Anesthesia Gas Machine Flashcards
1
Q
ideal properties of AGM
A
1) safe
2) efficient
3) economical
4) accurate
2
Q
standard 6
A
equipment - adhere to manufacturer’s operating instructions and other safety precautions to complete a daily anesthesia equipment check
3
Q
SPDD
A
supply
processing
delivery
disposal
4
Q
critical temperature
A
- temperature below which a gas is converted to a liquid
- requires drop in temperature to slow the molecules, so bulk supply cylinders are temperature controlled and pressurized
5
Q
critical temperature oxygen
A
-118 degrees Celcius
6
Q
critical temperature nitrous oxide
A
36.5 degrees Celcius
7
Q
DISS
A
Diameter Index Safety System - each gas has a unique diameter and threading on the hose to prevent misconnection of gases
8
Q
minimum reserve for bulk supply
A
1 day
9
Q
why store oxygen as a liquid?
A
optimize space
1 L of O2 liquid = 860 L of O2 gas
10
Q
pipeline supply pressure
A
50 psi (pounds per square inch)
11
Q
potential issues with pipeline supply
A
- pressure greater than or less than 50 psi
- cross connection
- contamination (particulate, bacterial, water)
- leak of gas
12
Q
what happens if pipeline pressure less than 50 psi?
A
low pressure alarm + failsafe mechanism
13
Q
KISS
A
Key Index Safety System - connector at the end of a gas hose that connects it to the wall outlet; each gas has a unique key to prevent misconnections
14
Q
floating valve
A
- promotes unidirectional flow of gas in AGM system
- opens/closes with pressure
- when there is pressure behind the valve, it will open; moves in the one direction gas flow pushes it so will only open one way
15
Q
FUC
A
different names for floating valves
Floating
Unidirectional
Check
16
Q
locations of floating valves
A
- between supply (cylinder or pipeline) and AGM
- before common gas outlet
- inspiratory and expiratory valves
17
Q
ball and spring valve
A
- ALL OR NOTHING
- if you depress the valve, it delivers everything
- if you let up on the valve it stops
18
Q
location of ball and spring valve
A
O2 flush valve
19
Q
diaphragm valve
A
- this is a pressure reducing valve
- reduces pressure from high to low to make it more manageable
- gas enters regulator at high pressure, hits diaphragm with a spring above it that provides a constant downward force, some of the high pressure is absorbed, pressure of gas that flows out is lower
20
Q
location of diaphragm valve
A
1st and 2nd stage regulators
21
Q
supply safety systems
A
- color coding - cylinders and hoses
- PISS - cylinder
- KISS and DISS - pipeline supplies to AGM
22
Q
PSIA
A
- pounds per square inch absolute
- PSIA = Pgauge + Patm
23
Q
PSIG
A
- pounds per square inch gauge
- PSIG = Patm - Pabsolute
24
Q
Bourdon Gauge
A
- measures high pressure relative to pressure of atmosphere
- thin walled tube straightens when exposed to pressure to move the indicator needle
25
hanger yoke
- place the cylinder connects to back of AGM
- orients the cylinder properly
- unidirectional flow due to presence of check/floating valve
- ensures tight gas seal
26
hanker yoke gasket
exists between gas outlet of cylinder and AGM to prevent leak
27
safe handling of cylinders
ALWAYS:
-protect cylinder valve when carrying (most fragile part(
NEVER:
-stand cylinder upright without support
-leave plastic cover on port
-use more than one washer between cylinder port and yoke
-rely on color for contents, READ the label
-oil the valve
-remove a cylinder from a yoke without filling space with yoke plug
28
safety valve of cylinder
prevents explosion if cylinder is exposed to extreme heat by providing a safe release of pressure
29
what can the safety valve of a cylinder be made of?
- frangible copper disc
- spring loaded valve
- fusible plug (wood's metal)
30
frangible copper disc
bursts when pressure is in excess of the service pressure by a factor of 2
31
spring-loaded valve
- opens when pressure increases, and closes when pressure decreases
- same thing as pressure relieving valve
32
Wood's Metal
fusible plug that melts at a predetermined temperature to release gas from the cylinder safely when exposed to heat
33
wood's metal melting temperature
157-220 degrees Fahrenheit
34
wood's metal contents
Bismuth (50%)
Lead (25%)
Tin (12.5%)
Cadmium (12.5%)
35
adiabatic compression ignition
- high pressure waves recompress, raising temperature
| - crack cylinder - allows dust/debris to clear so it doesn't ignite
36
trans fill cylinder
filling a small cylinder from a large one
| DON'T DO IT
37
PISS
Pin Index Safety System - each cylinder valve for a gas has a unique arrangement of holes that correspond to its intended contents; holes mate up with the specific hanger yoke for that gas
38
oxygen pin locations
2-5
39
nitrous oxide pin locations
3-5
40
medical air pin locations
1-5
41
7 required markings of cylinders
1) regulatory body (DOT) type and material of cylinder
2) serial number
3) purchase, user, manufacturer
4) manufacturer's manual
5) manufacturer's identifying symbol
6) retest date, re-tester, ID symbol, 110% filling, ten-year test interval
7) neck ring owner's ID
42
cylinder construction specifications
- entirely made of steel (meets chemical/physical requirements) except those to go in MRI suite (made of molybdenum alloy)
- walls 3/8 inch thick
- give pressure is service pressure
- tested at 1.66 times service pressure
43
FDA
Federal Food, Drug, & Cosmetics Act - regulates medical gases contained in cylinder
44
USP
United States Pharmacopoeia - sets standard for potency and purity
45
DOT
Department of Transportation -regulates cylinder design, construction, testing, marking, handling, filling, transportation, and disposal
46
CGA
Compressed Gas Association - sets standards for safe practice
47
NFPA
National Fire Protection Association - location, construction, installation of bulk systems; also has role in setting cylinder standards
48
E cylinder
most common size; attaches to hanger yoke on back of AGM
49
H cylinder
Large, stand alone cylinders that are chained to wall
50
cylinder use in anesthesia
emergency back up supply
51
green
oxygen
52
blue
nitrous oxide
53
yellow
medical air
54
oxygen cylinder pressure
1900 psi
55
nitrous oxide cylinder pressure
745 psi
56
medical air cylinder pressure
1900 psi
57
oxygen E cylinder capacity (L)
660 L
58
nitrous oxide E cylinder capacity (L)
1590 L
59
medical air E cylinder capacity (L)
625 L
60
five tasks of oxygen in AGM
1) proceeds to fresh gas flowmeter
2) powers through oxygen flush
3) activates fail-safe
4) activates low oxygen pressure alarms
5) compresses bellows of mechanical ventilators
61
other names for flowmeter
rotameter
| flow control system
62
minimum oxygen flow requirement
250 mL/min - oxygen required to meet basal metabolic rate
63
two flowmeter flows
low - up to 1 L/min
| high - up to 10-12 L/min
64
why is oxygen positioned closest to common gas outlet?
if there is a leak in any other flowmeter, the oxygen delivered to patient will be less affected if it is closest to the common gas outlet
65
components of flowmeter
- knob
- needle valve
- valve stops
- flow tube/Thorpe tube
- indicator float
66
oxygen knob
color coated and fluted so easy to find in an emergency
67
needle valve
what controls how much flow the patient receives - like a roller clamp on IV tubing; as you turn the flow up, the needle moves out allowing more gas (and thus higher flows)
68
valve stop
prevents damage to the needle valve; just like a door stopper
69
Thorpe tube/flowtube
- tapered glass tube (variable orifice)
- smaller at bottom and large at the top
- diameter = gas specific
- as orifice widens, greater flows required to create the same pressure difference across the bobbin - float higher in the tube indicating a higher liter flow
70
indicator float
- ball or bobbin
- MUST rotate to indicate the flow of gas
- ball reads in middle
- bobbin reads at the top
71
electronic flowmeter
- flow captured electronically
- chamber filled to a set pressure and then the gas is allowed to proceed
- # of times this cycle occurs per minute can be converted to gas flow
- 5 times more accurate than thorpe tube
72
oxygen flush valve
- ball and spring valve
- delivers 35-73 L/min at 50psi
- proceeds directly from gas supply (pipeline or cylinder) straight to common gas outlet; bypasses vaporizers so decreases agent
- DO NOT USE WHEN ATTACHED TO PATIENT
73
fail-safe mechanism
- if oxygen pressure falls below a certain limit, then there is not enough pressure to hold open the valves for other medical gases (nitrous oxide and medical air)
- designed to prevent the delivery of a hypoxic mixture to the patient
74
low pressure alarm
- signals low pressure of oxygen delivery
- failsafe is initiated at this time
- audible internal alarm
- pressure differs by manufacturer
75
low pressure alarm ohmeda
28 psi
76
low pressure alarm draeger
37 psi
77
proportioning system
- other names - hypoxic guard or link 25
- ratio of nitrous oxide to oxygen is kept at 3:1
- ensures final breathing mixture is at least 23-25% oxygen
78
mechanical link proportioning system ohmeda
- oxygen and nitrous oxide linked by a chain
| - oxygen flow increased automatically when nitrous oxide flow is increased
79
pneumatic link proportioning system in draeger
- maintains at least 23% oxygen
- does so by limiting flow of nitrous oxide
- shuts off nitrous oxide when pressure is less than 10 psi
- shuts of nitrous when oxygen flow is less than 200 mL/min
80
how can hypoxic mixture still occur despite safety mechanisms in place?
- misconnection of gas
- defective pneumatics or mechanics
- leaks downstream of flow control valves on flowmeters
- use of a third inert gas
81
components in a high-pressure system
- hanger yoke
- yoke block with check valves
- cylinder pressure gauge
- cylinder pressure regulators
82
components of an intermediate pressure system
-pipeline inlets, check valves, pressure gauges
-ventilator power inlet
oxygen pressure-failure devices
-flowmeter valve
-oxygen second-stage regulator (if present)
-flush valve
83
components of low pressure system
- flowmeter tubes
- vaporizers
- check valves
- common gas outlet
84
vaporizer
blends fresh gas flow with sufficient vapor of inhaled anesthetic gas to form clinically useful concentrations
85
vapor
gaseous state of a substance that is a liquid at room temperature and 1 atm of pressure
86
evaporation
- process of changing a liquid into a gas
- increase temperature, increase evaporation rate
- as evaporation proceeds, the remaining liquid and its container cool, bc heat energy carried from liquid
87
rate of vaporization depends on...
- temperature
- VP of liquid
- partial pressure of vapor above liquid
88
vapor pressure
pressure exerted by gas molecules as they exit the liquid phase in a closed container; molecules escape from volatile liquid to the vapor phase, creating a saturated VP at equilibrium
89
volumes %
- way to represent anesthetic vapor pressure
- volume of anesthetic vapor per 100 volumes of total gas
- to determine take the VP of anesthetic agent, divide by atmospheric pressure, and multiply by 100%
90
latent heat of vaporization
amount of energy it takes to convert 1 g of liquid to a vapor without a temperature change in the remaining liquid
91
specific heat
amount of energy needed to increase the temperature of 1g of a substance by 1 degree Celcius; vaporizers are made of metals with high specific heat to minimize temperature changes associated with vaporization
92
thermal conductivity
measure of how fast a substance and transmit heat
93
variable bypass vaporizer
- splitting device that allows some of the FGF to come in contact with the inhaled anesthetic and some to bypass it
- splitting ratio determined by internal resistance to gas flow, which is set by the control dials by the operator
- dial at high percent -- increased amount of gas flow through the vaporizing chamber (more anesthetic picked up)
94
measured flow vaporizer
- also called copper kettle or vernitrol
- anesthetic provider uses a formula to determine how much gas should be bubbled through anesthetic liquid
- amount set on an oxygen flowmeter (called oxygen vernitrol)
- concentration measured with dedicated thorpe tube (anesthetist adjusts and determines how much to supply)
- vaporizer output exits and then diluted in the total gas flow
- no automatic temperature control, so if the vaporizer cools, the VP lowers and the anesthetist needs to recalculate amount of gas flow -not as safe as modern
95
tec 6 injector vaporizer
- FGF passed through vaporizer in one circuit and it NEVER flows over or comes in contact with liquid agent
- vapor added to FGF as it flows through the vaporizer
- two control points - concentration control dial and transducer that is responsive to amount of FGF
- can be used for desflurane only (bc nearly boils at room temperature
- electrically heated - if power supply interrupted, must change anesthetic
- gas/vapor blender, NOT variable bypass
96
desflurane VP at 20 degrees celcius
669 mmHg
| nearly boils at room temperature
97
tec 6 + desflurane temperature and pressure
- heats to 39 degrees celcius
- pressurize to 1300 mmHg (saturated VP)
- provides a more consistent flow of gas
98
battery of tec 6 vaporizer
ONLY FOR ALARM
| NOT for the actual vaporizer
99
Tec 6 indicators/alarms
- warm up (amber)
- operational (green)
- no output (red)
- low agent (amber)
- alarm battery low (amber)
100
warm up (amber) tec 6
in warm up mode, can't turn control dial
101
operational (green) tec 6
vaporizer functional
102
no output (red) tec 6
vaporizer can't add agent vapor to gas flow due to lack of agent, tilting or malfunction
103
low agent (amber) tec 6
less than 250 mL agent in sump
104
alarm battery low (amber) tec 6
low battery voltage; battery ONLY powers alarms, not the vaporizer itself
105
tec 6 vaporizer checkout
- press and hold mute button until all lights/alarms activated
- turn on to greater than or equal to 1%
- unplug electrical connection
- "no output" alarm should ring in seconds - tests battery power for alarms
106
wicks and baffles
located inside vaporizing chamber of variable bypass vaporizer; increase the surface area for vaporization to optimally mix the carrier gas (FGF) and anesthetic vapor
107
factors that influence output of vaporizer
- flow rate
- temperature
- intermittent back pressure
- carrier gas composition
108
flow rate influence on vaporizer output
- flow through vaporizing chamber
- low rates (<250mL/min) and high rates (>15L/min) result in decreased agent output, one that is less than dial setting
- gas either spends less time in the vaporizing chamber or gas flow is not fast enough to pick up the proper amount of gas
109
temperature influence on vaporizer output
- as temp increases, greater gas flow is directed through the bypass chamber
- bimetallic strip decreases the flow through vaporizing chamber when temperature increases
110
intermittent back pressure influence on vaporizer output
positive pressure ventilation or high flows of oxygen flush valve create a back pressure in the vaporizer causing more FGF to be in vaporizing chamber; this increases concentration of inhaled anesthetic
111
carrier gas composition influence on vaporizer output
- second gas effect
- nitrous oxide is more soluble in the plasma so it pulls gases into the blood and creates new space for more gases in the alveoli
- increased concentration of anesthetic gas can be given
112
filler caps and filler ports
- used to fill the vaporizers with inhaled anesthetic
- color coded and fit specifically for each gas
- cannot cross fill vaporizers!!!
113
vaporizer interlock
- ensures only one vaporizer at a time is turned on
- gas will only enter the vaporizer that is turned on
- vaporizers must be properly seated
- if there are three vaporizer spots, and there is not one in the middle interlock system will not work!
114
hazards of modern vaporizers
- tipping - cannister tipped greater than 45 degrees, anesthetic leaks into bypass chamber
- overfilling - anesthetic can get into bypass chamber
- leaks - loose filler cap, o-ring junction, or mal-positioned; can cause patient recall
- simultaneous inhaled agent administration - removing center vaporizer can defeat interlock
- high VP agent placed in vaporizer of lower VP agent -concentration of agent delivered will be higher than what is dialed in
115
five common characteristics of modern vaporizers
- concentration control dial
- bypass chamber
- vaporizing chamber
- filler port or filler cap
- color coded tops
116
isoflurane VP at 20 degrees
239 mmHg
117
halothane VP at 20 degrees
243 mmHg
118
enflurane VP at 20 degrees
175 mmHg
119
sevoflurane VP at 20 degrees
170 mmHg
120
desflurane VP at 20 degrees
669 mmHg
121
circle system
- most popular ventilatory system in US
- can use for adults and children
- chemically cleanses CO2 by using absorbent - conservation of humidity and rebreathing of all other exhaled gases
- permits wide range of FGF
- allows for scavenging of waste gas
122
open anesthesia circuit
- do not use reservoir bag
- no rebreathing; high FGF
- no valves or tubing
- patient has access to atmospheric gases
123
semi-open anesthesia circuit
- higher FGF to ensure no rebreathing
- ventilate more waste gas
- has reservoir bag
- FGF higher than minute
124
semi-closed anesthesia circuit
- mechanism of contemporary circle systems
- some rebreathing occurs
- some waste flow is vented through the waste gas (APL) valve into the scavenging system
- used to deliver low flow anesthesia (1 L/min FGF)
125
closed
complete rebreathing occurs after CO2 is absorbed
126
advantages of circle system
- constant inspired concentrations
- conserves heat and humidity
- useful for all ages (use down to 10kg for pediatrics)
- useful for closed system or low flow anesthesia
- low resistance - less than ETT, but greater than NRB circuit
127
disadvantages of circle system
- relatively complex
- opportunities for misconnection or disconnection
- malfunction of unidirectional valves can occur (open - rebreathing, closed - occlusion)
- less convenient and portable than NRB circuits
128
components of circle system
- fresh gas inflow source
- unidirectional valves
- overflow/APL valve
- gas reservoir bag
- two corrugated 22mm diameter tubes
- y piece connector
- CO2 absorber
129
fresh gas inflow source
- from common gas outlet (comes from pipeline or cylinder supply)
- 4-5 L/min flows is optimal fresh gas flow
130
high flows in circle system
```
1-1.5 times the minute ventilation of patient
use for:
-pre-oxygenation
-induction (wash-in)
-emergence (wash-out)
```
131
low flows in circle system
- use during maintenance of anesthesia
| - conserves heat, humidity, and volatile anesthetic agent
132
unidirectional/floating/check valves
- opens with pressure and closes with pressure
- moves in the direction being pushed by gas flow only in one way
- just before the inspiratory and expiratory limbs of the circle system
- small flaps that allow gas flow in only one direction
- flap closes when flow is met from the opposite direction
133
APL valve
adjustable pressure limiting valve
134
overflow valve/APL/pop-off
- used during manual ventilation
- regulate pressure in breathing system during manual ventilation
- user controls ventilation of excess gas to scavenging system
- when pressure in system exceeds user-controlled setting, excess gas goes into the scavenging system
- open = set at min, most gas to scavenging system
- closed = set at 30-70 cm H2O, gas stays in circle system; amount depends on what APL set at
135
gas reservoir bag
- collection container for exhaled and fresh gas
- manual compression of bag sends gas into the CO2 absorbent and then to the inspiratory limb of circuit - allows for manual ventilation
- tactile aid to assess patient's spontaneous breathing efforts
136
two corrugated 22mm diameter tubes
- inspiratory and expiratory limbs, extends them to patient
| - most of the volume of circle system
137
y-piece connector
- connection at distal end of circle system that merges inspiratory and expiratory limbs
- where dead space begins
- can connect to filters, gas sampling line, ETT, mask, etc.
138
CO2 absorber
- serves to remove CO2 from expired gas to allow for safe rebreathing
- allows for conservation of gas and anesthetic
- decreases OR pollution
139
soda lime composition
- Ca(OH)2 - 94%
- NaOH - 5%
- KOH - <1%
- Silica - 0.2%
- moisture content (H2O) - 14-19%
140
soda lime chemical reactions
- CO2 + H2O --> H2CO3
- H2CO3 + NaOH --> Na2CO3 + H2O + HEAT (EXOTHERMIC)
- Na2CO3 + Ca(OH)2 --> CaCO3 + NaOH
141
absorptive capacity of soda lime
26L of CO2 per 100g of absorbent
142
compound a
- sevo + soda lime with sevo FGF < 2L/min
| - potential renal toxicity
143
carbon monoxide production
- highest risk is desflurane
| - desflurane >/= enflurane > isoflurane >> (halothane = sevoflurane)
144
soda lime color when exhausted
purple
145
baralyme color when exhausted
blue-grey
146
indicator for CO2 absorbent
- ethyl violet - pH sensitive
| - when pH reaches 10.3, changes from colorless (white) to blue/purple
147
litholyme
- lithium chloride
- void of strong bases (no NaOH or KOH)
- no compound A production
- permanent color change
- less heat, less expensive
148
spiralith
- enclosed in polymer sheet
- no color change indicator
- must use FiCO2 monitoring to determine rebreathing
149
size of CO2 absorbent granules
- 4 to 8 mesh
- 1/8 to 1/4 inch
- compromise between resistance to airflow and SA for absorptive capacity
150
non-rebreathing systems
- no unidirectional valves or CO2 absorbent
- WOB lower (bc no unidirectional valves)
- exhaled gas enters expiratory limb
- APL opens
- inspiration draws in gas from expiratory limb (fresh gas flow)
- semi-open system
151
advantages of non-rebreathing systems
- portable
- low resistance so low WOB
- no rebreathing
- inexpensive, few moving parts
- allows rapid changes in anesthetic
152
disadvantages of non-rebreathing systems
- lack conservation of moisture and heat
| - require high FGF (less economical in that way)
153
Mapleson systems
- semi-open/non-rebreathing systems
- described by prof. mapleson in 1954
- 5 different breathing circuit arrangements
- various arrangements of fresh gas inflow, tubing, reservoir bag, and expiratory valve
- classically mapleson A-E, and later F
154
mapleson A
- no rebreathing if FGF > alveolar ventilation
- for spontaneous ventilation need at least 70% of minute ventilation to prevent rebreathing
- for controlled ventilation, need FGF at least 2-3x minute ventilation
- overflow valve opens during expiration when max pressure reached
- inefficient with controlled ventilation
- exp/APL valve on patient side
155
mapleson B
- fresh gas inlet and overflow (APL) valve closer together to decrease rebreathing
- requires FGF 2-2.5x minute ventilation
156
mapleson C
- shorter expiratory limb than mapleson B
- FGF and APL in same location as mapleson B
- requires FGF 2-2.5x minute ventilation
157
mapleson D
- fresh gas inlet and overflow valve opposite mapleson A (FGF inlet close to patient, APL close to bag)
- requires FGF 2-3x minute ventilation
158
mapleson E
- valveless and bagless (basically t-piece)
- expiratory limb must be greater than patient TV to prevent entrainment of room air
- FGF 3x minute ventilation to prevent hypercarbia
159
mapleson F
- jackson-rees modification of mapleson D
- requires FGF 2-3x minute ventilation
- minimal dead space/low resistance
160
ABCDEF
```
A-APL on patient side
B-BOTH APL and FGF on patient side + corrugation
C-no corrugation
D-distant APL
E-no bag and no valve
F-no valve
```
161
bain circuit (coaxial mapleson D)
- inner tube that supplies fresh gas flow within the larger tube
- has bag and overflow/APL valve
- better scavenge than other versions of NRB circuits
162
advantages of bain circuit
- FGF warmed by exhaled gas
- improved humidification
- ease of scavenging waste gases
- lightweight
163
disadvantages of bain circuit
- unrecognized kink of inner tube
- rebreathing due to unknown disconnect of inner tube
- increased resistance
- FGF must be 200-300 mL/kg to prevent hypercarbia
164
pethick test
- tests inner gas hose of bain circuit for kink or disconnection
- occlude patient end of circuit
- close APL
- fill circuit using O2 flush valve
- release occlusion at elbow and flush
- venturi effect flattens reservoir bag if inner tube is patent
165
ventilator components
- power source
- drive mechanism
- cycling mechanism
- bellows mechanism
166
ascending bellows
- rise on expiration, fall on inspiration
- standing bellows
- more common and safer
167
descending bellows
- fall on expiration, rise on inspiration
- these are hanging bellows
- fills even when disconnected
- if they fall, take in outside air
- have addtl safety feature - CO2 apnea alarm
168
ventilation alarms
- high pressure (peak)
- low pressure
- continuing high pressure
- sub-atmospheric pressure
- low tidal vol/minute ventilation
- high RR
- reverse flow - incompetent expiratory vavle
- apnea/disconnect
169
ventilator hazards
- disconnection
- occlusion/obstruction
- misconnection
- failure of emergency O2 supply
- infection
170
WAGs
waste anesthesia gases
171
scavenger system
responsible for collecting and removing WAGS
172
active scavenger
requires suction, requires positive and negative pressure relief, closed and open assembly
173
passive scavenger
requires positive pressure relief, closed assembly
174
closed scavenger
- valves involved, passive or active disposal system
- adjustment knob controls how much suction applied
- accumulated gas will go into reservoir bag
- positive pressure release valve on reservoir bag will open at 5 cmH2O (hear a whistle), which is signal to adjust scavenge system
- if not adjusted, gases will release into OR
175
open scavenger
- no valves, open to the atmosphere
- only active disposal system
- reservoir required
- gas accumulates at bottom of canister; because it is heavier than air
- safer for patient bc no risk of barotrauma, but if used improperly can be unsafe for anesthetist
