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True or False:
Most of the inhalational anesthetic agents in use today are vapors at room temperature.
False. They are liquids, and must be converted into vapors before they can be used.
What is the "saturated vapor pressure"?
How does it differ from "vapor pressure"?
- pressure exerted against the walls of a closed container at 20°C
- SVP and VP are the same
If heat is added, more molecules enter the _____phase, and vapor pressure _________.
If heat is added, more molecules enter the vapor phase, and vapor pressure rises
If heat is taken away from the system, more molecules enter the _______ state and the vapor pressure will be _________.
If heat is taken away from the system, more molecules enter the liquid state and the vapor pressure will be lower
It is meaningless to talk about vapor pressure of a liquid without specifying the _______.
It is meaningless to talk about vapor pressure of a liquid without specifying the temperature
Vapor pressure depends on what 2 things?
liquid & temperature
Vapor pressure depends on ambient pressure (within the range of barometric pressures encountered in anesthesia).
No. Vapor pressure depends only on the liquid and the temperature. It is INDEPENDENT of atmospheric pressure.
What is the boiling point?
the temperature at which its vapor pressure is equal to the atmospheric pressure
What is a vapor?
The gaseous phase of a substance that is a liquid at room temperature and at atmospheric pressure.
What is the vapor pressure of Halothane at room temperature (20°C)?
What is the vapor pressure of enflurane at room temperature (20°C)?
What is the vapor pressure of isoflurane at room temperature (20°C)?
What is the vapor pressure of desflurane at room temperature (20°C)?
What is the vapor pressure of sevoflurane at room temperature (20°C)?
The partial pressure exerted by the vapor of a liquid agent depends only on the _________ of that agent and is unaffected by the _________.
The partial pressure exerted by the vapor of a liquid agent depends only on the temperature of that agent and is unaffected by the total pressure above the liquid.
What is vapor pressure?
The highest partial pressure that can be exerted by a gas at a given temperature
VP is essentially the partial pressure of the anesthetic in the container (Dalton's Law)
VP varies with each agent.
Volume percent is...
the number of units of volume of a gas in relationship to a total of 100 units of volume for the total gas mixture
_______ expresses the relative ratio of gas molecules in a mixture, whereas ________ expresses an absolute value
volume percent expresses the relative ratio of gas molecules in a mixture, whereas partial pressure expresses an absolute value
In a mixture of gases, each constituent gas exerts the same proportion of the total pressure as its volume is of the total volume.
- parial pressure/total pressure = volumes percent/100
T/F: A given volumes percent represents the same anesthetic potency under various barometric pressures.
False. This is true for partial pressure, but not volumes percent.
What is the heat of vaporization of a liquid?
the number of calories necessary to convert 1 gm of liquid into a vapor; can be expressed as the number of calories necessary to convert 1 ml of liquid into a vapor
Does the temperature of the liquid decrease or increase as vaporization proceeds?
- decreases–As vaporization removes the more energetic molecules, the remaining molecules have lower kinetic energy–
- Unless some means of supplying heat is available, the liquid will cool. As the temperature drops, so does the vapor pressure of the liquid and fewer molecules will be picked up by the carrier gas so that there is a decrease in concentration in the gas flowing out of the container.
Define specific heat.
the quantity of heat required to raise the temperature of 1g of the substance 1°C
The _______ the specific heat, the more heat required to raise the temperature of a given quantity of that substance.
The higher the specific heat, the more heat required to raise the temperature of a given quantity of that substance.
What is the specific heat of water?
Why is specific heat important?
- -considering the amount of heat that must be supplied to a liquid anesthetic to maintain a stable temperature when heat is lost as a result of vaporization
- -specific heat of choice of material from which vaporizer is constructed
Temperature changes more gradually for materials with a ______specific heat than for those with a _____specific heat.
Temperature changes more gradually for materials with a high specific heat than for those with a low specific heat.
What is vaporization?
The process of converting a liquid into a vapor
What is the latent heat of vaporization?
- the heat that is required by that process (converting liquid into a vapor)
- -# of calories required to change 1g of liquid into a vapor at a given temperature
Which volatile anesthetic requires an external heat source?
What is an example of the latent heat of vaporization being used as an anesthetic?
Ethyl chloride is stored as a liquid, and when put on topically, the cooling process anesthetizes the skin
What does volatile mean?
- Easily vaporized
- changing rapidly into a vapor
High or Low thermal conductivity minimizes temperature changes when the vaporizer is in use.
Examples of metals with high thermal conductivities...
Describe a concentration-calibrated vaporizer
The total gas flow from the anesthesia machine goes through the vaporizer and is divided into two parts. Some passes through the vaporizing chamber (the part of the chamber containing the liquid anesthetic agent), and the remainder goes through a bypass to the vaporizer outlet.
Describe a measured-flow vaporizer
A measured amount of gas is supplied to the vaporizer, and all of the gas passes through the vaporizing chamber. It is then diluted by additional flow from the machine.
The dial on the concentration-calibrated vaporizers control the agent concentration in ___________.
The dial on the concentration-calibrated vaporizers control the agent concentration in volumes percent
The ratio of bypass gas to gas going to the vaporizing chamber is called the
How is MAC related to potency?
Taking off a halogen that has a higher atomic weight and substituting it with a lower-atomic weight halogen results in
If two anesthetics have the same vapor pressure, the potency is similar.
Vapor pressure has no relationship to potency.
The two volatile anesthetics that are completely halogenated with fluorine are
As temperature increases, vapor pressure ____.
Is this linear?
What is the function of the vaporizer?
- to accurately enrich the gas mixture with
- anesthetic agent that eventually reaches the brain inducing/maintaining
Define thermal conductivity.
a measure of how quickly heat is conducted through a substance
Vaporizers are ideally made with what specific heat and thermal conductivity?
- higher specific heat to minimize temperature Δ
- higher conductivity to transfer heat to the gas more effectively
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