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*Anesthesia Concepts 2 > Scavenge, Capnography, CO2 Absorber > Flashcards

Scavenge, Capnography, CO2 Absorber Flashcards

1
Q

What is scavenging?

A
  1. collection of excess gases from administration or exhalation of gas
  2. removal of excess gas to outside working environment
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2
Q

Who regulates levels of anesthetic gases in the OR?

A

National Institute of Safety and Health (NIOSH)

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3
Q

What is the recommended levels of gases for:

  1. Volatile anesthetic
  2. N2O
  3. Volatile anesthetic with N2O
A
  1. 2 ppm
  2. 25 ppm
  3. 0.5 ppm
    (ppm = parts per million)
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4
Q

What are the 5 components of the scavenge system?

A
  1. gas collecting assembly
  2. transfer means (tubing to interface)
  3. scavenging interface (regulates +/- pressure?)
  4. gas disposal tubing
  5. gas disposal assembly
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5
Q

What 3 ways does gas get to the scavenging system?

A
  1. gas analyzer (occurs right before insp limb)
  2. ventilator relief valve (vent’s form of APL)
  3. APL
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6
Q

When does gas enter the scavenging system?

A

When the ventilator relief valve or APL has too much pressure, the excess is diverted to scavenger.

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7
Q

What does the gas collecting assembly do?

A
  1. capture excess gas

2. delivers gas to transfer means tubing

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8
Q

What size and type is the outlet connection for the gas collecting assembly?
What is the size for older machines?
Why is this sizing important?

A

30 mm, male-fitting
19 mm
so that it isn’t accidentally connected to other parts of the breathing system

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9
Q

What does the transfer means do?

What are 2 other names for the transfer means?

A
  • transfers gas from collecting assembly to interface

- exhaust tubing or hose and transfer system

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10
Q

Describe the size and diameter of the transfer means tubing. Why is this important?

A
  • short and large

- to carry high flows w/o increasing pressure

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11
Q

What color is the transfer means tubing? And what is it made of?

A

-yellow
-stiffer plastic
(must be kink resistant)

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12
Q

What is the purpose of the scavenging interface?

A

prevent pressure increases/decreases in scavenging system from being transferred to breathing system

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13
Q

What is another name for the scavenging interface?

A

balancing valve/device

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14
Q

How much pressure does the scavenging interface limit? Where does it limit the pressure?

A
  • limits to -0.5 to +5 cm H2O

- immediately downstream of gas collecting assembly

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15
Q

What size is the scavenging interface inlet?

A

-30 mm male connector

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16
Q

How does the scavenging interface regulate pressure and flow? (3)

A
  • positive pressure relief (protects in case of occlusion in system)
  • negative pressure relief (limits subatmospheric pressure)
  • reservoir capacity (matches intermittent gas flow from gas collecting assembly to continuous flow of disposal system)
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17
Q

What are the 2 types of scavenging interfaces?

A
  1. open

2. closed

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18
Q

How does the open scavenging interface work?

A
  • no valves, has holes in reservoir preventing buildup of pressure
  • requires central vacuum and reservoir = open canister
  • gas enters top of canister thru inner tube to base
  • adjustable vacuum control valve - suction on canister/reservoir must be higher or equal gas flow rate to prevent OR pollution
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19
Q

What are the 2 types of closed scavenging interfaces?

A
  1. positive-pressure relief only

2. postive and negative-pressure relief

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20
Q

What does the (closed) positive-pressure relief scavenging system consist of? Is disposal active/passive?

A
  • pressure relief valve only - valve opens with max pressure
  • passive disposal, no vacuum used, no reservoir bag needed
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21
Q

What does the (closed) positive and negative pressure relief scavenging system consist of?

A

-has positive pressure relief valve, negative pressure relief valve, reservoir bag

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22
Q 
Is the (closed) positive and negative pressure relief scavenging disposal active/passive?
What is the max level of positive and negative pressures and how does the system compensate for this?
A
  • active disposal via adjustable vacuum control valve with reservoir bag over distended (for excess positive pressure) or collapsed (for excess negative pressure)
  • gas vented to atm if pressure > +5 cm H2O
  • room air is sucked in if pressure is less than -0.5 cm
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23
Q

What happens if the primary negative-pressure relief valve in the (closed) positive/negative pressure scavenging system becomes occluded?

A

A back-up neg press relief valve opens at -1.8 cm H2O

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24
Q

What does the gas disposal tubing do?

A

connects scavenging interface to disposal assembly

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25
Q

Describe the gas disposal tubing.

Where should it be placed?

A
  • different in size/color from breathing system
  • is passive
  • hose is short and wide
  • overhead to prevent accidental obstruction/kinking
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26
Q

What is the gas disposal assembly?

A

-components used to remove waste gas from OR

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27
Q

What are the 2 types of gas disposal assembly?

Which is most common

A
  1. active (most common)

2. passive

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28
Q

Describe a PASSIVE gas disposal assembly. What type of pressure does it require?

A
  • positive pressure
  • pressure is raised above atm by pt exhalation, squeezing reservoir bag or from ventilator
  • waste gas goes out of building via window, pipes to an outside wall, extractor fan vented to outside air
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29
Q

What are the advantages and disadvantages of the PASSIVE gas disposal assembly?

A
  • adv: inexpensive, simple

- disadv: impractical in some buildings

30
Q

Describe the active system of the gas disposal assembly.

A
  • mechanical flow device moves gases and causes negative pressure in disposal tubing
  • must have negative pressure relief valve
  • connects exhaust of breathing system to hospital vacuum via interface controlled by a needle valve
31
Q

What are the advantages and disadvantages of the ACTIVE gas disposal assembly?

A
  • adv: convenient in large hospitals

- disadv: expensive vacuum and pipework, needle valve may need continual adjustment

32
Q

What are you checking with the scavenging system check?

How do you perform this check?

A
  • connections between scavenging system and APL valve, ventilator relief valve and waste-gas vacuum
    1. fully open APL valve and occlude y-piece
    2. allow scavenger reservoir bag to collapse and pressure gauge to be at zero
    3. activate O2 flush to distend reservoir bag, pressure gauge should read < 10 cm H2O
33
Q

How is capnography useful?

A
  1. ETT placement (gold standard)
  2. determine pt ventilation
  3. guide vent settings (too much/too little)
  4. detect abormalities i.e. PE, MH, disconnect, obstr a/w
34
Q

What are the contraindications to capnography?

A

there are NONE

35
Q

What clinical info can capnography provide?

A
  1. estimate PaCO2
    (PaCO2 > PEtCO2 with a gradient of 2-5 mmHg under general anesthesia i.e. PEtCO2 = 38, then PaCO2 around 40-45)
  2. evaluates dead space (increasing dead space, widens gradient)
36
Q

What are the 2 types of methods in measuring CO2 in expired gas?
Which is most common?

A
  1. colorimetric

2. infrared absorption spectrophotometry (most common)

37
Q

How does the colorimetric method of measuring CO2 work?

A
  • rapid (i.e. CO2 detector in ICU)

- uses metacresol purple impregnated paper that changes color in presence of acid (carbonic acid formed by CO2 + H2O)

38
Q

How does the infrared absorption spectrophotometry work?

A
  • gas mixture is analyzed

- CO2 is measured by detecting absorbance at specific wavelengths and filtering absorbance related to other gases

39
Q

What are the 2 types of measurement techniques used in capnography?

A
  1. mainstream

2. sidestream

40
Q

Describe mainstream capnography.

What are advantages/disadvantages?

A
  • aka flow thru
  • heated infrared measuring device placed in circuit
  • sensor must be clear of mucous
  • less time delay
  • potential burns, weight > kinks ETT
41
Q

Describe sidestream capnography.

Where is it sampled?

A
  • aspirates fixed amt gas/min (50-500 ml)
  • transport expired gas to sampling cell via tubing
  • infrared analysis by comparing sample to a parameter that is calibrated to 5% or 35 mmHg
42
Q

What are advantages/disadvantages of sidestream capnography?

What effect on pediatric sampling?

A
  • sampling is near ETT = best location
  • time delay, potential disconnect, condensation from exhalation
  • lower tidal volume = dilution
43
Q

What occurs in Phase I of the capnogram?

A
  • inspiration to first part of expiration
  • inspiratory baseline
  • no CO2
  • dead space exhaled
44
Q

What occurs in Phase II of the capnogram?

A
  • expiratory upstroke representing rising CO2 level
  • slope is determined by evenness of alveolar emptying
  • is a mixture of dead space and alveolar gas
45
Q

What occurs in Phase III of the capnogram?

A
  • alveolar plateau causing constant/slight upstroke
  • LONGEST phase
  • peak at end of plateau = where PEtCO2 reading is sampled
  • reflects PACO2 (alveolar) and PaCO2 (arterial)
46
Q

What is the normal range of PEtCO2?

A

30-40 mmHg

47
Q

What occurs in Phase IV of the capnogram?

A
  • beginning of inspiration

- CO2 concentration has a rapid decline to inspired value

48
Q

What are 5 characteristics of a capnogram tracing?

A
  1. frequency
  2. rhythm
  3. height
  4. baseline
  5. shape
49
Q

How do you assess capnography for ETT placement?

A

stable CO2 waveform for 3 breaths

50
Q

What does capnography NOT tell you about ETT placement?

A
  • Does not indicate proper position in trachea

- Must listen to bilat breath sounds!!

51
Q

What does capnography tracing tell you?

A
  1. adequacy of exhalation (i.e. asthma, COPD, etc)
  2. disconnect
  3. quality of CO2 absorption
  4. changes in perfusion/dead space
52
Q

*REVIEW VARIOUS ABNORMAL WAVEFORMS

A

*REVIEW VARIOUS ABNORMAL WAVEFORMS

53
Q

What are reasons why you may see rising CO2 when ventilation is unchanged? (6)

A
  1. malignant hyperthermia
  2. release of tourniquet (build up of lactic acid and CO2)
  3. release of aortic/major vessel clamp
  4. Bicarb IV
  5. insufflation (pumping) of CO2 into peritoneal cavity
  6. equipment defects (i.e. exp valve stuck, CO2 absorber exhausted)
54
Q

Why might you see a decrease in EtCO2?

A
  1. hyperventilation (decrease CO2 = increased minute vent)
  2. PE (rapid decrease) = VQ mismatch = increase in PaCO2 and PEtCO2 gradient
  3. cardiac arrest
  4. sample error (i.e. disconnect, high sample rate with high FGF)
55
Q

How does the CO2 absorber work?

What is the end product?

A
  • causes chemical neutralization of CO2
  • hydroxide of an alkali or alkaline metal (base) neutralizes carbonic acid
  • water, carbonate, heat
56
Q

What is the path of CO2 as it flows thru the absorber?

A

top to bottom

57
Q

What are 2 common absorbents (bases)?

A
  1. soda lime (sodium hydroxide)

2. amsorb plus (calcium hydroxide lime)

58
Q

What is soda lime made of?

A
  • 4% sodium hydroxide
  • 1% potassium hydroxid
  • 15% H2O (to react with CO2 = H2CO3)
  • 0.2% silica (hardens particles to prevent dust)
  • 80% calcium hydroxide
59
Q

How many liters can a soda lime CO2 absorber hold?

A

26 liters of CO2/100 g of absorbent granules

60
Q

How does soda lime absorb CO2? (chemical reaction)

A

SODA LIME

  • CO2 + H2O <> H2CO3 (carbonic acid)
  • H2CO3 reacts with hydroxides to form sodium (or potassium) carbonate and water and heat

=H2CO3 + 2NaOH (KOH) <> Na2CO3 (K2CO3) + 2 H2O + HEAT
=Na2CO3 (K2CO3) + Ca(OH)2 <> CaCO3 + 2NaOH (KOH)

(some CO2 may react directly with Ca(OH)2 [calcium hydroxide] but is much slower)

61
Q

What is calcium hydroxide lime made of?

A

-aka Amsorb PLus
-80% calcium hydroxide
16% water (creates carbonic acid)
1-4 % calcium chloride
-calcium sulfate and polyvinlypyrrolidine (adds hardness)

62
Q

How many liters can calcium hydroxide lime CO2 absorber hold?

A

10 liters of CO2/100 g of absorbent granules

63
Q

How does calcium hydroxide absorb CO2? (chemical reaction)

A

CO2 + H2O <> H2CO3

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

64
Q

What signals absorber exhaustion?

What happens to the color when absorber rests?

A
  • color conversion dependent on pH of acid or base

- color reverts back with rest

65
Q

When do you replace absorbent?

What is the most common color change?

A
  • 50-70% color change

- ethyl violet > from white to purple

66
Q

What are the sizes of absorbent granules?
What shape are the granules and why?
Why is there a blend of sizes?

A
  • # 4 (small) to #8 (large) mesh (mixture)
  • irregular to increase surface area
  • large and small mixture minimize resistance and can maintain absorbent capacity
67
Q

Why do absorbent granules have excessive powder?

A

channeling resistance and caking

68
Q

What is the hardness number of absorbent granules?
What should it be?
Why is silica added to soda lime?

A
  • % of what is remaining
  • > 75
  • to increase hardness
69
Q

What is channeling of CO2 absorbent granules?

Why is channeling a concern?

A
  • channels formed from exhaled gas through granules of low resistance (loosely packed granules)
  • air space occupied 50% of volume in cannister
  • absorbent along channels may exhaust and CO2 may filter thru channels that are not visible
70
Q

What effect does soda lime have if in contact with anesthetic gases? (3)

A
  • dry soda lime may degrade sevo, iso, enflurane, desflurane to carbon monoxide
  • degrades sevoflurane and halothene to unsaturated nephrotoxic compounds (compound A)
  • fire
71
Q

What are 5 recommendations on safe use of CO2 absorbents?

A
  • turn off all gas flow when machine not used
  • change absorber regularly or when color changes
  • change whole absorbent (not just one)
  • change when uncertain of state of hydration (i.e. FGF)
  • low flows preserve humidity in granules

*Anesthesia Concepts 2 (6 decks)

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