Dr.R.SelvakumarDr.R.SelvakumarAsst.Professor,Asst.Professor,G.R.H.,Madurai.G.R.H.,Madurai.

GAS LAWSGAS LAWS

Is it necessary for an Anesthetist to study Is it necessary for an Anesthetist to study about the about the BORINGBORING gas laws..? gas laws..?

Yes.,of course…..Yes.,of course…..

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

An new oxygen cylinder is being opened.How do you knowAn new oxygen cylinder is being opened.How do you knowwhether it will last for the entire surgical procedure or not..?whether it will last for the entire surgical procedure or not..?

Knowing the contents of the cylinder…Knowing the contents of the cylinder…

Relationship between the volume,pressure and temperatureRelationship between the volume,pressure and temperatureO2O2N2ON2O

Boyle’s lawBoyle’s lawCharles lawCharles lawGay-Lussac’s lawGay-Lussac’s law

Boyle’s law: At constant temp, volume is inversely proportionalBoyle’s law: At constant temp, volume is inversely proportional to its absolute pressure.to its absolute pressure.

Charles law: At constant press, volume is directly proportional toCharles law: At constant press, volume is directly proportional toIts absolute temp.Its absolute temp.

Gay-Lussacs law: At constant volume, pressure is directlyGay-Lussacs law: At constant volume, pressure is directly proportional to its absolute temp.proportional to its absolute temp.

PiVi/Ti = PfVf/TfPiVi/Ti = PfVf/Tf

Try this calculation…!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: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”

51 atm 25 atm 18 atm 75atm 94atm

20C -10C -20C 37C 45C

PRESSURE IN N2O CYLINDERSPRESSURE IN N2O CYLINDERS

ADIABATIC COMPRESSION:ADIABATIC COMPRESSION:

When a gas is subjected to sudden compression,heat energyis produced rapidly. If there is no time for dissipation of thisheat, the temperature of the system rises enormously.

First law of thermodynamicsFirst law of thermodynamics

Have you seen ice crystal formation over a cylinder valveHave you seen ice crystal formation over a cylinder valveif Nif N22O leaks through it?O leaks through it?

Joule-Thomson effectJoule-Thomson effect

Joule-Thomson effect:Joule-Thomson effect:

When a compressed gas is allowed free expansionthrough a narrow opening, the temperature of the surrounding falls rapidly.

We often talk about partial pressure when we refer gaseous We often talk about partial pressure when we refer gaseous pressures. What do you mean by that..?pressures. What do you mean by that..?

Daltons law of partial pressureDaltons law of partial pressure

0 0 0

x

X/4

X+x/4

Daltons law of partial pressure

Daltons law:Daltons law: In a mixture of gases having no chemical interaction In a mixture of gases having no chemical interaction between them,each constituent gas exerts the samebetween them,each constituent gas exerts the samepressure which it would have exerted if it alone had pressure which it would have exerted if it alone had occupied the volume of the mixture,provided theoccupied the volume of the mixture,provided thetemperature be the same as that of the mixture.temperature be the same as that of the mixture.

It follows that in a mixture of gases, the pressure exerted It follows that in a mixture of gases, the pressure exerted by each gas is the partial pressure and the pressure of a by each gas is the partial pressure and the pressure of a mixture of gases is the sum of the partial pressures of its mixture of gases is the sum of the partial pressures of its constituents.constituents.

Daltons law:Daltons law:

Daltons law:Daltons law:

In a mixture of gases, each constituent exerts the same In a mixture of gases, each constituent exerts the same Proportion of total pressure as its volume is to the Proportion of total pressure as its volume is to the total volumetotal volume

What happens in an alveoli?What happens in an alveoli?

O2 – 100CO2 – 40H2O – 47N2 - 573

Pulmonary capillary

vein arteryO2- 40CO2- 46H2O- 47N2- 627

O2- 100CO2- 40H2O- 47N2- 573

alveolus

On the Mount Everest…On the Mount Everest…

Altitude – 8800 m ( 29,000 ft )Altitude – 8800 m ( 29,000 ft )Atm. Pressure – 240 torrAtm. Pressure – 240 torrAlveolar OAlveolar O22 – 23 torr – 23 torr

PVOPVO22– 40 torr– 40 torr

Life is possible only when 100% OLife is possible only when 100% O22 is supplemented, when is supplemented, when

PAOPAO22 becomes 153 torr. becomes 153 torr.

Recently filled D-type NRecently filled D-type N22O cylinder weighs 53.45 kg withO cylinder weighs 53.45 kg with

Its contents. The tare weight of the cylinder is 24.48 kg.Its contents. The tare weight of the cylinder is 24.48 kg.How long will it last if the anesthetist draws 2 lpm of NHow long will it last if the anesthetist draws 2 lpm of N22O?O?

Try this calculation…!Try this calculation…!

Avagadros hypothesisAvagadros hypothesis

Avagadros hypothesis: Avagadros hypothesis:

One gram molecular weight of any gaseous substanceOne gram molecular weight of any gaseous substancewill occupy a volume of 22.4L at S.T.P and will contain will occupy a volume of 22.4L at S.T.P and will contain 6.023 x 106.023 x 102323 number of molecules number of molecules

If you want to give blood rapidly…If you want to give blood rapidly…What will you do?What will you do?

1.Put a wider gauge canula2.Increase the drip stand height3.Use a rapid infusion bag

Hagen-Poiseuille formulaHagen-Poiseuille formula

Hagen-Poiseuille Law: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 tube2. Proportional to the fourth power of the radius of the tube3. Inversely proportional to the viscosity of the fluid4. Inversely proportional to the length of the tube

Q = π r4 (P1- P2)/ 8ηl

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?

Flow through tubes…Flow through tubes…

•LAMINAR FLOW•TURBULENT FLOW Reynold’s number

“Viscosity affects laminar flow,whereas density affects theTurbulent flow.”

What is the common factor among the following..?

1.Gas stove2. Insect sprayer3. Venti oxygen mask4. Nebuliser5. Ventilator6. Bunsen burner

Have you used a Bunsen burner?Have you used a Bunsen burner?

Bernoulli’s theoremBernoulli’s theorem

00

0+-

Clinical application of Bernoulli’s theorem:Clinical application of Bernoulli’s theorem:

DIFFUSER ( VENTURI TUBE )DIFFUSER ( VENTURI TUBE )

COANDA EFFECTCOANDA EFFECT

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:COANDA EFFECT:

""That we have written an equation does not That we have written an equation does not remove from the flow of fluids its charm or remove from the flow of fluids its charm or mystery or its surprise." mystery or its surprise." ----Richard Feynman Richard Feynman [1964][1964]

••CoandaCoanda EffectEffect

Try to reason out…!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 lawLaplace law

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:I think I’ve confused you enough about:

1.Boyle’s law 2.Charles law3.Gay-Lussacs law 4.Avagadro hypothesis5.Daltons law 6.Law of thermodynamics7.Venturi principle 8.Joule-Thomson effect9.Laplace law 10.Hagen-Poiseuille formula