Physics Flashcards
How do you convert cmH2O to mmHg?
Multiply cmH2O by 0.74
How do you convert mmHg to cmH2O?
Multiply mmHg by 1.36
What is the critical temperature?
The temperature above which no amount of pressure can liquefy a gas
*critical temperature of N2O is 36.5 C (near room temp)
What are characteristics of a gas?
Molecules independent of each other
Constantly moving
Bombard sides of container creating pressure
No definite shape or volume
Fills whatever container
Measured with flowmeters and respirometers
What are the characteristics of a liquid?
Van der Waals force Molecules flow; sliding movement through substance Takes shape of container Has definite volume Measured with a cylinder
What are the characteristics of a solid?
Noncompressible
Lattice holds atoms/molecules close
Has definite volume and shape
Motion is limited
Only vibrates in placeHow do you convert degrees Celsius to unit Kelvin?
Add 273 to degrees Celsius
How do you convert degrees Celsius to Fahrenheit?
Multiply degrees Celsius by 9/5 then add 32
How do you convert degrees Fahrenheit to Celsius?
Subtract 32 from Fahrenheit then multiply by 5/9
What is Kelvin?
Unit of temperature
Same size as the unit Celsius
What is the First Law of Thermodynamics?
Heat is a form of energy and can be converted to other forms of energy, but neither can be created nor destroyed
What is the Second Law of Thermodynamics?
Heat always flows from warmer to cooler
There must exist a difference in temperature and the two things must be in contact
i.e. Air and body, body and table
What is Latent Heat of Vaporization?
Heat required to change a liquid substance to a gas (vapor) at a constant temperature
(If evaporation occurs, the remaining liquid loses heat)
What is Specific Heat Capacity?
The amount of heat required to raise the temperature of 1 kg of a substance by 1 K
Water is the standard
1 cal/g/degree C OR 1 kcal/kg/degree C
1 cal= 4.18 joules OR 1 kcal= 4,184 joules
What is Latent Heat of Fusion?
Heat required to change a solid to a liquid
What is Specific Latent Heat?
Energy required to convert 1 kg of a substance from one phase to another at a given temperature
(j/kg)
What is heat?
Kinetic energy of molecules of substance
Calorie (cal) is the energy needed to increase temperature of one gram of H2O by 1 degree C
1 kcal (4,184 J) is the energy needed to increase temperature of 1 kg of H2O by 1 degree C
What is heat capacity?
The amount of heat required to raise the temperature of an object by 1 K
Calculated by multiplying mass of an object by the specific heat capacity
What is critical pressure?
The pressure to liquefy a gas at its critical temperature
What is triple point?
Temperature at which ice, water, and water vapor are all in equilibrium
This is 0 degree C or 273 K
What is the boiling point?
Temperature at which vapor pressure becomes equal to atmospheric pressure and all liquid changes to gas phase
What is the saturated vapor pressure?
Pressure exerted by a vapor when, at any one temperature, an equilibrium is reached
The same number of molecules are vaporizing as are returning to liquid
*temperature dependent
What is Charle’s Law?
At a constant pressure the volume of a given gas varies directly with the absolute temperature
V1/T1=V2/T2
What is Boyle’s Law?
At a constant temperature, the volume of a given gas varies inversely with the absolute pressure
P1 x V1= P2 x V2
What is Gay Lussac’s Law (Third Perfect Gas Law)?
At a constant volume, the absolute pressure of a given mass of gas varies directly with the absolute temperature
P1/T1=P2/T2
What is Dalton’s Law of Partial Pressure?
In a mixture of gases the pressure exerted by each gas is the same as that would exert if it was alone in the container
Ptotal= P1 + P2 + P3……
What is Avogadro’s Hypothesis?
Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules (a mole)
One mole equals 6.022 x 10^23 (Avogadro’s number)
What is the Universal Gas Constant?
Gas laws combined with Avogadro’s Hypothesis
PV=nRT
n is the number of moles
P is directly proportional to “n”
What is Henry’s Law?
At a certain temperature, the amount of a given gas dissolved in a given liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid
What is cohesion?
Internal attractive forces between like molecules trying to stick together in the smallest shape possible
Ex: surface tension, Mercury, when overfill a milk glass but milk doesn’t spill over
What is force?
That which changes or tends to change the state of rest or motion of an object
Ex: Gravity, air through valves, fluid through IV, ETT on surrounding tissues
What is force measure in?
Newtons (N)
What is a Newton?
The force that will give a mass of 1 kg an acceleration of 1 m/s^2
What is Newton’s 2nd Law?
Force equals mass x acceleration
F= m x a
What is pressure?
Force applied over a surface
What is the unit of measurement for pressure?
Kilo pascal (kPa)
Or psi
What is a pascal?
Kilo pascal?
Pressure of 1 Newton acting over 1 square meter
N/m^2
Kilo pascal is the pressure of 1000 Newtons acting over 1 square meter
1000 N/m^2
What is absolute pressure?
Gauge pressure plus atmospheric pressure
What is psi?
Pounds per square inch
Atmospheric pressure is equivalent to…..
? bar ? kPa ? mmHg ? cmH2O ? psi
1 bar 100 kPa 760 mmHg 1034 cmH2O 14.7 psi
1 kPa is equivalent to….
? mmHg
? cmH2O
? psi
- 5 mmHg
- 34 cmH2O
- 147 psi
What is diffusion?
The continual movement of molecules among each other in liquids or in gases
Moves from areas of high to low concentration
Ex: gas-liquid barrier, gas-filled area, membrane
What is the Oil-Gas Partition coefficient?
Ratio of gas present in oil verses in the gas state
- higher oil-gas partition coefficient means drug is more potent
- shows how a drug will effect the CNS due to lipid bilayer
- nitrous least potent
What is partition coefficient?
The ratio of the amount of substance present in one phase compared with another, the two phases being of equal volume and in equilibrium
What is the blood-gas partition coefficient?
Reflects the proportion of the anesthetic that will be absorbed in the blood versus the amount of anesthetic that will leave the blood to diffuse into tissues (gas state)
*low blood-gas partition coefficient means low solubility and more likely to leave blood and enter tissues getting to the brain quicker, giving a more rapid induction
What is solubility coefficient?
The volume of gas which dissolves in one unit volume of the liquid at the temperature concerned
What is standard temperature and pressure (STP)?
0 degree C (273 K) and 760 mmHg (14.7 psi or 100 kPa)
There is no water vapor
At STP, one mole of any gas occupies how much volume?
22.4 Liters
Describe pressure in liquids?
Pressure is static, not moving at rest
P=h x dw
Height of column x density weight of liquid
What circumstances effect solubility?
Partial pressure of gas
Temperature
The gas
The liquid
What is Poiseuille’s Law?
Radius effects resistance and flow
P1-P2= resistance x flow
Flow= P1-P2/ (8nL/ pie x r^4)
Shows that radius (diameter) has a big direct effect on flow; an increase equals an increase in flow
What is Bernoulli effect?
Given a channel with a narrowing which then increases, the pressure measured along the channel is lowest at the narrowest point, often below atmospheric pressure
*so if an opening is created at the narrowest point, ENTRAINMENT occurs as air sucks in through the opening (going from an area of atmospheric pressure to a lower pressure)
What is Graham’s Law?
The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight
D ~ 1/square root of MW
What is Fick’s Law?
The rate of diffusion of a substance across a unit area is proportional to the concentration gradient
D ~ ( pressure gradient x A x S) / (d x sq root of MW)
-pressure gradient x surface area x solubility directly proportional to diffusion rate and thickness of membrane and molecular weight of molecule are indirectly proportional
What role does temperature play at the end of a case?
As temperature decreases, solubility of a gas increases….so if the patient is hypothermic, more inhalation agent will dissolve in the blood
- patient has to breathe off inhalation agent, so if it won’t convert to gas phase, takes longer to wake up
- Le Chatelier’s
What is adhesion?
Attractive forces between unlike molecules trying to stick to something different
Ex: when you dip a paper towel in a glass of water and the wetness climbs up fibers pass the water line; meniscus
What is surface tension? What is its clinical significance?
Cohesive forces at the surface of a liquid that tend to keep liquid in the most compact form
Heating lowers surface tension
- alveoli would collapse due to surface tension but surfactant prevents by decreasing surface tension
What is the formula for resistance?
8nL/ (pie)r^4
n=viscosity; directly proportional
L= length of channel; directly proportional
r= radius of channel; inversely proportional
- If you double the radius, resistance to flow decreases 16x
- Shows that diameter matters the most in the amount of resistance
What are factors affecting resistance?
Diameter of channel (r)
Length of channel (L)
Nature of flow (laminar vs turbulent)
Viscosity of fluid (n)
What is turbulent flow?
Flow that is no longer smooth, but has swirls and eddies
Change occurs when going too fast, change in direction, change in diameter (from circuit to ETT), obstruction (biting ETT, mucus plug)
*an increase in resistance leads to a lost of energy
What is laminar flow?
Fluid movement in smooth layers; no turbulence or eddies
Flow through straight channels at a low rate
- flow is greatest at the center and becomes slower as it comes closer to the wall of the channel
- uses less energy
What is flow?
The quantity of fluid passing a point ok a given time
F= Q/t
Q= quantity t= time
If using 70% nitrous oxide, what effects can it have on air?
If using 50% nitrous oxide?
With 70%, an air bubble can increase 300% in one hour
With 50%, an air bubble can increase 100% in one hour
What clinical application relates to Gay Lussac’s Law?
The lower the pressure, the lower the boiling point of an agent and the less heat required to vaporize. Vaporizers are calibrated at sea level, and each agent’s boiling point calculated at that pressure. If there is a change in atmospheric pressure, lower atmospheric pressure will create lower boiling points, meaning vaporizers calibrated at sea level will give too much heat and put out MORE vapor.
*also with mission trips, if you go to a much warmer or cooler climate, gas cylinder pressure changes directly with temperature
What clinical application relates to Avogadro’s hypothesis?
At STP, one mole (equal to the substances weight) occupies 22.4 L of volume. When calculating remaining amount of nitrous oxide, take weight of N2O (minus the wt of container) figure out grams and divide by molecular weighty (44g) then multiply by 22.4 L to find out remaining volume
What clinical application relates to Henry’s Law?
- Over pressurizing
* breathing air under pressure as scuba diving forces more nitrogen into tissues
When and why is there a big decrease in patient temperature in the OR?
OR is cold Inhalation agent takes away heat IV agent takes heat Regional anesthesia cause peripheral dilation losing more heat * biggest decrease in temperature within the first hour due to: Uncovering patient Prepping and draping Anesthetic agents
If patient is hypothermic and having a delay in recovering….what can the anesthetist do?
Turn off the vaporizer Increase gas (O2) flow to get more O2 to the alveoli diluting the anesthetic concentration in the alveoli. Through diffusion, the anesthetic gas will move from the blood state to the lower concentrated area in the alveoli and allow the patient to breathe off
What is MAC?
Minimal alveolar concentration
Based on the effective dose for 50% of patients
The lower the MAC, the more potent the drug
What factors affect rate of diffusion?
Anything that increases motion or kinetic energy (heat) speeds up diffusion
Size of the molecule
Smaller moves faster, bigger moves slower
Difference in concentration
Bigger gradient, faster diffusion
What clinical applications relate to Fick’s Law?
Over pressurizing
Nitrous effects
- second gas effect
- diffusion hypoxia
- movement into air filled cavities
Second Gas Effect
Nitrous oxide is used as a carrier gas. It moves out of alveoli quicker and when displaced, it leaves the concentration of the second gas (anesthetic) greater helping to build it faster and putting the patient to sleep quicker
Movement into air filled cavities
Diffusion of nitrous oxide is greater than diffusion of nitrogen since air already has 79% nitrogen. Any air filled cavities (in the stomach, ETT cuff, LMAs, tempanoplasty) nitrous oxide diffuses in before nitrogen moves out, building more pressure
no nitrous oxide use in CL placements, laparoscopic GI cases, or ear surgeries
What happens with Diffusion Hypoxia?
Nitrous has a blood:gas solubility of 0.47 which is 34x greater than nitrogen, so N2O prefers the gas phase and easily comes out of the blood and into the alveolar tissue, causing a hypoxic mixture when too much goes in and causes an 02 percentage less than 21%
How can the radius’s effect on flow apply clinically?
The same amount of edema after surgery has a much greater effect on the airway of an infant with a much smaller airway while that same edema may have only an insignificant effect on an adult airway due to a larger diameter
How can Poiseuille’s Law apply clinically?
Can be used to predict resistance to flow with no turbulence
Length and viscosity increases resistance
*if you decrease the length by 1/2, you can double the rate of flow
How does Bernoulli’s effect apply clinically?
Venturi masks have an adapter with different size openings for entrainment of more or less room air in with the oxygen flow
What is temperature?
The parameter used to describe the amount of heat possessed
What are the four methods of heat transfer?
Conduction
Radiation
Convection
Evaporation
Describe conduction.
Heat movement through a substance by the transfer of kinetic energy from molecule to molecule
- metal has good conductivity
- air has poor conductivity
- heat loss is about 10% in the OR
- 2% by contact with the OR table
Describe radiation.
Heat transferred from warmer to cooler objects by emission and absorption of energy radiated in varying wavelength
Objects don’t have to touch
*accounts for about 40% heat loss in OR (largest % of heat loss)
In what ways can you decrease heat loss to radiation?
Surround the body with warm blankets
Describe convection?
Heat transfer occurs by moving fluid (liquid or gas)
Air adjacent to the body is warmed, it expands and moves away, carrying heat away with it
Ex: wind chill; convection air current
- accounts for 32% of heat loss (I.V.s, anesthetic gases, air)
- 2% loss in the respiratory tract by cool air we put in
In what ways can you decrease heat loss via convection?
Cover or insulate skin surface with blankets, drapes, etc
Warm inspired gases
Warm fluids
- heat lost mostly in head of infants
- adults factor is only body surface, not specifically head
Describe evaporation
Loss of latent heat of vaporization of moisture on the skin’s surface
-evaporation may be through the skin, mucosa of open wounds, or airway
- accounts for 28% of heat loss
- 8% is from the respiratory passages
Dependent on the amount of surface exposed and the difference in vapor pressure between the skin and surrounding air
In what ways can you decrease the amount of heat loss through evaporation?
Decrease gas flow rates
Use HME filters (trap exhaled breath to hold heat/moisture for next inhaled breath)
How does heat capacity apply clinically?
The body uses shivering (cause increase in heat production) to increase heat
- shivering uses a tremendous amount of oxygen
- increases myocardial O2 demand 400%
- not good for CAD and heart attack pts
- demerol and morphine help stop shivering BUT must keep pt temp up
- bear hugger only way to INCREASE actual temp rather than decrease heat loss
What is a clinical example of latent heat of vaporization?
When a N2O cylinder is allowed to empty rapidly, the cylinder becomes very cold and the water vapor from the surrounding air freezes or crystallizes on the cylinder (Joule-Thompson effect)
Types of electromagnetic radiation?
Ionizing
Non-ionizing
Describe ionizing radiation
-releases energy by removing electrons from atoms in tissues, creating ions that are very chemically reactive and hazardous
Includes x-rays and gamma rays released by radioactive isotopes; fluoroscopy
- rapidly multiplying cells are most vulnerable
- cancer cells and fetal cells (pregnant!)
Describe non-ionizing radiation.
- discharges its energy without creating ions or removing electrons from atoms in tissues
- includes infrared radiation, visible light, ultraviolet radiation as utilized with lasers
LASER stands for?
Light amplification by stimulated emission of radiation
How can you protect yourself from ionizing radiation?
- DISTANCE: the intensity of scattered radiation is inversely proportional to the square of the distance from the source; at least 3 FEET!
- 6 feet air=9 inches concrete=2.5 mm lead
- TIME: minimize time around radiation
- SHIELD: use barriers like lead aprons
Ionizing radiation exposure
- maximum yearly exposure no more than 5 rem or 5000 mrem
- one chest x-ray is about 25 mrem
- using fluoroscopy, during a routine procedure the exposure may be greater than 8,000 mrem
- heart catch may be greater than 75,000 mrem
How do you protect from non-ionizing radiation?
- EYEWEAR: must have lenses that filter the specific wavelength of the laser in use
- ensure patient has saline gauze border and eyewear
- non reflective instruments
- distance does NOT help
- FILTER MASK: intake of the plume, the vapor and cellular debris, may present significant risk
- debris size ranges from 0.1 to 0.8 um
- intact DNA of HPV and HIV found in plume
How can Boyle’s Law apply clinically?
-squeezing an ambu bag raises pressure and decreases the volume
- during inspiration, intrapulmonary pressure falls as volume increases
- during expiration, intrapulmonary pressure increases as volume decreases
Apply Charle’s Law clinically.
- the inflatable cuff of a LMA expands when placed into an autoclave
- Helium balloons on a mailbox shrink in the cold
Apply Dalton’s law clinically.
Air is 21% O2 and 79% N2, so atmospheric pressure (760mmHg) give you 160 mmHg (21%) O2 and 600 mmHg (79%) N2
What is the relationship between specific heat and temperature?
Temperature changes more gradually with a high specific heat than those with a low specific heat
-high latent heat of vaporization agents take more heat (energy) and more time to change to gas phase
Le Chatelier’s Principle:
A change in any of the factors in determining an equilibrium causes the system to adjust or reduce or counteract the effect of the change (solubility increases with decreasing temperature)
In what way can you decrease the amount of heat loss by conduction?
The use of foam pads on the OR table since foam pads act as a great insulator
Describe how a change in pressure is transmitted throughout the liquid-filled
system and give examples of clinical application.
Under static conditions in a liquid column, the pressure is the same in all directions at any given point.
In a closed system, any change in pressure is equally transmitted to all parts of the system –
think of manometers and your art line system.
What is absolute zero?
0 Kelvin
What is solubility?
The max amount of 1 substance (solute) that is able to dissolve into another
(solvent.) Solution is a homogenous mixture of a solute (gas) in a solvent (liquid)…this depends upon partial pressure of gas, temperature, gas (what is the solubility of that gas?), and liquid (what is preference? gas phase? Liquid phase?)
Define gram molecular weight.
placing gram after the element’s atomic number weight gives you the mole…example: Helium has atomic weight of 4, therefore, 4 grams of Helium = 1 mole of
Helium
How much radiation can you be exposed to?
5 rem or 5000 mrem
How much radiation can a pregnant person be exposed to?
500 mrem
