Medical Gas Systems and Vaporizers Objectives Flashcards
What are 2 sources for gases?
piped in and cylinders ( E size)
Name the colors associated with each of the following gases: Oxygen; Nitrous oxide; air; nitrogen; helium
O2: green N2O: blue air: yellow N: black He: brown
When are E size O2 cylinders considered full? How does the pressure reading change as the tank empties?
2000-2200psi & ~625-700L
as O2 is used; pressure falls PROPORTIONALLY
When is an air tank considered full? How does pressure reading change as the tank empties?
1900-2000psi w/ ~625L
Like O2: pressure falls in proportion to the amount left in the tank
When is an E tank of N2O considered full? Does the pressure reading indicate the amount left in the tank?
745psi w/ ~1590L
NO! N2O is stored as liquid; therefore pressure reading does not indicate amount left in the tank
When does the psi reading on a tank of N2O drop?
only when all of the liquid is evaporated, at which time the pressure will drop in direct proportion to the rate at which gas is used
At this point the tank is nearly empty
How do you figure out if your N2O tank is full?
weigh it
What agency specifies the purity of medical gases? Who regulates this?
United States Pharmacopeia; regulated by FDA
What agency dictates the requirements for manufacturing, filling, qualification, transportation, storage, handling, maintenance, re-qualification, and disposition of medical gas cylinders and containers?
DOT
What 3 things must be on each cylinder per the DOT?
Permanent markings: specific to each cylinder
Labeling: label or decal on side or shoulder; may not cover the permanent marking
Tags: Full, in use, empty
For the PISS system, there are 7 pin positions. What is the order of the #ed pin positions on the radius of the yoke?
left to right: 6; 5; 4; 7; 3; 2; 1
How big are the pins?
4mm in diameter and 6mm long except for pin 7, which is slightly thicker
Safe handling procedures for cylinders dictate that you should never leave a cylinder upright without ___________ and should never leave an __________cylinder on the machine
support; empty
What are some other safety handling procedures for cylinders?
Never leave the plastic tape on the port while installing the cylinder.
Never rely on the cylinder’s color for id of its contents
Never oil valves
How do you clear particles of dust, metal shavings and other foreign matter from the cylinder valve before applying any fitting?
slowly and briefly “crack” the valve away from you and others
Why should the valve always be fully open when a cylinder is in use?
marginal opening may result in failure to deliver adequate gas
What is vaporization? Why does it matter?
conversion of liquid to gas
the inhalation agents we use today are liquid that must be converted to vapor to be inhaled
What is vaporization dependent on?
vapor pressure
temperature
amount of carrier gas used
How are molecules of a volatile agent distributed in a closed container?
btw liquid and gas phases
What creates vapor pressure of a gas within a closed container?
the gas molecules inside the container bombard the surface of the liquid and the walls
What is vapor pressure contingent on?
temperature and physical characteristics of the liquid, i.e. boiling point?
What happens to vapor pressure as temperature increases?
it increases because more molecules enter vapor phase
What are the vapor pressures of the following gases at 20 degrees Celsius: Enflurane, Isoflurane, Halothane, Sevofluane, Desflurane?
Enflurane: 172mmHg Isoflurane: 240mmHg Halothane: 244mmHg Sevoflurane: 160mmHg Desflurane: 669mmHg
What does passing a carrier gas over the liquid anesthetic do?
shifts the equilibrium of gaseous and liquid phases toward the vapor phase;
What is the latent heat of vaporization? Where does this heat come from?
of calories required to change 1 gram of liquid into vapor w/o temperature change; energy for vaporization comes from the liquid itself (or an outside source)
If there is not an outside source of energy to supply the vaporization, what happens?
temperature of the liquid will drop
What happens as temperature drops to rate of vaporization?
rate of vaporization will further decrease (therefore we need a system to keep temp of liquid constant)
What is specific heat?
# of calories required to increase the temp of 1 gram of a substance by 1 degree C substance can be liquid, solid or gas
What does the specific heat of an anesthetic agent indicate?
how much heat must be added in order to maintain a constant rate of vaporization
What is thermal conductivity?
a measure of speed with which heat flows through a substance
The ____________ the thermal conductivity, the better the substance conducts heat.
higher
How does an increase or decrease in altitude affect barometric pressure?
increase altitude: decrease barometric pressure
decrease altitude: increase
When does boiling point occur?
when vapor pressure= barometric pressure
How are temperature and vaporization related?
direct: as temp goes up or down so does vaporization
What are 3 characteristics of modern vaporizers?
agent specific
temperature compensated
variable bypass
How does a variable bypass vaporizer work?
portion of the gas flow will pass into the vaporizing chamber where it will become saturated w/ vapor
The vapor-laden portion then rejoins the gas flow for dilution to deliverable concentrations
What must you do if you decide to bring your anesthetic vaporizer the next time you go the mountains?
re-calibrate it in order to assure accurate % delivered anesthetic gas
The % delivered is relative to the agent’s _________in comparison to the _________
vapor pressure; barometric pressure
What is a TEC 6 vaporizer used for?
How does it work?
only for Desflurane
electrically heated; constant temp/pressure
electromechanically coupled dual circuit, gas-vapor blender
What is the effect of altitude on vaporizers?
you are delivering a higher concentration of volatile agent at higher altitude/lower barometric pressure but maintaining same partial pressure
x’=x(p/p’)
What kind of vaporizer is an out of circuit, non-agent specific, measure flow, bubble through machine? Is it used a lot in the US?
copper kettle; no
How do you determine the vapor output in a copper kettle?
Vapor output = CGXVP/BPVP
CG= flow rate of carrier gas in L/mi
VP= vapor pressure of anesthetic
BP= barometric pressure
How do you determine anesthetic concentration in a copper kettle?
Vapor ouput (ml/min)/total gas flow (ml/min)
What is an example of an electronically controlled vaporizer?
aladin cassette
What are potential vaporizer hazards?
wrong agent in vaporizer contamination tipping overfilling simultaneous admin of more than 1 vapor leaks pumping effect
In the variable bypass vaporizer, describe what occurs when the temperature decreases
the bimetallic strip allows less of the gas into the bypass chamber and more into the vaporizing chamber
In the variable bypass vaporizer, describe what occurs when the temperature increases?
the bimetallic strip allows more of the gas into the bypass chamber and less into the vaporizing chamber
The Tec 6 vaporizer is heated to _____________
2 atmospheres
What must be available for the TEC 6 vaporizer?
electricity; it has to be plugged in
