3. Gas Flow & Measurement Flashcards
Flowmeters
Calibration?
Accuracy
Improved w/?
Measure flow rate gas pass thru
Individually calibrated gas
+/- 2%
Stannic Oxide -antistatic substance - reduce risk sticking
Where read from
When is O2 added
Top bobbin
Midpoint ball
Last gas added - prevents hypoxic mixture
CO2 still used?
Rates
Old machine
500ml/min - avoid hypercarbic
Turbulent flow
p
proport to
when p-v plotted
what shape
R2x Sq root pressure diff / L x density
Flow proport square root pressure diference
flow direct proport 1 divided square root length tube
flow direct proport 1 / square root denisty fluid
r = radius, L = length of tube, ΔP = pressure difference and ρ = density.
Flow is therefore inversely proportional to density and length and directly proportional to the pressure difference.
Relationship - pressure and flow - non linera
plotted = parabola
Air/O2 entrainment
100% − FiO2 = air/oxygen entrainment ratio
____________
FiO2 − 21%
Total flow =
=source gas flow + source gas flow × entrainment gas ratio
Beers Law
absorption of radiation by a given thickness of a solution of a given concentration same as that of twice the thickness of a solution of half the concentration
Bougner’s (or Lambert’s) law states
each layer of equal thickness absorbs an equal fraction of radiation which passes through it.
Boyle’s law states
that at constant temperature the volume of a given mass of gas varies inversely with absolute pressure.
Graham’s law states
that the rate of diffusion of a gas is inversely proportional to the square root of molecular weight.
Raoult’s law states
that the depression or reduction of vapour pressure of a solvent is proportional to the molar concentration of the solute.
Wave lengths in order shortest:
Xr, IR, UV, Visible, gamma
Gamma <10pm
Xray 0.01-10nm
IR 1 mm and 750 nm
Visible 400-700 nm
UV 100-400 nm (volatile)
Radio 100mm- 10000km
Carbon Dioxide
Produced
Density (& vs air)
Bond
Reactivity
BP
Crit temp
when does it turn dry ice
Crit pressure
Dissoc curve
Gas room temp
produced by the oxidation of carbon-containing substances / heating calcium (or magnesium) carbonate.
Its density at 298K is 1.98 kg/m3, about 1.5 times that of air.
The carbon dioxide molecule (O=C=O) contains two double bonds and has a linear shape. It has no electrical dipole.
As it is fully oxidised, it is not very reactive and in particular not flammable.
It has a boiling point of -79°C and a critical temperature of 31.2°C (not minus 31°C).
At temperatures below -78°C, carbon dioxide condenses into a white solid called dry ice.
Liquid carbon dioxide forms only at pressures above 5.1 atm; at atmospheric pressure,
it passes directly between the gaseous and solid phases in a process called sublimation.
The carbon dioxide dissociation curve is steeper and more linear than the oxygen dissociation curve.
Rotameter Shape Forces Flow @ high & low flows Calibrated @ atmos - altitide & hyperbaric
Vertical tapered tube - small bottom
Downward force on it caused by gravity is equal to the upward force caused by gas molecule
low flow is a function of the viscosity of the gas Poiseuille’s law
high flow, flow depends on the density of the gas Graham’s law
Hyperbaric chamber, a flowmeter will deliver less gas than the setting
Increasing barometric pressure (as happens with increasing altitude), the actual flow rate will be higher than the flowmeter reading
Crit temp
Crit pressure
Of
oxygen
co2
nitrous
Crit temp
temp above sub cant be liquefy by pressure alone
cirt pressure = press required to liqeufy vapour
-118 50
31 73
36.5 72
Critical temp =
temp above which gas can no longer liquefy any amt pressure
Poynting effect =
Describes how CT and pressure gas affected mix with another gas
typical describes entonox
viscosity:
measured in
represented by
temp
relationship hct + viscosity
relative of plasma and whole blood
measure poise -
rep n
force per unit surface area
divide velocity gradient between adjacent fluid layers
increase exponentially w/ rising hct
rel plasma 1.5
blood viscos 3.5
why are flow meters on the left
Boyle left handed - oxygen historically on left
not same world wide
North america
oxygen + n2o - reversed - hypoxic mix secondary to crack cant be admin
FLow -
1which is less turbulent - air vs o2/n2o
2 how is surf tension measure
3 critical flow rate =
1 air
2 newton / metre - acting length wall tubing
3 rate fluid gas flow above which turblent flow predom
crit flow 9mm int diam ett - crit flow 9lmin - above turbulent
laplace law tube
P = T/R
p - press grad across wall
Radius
Tension
Laplace law sphere
P = 2T / R
Reynolds number
what it predict
whats the formula
when laminar what forces dom
when turbulent what forces dom
predict laminar or turubulent flow
Pensity x velocity x diam / Viscosity
<2000 = laminar
> 3500 - turb
transitional between two
When LAMINAR = VIscous forces dom
Dep van der waals forces
and molecular cohesiveness
When TURBULENT = Inertial forces
Flow meter - constant orifice vary pres
pneumotachograph
water depression flow
variable orifice constant pressure
rotameters - heidbrink flow - bobbin no rotation rod shaped
wright respirometer
variable orifice variable presure
watersight flow
gas tube hole immersed water
constant orif constat pressure
bubble flow - gas pass thru tube soap fiml
thermistor flow mtere - rely cooling effect gas stream
Turubelent flow proport/inverse
Proport to radius of orifice squared + square root of pressure
Inversely proport to square root density fluid
Re = Dens x Vel X diam / viscosity
war
What does warming gases in terms flow
Warming = decreased density + increaseing viscoity
decreasing Re number = turbulent less likely
Capnography
IR
2.+ different atoms measure - luft
absorb spec co2 n2o close
may be inacc with high RR
reliably confirms ett
Charles law
Constant P
Volume mass
varies directly w.
absolute temp
Third gas law
Constant V
Abs pressure of given mass
vary directly
with absolute temp
Avagadro
equal volume gas at same temp and p
contain equal no molecules
wrights respirometer
turbine measures
gas volume
Tidal volume / Minute volume
Under reads <1/l min
affeceted by moisture - causes pointer stick
vs pneumotachograph - measure flow rate
such as peak flow
gas viscosity
Gas chromatog
Flame ionisation detector
Flame ionisation = inorganic vapours
H gas burning air - pot diff
Katharometer
thermal conductivity detector
inorganic gas detection / vapou
Electron capture
halogenated compounds
polarised voltage
benedict roth spiromter
Lightweight cylinder over breathing chamber w/ water seal
vertical displacement - sense and recorder pen on rotating drumm
high rr - inertia fluid = inacc
suitable for measure lim flow (few L)
larger volume measured - dry gas meter
paper - moved motor trigger by patients expiration
doesnt move pen directly
Pneumotachograph
Constant orifice
vary pressure
Resistance constant
pressure difference reflection flow
measured bi directionally
flow laminar - viscosity important
presence water also important = heated
integration flow - record volume
How Co2 measured
whats the spec for nitrous
does glass abs what about .9nacl
IR wavelegnth 4.28um
as abosrbs gains energy
as tferred to n2o - leave - absorb more - monit conc high inacc
Nitrous 4.4 -5.45um
Glass absorbs /
NaCl doesnt
Collison boradneing
energy IR absoprtion tmitted to anotehr dissimilar molecule
co2 + n2o
temp doesnt affect ir absoprtion
sapphire doesn’t block
Viscosity
Affects laminar flow per hagen poiseuille
Viscosity - inversely related to temp
Cannula gauge flow 22g 20 18 16 14
20-40 40-80 75-120 130-220 250-330 ml/min
What is gauge
Abbreviation for SWG - cross secitoanl area
number of wires of same diameter as cannla that would fit in hole - higher gauge - more fit - smaller number
Bobbin floats d/t
Pressure drop & cross section area
Downward force gravity = upward force gas molecules hitting bottom
In the variable orifice flowmeter,
the annular cross-sectional area varies while the pressure drop across the bobbin remains constant for all positions in the tube.
