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Dr.R.SelvakumarAsst.Professor,G.R.H.,Madurai. GAS LAWS

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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 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…!

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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 Boyle’s law Charles law Gay-Lussac’s law

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Boyle’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 to Its absolute temp. Gay-Lussacs law: At constant volume, pressure is directly proportional to its absolute temp. 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 doesn’t have a pressure gauge..? 0.67 “ Wt of N2O in the cylinder/ Wt of H2O,the cylinder can hold”

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51 atm 25 atm18 atm 75atm 94atm 20C -10C-20C 37C 45C 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 N 2 O 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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0 0 0 x X/4 X+x/4 Daltons law of partial pressure

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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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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:

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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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O2 – 100 CO2 – 40 H2O – 47 N Pulmonary capillary vein artery O2- 40 CO2- 46 H2O- 47 N O CO2- 40 H2O- 47 N alveolus

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On the Mount Everest… Altitude – 8800 m ( 29,000 ft ) Atm. Pressure – 240 torr Alveolar O 2 – 23 torr PVO 2 – 40 torr Life is possible only when 100% O 2 is supplemented, when PAO 2 becomes 153 torr.

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Recently filled D-type N 2 O cylinder weighs kg with Its contents. The tare weight of the cylinder is kg. How long will it last if the anesthetist draws 2 lpm of N 2 O? Try this calculation…! 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 x 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 = π r 4 (P1- P2)/ 8ηl

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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 Reynold’s 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? Bernoulli’s theorem

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Clinical application of Bernoulli’s theorem:

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DIFFUSER ( VENTURI TUBE )

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COANDA 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?

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COANDA EFFECT:

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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 ΔP= 2γ/ r

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I think I’ve confused you enough about: 1.Boyle’s law2.Charles law 3.Gay-Lussacs law4.Avagadro hypothesis 5.Daltons law6.Law of thermodynamics 7.Venturi principle8.Joule-Thomson effect 9.Laplace law10.Hagen-Poiseuille formula

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