Chem/Phys Exam 3 Flashcards
1
Q
Gas
A
- no definite shape or volume; conforms to container; fills contain; flows; is easily compressible and expandable
- gases that do not react chemically form homogenous mixtures
- molecules high kinetic energy, large distances, do not interact with each other or container
- ideal gas has NO intermolecular forces
- easily compressible and expandable
2
Q
Liquids
A
- definite volume. Conforms to shape of container; flows; NOT compressible
- molecular distance small, medium kinetic energy; inter-molecular forces hold condensed state but allow molecules to slide against each other
- RESIST compression*
3
Q
Remember: both gases and liquids are _________
A
Fluids
4
Q
Meyer-Overton Hypothesis
A
- The potency of a compound to induce general anesthesia is directly related to the compounds lipid solubility
- lipid solubility can be equated to the olive oil: water coefficient
5
Q
Meyer-Overton Hypothesis:
High partition coefficient
A
-higher partition coefficient, higher solubility, higher partitioning into compartment (blood, muscle fat)
6
Q
Low solubility Agents
A
- Higher MAC to produce anesthesia (Des MAC=6%, N2O MAC= 105%)
- Rapid onset and rapid recovery
7
Q
Higher Solubility Agents
A
- Lower MAC to produce anesthesia (Halothane MAC= .74%, Methoxyflurance MAC 0.15%)
- slower onset and rapid recovery
8
Q
Isoflurane: MAC in Oxygen, Oil:Gas (FAT) coefficient, Blood:Gas Coefficient
A
MAC in Oxygen= 1.15%
Oil: Gas (FAT)= 91
Blood:Gas= 1.4
9
Q
Sevoflurane MAC, Oil:Gas (FAT), Blood:Gas
A
MAC= 2%
Oil:Gas (FAT)= 50
Blood:Gas= .66
10
Q
Desflurane
A
MAC= 6% Oil:Gas= 18.7 (low) Blood:Gas= .42
11
Q
Nitrous Oxide
A
MAC= 105%
Oil:Gas (FAT)= 1.3
Blood:Gas= .47
12
Q
Saturated Vapor Pressure (SVP)
A
-the pressure in the vapor phase when it is in equilibrium with its liquid phase
13
Q
The SVP of a substance (anesthetic agent) at a specified T is the partial pressure of the substance in the vapor phase that is what?
A
-In equilibrium with its liquid (or solid) phase
14
Q
SVP for a given substance depends ONLY on
A
Temperature
-at a higher T, more molecules will be present int he gas phase at equilibrium and the vapor pressure and SVP will both be higher
15
Q
SVP is a _______________ of the substance.
SVP does NOT change in different ____________.
A
- SVP is a characteristic of the substance*
- The SVP does NOT change in different environments (ATM pressures or temperatures)
16
Q
SVP of water is a function of _______________
A
- Temperature
- As the temperature increases, more water is in the vapor form (humidity)
17
Q
Relative Humidity
A
-Amount of water vapor in the air compared to the amount the air could hold (SVP) at that temperature
18
Q
Summer Humidity
A
Higher=lots of moisture in the air, vapor pressure is higher
19
Q
Winter Humidity
A
Lower= drier air= vapor pressure is lower
20
Q
Low humidity makes us feel?
A
Up to 5-7 degrees cooler than air temp
21
Q
High humidity makes us feel?
A
5-7 degrees hotter than air temp
Humans are comfortable with a relative humidity at about 45%
22
Q
SVP effects on Anesthesia
A
-Inspired air is saturated with water vapor as it passes through trachea and bronchi
RA= 10mmHg
Larynx= 26-32 mmHg
Bronchi= 47 mmHg
23
Q
SVP water at 37 degrees C is ________ mmHg
A
47 mmHg
24
Q
Oxygen calculations: increasing humidity _____________ FIO2
A
Decreases
25
Dry Air (IC, IA)
O2= 21% of 760= PO2= 159 mmHg
26
Moist Air (IC, IA)
21% of (760- 47 (vapor pressure)) mmHg= PO2= 149 mmHg
27
SVP does NOT depend on what 4 things?
1. SVP does NOT depend on the amount of liquid present as long as there is liquid present
2. SVP does NOT depend on the amount (volume) of vapor present in the vapor phase
3. SVP does NOT depend on surface area
4. SVP does NOT depend on the presence of other gases
28
As surface area increases, what happens to the rate of vaporization?
- Rate of vaporization increases so equilibrium is reached sooner
- but the rate of condensation also increases so the SVP remains the same
29
Each gas exerts the pressure it would as if they were the only gases occupying the volume--- similar to whose law?
Daltons Law: all SVP have to add up to 760 mmHg
30
Boiling Point
-At the boiling point, evaporation occurs throughout the liquid. -Gas molecules within the liquid form bubbles that rise to the surface
31
At the boiling point, the vapor pressure of the liquid equals ________________
Ambient pressure
32
At the boiling point, pressure inside the bubbles that form is sufficient to prevent them from _____________
Collapsing
33
At the boiling point, Temperature does NOT ___________ with added heat
Increase
| Added heat causes change of state (liquid to gas)
34
The boiling point of water at 760 mmHg is ____________
- 100 degrees Celsius
- The vapor pressure of water reaches 760 mmHg (1 atm) at 100 degrees celsius
- At high altitude (Denver) atmospheric pressure is 635 mmHg and water boils at 95 degrees celsius (be careful when cooking food here)
35
At the boiling point of a liquid (3)
1. Evaporation occurs throughout the liquid, not just at the surface
2. Vapor pressure- ambient pressure
3. T does NOT increase when additional heat is added
36
Latent Heat of Vaporization
The amount of heat required to convert 1 gram of liquid into 1 gram of vapor at a given T
-the heat of vaporization requires energy that must be absorbed from the surroundings
37
Hvap H2O at 100 degrees C:
540 cal/gram (boiling) needed to convert from water to vapor
38
Hvap H2O at 37 degrees
576 cal/gram needed to convert water to vapor
39
Hvap H2O at 20 degree C:
585 cal/gram to convert water to vapor
40
Vapor pressure is inversely related to _______________
Boiling point
41
Isoflurane Vapor Pressure at 20 C and boiling point:
1. 238 mmHg
| 2. 48 C
42
Diethyl Ether vapor pressure and boiling point
1. 442 mmHg
| 2. 35 C
43
Desflurane Vapor Pressure at 20 degree C and boiling point:
1. 670 mmHg
2. 23 C
* **** problematic because our OR rooms can get to (73 F)
44
Autoclaves- Sterilization
1. Decreased Atm, water boils at lower temp, food cooks slow
2. Increased pressure, water boils at a higher temp, food cooks faster
3. Autoclaves increase pressure and water boils at a higher temp
4. Under pressure, steam at 100 C has 7X the heat of water at 100 degree C
5. The higher heat steam under pressure kills organisms
45
Gas-Liquid Phase Changes:
| To condense a gas into a liquid (2)
1. Lower the temperature- decreases the vapor pressure and pressure-temperature combination is NOT above the boiling point
2. Increase the ambient pressure- VP is no longer above ambient and P-T combination is below the boiling point
46
Gas-Liquid phase changes:
| To convert a liquid to a gas (2)
1. Increase the temperature- increases the vapor pressure and pressure-temperature combination IS above the boiling point
2. Decrease the ambient pressure- VP is above ambient and P-T combination IS above the boiling point (vaporize)
47
Phase changes:
| As you __________ the temperature, you will take water from solid to liquid to gas
INCREASE
48
Phase Changes:
| By ____________ pressure on water, you can convert a gas to a liquid, or a gas to a solid
INCREASING pressure
49
Gas phase changes:
| As you increase _________, CO2 freezes at a lower temperature because of increased _____________
Pressure, pressure
50
Triple Point
All 3 phases exist in equilibrium: solid, gas, liquid
51
Critical Point
1. Liquid and gas phases cannot be distinguished
2. Temperature is critical Temperature, Pressure is critical pressure
3. Above critical temp, no matter how much pressure is applied, substance will only exist as a GAS. IT CANNOT BE LIQUID
4. Critical pressure is the pressure needed to FORCE a gas into a liquid state at the critical temperature
52
Critical Temp of common gases
1. O2
2. N2O
3. CO2
1. O2= -116 C
2. N2O= 36.5 C
3. CO2= 31 C
53
If the room temp (20 C) is higher than the Tcritical the substance only exists as ____________ form at room temp
Gaseous
54
At room temp, how does oxygen exist?
1. Only a gas at room temp
2. PSIG Oxygen shows amount of gaseous O2 in the tank
3. Full oxygen tank is 2200 PSIG and 625 liters of volume
55
At room temp, how does nitrous oxide exist?
1. Liquid and Gas at room temp. Once liquid is gone from Nitrous tank, we are running on vapor and tank needs to be replaced
2. Nitrous oxide contains liquid and gases N2O so PSIG doesn't tell you much about how much N2O is left in the tank
3. Full tank has 745 PSIG and a volume of 1,590 liters
56
Laminar flow vs Turbulent flow
1. Laminar flow is smooth and efficient
| 2. Turbulent flow is not smooth and less efficient
57
Viscosity
Inherent property of a fluid that resists flow
58
Friction
Resistance to flow from surface interaction and is proportional to fluid viscosity
59
Laminar fluid flow (Hagen-Poiseuille's Law)
Q= pi x r^4 x pressure change/ 8 x N x L
Q=flow
Pi= 3.14159
R=radius
Pressure change
N= fluid viscosity
L= length (tube, vessel, IV cath, ETT, etc)
60
Flow is directly proportion to
The 4th power of the radius
Radius doubles, flow goes up r^4= 2^4= 16 fold increase in flow
22 G IV has inner diameter of .006
18G IV has inner diameter of .017
So the radius of an 18G IV is almost 3X the radius of a 22G IV
Flow through an 18G IV can be 3^4 or 81 X the flow rate of a 22G IV
61
Laminar Flow H-P: beta 2 inhalers
- Flow is directly proportional to the 4th power of the radius
- Beta 2 inhalers bronchodilate and increase the radius of bronchioles to increase the flow
62
Flow is also directly proportional to the pressure gradient:
1. Pressure gradient= inflow pressure-outflow pressure
2. Raising the IV pole higher, creates increased pressure due to gravity= faster fluid flow
3. Use H-P to explain why increased heigh of the IV pole makes the IV run faster
63
H-P: Flow is inversely proportional to the viscosity of the fluid
- Viscosity is the PRIMARY property of a solution that determines when flow is laminar
- a unit of PRBC from the blood bank is very viscous and flow is very slow (that's why we add .9NS to blood before infusing)
64
Eisenmenger's syndrome
- High red blood cell counts which results in viscous blood and poor flow
- these patients have treatment which involves removing fluid and replacing with saline to decrease viscosity of blood
65
Anemic patients
Very thin blood (low viscosity) and flow through small vessels is actually quite fast and more laminar
66
Flow is inversely proportional to the length of the tube (IV or ETT)
1. Short IV catheters actually allow for higher rates of fluid administration than long IV catheters
2. Much easier to pump blood through a 16G IV than a central line
3. Same applies to gas flow through a long ETT
- used to be popular to cut off ETT to allow for increased flow
- actual clinical effect of L is minimal, especially compared to effect of radius
67
Resistance to Flow- Reverse H-P equation
R (resistance)= change in pressure/ flow
For laminar flow R (resistance)= 8 x N x L/ pi x r^4
-note: H-P upside down equation without the pressure change
68
Resistance is inversely proportional to r^4
1. Opposite of flow and for same reasons
| 2. Greater radius allows for less resistance and greater flow
69
Resistance is directly proportional to viscosity
1. Opposite of flow and for same reasons
| 2. Thicker fluids have greater resistance and flows more slowly
70
Resistance is directly proportional to length of tube
1. Opposite of flow for same reasons
| 2. Longer IV catheters provide greater resistance for longer and reduce flows
71
Turbulent Flow
- High velocity causes turbulence
- Rough tubing walls cause turbulence (carotid plaque-thrill/bruit)
- kinks or bends in the tube (tortuous aorta)
- flow through an orfice (narrowed or branching arteries/airways)
72
Turbulence ________ resistance to flow
Increases
- turbulent flow increases resistance to ventilation
- increased resistance to ventilation requires increased pressures (PIPs)
73
Reynold's number (Re) predicts when flow changes from laminar to turbulent
```
Re= V x D x P / N
V= velocity
D= tube diameter
P=fluid density
N= fluid viscosity
-when re 1,500-2,000 flow changes from laminar to turbulent
```
74
What determines flow when flow becomes turbulent?
DENSITY determines flow, not viscosity
75
Reynolds number: example 700 and 3,000
```
700= laminar flow
3,000= turbulent flow
```
76
Helium
1. Has a very low density
2. Heliox is a mixture of helium/oxygen that allows for decent flow of gas when there is a lot of turbulence
3. Upper airway obstruction causes turbulence so we use heliox to ventilate these patients
77
Bernoulli's Principle
1. When flow speeds up, the pressure exerted on the side walls decreases
- pressure through a narrowed vessel decreases (not necessarily a good thing)
- frequently a pressure drop off post vessel wall narrowing
78
Venturi's Effect
When fluid flows through a constriction in a tube, the velocity of the flow increases
79
Coanda Effect
-Past the constriction, fluid tends to follow a curved surface/path upon emerging from that constriction
-Think about blood flow post constriction and branching blood vessels post constriction
How might this reduce blood flow/pressure to a susceptible area? Ischemic areas blood could continue to get shunted away from that area
80
Venti Mask
1. Narrowed opening through which oxygen flows at a given rate
2. Oxygen speeds up as it exits the narrowed opening
3. The reduction in pressure entrains room air and the oxygen is diluted out to VERY specific FiO2
4. Jet vents work the same way- jet of Heliox- entrainment of room air
5. Asthma nebulizers- jet of medicine, flow through narrow airways and entrain air
81
Flicks Law of Diffusion equation
Rate of diffusion= (P1-P2) x Area x Solubility/ membrane thickness X square root of molecular weight
82
Diffusion is directly proportion to: (3)
1. Change in partial pressure
2. Area of membrane over which diffusion takes places (larger surface area=more diffusion, smaller=less)
3. Solubility of the gas in the membrane (very soluble=mores through at a greater extent)
83
Diffusion is inversely related to: (2)
1. Membrane thickness (thicker membranes take long to diffusion through)
2. Square root of molecular weight--- Graham's Law
84
Why does the rate of diffusion decrease over time?
- equilibrium
| - As the gradient (P1-P2) becomes smaller, there's less rate of diffusion.
85
Fick: 2nd gas effect of anesthesia gases
- When large amount of insoluble gas (N2O- low molecular weight) diffuses rapidly from the lungs (large membrane area) into the blood because of the high pressure gradient
86
Fick- diffusion hypoxia
- N2O rushes out of the blood and into the lungs and reduces the concentration of oxygen in the lungs
- FiO2 then drops below 21% if oxygen flow rates are not increased to compensate
87
FIck- Increased pneumothorax, pneumocephalus, or bowel gas
- N2O is 31 X more soluble in the blood than in nitrogen (this is why it moves so fast)
- as blood flows by the gas pocket, it has lots of N2O which freely moves in because there is a concentration gradient (P1-P2)
- N2 is much less soluble and does not move into blood as rapidly
- Net result, N2O diffuses into closed air spaces more rapidly than N2 diffuses out, and the air space either expands or pressure increases until it pops
- If you have N2O running and turn it off- it could reduce size of gas space
88
Fick- rate of diffusion ___________ as the square root of the distance increases
1. Rate of diffusion decreases
| 2. Diffusion down a nerve sheath takes time
89
Flicks- Concentration ___________as the square of the distance increases
- decreases
- as you get farther down the nerve sheath, the concentration of medicine around the nerve decreases
- Think in 3-D: when you inject medicine in a given spot and need diffusion outward from that spot (into a nerve sheath) it will take time
90
Gas Diffusion Pearls
- As long as there is a concentration gradient there will be a diffusion of substance (gas or liquid)
- When there is not pressure gradient, diffusion stops and equilibrium is reached (this is very rare, especially for anesthetic gases
- Diffusion of our anesthetic gases from lungs to blood (induction) or for blood to lungs (emergence) requires a concentration gradient
91
Is CO2 or O2 diffusion faster across alveolar-capillary membrane?
- CO2 is more soluble in fluid than O2
| - there is also a large pressure gradient between blood and alveoli
92
Adiabatic Compression
- Adiabatic means NO transfer of heat or matter between the system and its surroundings
- typically because process is so fast there is no time for heat exchange
93
When a cylinder of compressed gas (O2) is opened into a closed space (anesthesia machine piping) what happens?
1. Pressure within pipes increases rapidly
2. When pressure increases that rapidly, temp increases
3. Increases happen so fast that there is no time to dissipate the pressure of heat (adiabatic)
4. A fire could ignite or explosion could occur
94
Joule-Thomson Effect=adiabatic expansion
- when a compressed gas (under pressure) is released rapidly into a space (room) cooling occurs
- gases warm (temperature of gas increases when they are compressed
- there is NO loss of heat or matter between the cylinder and the surroundings so the process is called adiabatic
- this is why oxygen released from a O2 tank at high flow is very cold (regulators can ice up or freeze)
- Let air out of bike tires rapidly=cold
95
When N2O is released from N2O cylinder what happens?
1. Liquid N2O converts to gaseous N2O
2. When liquid converts to gas, latent heat of vaporization causes a heat less and the tank cools on the outside
3. As the cylinder cools, what happens to gauge pressure?
(As temp cools, pressure decreases=Gay-Lussascs Law)
96
Heat Loss by the body:
1. Radiation
2. Convection
3. Evaporation
4. Conduction
1. Radiation= 40-60% heat loss, radiating out of patients
2. Convection= 15-30% heat loss, (2% from heating cold dry gas in lungs) air flowing over the body
3. Evaporation= 20-25% heat loss (8% from respiratory evaporation)
4. Conduction= <5% heat lost (depends on surface contact on OR table and temp or table when contacted)
- MOST heat loss normally comes from radiation (COVER the patient)
- Volatile anesthetic cause vasodilation which increases blood flow to skin and increase radiant heat loss******
97
Fluid definition
-Any material that has the ability to flow when acted up by outside forces
-Has no fixed shape and conforms to the shape of its container
-Liquid- resist compression
Gas- easily compressible and expandable*
98
Hydrodynamics
- study of fluids in motion
99
Hydrostatic
Study of fluids that are NOT moving
100
Adhesion
- Force of attraction between different types of molecules
- Adhesive forces draw water inside of thin tubes
- Causes capillary action
- water has concave adhesion on glass (Ruth's Notes)
- mercury is convex (Ruth's Notes)
101
Cohesion
- force of attraction between the same molecules
| - causes surface tension (beads up instead of spreading out)
102
Surface Tension
-elastic tendency of a fluid surface which makes it acquire the least surface area possible
-the force required to increase the surface area of a fluid in dynes/cm
-surface molecules align and can act as skin
(Bugs walking on water)
103
Surface Tension of Alveolar Fluid
- surface tension of alveolar fluid (water) creates a polar force that promotes alveolar collapse
- water molecules are very polar
- surfactant keeps alveoli from collapsing
104
Surfactant
- lipoprotein complex (phospholipoprotein) formed by type II alveolar cells (helps hold alveoli open, helps compliance in lungs. Not only keep them from collapsing but helps them open easier)
- proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region
- the hydrophilic end attaches to the water and hydrophobic end pull away from the water, breaking up the surface tension (skin)
105
Law of LaPlace
T= P x R (cylinder)
T= P x R/ 2 (sphere)
Relationship between wall tension, pressure and radius
-wall tension is proportional to the radius (If P is constant)
-pressure is inversely proportional to radius is T is constant
-the larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure
-in spheres, the Tension is increased twice as much with increasing radius as compared to cylinder (2T=P X R)
-thicker walls have less tension
106
Surfactant stabilizes alevoli- how?
1. Surfactant decreases the pressure in the alveoli by decreasing wall (surface) tension
2. Without surfactant, pressure would be greater in the smaller alveoli
3. Surfactant lowers surface tension more in smaller alveoli
107
Critical Closing Pressure or Volume
- in very small vessels or alveoli, wall tension is low collapsing force of external pressure may be greater than distending force
- if critical closing pressure (or volume) is reached, vessel or alveoli may collapse (now tends to occur at end of expiration)
108
PEEP
- positive end expiratory pressure
- application of pressure above atmospheric throughout expiration
- recruit alveoli and keep vulnerable ones from collapsing
- especially important in neonate and children who have immature alveoli or surfactant production
109
Transmural Pressue
-pressure from the inside acts to expand or increase vessel or airway diameter
-external pressure acts from outside to try and collapse the vessel or alveoli
Equation: internal pressure minus external pressure (or the net pressure across the walls of the vessel)
110
LaPlace and Wall Thickness
- equation: T= P x R / Wall thickness (cylinder)
OR T= P x R / 2 x wall thickness (sphere)
-as a consequence of flow through a tube and the transmural pressure, tension is generated in the walls of the tube
-wall tension or stress is inversely related to wall thickness
-the thicker the wall, the less stress the alveoli or vessel will be under
111
What happens when vessels balloon out?
- Aneurysm
- radius is increased so wall tension is increased
- wall thickness is decreased with increases wall tension
- internal pressure is reduced which also increases transmural pressure
112
Ohm's Law and Hagen-Poiseuille's Law
HP is analogous to Ohm's Law describing electrical current as I= V / R (flow is current and pressure is voltage)
-Flow is directly related to the pressure drop across the system and inversely related to resistant
113
Velocity
- distance the fluid travels with respect to time
| - in blood, often referred to as cm/sec
114
Flow rate
- volume of fluid that is moving per unit of time
- in blood, often referred to as ml/min which is equivilant to cardiac output ( flow rate is often referred to as Q)
Flow= pressure/ resistance
115
Flow of blood in a vessel is related to velocity by the following equation?
Flow= mean velocity X cross sectional area ( pi x r^2)
Or
Flow= v X r ^2
116
Why is laminar flow better than turbulent?
- laminar flow is more efficient: uses less energy so fluid can travel faster and which leads to more output
- important when considering the work of breathing
117
Laminar flow and viscosity
- flow is greatest in the center and approaches zero near the outer edges
- in laminar flow, the velocity different between lawyers depends on th ease with which the layers slide on one another, or the VISCOSITY of the fluid
118
Viscosity
- the measure of the internal friction of a moving fluid (thickness)
- flow rate is inversely related to viscosity (more viscous the less flow)
- viscosity of a liquid increases as the temperature is decreased
- viscosity of a gas increases as the temperature is increased (particles bounce around more all directions, layers don't slide as easily)
119
2 factors affecting viscosity:
1. Hematocrit
2. Coagulation status
(As both increase, viscosity increases, which decreases flow)
120
Length and diameter affecting flow?
- shorter tubing will produce proportionally larger flow rates
- example: adding 6 inches to your 12 foot IV tubing will decrease your flor rate by 1/2 if you keep the pressure the same
- Flow is directly proportional to the 4th power of the radius of the tube
- example: changing from 3 ETT to size 6 ETT (flow would increase by a 16 fold)
121
Flow past constrictions
- blood flow that goes in must equal the blood flow that goes out
- the velocity must increase where the diameter is smaller
- if the pressure is not high enough to increase velocity, flow will be reduced
122
Critical Velocity
- is the velocity above which flow changes from laminar to turbulent
- reynolds number is an index that is used to predict when flow becomes turbulent (density is now important)
- flow turns turbulent when reynolds number is above 2000
123
Turbulent flow is increased with: (4)
1. High velocity
2. High density
3. Large tube diameters
4. Low viscosity
124
Critical FLOW rate
- at flow rates below critical flow rate, laminar flow is replaced by turbulent flow
- turbulent flow is promoted by:
1. Low viscosity
2. Small tube diameter
3. High density
125
Variable Orifice Flow Meters
- depending on the bob shape and density, the tube shape and fluid density and viscosity, the flow rate is linearly proportional to the height of the bob in the tube
- each is calibrated for the gas it is measuring
126
Where do you read flow meters at?
1. Circle bobber: read in the middle
| 2. All of the other shaped bobbers, read at the top or the thickest part of the bobber
127
Flow meter sequence: where is oxygen in the circuit?
1. Oxygen is always on the outlet side (closer to it), decreases chance of losing oxygen in the circuit
128
Bernoulli's principle
- as flow passes through a narrowing in a tube, the velocity of that flow increases and there is a corresponding decrease in the pressure at the area of narrowing
- drop in pressure is explained by the conversation of energy law
