Physics Review Flashcards
Describe Solids
Closely approximated atoms due to lattice and greatly influenced by intermolecular forces. Non-compressible and have volume, shape, and limited motion. If you add heat, the lattice structure breaks down, and molecules move further apart. Ex- Ice melting.
Describe Liquids
Molecules exert weaker forces on each other, known as Van der Waals forces. Allows molecules to flow and move throughout the substance. A decrease in the force between molecules enable them to take the shape of a container while still having volume. Have more kinetic energy than solids.
What are Van der Waals forces?
A weak force exists between molecules in a liquid state. Allows for molecules to flow.
Describe Gases
Molecules are independent of each other and constantly moving, hitting the side of their container. No definite shape or volume. Pressure can be generated by the compression of gas in a chamber and is measured by flowmeters or respirometers. This pressure is the force exerted by the gas on the chamber walls.
What is the pressure exerted by vapor when, ay any one temperature, an equilibrium is reached at which the same number of molecules are vaporizing as are returning to liquid?
Saturated Vapor Pressure
What is the temperature at which vapor pressure becomes equal to atmospheric pressure and at which all liquid changes to gas?
Boiling point
Describe the relationship between vapor pressure and boiling points.
They are inversely related. The lower the boiling point, the higher the vapor pressure. This is why there are specific vaporizers needed for specific anesthetic gases.
This means vapor pressure is temperature dependent.
Is vapor pressure a function of volume, temperature, or pressure?
Temperature
What are the vapor pressures for gases at 20 degrees C?
Sevoflurane, 170 mmHg
Isoflurane, 240 mmHg
Halothane, 244 mmHg
Desflurane, 669 mmHg
Describe Force
Force is what changes or tends to change the state of rest or motion of an object. This is measured in N (newton).
N- gives a mass of 1 kg an acceleration of 1 m/s^2
Equation: F=ma
This is mass multiplied by acceleration (Newton’s second law)
Ex- gravity, force of air through valves in ventilator, force of fluid through IV, force of ETT on surrounding tissue.
Describe Pressure
Pressure is the force applied over a surface area. It is measured in pascal (Pa). This is the pressure of 1 newton acting over 1 square meter - N/m^2
What do we typically use to measure pressure?
The kPa or the kilopascal. This is used because the pascal is too small of a number to be manageable.
psi is pounds per square inch and is also used to measure pressure. (British)
Atmospheric Pressure = 1 bar
Provide the remaining conversions
= 100 kPa
=760 mmHg
=1034 cmH2O
=14.7 psi
1 kPa = 7.5 mmHg
= 10.34 cmH2O
=0.147 psi
What is absolute pressure?
This equals gauge pressure plus atmospheric pressure. (gauge pressure is the important parameter in most cases)
Ex- gas-cylinder pressures (psig or pounds per square inch gauge). When a cylinder is empty, it will say 0 psi or 0 bar. This does not mean that it is truly empty, but the O2 is equal to atmospheric pressure (14.7 psi or 1 bar), and no more gas can be removed.
What is important to remember with gas laws?
Temp must be measure in Kelvin for gas laws. Remember Kelvin = Celcius + 273. There is no degree sign.
Absolute zero 0 K or -273 degrees C
1 unit K is 1 degree C
What is Boyle’s Law?
At a constant temperature, the volume of a given gas varies inversely with the absolute pressure.
Equation: P1 x V1 = P2 x V2
If volume goes up, pressure goes down. Ex- squeezing ambu bag raises pressure and decreased volume. OR with inspiration, intrapulmonary pressure falls and volume increases. During expiration, intrapulmonary pressure increases and volume decreases.
What is Charles’ Law?
At a constant pressure, the volume of a given gas varies directly with the absolute temperature. Increasing temperature causes molecules to increase movement and thus take up more volume.
Equation: V1/T1 = V2/T2
A direct relationship means that as one increases, the other increases also.
Ex- Helium balloons shrink in the cold.
What is Gay Lussac’s Law?
Also known as the 3rd perfect gas law.
At a constant volume, the absolute pressure of a given mass of gas varies directly with the absolute temperature.
Equation: P1/T1 = P2/T2
Meaning that if temperature lowers, the pressure lowers; if temperature increases, the pressure increases. Like tire pressure in summer and winter.
Application: The lower the atmospheric pressure, the lower the boiling point.
What is Dalton’s Law of Partial Pressures?
In a mixture of gases, the pressure exerted by each gas is the same as that it would exert if it were alone in the container.
Ex- in a cylinder of air with a pressure of 100 kPa, the O2 would exert 21% or 21 kPa, and nitrogen would exert 79% or 79 kPa.
Partial pressure exerted by any single gas in a combination of gases is directly proportional to its % composition of the gas mixture.
Equation: P1 + P2 + P3 = P total
What is partial pressure?
The pressure exerted by a single component of a mixture of gases.
In the atmosphere at sea level, partial pressures are
O2, 160 mmHg (21%)
N2, 600 mmHg (79%)
Total is 760 mmHg.
In the mountains where the atmospheric pressure is 550 mmHg:
O2, 550 mmHg x 21% = 116 mmHg
N2, 550 mmHg x79% = 434 mmHg.
Application: what is the partial pressure of CO2 if its concentration in the end-tidal gases is 5%? 5% x 760 mmHg = 38 mmHg
What is Avogadro’s Hypothesis?
Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules (a mole).
We have to discuss gas molecules in moles instead of masses, because gas molecules have different molecular weights. So if one mole of any gas at STP occupies 22.4 L, that means 2 gm hydrogen or 32 gm Oxygen or 44 gm CO2, or 44 gm nitrous oxide occupies 22.4 L.
What is Avogadro’s number?
6.022 x 10^23
It is the number of atoms/molecules in one mole.
What is STP?
This is standard temperature and pressure. At STP, one mole of any gas occupies 22.4 liters. STP is 0 degrees C, 760 mmHg, dry (no H2O vapor).
22.4 L = 44 g.
44g = 1 mole
Application: a nitrous oxide container is full and contains 3.4 kg of the gas. If the measurements are made at STP, what volume of nitrous oxide is obtained from this cylinder?
44g (1 mole) of N2O is 22.4 L at STP.
X liters/3400 g = 22.4 L/44 g
X = 1730 liters
What is Universal Gas Constant?
This is the gas laws combined with Avogadro’s hypothesis.
Constants: PV, V/T, P/T
PV/T = universal gas constant (nR)
PV = nRT (n is the number of moles)
Explain why the pressure gauge does not act as a content gauge for nitrous oxide.
Nitrous in a cylinder is a liquid with the pressure measuring the vapor above the liquid. Unlike O2 or air, which lowers in pressure as it empties, nitrous pressure remains constant as long as liquid remains in the container. This is why nitrous pressure will remain the same until the liquid is gone, moving from full to empty instead of gradually decreasing.
Applying avodadro’s number can be done to determine amount of nitrous left.
Universal Gas Law (ideal gas law)
PV = nRT
In application to a cylinder of gas, V is constant, R is a constant (R is universal gas constant), T is held constant, so P is directly proportional to n.
So as moles decrease, the pressure decreases.
What is critical temperature?
The temperature above which no amount of pressure can liquify a gas
This is important for nitrous
What is critical pressure?
The pressure to liquify a gas at its critical temperature.
Gas can liquify at its critical temperature but not at a temperature any higher. The critical temp of nitrous is 36.5 C. because it is stored below that temp, it is in liquid form.
What does solubility depend on?
Partial pressure of a gas
Temperature
Gas
Liquid
What is a solution?
A homogenous mixture of a solute (gas) in a solvent (liquid)
Application: we think of this in terms of the gas content in the blood through the alveoli. The pressure gradient determines how much gas goes into the blood.
What is saturated vapor pressure?
partial pressure exerted by a vapor over a liquid in a closed container when equilibrium has been met between the liquid and the vapor.
Molecules of the gas will dissolve into the liquid and an equilibrium will be attained where as many molecules of gas are entering the liquid as leaving the liquid. This is a saturated solution.
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.
ex- breathing air under pressure as scuba divers cause more nitrogen into solutions in tissues.
Henry like to scuba dive.
When you increase O2 concentration, you are increasing the partial pressure and this aids diffusion into the blood. “over pressuring”
Given an anesthesia example of Henry’s law
Increasing the concentration of isoflurane in the blood involves increasing the concentration or partial pressure. This is utilized at induction of anesthesia when a higher concentration of the anesthetic than necessary for maintenance is given as a loading dose is delivered to speed uptake. This is concentrating effect or over pressuring.
Ex- sevoflurane indiction 4-8% while maintenance is 1-4%.
Describe 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 temp. As the temperature of the liquid increases, the amount of gas dissolved decreases. This is because gas becomes a liquid in cooler temps, increasing the ability to dissolve in liquid, but converts back to a gas in higher temps.
What happens if a patient is cold at the end of an anesthetic?
The inhaled anesthetic will be more soluble in the blood, causing the patient to wake up more slowly.
What is solubility coefficient?
The volume of gas which dissolves in one unit volume of the liquid at the temperature concerned.
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)
How does gas affect solubility?
The solubility coefficient of a gas at body temperature explains how dissolvable a gas is.
Ex. Oxygen = 0.024 and carbon dioxide is 0.57 at body temperature. This shows that CO2 is 20 times as soluble as O2. In anesthesia, we look at the partition coefficient as a ratio and it is stated for 37 C unless stated otherwise.
Ex. if 1 liter of nitrous oxide above 1 liter of blood at 37 degrees C, the volume of nitrous oxide dissolved in the blood is 0.47 liters. So blood-gas partition coefficient is 0.47.
Order listed is important. blood-gas is 0.47 to 1, gas blood is 1 to 0.47.
What is the blood-gas partition coefficient?
This reflects the proportion of the anesthetic that will be absorbed in the blood vs the amount of anesthetic that will leave the blood to dissolve into tissues.
We can use this to compare different anesthetic agents. The lower this b-g coefficient, the faster the induction. Low b-g coefficient means poorly soluble. Equilibrium between gas and blood and brain is reached rapidly.
Inhaled agents with low solubility cause buildup in alveoli, producing the rapid induction of anesthesia.
What is the oil-gas partition coefficient?
The ratio of a gas present in oil vs in the gas state.
Indicates how efficiently a gas can access and affect the sites of action.
The higher the oil-gas coefficient (lipid-solubility) the more potent the anesthetic gas.
Fat is an important substance in cell membranes and neurons. Solubility of gases can be measured in oil, which is similar to fat in tissues.
What is the most and least potent gas? What does this mean about their solubility?
Halothane is the most potent, it has the highest oil-gas coefficient. Nitrous is the least potent, it has the lowest oil-gas coefficient.
Diffusion is the continual movement of molecules among each other in liquids and gases. Which way do they move?
From high to low concentration
Diffusion can happen across …
gas-liquid barrier, gas-filled area, and membranes.
Gas can diffuse through into other gases
Discuss diffusion and what it is directly or indirectly proportional to in gases.
Diffusion is directly proportional to the pressure gradient, surface area, and solubility of the gas. It is indirectly proportional to the thickness of the membrane and the size of the molecule.
More soluble, more diffusion.
Bigger (more of) a molecule or thickness of membrane, less diffusion.
What affects diffusion in/through gases?
Thickness of the membrane (d)
size of the molecule (MW)
surface area of the membrane (A)
solubility of the gas (S)
Pressure gradient (P1-P2 or delta P)
What is Fick’s Law?
The rate of diffusion of a substance across unit area is proportional to the concentration gradient
Ex. Overpressuring for induction or increasing the FiO2 to increase PaO2.
This explains concentration effect, second gas effect, diffusion hypoxia, and expanded air-filled spaces with nitrous.
What is Graham’s Law?
The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
So increased MW, decreased diffusion.
Another concerning factor is the membrane- its area, thickness, and makeup.
Discuss second gas effect of nitrous oxide
this is a theoretical situation because nitrous would not render someone unconscious unless it were at 104%. It is used as a carrier gas for the other gases because it helps build alveoli content up faster.
Why is there diffusion hypoxia when using nitrous oxide?
Nitrous has a low solubility, so it comes out of the blood rapidly. This rush of nitrous from the lungs will overwhelm the oxygen concentration in the alveoli. We give 100% O2 when turning off the nitrous to counter this.
Why is nitrous avoided in certain surgeries?
Nitrous has a blood-gas coefficient of 0.47 which is 34 times greater than nitrogen at 0.014. Thus, nitrous can leave the blood to enter an air-filled cavity 34 times faster than nitrogen can leave the cavity to enter the blood. If there is a compliant wall, the volume of gas will expand. ex. pneumothorax, intestinal gas. Additionally if there are noncompliant walls, such as a surgical graft in the middle ear, the nitrous can cause the ear drum or graft to burst.
What are the 2 components of fluid flow?
Cohesion and Adhesion
Explain cohesion (fluid flow)
internal attractive forces between like molecules trying to stick together in the smallest shape possible.
ex. liquid pulling on itself; mercury
Explain Adhesion (fluid flow)
The attractive forces between unlike molecules trying to stick to something different
ex. attracted to the container; water
Explain surface tension
Cohesive factors at the surface of a liquid that tend to keep liquid in its most compact form.
ex. dome at the top of a full glass.
What does heating do to surface tension?
Why does this matter to us?
Heating lowers surface tension.
This matters to us because of alveoli and surfactants. The alveoli would collapse due to surface tension of the liquid, but surfactant reduce the surface tension and prevents that collapse when the walls of the alveoli come together during expiration. When the surfactant is absent, alveoli collapse can occur (premature neonates)
Formula for pressure in liquids
P = hdw
height of column x density weight of liquid
If it is static, it is not moving or at rest. This also means that pressure is the same in all directions at any given point.
Explain pressure in liquids
Remember that pressure is equal to force per unit area
Force in a liquid is from the column of liquid of a specific density and height above the point of measurement- from the weight of the liquid column.
In a closed system, any change in pressure is equally transmitted to all parts of the system.
Manometer for H2O and Hg
Density of H2O = 1 gm/cc
Density of Hg = 13.6 gm/cc
Compare 7.5 mmHg = 10.2 cm H2O
Converting cm H2O to mmHg: 0.74x
Converting mmHg to cm H2O: 1.36x
The densities are different. Conversions do not change much, but remember changing from cm to mm
Another difference is the reaction of the liquid in the manometer. H2O adhesive forces to the side of the column. Mercury has surface tension to itself.
Ex. MAP 50 mmHg v 68 cm H2O
Explain Flow
The quantity of a fluid passing a point in a given time.
F=Q/t
Q = quantity
t = time
P1-P2
Has to have a pressure gradient. Meaning there has to be a difference in pressure between the starting point and ending point of the flow. Once flow is established, it is either laminar or turbulent.
How is static fluid pressure determined?
depth of the fluid, the density of the fluid, and any outside pressure exerted on it.
Explain laminar Flow
This is fluid movement in smooth layer with no turbulence. Typically a straight channel at low rates of flow.
Flow is greatest at center and slower at walls of channel.
This flow has the least resistance and the movement of air in the respiratory tract is a great example. The air movement is mostly laminar, but changes to turbulent during speaking, coughing, or deep breathing when velocity is increased.
Explain turbulent flow
Flow is no longer smooth and has swirls and eddies.
Laminar flow changes to turbulent when critical velocity is reached, the direction is changed, or flow is obstructed. Resistance to flow is increased.
Energy is lost- this requires a greater pressure gradient.
Examples of when this happen is a kink in tubing, y connector sites. Anything that increases the resistance decreases the flow and requires an increase in pressure.
Explain factors affecting resistance
The factors include:
diameter of the channel (r)
length of the channel (L)
nature of the flow (laminar v turbulent)
viscosity of the fluid (n)
Discuss viscosity
Viscosity is the fractional forces between layers within a fluid. cohesive forces which weaken as temperature increases. It is influenced by temperature: increase temp = decrease viscosity. decrease temp = increase viscosity
more viscosity, more thickness. blood is more viscous than water.
Crystalloid IV fluids have lower viscosity than blood. In the clinical setting, the viscosity of blood is influenced by the hematocrit, pt age (increases with age), smokers (increased), and can be lowered by the molecular wt dextran.
Discuss Hagen-Poiseuille equation derivative
This is an equation that explains the factors that affect flow.
Resistance = 8nL/(pie)r^4
n is viscosity which is directly proportional to resistance
L is the length of the channel, which is directly proportional to resistance.
r is the radius of the channel which is inversely proportional to the resistance to the fourth power.
If you double the radius of the channel, the resistance to flow decreases 16x
Application: flow through different sized IV catheters or ETTs.
Physiological application: muscular work increases demand for blood flow while the heat generated slightly decreased blood viscosity making it flow easier.
Poiseuille’s Law formula
P1-P2 = resistance x flow
or
flow = p1-p2/8nL/(pie)r^4
Describe poiseuille’s law
This looks at the flow rate in relation to resistance and the pressure gradient if you have ideal fluid with no turbulence.
For this equation, flow is directly proportional to pressure. The radius or diameter of channel has the greatest effect on flow. Once turbulence occurs, this law can no longer be used to predict resistance.
To maintain flow rates, the pressure gradient must increase or the turbulence must be removed.
What is the 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.
This narrowing causes increased velocity, thus increased kinetic energy. To maintain unchanged sum of energy, the potential energy must decrease.
If an opening is located at the narrowing where the pressure is lower than atmospheric, entrainment could occur. This type of system is called the venturi system.
Another type of entrainment where O2 moving at high speed picks up air into flow to reduce O2 concentration.
What forms of energy are contained in fluid?
Potential energy associated with pressure and kinetic energy associated with its flow.
energy can neither be created nor destroyed. The sum of energy must remain unchanged.
Explain Laplace’s Law
Relationship of wall tension, pressure, and radius of cylinders (vessels) and spheres (ventricles and alveoli)
Clylinders: T = Pr
Spheres: 2T = Pr
Aneurysm in aorta- in aneurysm with greater radius, wall tension increases (direct relationship of tension to radius) P = T/r
How does surfactant affect Laplace’s Law?
Surfactant lowers the surface tension in the alveoli and prevents the effects of this law.
Equations for normal aorta and aneurysm in regards to Laplace’s Law
Normal Aorta: 100 mmHg (P) x 2 cm (r) = T
Aneurysm: 100 mmHg (p) x 4 cm (r) = T x 2
What is heat?
The kinetic energy of molecules of substance
What is calorie (cal)?
What is kcal?
Calorie is the energy needed to increase temperature of one gram of H2O 1 degree C.
1kcal = C = 4184 joules = energy to increase temperature of 1 kg H2O 1 degree C.
What is temperature?
The parameter used to describe the amount of heat possessed.
What are the temperature conversions?
T celcius = 5/9 (T fahreheit -32 degrees) F to C
T fahre = 9/5 (T celcius + 32 degrees) C to F
T kelvin = celcius + 273 C to K
Discuss the Kelvin
This is the necessary unit for calculations in gas laws.
The kelvin is the same as the celcius unit, so at times these are interchanged.
Kelvin is not recorded in degrees. 0K is the absolute zero because at this temperature, all atomic motion ceases.
What is the triple point
The temperature at which water, ice, and water vapor are all at equilibrium. This is 0 degree celcius or 273.15 K.
First law of thermodynamics
Heat is a form of energy and can be converted to other forms of energy, but neither created or destroyed
Second law of thermidynamics
Heat always flows from warmer to cooler. There must exist a difference in temperature and the two things must be in contact.
What are the 4 methods of heat transfer?
Conduction
Radiation
Convection
Evaporation
Discuss conduction
Heat movement through a substance by the transfer of kinetic energy from molecule to molecule.
Metal is a good conductor. Air gas poor conductivity qualities.
This form of heat loss is not a real factor in the heat loss of an anesthetized pt as they are only in contact with the foam pad and it is a thermal insulator. (2%)
Discuss Radiation
Heat is transferred from warmer to cooler objects by emission and absorption of energy radiated in varying wavelengths.
Objects do not have to touch.
This accounts for the largest percentage of normal heat loss from the body. (40%)
-this can be minimized by surrounding the body with warm objects and accelerated by surrounding it with cooler objects.
The difference in temp of the objects determined the rate of heat transfer.
Discuss convection
Heat transfer occurs by moving fluid (liquid or gas)
air adjacent to the body is warmed, it expands and moves away, and it carries heat with it.
-this is why we warm gas or blood when it is delivered to the patient. This type causes 32% of heat loss in the anesthetized pt. Reduce this by using cotton blankets, surgical drapes, plastic sheeting
-a single layer to trap air reduced heat loss by about 30%.
-have to consider the amount of skin surface covered. popular misconception that a large amount of heat is lost in adults through the head, this is however true in neonates and infants due to the head being a a high percentage of body surface area.
-can also occur in respiratory tract. warmed air is the prevention.
ex- wind chill and convection air current. heat rises, cool air lowers.
Explain evaporation
This is the loss of latent heat of vaporization of moisture on the skin’s surface.
If evaporation occurs (latent heat of evaporation), the remaining liquid loses heat.
This accounts for 28% of heat loss in anesthetized pts.
Can occur in surgical wounds and respiratory tract.
what is latent heat of vaporization
The heat required to turn liquid into vapor.
If temp is decreased, vaporization is decreased. This is why some vaporizers have heaters.
What two factors influence evaporation?
Difference in vapor pressure between skin surface and surrounding air (amount heat lost can be increased ten times by sweating)
The amount of surface exposed.
What is specific heat capacity?
The amount of heat required to raise the temperature of 1 kg of a substance by 1 kelvin.
H2O is the standard: 1 cal/g/degree celcius = 1kcal/kg/degree celcius
1 cal = 4.18 joules
joules is the energy required.
Discuss specific heat capacity
Temp changes more gradually for materials with a high specific heat than those with a low specific heat
The materials chosen for vaporizers need to have higher specific heat capacity so that they cool off slower.
We also need to know the specific heat of the volatile anesthetic agent, so we know how much heat to apply to increase its temperature to the point of vaporization
Discuss Heat Capacity
The amount of heat required to raise the temp of an object by 1 kelvin.
This is calculated by multiplying the mass of the object by the specific heat capacity.
ex. 70 kg pt trying to increase his temp from 36 to 37 C, how many minutes of shivering would it take?
-Basal heat production is 50 W/m^2 (average man 80W)
-shivering can increase production up to 4 times. (320W)
-shivering also increases the amount of O2 that the myocardium needs.
knowing heat capacity of an object allows us to calculate the effect of changes in heat production.
70 kg pt trying to increase his temp from 36 to 37 C, how many minutes of shivering would it take?
tissue specific heat capacities can be approximated to a mean of 3.5 kJ/kg/degree celcius
-for a 70 kg pt, it would be 245 kJ/degree celcius.
The additional heat production from shivering is 240W or 240 x 60 joules/min. This is 14.4 kJ/min. If 245 kJ are needed to increase temperature 1 degree C, then it will take 245/14.4 minutes or 17 minutes of shivering.
What is specific latent heat?
energy required to convert 1 kg of a substance from one phase to another at a given temp. (J/kg)
what is latent heat of fusion?
The heat required to change a solid to a liquid.
What is latent heat of vaporization?
heat required to change a substance from a liquid to a gas at a constant temp
ex- when N2O cylinder is allowed to empty rapidly, the cylinder becomes very cold and the water vapor from the surrounding air freezes on the cylinder. (this is the joule-thompson effect)
if a vaporizer had lower temps, the liquid would be less volatile, and the amount of agent vaporized would decrease
Discuss atomic structure
atoms are comprised of protons (+), neutrons(-), and electrons(-). The element is determined by the number of protons. The number of neutrons determines the isotope and the stability of the nucleus.
Discuss unstable isotopes
unstable isotopes may emit beta particles (electrons). The nucleus may attract and capture an electron. Alpha particle is lost consisting of two protons and two neutrons. The nucleus may split into several parts.
After the isotope has decayed, it is common that it will emit an electromagnetic wave or gamma ray.
discuss Ionizing electromagnetic radiation
releases energy by removing electrons from atoms in tissues.
Creating ions that are very chemically reactive and very hazardous. included xrays and gamma rays released by radioactive isotropes.
this can be harnessed and used as medical xrays.
Discuss non-ionizing electromagnetic radiation
discharges its energy without creating ions or removing electrons from atoms in tissues.
This included infrared radiation, visible light, ultraviolet radiation as utilized with lasers.
LASER- light amplification by stimulated emission of radiation.
Protection- ionizing radiation
Distance is the intensity of scattered radiation in inversely proportional to the square of the distance from the source.
Distance is the best form of protection: at least 3 feet away. 6 feet of air is the equivalent of 9 inches of concrete or 2.5 mm lead.
- 0.25 to 0.5 mm lead sheeting blocks most scattered radiation.
Time- minimize time around radiation
shielding- use barriers, like lead aprons.
What is the greatest source of radiation in the OR?
fluoroscopy. (used by ortho, neuro, uro, general, and vascular surgery.)
Exposure is due to x-rays scattered by both patient and other surfaces. (it bounces off reflective surfaces like light)
What is needed for protection during fluoroscopy procedures
a lead apron with 0.35 mm lead thickness equivalence should be sufficient for most procedures. For high workload, a wrap around apron with 0.25 led equivalence that overlaps on the front to provide 0.5 mm (.25 to .25) and 0.25 mm on the back would be ideal.
Radiation exposure stats
Max yearly occupational exposure is no more than 5 rem or 5000 mrem.
One chest xray is 25 mrem
routine fluoroscopy exposure may be greater than 8000 mrem.
monitoring shows that one person rarely absorbs more than 50 mrem a year.
actively dividing cells are affected by radiation, making tumors and fetuses susceptible.
Discuss protection for non-ionizing radiation
eyewear- must have lenses that filter the specific wavelength of the laser in use. instruments should be non-reflective. distance does NOT help.
The wavelength matters.
reflected radiation injuries include cornea burns, optic nerve injury, and cataract formation.
A properly fitting filter mask is important to prevent intake of plumes, vapor, and cellular debris. Debris sizes range from 0.1 to 0.8 micrometer (um)
-intact DNA of HPV and HIV proviral DNS found in plume.
