Vaporizers

Question 1

What 3 factors influence vaporization?

Answer 1

vapor pressure, temp, amount of carrier gas

Question 2

How is vapor pressure created in a container of volatile gas?

Answer 2

molecules of volatile gas bombard surface of liquid volatile and the walls of container

Question 3

What phases of matter exist in a volatile’s container?

Answer 3

gas and liquid

Question 4

When is a container of volatile “saturated”

Answer 4

When molecules of volatile rate of evaporation = rate of condensation.

Question 5

A MAC of isoflurane is?

Answer 5

1.2 % (at 760 mmHg and 20 C)

Question 6

What are the vapor pressures of the following volatiles at 20 C? sevoflurane = enflurane = isoflurane = halothane = desflurane =

Answer 6

sevoflurane = 157 mmHg enflurane = 172 mmHg isoflurane = 240 mmHg halothane = 244 mmHg desflurane = 669 mmHg

Question 7

True or false vaporizers are agent specific?

Answer 7

True.

Question 8

When selecting “dose” of volatile, the anesthesia provider is selecting a _____. How is it calculated?

Answer 8

volume % volume % = pp of gas x total pressure (atmosphere) x 100%

Question 9

Why is temperature important to vaporizers? What’s the significance?

Answer 9

As temperature increases, so does pressure which means more molecules of volatile in gas phase. As temperature decreases, pressure decreases, less volatile in gas phase, could result in pt awareness.

Question 10

What is the heat of vaporization?

Answer 10

Number of calories req to change 1 g of liquid into vapor w/ out temp change.

Question 11

What happens to the temperature of the liquid in a vaporizer as liquid volatile becomes a gas (w/ no outside heat source). Whats the significance?

Answer 11

it cools the liquid as more agent vaporizes. subsequently reduces vaporization and causes inconsistency in delivery anesthetic. therefore, vaporizers must be designed to compensate for cooling that results from evaporation

Question 12

What is specific heat?

Answer 12

Number of calories required to increase temp of 1 g of substance 1 degree C

Question 13

Why is it important for vaporizers to be built from materials with high specific heat?

Answer 13

Resists changes in temperature that result from volatile evaporating to enable a constant temperature and therefore a consistent delivery of anesthetic

Question 14

Is evaporation of a liquid a cooling or a heating process?

Answer 14

Cooling

Question 15

Describe thermal conductivity.

Answer 15

Measure of speed w/ which heat flows through a substance. Higher thermal conductivity the better substance conducts heat

Question 16

Are vaporizers made with materials that have high thermal conductivity or low thermal conductivity? Why?

Answer 16

High, maintains a consistent temp in vaporizer and therefore a consistent delivery of gases

Question 17

Describe how changes in altitude affect barometric pressure.

Answer 17

High altitude, low pressure. Low altitude, increase pressure

Question 18

Describe boiling point. What happens at BP? What is the significance?

Answer 18

When VP = barometric pressure, liquid will undergo rapid vaporization. If volatiles boil we lose control of its delivery. We do not want volatiles to boil.

Question 19

Describe the relationship between temp and vaporization.

Answer 19

Direct. As temp increases, vaporization increases.

Question 20

What are the four types of vaporizers?

Answer 20

variable bypass, dual circuit/Tec 6 - desflurane, cassette vaporizer, injection vaporizer

Question 21

Part of the function of a vaporizer is to ______ volatile agent because the concentration of saturated gas is _______.

Answer 21

dilute, too high. volatile gas must be diluted to achieve pt safe dosing

Question 22

What is a MAC of sevoflurane?

Answer 22

2.2 %

Question 23

Describe variable bypass vaporizer.

Answer 23

Pressure and Temp compensated. Has vaporizing chamber and bypass chamber. Portion of gas flow bypasses vaporizer, portion passes into vaporizing chamber where it picks up anesthetic. Gets delivered to pt at the set amount. Chamber leading to vaporizer is maze shaped (Baffle) to prevent retrograde flow of anesthetic gas and subsequent large dose of anesthesia. It is also shaped so that slows the flow of gas to ensure maximum contact w/ anesthetic gas. BiMetal strip expands and contracts based on temperature (one way if cooled, one way if heated and influences amount of FGF.

Question 24

Describe a splitting ratio of 12:1 and what that means in a bypass vaporizer.

Answer 24

-Determine PP of anesthetic. -Determine how much of total gas flow going to vaporizer (smaller # of ratio) -Of that gas determine how much anesthetic gas will be picked up -Add this to total gas flow

Question 25

What would happen if you accidentally put high VP volatile in a low VP volatile’s vaporizer?

Answer 25

pt overdose, will deliver more anesthetic, can also cause hypoxic mixture of gases, especially at high altitude

Question 26

What would happen if you accidentally put low VP volatile in a high VP volatile’s vaporizer?

Answer 26

underdose of anesthesia, could cause pt awareness

Question 27

What could happen in the event that a vaporizer is contaminated?

Answer 27

bacteria could produce byproducts that are toxic

Question 28

What happens if a vaporizer is tipped over?

Answer 28

could cause an overdose of anesthetic, too much of volatile outside of vaporizing chamber

Question 29

What could happen by overfilling a vaporizer?

Answer 29

could cause an overdose,

Question 30

What could happen by overfilling a vaporizer?

Answer 30

could cause an overdose

Question 31

What could happen with a leak in a vaporizer?

Answer 31

could cause an underdose and pt awareness

Question 32

What are the volatile gas colors for: sevoflurane isoflurane desflurane halothane

Answer 32

sevo - yello iso - purple des - blue halo - red

Question 33

What type of vaporizer requires consideration of barometric pressure? And for what volatile?

Answer 33

TEC 6, desflurane

Question 34

Describe TEC 6 vaporizer.

Answer 34

For desflurane. Electrically heated 39 C, pressurized to 2 atm which allows for consistent output. Needs to be preheated. Have two independent gas circuits parallel to one another and are blended.

Question 35

Why does desflurane need a TEC 6 vaporizer?

Answer 35

Desflurane VP is 669 at 20C which puts it at high risk for boiling at atmospheric pressure and would require very high gas flows to adequately dilute the volatile to safe pt ranges. Boiling would cause uncontrolled desflurane.

Question 36

What’s a MAC of desflurane?

Answer 36

6.6%

Question 37

What two factors affect TEC 6 vaporizers? How?

Answer 37

altitude - need to deliver dialed higher concentration at lower barometric pressure/higher altitude carrier gas - if carrier gas < 100% O2 will deliver reduced volatile bc it is calibrated to 100% O2, ex w/ low flows gas and N2O, desflurane output reduced 20% bc of dilution

Question 38

How do you calculate how much % required of desflurane at a given altitude?

Answer 38

req % = (normal % setting x 760) / ambient pressure mmHg

Question 39

Describe Aladin Cassette Vaporizer.

Answer 39

cassettes are interchangeable, and serve as vaporizing chambers (has pressure and temperature transducers), has bypass chamber to achieve safe pt dose of volatile, includes fan that warms air to offset cooling that occurs w/ high gas flows/high dial settings. There is an electronic control of carrier gas ratio to reduce risk of hypoxic gas mixture. Has a seperate, perm. control unit in the anesthesia machine. Has a safety relief valve if pressure in cassette > 2.5 atm. When cassette is removed from machine valves close to ensure no gas escapes. Valve to prevent liquid anesthetic entering FGF. Has an overfilling mechanism. Tipping is ok.

Question 40

What is special about the desflurane Aladin cassette design?

Answer 40

when vaporizing chamber pressure > bypass chamber (if desflurane at its boiling point), one way check valve closes and prevents carrier gas from entering cassette. the vaporizer then functions as an injector instead of a bypass unit.

Question 41

Describe injection type vaporizer.

Answer 41

electronically controlled, agent specific, all digital, no dial, gas from anesthesia machine flows thru gas inlet, the pressure from the gas forces liquid anesthetic thru injector and it is injected into the vaporizing chamber in small increments until anesthetic volume desired is achieved. Output is monitored by gas analysis downstream. Has an optical sensor in vaporizer to monitor integrity of injections.