Gas Systems and Vaporizers

Question 1

What is the color coding system for:

1. O2
2. N2O
3. air
4. nitrogen
5. helium

Answer 1

1. green
2. blue
3. yellow
4. black
5. brown

Question 2

How much psi and liters does a full E size cylinder for O2, air, and N2O hold?

Answer 2

1. O2 = 2000-2200 psi = 625-700 liters
2. air = 1900-2000 psi = 625 liters
3. N2O = 745 psi = 1590 liters

Question 3

What is N2O stored as?
How is it measured?
What does the pressure of the tank not indicate?

Answer 3

• 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

Question 4

Where can you look up the purity of medical gases?

Who enforces the purity?

Answer 4

• U.S. Pharmacopoeia

- FDA

Question 5

Who regulates all aspects of medical gas cylinders?

Answer 5

Dpmt of transportation (DOT)

Question 6

Describe the permanent markings, labels/decals, tags

on cylinders.

Answer 6

-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

Question 7

What is vaporization?

Answer 7

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

Question 8

What 3 things are dependent on vaporization?

Answer 8

1. vapor pressure
2. temperature
3. amount of carrier gas used

Question 9

What is vapor pressure?

Answer 9

-gas molecules bombard surface of liquid (tension) and the walls of the container creating a vapor pressure

Question 10

What are the vapor pressures for: (at 20 degrees C)

1. halothane
2. isoflurane
3. desflurane
4. enflurane
5. sevoflurane

Answer 10

1. 244 mmHg
2. 240 mmHg
3. 669 mmHg
4. 172 mmHg
5. 160 mmHg
   (these are relateive to atm pressure = 760 mmHg)

Question 11

What effect does heat/cold have on vapor pressure?

Answer 11

it increases/decreases rate of vaporization

Question 12

What is latent heat of vaporization?

Answer 12

of calories to change 1 gram of liquid into vapor w/o a temperature change

Question 13

Where does the energy of vaporization come from?

Answer 13

the liquid itself (or an outside source)

Question 14

What is specific heat of vaporization?

Answer 14

# of calories to increase temp 1 gram of a substance by 1 degree C
(substance can be liquid, sold, gas)

Question 15

What is thermal conductivity?

Answer 15

measure of speed with which heat flows thru a substance

Question 16

What does higher thermal conductivity indicate?

Answer 16

the better the substance conducts heat

Question 17

What effect does altitude have on barometric pressure?

Answer 17

increased altitude = decreased pressure

decreased altitude = increased pressure

Question 18

When does boiling point occur?

Answer 18

when vapor pressure = barometric pressure

Question 19

What effect does temperature have on vaporization?

Answer 19

increased temp = increased vaporization

decreased temp = increased vaporization

Question 20

What are 3 characteristics of vaporizers?

Answer 20

1. agent specific
2. temperature compensated (piece of vaporizer)
3. variable bypass (chamber in vaporizer)

Question 21

What is variably bypass vaporizer?

Answer 21

• 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

Question 22

If altitude changes occur, what must happen to the vaporizer?

Answer 22

-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)

Question 23

What is special about desflurane?

Answer 23

it is highly volatile (goes into vapor easily) due to its vapor pressure (669 mmHg) so close to atm pressure (760 mmHg)

Question 24

What is the TEC 6 vaporizer?

Answer 24

• 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

Question 25

What is the altitude effect on variable bypass of vaporizers?

Answer 25

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’)

Question 26

What is the altitude effect on TEC 6 vaporizer?

Answer 26

• 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

Question 27

What are copper kettles?

Answer 27

-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

Question 28

What are potential vaporizer hazards?

Answer 28

1. wrong agent
2. contamination
3. tipping
4. overfilling
5. simultaneous admin of more than one vapor
6. leaks
7. pumping effect

Question 29

What is high-low-high and low-high-low regarding wrong agent in vaporizer?

Answer 29

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)

Question 30

What is the pumping effect with vaporizer use?

Answer 30

-tends to occur when pipeline gas is used by multiple people at same time (i.e. preoxygenation for first case) causing a pumping effect