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Intro to Anesthesia Summer 18 > Physics and Math > Flashcards

Flashcards in Physics and Math Deck (36):

Definition: Molecular Theory of Matter

Matter is made of minute particles called molecules, that exist in various states (solid, liquid, or gas).


Definition: Kinetic Theory of Matter

Molecules are in constant motion (random motion) and have a degree of attraction between them called van der waals forces


Definition: Critical Temperature

temp above which a gas cannot be liquefied regardless of how much pressure is applied

O2 is gas


Avagadro's Hypothesis and Number

mole-numbering system

1 mole= 6.02 x 10^23 molecules

Hypothesis: 2 different containers containing 2 different gases at the same temp and pressure= same number of molecules

1mole= 1gram x molecular weight
ex) 1mole occupies 22.4L
6.02x10^23 molecules of O2=32g occupies 22.4L


Physics in Context

Calibration of vaporizers is done using Avagadro's hypothesis

ex) Sevo =200g=1mole=22.4L at stp


Gas Laws

-Gay Lussac
I-deal Gas Law


Universal Gas Constant for Boyle, Charles, Gay Lussac, and Ideal Gas Law

Boyles: PV= Constant (k1)
Charles: V/T= Constant (k2)
Gay Lussac: P/T= Constant (k3) (3rd Law)

Perfect gas law + Avagadro's hypothesis:
PV/T= Constant (k4), for any given quantity of gas


Boyle's Law

-PV : Volume of an ideal gas is inversely proportional to the pressure (V=1/P)
-Temperature is constant
ex) Squeezing (pressure) Reservoir bag causes the volume to decrease
ex) A full E cylinder of oxygen will empty 625-650 L into the atm (Pressure decreases, Volume increases)
ex) spontaneous breathing- intrapulmonary pressure becomes negatiive (decreases), intrapulmonary volume increases
ex) Bellows on ventilator- As pressure increases, the volume of the bellows decreases


Charle's Law

-V/T: Volume is proportional to temperature(Kelvin)
-Pressure remains constant
ex) Balloons burst on hot days


Gay Lussac's Law

-P/T: Pressure is proportional to Temperature(Kelvin)
-Volume is constant
ex) Tec 6- increasing temperature surrounding the gas which gave the false increasing atmosphere-boils
ex) Full cylinder of compressed gas moved from the air conditioned hospital (70degrees) to loading dock (100degrees), the pressure increases


Charles + Gay-Lussac's Law

For given mass, at constant pressure, the volume is directly proportional to the temperature
C= Constant pressure


Universal (Ideal) Gas Law

-Combines Boyle's, Charles', and Gay Lussac's Law + Avagadro's law
-n= # moles of gas
-R= universal gas constant
-T= temperature (Kelvins)
-P= pressure
-V= volume

ex) Cylinder of compressed gas empties, the pressure falls - cylinder has constant volume, the # of moles decrease as gas exits, so pressure decreases



A mol of a pure substance: mass(g)= molecular mass (amu). A mol of any material will contain Avogadro's number of molecules.
ex) C (atomic mass 12.0amu): 1 mol C= 12g


General Gas Law

-Dalton's Law
-Fick's Law of Diffusion
-Graham's Law
-Henry's Law


Dalton's Law

Total P= P1 +P2 + P3 (Total pressure= sum of partial pressure)

-In a mixture of gases, the pressure exerted by each gas is the same as that which it would exert if it alone occupied the container

ex) atm pressure is 760mmHg, O2 21%, N 79%
P Oxygen = 159mmHG
P Nitrogen= 600.4

ex) 50% N2O + 44% O2 + 6% Desflurane = 100% mix to pt =
(.5x760) + (.44x760) + (.06x760) = 1.0x760


Ficks Law of Diffusion

Rate of diffusion of a substance across a membrane is related to:
1) Concentration gradient (pp difference of gas across the membrane- Directly proportional
2) SA of membrane- Directly proportional
3) Solubility- (Directly proportional)
4) Thickness membrane- Inversely proportional
5) Molecular Weight- Inversely proportional

Vgas= (Area x Solubility x PP difference)/(Molecular Wt x Distance)

- 2nd gas effect: high inspired concentration of 1st gas(N2O), accelerates uptake of companion gas -Uptake and Distribution of Anesthetic Gases
- Concentration effect- Uptake of high volumes of N2O concentrates the remaining 2nd gas
-Diffusion hypoxia- Diffusion of gases across the alveoli-capillary membrane
-Expansion of air pockets- when using N2O (N2O is 34x more soluble in blood than N2; therefore volume N2O diffusing in > volume N out)
-Expansion of ET cuff- N2O diffuses accross plastic as well
-Placental Transfer- durgs and O2


Graham's Law

A gas diffuses at a rate that is inversely proportional to the square root of its molecular weight

- Molecular weight increases, rate of diffusion decreases


Henry's Law

Amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in contact with the solution
-Allows calculation of O2 and CO2 dissolved in blood
O2: .003ml/100ml blood/mmHg PP
CO2: .067ml/100ml blood/mmHg PP

- Can estimate PaO2 when delivering certain amounts of oxygen by multiplying FiO2 x 5


General Laws

-Critical Temperature
-Adiabetic Heat Process
-Joule-Thompson Effect
-Poiseuille's Law
-Bernoulli and Venturi
-Beer's Law
-Law of La Place
-Ohm's Law


Critical Temperature

Definition: temp above which a substance goes into gaseous form in spite of how much pressure is applied
-Gas cannot be liquefied if the ambient temperature is greater than critical temperature
-Gas can be liqufied if sufficient pressure is applied at ambient temp below the critical temperature

O2: Critical Temp: -119C

N2O: Critical temp 39.5 C, therefore, N2O is stored as a liquid at pressure of 745mmHg and at room temp


Adiabatic Cooling

-Occurs when matter changes phase
-Implies a change in temperature of the mattter w/o gain or loss of heat

ex) N2O cylinder opened fully-> frost can form on the outlet due to cooling


Joule-Thompson Effect

Expansion of gas causes cooling

ex) as gas leaves a cylinder, the expansion cools the surrounding air causing condensation of moisture on the cylinder


Poiseuille's Law Applied with Laminar Flow

Describes rate of flow and:
1) Pressure gradient across length of tube- Direct
2) Radius^4 of tube- Direct
3) Length of tube- Inverse
4) Viscosity of fluid- Inverse

Q= (pi x r^4 x delta x P)/8nL

ex) IV flows, Airways, Vascular flow (Polycythemia vs Anemia), Thrope Tube (low flows)


Laminar to Turbulent

Viscosity- determinant of flow when flow is laminar (low flow rates)

Density- determinant of flow when its turbulent. Ratio of mass to volume. D=m/v. Determines the rate of flow meters when rate of gas flow is high through variable orifices flow meter.
ex) Heliox

Reynold's number= (velocity x density x diameter)/ viscosity

Raynold's Number >2000= Turbulent flow


Thorpe Tubes

Thorpe Tubes= Flowmeters

-Low flow- the annular-shaped orifice around the float is tubular(Poiseuille's Law) flow is governed by viscosity

-High flow- (wider top part of the float tube), the annular opening is more like an orifice and density governs flows


Factors that Change Flow from Laminar to Turbulent

1) Increased velocity
2) Bend >20degrees
3) Irregularity in the tube
4) Reynolds # > 2000


Bernoulli's Theorem

-Pressure and velocity
-Lateral wall pressure is LEAST at point of greatest constriction and speed is the GREATEST
-Flow will be faster through the constricted portions and slower at the wider portions of tube

Narrow Diameter= Decrease LWP = Increase speed
Wider Diameter= Increase LWP = decrease speed


Bernoulli and Venturi- Venturi Tube and Application

Venturi Tube- application of Bernoullis equation to measure fluid flow

-fluid flows through diff cross sectional areas in different portions of the tube
-As tube narrows, velocity of fluid increases thus dropping pressure
-Velocity of the fluid can be found by measuring the pressure

-Lateral Pressure of rapidly flowing fluid in a constricted tube can be subatmospheric, hence a sidearm on that portion of the tube can be used to aspirate another fluid into the tube
ex) Nebulizers, Venturi O2 Masks (24-40% O2), Jet Vent


Beer's Law (Beer-Lambert Law)

-Absorption of radiation by a given thickness of a solution of a given concentration is the same as that of 2x the thickness of a solution of half the concentration (Beer)

-Each layer thickness absorbs an equal fraction of the radiation that passes through (Lambert)


Pulse Oximetry (Beer's Law Application)

2 LEDs:
1) One (Red) emits light at 660nm
2) One (Infrared) emits light at 940nm
Shines across pulsatile tissue bed
Measures absorption on opposite side
Compare Red vs Infrared light
Calculate O2 sat

OXYHGB 940nm (IR light)
DEOXYHGB 660nm (Red light)


Errors in Pulse Oximetry

-Artifact (ambient light, low perfusion, motion)
- Alt. Species of Hemoglobin
Carboxyhgb: False High
Methgb: SaO2>85%: False Low
SaO2<85%: False High
HgbF: No Effect
HgbS: No Effect
-Polycythemia: No Effect
-Mythylene & Isossufan Blue: False Low
-Indocyanin Green & Indigo Carmine: Slight Decrease
-Blue Nail Polish: False Low


La Place

Pressure gradient across the wall of a SPHERE or TUBE/CYLINDER (vessel, ventricle, alveolus) is rt:
1) Wall tension (T)- Directly
2) Radius (r)- Inversely

ex) Normal Alveoli and the need for surfactant during expiration
ex) Vascular Pathology- Aneurysm rupture d/t increased wall tension
ex) Ventricular volume and work of the hear-a dilated ventricle has greater tension in its wall (end diastolic pressure rises)


Ohm's Law

Resistance which will allow one ampere of current to flow under the influence of a potential of one volt



E(Voltage)-I(current flow or amp) R(resistance)

ex) Strain Gauges in Pressure Transducers
ex) Thermistors


Electricity in the OR

1) Metal is a good conductor, your patient is lying on a metal bed, surgery causes bleeding, blood is wet, the room is full of electrical equipment->Risk to pt=BURNS

2) Macroshock: Current distributed through the body, culprit: faulty wiring, improper grounding

3) Microshock: Current applied in or near the heart, culprit pacing wires, fault equipment during cardiac cath

4) Electrocautery



-1 milliamp= skin tingling/perception
-5 milliamps =maximal "harmless" current
- 10-20 milliamps= let go of source
- 50 milliamp = pain, LOC, mechanical injury
- 100-300 milliamps= V-Fib, resp intact
-6000 milliamps= complete physiological damage



50-100 microamps= V-FIb