Vaporizers Flashcards
What 3 factors influence vaporization?
vapor pressure, temp, amount of carrier gas
How is vapor pressure created in a container of volatile gas?
molecules of volatile gas bombard surface of liquid volatile and the walls of container
What phases of matter exist in a volatile’s container?
gas and liquid
When is a container of volatile “saturated”
When molecules of volatile rate of evaporation = rate of condensation.
A MAC of isoflurane is?
1.2 % (at 760 mmHg and 20 C)
What are the vapor pressures of the following volatiles at 20 C? sevoflurane = enflurane = isoflurane = halothane = desflurane =
sevoflurane = 157 mmHg enflurane = 172 mmHg isoflurane = 240 mmHg halothane = 244 mmHg desflurane = 669 mmHg
True or false vaporizers are agent specific?
True.
When selecting “dose” of volatile, the anesthesia provider is selecting a _____. How is it calculated?
volume % volume % = pp of gas x total pressure (atmosphere) x 100%
Why is temperature important to vaporizers? What’s the significance?
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.
What is the heat of vaporization?
Number of calories req to change 1 g of liquid into vapor w/ out temp change.
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?
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
What is specific heat?
Number of calories required to increase temp of 1 g of substance 1 degree C
Why is it important for vaporizers to be built from materials with high specific heat?
Resists changes in temperature that result from volatile evaporating to enable a constant temperature and therefore a consistent delivery of anesthetic
Is evaporation of a liquid a cooling or a heating process?
Cooling
Describe thermal conductivity.
Measure of speed w/ which heat flows through a substance. Higher thermal conductivity the better substance conducts heat
Are vaporizers made with materials that have high thermal conductivity or low thermal conductivity? Why?
High, maintains a consistent temp in vaporizer and therefore a consistent delivery of gases
Describe how changes in altitude affect barometric pressure.
High altitude, low pressure. Low altitude, increase pressure
Describe boiling point. What happens at BP? What is the significance?
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.
Describe the relationship between temp and vaporization.
Direct. As temp increases, vaporization increases.
What are the four types of vaporizers?
variable bypass, dual circuit/Tec 6 - desflurane, cassette vaporizer, injection vaporizer
Part of the function of a vaporizer is to ______ volatile agent because the concentration of saturated gas is _______.
dilute, too high. volatile gas must be diluted to achieve pt safe dosing
What is a MAC of sevoflurane?
2.2 %
Describe variable bypass vaporizer.
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.
Describe a splitting ratio of 12:1 and what that means in a bypass vaporizer.
-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
What would happen if you accidentally put high VP volatile in a low VP volatile’s vaporizer?
pt overdose, will deliver more anesthetic, can also cause hypoxic mixture of gases, especially at high altitude
What would happen if you accidentally put low VP volatile in a high VP volatile’s vaporizer?
underdose of anesthesia, could cause pt awareness
What could happen in the event that a vaporizer is contaminated?
bacteria could produce byproducts that are toxic
What happens if a vaporizer is tipped over?
could cause an overdose of anesthetic, too much of volatile outside of vaporizing chamber
What could happen by overfilling a vaporizer?
could cause an overdose,
What could happen by overfilling a vaporizer?
could cause an overdose
What could happen with a leak in a vaporizer?
could cause an underdose and pt awareness
What are the volatile gas colors for: sevoflurane isoflurane desflurane halothane
sevo - yello iso - purple des - blue halo - red
What type of vaporizer requires consideration of barometric pressure? And for what volatile?
TEC 6, desflurane
Describe TEC 6 vaporizer.
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.
Why does desflurane need a TEC 6 vaporizer?
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.
What’s a MAC of desflurane?
6.6%
What two factors affect TEC 6 vaporizers? How?
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
How do you calculate how much % required of desflurane at a given altitude?
req % = (normal % setting x 760) / ambient pressure mmHg
Describe Aladin Cassette Vaporizer.
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.
What is special about the desflurane Aladin cassette design?
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.
Describe injection type vaporizer.
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.
