4. Gas Supply & Delivery Flashcards
Boyles law
At a constant temperature the volume of a fix mass of gas is inversely proportion to its pressure
PV=K or V =1/P
Oxygen available in cylidner
Charles law
At a constant pressure - volume of gas directly proportional to abs temperature
V proport T
Gay-Lussacs / 3rd gas law
Constant volume, absolute pressure of gas directly proport to abs temp
P/T=K, P proport T
Hydrogren thermoter
Henrys Law
amt dissolved gas in a liquid is proportional to its PP above the liquid
the bends / hyperbaric o2
Daltons law
Mixture of gases = pressure each exerts is the same as it would exert if it alone occupied the volume
Define solid liquid gas
All sub - atoms/ compounds ‘molecules’
Solid - arranged tight lattice - strong forces between molecules - contin motion oscilating mean positon
Liquid more energy than solid -
molecules free to move thru liquid -
weaker van der waals forces
Gas -
escaped van der waals forces -
free to move individually
Universal gas law
Combine Boyle & Charles
Presure c volume = number of moles of gas x universal constant c temperute
PV=nRT
Critical Temperature
Temperature above which a gas cannot be liquefied no matter how much pressure applied
oxygen -118
No2 36.5
Co2 31
Temp below - sub exists liq and vapour
Critical pressure
Pressure required to liquefy a gas at its crit temp
Gas V Vapour
Gas is above crit temp
Vapour -
gaseous form at temp below crit temp
gas cannot be liquefy
Avagadro’s constant
Equal volumes of gases under STP containt same number of molecules
Diff molec weight - actual mass different
Mole
quant sub cotain= number molecules as atoms .012g C12
6.022 x 10^23
1 mole of any gas at stp 6.022 x 10^23 & occupy 22.4l
Flow
what is it
how measured
Quantity of fluid passing point per unit time
gas or liquid
L or ML per Min or Hour
Laminar flow
how does the fuid move
which is fastest
what does halving diameter do?
is there flow on the vessel wall?
Fluid move smoothly Molecules moving parallel Smooth tubes @ low flow rates Concentric ring - fastest in centre x2 fast sides Frictional forces sides - slowing
halving diameter - decrease 16 fold
No flow apporach walls vessel
Turbulent flow
Disordered - swirls eddies & vortices
Irregular tubes @ constriction, corner, narrowing / fast flow rates
Less efficient - conversion laminar to turbulent = reduce flow for given pressure drop
Hagen-Poiseuille
= Delta P Pi Radius ^4 / 8 n L Newtonian fluids (constant viscosity) FLow proport change pressure, inversere to length radiues fourth power
Viscosity v Density
Viscosity - resistance to flow
Density Mass substance / unit volume
Reynolds number
Dimensionless number
Predict if flow will turbulent or laminar
vpD/n
liner velocity x density x diameter divide viscosity
<2000 - linear
2000-4000 - usually turb
>4000 turbulent
Decrease WOB w/ flow
Heliox - less dense x5 vs air - improve flow
Big ETT
Bernoulli principle
Increase in velocity of fluid - simultaneous w/ decrease in pressure difference
Bernoulli effect demonstrated
Fluid flow flow thru constriction in tube / aerofoil surf
Fluid flow down tube - 2 energy -
kinetic energy - how quick flowing
Potetnial energy pressure drop
At narrow - velocity increase - kinetic energy increase
Potential energy must decrease = pressure drop
1st Law of thermodynamics
total energy universe - same
Cylinders
Anaes machine
Oxygen cylinders size? Increments
C - D - E volume
N2o - cylinderes
C - D - E
Entonox Sizes
E is fitted to anaes
O2 - C->j
Volume doubles
D 340l E 680l
N2O
C 450 D 900 E 1800
Entonox D G J
Mapleson A Draw Efficient Also called Min FGF
Efficient spont ventilation - min FGF of 70ml/kg.min
Magill / Lack (Coaxial)
Not suit <25kg
increased dead space at the distal / patient end
Mapleson D Draw Efficient Also called Min FGF
Bain - coaxial D
Controll vent 70mls/kg/min to maintain normocapnia
Ineff during SV
Mapleson E &; F
draw
another name for each
when can be used
whats the fgf
E - ayres t piece F - Jackson rees mod paeds <20kg - low resistancew FGF x2-3 mv - SV No resevoir bag
Humphrey ADE system
Mapleson A, D or E dependent on position
HFNO
What is it?
What can it do
benefits x4
Humidified, titrated oxygen therapy matching or even exceeding the patients’ inspiratory flow rates.
high-flow oxygen delivery system that provides up to 60 litres per minute of warmed and humidified gas enabling an accurate delivery of an FiO2 of between 0.2 and 1.0 irrespective of the patient’s peak inspiratory flow rates.
Benef A reduction of anatomical dead-space by increasing pharyngeal washout Reduced work of breathing Provides an element of CPAP Improvement of mucociliary clearance.
Is SVP affected by ambient temperature
saturated vapour pressure (SVP) of a volatile agent is unaffected by ambient pressure.).
SVP of sevoflurane
at a temperature of 20°C is approximately 21 kPa or 21% of the atmospheric pressure (100 kPa)
% vaporiser output
% vaporiser output = % calibrated x (calibrated pressure/ambient pressure)
At standard atmospheric pressure the vaporiser output = 2% x (100kPa/100kPa) = 2%
At an atmospheric pressure of 200kPa the vaporiser output = 2% (100kPa/200kPa) = 1%
The clinical effects of the volatile agents are determined by their partial pressure in
tissues. Ultimately the output of the vaporiser is unaffected as the partial pressure of the volatile agent delivered is the same at each ambient pressure ( 2% of 100kPa = 2kPa and 1% of 200kPa=2kPa)
Lack system or coaxial Mapleson A
Mod A fresh gas flows through an outer tube (30 mm) and exhaled gases flow through the inner tube (14 mm).
APL What is it What is the function How does it work Pressure needed during during SV The disc
adjustable pressure limiting valve / expiatory valve allows exhaled gas & excess fresh gas to leave the breathing system.
3 ports - inlet - patient - exhaust
It is a one-way,
adjustable spring-loaded valve,
gases escape - pressure exceeds the valve opening pressure.
During spontaneous ventilation a pressure of less than 1 cm of water (0.1 kPa) is needed when the valve is in the open position (not 2 cm of H2O).
The disc rest on knife edge seating Hydrophobic
Stop condensation cause stick
Resevoir bag - pressure limit
Why (what law)
The reservoir bag is highly compliant and when over inflated, the rubber bag can limit the pressure in the system to about 40 cm of H2O.
This is due to the law of Laplace, which states that the pressure will fall as the radius of the bag increases:
Pressure = 2 x tension/radius.
VIE Use What is it How is it stored** How does it work
Positioned on
Safety valve @ what pressure
Pressure regulator
Vacuum insulated evaporator
Supply + Store O2
Thermally insulated container
vacuum shell
insulate 1500 litres O2
As liquid, @ temp -170 to -150 C, pressure 5-10atm (beneath crit temp)
Latent heat vaporisation, taken liquid O2 in
VIE - low temp
Weighing balance - measure mass liquid (resupply from tanker)
safety release 15bars
1700kpa - allows o2 to escape
Pressure regulator maintains the pressure of the gas entering into the pipeline at 400 kPa.
Helium
Properties
BP, density, solubility
Supplied
Affect vaporiser?
Inert gas - found air 5.25 ppm
Second lightest - atomic no 2 & wt 4.0026
Low boiling point, low density, low solubility and high thermal conductivity.
Has a density of 0.1785 g/L at 20oC, which is less than nitrogen.
Is the least soluble of all gases in water.
Brown cylinder 137 bar
Mix w/ O2 - brown / white quart shoulder
Negligible
Non return pressure valve
Protect Vaporiser & flow meter from back pressure
Downstream of vaporiser
Emergency flush
bypasses vaporiser & flow meter @45l min & 4 bar
Flow meter panel
O2 last to added to back bar
sit left but last aded
O2 Cylinder colour & pin index
Oxygen - Pin index 2+5, black body and white shoulder
Air colour & pin index
- Pin index 1+5, grey body and black and white quarter shoulder
Nitrous oxide colour & pin index
- Pin index 3+5, blue body and blue shoulder.
Soda lime
Biggest componenet
Silicates
Granules
Calcium hydoxide mostly
Silicates harden the granules and prevent disintegration.
4-8 mesh
uniform sphere 3-4mm diam
1kg can absorb 120L CO2
larger particles size -= less resistance to flow
can heat to 40C
humdifies Inspired gases
Can produce carboxyhb
Formula for Soda lime
CO2 + Ca(OH)2 → CaCO3 + H2O + heat
Risk w/ soda lime
How it occurs
what does it occur more with
What is another risk
with that type of flow
Dry
passing oxygen - long periods,
subsequent use using any of the volatile
Carbon monoxide.
High concentrations CO:
desflurane
enflurane.
CO production from isoflurane is less but still significant.
Also sevoflurane and halothane can produce smaller amounts of CO.
sevoflurane there is the potential for the generation of compound A with low-flow anaesthesia
Rotameter consists
vertical tapered tube
smallest diameter at bottom
Cylinders of compressed vapours and gases have the following pressures when full at 15°C
Oxygen Entonox Medical air Carbon dioxide Nitrous oxide & psi Cyclopropane
13700 kPa
Entonox 13700 kPa
Medical air 13700 kPa
Carbon dioxide 5000 kPa (723 psi)
Nitrous oxide 4400 kPa
Cyclopropane 436 kPa.
Pressure for pipeline gas
CO2 & n2o
All pipeline gases are supplied at 4 bar (or 400 kPa), but compressed air is also supplied at 7 bar for power tools.
Carbon dioxide and nitric oxide are usually only supplied in cylinders.
Adequate ventilation is required in areas where anaesthetic gases
m3/s
recov ery air charnge
Operating theatres 0.65 m3/second
Anaesthetic rooms 0.15 m3/second
Preparation rooms 0.1 m3/second.
Recovery rooms require 15 air changes per hour
How do HAFOE work
Bernoulli principle - speed and kinetic energy and fall in pressure that causes entrainment of large volumes of air into a flow of 100% oxygen into the nozzle of HAFOE masks.
How prevent hypoxic mix w/ Nitrous
Oxygen - nitrous oxide chain link
two gears connected - as nitrous oxide turned - oxgen flow will turn
min 25%
Helium v Nitrogen at depth
Nitrogen narcosis - avoid breathing He Oxygen mix
He - 1/2 soluble vs N - less discoled tissue
This wh Helium not use in lower airway obstruction -
flow laminar - depends viscosity and not density
Nitrous oxide
Bl:Gas
Mac
Fliing ratio cylinder in uk
crit temp
crit press
boiling point
Bl.Gas - 0.47 Mac 105 Filling ratio .75 Crit temp 36.5 Crit press 72.6 BP -88
Various pin indices
oxygen 2 5 Air 1 5 N2O 3 5 He - no pin Entonox 7
What are stored in vapour form at room tempreature
N20
Entonox
CO2
Not
He
O2
Gas - gasesous at RT - Crit temp is below RT
CT -temp above which cant be liqufy by pressure
below room temp cant be lquefy cant liquefy - store gas
Vapour - gasesous form benath crit temp
CO2 31
+ N2o 31
= vapour at room temp
Vaporisers
Resistance
Inside circl
outside circl
goldman and oxford mini - inside
in - low resistance
plenum outside - tec
tect mark 3-5 - bimetallic strip outside chamber
interlock selecta tec mark 4+5
Cu give heat gas - maint temp
spec heat cap .39j/g k
Coanda
explain
does the fluid need be contionous
Point constriction - pressure falls
if at point - touchign wall - nothing entrained as negative pressure spent holding stream ajcanet to wall
Change low - can dislodge - DOESNT need be continous
Fluid logic ventilator relies on
Coanda effect
fluid - contact curved surface - follow line of surface
altering direction flow
Combustion
What stochiometric conc
which is more violent o2 or n2o and o2
where can apg lavel equip be used
Stochiometric concentration -
no vapour or oxidising agent once combustion reaction complete
stoch conc diff oxygen and air
explosion violent with n2o and oxygen than pure oxyg
apg label equip can be used zone contains anes mix ocy or ntrious
Flow trigger
reduce wob vs pressure - always bf gas flow
no dleay inspiratiory valve
Flow cycles
PS vent - reduction in PIF
Volume cycle
begin expiration once set tv delivered
Cylinders
what used medical
how often tested
whats the plastic disc
H not used for medical gases
D E F G J are
tested 5-10years
plastic disc around neck indicated when last tested
VIC
VOC
flows and conc
VIC low flows - conc higher than dialled up
inflow - unknown conc
VOC - lower than dialled up
monitoring is important
conc depend uptake
Is it the poyting affect that causes seperation of entonox
what can prolong use done
what pressure prone to sep
whats the pseudocrit temp
increase temp increases or decreases risk
no.
it is Lamination
at temps below pseudocrit -5.5 - liquefaction and seperation - can equal hypoxic mix
poynting - means formed - oxygen buble thru nitrous
prolong use - bm suppresion
117 bar most prone seperation
increase temp decreases risk sep
Tec 6
FGF enter?
Dial calibrated how and to what
capacity
Heat what temp
what pressure
whats svp when heat and pressure
FGF doesnt enter vape chamber
Dial 0-18%
1%- 12
2% after
Sum cap 450
Heated 39
2atm
when heat 39 - SVP 194
