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# Dr.R.Selvakumar Asst.Professor , G.R.H.,Madurai . - PowerPoint PPT Presentation

GAS LAWS. Dr.R.Selvakumar Asst.Professor , G.R.H.,Madurai . Is it necessary for an Anesthetist to study about the BORING gas laws..?. Yes.,of course…. Better understanding of the behavior of anesthetic gases Smooth conduct of anesthesia For the proper use of Boyles machine

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Presentation Transcript

GAS LAWS

Dr.R.Selvakumar

Asst.Professor,

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…!

An new oxygen cylinder is being opened.How do you know

whether it will last for the entire surgical procedure or not..?

Knowing the contents of the cylinder…

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

Boyle’s law

Charles law

Gay-Lussac’s law

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

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?

N2O CYLINDERS:

• Filling ratio
• Critical temperature
• Why older machine doesn’t have
• a pressure gauge..?

0.67

“Wt of N2O in the cylinder/ Wt of H2O,the cylinder can hold”

75atm

94atm

25 atm

18 atm

51 atm

37C

45C

-10C

-20C

20C

PRESSURE IN N2O CYLINDERS

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

Have you seen ice crystal formation over a cylinder valve

if N2O leaks through it?

Joule-Thomson effect

Joule-Thomson effect:

When a compressed gas is allowed free expansion

through a narrow opening, the temperature of the

surrounding falls rapidly.

We often talk about partial pressure when we refer gaseous

pressures. What do you mean by that..?

Daltons law of partial pressure

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.

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.

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?

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

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.

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?

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

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

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 = π r4 (P1- P2)/ 8ηl

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?

Flow through tubes…

• LAMINAR FLOW
• TURBULENT FLOW
• Reynold’s number

“Viscosity affects laminar flow,whereas density affects the

Turbulent flow.”

What is the common factor among the following..?

1.Gas stove

2. Insect sprayer

4. Nebuliser

5. Ventilator

6. Bunsen burner

Have you used a Bunsen burner?

Bernoulli’s theorem

In the IRCU, you’ve 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

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

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

ΔP= 2γ/ r

I think I’ve confused you enough about:

1.Boyle’s law 2.Charles law

5.Daltons law 6.Law of thermodynamics

7.Venturi principle 8.Joule-Thomson effect

9.Laplace law 10.Hagen-Poiseuille formula