Gases Flashcards
How much of air is Oxygen?
21%
depends on altitude
Sea level air & pressures
760 mm Hg/torr
&
21% O2 = 160 mmHg (partial pressure of O2)
Increasing altitude decreases pO2, thus…
decreased driving force of O2 entry into tissues (diffusion)
what pressure/altitude do we become concerned with SpO2
~500 mmHg atmospheric pressure
10-12k feet
not enough O2 in air
hyperbaric therapy
up to 1300 mmHg
increases pO2
increases:
O2 diffusion into tissue & O2 blood solubility
crosses into tissue better
Normal O2 sat
98%
Above 98% requires much higher [ ] not very beneficial
At what PO2 do we see a decrease in sat?
when do we see a major effect in O2 tissue delivery?
below 100 mmHg (starts to decrease)
below 70 mmHg (now concerned)
How does pH affect the oxyhgb curve?
Left shift = high pH
Right shift = low pH
A (high/low) pH makes the oxyhgb curve easier to saturate
Left shift = easier to saturate
(high pH)
DPG
2,3- diphosphoglyceric acid
Produced in RBC to control O sat
more DPG = R shift
Oxygen Deficiency
Causes
low inspired fraction (FIO2) (low room [ ])
increased diffusional barrier (lung scarring)
hypoventilation
ventilation – perfusion mismatch
_____ [ ] stimulates respiratory drive & ventilation rate.
increased PCO2
Which stimulates ventilation more?
higher PCO2
low PO2
higher PCO2
T/F
The body will not increase ventilation d/t low PO2 alone. PCO2 must be elevated.
False
a low PO2 w/ high PCO2 can still increase resp. drive
(high PCO2 is just a more effective stimulator)
Hypoxic effects
Increased ventilation
sympathetic stimulation (tachycardia, decreased PVR <= local effect)
pulmonary vasoconstriction (optimize V/Q)
impaired CNS function
anerobic metabolism (decreased ionic gradients – ↑ lactic acid, H+, Ca++, Na+ => cell death)
Tissue hypoxia
local control mechanism
produce nitric oxide
into muscle
increase BF and perfusion
local vasodil8n
all to get more O2 into tissue
An increase of ___, especially, will trigger auto lysis.
Ca++
(H+ and Na+ also can)
Due to dissociation curve, increasing inspired O2 [ ] …..
does not greatly increase blood O2
Giving 100% not always beneficial bc O2sat is 98% until 90 PO2
will help if hypoxic d/t:
low hgb, BF or RR
damaged diffusion barrier in lungs
hyperbaric therapy uses
deep tissue/bone infxn
O2 toxicity
over-exposure => peroxide formation
H2O2 formed from oxygen and water
Very reactive & can damage tissue
Why does increased PCO2 lead to resp acidosis
using LeChat’s principle:
(CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-)
increasing CO2 = increased carbonic acid = increased H+ = low pH
Why is hypocarbia used in neurosurgery?
resp alkalosis can constrict cerebral vessels and decrease brain size
T/F
CO2 is commonly used to increase RR
False
it would work but also changes blood pH
CO2 in Cardiac Sx
decrease air (insoluble N2) around heart
main drive mechanism for vasodilation of many arterioles
Nitric Oxide (NO)
Nitric Oxide (NO) & the oxyhgb curve
may shift left
increasing the oxygen affinity of hemoglobin
Nitric Oxide (NO) is a ___ moelecule
signaling
main use in pulmonary function testing, laser airway surgery and diving
Helium
Helium in airway Sx
reduce O2
T/F
Helium is reactive
False
inert gas
Why use Helium in diving tanks?
Diving = increased pressure around us
O2 pressure in tank will double
too much pO2 = H peroxide
mix w/ He to decrease high O2 pressure
Why can we apply gas laws to our volatile agents?
VAs: liquid –> gas phase
only small deviation from “ideal gas”
Transport Processes
Osmosis (mvmt across semi-perm membrane)
Fick’s law of diffusion
Grahams’s law of diffusion
Osmosis requires….
-semi-permeable membrane
-difference in [ ] of solutes on each side
T/F
Albumin can move via osmosis
False
too large (MW ~69K)
Albumin is higher in the ___
ECF
Sq. Root of the Molecular Weight
is a measure of the ___
(Fick’s Diffusion)
molecular diameter
large # = larger diameter = slower diffusion
Fick’s law of diffusion
What increases diffusion rate?
Higher:
partial pressure gradient
membrane area
solubility of a gas in the membrane
lower:
membrane thickness
sq. root of the MW
Grahams’s law of diffusion
Faster diffusion:
lower sq rt of gas’ density
Slower diffusion:
higher Gas density => higher M. Mass
Grahams’s law of diffusion
rate of diffusion is inversely proportional to ….
the square root of the molar mass
(assuming ideal gases)
the … in a gas is the same for all gases at the same temperature and pressure
number of molecules
Which law focuses more on molar mass?
Fick’s diffusion
Grahams’s diffusion
Grahams’s diffusion
(Fick’s includes MW)
Henry’s Law
↑ partial pressure = ↑ dissolve in a liquid
T/F
Hgb is the only transport mechanism for O2 transport
False
can also diffuse O2 into tissue using pressure
Hgb = primary method
amount of O2 that dissolves in blood
0.003 ml/100 ml blood/mmHG partial pressure
ex: PaO2 300 mmHG
300 mmHG x 0.003 = 0.9 ml O2/100 ml blood
PP of NO @ sea level
600 mmHg
O2 = 160 mm Hg/21%
If the PaO2 is 300 mmHg, how much O2 is dissolved in 100 ml of blood?
0.9 ml O2 per 100 ml blood
multiply PaO2 by 0.003 and put that over 100m ml of blood
Gases flow as a __
fluid/liquid
Bromine is a good example
colored & high density
Laws are based on ___ flow
laminar
Laminar flow
Molecules move relative to one another (rush hour; traffic moving along together)
Against walls = slowest (interact w/ wall,) resistance
Center moves fastest
Resistance from walls can affect center molecules as well
Laminar = Peak rate of movement
Turbulent flow
Started as laminar but something disrupted
Molecules bounce off walls and affect other molecules
____ flow is predictable via math
laminar
turbulent is unpredictable
What flow do we see in the lungs and tubing?
A mix of both laminar & turbulent
can become turbulent in kinks/curves
sort themselves back into laminar
Has the greatest effect on airway resistance
radius of tube
What increases and decreases airway resistance?
higher resistance:
↑tubing length & viscosity
↓ tubing diameter
lower resistance:
↑tubing diameter
how does diameter affect laminar flow
larger diameter = more laminar flow
T/F
Small changes in radius = big changes in resistance
True
How does narrowing of tubing affect flow and speed?
increased speed in narrowed space
Once opens back up, some temporary turbulent flow
When do we see turbulent flow in anesthesia?
High flow rate
Rough/corrugated tube
Kinks
bends
sudden changes in diameter
flow thru an orifice
Why do we use corrugated tubing?
1) turbulent flow is limited d/t size of diameter
2) smooth tubing = increased risk of kinks
Corrugated will bend before it kinks
resistance increases proportionately with flow
turbulent flow
Fluid Flow
Poiseuille’s Law
Bernoulli’s Principle
Venturi Principle
Reynolds Number
help predict laminar/turbulent flow
low (<1000) = laminar
high (>1500) = turbulent
in between = we don’t know
more abt relative #s vs. exact values
(Will not have to calculate; know what values mean)
Fluid density vs. viscosity
density is based on weight
viscosity based on interactions
Poiseuille’s Law
F = (πr4ΔP)/(8ηL)
relationships
F = rate of fluid flow
greater flow:
↑ radius
↑ pressure gradient (ΔP)
lower flow:
↑ viscosity (η)
↑ length (L)
Bernoulli’s Principle
Is based on ___ rather than flow
total conservation of energy
Bernoulli’s Principle determines …
energy of fluid flow (E)
E = PV + mgh + ½ mv2
potential energy of pressure (PV)
(Bernoulli’s Principle)
E = PV + mgh + ½ mv2
raising the uncapped end of a tube of liquid increases its potential energy (gravitational pull)
A narrowed portion of a tube will show…
greater velocity
lower pressure
Venturi/venti masks follow which principle
Bernoulli’s
lower pressure can draw another fluid into the narrowing
Bernoulli’s Principle
increasing the fluid velocity (through a narrowing) will cause a pressure decrease in the narrowing if…
E is constant
mgh
potential energy of gravity
½ mv2
kinetic energy of movement
In a narrowing, assuming _____ , resistance (R) and pressure will decrease in the narrowing
constant flow
Flow exiting the narrowing becomes ___
turbulent
Turbulent flow is more related to (density/viscosity)
density
In turbulent flow, the density (ρ) is inversely proportional to the flow
dialing flow rate mechanism
fluid/gas flows thru system
alters diameter of orifice
allows different amount of venturi effect to pull gas into fluid’s flow
Venturi Principle
Allows another tube attached ____ in this region to have fluid pulled into main flow path
at a right angle
Absolute humidity
mass of water vapor in a given volume of air
Set # no matter the location
Relative humidity (%)
(Actual vapor pressure / Saturated vapor pressure) x 100
Why isn’t humidity constant?
saturated VP changes based on T
at diff temps, diff amounts of water are soluble
(Relative humidity (%) = (Actual vapor pressure / Saturated vapor pressure) x 100)
water vapor is more soluble in the air when it’s…
very warm
Dew point
Actual vapor pressure = Saturated vapor pressure
water begins to condense
Water condenses on a cold drink on a hot day b/c
Sat VP drops
actual VP/Sat VP becomes 1:1
condensation!
Ohm’s Law
E = IR
E = energy (in Volts)
I = current (in Amperes)
R = resistance (in Ohms)
Can be used to quickly tell if too much current is being drawn from source.
T/F
Electric and water move similarly
⚡️ 💧
energy = pressure
Current = flow
Resistance = Resistance
Too much electrical components on anes machine (current/flow requirement)
Flow requirements increase
exceed max current/flow = Pop breaker
difficult to resume flow at that point
Which of these values doesn’t change?
E
this tells us that current (Amps) & resistance (ohms) share a relationship
If we exceed max current a wire can handle
try to pull too many e-
resistance ↑↑↑↑ as flow ↑
increase in resistance = heat = melt wire= fire
Boyle’s Law
pressure and volume of a gas have an inverse relationship
Gay-Lussac’s Law
pressure of a given mass of gas varies directly with the absolute temperature of the gas, when the volume is kept constant.
Charle’s Law
volume of a given mass of gas varies directly with the absolute temperature
Combined Gas Law
that pressure and volume are inversely related to each other, and that they are both directly related to temperature
Ideal Gas Law
under the same temperature, pressure and volume all gases contain the same number of molecules
Dalton’s Law of Partial Pressures
the total pressure by a mixture of gases is equal to the sum of the partial pressures of each of the constituent gases
