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INTRO TO NURSE ANESTHESIA > Scavenging Capnography CO2 Absorption > Flashcards

Scavenging Capnography CO2 Absorption Flashcards

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1
Q

Scavenging Definition:

A

Collection- of excess gases from equipment used in administering anesthesia, or exhaled by patients.

Removal- of these excess gases to an appropriate place of discharge outside the working environment

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2
Q

NIOSH Recommended Levels of Anesthetic Gases in OR?

A

Volatile Halogenated Anesthetic alone = 2 ppm
Nitrous Oxide = 25 ppm
Volatile Anesthetic with Nitrous Oxide = 0.5 ppm

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3
Q

5 basic components of scavenging system

A 
Transfer means
Gas disposal assembly
Gas disposal tubing
Scavenging interface
Gas collecting assembly
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4
Q

Gas Collecting Assembly

A
  1. Captures excess gases at the site of emission.
  2. Delivers them to the transfer means tubing.
  3. Outlet connection usually 30mm (19mm on older machines) male-fitting.
  4. Size of connections is important so that it doesn’t connect to other components of breathing system.
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5
Q

Transfer Means

A
  1. Also called exhaust tubing or hose and transfer system.
  2. Conveys gas from the collecting assembly to the interface.
  3. Usually a tube with female-fitting connectors on both ends.
  4. Tubing is short and large diameter, to carry a high flow of gas w/o a significant increase in pressure.
  5. Must be kink resistant.
  6. Must be different from breathing tubes
    - Color coded yellow and stiffer plastic
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6
Q

Scavenging Interface

A
  1. Also called the balancing valve, or balancing device.
  2. Prevents pressure increases or decreases in the scavenging system from being transmitted to the breathing system.
  3. Interface limits pressures immediately downstream of the gas-collecting assembly to between -0.5-+3.5cm H2O.
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7
Q

3 basic elements of the scavenging interface

A
  1. Positive pressure relief-protects patient and equipment in case of occlusion of system.
  2. Negative pressure relief-limit sub-atmospheric pressure.
  3. Reservoir capacity-matches the intermittent gas flow from gas collecting assembly to the continuous flow of disposal system.
    2 Types: Open or Closed
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8
Q

Where should the scavenger interface be be situated?

A

Should be situated as close to gas-collecting assembly as possible.

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9
Q

Describe Open Scavenging interface

A

No valves - is open to the atmosphere via “relief ports” in reservoir, avoiding buildup of positive or negative pressures.
Require use of a central vacuum system and a reservoir (open canister –size should allow for high waste gas flows).
Gas enters the system at the top of the canister and travels through a narrow inner tube to the base.
Vacuum control valve can be adjusted – varies the level of suction on the canister/reservoir – must be > excess gas flow rate to prevent OR pollution

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10
Q

Describe closed Scavenging interface

A

Two Types:
1. POSITIVE-PRESSURE RELIEF ONLY
-Single positive-pressure relief valve opens when a max. pressure is reached
-Passive disposal – no vacuum used, no reservoir bag needed
2. POSITIVE-PRESSURE AND NEGATIVE-PRESSURE RELIEF
Has a positive-pressure relief valve, negative-pressure relief valve, and a reservoir bag.
Used with an active disposal systems -Vacuum control valve adjusted so that the reservoir bag is NOT over distended or completely deflated
Gas is vented to the atmosphere if the system pressure exceeds +5.0 cm H2O
Room air is entrained if the system pressure is less than -0.5 cm H2O.
A backup negative-pressure relief valve opens at -1.8 cm H2O if the primary negative-pressure relief valve becomes occluded.

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11
Q

Gas-Disposal Tubing

A
  1. Connects the scavenging interface to the disposal assembly.
  2. Should be different in size and color from the breathing system.
  3. With a passive system the hose should be short and wide.
  4. Tubing running overhead ideal to prevent accidental obstruction and kinking
  5. If connected to an active gas disposal system it must be a DISS connector
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12
Q

Gas-Disposal Assembly

A

Consists of components used to remove waste gases from the OR.
2 Types:
Active-a mechanical flow-inducing device moves the gases (produces negative pressure in disposal tubing; must have negative pressure relief)
Passive-pressure is raised above atmospheric by the patient exhaling, manual squeezing of the reservoir bag or ventilator (needs positive pressure).

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13
Q

Passive system of Gas-Disposal assembly

A

The waste gases is directed out of the building via:
An open window
A pipe passing though an outside wall
An extractor fan vented to the outside air
Advantages: inexpensive to set up, simple to operate.
Disadvantages: may be impractical in some buildings.

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14
Q

Active system of Gas disposal assembly

A

These systems connect the exhaust of the breathing system to the Hospital vacuum system via an interface controlled by a needle valve.
Advantages: convenient in large hospitals where many machines are in use in different locations.
Disadvantages: vacuum system and pipework is a major expense.Needle valve may need continual adjustment.

Most commonly used in hospitals.

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15
Q

Scavenging System Check

A

Ensure proper connections between the scavenging system and both APL valve and ventilator relief valve and waste-gas vacuum
Fully open APL valve and occlude Y- piece
With min. O2 flow, allow scavenger reservoir bag to collapse completely and verify that pressure gauge reads zero
With the O2 flush activated, allow scavenger reservoir bag to distend fully, and then verify that pressure gauge reads less 10 cm H2O pressure

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16
Q

Purpose of Capnography

A
  1. Gold standard for patient ventilation assessment
  2. Used to confirm ETT or LMA placement
  3. In general anesthesia without an airway, helps determine if patient is adequately exchanging air/oxygen
  4. Guide ventilator settings- avoid too much or too little ventilation
  5. Detect circuit disconnections
  6. Detect circulatory abnormalities- pulmonary embolism, occult hemorrhage, hypotension
  7. Detect excessive aerobic metabolism: Malignant hyperthermia
  8. THERE ARE NO CONTRAINDICATIONS
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17
Q

Capnography – Clinical Uses

A
  1. May be used as estimate of PaCO2 , PaCo2>PEtCO2
    * Average gradient = 2-5mmHg under GA
  2. Used as an evaluation of dead space
  3. V/Q mismatch problems
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18
Q

Methods of Measuring CO2 in Expired Gases

A
  1. Colorimetric

2. Infrared Absorption Spectrophotometry-Most common

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19
Q

Describe Colorimetric

A
  1. Rapid assessment of CO2 presence
  2. Uses metacresol purple impregnated paper (changes color in presence of acid)
    • CO2 combines with H2O—carbonic acid–paper changes color
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20
Q

Infrared Absorption Spectrophotometry

A
  1. Gas mixture analyzed
  2. A determination of the proportion of its contents
  3. Each gas in mixture absorbs infrared radiation at different wavelengths
  4. The amount of CO2 is measured by detecting its absorbance at specific wavelengths and filtering the absorbance related to other gases
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21
Q

Measurement techniques of capnography

A

Mainstream capnography

Sidestream capnography

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22
Q

Describe Mainstream Capnography

A
  1. Heated infrared measuring device placed in circuit
    - Potential burns
  2. Sensor window must be clear of mucous
  3. Less time delay
  4. Weight- kinks ETT + increase dead space
    - Less of an issue with newer technology
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23
Q

Describe Sidestream Capnography

A
  1. Aspirates fixed amt gas/minute (30-500ml/minute)
    - Pediatric sampling- lower Vt = dilution
  2. Transport expired gas to sampling cell via tubing
  3. Best location for sampling near ETT
  4. Time delay
  5. Potential disconnect source
  6. Water vapor- condensation- traps/filters used
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24
Q

Phase 1 of capnography

A
  1. An inspiratory baseline
  2. Should have no CO2 reading
  3. Inspiration and first part of expiration
  4. Dead space gas exhaled
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25
Q

Phase 2 of capnography

A
  1. An expiratory upstroke
  2. Sharp upstroke represents rising CO2 level in sample
  3. Slope determined by evenness of alveolar emptying
  4. Mixture of dead space and alveolar gas
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26
Q

Phase 3 of capnography

A
  1. Alveolar Plateau
  2. Constant or slight upstroke
  3. Longest phase
  4. Alveolar gas sampled
    * *Peak at end of plateau is where the reading is taken- End Tidal Partial Pressure of CO2 (PEtCO2)
  5. Normal Value = 30-40mmHg
  6. Reflection of PACO2 and PaCO2
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27
Q

Phase 4 of capnography

A
  1. Beginning of Inspiration

2. CO2 concentration- rapid decline to inspired value

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28
Q

Waveform Changes Slow rate of rise in Phase II

Steep upslope of Phase III (in extreme cases may not see phase III)

A

Obstructive Lung Disease Pattern: COPD, Asthma, Broncho-constriction, Acute Obstruction

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29
Q

Rebreathing waveform changes

A

If value remains above baseline (Zero) at end of phase IV => Rebreathing Causes of Rebreathing: 1. equipment dead space

  1. exhausted CO2 absorber
  2. inadequate fresh gas flows
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30
Q

waveform changes spontaneous ventilation/ recovery from neuromuscular blockade

A

Clefts during phase III that indicate spontaneous breathing efforts during controlled mechanical ventilation.

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31
Q

waveform changes

Cardiac oscillations

A

Cardiogenic oscillations at the end of exhalation as flow decreases to zero and the beating heart causes emptying of different lung regions and back-and-forth motion between exhaled and fresh gas.

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32
Q

What are some causes of Rising CO2 when Ventilation Unchanged

A

Malignant Hyperthermia
Release of Tourniquet
Release of Aortic/Major Vessel Clamp
IV Bicarb administration
Insufflation of CO2 into peritoneal cavity
Equipment Defects (e.g. expiratory valve stuck, CO2 absorbent exhausted)

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33
Q

What are causes of decrease in EtCO2

A

Hyperventilation- gradual decrease reflects increased minute ventilation
Rapid decrease- PE (thrombus, fat, amniotic fluid, air) V/Q mismatch. Increase in PaCO2-PEtCO2 gradient.
Cardiac Arrest
Sampling error- disconnect(s), high sampling rate with elevated fresh gas flow

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34
Q

Waveform interpretation and inspection 5 characteristics

A 
Frequency
Rhythm
Height 
Baseline
Shape
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35
Q

Tracing interpretation Primary use of waveform

A

Verify placement of ETT in the trachea
Presence of stable CO2 waveforms for 3 breaths > 30 mmHg indicates tracheal intubation
Does NOT indicate proper position within the trachea- LISTEN to BBS!

36
Q

Explain how the Carbon Dioxide Absorber work and end products

A
  1. Chemical neutralization of CO2
  2. Base neutralizes an acid
  3. Acid: carbonic acid – formed by reaction of CO2 and H2O
  4. Base: hydroxide of an alkali or alkaline earth metal
  5. End product: water, a carbonate, & heat
37
Q

Describe the components Classic CO2 absorber and issues with it

A

Example of a Classic Absorber with two canisters, a dust/moisture trap at the bottom and a side tube at the right
Issues:
Couldn’t change during the case because disturbs circle system integrity
Common source of leaks

38
Q

Modern single canister models Have bypass feature so you can change out during the case
True or false

A

True

39
Q

Common Absorbents used are?

A
  1. Soda Lime (Sodium hydroxide lime)
  2. Amsorb Plus(Calcium Hydroxide lime)
    Baralyme Barium hydroxide lime
  3. Litholyme (Lithium Hydroxide)
40
Q

Soda Lime (Sodium hydroxide lime) consists of

A 
4% sodium hydroxide
1% potassium hydroxide
15% H2O
0.2% silica
80% calcium hydroxide
41
Q

Silica in soda lime is added for

A

Silica added for hardness to prevent dust

42
Q

Soda lime absorption capability

A

Capable of absorbing 26 liters of CO2/100g of absorbent granules
***Capable of absorbing 26 liters of CO2/100g of absorbent granules

43
Q

Why is moisture/water essential to soda lime?

A

Moisture is essential. Reaction takes place between ions that only exist in presence of water
Water is present as thin film on granule surface

44
Q

Explain soda lime reaction

A

CO2 + H2O <=> H2CO3
H2CO3 + 2NaOH (KOH) <=> Na2CO3 (K2CO3) + 2H2O + HEAT
Na2CO3 (K2CO3) + Ca(OH)2 (quick reaction) <=> CaCO3 + 2NaOH (KOH) + HEAT

45
Q

Name the reaction:
CO2 + H2O <=> H2CO3
H2CO3 + 2NaOH (KOH) <=> Na2CO3 (K2CO3) + 2H2O + HEAT
Na2CO3 (K2CO3) + Ca(OH)2 (quick reaction) <=> CaCO3 + 2NaOH (KOH) + HEAT

A

Carbon dioxide combines with water to form carbonic acid. Carbonic acid reacts with the hydroxides to form sodium (or potassium) carbonate and water and heat.

46
Q

Some CO2 may react directly with Ca(OH)2<=> CaCO3 + H2O + HEAT
Is this a fast or slow reaction?

A

slow

47
Q

Amsorb Plus aka Calcium Hydroxide Lime consists of

A

80 % calcium hydroxide
16% water
1-4% calcium chloride

48
Q

What adds hardness to Amsorb Plus aka Calcium Hydroxide Lime

A

Calcium sulfate and polyvinlypyrrolide added hardness

49
Q

Amsorb Plus aka Calcium Hydroxide Lime is absorbing capacity

A

Capable of absorbing 10 liters of CO2/100g of absorbent granules

50
Q

Explain Calcium Hydroxide Lime reaction

A

CO2 + H2O <=> H2CO3
H2CO3 + Ca(OH)2 <=> CaCO3 + 2 H2O + HEAT
Carbon dioxide + water= carbonic acid
carbonic acid + calcium hydroxide= calcium carbonate + water + heat

51
Q

Baralyme aka Barium Hydroxide Lime Consist of:

A

20% BaOH and 80% CaOH

Small amounts of NaOH and KOH may be added

52
Q

Describe Baralyme aka Barium Hydroxide granules

A

Granules are 4-8 mesh

53
Q

Baralyme aka Barium Hydroxide hardening agent?

A

No hardening agent is needed

54
Q

Baralyme aka Barium Hydroxide requires water

A

NO

55
Q

Baralyme aka Barium Hydroxide efficiency compared to soda lime

A

It is slightly less efficient than soda lime but less likely to dry out

56
Q

Baralyme aka Barium Hydroxide absorption capacity

A

Absorptive capacity similar to soda lime 26 liters of CO2 per 100 grams granules

57
Q

Chemical Reaction of Barium Hydroxide lime

A
  1. Ba(OH) + 2(8H2O) + CO2 => BaCO3 + 9H2O + Heat
  2. 9H2O + 9CO2=>9H2CO3
  3. 9H2CO3 + 9Ca(OH)2=> 9CaCO3 + 18H2O + Heat
58
Q

Litholyme: Lithium Hydroxide Monohydrate consists of

**(note: there is also an anhydrous formulation)

A
  1. 75% lithium hydroxide (LiOH)
  2. 12-19% H2O
  3. <3% lithium chloride (LiCl)
59
Q

Litholyme: Lithium Hydroxide Monohydrate reaction:

A

2 LiOH * H2O + CO2 <=> Li2CO2 + 3H2O – HEAT

60
Q

1 lb of Litholyme: Lithium Hydroxide Monohydrate absorbs

A

1 pound of LiOH absorbs 0.91 lb of carbon dioxide

61
Q

Replace absorbents with color change at what percent

A

Replace absorbent with 50-70% color change

62
Q

Color absorbents reverts back with rest true or false?

A

True (especially in NaOH containing formulations)

63
Q

Most common dye indicator signaling absorbent exhaustion

A

Ethyl violet – most common—

64
Q

Critical ph of Ethyl violet

A

critical pH = 10.3

65
Q

Color conversion signals absorber exhaustion in Ethyl violet

A

from White to

Purple

66
Q

Size of absorbent granules? and why are they sized this way

A

4-8 mesh (granule size= number of openings per inch in a sieve through which particles can make it through)
Smaller granules increase resistance

67
Q

The irregular shape of absorbent granules provides?

A

Irregular shape – increased surface area

Provide greater surface area

68
Q

Blend of large & small minimize resistance with little sacrifice in absorbent capacity. True or False

A

True

69
Q

Granules hardness number should be?

A

greater than 75

70
Q

Excessive powder leading to

A

channeling and resistance & caking

71
Q

What process use to test the hardness of absorbent granules?

A

Tested with steel ball bearings & screen pan

72
Q

Channeling can result from?

A

Results from loosely packed granules

73
Q

Preferential passage of exhaled gas flow through absorber via pathways of low resistance? True or False

A

True

What for channeling

74
Q

Channeling can lead to rebreathing?

A

True
CO2 may filter through channels not visible
CO2 monitoring

75
Q

How do manufacturers prevent channeling

A

Some manufacturers now use a polymer to bind the granules in pre-formed channels to prevent channeling

76
Q

Problems with absorbents: Compound A

A

CO2 granules degrade volatile anesthetics agents to some extent, especially sevoflurane
CO2 absorbents containing KOH and to a lesser extend NaOH

77
Q

manufacturer recommended flow rates for Sevo in order to prevent Compound A?

A

not more than 2 MAC hours at flow rates of 1 to <2 L/min.

78
Q

Which anesthetic agent is associated with highest accumulation of carbon monoxide

A

Deflurane is associates with the highest accumulation of carbon monoxide.

79
Q

Carbon monoxide has been known to accumulate in desiccated (dry) absorbents containing_____ when they are not used for 24-48 hours?

A

NaOH and KOH

80
Q

High flow through a system for prolonged time (such as if one forgets to turn down the O2 flow over the weekend) =

A

drys it out

81
Q

With dried out absorbent, a slow reaction occurs with the volatile agents and absorbents that produces CO can result in critically high levels______ of in exposed patients

A

carboxyhemoglobin

82
Q

Problems with Baralyme absorbents?

A

Fires:

now withdrawn from the market

83
Q

Anesthesia Safety Foundation Recommendation on Safe Use of Carbon Dioxide Absorbents

A
  1. Turn off all gas flow when the machine is not in use
  2. Change absorbent regularly
  3. Change absorbent whenever the color change indicates exhaustion
  4. Change all absorbent, not just one canister
  5. Change absorbent when uncertain of the state of hydration, such as if FGF
  6. Low flows preserve humidity in granules
84
Q

During which phase of respiration does gas flow through absorber

A

Inhalation

85
Q

During _____, gases flow through the mask, into the rebreathing bag, and out the APL valve.

A

exhalation

Fresh gas continues to flow from the common gas outlet at the machine into the common gas inlet at the absorber.

INTRO TO NURSE ANESTHESIA (10 decks)

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