Gas Systems & Scavenging Flashcards
Carter/maggie+ bowman
1
Q
link 25 proportioning system in newer machines is
A
internalized. As dials are electric, you cannot turn on nitrous oxide without oxygen flowing.
2
Q
color of helium cylinder
A
brown
3
Q
Full E sized oxygen cylinders have ___ volume and ___ pressure
A
625-700 L at 2000 - 2200 PSI
4
Q
Full E sized air cylinders have ___ volume and ___ pressure
A
~625 L at 1900 PSI
5
Q
In air and oxygen cylinders, pressure falls in
A
proportion to the volume remaining in the tank
6
Q
Full E sized N2O cylinders have ____ volume and ____ pressure
A
1590 L and 745 PSI
7
Q
purity of medical gases is specified and enforced by
A
Specified us US Pharmacopeia or national formulary
Enforced by FDA
8
Q
Cylinder Label
A
each cylinder must have a label or decal on the side or on the shoulder. But not covering any permanent markings.
9
Q
Cylinder Label shows (3)
A
the compressed gas association marking system.
Diamond shape, name of gas, signal word with statements of hazards and measured to be taken. Hazard Status Caution words
10
Q
DOT permanent markings on cylinders (6)
A
Include: cylinder type, working PSI serial number date of manufacture neck rick identification restest markings
11
Q
7 safe handling procedures for cylinders
A
- Never stand a cylinder upright without support
- Never leave empty cylinders on the machine
- Never leave the plastic tape on the port while installing the cylinder
- Never rely on the cylinders color for identification of its contents
- Never oil valves
- Before any fitting is applied to the cylinder valve, particulates of dust, metal shavings, and other foreign matter should be cleared from the outlet by slowly and briefly cracking the valve a way from you and/or other personnel
- The valve should always be fully open when a cylinder is in use. Marginal opening may result in failure to deliver adequate gas.
12
Q
vapor pressure sevoflurane
A
160 mmHg
13
Q
vapor pressure enflurane
A
172 mmHg
14
Q
vapor pressure isoflurane
A
240 mmHg
15
Q
vapor pressure halothane
A
244 mmHg
16
Q
vapor pressure desflurane
A
669 mmHg
17
Q
Tec 6 vaporizer maintains
A
a temp of 39 and atm of 2 for desflurane, constant temp/pressure
18
Q
Gas-vapor blender =
A
tec 6 vaporizer
19
Q
pressure regulating valve in Tec 6
A
down regulates the desflurane to 1.1 atm
20
Q
Aladdin cassettes are
A
computer controlled variable by pass vaporizers
21
Q
Copper Kettle is unique in that it (4)
A
has its own dedicated flow meter
is out of the circuit
non-agent specific
bubble through
22
Q
Steps of gas through copper kettle (~4 steps)
A
Air flows from dedicated flow meter into copper kettle, into loving cup,
loving cup forces it back down,
then bubbles through the gas diffuser disk that is filled with anesthetic of your choice,
is laden with anesthetic gases, flows out o f copper kettle as a very highly concentrated anesthetic, joins rest of gas flow.
23
Q
copper kettle calculation
A
(Carrier Gas x Vapor Pressure) / Barometric Pressure - Vapor Pressure = Vapor output in mL/min
then! [Vapor Output] in mL/min / [total gas] flow in mL/min
24
Q
variables you can change in copper kettle calculation
A
Carrier gas and total gas flow
25
If you accidentally put an anesthetic with high vapor pressure in a low vapor pressure vaporizer
High- low -> High
higher concentration than set
26
If you accidentally put an anesthetic with low vapor pressure in a high vapor pressure vaporizer
Low - high ->
Lower concentrations than set
27
Definition of scavenging
COLLECTION of excess gases from equipment used in administering anesthesia or exhaled by patients and REMOVAL of these excess gases to an appropriate place of discharge outside the working environment.
28
NIOSH recommended levels of anesthetic gases in OR
volatile halogenated anesthetic alone = 2 ppm
nitrous oxide = 25 ppm
volatile anesthetic with nitrous oxide = 0.5 ppm
29
Basic Components of Scavenge (5)
1. Gas collecting assembly
2. Transfer means
3. Scavenging interface
4. Gas disposal tubing
5. Gas disposal assembly
30
Size of connections in scavenging system is important so that
it is unable to connect to other components of the breathing system
31
Gas Collecting Assembly (Does)
captures excess gasses at the site of emission and delivers them to transfer tubing
32
Gas Collecting Assembly connection is usually
30 mm (19mm) in older machines and male fitting.
33
Transfer means of scavenge system
- also called:
- function
Also called exhausted tubing or transfer system.
function: conveys gas from the collecting assembly to the interface
34
Transfer means of scavenge system details (5)
usually a tube with female fitting connectors on both ends
tubing is short with a large diameter to carry a high flow of gas w/o a significant increase in pressure
must be kink resistance
must be different from breathing tubes
color coded yellow and stiffer plastic
35
problem with NIOSH recommended levels
"Theres no safe level of gas exposure and its questionable where these numbers came from"
36
Scavenging interface function (3)
prevents pressure increases or decreases the scavenging system from being transmitted to the breathing system
also called the balancing valve or balancing device
interface limits pressures immediately downstream of the gas collecting assembly to between -0.5 to 3.5 cmH2O.
37
Scavenging interface details
inlet should be 30 mm male connector
should be situated as close to gas-collecting assembly as possible
38
3 basic components of the scavenging interface
positive pressure relief - protects pts and equipment in case of occlusion in system
negative pressure relief - limit sub atmospheric pressure
reservoir capacity - matches the intermittent gas flows rom gas collecting assembly to the continuous flow of disposal system
39
2 types of scavenging interfaces
open
| closed
40
Open interface scavenging system
No valves!
Is open to the atmosphere via "relief ports" in reservoir, avoiding build up of positive and negative pressure
- must have high vacuum flow to prevent pollution of OR.
requires reservoir and vacuum
41
Positive Pressure Relief only closed scavenge system
Only positive pressure relief valve
Disposal is passive, no vacuum, pressure comes from expiration
Gas vents to a non circulating HVAC or a window,
No reservoir bag needed
42
Positive+ Negative relief closed scavenge system (5)
used with active disposal (vacuum)
has a reservoir bag
gas is vented to the atmosphere if pressure is over +5cmH2O
Room air is entrained if pressure is below -0.5cmH2O
BACKUP negative pressure valve at -1.8cmH2O if first one becomes occluded
43
In positive+negative relief closed scavenge system, adjust the vacuum control valve so that
the reservoir bag is appropriately inflated
| i.e. neither overly distended or completely deflated
44
Reservoirs in scavenging systems should match the
intermittent volume from pt expiration/gas collecting assembly to the continuous flow of the disposal system
45
Gas disposal tubing that is connected to an active gas disposal system requires
a DISS
46
Gas disposal tubing for passive systems should be
short and wide (decrease resistance, increase flow)
47
Gas disposal tubing to ensure no kinks should be
running overheard to prevent accidental obstruction (stepping) or kinking
48
Gas Disposal Assembly consists of
Components used to remove waste gases from OR . Two types, active and passive
49
Active Disposal Assembly advantages/disadvantages
Vacuum! Connected from breathing system to hospital vacuum via an interface controlled by needle valve
advantage: convenient in large hospitals where many different machines are used in different locations
disadvantage: expensive to have network, needle valve may need continual readjustment
50
Passive Disposal Assembly advantages/disadvantages
Waste gas is directed out of building via open window, pipe passing to outside wall, fan to outside
advantage: Cheap! simple
disadvantage: may be impractical in some buildings
51
Scavenging System Check (3)
1. Ensure proper connections between scavenging system and both APL VALVE and VENTILATOR RELIEF VALVE to waste gas vacuum
2. Fully open APL valve and occlude Y-Piece, with minimal O2 flow collapse scavenger bag and ensure it reads 0 and not negative pressure (appropriate vacuum)
3. Fully open APL valve and occlude Y-piece ,with high gas flow allow reservoir bag to distend and ensure that pressure does not rise to greater than 10 cmH2O.
52
Capnometry vs Capnography
Capnometry: quantification of carbon dioxide concentration
Capnography: actual graph of capnometry values over time
53
"Purposes" of capnograhy (8)
1. gold standard to determine if patient is being ventilated, critical, life-saving monitor
2. used to confirm ETT/LMA placement
3. Without an airway, helps determine if pt is adequately exchanging air/oxygen
4. Guide ventilator settings (avoids too much or too little ventilation )
5. Detect circuit disconnections
6. Detect CIRCULATORY abnormalities - (PE, occult hemorrhage/hypotension)
7. Detect excessive aerobic metabolism (Malignant hyperthermia)
8. Standard for VAE detection
54
contraindications to capnography
there are none
55
"Clinical uses" of capnography (2)
May be used as ESTIMATE of PaCo2
Used as an evaluation of dead space
56
EtCO2 compared to PaCo2
PaCo2 > EtCo2 by approx 2-5 mmHg
57
Methods of Measuring CO2 in Expired gases
1. colorimetric
| 2. infrared absorption spectrophotometry (most common)
58
Colorimetric co2 detector uses
metacresol purple paper (turns color with present of carbonic acid)
59
Infrared Absorption Spectrophotometry works
- by analyzing the gas mixture
- determination by proportion of gas contents
- each gas in mixture absorbs infrared radiation at different wave lengths, amount of CO2 is measured by detecting its absorbable at specific wavelengths and filtering the absorbance related to other gases
60
measurement techniques of etco2 include (2)
main stream and side stream capnography
61
mainstream capnography
advantages
disavtanges
advantages: Less time delay
disadvantages: potential for burns r/t heated circuit,
increases dead space
heavy -> can kink ETT.
62
Side stream capnography works by
aspirating a fixed amount of gas/minute to analyze in the sampling cell via tubing
63
side stream capnography should be
as close to ETT as possible
64
Potential problems with side stream capnography
time delay
potential disconnect
water vapor condensation, traps/filters used
65
capnogram =
Pco2 vs time
has 4 phases
66
Phase 1 of capnogram (4)
Should have no CO2 reading,
represents inspiration and beginning of expiration.
Dead space gas exhaled.
Inspiratory baseline
67
Phase 2 of capnogram (3)
An expiratory upstroke!
Sharp upstroke represents rising CO2 level in sample
mixture of dead space and alveolar gas
68
Slope of line in phase 2 of capnogram represents (~3)
evenness of alveolar emptying
straight = healthy, no air trapping
sloped = air trapping
69
Phase 3 of capnogram (5)
Alveolar plateau
Constant or slight upstroke
Longest phase
Alveolar gas is sampled
Peak at the end of plateau is where reading is taken
70
Reading of ETCO2 is taken at
peak of phase 3 (alveolar plateau)
71
Phase 4 of capnogram (2)
Beginning of inspiration
co2 concentration has rapid decline to inspired value
72
5 characteristics of capnogram
```
frequency
height
rhythm
baseline
shape
```
73
Primary use of capnogram is to
verify ETT placement in the trachea vs esophagus
74
Indications of tracheal intubation on capnogram
presence of stable CO2 waveforms for 3 breaths >30mmHG
75
Causes of rebreathing = (3)
equipment dead space
exhausted CO2 absorber
inadequate FGF
76
Contributors to rising CO2 when ventilation unchanged (6)
1. malignant hyperthermia
2. release of tourniquet
3. release of aortic/major vessel clamp
4. IV bicarb administration
5. insufflation of CO2 into peritoneal cavity
6. equipment defects, (expiratory valve stuck CO2 exhausted)
77
Gradual Decrease in ETCO2
likely hyperventilation, reflects increased minute ventilation
78
Rapid decrease in ETCO2
- PE, V/Q mismatch
- Cardiac arrest
? Sampling error
79
Sampling errors in ETCO2
disconnects, high sampling rate with elevated FGF
80
Capnogram pattern in obstructive lung disease
COPD/Asthma/Bronchoconstriction/Acute obstruction
- slow rate of rise in Phase ii
- steep upslope of phase iii (in extreme cases may not see phase iii)
81
Spontaneous ventilation/recovery from neuromuscular blockade on a capnogram
tugging the middle of plateau
82
Carbon dioxide absorber works by (~5)
```
chemical neutralization of cO2
Base neutralizes an acid
acid:carbonic acid (formed by CO2/H2O)
base: some hydroxide (alkali or alkaline earth metal)
end product: water, a carbonate, heat
```
83
Older CO2 absorbers (2 canisters) were a problem because (2)
1. couldn't change during the case because disturbs circle system integrity
2. common sources of leaks
84
Modern single canister models have
bypass feature so you can change during case
85
4 common absorbents
1. soda lime (sodium hydroxide lime)
2. amsorb plus (calcium hydroxide lime)
3. baralyme
4. litholyme (lithium hydroxide)
86
Soda lime contains %
Sodium Hydroxide Lime
```
4% sodium hydroxide
1% potassium hydroxide
15% H2O
0.2% silica
80% calcium hydroxide
```
87
Characteristics of soda lime
silica added for hardness to prevent dust
capable of absorbing 26 L of CO2 for 100 g of absorbent granules
water is present as thin film on granule surface
MOISTURE IS ESSENTIAL reaction makes place between ions that only exist in presence of water
a pound of CaOH can absorb 0.59 lb of CO2
88
Soda Lime Reaction
| formula
CO2+H2O H2CO3 + 2NAOH(KOH) NA2CO3(K2CO3) + 2H2O + HEAT
^predominant reaction b/c faster^
slower reaction:
CO2 + Ca(OH)2 CaCo3 + h2o + heat
89
Soda Lime Rxn in words
"Carbon dioxide combines with water to form carbonic acid, carbonic acid reacts with the hydroxides to form sodium (or potassium) carbonate, water, and heat.
Some carbon dioxide reacts CaOh2 but this reaction is much slower.
90
Amsorb Plus (Calicum Hydroxide Lime) contains
80% calcium hydroxide
16% water
1 -4 % calcium chloride
91
Characteristics of calcium hydroxide lime/Amsorb Plus (2)
1. calcium sulfate and polyvinlyprrolidine added hardness to prevent dust
2. capable of absorbing 10L of CO2/100g of absorbent granules
92
Calcium Hydroxide Lime/Amsorb Plus Reaction Formula
CO2 + H2O H2CO3 + Ca(OH)2 CaCO3 + 2H20 + heat
93
Calcium hydroxide rxn in words
carbonic acid + calcium hydroxide calcium carbonate + water + heat
94
Baralyme was voluntarily pulled from market b/c of
risk of fire
95
Baralyme (Barium Hydroxide) consists of
20% Barium Hydroxide
| 80% Calcium Hydroxide
96
Characterstics of Baralyme (7)
Small amounts of sodium/potassium hydroxide may be added
Granules are 4-8 mesh
No hardening agent is needed
It is slightly less efficient than Soda lime but is less likely to dry out
No water
Implicated in fires
Absorptive capacity similar to soda lime of 26 L co2 / 100 g granules
97
Baralyme Reaction formula
BaOH + 2(8H2O) + CO2 -> BaCO3+ 9H2O + heat.
9h2o + co2 -> 9H2CO3
9H2CO3 + 9Ca(OH)2 -> 9CaCO3 + 18H2O + heat
98
Litholyme (Lithium Hydroxide Monohydrate) components
75% lithium hydroxide (LiOH)
12-19% H2O
<3% lithium chloride
99
Characteristics of litholyme
also comes in anhydrous form
1 pound of LiOH absorbs 0.91 lb of CO2
100
Litholyme reaction formula
2LiOH + H2O + CO2 Li2CO2 + 3H2O - heat
101
Indicators (5 things to know)
1. An acid or base whose colors depends on pH
2. Color conversion signals absorber exhaustion
3. Replace absorbent with 50 - 70% color change
4. Color reverts back with rest, especially in NaOH containing formulas
5. Ethyl violet - most common, critical pH 10.3
102
Phenolphthalein
fresh; white
| used; pink
103
Ethyl Violet
fresh; white
| used; purple
104
Clayton Yellow
fresh; red
| used; yellow
105
Ethyl Orange
fresh; orange
| used ; yellow
106
mimosa 2
fresh; red
| used; white
107
Size of absorbent granules (4)
4-8 mesh in size
irregular shape -> increased surface area
small granules increase resistance but also provide greater surface area
blend of large and small minimize resistance with little sacrifice in absorbent capacity
108
Granule hardness (3)
Not enough hardness = excessive powder which can lead to channeling and caking
Hardness is tested with steel ball bearings and screen pan
& of original remaining = hardness number,
hardness number should be >75
109
Silica in soda lime
is to increase hardness
110
Channeling results from
loosely packed granules
111
Some manufactures may now use
a polymer to bind the granules in pre-formed channels to prevent channeling
112
Air space in the co2 absorber occupies
48 to 55%
113
Strong bases capable of degrading volatile gases
absorbents containing KOH and also NaOH
114
Compound A has been found
to cause nephrotoxic effects In rats
115
To prevent theoretical formation of compound A
Manufactures recommend not more than 2 MAC hours at flow rates <2 L/min
116
Carbon monoxide has been known to accumulate
in desiccated (Dry) NaOH and KOH containing absorbents when they are not used for 24 to 48 hours.
117
With dried out absorbents a slow
reaction occurs with the volatile agents and absorbents that produces carbon monoxide, can result in critically high levels of carboxyhemoglobin in exposed patients .
118
Desflurane is associated with
highest accumulation of carbon monoxide
119
Anesthesia Safety Foundation Recommendation on Safe Use of Carbon Dioxide Absorbents (6)
1. Turn of 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
120
DISS and PISS are required
for all anesthesia machines
121
KISS
key index safety system, part of vaporizer
122
At altitude, you need to increase concentration of
tec-6 vaporizer, desflurane.
because tec 6 will heat des to 39 / 2 atm regardless of ambient temperature to deliver a constant percentage that will be lower at 350 mmHG thats 750 mmHg
123
Vaporizers are made of metals with
high specific heats and high thermal conductivity to maintain uniform internal temp
124
Most vaporizers are (3)
temperature compensated
agent specific
variable by-pass
125
Potential Vaporizer Hazards (7)
Wrong agent in the vaporizer
(high - low high or low - high - low)
Contamination (leaving it open)
Tipping
Overfilling
Simultaneous administration of vapors
leaks
pumping effect
(alternating pressure in pipeline that ends up giving more gas than expected)
126
Not enough hardness =
Not enough hardness = excessive powder which can lead to channeling and caking
