Exam Three Flashcards
Gas
- No definite shape or volume; conforms to container; fills container; flows; is easily compressible
- Gases that don’t 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
Liquids
- 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
Meyer-Overton Hypothesis
The potency of a compound to induce general anesthesia is directly related to the compounds lipid solubility.
Suggests that onset of anesthesia occurs when sufficient molecules of the anesthetic agent have dissolved in the cell’s lipid membranes, resulting in anesthesia.
Low Solubility Agents
- Higher MAC to produce anesthesia (Desflurance MAC = 6%; N 2 O MAC = 105%)
- Rapid onset and rapid recovery
Higher Solubility Agents
- Lower MAC to produce anesthesia (Halothane MAC 0.74%; Methoxyflurane MAC 0.15%)
- Slower onset and rapid recovery
Solubility of Anesthetic Agents
Iso - 1%, 1:4
Sevo - 2%, 0.69
Des - 6%, 0.42
Nitrous - 105%, 0.47
Saturated Vapor Pressure
- The pressure in the vapor phase when it is in equilibrium with its liquid phase
- The SVP of a substance (anesthetic agent) at a specified Temp is the partial pressure of the substance in the vapor phase that is in equilibrium with its liquid (or solid) phase.
SVP for a given substance depends ONLY on _______
Temperature.
At a higher Temp, more molecules will be present in the gas phase at equilibrium and the vapor pressure and SVP will BOTH be higher.
The SVP does or SVP is a characteristic of the substance.
SVP is a characteristic of the substance. The SVP does NOT change in different environments (atm pressures or temperatures)
ie: When you raise the temp, more will vaporize but the SVP stays the same
SVP of water is a function of ________
temperature.
As the temperature increases, more water is in the vapor form (humidity)
Relative Humidity
= amount of water vapor in the air compared to the amount the air could hold (SVP) at that T.
- Summer humidity higher = lots of moisture in the air
- Winter humidity lower = drier air
SVP effects on anesthesia
RA =
Larynx =
Bonchi =
RA 10 mmHg
larynx 26-32 mm Hg bronchi 47 mmHg
SVP does NOT depend on _______
- the amount of liquid present as long as there is liquid present.
- the amount (volume) of vapor present in the vapor phase.
- surface area
- the presence of other gases
Boiling Point
- Evaporation occurs throughout the liquid (not just @ surface).
- Vapor pressure = ambient pressure
- Temperature does NOT increase with added heat
• The boiling point of water at 760 mmHg (1atm) is 100 C
Latent Heat of Vaporization
• The amount of heat required to convert 1 gram of liquid into 1 gram of vapor at a given T
Vapor pressure is inversely related to ______
Boiling Point.
ie: VP des 670, BP 23
VP iso 238, BP 48
VP sevo 157, BP 56
Autoclaves
- Autoclaves increase pressure and water boils at higher temps
- Under pressure, steam at 100 C has 7X the heat of water at 100 C
Decrease pressure = water boils @ lower temp
Increase pressure = water boils @ higher temp
To condense a gas into a liquid
Lower the temp & increase the ambient pressure
To convert a liquid to a gas
Increase the temp and decrease the ambient pressure
Critical Temp of Common Gases
O2 = -116C N2) = 36.5 C Co2 = 31 C
Laminar Flow vs Turbulent Flow
Laminar flow is smooth and efficient. Turbulent flow is not smooth and less efficient.
Viscosity
is an inherent property of a fluid that resists flow
Friction
is resistance to flow from surface interaction and is proportional to fluid viscosity
Laminar fluid flow (Hagen-Poiseuille’s Law)
• Q = 𝜋𝑟^4 ∆P/8nL
• Q = flow 𝜋 = 3.14159265358979, r=radius ∆P = pressure gradient (change) n=fluid viscosity L=length (of tube/vessel/IV catheter/ETT/etc)
Flow is directly proportional to ______
the 4th power of the radius.
• Radius doubles, flow goes up r 4 = 2 4 = 16-fold increase in flow.
- 22g IV has inner diameter 0.012”(r=0.006)
- 18g IV is 0.033” (r=0.017)
Flow is also directly proportional to ______
the pressure gradient (∆P)
- ∆P = inflow pressure – outflow pressure
- Raising the IV pole higher, creates increased pressure due to gravity = faster fluid flow**
Flow is inversely proportional to _____
the viscosity of the fluid.
- Viscosity is the primary property of a solution that determines when flow is laminar
- PRBCs from the blood bank is very viscous and flow is very slow
Flow is also inversely related to ______
the length of the tube (IV or ETT)
Short IV catheters actually allow for higher rates of fluid administration than do longer IV catheters
Resistance to flow (reverse H-P)
- R (resistance) = ∆P/Q • For laminar flow R = 8nL/𝜋𝑟^4
* NOTE: H-P upside down without the ∆P term
Resistance is inversely proportional to ______.
- Resistance is inversely proportional to r^4
* Greater radius allows for less resistance and greater flow
Resistance is directly proportional to ______.
viscoscity & length of tube
Turbulent Flow Causes
high velocity, rough tubing walls, kinks/bends, flow through an orifice
Turbulence ______ resistance to flow
Increases
- Turbulent flow increases resistance to ventilation
- Increased resistance to ventilation requires increased pressure (PIPs)
Reynolds Number
predicts when flow changes from laminar to turbulent
700 = laminar 3000 = turbulent
What determines flow when flow becomes turbulent?
When flow becomes turbulent, density, NOT viscosity, determines flow.
Bernoulli’s Principle
- When flow speeds up, the pressure exerted on the side walls decreases
- Frequently a pressure drop off post vessel wall narrowing
- As flow passes through a narrowing in a tube, the velocity of that flow increases and there is a corresponding decrease in pressure at the area of narrowing.
Venturi’s Effect
When fluid flows through a constriction in a tube, the velocity of the flow increases
Coanda Effect
Past the constriction, fluid tends to follow a curved surface/path upon emerging from that constriction
Fick’s Law of Diffusion
(P 1 – P 2 ) * (Area) * (Solubility)/
(membrane thickness)* sqrtMW
Diffusion is directly proportional to _______
- Change in partial pressure (P 1 – P 2 ), or, ∆P
- Area of the membrane over which diffusion is taking place
- Solubility of the gas in the membrane
Diffusion is inversely related to _______
- Membrane thickness
* The square root of the molecular weight (graham’s law)
Why does the rate of diffusion decrease over time?
Equilibrium - pressure difference (p1-p2) gets narrower and narrower that’s why rate of diffusion changes over time
Diffusion Hypoxia
N2O rushes out of the blood and into the lungs and reduces the concentration of oxygen in the lungs. The FiO 2 can drop below 21% if you don’t increase oxygen flow rates to compensate
Adiabatic Compression
Adiabatic means no transfer of heat or matter between the system and its surroundings
Joule-Thomson Effect (adiabatic expansion)
• When a compressed gas (under pressure) is released rapidly into space (a room), cooling occurs
• There is no loss of heat or matter between the cylinder and the surroundings so the process is called adiabatic
“Joule is Cool”
Heat Loss - Radiation
40-60% heat lost
Heat Loss - Convection
15-30% heat lost (2% from heating cold dry gas in lungs)
Heat Loss - Evaporation
20-25% heat lost (8% from respiratory evaporation)
Heat Loss - Conduction
<5% heat lost (depends on surface contact w OR table & temp of table)
From which source does the MOST heat loss occcur?
- MOST heat loss normally comes from radiation (COVER the patient)
- Volatile anesthetics cause vasodilation which increases blood flow to the skin and increases radiant heat loss!!!
Adhesion
Force of attraction between different types of molecules (causes capillary action)
Cohesion
Force of attraction between the same molecules (causes surface tension)
Surface Tension
The elastic tendency of a fluid surface which makes it acquire the least surface area possible.
Surface Tension of Alveolar Fluid
alveolar fluid (water) creates a polar force that promotes alveolar collapse.
Surfactant
decreases the pressure in the alveoli by decreasing wall (surface) tension.
Law of LaPlace
- Wall tension is proporIonal to the radius (if P is constant)
- Pressure is inversely proporIonal to radius (if T is constant)
Increased radius = increased wall tension
Law of LaPlace Cylinders
T=PR
Law of LaPlace Spheres
T=PR/2
or
2T=PR
Critical Closing Pressure
in very small vessels or alveoli, wall tension is low & collapsing force of external pressure may be greater than distending force.
If CCP is reached, alveoli may collapse
PEEP
Recruit alveoli and keep vulnerable ones from collapsing.
** especially important in neonates
Transmural Pressure
• Pressure from the inside acts to expand or increase vessel or airway diameter
• External pressure acts from the outside to try and collapse the vessel or alveoli.
TP = P internal - P external
Velocity
distance fluid travels over time (cm/sec)
Flow Rate
volume of fluid moving over time (mL/min)
Viscosity
- Measure of the internal friction of a moving fluid (thickness) • Flow rate is inversely related to viscosity (the more viscous the less flow)
- Viscosity of a liquid increases as the temperature is decreased
- The viscosity of a gas increases as the temperature is increased (particles bounce around more all directions, layers don’t slide as easily)
Flow Past Constrictions
- Flow in = flow out
- Velocity must increase @ smallest diameter
- If pressure can’t increase velocity, flow is reduced
Critical Velocity
velocity above which flow changes from laminar to turbulent.
Turbulent flow is increased with _____
- high velocity
- high density
- large tube diameters • low viscosity.
