Gas Systems and Vaporizers Flashcards
What composes the DISS system
- consists of body, nipple, nut combo
- required for eveyr anesthesia machine
- non interchangeable connections
What are the common PISS nubmers we should know?
- Air (1,5)
- Oxygen (2,5)
- N2O (3,5)
- co2 (1,6)
- Entonox (7)
What color is nitrogen
Black
What color is helium
Brown
Who specifies purity of medical gases?
SPECIFIED by US Pharmacopeia/National Forumlary (USP/NF)and enforced by FDA
What does DOT regulate?
- Requirements for manufacturing
- filling
- qualification
- transportation
- storage
- handling
- maintenance
- re-qualification
- disposition of medical gas cylinders and containers
What do the cylinder markings indicate?
- Cylinder speicfication, cylinder material type, service/working pressure in PSI
- Serial number
- date of manufacture
- neck ring ID
- Retest marking
- is 10% overfill, star is meets qualification for 10yr retest instead of 5
- 4 is mont, L is fcaility, 60is year then eithe r+ or star
What do cylinder labels show?
Labels show Compressed Gas Association (CGA) marking system.
Diamond shape denotes hazard class
Left is name of contained gas
Statement of hazards to Right
LABELING CANNOT COVER PERMANENT MARKINGS
What is the purpose fo tags on cylinder?
- Full, inservice, empty connected by perforations
What is the safe handling procedures for cylinders?
- Never stand upright without support
- Never leave empty cylinder on machine
- Never leave plastic tape on port when installing cylinder
- Never rely only on cylinders color for ID of contents
- Never oil valves
- Crack cylinder away from you before mounting (adabatic)
- Valve should be fully open when in use
What does vaporization depend on?
- Vapor pressures
- moluecules of volatile agnet in closed container are distributed b/w liquid and gas phase
- Gas molecules bombard the surface of liquid and walls creating vapor pressure
- Temperature
- as temp increase, more molucules enter vapor phase so vapor pressure increases
- Amount of carrier gas used
Anesthetics are “volatile agents” because they convert to gas easily
Sevoflurane’s Vapor pressure?
160mmHg
Enflurane’s vapor pressure
172 mmHg
Isoflurane vapor pressure?
240 mmHg
Halothane vapor pressure?
244 mmHg
Desflurane vapor pressure
669mmHg
Describe the effect of temperature on vaporization of liquid?
- At room temp. L and V in equilibirum
- With heat, equation favors Vapor
- With cold, equation favors L
- wITH FGF over vaporizer, favors V
What happens to % sevoflurane compared to dial setting at very high flows and very low flows??
- At incredibly high flows- increased pressure variable bypass, decreases anesthetic gas delivered compared to what is dialed
- At very, very low flows (i.e. 0.2 L/min), delivering slightly less than what is on dial
Generic principle, increased flow causes increase pressure in vaporizer. This causes decreased amount of vapor (henry’s law)
What is latent heat of vaporization?
- Number of calories required to change 1 gram of liquid into vapor WITHOUT temp change
- Energy for vaporization comes from liquid itself (or outside source)
- in the absence of outside source of energy, temp of liquid itself will decrease during vaporization
- this causes rate of vaporization to further decrease
- we need system where temp of liquid remains constant
*
- in the absence of outside source of energy, temp of liquid itself will decrease during vaporization
What is specific heat?
- Number of calories required to increase the temp of one gram of a substance by one degree centigrade
- substance can be liquid, solid, gas
- Concept of specific heat is important in design, operation construction of vaporizers
- 1) Specific heat of anesthetic agent is important because it indicates how much heat must be supplied to liquid to maintain constant temp when heat lost during vaporization
- 2) Select vaporizer component materials that have high speicfic heat becuase these materials better resist temp changes associated with vaporization
What is thermal condictivity and why is it important with vaporizers?
- Thermal conductivity is the measure of speed with which heat flows through substance
- Higher thermal conductivity, better system conducts heat
- vaporizers are constructed of metals that have high thermal conductivity which helps maintain uniform internal temp during evaporation by allowing them to absorb environmental heat more effectively
What are principles of variable bypass vaporizers?
- agent specific
- temp compensated
- variable bypass
What is the variable bypass vaporizer?
- Portion of gas flow will pass into vaporizing chamber where it will become saturated with vapor
- The vapor laden portion then rejoins the gas flow for dilution to deliverable concentrations
What does temperature compensating valve do?
- If hot, valve moves to right, allowing more gas to bypass vaporizer
- If cold, direct more air into vaporizer
What is the tec 6 vaporizer for?
- For desflurane due to high volatility
- Uses electrical filament to heat desflurane to 39degrees, 2 atm of pressure. The high pressure removes need for pressurized carrier gas- instead fresh or diluent gas is ENTIRELY SEPARATE from vaporizing chamber
Is tec 6 a variable bypass vaporizer?
NO, it is gas-vapor blender
What is the working pressure in a tec 6 vaporizer?
1.1 atm
What is the purpose of the differential pressure transducer?
- This detects the FGF moving through circuit, with higher FGF, higher pressure is detected, sent to control electronics to allow more desflurane to be released by pressure regulating valve. This allows more desflurance to be released to maintain desired concentration
What is the purpose of R1?
Provide resistance to create backpressure of FGF to differential pressure transducer
What is R2 in TEC 6 vaporizer?
Concentration control valve
What is the aladin cassette?
Has CPU that uses information to titrate gases
What is the copper kettle?
- Non-agent specific
- measured flow, bubble through
- dedicated flowmeter for kettle (measured flow)
- gas comes up through central tube of vaporier to “loving cup”
- flow of gas then directed down toward liquid (bubble thorugh)
- highly concentrated vapor then exits the vaporizer and is diluted into fresh gas flow
How do you calculate the vpaor output of copper kettle?
CGxVP
BP-VP
How do you calculate anesthetic concentration of copper kettle calculations
vapor otuput in mL/min
total gas flow in mL/min
What is the effect of altitude on vaporization?
- Increased altitude- decrease barometic pressure
- Decreased altitude- increase barometric pressure
- % delivered relative to agent’s vapor pressure in comparison to barometric pressur
- vaporizer much be recalibrated to assure accurate % delievered anesthetic gas
- If not recalibrated, PP remains same, but concnetration looks different (i.e. 2 vs 4%)
What is altitude effect on variable bypass vaporizers?
- Delivering higher concentration of volatile agnet at higher altitude/lower barometric pressure but maintaining same partial pressure
- x’=x(p/p’)
What is altitude effect on tec 6 vaporizors?
Required dial setting= normal dial setting (%) x 760 mmHg
ambient pressure (mmHg)
Effect is that you would have to delivery higher dialed concentration of des at higher altitude/lower barometric pressure. Conversely, you would alter concnetration dial to decrease output in lower altitude to avoid delivering overdose of anesthetic
What are potential vaporizer hazards?
- Wrong agent in vaporizer
- high VP (agent)- low vp(vaporizer)- high anesthetia output
- Low VP(agent)- high VP(vaporizer)- low anesthesia output
- Contamination- dust/particles left in if bottle open
- Tipping- spilling
- Overfilling
- Simultaneous admin of more than one vapor (interlocking)
- Leaks (r/o with AM machine check)
- Pumping effect- occurs when all ORs start at same time, all pipelines are pumping at same time, fluctuation in pipeline pressure. suddent increase in anethetic output?
