Gas Systems and Vaporizers Flashcards
What is the color coding system for:
- O2
- N2O
- air
- nitrogen
- helium
- green
- blue
- yellow
- black
- brown
How much psi and liters does a full E size cylinder for O2, air, and N2O hold?
- O2 = 2000-2200 psi = 625-700 liters
- air = 1900-2000 psi = 625 liters
- N2O = 745 psi = 1590 liters
What is N2O stored as?
How is it measured?
What does the pressure of the tank not indicate?
- liquid
- pressure will remain 745 psi until last drop of N2O left and then go to 0; must be weighed to measure amount
- it does not reflect amount left in tank
Where can you look up the purity of medical gases?
Who enforces the purity?
- U.S. Pharmacopoeia
- FDA
Who regulates all aspects of medical gas cylinders?
Dpmt of transportation (DOT)
Describe the permanent markings, labels/decals, tags
on cylinders.
-permanent markings = DOT specification number of PSI, manufacturer, serial number
(if there is no star, must be tested every 5 years instead of every 10 years)
-labels/decals of contained gas, “CAUTION” instructions, “nonflammable”
-tags indicating full/in use/empty
What is vaporization?
conversion of liquid to gas (necessary for inhaled anesthetics) - molecules of a volatile agent in a closed container are distributed b/n liquid and gas phases
What 3 things are dependent on vaporization?
- vapor pressure
- temperature
- amount of carrier gas used
What is vapor pressure?
-gas molecules bombard surface of liquid (tension) and the walls of the container creating a vapor pressure
What are the vapor pressures for: (at 20 degrees C)
- halothane
- isoflurane
- desflurane
- enflurane
- sevoflurane
- 244 mmHg
- 240 mmHg
- 669 mmHg
- 172 mmHg
- 160 mmHg
(these are relateive to atm pressure = 760 mmHg)
What effect does heat/cold have on vapor pressure?
it increases/decreases rate of vaporization
What is latent heat of vaporization?
of calories to change 1 gram of liquid into vapor w/o a temperature change
Where does the energy of vaporization come from?
the liquid itself (or an outside source)
What is specific heat of vaporization?
# of calories to increase temp 1 gram of a substance by 1 degree C (substance can be liquid, sold, gas)
What is thermal conductivity?
measure of speed with which heat flows thru a substance
What does higher thermal conductivity indicate?
the better the substance conducts heat
What effect does altitude have on barometric pressure?
increased altitude = decreased pressure
decreased altitude = increased pressure
When does boiling point occur?
when vapor pressure = barometric pressure
What effect does temperature have on vaporization?
increased temp = increased vaporization
decreased temp = increased vaporization
What are 3 characteristics of vaporizers?
- agent specific
- temperature compensated (piece of vaporizer)
- variable bypass (chamber in vaporizer)
What is variably bypass vaporizer?
- portion of gas flow passes into vaporizing chamber where it will become saturated with vapor
- this vapor-saturated portion rejoins gas flow for dilution to deliverable concentrations
If altitude changes occur, what must happen to the vaporizer?
-re-calibration to assure accurate % delivered anesthetic gas
-% delivered is related to agent’s vapor pressure compared to barometric pressure (atm)
(increased altitude = decreased pressure, vice versa)
What is special about desflurane?
it is highly volatile (goes into vapor easily) due to its vapor pressure (669 mmHg) so close to atm pressure (760 mmHg)
What is the TEC 6 vaporizer?
- special vaporizer for desflurane that creates a false higher pressure with heat (requires outlet) to increase pressure in vaporizer to 2 atm = 1520 mmHg
- makes desflurane think it is in a higher pressure so it stays liquid
What is the altitude effect on variable bypass of vaporizers?
you are delivering a higher concentration of volatile agent at higher altitudes (lower barometric pressure) but maintaining same partial pressure of agent
x’ = x (p/p’)
What is the altitude effect on TEC 6 vaporizer?
- effect is that you have to deliver higher dialed concentrations of Des at higher altitude (lower barometric pressure); conversely, you would alter concentration dial to decrease output in lower altitude to avoid delivering overdose of anesthetic
- required dial setting = normal dial setting (%) x 760 mmHg/ambient pressure mmHg
What are copper kettles?
-historical vaporizers
-used flowmeter for kettle (MEASURED FLOW)
-gas enters thru central tube in vaporizer to “LOVING CUP”
-flow of gas down toward liquid (BUBBLE THRU)
-highly concentrated vapor exits vaporizer and is diluted into fresh gas
(the most dilution to liquid = more vapor needed for deliver = costly)
-SUMMARY: vapor pressure of agent effects concentration delivered
What are potential vaporizer hazards?
- wrong agent
- contamination
- tipping
- overfilling
- simultaneous admin of more than one vapor
- leaks
- pumping effect
What is high-low-high and low-high-low regarding wrong agent in vaporizer?
hi-lo-hi = high vapor pressure agent into vaporizer that is for low vapor pressure = high concentration (overdose) lo-hi-lo = low vapor pressure agent into vaporizer that is for high vapor pressure = low concentration (underdose)
What is the pumping effect with vaporizer use?
-tends to occur when pipeline gas is used by multiple people at same time (i.e. preoxygenation for first case) causing a pumping effect
