Physics for the Nurse Anesthetist~Quiz 3 Flashcards Preview

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Flashcards in Physics for the Nurse Anesthetist~Quiz 3 Deck (65):

What is solubility?

Solubility the maximum amount of one substance(solute) that is able to dissolve into another(solvent).


What are three factors that may affect the solubility of solutes in solvents.

The intermolecular interactions between substances, temperature and pressure.

*pressure exhorts little to no influence on solubility of solids and liquids. But GAS solubility in a liquid is directly proportional to pressure.


What does the phrase "like dissolves like", mean?

Solubility is enhanced by intermolecular interactions between substances that have similar electron configurations. For example, H2O and salts(NaCL) have similar polarity.


What is the difference between endothermic versus exothermic reactions?

Define endothermic reactions!

Endothermic(into)- consumes heat rather produces heat, with endothermic reactions, solubility is increased with increased temperature. Energy is required to break the chemical bonds of substances that are dissolving. Most often this is an endothermic reactions which means it requires more energy than it produces.


What is the difference between endothermic versus exothermic reactions?

Define exothermic reactions!

Exothermic(out)- Occasionally the process may be exothermic, meaning energy is released in excess of the energy required to break the bonds of the solute.


How is gas solubility in gases altered by temperature?

-Gas solubility in liquids is inversely related to temperature.
-as temperature increases, less gas is able to dissolve into the liquid.
-Lower temperature slows the kinetic energy of gas molecules, allowing them to dissolve into liquids.


What is a clinical example of temp affecting solubility?

The slower emergence of a hypothermic patient receiving general anesthesia. The hypothermic patient retains anesthetic gases in the blood due to increased solubility related to temperature.


What is Henry's Law?

At a constant temperature, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas at equilibrium above the gas-liquid interface.


What happens to the amount of salt that dissolves in whiter with increasing temperature? What happens to the amount of gas that dissolves in liquid with increasing temperature? What principle applies?

-The solubility of a salt increase with increasing temperature. More salt dissolves in water when temperature increases.
-The solubility of a gas decreases with increasing temperature.
-Less gas dissolves in water when temperature increase.
-LeCatelier's principle applies to both situations.


If you heat a solvent, what happens to the solubility of a non-gaseous solute such as sodium chloride?

The solubility of a non-gaseous solute increases when the liquid is heated.


What effect does hypothermia have on gas solubility?

As a liquid is cooled, more gas dissolves in the liquid; therefore, hypothermia will cause an increase in gas solubility.


Is the blood solubility and the tissue solubility of an inhaled volatile agent increased or decreased in the hypothermic patient?

-the amount of gas that dissolves in solution is inversely proportional to temperature.
-the lower the temperature, the greater the amount of gas dissolved in solution.
-in the hypothermic patient, therefore, the solubility of an inhaled volatile agent in blood and in tissue increased.


What is the Ostwald Solubility Coefficient?

The higher the blood gas partition coefficient(also called Ostwald Solubility Coefficient), the longer it takes to induce anesthesia and the longer it takes to emerge from anesthesia.

For example: Desflurane at 0.42, is the quickest on and the quickest off while Isoflurane at 1.4 is the slowest on and the slowest off


What are the anesthetic Blood Gas Coefficients for Des, N2O, Sevo and Iso?

Anesthetic Blood/Gas Partition Coefficient
DES 0.42
N2O 0.47
SEVO 0.6
ISO 1.4


The agent follows what series of partial pressure gradients to reach its target the brain?

delivered--->inspired--->alveolar--->arterial--->brain & tissue


The Ostwald solubility coefficient is a measure of what?

It is a measure of the solubility of a gas in a fluid.


What is the definition of the Ostwald solubility coefficient? What is the significance of the Ostwald solubility coefficient in anesthesia?

-the Ostwald solubility coefficient is defined as the ratio of the concentration of gas dissolved in solution to the concentration of gas in the gas phase at equilibrium at 37 degrees.
-Blood-gas partition coefficient for inhalational anesthetics are derived from Ostwald solubilities.


What is the formula associated with Henry's Law?

p = k * c

Where p is the partial pressure of the solute above the solution, k is Henry's constant, and c is the concentration of the solute in the solution.


As stated by Henry's law, what will happen to the solubility of gas as the partial pressure of a gas increases?

Increasing the partial pressure of a gas above a liquid will increase the amount of gas that dissolves in the liquid.


What are two clinical examples that reflect the direct relationship of pressure and solubility described by Henry's Law?

1. Increasing delivery of oxygen to patients to increase arterial oxygenation
2. and over pressuring(high concentration) of anesthetics to increase the end tidal of the volatile agent upon induction


Describe what "Overpressuring" is referring.

It is the process of significantly increasing a volatile anesthetic concentration(partial pressure) delivered to a patient to increase the alveolar concentration, and therefore the amount dissolved in the blood, to speed uptake.


What is the solubility coefficient of O2 and of Co2 that is related to Henry's Law?

O2=0.003 ml/100 ml blood/mmHg of Ox
C)2=0.067 ml/100 ml blood/mmHg of CO2


What is Henry's Law?

Henry's law states that the amount of gas that will dissolve in solution is proportional to the partial pressure of the gas in contact with the solution.


Henry's Law is used for what two purposes?

Henry's Law is used to calculate:
1. the amount of oxygen dissolved in blood(O2 dissolved= PO2 X 0.003
2. the amount of carbon dioxide dissolved in blood(CO2 dissolved = 0.067 X PCO2)


If the oxygen partial pressure in arterial blood increases from 50 mmHg to 350 mmHg, the amount of dissolved oxygen increases by how much?

at 50 mmHg(X 0.003)--->0.15 ml O2/100 ml blood
at 350 mmHg(X 0.003)--->1.05 ml O2/100 ml blood
The increase in dissolved O2 is 1.05 - 0.15 = 0.90 ml O2/100 ml blood


How much O2 is dissolved in arterial blood when the PaO2 is 300 mmHg?

0.9 ml O2 are dissolved in 100 ml blood


How much does dissolved O2 increase in blood when PaO2 increases from 100 mmHg to 500 mmHg?

1.2 ml O2/100 ml blood


How much O2 is dissolved if the FiO2 is 40%?

if the inspired O2 is given, estimate the PaO2 by multiplying the inspired concentration by 5.

so the answer would be 200 mmHg X 0.003 = 0.6 ml O2/100 ml blood


How much CO2 is dissolved in blood when the CO2 is 59 mmHg?

3.35 ml CO2 are dissolved per 100 ml blood


What is diffusion?

 Diffusion is the process of net movement of one type of
molecule through space as a result of random motion
intended to minimize a concentration gradient.
 Kinetic energy allows molecules to move freely in a fluid,
and therefore mixtures of fluids tend to evenly distribute
 Molecules with smaller mass will diffuse faster


What does Graham's law state?

Graham's law states that a gas diffuses at a rate that is inversely proportional to the square root of its molecular weight

r=1 divided by the square root of mw

(r=rate of diffusion, mw=molecular weight)


Give an example of Graham's Law

Helium will diffuse faster than oxygen, which will diffuse faster than nitrous oxide


Permeable vs. Semi‐permeable Membrane:

-Permeable membrane generally allows uniform distribution of all molecules

-Semi‐permeable or selectively permeable membrane like a cell membrane allows some molecules to pass through but not others.


What is osmosis?

 Osmosis is the movement of water across a semipermeable membrane to equilibrate a concentration
 Semi‐permeable membranes are permeable to water only and not to solute.


Osmotic and Oncotic Pressure

 Osmotic pressure is a force needed to stop osmosis from occurring.
 Oncotic pressure is the osmotic pressure caused by
plasma proteins and electrolytes in capillaries.
 Oncotic pressure balances the hydrostatic pressure
tendency to push water out of the capillaries.
 Our vascular system is a semipermeable membrane that
responds to intravascular delivery of colloids by
sequestering fluid


What is the normal oncotic pressure?

approximately 28 mmHg


Of albumin and the electrolytes Na, CL, K and Phos...which exerts oncotic pressure and which can cross a semipermable membrane?

electrolytes such as Na, CL, ext are small solutes and do not exert an osmotic effect, These ions do not penetrate lipid bylayers but diffuse via channels.

Albumin is a substance that does not penetrate the capillary walls and provides the osmotic pressure of blood.


Explain Diffusion in Anesthesia

 Diffusion is a passive process.
 N2O diffuses into air‐filled cavities; therefore, the
delivery of N2O is contraindicated in patients with
pneumothorax or where air‐filled cavity expansion
is undesirable.
 N2O‐expansion of ETT cuffs may cause tracheal
mucosal damage.


What do we learn from Fick's Law?

Fick’s law for diffusion of a gas across a tissue plane is an
encompassing law that accounts for
 Partial pressure gradient (P1‐ P2 = ΔP)
 Membrane area
 Solubility of gas in membrane
 Membrane thickness
 Square root of the molecular weight

Diffusion rate=(P1-P2)X(Area)X(Solubility) divided by (Membrane thickness) X (square root of MW)

*just recognize formula*


What are three applications of Fick's Law?

1. Concentration effect
2. Second gas effect
3. Diffusion hypoxia


What is the Concentration effect?

The higher the concentration of anesthetic agent delivered, the faster anesthesia is achieved. This is also referred to as overpressuring. As with any drug, the larger the initial dose administered, the faster the onset of action.


What is the Second gas effect?

The second gas effect is a phenomenon in which two anesthetics of varying onset speeds are administered together. A high concentration of a fast anesthetic (N2O) is administered with a slower anesthetic gas. The slower gas achieves anesthetic levels more quickly than if it had been given alone.


What are the consequences of differences in blood solubility between N2O and N2?

BGP: N2 = 0.014 N2O = 0.470
N2O is 34 times more blood soluble than N2
Compared with N2O, the carrying capacity of the blood for N2 is very poor.
Because of this difference, gas spaces change pressure or volume when N2O is turned on and off.
According to Fick's law of diffusion, the rate of diffusion of a gas into or out of blood is proportional to its blood solubility.
Hence, N2O diffuses in greater amounts(34 times greater) into or out of blood than N2


Explain the Concentration Effect as related to N2 and N2O.

-With the patient breathing room air, atmospheric N2 is
equilibrated with body N2 (the amount of N2 entering
the blood from the alveoli equals the amount of N2
entering the alveoli from the blood.)

-When N2O is turned on, N2O diffuses into the
blood in much greater quantities than N2 leaves
the blood because N2O is much more blood‐soluble
(34x) than N2.

-Because N2O leaves the alveoli, the alveoli shrink in
size so the alveolar concentration of N2O remains

-The sustained high N2O concentration in the alveoli
permits a more rapid uptake of N2O by the blood (the
diffusion gradient remains elevated).


Explain the Concentration and Second Gas Effects as related to Isoflurane and N2O.

-Before administering inhalation agents, N2 is in equilibrium. When N2O and ISO is turned on
simultaneously, N2O diffuses into the blood from the alveoli in much greater amounts than N2 diffuses
from the blood into the alveoli (N2O is 34x more soluble in blood than is N2).

-Consequently, because N2O is diffusing out of the alveoli at a greater rate than N2 is diffusing into the alveoli, the alveoli “shrink”. The concentration of both the
second gas (ISO) and N2O remain elevated.

-Because concentration of the second gas (ISO) is sustained, the rate of diffusion of the second gas (ISO) remains elevated. The uptake of a volatile agent
is increased when it is administered simultaneously
with N2O. This is the second gas effect, which is explained by Fick’s law of diffusion.


What is Diffusion Hypoxia?

When N2O is turned on, the quantity of N2O diffusing
from alveoli to blood vastly exceeds the amount of N2
diffusing from the blood to alveoli (compared with N2O,
the blood carries much less N2).
 When N2O is turned off, the quantity of N2O diffusing
from blood to alveoli is much greater than the amount of
N2 diffusing from the alveoli to blood; the blood has
limited capacity to hold N2 (poor solubility).
 Alveoli expand and gases such as CO2 and O2 are diluted.
 If the patient was breathing room at this time, the O2
partial pressure would fall to levels that cause temporary
 This phenomenon is called dilutional hypoxia or diffusion
hypoxia and is explained by Fick’s law of diffusion.
 Administration of 100% oxygen for several minutes when
anesthesia is terminated entirely avoids this potential


Which diffuses faster, CO2 or O2?

Even though CO2 is larger than O2, CO2 diffuses 20 times faster across the alveolar and capillary membranes than O2, because it is much more (about 20 x more) soluble in fluid than O2


When does equilibrium occur in the body?

Equilibrium of an inhalational agent (or any other gas)
occurs in the body when the partial pressure of the gas is
the same everywhere.


How does a fetus receive oxygen and medicine across the palcenta?

simple diffusion


What is required for a gas to diffuse from alveoli to blood?

a partial pressure gradient


What 4 main factors determine diffusion rates across membranes for gases?

1. Concentration Gradient(non-ionized substances)
2. Electrochemical gradient(for ions)
3. lipid solubility
4. size


What are the agents that poorly penetrate the blood-brain barrier or placental barrier?

Lipid-insoluble(such as ionized substances) and/or large molecules(with high molecular weight)


What molecules do not penetrate the lipid bilayers?

ions for example Na


According to Fick's law of diffusion the rate of diffusion is directly proportional to what three factors?

1. partial pressure difference of the gas across the membrane.
2. the area of the membrane
3. the solubility of the gas in the membrane


According to Fick's law, the amount of gas diffusing is indirectly proportional to(2)?

1. the thickness of the membrane
2. the square root of the molecular weight of the gas.


When N2O is turned on, air bubbles expand. Whose law applies and why?

Ficks law of diffusion
Diffusion if proportional to solubility
Fick's law states, in part, more soluble gases diffuse in greater quantities.
N2O is 34 times more soluble in blood than N2.
the quantity of N2O diffusing out of the blood into the bubble is greater than the quantity of N2 diffusing from the bubble into the blood.


What inhalational anesthetic would you avoid if a patient had a permanent pacemaker implanted a day or two before surgery.

Avoid N2O, a small amount of air remains in the pre pectoral pacemaker pocket. When N2O turned on this gas expands which can lead to loss of function.
Ficks Laws applies


Identify the two laws that apply to diffusion of N2O and other gases.

1. Ficks law of diffusion
2. Grahams law


Gases diffuse down a partial pressure gradient across tissues such as the alveolar-capillary membrane. What law explains this?

Ficks Law of diffusion


Gases that are more blood soluble will diffuse across a liquid/gas interface such as the alveolar capillary membrane in greater or lesser quantities than a less soluble gas? What law applies?

Gases that are more blood soluble diffuse in greater quantities across liquid/gas interfaces, as described by Fick's law of diffusion


What law explains diffusion hypoxia?

Fick's law of diffusion


Whose law applies to the diffusion of gases between a gas phase and a liquid phase?

Fick's law of diffusion


What happens to the volume of the cuff of the ETT when N2O is turned on? Explain this phenomenon? Whose law applies?

The cuff will expand because more N2O will diffuse into the cuff from the surface of the trachea.
Fick's law applies


What law explains the Concentration effect, second gas effect and diffusion hypoxia?

Ficks law of diffusion because N2O is more blood-soluble than N2.
According to Fick's law for gases, the gas that is more blood-soluble diffuses in greater quantities from alveoli to blood and from blood to alveoli


Describe the second gas effect.

When one gas delivered at a high inspired concentration accelerates the blood uptake of a concurrently administered companion gas.

This is explained by Fick's law of diffusion