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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
Q

Capnogram Phase 1

A

inspiratory baseline, no CO2
inspiration and 1st part of expiration
dead space gas exhaled

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26
Q

Capnogram Phase 2

A

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
Q

Capnogram Phase 3

A 
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
Q

Capnogram Phase 4

A

beginning of Inspiration

CO2 concentration- rapid decline to inspired value

29
Q

5 Characteristics of Capnogram Tracing

A 
Frequency
Rhythm
Height
Baseline
Shape
30
Q

Primary use of Capnogram

A

verify placement of ETT in trachea

  • 3 stable CO2 waveforms >30mmHg
  • doesn’t indicate proper position (listen)
31
Q

Trace Intepretation

A

Determine adequacy of min ventilation
disconnect indicator
Assess quality of CO2 absorption
Monitor changes in perfusion or dead space

32
Q

Slow rate of rise in Phase 2

Little/no phase 2

A

Obstructive lung disease pattern

COPD, asthma, bronchoconstriction, acute obstruction

33
Q

Rebreathing

A

tracing remains above baseline (zero) at end of phase 4

Causes: equipment dead space, exhausted CO2 absorber, inadequate fresh gas flows

34
Q

dip/bumps in phase 3 plateau

A

spontaneous ventilation
recovery from NMB
curare cleft

35
Q 
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 (exp valve stuck, absorbent exhausted)
–> most the time = under-ventilating

36
Q

Decrease in EtCO2

>Flows will < CO2

A
  • 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
Q

CO2 Absorber

A
  • chemically neutralizes CO2
  • needs dust/moisture trap
  • Air flows from the top down
38
Q

CO2 Absorber

Basic Function

A

CO2+H2O = H2CO3 (carbonic acid)
-Need base to neutralize
(hydroxide of alkali/alkaline earth metal)
-End Product: H2O, CO3-2, heat

39
Q

Absorbents 4

A

Soda Lime (Sodium Hydroxide lime)
Amsorb Plus (Calcium hydroxide lime)
Baralyme
Litholyme (lithium hydroxide)

40
Q

Soda Lime contents

A 
0.2%  Silica
1%      Potassium hydroxide
4%     sodium hydroxide
15%   H2O
80%  Calcium hydroxide
41
Q

Soda Lime
absorbs?
granules?

A

-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
Q

How much CO2 does an adult expire?

A

12-15 L CO2/hr

43
Q

Soda Lime Reaction

A

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
Q

Calcium Hydroxide Lime Contents

(aka Amsorb Plus)

A

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

calcium sulfate + polyvinlypyrrolidine for hardness

45
Q

Calcium hydroxide lime

absorbs?

A

10 L CO2/ 100g of absorbent granules

less risk of compound A and CO

46
Q

Calcium hydroxide lime

Reaction

A

1) CO2 + H2O <=> H2CO3 (carbonic acid)

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

47
Q

Baralyme
contents?
granule size

A

20% BaOH
80% CaOH
small amounts of Na/K-OH may be added

granule 4-8 mesh
no hardening agent needed

48
Q

Barium hydroxide lime
Reaction
(aka Baralyme)

A

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
Q

Baralyme

absorbs?

A

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
Q

Lithium Hydroxide Contents

aka Litholyme

A

<3% lithium chloride (LiCl)
12-19% H2O
75% lithium hydroxide (LiOH)

51
Q 
Lithium Hydroxide (Litholyme)
   Reaction
A

2 LiOH * H20 + CO2 <=> Li2CO2 + 3H2O + heat

52
Q

Indicators

A

-Acid or base whose color depends on pH
-Color conversion = absorber exhausted
reverts back with rest
-replace w/ 50-70% color change

53
Q

Phenolphthalein Indicator color changes

A 
Fresh = white
Exhausted = pink
54
Q

Ethyl Violet Indicator

A 
Fresh = white
Exhausted = Purple

most common, critical pH 10.3

55
Q

Clayton Yellow Indicator

A 
Fresh = Red
Exhausted = Yellow
56
Q

Ethyl Orange Indicator

A 
Fresh = orange
Exhausted = Yellow
57
Q

Mimosa 2 Indicator

A 
Fresh = Red
Exhausted = White
58
Q

Absorbent Granules

A

Size: 4-8 Mesh
Shape: irregular (= > SA)
small = increased resistance

*Mix of large/small = minimize resistance w/ little sacrifice in absorbent capacity

59
Q

Granule Hardness

A

Excessive powder = channeling resistance and caking

  • tested w/ steel ball bearings and screen pan
  • % of original left = hardness #
  • *hardness # should be >75 **
60
Q

Channeling

A

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
Q

Problem with Absorbents

A

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
Q

Problem with Absorbents: CO

A

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
Q

Problem w/ Absorbents:

Fire

A

Barlyme and Soda Lime

  • dehydration (desication) of granules
  • high FGF will dehydrate more
64
Q

6 Recommendations on Safe Use of CO2 Absorbents

A
  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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