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Scavenging Flashcards

1
Q

Scavenging

A

Collection of excess gases from equipment used in administering anesthesia or exhaled by patient

Removal of these 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 w/ N20: .5 ppm

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3
Q

5 Components of Scavenging System

A
  1. Gas collecting assembly
  2. Transfer means (30mm tubing)
  3. Scavenging interface
  4. Gas disposal tubing
  5. Gas disposal assembly
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4
Q

Gas Collecting Assembly

A

capture excess gas at the site of emission and
Delivers them to the transfer means tubing
Outlet connection 30mm male fitting (19mm on old)

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5
Q

Transfer Means

(also called exhaust tubing/hose, transfer system)

A

convey gas from collecting assembly to the interface
tube w/ female fitting connections on ends
Short and large diameter tubing (carries high flow gas w/ sig increase in pressure)
Must be kink resistant and different from breathing tubes

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6
Q

Scavenging Interface

also called balancing valve or balancing device

A

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

Limits pressure immediately downstream of gas collecting assembly to - .5 to +3.5 cm H2O

Inlet 30mm male connector & situated as close to gas-collecting assembly as possible

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7
Q

3 Basic Elements of Scavenging Interface

A

1) + Pressure Relief: protect pt and equipment in case of system occlusion
2) - Pressure Relief (sub-atmospheric pressure)
3) Reservoir Capacity: matches intermittent gas flow from gas collecting assembly to the continuous flow of disposal system

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8
Q

Open Scavenging Interface

A
  • No valves (open to atmosphere via holes in reservoir)
  • Require central vacuum system and reservoir
  • Gas enters the system at top of canister and travels through narrow inner tube to base
  • Vacuum control valve can be adjusted, must be >/= excess gas flow rate to prevent OR pollution
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9
Q

Closed Scavenging Interface

2 Types

A

1) Positive Pressure Relief Only

2) PP and Neg Pressure Relief

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10
Q

Closed Scavenging Interface

Positive Pressure Relief Only

A

single +pressure relief valve opens when a max pressure is reached

Passive disposal (no vacuum or reservoir bag needed)

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11
Q

Closed Scavenging Interface

Positive-Pressure and Negative Pressure Relief

A

> PP relief valve and Neg Pressure relief valve and reservoir bag
Used w/ active disposal system
Gas vented to atmosphere if system pressure exceeds 3.5cm H2O
RA is entrained if system pressure

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12
Q

Gas Disposal Tubing

A

Connects scavenging interface to the disposal assembly
Should be different in size and color from breathing system
W/ passive system the hose should be short and wide
avoid kinks and obstruction

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13
Q

2 Types of Gas Disposal Assembly

A

components used to remove waste gases from OR

1) Active
- mechanical flow-inducing device moves gases
- creates - pressure in disposal tubing
- need NP relief valve
2) Passive
- raise pressure above atmospheric by pt exhaling, manual squeezing of reservoir bag, or mech ventilation
- need + pressure

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14
Q

Passive System

advantages and disadvantages

A

Waste gas directed out by:

  • open window
  • pipe passing through an outside wall
  • extractor fan vented to outside air

Inexpensive to set up and simple to operate

Impractical in some bldgs

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15
Q

Active System

advantages & disadvantages

A

connect exhaust of breathing system to hospital vacuum via interface controlled by a needle valve

Convenient in large hospital w/ many machines in different locations

major expense of vacuum system and pipework, needle valve may need continual adjustment

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16
Q

Scavenging System check

A

-ensure proper connections b/t APL and ventilator relief valve and waste gas vacuum
-fully open APL valve and occlude Y piece
allow scavenger reservoir bag to collapse and verify pressure gauge read 0
-activate O2 and have reservoir bag distend fully and make sure pressure gauge <10 cm H2O

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17
Q

Capnography

A

Gold Standard to confirm ETT placement
Ventilation adequate
Detect abnormalities (PE, MH, disconnection, obstructive airway, hypotension

no contraindications

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18
Q

Capnography Estimation

A

estimates PACO2
2-5 mmHG under arterial sample
d/t deadspace

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19
Q

2 Methods of Measuring CO2 in Expired Gas

A

Colorimetric

Infrared Absorption Spectrophotometry

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20
Q

Colorimetric CO2 Measuring

A

rapid assessment of CO2 presence
use metacresol purple impregnated paper
CO2 + H2O –> carbonic acid –> purple color

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21
Q

Infrared Absorption Spectrophotometry

CO2 Monitoring

A
  • Most common
  • gas mixture analyzed to determine proportion of contents
  • each gas in mixture absorbs infrared radiation @ different wavelengths
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22
Q

2 Measurement Techniques

A

Mainstream Capnography

Sidestream Capnography

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23
Q

Mainstream Capnography

A

aka Flow through

  • Heated infrared measuring device placed in circuit
  • sensor window must be clear of mucous
  • less time delay (only measure expired gas)
  • potential burns and weight kinks ETT
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24
Q

Sidestream Capnography

A

Aspirates fixed amount gas/minute (50-250ml)
transports expired gas to sampling cell via tubing
uses infrared analysis: compare sample to known quantity (requires calibration w/ 5% or 35mmHg)
best location to sample is near ETT
Time delay of (4-5 breaths)
Potential disconnect source
Pediatric sampling lowers Vt = dilution
water vapor condensation occurs so need a trap/filter

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25
Capnogram Phase 1
inspiratory baseline, no CO2 inspiration and 1st part of expiration dead space gas exhaled
26
Capnogram Phase 2
expiratory upstroke sharp upstroke represents rising CO2 level in sample slope determined by evenness of alveolar emptying mixture of dead space and alveolar gas
27
Capnogram Phase 3
``` Alveolar plateau constant or slight upstroke longest phase alveolar gas sampled Peak at end of plateau is where reading is taken = PEtCO2 30-40mmHg Normal reflection of PACO2 and PaCO2 ```
28
Capnogram Phase 4
beginning of Inspiration | CO2 concentration- rapid decline to inspired value
29
5 Characteristics of Capnogram Tracing
``` Frequency Rhythm Height Baseline Shape ```
30
Primary use of Capnogram
verify placement of ETT in trachea - 3 stable CO2 waveforms >30mmHg - doesn't indicate proper position (listen)
31
Trace Intepretation
Determine adequacy of min ventilation disconnect indicator Assess quality of CO2 absorption Monitor changes in perfusion or dead space
32
Slow rate of rise in Phase 2 | Little/no phase 2
Obstructive lung disease pattern | COPD, asthma, bronchoconstriction, acute obstruction
33
Rebreathing
tracing remains above baseline (zero) at end of phase 4 | Causes: equipment dead space, exhausted CO2 absorber, inadequate fresh gas flows
34
dip/bumps in phase 3 plateau
spontaneous ventilation recovery from NMB curare cleft
35
``` Rising CO2 (when ventilation unchanged) ```
Malignant Hyperthermia Release of tourniquet Release of Aortic/Major Vessel Clamp IV Bicarb administration Insufflation of CO2 into peritoneal cavity Equipment defects (exp valve stuck, absorbent exhausted) --> most the time = under-ventilating
36
Decrease in EtCO2 | >Flows will < CO2
- Hyperventilation (gradual increase = increased min ventilation) - Rapid decrease = PE, VQ mismatch (increase in PaCO2-PEtCO2 gradient) - Cardiac arrest - Sampling error (disconnect, high sampling rate w/ elevated FGF)
37
CO2 Absorber
- chemically neutralizes CO2 - needs dust/moisture trap - Air flows from the top down
38
CO2 Absorber | Basic Function
CO2+H2O = H2CO3 (carbonic acid) -Need base to neutralize (hydroxide of alkali/alkaline earth metal) -End Product: H2O, CO3-2, heat
39
Absorbents 4
Soda Lime (Sodium Hydroxide lime) Amsorb Plus (Calcium hydroxide lime) Baralyme Litholyme (lithium hydroxide)
40
Soda Lime contents
``` 0.2% Silica 1% Potassium hydroxide 4% sodium hydroxide 15% H2O 80% Calcium hydroxide ```
41
Soda Lime absorbs? granules?
-Absorbs 26 L CO2/ 100g of absorbent granules -Silica added for hardness (prevent dust) -Water present as thin film on surface (need to get ions and rxn to take place)
42
How much CO2 does an adult expire?
12-15 L CO2/hr
43
Soda Lime Reaction
1) CO2 + H2O <=> H2CO3 2) H3CO3 + 2NaOH (or KOH) <=> Na2CO3/ K2CO3 (carbonates) +2H2O + Heat 3) Na2CO3/K2CO3 + Ca(OH)2 <=> CaCO3 + 2NaOH/KOH + Heat CO2 + water = carbonic acid, carbonic acid + hydroxides = sodium/potassium carbonates + water + heat
44
Calcium Hydroxide Lime Contents | (aka Amsorb Plus)
1-4% calcium chloride 16% water 80% calcium hydroxide calcium sulfate + polyvinlypyrrolidine for hardness
45
Calcium hydroxide lime | absorbs?
10 L CO2/ 100g of absorbent granules less risk of compound A and CO
46
Calcium hydroxide lime | Reaction
1) CO2 + H2O <=> H2CO3 (carbonic acid) | 2) H2CO3 + Ca(OH)2 <=> CaCO3 (carbonate) + 2H2O + heat
47
Baralyme contents? granule size
20% BaOH 80% CaOH small amounts of Na/K-OH may be added granule 4-8 mesh no hardening agent needed
48
Barium hydroxide lime Reaction (aka Baralyme)
1) Ba(OH) + 2 (8H2O) + CO2 <=> BaCO3 + 9H2O + heat 2) 9H2O + 9CO2 <=> 9H2CO3 (carbonic acid) 3) 9H2CO3 + 9Ca(OH)2 <=> 9 CaCO3 + 18H2O + heat
49
Baralyme | absorbs?
26 L CO2 / 100g granules no water + produces a lot of heat = fires = off market *less efficient than soda lime, but less likely to dry out
50
Lithium Hydroxide Contents | aka Litholyme
<3% lithium chloride (LiCl) 12-19% H2O 75% lithium hydroxide (LiOH)
51
``` Lithium Hydroxide (Litholyme) Reaction ```
2 LiOH * H20 + CO2 <=> Li2CO2 + 3H2O + heat
52
Indicators
-Acid or base whose color depends on pH -Color conversion = absorber exhausted reverts back with rest -replace w/ 50-70% color change
53
Phenolphthalein Indicator color changes
``` Fresh = white Exhausted = pink ```
54
Ethyl Violet Indicator
``` Fresh = white Exhausted = Purple ``` most common, critical pH 10.3
55
Clayton Yellow Indicator
``` Fresh = Red Exhausted = Yellow ```
56
Ethyl Orange Indicator
``` Fresh = orange Exhausted = Yellow ```
57
Mimosa 2 Indicator
``` Fresh = Red Exhausted = White ```
58
Absorbent Granules
Size: 4-8 Mesh Shape: irregular (= > SA) small = increased resistance *Mix of large/small = minimize resistance w/ little sacrifice in absorbent capacity
59
Granule Hardness
Excessive powder = channeling resistance and caking - tested w/ steel ball bearings and screen pan - % of original left = hardness # * *hardness # should be >75 **
60
Channeling
preferential passage of exhaled gas flow through absorber via pathways of low resistance - from loosely packed granules - absorbent along channels may exhaust - air space =48-55% of volume
61
Problem with Absorbents
CO2 granules degrade volatile anesthetics to some extent -4x as much sevo breaks down as Baralyme as in soda lime -Sevo --> compound A Compound A has toxic renal and pulm effects recommend at-least 2L FGF
62
Problem with Absorbents: CO
Carbon monoxide: accumulates in absorber not used w/in 24-48hrs - slow rxn w/ volatile agents and absorbents - Desiccated (dry) soda lime may react w/ sevo/ iso/ enflurane/ desflurane => CO - Desflurane highest accumulation of CO - flush w/ 100% O2 for 15mins before use
63
Problem w/ Absorbents: | Fire
Barlyme and Soda Lime - dehydration (desication) of granules - high FGF will dehydrate more
64
6 Recommendations on Safe Use of CO2 Absorbents
1. Turn off all gas flow when machine not in use 2. Change absorbent regularly 3. Change absorbent whenever color indicates exhaustion 4. Change all absorbent (not just 1 canister) 5. Change absorbent when uncertain of state of hydration 6. Low flows preserve humidity in granules

Chem/ Phys (8 decks)

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