Gas Supplies, Breathing Systems and Ventilators Flashcards
Critical Temperature
The temperature above which a substance cannot be liquefied irrespective of the amount of pressure applied.
Critical pressure
The minimum pressure required to liquefy a gas at its critical temperature.
Gas definition
A compressible fluid where intermolecular spacing is so large that intermolecular forces are negligible.
Vapour definition
A gas below its critical temperature, thus compression to the liquid is possible
What is a fixed gas
Gas above its critical temperature
How does a VIE work
double skinned steel tank with a vacuum of 0.16-0.3kpa between the skins
What temp is vie kept at
-160-180 (below critical temp of -118)
Critical temp of N2O
36.4
how full should an n2o cylinder be
75% of the weight of the water that would fill the cylinder
based on weight and not volume- differing densities of nitrous and water mean the cylinder willl not be 75% full by volume
What is entonox?
50:50 oxygen : nitrous by volume (not weight)
Pseudocritical temp of entonox
-5.5 c
how often are cylinder checked
5 years
What are cylinders made of
molybdenum steel
Which mapleson circuits are used in paeds?
E/F
what is a waters circuit most similar to
mapleson C
Examples of mapleson A circuits
Magill + lack
When is mapleseon A efficient/inefficient
efficient in spontaneous ventilation, inefficient in controlled ventilation
Where is the apl valve in mapleson D
machine end
Main constituent of soda lime?
calcium hydroxide (75%)
only 4% sodium hydroxide
Soda lime/CO2 reaction has what properties
exothermic
produces 1 mole water for each mole CO2 removed
What does the pethick procedure test for?
Fracture of the inner fresh gas tube at the common gas outlet in a bain circuit (results in a big increase in dead space)
Are bain circuits affecred by the length of the system?
no
HOw much fresh gas flow does a mapleson A circuit require?
70% MV
WHat is the lack modification?
Removes the APL valve from the patient mask in mapleson A circuit
WHat does a cardiff aldasorber use
absorbs volatiles onto activated charcoal
HOw much carbon dioxide will 1kg of soda lime absorb?
120L
Co-axial version of the mapleson A?
lack system
SIze of a resevoir bag?
Approx 2L
What is the jackson rees modification to a mapleson E?
SPecialised resevoir bag with an opening to allow controlled leak and variable PEEP (mapleson F)
Pros of resevoir bags?
-prevent wastage of fresh gas flow during expiratory pause
- Rough visual assesment of the volume of ventilation
-Act as a resevoir as the machine cannot provide the peak inspiratory flow req in normal respiration
HOw much fgf does a bain (mapleson D) need
2-3x MV to prevent rebreathing
What affects rate of change of vapour conc in a circle system?
system volume
FGF rate
Net gas uptake
WHat is in baralyme
calcium hydroxide and barium hydroxide
Is the soda lime reaction influenced by water?
Generates water, but the presence/absence of water does not affect ability to absorb co2
MAC of nitrous oxide?
105%
Is nitrous oxide inert?
No, with sufficient heat dissociates to become an avid oxidant
What does Nitrous cylinder look like?
FRench blue, pin index 3 + 5
Why does soda lime require some water for the absorption process
Dry soda lime can generate carbon monoxide when using volatiles containing the CHF2 moiety
What does the letter classification mean on a gas cylinder?
Size
Two letters are the new aluminium/kevlar cylinders, one letter is the old molyb. cyllinders
what is the pressure in an oxygen cylinder on the back of an anaesthetic machine?
137bar (size E)
Pressure inside a nitrous cyllinder?
44bar
Weight of an E sizy nitrous cyllinder when empty?
5.4kg
filling ratio for nitrous in the UK?
0.75
What is the gas pressure in pipes in hosp?
4 bar, apart from surgical air which is 7 bar
