacuum system and pipework is major expense; needle valve may need continual adjustment

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41
Q

T/F: the passive system of the gas disposal assembly is most commonly used in hospitals

A

false; active is

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42
Q

how do you perform a scavenging system check: 4 steps

A
  1. ensure proper connections btw scavenging system and both the APL valve and vent relief valve and waste gas vacuum
  2. fully open APL valve and occlude y piece
  3. with minimal O2 flow; allow scavenger reservoir bag to collapse completely and verify that pressure gauge read zero
  4. w/ O2 flush activated; allow scavenger bag to fully expand and then verify that the pressure gauge reads below 10cm H2O
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43
Q

T/F: capnography is the gold standard for confirmation of ETT placement?

A

true

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44
Q

What are some purposes of capnography?

A

confirm ETT placement; determine if patient is being ventilated; guide vent settings; detect abnormalities

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45
Q

T/F: there are some contraindications for using capnography

A

false: THERE ARE NO CONTRAINDICATIONS

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46
Q

What are some clinical uses of capnography?

A

estimate PaCO2 ( PaCO2 > PeCO2 by ~ 2-5mmHg); used to eval dead space

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47
Q

What methods are used to measure CO2 in expired gas?

A

colorimetric; infrared absorption spectrophotometry

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48
Q

how does colorimetric method work?

A

rapid assessment
uses metacresol purple impregnated paper which changes color in presence of acid
H2O + CO2= carbonic acid and paper changes color

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49
Q

How does the infrared absorption spectrophotometry work?

A

the amount of co2 is measured by detecting its absorbents at specific wavelengths and filtering the absorbents related to other gases

50
Q

What are the 2 measurement techniques of capnography?

A

mainstream and sidestream

51
Q

How is mainstream capnography used?

A

heated infrared measuring device placed in circuit

52
Q

t/f: mainstream capnography is also called flow through?

A

true

53
Q

t/f mainstream capnography has a longer time delay than side stream?

A

false; less time delay than sidestream

54
Q

What do you want to make sure w/ mainstream capnography?

A

sensor window must be cleared of mucus

55
Q

What are some disadv of mainstream capnography?

A

potential burns and weight of it can kink ETT

56
Q

How is sidestream capnography used?

A

aspirates fixed amount of gas/min (50-500ml)
transports expired gas to sampling cell and uses IR analysis
compares sample to known quantity

57
Q

what does sidestream capnography require?

A

calibration of known quantity to compare sample to

usually 5% or 35mmHg

58
Q

T/F: the best placement for the sidestream is closest to the anesthesia machine

A

false: closest to ETT

59
Q

What are some disadv to sidestream capnography?

A

time delay; potential disconnect source; pediatric sampling- lower Vt= dilution
water vapors/condensation: traps and filters must be used

60
Q

how many phases are in the capnography waveform?

A

4

61
Q

phase I is the ________ baseline

A

inspiratory

62
Q

phase I is considered to be___________and the first part of ____________

A

inspiration; expiration

63
Q

In phase I there is no _____________

A

CO2

64
Q

What type of gas is considered to be exhaled in phase 1?

A

dead space exhaled gas

65
Q

Phase II of the capnography wave form is the _________

A

expiratory upstroke

66
Q

What does phase II represent?

A

sharp upstroke that represents rising CO2 level in sample

67
Q

How is the slope of phase II determined?

A

evenness of alveolar emptying

68
Q

What type of gas is considered to be exhaled in phase II?

A

mixture of dead space and alveolar gas

69
Q

Phase III of capnography wave form is the ___________

A

alveolar plateau

70
Q

What is the characteristic of the phase III plateau?

A

constant or slight upstroke; long phase

71
Q

What type of gas is considered exhaled during phase III?

A

alveolar gas

72
Q

Where is end tidal CO2 measured?

A

peak a the end of phase III plateau

73
Q

What is the normal range for end tidal CO2?

A

30-40mmHg

74
Q

End tidal CO2 can be considered a reflection of _______ and __________

A

PACO2 & PaCO2

75
Q

Phase IV of the capnography wave form is the ________

A

beginning of inspiration

76
Q

What is characteristic of Phase IV waveform?

A

rapid decline in CO2 concentration to inspired value

77
Q

during end tidal tracing interpretation, what are the 5 things to look at?

A
  1. frequency
  2. rhythm
  3. height
  4. baseline
  5. shape
78
Q

Presence of stable CO2 waveforms for __________breaths indicated tracheal intubation.

A

3

79
Q

T/F: end tidal CO2 indicates proper position of ETT in trachea?

A

false; must listen for bilateral breath sounds

80
Q

What are some other observations one can make from end tidal tracings?

A

frequency of Ve; disconnet indicator; quality of CO2 absorption; changes in perfusion or dead space

81
Q

What changes will one see in the CO2 waveform of a patient w/ obstructive lung disease?

A

slow rate rise in phase II and little or no phase III

82
Q

What are some examples of obstructive lung disease?

A

COPD, asthma, bronchospasm, acute obstruction

83
Q

What changes in the CO2 tracing would one see if the esophagus was intubated?

A

any CO2 in stomach will quickly vanish, usually w/in 3 tidal volumes and the waveform will become essentially a flat line

84
Q

How would one be able to distinguish if a patient is rebreathing via the CO2 tracing?

A

the CO2 tracing remains above the baseline (zero) at the end of phase IV

85
Q

What are some causes of rebreathing?

A

equipment dead space, exhausted CO2 absorber, inadequate FGF

86
Q

What would a waveform look like when a patient is beginning to spontaneously breath/recover from NMb?

A

there will be a curare cleft in phase III

87
Q

What are cardiac oscillations and what does it do to the CO2 tracing?

A

the pumping of the heart can repeatedly press on the lungs and disturb the capnography graph causing oscillations in phase IV. It is not a concern.

88
Q

What are some cuases of rising CO2 if the ventilation is unchanged?

A

MH, release of tourniquet; release of major vessel that was clamped; IV bicarb admin; insufflation of CO2 into peritoneal cavity; equipment defects

89
Q

What are some causes of a decrease in ETCO2?

A

hyperventilation, PE, cardiac arrest, sampling error

90
Q

What would the characteristics of the ETCO2 waveform be if the decrease in ETCO2 was caused by hyperventilation vs. PE?

A

hyperventilation: gradual decrease reflects increase in MV
PE: rapid decrease, increase in PaCO2 and PECO2 gradient

91
Q

What is the purpose of the CO2 absorber?

A

chemical neutralization of CO2, base neutralizes acid

92
Q

What is the acid and how is it formed?

A

H2CO3 is formed from CO2 and H2O

93
Q

What is the base of a CO2 absorber?

A

hydroxide of an alkali or alkaline earth metal

94
Q

What is the end product of the reaction in a CO2 absorber?

A

H2o, carbonate, heat

95
Q

What are the 2 common types of CO2 absorber?

A

soda lime and amsorb plus (Ca hydroxide lime)

96
Q

What are the components of soda lime?

A 
4% sodium hydroxide
1% ptassium hydroxide
15% H2O
0.2% silica
80% calcium hydroxide
97
Q

Why is silica added to soda lime?

A

for hardness and to prevent dust

98
Q

What is the absorbent capacity of soda lime?

A

26L of CO2/100g of granules

99
Q

Why is H2O in soda lime?

A

thin film on granule surface and moisture is essential for reaction to take place; it only takes place btw 2 ions if there is H2O

100
Q

Describe the soda lime reaction

A

CO2 + H2O=H2CO3
H2CO3 + 2NaOH (KOH)= Na2CO3(K2CO3) + 2H2O + heat (fast)
Na2CO3(K2CO3) + Ca(OH)2= CaCO3 +2NaOH (KOH)
some CO2 many react directly w/ Ca hydroxide but is much slower

101
Q

What are the components of amsorb plus?

A

80% calcium hydroxide
16% H2O
1-4% calcium chloride
calcium sulfate and polyvinlypyroolidine for added hardness

102
Q

What is the absorbent capacity of calcium hydroxide lime (amsorb plus)

A

10L of CO2/100g of granules

103
Q

Describe the calcium hydroxide lime reaction

A

CO2 + H2O =H2CO3

H2CO3 + Ca(OH)2 = CaCO3 + 2H2O + heat

104
Q

How do you know if the CO2 canister is exhausted?

A

an acid or base whose color depends on the pH; color conversion = exhaustion

105
Q

what color is most common to signify exhaustion?

A

ethyl violet

106
Q

When should you change the canister graules?

A

when it is 50-70% exhausted

107
Q

What must be aware of w/ the color change in CO2 absorber?

A

color reverts back to normal w/ rest

108
Q

What are the diff types of indicators used and their associated color changes w/ regards to CO2 absorbers?

A 
phenolphtalein: white to pink
ethyl violet: white to purple
clayton yello: red to yellow
ethyl orange: orange to yellow
mimosa 2: red to white
109
Q

What is the general size of the granules?

A

4-8mesh

110
Q

What is the general shape of granules, and why?

A

irregular: gives more SA

111
Q

Small granules _______ resistance?

A

increase

112
Q

Why do they blend small and large granules?

A

to minimize resistance w/ little sacrifice in absorbent capacity

113
Q

What should the granules hardness be?

A

75 or greater

114
Q

What is channeling in regards to the CO2 absorber?

A

preferential passage of exhaled gas flow through the absorber via pathways of least resistance

115
Q

How does channeling happen and why is not good?

A

results from loosely packed granules and the granules along the pathways can become exhausted and you may not notice from the outside
rebreathing of CO2 may occur

116
Q

How can you prevent channeling?

A

make sure the granules are tightly packed and/or shake the canister to close any open pockets in the canister

117
Q

What happens if the soda lime becomes dry from high gas flow?

A

it can degrade sevo, iso, desflurane and enflurane to CO

118
Q

What happens specifically to sevo and halothane if it comes in contact w/ dry soda lime?

A

they degrade to unsaturated nephrotoxic compounds (compound A)

119
Q

Dry gas may be a _______

A

fire hazard

120
Q

What are some recommendations on safe use of CO2 absorber?

A

turn off all gas flows when the machine is not in use; change absorbent frequently, change when granules are exhausted; change all abosrbent; change granules if uncertain of exhaustion; low flows preserve humidity

610 Anesthesia Concepts (6 decks)

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