Vaporisers Flashcards
Heat Compensating mechanisms in vaporisers are
Increase the amount of gas passing over the vapour (bimetallic strip)
Use a heater to keep temperature constant (Desflurane)
Increase the area of a liquid that can produce vapour (by having wicks in vaporiser)
Make vaporiser of metals that easily conduct heat from the atmosphere into the liquid (copper)
How does the bimetallic strip work
Based on principle that different metals will expand at different rates when heated.
Consists of two bars of different metals riveted together.
As the temperature in the vaporiser changes, due to vaporisation, the metals expand or contract by different amounts and this causes the strip to bend.
This bending causes the bimetallic strip to act as a valve which regulates the amount of carrier gas that bypasses the vaporisation chamber
As temperature cools more gas is passed over the volatile agent.
If temperature rises less gas is passed over the volatile agent
How do vaporisers work
Fresh gas flow is split into 2 streams to
1. vaporizing chamber
2. bypass channel
Control dial adjusts amount of FGF through vaporising chamber
Compensation for cooling occurs by
1.bimetallic strip/bellows
2.copper casing
Features of vaporizers
Allow specific conc of volatile agent to be added to patient breathing circuit
Agent specific
Fresh gas enters vaporiser only when it is turn on
Only one vaporiser can be turned on at once (safety feature)
The vaporizer can only be turned on when it is fully locked in position (safety feature)
Precautions when filling a vaporizer
Check the label and expiry date before beginning.
What test should be carried out every time a vaporiser is change
leak test
Check O rings on manifold for damage/present
Vaporizer safety precautions
Check vaporizer is adequately filled but not overfilled
Check vaporizer is correctly seated on back bar and not tilted
Check vaporiser moves throughout whole range
Check for leaks when on and off
Perform leak test every time vaporizer is changed
Check O ring on manifold for damage/present
Vaporiser must be at local ambient temp
Do not carry vaporizer by control dial
Vaporizer identification label
Safety features of vaporisers
Only one vaporiser can be turned on at a time and fresh gas only enters vaporiser when it is turned on
Vaporiser will not turn on if it is not fully locked into position
Colour coded keyed fillers which only fit on correct bottle and into correct vaporiser
Name of system which prevents the inadvertent administration of two agents simultaneously
Selectatec System
How are volatile agents administered
As vapour into lungs and diffuse across respiratory membrane and into blood.
What is MAC
MAC is the minimum alveolar concentration of an volatile agent that is required to produce no reflex response to a skin incision in 50% of patients . It is an indication of the potency of each agent. The lower the MAC, the more potent the agent.
The primary effect of volatile agents is on
the brain
The speed at which a volatile agent act on the brain is determined by
The blood gas solubility
Relatively insoluble volatile agents, such as desflurane and sevoflurane, produce rapid induction and recovery times, where as more soluble agents produce much slower times.
A highly soluble volatile agent will
A highly soluble agent will dissolve in large quantities into the blood and the levels in the brain with rise slowly
This produces slow induction and recovery times
An insoluble agent will
not easily dissolve into the blood and so levels in the brain will rise quickly
This produces rapid induction and recovery times
