Chem Phys Math Review Flashcards
Molecular Theory of Matter states
states that matter is made of minute particles called molecules, that exist in various states (solid, liquid, gas, or plasma).
Kinetic Theory of Matter states
states that molecules are in constant motion (random motion) and have a degree of attraction between them called van der waals forces.
Critical Temperature is
the temp. above which a gas cannot be liquefied regardless of how much pressure is applied
What are the basics of Chemistry
Atoms: building block
Protons, neutrons, electrons
# Protons= Atomic #
Outermost shell electrons: valence electrons
Electrons (-) attracted to nucleus (+) to maintain orbital shell
Incomplete shells allow atoms to react with one another
Full shell: non-reactive
What are ION’s
- atoms carrying positive or negative charge
Positive charge= cations- lost electrons
Negative charge= anions- gained electrons
Types of bonds:
- ionic
- covalent
- polar covalent
H2O= polar covalent
Property that makes H2O a good solvent for other polar substances but not for non-polar substances (like oils)
Gas solubility in liquids:
Is inversely related to temperature
Clinical example: hypothermic patients receiving volatile agent general anesthetics
**Slower wake up
What is the relationship between gas and temperature?
As temperature increases, less gas is able to dissolve into a liquid. An increased temperature represents greater kinetic energy. Greater kinetic energy allows dissolved gas molecules to escape and prevents further dissolving. Lower temperature slows the kinetic energy of gas molecules, allowing them to dissolve into liquids.
Gas solubility in a liquid
is directly proportional to pressure
Henry’s Law
At constant temperature:
The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in contact with the solution.
How is Henry’s Law applied?
Allows calculation of O2 and CO2 dissolved in blood:
Need to know solubility coefficient:
O2= .003ml/100ml blood/mmHg partial pressure
CO2= .067 ml/100ml blood/mmHg partial pressure
For example:
ABG: pH 7.44, PaO2 600mmHg, PaCO2 35mmHg, HCO3 25
How much O2 and CO2 is dissolved in blood?
What are some examples of Henry’s Law being applied.
- Increasing FiO2 is an application of Henry’s law
- Over pressuring the vaporizer is another example (we increase the concentration set on the vaporizer to speed up delivery to the blood and, therefore, the brain)
Calculate O2 Delivery
DO2 = CO x [(1.34 x hgb x SpO2) + (PaO2 x 0.003)]x 10
Temperature affects solubility
Increased temp= decreased solubility
Decreased temp= increased solubility
What is Graham’s Law
A gas diffuses at a rate that is inversely proportional to the square root of its molecular weight
Thus as molecular weight ↑ the rate of diffusion ↓
Faster diffusion of smaller molecules
what happens with anesthetic emergence in a hypothermic patient??
hypothermia can prolong emergence
Diffusion of nitrous oxide in Anesthesia examples?
Nitrous oxide diffuses into air-filled cavities
- Contraindicated in patients with pneumothorax or where air-filled cavity expansion is undesirable
- Nitrous oxide expansion of endotracheal cuffs may cause tracheal mucosal damage
- Distention of the bowel during nitrous oxide delivery has also been documented
What is Apneic oxygenation:
continual diffusion of oxygen into the blood is driven by a concentration gradient that continually diffuses oxygen into the alveoli via the ventilator circuit
Explain Fick’s Law for diffusion of gas
Fick’s law for diffusion of a gas across a tissue plane is an encompassing law that accounts for molecular weight, concentration gradient, solubility, and membrane interactions.
Fick’s law states that diffusion of a gas across a semipermeable membrane is directly proportional to the partial pressure gradient, the membrane solubility of the gas, and the membrane area, and is inversely proportional to the membrane thickness and the molecular weight of the gas.
The rate of diffusion of a substance across a membrane is related to:
Concentration gradient (partial pressure difference of gas across the membrane) – Directly proportional
Membrane surface area– Directly proportional
Diffusion coefficient (Solubility) – Directly proportional
Thickness of the membrane – Inversely proportional
Molecular weight – Inversely proportional
Vgas = Area x Solubility x Partial pressure difference/ Molecular Wt x Distance
Examples of Clinical Applications of Fick’s Law
Allows determination of pulmonary gas exchange
Diffusion hypoxia
COPD- reduced alveolar surface tension- slower induction
Placental drug transfer
2nd gas effect:
the rapid uptake of high concentrations of nitrous oxide at induction of inhalational anesthesia produces an increase in alveolar concentrations of oxygen and the accompanying volatile anesthetic agent
During emergence from nitrous oxide anesthetic, rapid elimination of nitrous oxide from the lungs dilutes other alveolar gases, producing alveolar “diffusion hypoxia.” This phenomenon is driven by the same mechanism as the second gas effect—but in the reverse direction.
Describe Fick’s Law and expansion
Expansion of air pockets when N2O is in use (N2O is 34x more soluble in blood than N2 the volume nitrous oxide diffusing IN is > volume nitrogen OUT)
Expansion of the endotracheal tube cuff when nitrous oxide is in use
Placental Transfer of Drugs; Oxygen
Pressure
torr –>mmhg
kPa–>cm H2O etc
1 torr = 1mm Hg
1kPa = 10.2cm H 2 O = 7.5mm Hg
1atm (atmosphere) = 760mm Hg = 760 torr = 1 bar = 100kPa = 1020cm H 2 O = 14.7lb/in 2
Describe the Bourdon Gauge and how it is used in anesthesia
used in anesthesia to measure high pressures, such as in gas cylinders, and are zero referenced to atmospheric pressure
Bourdon gauges contain a coiled tube that expands as pressure is applied.
A linkage connects the coil to a rotating arm that records the pressure.
Gauge pressure is zero referenced at atmospheric pressure and reads zero at 760mm Hg at sea level.
Gauge pressure is absolute pressure minus atmospheric pressure.
Gas Laws allows us to
- Allows us to predict gas behavior
- Know the variable and the constant
- Could these guys possibly be violent?
Boyle’s Law
Pressure P and the volume V of a confined gas held at a constant temperature
The volume of an ideal gas is inversely proportional to the pressure- Thus as pressure ↑ the volume ↓
P1 x V1 =P2 xV2
Application of Boyle’s law
Reservoir Bag on Anesthesia Machine –Applying pressure (squeezing it) causes the volume to decrease
e.g.
Diaphragm contraction
Pneumatic bellows
Squeezing bag
Bourdon gauge to calculate remaining O2 in tank
Application of Boyle’s law to a full E cylinder
A full E cylinder of oxygen will empty 625-650 L into the atmosphere
The explanation is based on Boyle’s law: The relatively small volume of gas in the cylinder is at high pressure. When it is released to the atmosphere where there is a relatively low pressure, a large volume results
Pressure ↓ and Volume ↑
Application of Boyle’s law to spontaneous breathing and bellows on ventilator
Spontaneous breathing- When intrapulmonary pressure becomes negative (decreases), intrapulmonary volume increases
Bellows on ventilator- As pressure increases, the volume within the bellows decreases
Charles’ Law
Relationship between the Volume of a gas and how it varies with Temperature
Charles’s Law states that the volume of a given gas is directly proportional to the Kelvin Temperature provided the amount of gas & the pressure remains constant.
Volume is proportional to temperature
Thus as temperature ↑ the volume ↑
Application of Charles’ Law
LMA cuff ruptures in an autoclave
Gay Lussac’s Gas Law
Relationship between the Pressure of a gas and its Temperature.
At constant Volume, the pressure of a gas sample is directly proportional to the Kelvin Temperature.
Thus as the temperature ↑ the pressure ↑
Application of Gay-Lussac’s Law
A full cylinder of compressed gas is moved from the air conditioned hospital (70 degrees) to the loading dock (100 degrees Fahrenheit)- What happens to the pressure in the cylinder???
And visa-versa if the cylinder is moved from hot to cold environment then the pressure would decrease
Universal (Ideal) Gas Law
PV = nRT
Combines Boyle’s, Charles’ & Gay Lussac’s Laws + Avagadro’s Law:
n = # moles of gas
(A mole (mol) of a pure substance is a mass of the material in grams that is numerically equal to the molecular mass in atomic mass units (amu). A mole of any material will contain Avogadro’s number of molecules. For example, carbon has an atomic mass of exactly 12.0 atomic mass units – a mole of carbon is therefore 12 grams.
R= universal gas constant 0.0821 liter- atm/K/mole
P= Pressure
T = absolute temperature
V= Volume
Reduce to P= T/V or T/P=V or T/V=P
Avagadro’s Hypothesis & Number
Avagadro introduced a molecular numbering system known as the mole
1 mole contains 6.02 x 1023 molecules
Avagadro hypothesized that if you had 2 different containers containing 2 different gases at the same temp and pressure, then they contain the same number of molecules
One mole is one gram multiplied by the molecular weight: e.g. 1 mole 02 = 32 grams.
It has been found that 1 mole of any substance occupies 22.4 liters so: 6.02 x 1023 molecules of 02 = 32 grams and occupies 22.4 L.
Application of Avagadro’s Hypothesis & Number
Calibration of vaporizers is done using Avagadro’s hypothesis.
Molecular weight of Sevoflurane is 200, so 200 g Sevo is 1 mole, and would occupy 22.4 l at s.t.p.
If we put 20g of Sevo (0.1 mole) into a vaporizer, and allow it all to vaporize, it would occupy 2.24 litres
Dalton’s Law of Partial Pressures
Total Pressure of a gas mixture is the sum of the Partial Pressure of each gas.
Total P = P 1 + P 2 + P3…
Dalton’s law states that in a mixture of gases, the pressure exerted by each gas is the same as that which it would exert if it alone occupied the container.
Application Dalton’s Law
We know that the air is 21% Oxygen and 79% Nitrogen, so we can calculate the partial pressure of each gas by multiplying the total atmospheric pressure by the fractional concentration of each gas:
760 mmHg x 21% = l59 mmHg, this is the partial pressure of Oxygen in the container.
What is it for nitrogen???
We know that the air is 21% Oxygen and 79% Nitrogen, so we can calculate the partial pressure of each gas by multiplying the total atmospheric pressure by the fractional concentration of each gas:
760 mmHg x 21% = l59 mmHg, this is the partial pressure of Oxygen in the container.
What is it for nitrogen???
Dalton’s Law Application to inhalation anesthetics
Generally, when we provide an inhalation anesthetic, we use a combination of inhaled agents.
Commonly used agents might be:
50% N20
+ 44% O2
+ 6%Desflurane =100% Mix to patient
What is the definition of MAC
The definition of MAC is the concentration of the vapor (measured as a percentage at 1 atmosphere, i.e the partial pressure) that prevents the reaction to a standard surgical stimulus in 50% of subjects. Since most of us work at about 1 atmosphere, we can still think in terms of% concentration, but what is physiologically important is the partial pressure (mm Hg), not the concentration.
At a higher altitude where the barometric pressure is ½ that at sea level, the amount of isoflurane vapor output increases due to the lower barometric pressure. Therefore, the settings that delivered 2% isoflurane now deliver 4% isoflurane. However, according to Dalton’s law, the partial pressure of isoflurane delivered would be approximately the same at both altitudes since 2% isoflurane at 760mm Hg (15.2 mm Hg) is the same as 4% isoflurane at 380mm Hg (15.2 mm Hg)
Critical Temperature
Definition: The temp above which a substance goes into gaseous form in spite of how much pressure is applied.
A gas cannot be liquefied if the ambient temperature is greater than critical temperature
A gas can be liquefied if sufficient pressure is applied at ambient temp below the critical temperature
Critical Temperature Application: Oxygen - gas
Critical Temp of O2 = - 119 degree C.
Therefore, O2 cannot be liquefied at room temp no matter how much pressure is applied to it
Recall: A gas can be liquefied if sufficient pressure is applied at ambient temp below the critical temperature
How is O2 supplied and stored at hospitals?
The main supply of oxygen in a hospital is in liquid oxygen stores. Huge quantities of gas can be stored in this way and is more economical. The containers are insulated from the outside and the temperature is kept at -160 degress C.
Critical Temperature Application: Nitrous Oxide - Liquid
Critical temp = 36.5 degrees C
Room temp. ~ 25 degrees C
Therefore, pressure can be applied to liquefy N2O at room temp
Hence, N2O is stored as a liquid at pressure of 745 mmHg and at room temp.
Recall: A gas can be liquefied if sufficient pressure is applied at ambient temp below the critical temperature
ADIABATIC Cooling
Occurs when matter changes phase
The term adiabatic implies a change in temperature of the matter without gain or loss of heat
Clinical Application- N2O cylinder opened fully-> frost can form on the outlet due to cooling
Joule-Thompson Effect
Expansion of a gas causes cooling
Clinical Application:
As gas leaves a cylinder, the expansion cools the surrounding air causing condensation of moisture on the cylinder
Poiseuille’s LawApplied with Laminar Flow
Describes the relationship between rate of flow and:
1) pressure gradient across length of tube – direct
2) radius4 of the tube – direct
3) length of the tube – inverse
4) viscosity of the fluid -inverse
Applications of Poiseuille’s Law:
IV Flow
Airways
Vascular flow – Polycythemia vs. Anemia
Thorpe Tubes – at low flows
Laminar to Turbulent
Viscosity is a determinant of flow when flow is laminar (low flow rates).
Density is a determinant of flow when it is turbulent. Density is the ratio of mass to volume. D=mass/volume. Determines the rate of flow in flow meters when rate of gas flow is high through variable orifice flow meter. Example: Heliox
Thorpe Tubes
Thorpe tube is an older term for flowmeters.
At low flows, the annular-shaped orifice around the float is (relatively) tubular so (according to Poiseuille’s Law) flow is governed by viscosity.
At high flows (indicated on the wider top part of the float tube), the annular opening is more like an orifice, and density governs flows.
Factors that Change Flow from Laminar to Turbulent
Increased velocity
Bend >20 degrees
Irregularity in the tube
Laminar–> Turbulent Flow
Reynold’s Number =
velocity ∙ density ∙ diameter/ viscosity
Reynold’s Number > 2000 = TURBULENT FLOW
Bernoulli’s Theorem
Relates pressure and velocity and how they interact
The lateral wall pressure is LEAST at the point of greatest constriction and the speed is the GREATEST
Thus, flow will be faster through the constricted portions and slower at the wider portions of a tube
Narrow Diameter = ↓ Lateral wall pressure = ↑ Speed
Wider Diameter = ↑ Lateral wall pressure = ↓ Speed
Clinical Applications of Bernoulli and Venturi
The lateral pressure of rapidly flowing fluid in a constricted tube can be subatmospheric, hence a sidearm on that portion of the tube can be used to aspirate another fluid into the tube.
Nebulizers
Venturi Oxygen Masks (24-40% O2)
Jet Ventilation
Beer’s Law aka Beer-Lambert Law
Absorption of radiation by a given thickness of a solution of a given concentration is the same as that of twice the thickness of a solution of half the concentration (Beer)
Each layer of equal thickness absorbs an equal fraction of the radiation that passes through it (Lambert)
Clinical Applications: Beer’s Law
Pulse Oximetry 2 LEDs: One (RED) emits light at 660nm One (INFRARED) emits light at 940 nm Shine across pulsatile tissue bed Measure absorption on opposite side Compare RED vs. INFRARED light Calculate Oxygen saturation OXYHGB 940 nm (IR Light) DEOXYHGB 660 nm (RED LIGHT)
Errors in Pulse Oximetry
Artifact (ambient light, low perfusion, motion)
Alternate Species of Hemoglobin
Carboxyhgb: FALSE HIGH
Methgb: If SaO2 > 85% FALSE LOW
If SaO2 < 85% FALSE HIGH
HgbF: No Effect
HgbS: No Effect
Polycythemia: No Effect
Methylene & Isosulfan Blue: FALSE LOW
Indocyanine Green & Indigo Carmine: Slight Decr.
Blue Nail Polish: FALSE LOW
Law of La Place
Pressure gradient across the wall of a SPHERE or TUBE/CYLINDER (blood vessel, ventricle, alveolus) is related to:
Wall tension (T) – Directly
Radius (r) – Inversely
T=Pr
Clinical Applications Of La Place’s Law
Normal Alveoli and the need for surfactant during expiration
Vascular Pathology- Aneurysm rupture due to increased wall tension
Ventricular volume and work of the heart- a dilated ventricle has greater tension in its wall (end diastolic pressure rises)
Ohm’s Law
That resistance which will allow one ampere of current to flow under the influence of a potential of one volt
W(Resistance) = Potential (volt)
Current (ampere)
OR
E (Voltage) = I(current flow or amp) R(resistance)
E=IR
Clinical Applications of Ohm’s Law
Strain Gauges in Pressure Transducers
Thermistors
Electricity in the OR
Metal is a good conductor, your patient is lying on a metal bed, surgery causes bleeding, blood is wet, the room is full of electrical equipment RISK TO THE PATIENT = BURNS
Macroshock: Current distributed through the body, culprit: faulty wiring, improper grounding
Microshock: Current applied in or near the heart, culprit pacing wires, fault equipment during cardiac cath
Electrocautery
MACROSHOCK:
1 milliamp skin tingling/perception
5 milliamps maximal “harmless” current
10-20 milliamps let go of source
50 milliamps pain, LOC, mechanical injury
100-300 milliamps V-Fib, resp intact
6000 milliamps complete physiologic damage
MICROSHOCK
50 - 100 microamps V-Fib
Which law allows us to calculate the O2 and CO2 dissolved in the blood?
Henry’s law
State the gas law:
At constant temperature:
The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in contact with the solution
Henry’s Law
Gas solubility in liquids: _________ related to temperature
inversely
Gas solubility in a liquid is________ to pressure
directly proportional
A gas diffuses at a rate that is __________ to the square root of its molecular weight
inversely proportional
State the associated gas law:
As a cylinder of compressed gas empties, the pressure falls
The ideal (universal) gas law
The cylinder has a constant volume. The number of moles (n) of gas decreases as gas exits the cylinder, so Pressure decreases.
