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N928 - Basics of Anesthesia > Anesthesia Gas Machine > Flashcards

Anesthesia Gas Machine Flashcards

1
Q

ideal properties of AGM

A

1) safe
2) efficient
3) economical
4) accurate

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2
Q

standard 6

A

equipment - adhere to manufacturer’s operating instructions and other safety precautions to complete a daily anesthesia equipment check

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3
Q

SPDD

A

supply
processing
delivery
disposal

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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
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5
Q

critical temperature oxygen

A

-118 degrees Celcius

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6
Q

critical temperature nitrous oxide

A

36.5 degrees Celcius

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7
Q

DISS

A

Diameter Index Safety System - each gas has a unique diameter and threading on the hose to prevent misconnection of gases

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8
Q

minimum reserve for bulk supply

A

1 day

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9
Q

why store oxygen as a liquid?

A

optimize space

1 L of O2 liquid = 860 L of O2 gas

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10
Q

pipeline supply pressure

A

50 psi (pounds per square inch)

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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
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12
Q

what happens if pipeline pressure less than 50 psi?

A

low pressure alarm + failsafe mechanism

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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

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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
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15
Q

FUC

A

different names for floating valves
Floating
Unidirectional
Check

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16
Q

locations of floating valves

A
  • between supply (cylinder or pipeline) and AGM
  • before common gas outlet
  • inspiratory and expiratory valves
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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
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18
Q

location of ball and spring valve

A

O2 flush valve

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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
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20
Q

location of diaphragm valve

A

1st and 2nd stage regulators

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21
Q

supply safety systems

A
  • color coding - cylinders and hoses
  • PISS - cylinder
  • KISS and DISS - pipeline supplies to AGM
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22
Q

PSIA

A
  • pounds per square inch absolute

- PSIA = Pgauge + Patm

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23
Q

PSIG

A
  • pounds per square inch gauge

- PSIG = Patm - Pabsolute

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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

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25
Q

hanger yoke

A
  • 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
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26
Q

hanker yoke gasket

A

exists between gas outlet of cylinder and AGM to prevent leak

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27
Q

safe handling of cylinders

A

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

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28
Q

safety valve of cylinder

A

prevents explosion if cylinder is exposed to extreme heat by providing a safe release of pressure

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29
Q

what can the safety valve of a cylinder be made of?

A
  • frangible copper disc
  • spring loaded valve
  • fusible plug (wood’s metal)
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30
Q

frangible copper disc

A

bursts when pressure is in excess of the service pressure by a factor of 2

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31
Q

spring-loaded valve

A
  • opens when pressure increases, and closes when pressure decreases
  • same thing as pressure relieving valve
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32
Q

Wood’s Metal

A

fusible plug that melts at a predetermined temperature to release gas from the cylinder safely when exposed to heat

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33
Q

wood’s metal melting temperature

A

157-220 degrees Fahrenheit

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34
Q

wood’s metal contents

A

Bismuth (50%)
Lead (25%)
Tin (12.5%)
Cadmium (12.5%)

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35
Q

adiabatic compression ignition

A
  • high pressure waves recompress, raising temperature

- crack cylinder - allows dust/debris to clear so it doesn’t ignite

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36
Q

trans fill cylinder

A

filling a small cylinder from a large one

DON’T DO IT

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37
Q

PISS

A

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

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38
Q

oxygen pin locations

A

2-5

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39
Q

nitrous oxide pin locations

A

3-5

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40
Q

medical air pin locations

A

1-5

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41
Q

7 required markings of cylinders

A

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

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42
Q

cylinder construction specifications

A
  • 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
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43
Q

FDA

A

Federal Food, Drug, & Cosmetics Act - regulates medical gases contained in cylinder

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44
Q

USP

A

United States Pharmacopoeia - sets standard for potency and purity

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45
Q

DOT

A

Department of Transportation -regulates cylinder design, construction, testing, marking, handling, filling, transportation, and disposal

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46
Q

CGA

A

Compressed Gas Association - sets standards for safe practice

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47
Q

NFPA

A

National Fire Protection Association - location, construction, installation of bulk systems; also has role in setting cylinder standards

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48
Q

E cylinder

A

most common size; attaches to hanger yoke on back of AGM

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49
Q

H cylinder

A

Large, stand alone cylinders that are chained to wall

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50
Q

cylinder use in anesthesia

A

emergency back up supply

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51
Q

green

A

oxygen

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52
Q

blue

A

nitrous oxide

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53
Q

yellow

A

medical air

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54
Q

oxygen cylinder pressure

A

1900 psi

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55
Q

nitrous oxide cylinder pressure

A

745 psi

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56
Q

medical air cylinder pressure

A

1900 psi

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57
Q

oxygen E cylinder capacity (L)

A

660 L

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58
Q

nitrous oxide E cylinder capacity (L)

A

1590 L

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59
Q

medical air E cylinder capacity (L)

A

625 L

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60
Q

five tasks of oxygen in AGM

A

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

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61
Q

other names for flowmeter

A

rotameter

flow control system

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62
Q

minimum oxygen flow requirement

A

250 mL/min - oxygen required to meet basal metabolic rate

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63
Q

two flowmeter flows

A

low - up to 1 L/min

high - up to 10-12 L/min

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64
Q

why is oxygen positioned closest to common gas outlet?

A

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

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65
Q

components of flowmeter

A
  • knob
  • needle valve
  • valve stops
  • flow tube/Thorpe tube
  • indicator float
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66
Q

oxygen knob

A

color coated and fluted so easy to find in an emergency

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67
Q

needle valve

A

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)

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68
Q

valve stop

A

prevents damage to the needle valve; just like a door stopper

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69
Q

Thorpe tube/flowtube

A
  • 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
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70
Q

indicator float

A
  • ball or bobbin
  • MUST rotate to indicate the flow of gas
  • ball reads in middle
  • bobbin reads at the top
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71
Q

electronic flowmeter

A
  • 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
Q

oxygen flush valve

A
  • 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
Q

fail-safe mechanism

A
  • 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
Q

low pressure alarm

A
  • signals low pressure of oxygen delivery
  • failsafe is initiated at this time
  • audible internal alarm
  • pressure differs by manufacturer
75
Q

low pressure alarm ohmeda

76
Q

low pressure alarm draeger

77
Q

proportioning system

A
  • 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
Q

mechanical link proportioning system ohmeda

A
  • oxygen and nitrous oxide linked by a chain

- oxygen flow increased automatically when nitrous oxide flow is increased

79
Q

pneumatic link proportioning system in draeger

A
  • 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
Q

how can hypoxic mixture still occur despite safety mechanisms in place?

A
  • misconnection of gas
  • defective pneumatics or mechanics
  • leaks downstream of flow control valves on flowmeters
  • use of a third inert gas
81
Q

components in a high-pressure system

A
  • hanger yoke
  • yoke block with check valves
  • cylinder pressure gauge
  • cylinder pressure regulators
82
Q

components of an intermediate pressure system

A

-pipeline inlets, check valves, pressure gauges
-ventilator power inlet
oxygen pressure-failure devices
-flowmeter valve
-oxygen second-stage regulator (if present)
-flush valve

83
Q

components of low pressure system

A
  • flowmeter tubes
  • vaporizers
  • check valves
  • common gas outlet
84
Q

vaporizer

A

blends fresh gas flow with sufficient vapor of inhaled anesthetic gas to form clinically useful concentrations

85
Q

vapor

A

gaseous state of a substance that is a liquid at room temperature and 1 atm of pressure

86
Q

evaporation

A
  • 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
Q

rate of vaporization depends on…

A
  • temperature
  • VP of liquid
  • partial pressure of vapor above liquid
88
Q

vapor pressure

A

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
Q

volumes %

A
  • 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
Q

latent heat of vaporization

A

amount of energy it takes to convert 1 g of liquid to a vapor without a temperature change in the remaining liquid

91
Q

specific heat

A

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
Q

thermal conductivity

A

measure of how fast a substance and transmit heat

93
Q

variable bypass vaporizer

A
  • 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
Q

measured flow vaporizer

A
  • 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
Q

tec 6 injector vaporizer

A
  • 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
Q

desflurane VP at 20 degrees celcius

A

669 mmHg

nearly boils at room temperature

97
Q

tec 6 + desflurane temperature and pressure

A
  • heats to 39 degrees celcius
  • pressurize to 1300 mmHg (saturated VP)
  • provides a more consistent flow of gas
98
Q

battery of tec 6 vaporizer

A

ONLY FOR ALARM

NOT for the actual vaporizer

99
Q

Tec 6 indicators/alarms

A
  • warm up (amber)
  • operational (green)
  • no output (red)
  • low agent (amber)
  • alarm battery low (amber)
100
Q

warm up (amber) tec 6

A

in warm up mode, can’t turn control dial

101
Q

operational (green) tec 6

A

vaporizer functional

102
Q

no output (red) tec 6

A

vaporizer can’t add agent vapor to gas flow due to lack of agent, tilting or malfunction

103
Q

low agent (amber) tec 6

A

less than 250 mL agent in sump

104
Q

alarm battery low (amber) tec 6

A

low battery voltage; battery ONLY powers alarms, not the vaporizer itself

105
Q

tec 6 vaporizer checkout

A
  • 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
Q

wicks and baffles

A

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
Q

factors that influence output of vaporizer

A
  • flow rate
  • temperature
  • intermittent back pressure
  • carrier gas composition
108
Q

flow rate influence on vaporizer output

A
  • 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
Q

temperature influence on vaporizer output

A
  • as temp increases, greater gas flow is directed through the bypass chamber
  • bimetallic strip decreases the flow through vaporizing chamber when temperature increases
110
Q

intermittent back pressure influence on vaporizer output

A

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
Q

carrier gas composition influence on vaporizer output

A
  • 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
Q

filler caps and filler ports

A
  • used to fill the vaporizers with inhaled anesthetic
  • color coded and fit specifically for each gas
  • cannot cross fill vaporizers!!!
113
Q

vaporizer interlock

A
  • 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
Q

hazards of modern vaporizers

A
  • 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
Q

five common characteristics of modern vaporizers

A
  • concentration control dial
  • bypass chamber
  • vaporizing chamber
  • filler port or filler cap
  • color coded tops
116
Q

isoflurane VP at 20 degrees

117
Q

halothane VP at 20 degrees

118
Q

enflurane VP at 20 degrees

119
Q

sevoflurane VP at 20 degrees

120
Q

desflurane VP at 20 degrees

121
Q

circle system

A
  • 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
Q

open anesthesia circuit

A
  • do not use reservoir bag
  • no rebreathing; high FGF
  • no valves or tubing
  • patient has access to atmospheric gases
123
Q

semi-open anesthesia circuit

A
  • higher FGF to ensure no rebreathing
  • ventilate more waste gas
  • has reservoir bag
  • FGF higher than minute
124
Q

semi-closed anesthesia circuit

A
  • 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
Q

closed

A

complete rebreathing occurs after CO2 is absorbed

126
Q

advantages of circle system

A
  • 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
Q

disadvantages of circle system

A
  • 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
Q

components of circle system

A
  • fresh gas inflow source
  • unidirectional valves
  • overflow/APL valve
  • gas reservoir bag
  • two corrugated 22mm diameter tubes
  • y piece connector
  • CO2 absorber
129
Q

fresh gas inflow source

A
  • from common gas outlet (comes from pipeline or cylinder supply)
  • 4-5 L/min flows is optimal fresh gas flow
130
Q

high flows in circle system

A 
1-1.5 times the minute ventilation of patient 
use for: 
-pre-oxygenation
-induction (wash-in)
-emergence (wash-out)
131
Q

low flows in circle system

A
  • use during maintenance of anesthesia

- conserves heat, humidity, and volatile anesthetic agent

132
Q

unidirectional/floating/check valves

A
  • 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
Q

APL valve

A

adjustable pressure limiting valve

134
Q

overflow valve/APL/pop-off

A
  • 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
Q

gas reservoir bag

A
  • 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
Q

two corrugated 22mm diameter tubes

A
  • inspiratory and expiratory limbs, extends them to patient

- most of the volume of circle system

137
Q

y-piece connector

A
  • 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
Q

CO2 absorber

A
  • serves to remove CO2 from expired gas to allow for safe rebreathing
  • allows for conservation of gas and anesthetic
  • decreases OR pollution
139
Q

soda lime composition

A
  • Ca(OH)2 - 94%
  • NaOH - 5%
  • KOH - <1%
  • Silica - 0.2%
  • moisture content (H2O) - 14-19%
140
Q

soda lime chemical reactions

A
  • CO2 + H2O –> H2CO3
  • H2CO3 + NaOH –> Na2CO3 + H2O + HEAT (EXOTHERMIC)
  • Na2CO3 + Ca(OH)2 –> CaCO3 + NaOH
141
Q

absorptive capacity of soda lime

A

26L of CO2 per 100g of absorbent

142
Q

compound a

A
  • sevo + soda lime with sevo FGF < 2L/min

- potential renal toxicity

143
Q

carbon monoxide production

A
  • highest risk is desflurane

- desflurane >/= enflurane > isoflurane&raquo_space; (halothane = sevoflurane)

144
Q

soda lime color when exhausted

145
Q

baralyme color when exhausted

146
Q

indicator for CO2 absorbent

A
  • ethyl violet - pH sensitive

- when pH reaches 10.3, changes from colorless (white) to blue/purple

147
Q

litholyme

A
  • lithium chloride
  • void of strong bases (no NaOH or KOH)
  • no compound A production
  • permanent color change
  • less heat, less expensive
148
Q

spiralith

A
  • enclosed in polymer sheet
  • no color change indicator
  • must use FiCO2 monitoring to determine rebreathing
149
Q

size of CO2 absorbent granules

A
  • 4 to 8 mesh
  • 1/8 to 1/4 inch
  • compromise between resistance to airflow and SA for absorptive capacity
150
Q

non-rebreathing systems

A
  • 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
Q

advantages of non-rebreathing systems

A
  • portable
  • low resistance so low WOB
  • no rebreathing
  • inexpensive, few moving parts
  • allows rapid changes in anesthetic
152
Q

disadvantages of non-rebreathing systems

A
  • lack conservation of moisture and heat

- require high FGF (less economical in that way)

153
Q

Mapleson systems

A
  • 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
Q

mapleson A

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
Q

mapleson B

A
  • fresh gas inlet and overflow (APL) valve closer together to decrease rebreathing
  • requires FGF 2-2.5x minute ventilation
156
Q

mapleson C

A
  • shorter expiratory limb than mapleson B
  • FGF and APL in same location as mapleson B
  • requires FGF 2-2.5x minute ventilation
157
Q

mapleson D

A
  • 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
Q

mapleson E

A
  • 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
Q

mapleson F

A
  • jackson-rees modification of mapleson D
  • requires FGF 2-3x minute ventilation
  • minimal dead space/low resistance
160
Q

ABCDEF

A 
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
Q

bain circuit (coaxial mapleson D)

A
  • 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
Q

advantages of bain circuit

A
  • FGF warmed by exhaled gas
  • improved humidification
  • ease of scavenging waste gases
  • lightweight
163
Q

disadvantages of bain circuit

A
  • 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
Q

pethick test

A
  • 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
Q

ventilator components

A
  • power source
  • drive mechanism
  • cycling mechanism
  • bellows mechanism
166
Q

ascending bellows

A
  • rise on expiration, fall on inspiration
  • standing bellows
  • more common and safer
167
Q

descending bellows

A
  • 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
Q

ventilation alarms

A
  • 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
Q

ventilator hazards

A
  • disconnection
  • occlusion/obstruction
  • misconnection
  • failure of emergency O2 supply
  • infection
170
Q

WAGs

A

waste anesthesia gases

171
Q

scavenger system

A

responsible for collecting and removing WAGS

172
Q

active scavenger

A

requires suction, requires positive and negative pressure relief, closed and open assembly

173
Q

passive scavenger

A

requires positive pressure relief, closed assembly

174
Q

closed scavenger

A
  • 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
Q

open scavenger

A
  • 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

N928 - Basics of Anesthesia (17 decks)

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