Gas Machine

Question 1

Coaxial circle system

Answer 1

Breathing hose with inspiratory limb contained in the expiratory limb
-Less bulky, heats and humidifies itself

Question 2

APL Valve

Answer 2

“Adjustable pressure limiting”

• Open for spontaneous respiration
• Partially open for manual/assisted ventilation
• Closed -> Barotrauma

Question 3

FGF for rebreathing or not

Answer 3

• <0.5 L/min = full reliance on absorbant

- >5-8 L/min = little reliance on absorbant, exhaled CO2 is diluted and sent to scavenger

Question 4

Sodalime (catalyst, equation, problem)

Answer 4

• 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

Question 5

Amsorb plus (catalyst, equation, problem)

Answer 5

• Catalyst: Calcium hydroxide or calcium chloride
• H2CO3 + Ca(OH)2 -> CaCO3 + 2H2O + heat
• Less strong bases than sodalime, need more = more expensive

Question 6

CO2 absorbent (size, indicator)

Answer 6

Granules 4-8 mesh size, optimizes surface area and resistance to air flow through
Indicator: Ethyl violet, critical pH=10.3

Question 7

Hypercarbia clinical manifestations

Answer 7

• Increased RR
• Increased TV
• Ventricular irritability
• Flushing face/neck/thorax
• Increased ICP

Question 8

Circuit pressure gauge

Answer 8

Measures breathing circuit pressure between expiratory and inspiratory valves
-Detects cuff leaks in ETT

Question 9

NIOSH recommendations for WAG exposure (N2O vs Halogenated agents vs both)

Answer 9

N2O < 25ppm
Halogenated agents <2ppm
Halogenated agents + N2O <0.5ppm

Question 10

OR ventilation system turnover

Answer 10

10 exchanges/hour

-Single most important factor in decreasing the anesthetic air pollution

Question 11

Scavenging system interface, preferred type

Answer 11

Interface protects circuit/vent from positive/negative pressure
-Active=to wall suction >30L/min, open interface

Question 12

Boiling point (vapor)

Answer 12

Temperature at which vapor pressure = atmospheric pressure

-Added energy/heat doesn’t increase temp, just changes to vapor

Question 13

Interlock safety mechanism

Answer 13

For vaporizers to ensure only one is used at a time

Question 14

Flow over vs injected vaporization

Answer 14

Flow over is used for all inhalation agents except desflurane, which is injected

Question 15

Modern vaporizers (3 qualities)

Answer 15

Variable bypass
-Constant concentration
-Regulate flow through bypass/vaporizing
Agent specific
-With keyed fillers
Temperature compensated
-Steady output despite temperature changes

Question 16

Specific heat

Answer 16

Calories required to increase the temperature of 1g of a substance by 1 degree C

Question 17

Thermal conductivity

Answer 17

The speed at which heat flows through a substance

Question 18

Latent heat of vaporization

Answer 18

Energy required to change 1g of liquid to a vapor without a change in temperature
-Leads to a loss in heat from the liquid

Question 19

Vapor pressure

Answer 19

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

Question 20

Desflurane vaporizers and elevation

Answer 20

Doesn’t change concentration but decreases the partial pressure of the agent, so you need to increase the concentration

Question 21

Temperature compensation of vaporizers

Answer 21

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

Question 22

Pumping effect

Answer 22

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

Question 23

Tec 6 Injector

Answer 23

• 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

Question 24

Aladin cassette vaporizer

Answer 24

• 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

Question 25

Common gas outlet

Answer 25

• Receives all gasses and vapors, delivers them to the breathing system
• O2 flush goes directly here
• Common location for a disconnection

Question 26

Nonrebreathing vs rebreathing systems

Answer 26

Non
-Exhaled gasses with CO2 are removed from the system
Rebreathing
-Inhalation of previously expired gasses
-CO2 may or may not have been removed

Question 27

Mechanical dead space

Answer 27

Volume in circuit where gasses are rebreathed without change in composition
Where inhaled/exhaled gasses meet
-ETT, mask, up to Y piece

Question 28

Active humidification of circuit problem

Answer 28

Less effective at preventing hypothermia

Question 29

Mapleson breathing circuit (characteristics, examples, best types for spontaneous breathing vs controlled ventilation)

Answer 29

-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)