Anesthesia Gas Machine Flashcards
Pipeline Supply
Bulk gases delivered to back AGM
Intermediate pressure
50psi
DISS/KISS
Cylinder Supply
High pressure
Requires pressure regulator to ↓45-50psi
PISS
Floating Valve
Unidirectional or check valves (FUCk) Interface b/w pipeline supply & AGM Opens & closes w/ pressure Allows gas to enter machine Promotes one-way flow & prevents backward flow into tank or pipeline
Ball & Spring
All or nothing
O2 flush 35-75L/min @ 50psi directly from gas supply to CGO (bypasses vaporizers ↓volatile agent delivered to patient → recall risk)
Diaphragm Valve
Pressure reducing ↓pressure to lower, constant
1st & 2nd stage regulators
Maintains constant gas flow w/o changing supply pressure
AANA Standard 6
Equipment
American Society for Testing & Materials
ASTM
Specifies minimum performance & safety requirements used in AGM design for human use to enhance patient/operator safety
FDA
Federal food, drug, & cosmetic act
Regulates medical gases contained in cylinders
US Pharmacopeia
FDA
Sets potency & purity standards
Department of Transportation
DOT
Cylinder design, construction, testing, marking, handling, filling, & transportation
Compressed Gas Association
CGA
Sets standards on safe practice
National Fire Protection Association
NFPA
Location, construction, & bulk systems installation
Critical Temperature
Temperature below which gas converted to liquid form by pressure
Oxygen -118°C
Safety Systems
- Color coding
- Key filler caps & ports
- DISS/KISS/PISS
- Interlock system
- Link 25 or hypoxic guard
- CO2 absorber
- Unidirectional valves
Safety relief devices to prevent rupture - Frangible copper disc
- Spring-loaded valve
- Fusible plug (Wood’s metal)
Pin Index Safety System
PISS
Holes in cylinder valve that corresponds w/ 2 pins in the hanger yoke
6 numbered positions
Hanger Yoke
Connects cylinder to AGM
Orients the cylinder
Provides unidirectional flow (floating valve)
Ensures gas-tight seal
Oxygen PISS
2 + 5
Air PISS
1 + 5
N2O PISS
3 + 5
Wood’s Metal
Safety pressure relief device
Fusible plug that melts at predetermined temperature to release gas from cylinder
Alloy w/ bismuth, lead, tin, & cadmium
Cylinder Labeling & Markings
Regulatory body DOT cylinder type & material
Serial number
Purchase, user, & manufacturer
Manufacturer’s number
Manufacturer’s identifying symbol
Re-test date, re-tester, ID symbol, 110% filling, 10yr test interval
Neck ring owners ID
Cylinder Construction
Walls 3/8” thick
Tested at 1.66x the service pressure
Interior hydrostatic pressure test at least 1x every 5yr
Adiabatic Compression/Expansion
Rapid compression (exothermic) heat liberation does not have time to dissipate
Things in vicinity or in contact w/ gas will heat up
Rapid expansion (endothermic) surrounding area will feel cold
OR insulated area where compression/expansion occurs ჻ heat trapped and unable to dissipate
Oxygen Cylinder
660L/1900psi
Ensure at least 1000psi
2 & 5
Green
N2O Cylinder
1590L/745psi
Critical temperature 36.5°C
3 & 5
Blue
Air Cylinder
625L/1900psi
1 & 5
Yellow
E-Cylinder Calculation
Available psi x 0.347 = L
Total L / L/min flow = min remaining
Boyle’s Law
P1V1= P2V2
Low Pressure System
Flowmeters
Vaporizers
Fresh gas outlet (CGO)
Check valves
Intermediate Pressure System
45-55psig Receives gases from pipeline Unidirectional check valve DISS/KISS Pipeline inlets Check valves Pressure gauges Flowmeter valve
High Pressure System
Receives gases from cylinders at high variable pressures → regulators → lower, more constant pressures Pipeline supply 50psi E-Cylinders (745-1900psi) Hanger yoke & PISS O2 flush 35-75L/min @ 50psi Ends at regulator
Failsafe Valve
Designed to prevent unintentional hypoxic mixture delivery
Stops N2O delivery when O2 supply pressure falls below threshold setting
Low O2 Pressure Alarm
Low O2 pipeline or cylinder delivery
<30psi
Low Flow L/min
< 1Lpm
High Flow L/min
10-12Lpm
O2 Flowmeter
Fluted knob w/ 8 flutes
Positioned closest to the CGO to prevent hypoxic mixture (less likely to mix when downstream - closest to patient)
O2 always added to the gas mixture last (prior to vaporizers)
Flowmeter Components
Rotameters
- Knob
- Needle valve controls gas flow
- Valve stops prevent damage to needle valve from excessive force
- Flow tube
- Indicator float (ball or bobbin)
Minimum AGM Flow
O2 flow 200-300mL/min
Flowmeters
Thorpe tube
Tapered glass tube
Constant-pressure, variable orifice
R = P/ Q
Link 25
Hypoxic guard system
Proportioning system
N2O:O2
3:1 ratio
Dalton’s Law
Volume % = partial pressure / total ambient pressure x 100
P1 + P2 + P3 + PN = Total pressure
Vapor Pressure
Molecules escape from volatile liquid into vapor phase creating saturated vapor pressure at equilibrium
Pressure exerted by vaporized molecules
↑temperature ↑vapor pressure
Variable Bypass Vaporizers
Flow over vaporization method
Concentration dial splits stream into bypass & carrier
Flow over gas picks up liquid volatile agent
Calibrated specific to each volatile anesthetic agent
DO NOT TIP >45°
Vaporizer Complications
Vaporizer tipped >45° ↑concentration → overdose
Overfilling → volatile anesthetic liquid able to enter bypass chamber
Leaks - loose filler cap, O-ring junction, or malposition
Simultaneous inhaled agent administration - vaporizers not side-by-side interlock system possible to override
Higher VP agent place in lower VP agent vaporizer ↑concentration delivered
Gas-Vapor Blender
Tec 6
Measured flow
Bubble through vaporization
Heated to 39°C
Desflurane Tec 6
Gas-vapor blender
VP 669mmHg
BP 24°C
Electrically heated 39°C
Tec 6 Alarms
Warm-up mode = amber Operational = green No output = red Alarm battery low = amber - Lack agent, tilting, or malfunction - Low agent <250mL Internal battery only powers alarms NOT vaporizer
Circle System Components
FGF inflow source Overflow valve APL Gas reservoir bag Unidirectional valves Corrugated 22mm diameter tubes x2 Y-piece connector CO2 absorber
Semi-Closed System
Low FGF < minute ventilation
Some rebreathing
Semi-Open System
High FGF > minute ventilation
No rebreathing
Closed System
FGF = patient uptake
Complete rebreathing
Requires functional CO2 absorber
APL valve closed
CO2 Absorption
Soda lime & baralyme
Colorless when fresh
Exhausted pH 10.3 → purple (soda lime) & blue-grey (baralyme)
4 to 8 mesh
Soda Lime
Ca(OH)2 NaOH KOH Silica H2O
Mapleson
Semi-open (non-breathing)
A-F
Mapleson A
APL on patient side
Mapleson B
Both APL & FGF on patient side w/ corrugation
Mapleson C
No corrugation
Mapleson D
Distant APL
Mapleson E
Easy (no bag or valve)
Mapleson F
Jackson-Rees modification to Mapleson D
No APL valve on FGF
Bain Circuit
FGF warmed by exhaled gases (improved humidification)
100-300mL/kg to prevent hypercarbia
↑resistance
Pethick test to check inner gas hose integrity
Rebreathing d/t unrecognized inner tube disconnect or kink
Ascending Bellows
Standing bellows
Ascend on expiration
Descend on inspiration
Unable to fill when disconnected or leak present
Descending Bellows
Hanging bellows
Fall/lower on expiration
Fill even when disconnected
WAGs
Waste anesthesia gases
Scavenger Systems
Active (suction)
Passive
Open
Closed