1
Q
Who makes standards for recommended levels of anesthetics gases in OR?
A
NIOSH (National Institute for Occupational Safety and Health)
2
Q
What are NIOSH’s standards for halogenated anesthetic alone in OR?
A
2 ppm
3
Q
What is NIOSH’s standard for level of NO in OR?
A
25 ppm
4
Q
What is NIOSH’s standard for volatile agent with NO in OR?
A
0.5ppm
5
Q
What are the 5 basic components of the scavenging system?
A
1) Gas Collecting Assemby
2) Transfer means
3) Scavenging Interface
4) Gas Disposal tubing
5) Gas disposal assembly
6
Q
Describe the gas collecting assembly.
A
- Captures excess gases at site of emission
- Delivers them to transfer means tubing
- Outlet connection is 30 mm (19 on older machine) male-fitting
- Size of connections is important so that it doesn’t connect with other components of breathing system
7
Q
Describe the transfer means
A
- 2nd piece
- Also called exhaust tubing, hose and transfer system
- Conveys gas from collecting assembly to the interface
- Usually a tube with femalt-fitting connetors on both ends
- Tubing is short and large diameter, to carry high flow of gas with out significant increase in pressure
- Must be kink resistant
- Must be different than breathing tubes - may be color coded and stiffer plastic
8
Q
Describe Scavenging Interface
A
- third piece in system
- Prevents pressure increases or decreases in scavenging system from being transmitted to breathing system
- Also called balancing valve or balancing device
- Interface limits pressure immediately downstream of gas-collecting assembly to between 0.5-3.5 cmH2o
- Inlet 30 mm male connector
- Should be situated as close to gas-collecting assembly as possible
- 3 basic elements
- 1)positive pressure relief
- 2)negative pressure relief
- 3)reservoir capacity
9
Q
What are 3 basic elements for scavenging interface and their purpose?
A
1) Positive pressure relief
* protects pt and equipment in case of occlusion of system
2) Negative pressure relief
* limit sub atmospheric pressure
3) Reservoir capacity
* matches intermittent gas flow form gas collecting assembly to the continuous flow of disposal system
10
Q
What are the two type of scavenging interfaces?
A
Open and closed
11
Q
What is an open interface for a scavenging unit?
A
- No valves
- open to atmosphere via relief ports in reservoir, avoiding buildup of positive and negative pressure
- Require vacuum
- Require reservoir
- Gas enters at top of canister and travels through inner tube to base
- Vacuum control can be adjusted- varies level of suction on canister/reservoir.
- Must be > FGF rate to prevent OR pollution
12
Q
What is a closed interface for the scavenging unit?
A
Two types
- Positive pressure relief only -
- single positive pressure valve opens when max pressure reached -
- Passive disposal
- no vacuum used, no reservoir bag needed
- Positive pressure and negative pressure relief
- Has positive pressure valve, negative pressure valve and reservoir bag
- Used with ACTIVE disposal systems
- vacuum control adjusted so reservoir bag not overdistended or deflated
- Gas vented to atmosphere if pressure exceeds +5 cm h2o -
- RA entrained if less tha -0.5 cmh2o
- Back up negative pressure relief vavle opens at -1.8 if first becomes occluded
13
Q
What are the components of the positive pressure relief closed interface?
A
Only positive pressure valve
No reservoir,
no vacuum
14
Q
What are the components of the positive and negative pressure relief closed interface?
A
Positive pressure relief valve Negative pressure relief valve Reservoir bag NEED VACUUM
15
Q
Describe the gas disposal tubing
A
- Connect scavenging interface to disposal assembly
- Different size and color than breathing system
- Passive systme hose needs to be short and wide
- Tubing needs to run overhead to prevent obstruction and kinking
- If connected to active gas disposal system, need DISS connector
16
Q
Describe the gas disposal assembly
A
- Consists of components used to remove waste gases from OR 2 types
- Active- produces negative pressure in disposal tubing, needs negative pressure relief
- Passive- pressure is raised above atmospheric by patient exhaling, manual squeezing of reservoir bag, or ventilator (needs positive pressure)
17
Q
Describe the passive system along with advantages and disadvantages.
A
Waste gas flows outside building via: open window pipe passing through wall extractor fan
Advantages:
- Inexpensive set up
- simple to operate
Disadvantage:
- impractical in some buildings
18
Q
Describe the active system
A
System connect exhaust of breathing system to hospital vacuum system via an interface controlled by needle valve Advantage:
- Convenient for large hospitals where many machines used in diff locations
Disadvantage:
- Vacuum system and pipework major expense
- Needle valve may need continual adjustment
19
Q
Describe the scavenging system check
A
- Ensure proper connection bw scavenging systme 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 pressure gauge reads zero
- With o2 flush activated, allow scavenger reservoir bag to distend fully, verify pressure reads less than 10 cmh2o
20
Q
What is the gold standard to determine if patient is ventilated
A
ETCO2
21
Q
What is the purpose of capnography?
A
- Ventilator settings- avoid too much or little ventilation
- Placement- confirm placement in trachea instead of esophagus
- Aerobic metabolism- MH
- Circulatory abnormalities- PE, hypotension, occult hemorrhage, cardiac arrest
- Exchange air/o2- without airway, helps make sure pt exchanging air
- Detect circuit disconnections
VPACED
22
Q
What are the clinical uses of capnography?
A
- Provide estimate of PaCO2 (PaCO2 >PETCO2)
- 2-5 mmHg under GA
- Evaluation of dead space. V/Qmismatch= Gradient increase= dead space increase
23
Q
What are methods of measuring CO2 in expired gas?
A
Colorimetric
Infrared Absorption Spectrophotometry
24
Q
What is colorimetric measuring of CO2?
A
Rapid assessment of CO2 presence Metacresol Purple impregnanted paper
- changes color when co2 combines with H2O
25
What is infrared absorption spectrophotometry
* Most common analyzer
* Determination of the proportion of its contents
* Each gas in mixture absorbs infrared radiation at diff wavelengths
* Amt CO2 measured by detecting its absorbance at specific wavelenghts and filtering absorbance related to to other gases
26
What are two types of infrared absoprtion spectrophotometry?
Mainstream
Sidestream
27
Describe mainstream capnography.
* Flow through
* Heated infrared measuring device in circuit
* has to be heated to avoid effects of h2o condensation
* Sensor window must be clear of mucous
* Less time delay
* Weight- kinks ETT and increase dead space
* less of issue with new tech
28
Describe Sidestream Capnography.
* Aspirates fixed amt gas/minute (30-500mL/minute)
* may need to consider with ped sampling
* Transport expired gas to sampling cell via tubing -
* Best location near ETT
* Time delay
* Potential disconnect source
* Water vapor- condensation- traps/filters used
29
Describe phase 1 in capnography
* inspiratory baseline
* no co2 reading
* inspiration and first part expiration
* dead space exhaled= should be 0
* if not co2 scrubber is exhausted or pt rebreathing
30
Describe phase II in capnography
* expiratory upstroke
* sharp upstroke represents rising co2 level in sample leaving evently
* Slope determined by evenness of alveolar emptying
* Mixture of dead space and alveolar gas
* Asthma attack more slanted and may lose it all together in severe bronchospastic episode
31
Describe phase III Capnogrpahy
* Plateau region of capnograph corresponds to pco2 in alveolar ventilation
* Constant or slight upstroke
* LONGEST phase
* **Alveolar** gas sampled
* Peak at end of plateau is where reading taken
* Normal 30-40
* Adjust tidal volume to reach taget
* Reflection of PACO2 and Paco2
32
Describe phase IV capnogrpahy
Sharp downstroke of PCO2 occurs as fresh inspired gas moves past sampling site and washes out remaining CO2
* Beginning of inspiration
* CO2 concentration rapid delcine to inspired value
33
What are 5 characteristics to the ETCO2 curve?
1. Frequency
2. RHythm
3. Height
4. Basline
5. Shape
34
Normal capnogram
35
Normal capnograph during spontaneous breathing
36
Increased upslope of phase III, may occur durign bronchospasm, (asthma, copd) or partially obstructed ETT or breathing circuit
37
Cardiogenic oscillations at end of exhalation as flow decreases to 0 and beating heart causes emptying of diff lung regions and back and forth motion b/w exhaled and fresh gas
38
Clefts during phase III that indicate spontaneous breathing efforts during controlled mechanical ventilation
39
Esophageal intubation
40
Rebreathing CO2. as may occur with faulty expiratory valve or exhausted absorber system. Inspired CO2 is consistenly\>0
41
Faulty inspiratory valve, resulting in a slower downslope, which extends into inhalation phase (IV) as co2 in the inspiratory limb is rebreathed
42
2 peaks in phase III that suggest sequential emptying of 2 heterogenous compartments, may be seen in patient with SOLT
43
Faulty Inspiratory Valve
44
Sudden shortening of duration of phase III during controlled mechanical ventilation suggests abrupt onset of ruptured or leaking ETT cuff
45
* Dual plateua in phase III suggests presence of leak in sidestream sample line
* Ealy portion of phase III abnormally low because of dilution of exhaled gas with ambient air
* Sharp increase in CO2 at end of phase III reflects diminished leak resulting form increased circuit pressure at onset of inspiration
46
What are we looking to verify ETT placement?
Presence of stalbe CO2 waveform for \>3 breahts indicated tracheal intubation
NEED to listen to BBS for placement within trachea
47
What causes rising in CO2 when ventilation unchanged?
1. Malignant Hyperthermia
2. Release tourniquet
3. Bicarb administration
4. Insufflation of CO2 into periotneal cavity
5. Equipment defect (exp valve stuck, CO2 absorbent exhausted
6. Release aortic/major vessel clamp
MR. BIER- died because of high CO2
48
What causes decrease in ETCO2?
1. Hyperventilation
2. Arrest
3. Sampling error
4. V/Q mismatch
5. Increase PACO2-PETCO2
6. PE
#1 is gradual
4-6 is rapid change
HAS VIP
49
What is the generic process for all carbon dioxide absorbers?
CO2 +H2O make Carbonic acid (H2CO3). OH of an alkali or alkaline earth metal neutralizes the acid (base neutralizes acid).
End product is water, carbonate, heat
50
What were issues with classic absorbers?
* Couldn't change during case because disturbs circle system integrity
* Common source of leaks
51
What are are the benefits of modern CO2 absorbers?
Can change during case
much less issues with leaks
52
What are the common absorbents?
* Baralyme
* Amsorb Plus (Calcium Hydroxide lime)
* Litholyme (Lithium hydroxide)
* Soda Lime (Sodium hydroxide lime)
BALS
53
What are the compounds and percentages in soda lime?
* 0.2% Silica- hardness
* 1% Potassium hydroxide
* 4% Sodium Hydroxide
* 15% H2O
* 80% Calcium hyhdroxide
(0.2-looks like an S, KOH is the “kid” and has the next smallest amount, Naoh next, need a decent amount of water (15), CaOH always 80%)
54
What are some characteristics of Soda Lime? What is it efficiency?
* Silica added for hardness to prevent dust
* Capable of absorinb 26 L co2/100g absorbent granules
* 1 lb CaOH absorbs 0.59 lb CO2
* Water is present as thin film on granule surface
* Moisture is essential. Reaction only takes place between ions that only exist in presence of water
55
What is the generic principle of soda lime's reaction, and what is the chemical reaction formula?
* Carbom dioxide combines with water to form carbonic acid. Carbonic acid reacts with hydroxide to form sodium (or potassium) carbonate. water and heat
1. CO2+ H2O⇔ H2CO3
2. H2CO3+ NaOH (KOH)⇔ Na2CO3 (K2CO3)+ 2H2O + Heat
3. Na2CO3 (K2CO3) + Ca(OH)2(*quick reaction)* ⇔ CaCO3 + 2NaOH (KOH) + heat
SOME CO2 may react directly with Ca(OH)2, but this reaciton is MUCh slower (CaCO3 + H2O+Heat)
56
What are the percentages and components of Calcium hydroxide lime?
* AKA Amsorb plus
* 80%Ca Hydroxide
* 16% H2O
* 1-4% Calcium chloride
* Calcium sulfate and polyvinylpyrroldine added hardness
* Capable of 10L CO2/100g absorbent granlues
* less efficient than Soda Lime
57
What is the chemical reaction for Calcium hydroxide lime?
1. CO2+H2O ⇔ H2CO3
2. H2CO3 + Ca(OH)2⇔ CaCO3+ 2H2O+ Heat
58
What does Baralyme consists of?
* 20% BaOH, 80% CaOH
* Small amounts NaOH KOH added
59
What are some characteristics of baralyme?
Granules 4-8 mesh
No hardening agent needed
Slightly less efficient than soda lime, but less likely to dry out
No water
implicated in fires
Absorptive capacity similar to soda lime 26L of CO2/100grams granules
60
What is the chemical reaction of barium hydroxide lime?
1. Ba(OH) + 2(8H2O) +CO2⇔ BaCO3+ 9H2O +Heat
2. 9 H2o+ 9CO2⇔9H2CO3
3. 9H2CO3+ 9Ca(OH)2⇔9CaCO3+18H2O+Heat
61
Litholyme components and percentages?
* 75% LiOH
* 12-19% H2O
* \<3%lithium chloride
62
Reaction of lithium hydroxide monohydrate?
2LiOH \*H2O +CO2⇔LI2CO2+3H2O- heat
63
What is the efficiency of Litholyme
* 1 pound LiOH absorbs 0.91 lb co2
64
Talk about the purpose of indicators in co2 absorber?
* Color conversion signals absorber exhaustion
* Color reverts back with rest (especially in NaOH containing formulations)
* Replace absorbent with 50-70% color change
* Ethyl violet-most-common- critical pH 10.3
65
What are the characteristics of absorbent granules?
* 4-8 mesh (number openings/in in a sieve through whichparticales can make it through)
* Irregular shape- increased SA
* Small granules increase resistance
* BUT they have more SA
* Need blend of large and small granules to minimize resistance with little sacrifice in absorbent capacity
Grapes vs Watermelons
66
What is purpose of granule hardness and how is it tested?
* Excessive powder can cause channeling resistance and caking
* Soda lime- silica added to increase hardness
* Tested with steel ball bearings and screen pan
* %origianl remaining= hardness number
* Hardness number needs to be \>75
67
What causes channeling in absorber?
* Preferential passage of exhaled gas flow through absorber via pathways of low resistance
* Results from loosely packed granules
* Air space 48-55% of volume of canister (normal)
* Absorbent along channels may exhaust
* CO2 filter may not be visible through channels
* CO2 monitoring needs to be used
* Some manufacturers now use a polymer to bind the granules in pref-roemd channels to prevent channeling
68
What can develop with sevoflurane in contact with absorbent molecules?
* CO2 granules degrade volatile anesthetics agents to some extent, especially sevoflurane
* When degraded by strong base in co2 absorbents (esp KOH and lesser extent NaOH), sevo forms compound A
* has been shown to cause nephrotoxicity in rats
* Does not appear to be issue with absorbents with no KOH/NaOH
* Therefore manufacturer recommneds not more than 2MACH hr at flow rates 1-2L/min
* Most provider use 2 L FGF with sevo although practice not EBP.
* new absorbents don't form compound A
*
69
Why are you concerned if your absorbent dries out?
* Carbon monoxide accumulates in desiccated (dry) NaOH and KOH containing absorbents when not used for 24-48 hrs (i.e. soda lime, baralyme)
* high flow through system for long time= drys it out
* With dried out absorbent, slow reaction occurs with volatile agents and absorbents that produce CO
* Result in critically high levels of CARBOXYHYMOGLOBIN exposed patients
* Desflurance is associated with highest accumulation of CO
70
What are anesthesia safety's fondation recommendation on safe use of carbon dioxide absorbents?
* OCULAR
* Off- all gas flows off
* Color change- change when color change indicates exhaustion
* Uncertain of state of hydration
* Low flows preserve humidity in granules
* All absorbent- change
* Regularly
71
When does the gas flow go through CO2 absorber?
Inhalation
72
What is pathway of gas in absorber?
* Gases go from rebreathing bag
* down center absorber
* up through common fresh gas inlet
* out through inspiratory limb
73
What is pathway of gases during exhalation by the CO2 absorber?
* Gas flows through the mask, into rebreathing bag and out the APL valve
* Fresh gas continues to flow from common gas outlet at machine into common gas inlet at absorber
74
What would happen is you put desflurane in regular virally bypass vaporizer?
Potential delivery of hypoxic mixture and massive overdose of anesthetic gases
75
Obstruction of the scavenging systems transfer tubing can cause what?
Barotrauma and increased breathing circuit pressure
76
Inadequate vacuum setting in an open scavenging system will cause...
Leaking of excess scavenged gases to the OR
Intro Anesthesia Part II
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