Gas Machine Flashcards
Coaxial circle system
Breathing hose with inspiratory limb contained in the expiratory limb
-Less bulky, heats and humidifies itself
APL Valve
“Adjustable pressure limiting”
- Open for spontaneous respiration
- Partially open for manual/assisted ventilation
- Closed -> Barotrauma
FGF for rebreathing or not
- <0.5 L/min = full reliance on absorbant
- >5-8 L/min = little reliance on absorbant, exhaled CO2 is diluted and sent to scavenger
Sodalime (catalyst, equation, problem)
- Catalyst: Sodium hydroxide or KOH
- H2CO3 + 2NaOH -> Na2OH3 + 2H2O + heat
- Compound A - nephrotoxic, more risk if have low FGF, sevo, increased temperature, dessication of sodalime leads to production
Amsorb plus (catalyst, equation, problem)
- Catalyst: Calcium hydroxide or calcium chloride
- H2CO3 + Ca(OH)2 -> CaCO3 + 2H2O + heat
- Less strong bases than sodalime, need more = more expensive
CO2 absorbent (size, indicator)
Granules 4-8 mesh size, optimizes surface area and resistance to air flow through
Indicator: Ethyl violet, critical pH=10.3
Hypercarbia clinical manifestations
- Increased RR
- Increased TV
- Ventricular irritability
- Flushing face/neck/thorax
- Increased ICP
Circuit pressure gauge
Measures breathing circuit pressure between expiratory and inspiratory valves
-Detects cuff leaks in ETT
NIOSH recommendations for WAG exposure (N2O vs Halogenated agents vs both)
N2O < 25ppm
Halogenated agents <2ppm
Halogenated agents + N2O <0.5ppm
OR ventilation system turnover
10 exchanges/hour
-Single most important factor in decreasing the anesthetic air pollution
Scavenging system interface, preferred type
Interface protects circuit/vent from positive/negative pressure
-Active=to wall suction >30L/min, open interface
Boiling point (vapor)
Temperature at which vapor pressure = atmospheric pressure
-Added energy/heat doesn’t increase temp, just changes to vapor
Interlock safety mechanism
For vaporizers to ensure only one is used at a time
Flow over vs injected vaporization
Flow over is used for all inhalation agents except desflurane, which is injected
Modern vaporizers (3 qualities)
Variable bypass -Constant concentration -Regulate flow through bypass/vaporizing Agent specific -With keyed fillers Temperature compensated -Steady output despite temperature changes
Specific heat
Calories required to increase the temperature of 1g of a substance by 1 degree C
Thermal conductivity
The speed at which heat flows through a substance
Latent heat of vaporization
Energy required to change 1g of liquid to a vapor without a change in temperature
-Leads to a loss in heat from the liquid
Vapor pressure
Pressure produced when vapor particles above a liquid in a sealed container collide with the container walls
- Increases with temp but not pressure
- Depends on physical characteristics of the liquid and temperature
Desflurane vaporizers and elevation
Doesn’t change concentration but decreases the partial pressure of the agent, so you need to increase the concentration
Temperature compensation of vaporizers
Bimetallic strip or expansion element
- Directs gas flow to bypass chamber when temperature is increased
- Made of copper/bronze: increased thermal conductivity
- Decreased temp: strip bends to direct gas to vaporizer
Pumping effect
Intermittent backpressure to vaporizers from positive pressure ventilation or O2 flush valve, could lead to vaporizer output
-One way check valve by the common gas outlet protects against this
Tec 6 Injector
- Electronic vaporizer for desflurance
- No FGF through it, injects a precise amount of vapor directly to the FGF
- Heats to 39C, pressure to 2atm
- Output varies inversely with elevation
Aladin cassette vaporizer
- Electronically controlled, flow over, variable bypass, and measured flow
- 2 parts: Vaporizing chamber, concentration control
- Can be tipped in any direction without worrying about spilling
Common gas outlet
- Receives all gasses and vapors, delivers them to the breathing system
- O2 flush goes directly here
- Common location for a disconnection
Nonrebreathing vs rebreathing systems
Non -Exhaled gasses with CO2 are removed from the system Rebreathing -Inhalation of previously expired gasses -CO2 may or may not have been removed
Mechanical dead space
Volume in circuit where gasses are rebreathed without change in composition
Where inhaled/exhaled gasses meet
-ETT, mask, up to Y piece
Active humidification of circuit problem
Less effective at preventing hypothermia
Mapleson breathing circuit (characteristics, examples, best types for spontaneous breathing vs controlled ventilation)
-No CO2 absorber
-Nonrebreathing circuit (depends on FGF)
-Ambu bag, T piece
-Types A-F
A: Best for spontaneous breathing
D: Best for controlled ventilation (Bain circuit modification)
