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Flashcards in Vaporizers Deck (15)
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Volatile Anesthetic Agent

-liquid at room temperature
-at room temperature, all the gaseous forms of common anesthetic agents exist as vapors. Somehow we need to get these to the patient*


flow of vaporizer is dependent on what?

1. Flow rates or carrier gas flow rate


Vaporizer is in which part of the pressure system?

1. Low flow system


Temperature compensated concentration-calibrated variable bypass vaporizer:

-most common type of modern day vaporizer
-fresh gas enters vaporizer where its flow is split between a larger bypass flow and a smaller flow to the vaporizing chamber or sump
-int he sump is the agent at its SVP
-saturated vapor mixes with bypass flow, which dilutes it to the concentration dial setting


Saturated Vapor Pressure

-when placed in a closed container at normal atmospheric pressure and room temp, a potent inhaled anesthetics is in liquid form
-some anesthetic molecules escape from the surface of the liquid to enter the space above as a gas or vapor
-at constant temp, an equilibrium is established between the molecules in the vapor phase and those in liquid phase
-the gas phase above the liquid is said to be saturated when it contains all the anesthetic vapor it can hold at a given temperature, at which time the pressure exerted by the vapor is referred to as its SVP at that temp*



Sevo: 160 mmHg
Iso: 238 mmHg
Des: 660 mmHg

partial pressure/total pressure= volume %


What concentrations do we aim for?

MAC: minimum alveolar concentration: the MAC value for an inhalation agent is on that causes a lack of response to painful stimulation in 50% patient. The painful stimulation would be equivalent to a surgical incision
-Typically, in order to cover nearly the entire population, agents will be administered above 1 MAC (1.2-1.3 MAC)
-dont forget synergy of narcotism and other IV drugs


Variable Bypass (Flow over method)

-controls how much gas goes through vaporizer


Splitting ratio

vaporizing chamber flow rate: by pass path way flow rate


Why temperature compensated?

Heat of vaporization:
1. energy (heat) is required to promote the vaporization process
2. heat is drawn from the liquid anesthetic itself as well as the container in vaporization process
3. as vaporization proceeds, the cooling of the liquid anesthetic and the container would tend to slow the vaporization process
4. since the vaporization is a temperature dependent process, if no heat is added, vaporizer output would decline
5. accordingly, many vaporizers have temperature compensatory systems to ensure that heat loss due to vaporization is compensated and therefore does not reduce output


simple variable bypass: issues

-high flows would result in inadequate vaporization
wiking: increases the surface area (wicking absorbs more gas so there's more surface area)
-accuracy of concentration with mechanical control knobs


Electronic Vaporizer: Aladin Cassette

-similar to the mechanical variable bypass vaporizer, except a computer controls flows through the vaporizing chamber


Why is des different than other gases?

-Very high SVP= a conventional vaporizer would require really high flows to dilute it down to acceptable level
-it has a low boiling point (23.5 C)
at room temp, it will intermittently boil resulting in large fluctuations in agent delivery. When boiling, there is be excessive agent delivery; however, it will then cool due to large loss of latent heat of vaporization, resulting in an exponential decrease in SVP and under-delivery of agent


Ohmeda Tec 6

-overcomes problems with des by using electrical filament that heats the des to 39C, raising its SVP to 194 kPa, that is nearly, 2 ATM
-in addition to providing a stable SVP, this high pressure removes the need for pressurized carrier gas-instead, the fresh or diluent gas is entirely separate from vaporizing chamber


Safety in vaporizers

-color coded and each has its own key code