Dr.R.Selvakumar

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GAS LAWS
Dr.R.Selvakumar Asst.Professor, G.R.H.,Madurai.
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Is it necessary for an Anesthetist to study
about the BORING gas laws..?
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Yes.,of course..

• Better understanding of the behavior of
  anesthetic gases
• Smooth conduct of anesthesia
• For the proper use of Boyles machine
• To escape from an explosion!

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An new oxygen cylinder is being opened.How do you
know whether it will last for the entire surgical
procedure or not..?
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Knowing the contents of the cylinder

• Relationship between the volume,pressure and
  temperature
• O2
• N2O

Boyles law Charles law Gay-Lussacs law
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Boyles law At constant temp, volume is
inversely proportional to its absolute
pressure. Charles law At constant press, volume
is directly proportional to Its absolute
temp. Gay-Lussacs law At constant volume,
pressure is directly proportional to its
absolute temp.
PiVi/Ti PfVf/Tf
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Try this calculation!
An O2 cylinder indicates a pressure of 132 atm
while being transported in hot weather when the
temp is 44C. What pressure will be indicated when
it is placed in a cool operation theatre when
the temp is 20C?
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N2O CYLINDERS

• Filling ratio
• Critical temperature
• Why older machine doesnt have
• a pressure gauge..?

0.67
Wt of N2O in the cylinder/ Wt of H2O,the
cylinder can hold
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75atm
94atm
25 atm
18 atm
51 atm
37C
45C
-10C
-20C
20C
PRESSURE IN N2O CYLINDERS
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ADIABATIC COMPRESSION
When a gas is subjected to sudden
compression,heat energy is produced rapidly. If
there is no time for dissipation of this heat,
the temperature of the system rises enormously.
First law of thermodynamics
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Have you seen ice crystal formation over a
cylinder valve if N2O leaks through it?
Joule-Thomson effect
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Joule-Thomson effect
When a compressed gas is allowed free
expansion through a narrow opening, the
temperature of the surrounding falls rapidly.
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We often talk about partial pressure when we
refer gaseous pressures. What do you mean by
that..?
Daltons law of partial pressure
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Daltons law of partial pressure
0
0
X/4
0
x
Xx/4
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Daltons law In a mixture of gases having no
chemical interaction between them,each
constituent gas exerts the same pressure which it
would have exerted if it alone had occupied the
volume of the mixture,provided the temperature be
the same as that of the mixture.
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Daltons law
It follows that in a mixture of gases, the
pressure exerted by each gas is the partial
pressure and the pressure of a mixture of gases
is the sum of the partial pressures of its
constituents.
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Daltons law
In a mixture of gases, each constituent exerts
the same Proportion of total pressure as its
volume is to the total volume
What happens in an alveoli?
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alveolus
O2 100 CO2 40 H2O 47 N2 - 573
O2- 40 CO2- 46 H2O- 47 N2- 627
O2- 100 CO2- 40 H2O- 47 N2- 573
artery
vein
Pulmonary capillary
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On the Mount Everest
Altitude 8800 m ( 29,000 ft ) Atm. Pressure
240 torr Alveolar O2 23 torr PVO2 40 torr
Life is possible only when 100 O2 is
supplemented, when PAO2 becomes 153 torr.
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Try this calculation!
Recently filled D-type N2O cylinder weighs 53.45
kg with Its contents. The tare weight of the
cylinder is 24.48 kg. How long will it last if
the anesthetist draws 2 lpm of N2O?
Avagadros hypothesis
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Avagadros hypothesis
One gram molecular weight of any gaseous
substance will occupy a volume of 22.4L at S.T.P
and will contain 6.023 x 1023 number of
molecules
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If you want to give blood rapidly What will you
do?
1.Put a wider gauge canula 2.Increase the drip
stand height 3.Use a rapid infusion bag
Hagen-Poiseuille formula
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Hagen-Poiseuille Law
When a fluid flows through a tube, then the
quantity of the flow(Q) is 1. Proportional to
the pressure difference between the two ends of
the tube 2. Proportional to the fourth power of
the radius of the tube 3. Inversely proportional
to the viscosity of the fluid 4. Inversely
proportional to the length of the tube
Q p r4 (P1- P2)/ 8?l
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Try to answer these questions..!
1.Why acute bends in the breathing circuits are
avoided? 2.What is the rationale behind in giving
Helium-O2 mixture for the patients with
partial upper respiratory tract obstruction?
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Flow through tubes

• LAMINAR FLOW
• TURBULENT FLOW
• Reynolds number

Viscosity affects laminar flow,whereas density
affects the Turbulent flow.
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What is the common factor among the following..?
1.Gas stove 2. Insect sprayer 3. Venti oxygen
mask 4. Nebuliser 5. Ventilator 6. Bunsen burner
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Have you used a Bunsen burner?
Bernoullis theorem
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Clinical application of Bernoullis theorem
0
0
-

0
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DIFFUSER ( VENTURI TUBE )
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In the IRCU, youve taken O2 for 2 patients from
one Flow meter by incorporating a bifurcator in
the line
Will both the patients get equal amount of O2?
COANDA EFFECT
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COANDA EFFECT
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(No Transcript)
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Try to reason out!
1.Why the rain water takes a globular shape? 2.
When the lung decreases in size during
expiration how the alveoli remain patent
without getting emptied into nearby alveoli?
Laplace law
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Laplace law
The excess pressure inside a spherical
gas-liquid interface is equal to twice the
co-efficient of surface tension divided by the
radius of the interface
?P 2?/ r
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I think Ive confused you enough about
1.Boyles law 2.Charles law 3.Gay-Lussacs
law 4.Avagadro hypothesis 5.Daltons law 6.Law
of thermodynamics 7.Venturi principle 8.Joule-Tho
mson effect 9.Laplace law 10.Hagen-Poiseuille
formula