Physics And Equipment Flashcards
Why is Helium useful in cases of airway constriction/masses?
Helium has a much lower density and will improve turbulent flow
Describe N2O Gas Cylinders
Blue
Contain 1590L of gas at 750PSI
Gauge will continue to read 750PSI, until only 1/4 of gas (~400L) remains
What is Laplace’s Law?
Tension = (Pressure x Radius) / Thickness
The surface tension of a sphere is directly proportional to the radius and pressure within the sphere
Describe the 4 Main Gas Laws
Henry’s Law - at constant temperature, the concentration of a dissolved gas is directly proportional to the partial pressure of that gas (i.e. increasing the dial on a gas vaporizer)
Boyle’s Law - a fixed mass of gas at constant temperature will have a constant pressure-volume relationship (P1V1=P2V2)
Gay-Lussac’s Law - the pressure of a given mass of gas is directly proportional to its temperature when at a constant volume (i.e. pressure of an ETT cuff increasing with increased temperature)
Dalton’s Law - the total pressure exerted by a mixture of gases is the sum of the individual gases’ partial pressure (i.e. requiring higher concentrations at higher altitudes)
Describe O2 Gas Cylinders
Green
Contains 625L at 2000PSI
What are the roles of 1st- and 2nd-stage regulators?
1st-stage regulators reduce pressured to 45PSI
2nd-stage regulators reduce pressure to around 15PSI
What is the anesthesia machine fail safe valve?
Also called the pressure sensor shut off valve
Functions to prevent delivery of hypoxic gas mixtures
When O2 pressure drops below 25PSI, valve discontinues the flow of N20
How does transducer level effect A-line blood pressure readings?
A difference of 10cm results in a change of 7mm Hg
List the volatile agent vapor pressures
Sevoflurane = 160 Enflurane = 172 Isoflurane = 240 Halothane = 243 Desflurane = 669
What is the formula for anesthetic volatile concentration delivered?
(vapor pressure x flow through vaporizer) / [(barometric - vapor pressure) x (flow through vaporizer + dilutent flow)]
Describe the phases of the CO2 Capnogram
4 Phases:
1) Inspiratory baseline
2) Expiratory upstroke - mixing of gas from dead space and alveoli
3) Expiratory baseline - CO2 rich alveolar gas
4) Inspiratory downstroke
What is the maximum FiO2 that can be delivered via nasal cannula?
45%
4% per liter (up to 6L) over the 21% found in room air
Describe pacemaker nomenclature
First letter identifies the chamber paced
Second letter identifies which chamber is sensed
Third letter describes the response
What is the reason for the difference between EtCO2 and arterial CO2?
Alveolar dead space
What is the difference between minute ventilation and alveolar ventilation?
Minute ventilation = tidal volume x respiratory rate
Alveolar ventilation = (tidal volume - dead space) x respiratory rate
Describe laminar and turbulent flow
At low flow rates, respiratory flow tends to be laminar - dependent on viscosity
At high flows, respiratory flow becomes turbulent - dependent on density
What are the advantages of calcium hydroxide lime over soda lime?
- Compound A is not formed when used with Sevoflurane (no NaOH or KOH)
- Does not produce any carbon monoxide
- Indicator dye does not revert back to normal after conversion
However, it is more expensive and had half the absorptive capacity of soda lime
How does pulse oximetry work?
Via transillumination of tissue with 2 different wavelengths of light
940 nm for oxyhemoglobin
660 nm for deoxyhemoglobin
List the gas cylinder colors
Air - yellow Helium - brown Carbon dioxide - grey Nitrogen - black Nitrous oxide - blue Oxygen - green
List some reasons for error in pulse oximetry
No pulse or low peripheral perfusion
- hypotension, hypothermia, hypovolemia, severe anemia
Presence of hemoglobin variants or dyes
- Carboxyhemoglobin is seen as oxyhemoglobin (results in overestimation of O2 sat)
- Methemoglobin causes a sat of 85%
- Dyes (methylene blue, indocyanine green) transiently lower sat readings
What is the equation for MAP?
1/3(Systolic BP) + 2/3(Diastolic BP)
How does a peripheral arterial waveform differ from a central waveform?
Relative to a more central arterial waveform, a more peripheral waveform will have a:
- higher systolic
- wider pulse pressure
- more delayed and slurred dicrotic notch
- more pronounced diastolic wave
Describe the CVP Waveform. What are some abnormal findings and their causes?
a wave - atrial contraction at end diastole
c wave - tricuspid valve bulging during early systole
x descent - atrial relaxation mid-systole
v wave - venous return to atrium in late systole
y descent - atrial emptying as the tricuspid valve opens in early diastole
A-fib - loss of a waves
AV dissociation - “cannon a waves”
Tricuspid regurg - tall c and v waves, loss of x descent
Tricuspid stenosis - tall a and v waves, loss of y descent
RV ischemia or pericardial constriction - “M’ or “W”
Tamponade - dominant x descent, minimal y descent
What are normal PA catheter pressures
RA = 1 - 5 mm Hg RV = 15 - 30 / 1 -5 mm Hg PA = 15 - 30 / 5 - 15 mm Hg (mean of 10-20) PCWP = 5 - 12 mm Hg
Describe SVR and PVR
SVR = (MAP - CVP)/CO x 80
normal is 1200-1500
PVR = (mean PAP - PCWP)/CO x 80
normal is 50-150
Describe the territories covered by different leads of the EKG
II, III, and aVF monitor the right atrium and right ventricle (RCA)
V3-V5 monitor the anterior lateral left ventricle (LAD)
I and aVL monitor the lateral left ventricle (L circumflex)
What is the proper way to deal with a tipped anesthetic vaporizer?
Set the vaporizer at low concentration and flush with oxygen at 10 L/minute for 30 minutes
What type of circuits are Mapleson systems? Which is better for spontaneous breathing? What about controlled ventilation?
“Semi-open systems”
Relative efficiency for spontaneous ventilation: A > D > C > B
- “all dogs can bite”
Relative efficiency for controlled ventilation: D > B > C > A
- “dog bites can ache”
What type of circuit is the circle breathing system? What are the essential complements? What are the rules for arrangement?
“Semi closed system”
Essential components: reservoir bag, 2 corrugated tubes, 2 unidirectional valves, a CO2 absorbent, and an overflow valve
Rules:
- FGF should enter the system proximal to the inspiratory valve
- Unidirectional valve must be located between the pt and the reservoir bag on both limbs
- Overflow valve cannot be place between the pt and the inspiratory valve
How are the number of TOF twitches correlated to % of blocked nerve receptors?
0/4 twitches - 100% blocked 1/4 twitches - 90% blocked 2/4 twitches - 85% blocked 3/4 twitches - 80% blocked 4/4 twitches - 75% or less blocked
What is the major mechanism of heat loss for anesthetized pts in the OR?
Radiation
How are anesthesia machine bellows classified? What are two types? Which is safer?
Bellows are classified according to their movement during expiration
- ascending bellows rise during expiration
- descending bellows fall during expiration
Ascending bellows are thought to be safer, because during a circuit disconnect, the bellows will not fill
How can you estimate the amount of time left to use an O2 E-cylinder?
Time remaining (hrs) = PSI / (200 x flow rate)
What is the significance of ultrasound probe frequency?
High frequency = better resolution, limited penetration
Low frequency = better penetration, limited resolution
What are the advantages and disadvantages of semi-open Mapleson systems?
Advantages:
- small resistance and small dead space
- easy to use, not bulky
- absence of valves so minimal malfunction
Disadvantages:
- loss of heat and humidity
- poor ability to scavenge
- relatively high fresh gas flow required to prevent rebreathing
What are the advantages and disadvantages if semi-closed circle circuits?
Advantages:
- conservation of heat and humidity
- good ability to scavenge
Disadvantages:
- more resistance and more dead space
- bulkier
- valves can malfunction
What are the effects of Trendelenburg positioning?
Reductions in FRC, TLC, and pulmonary compliance
Increase in shunt (perfusion without ventilation)
Transient increase in venous return, leading to increased cardiac output
Abdominal contents shift cephalad, which can cause an accidental mainstem intubation
Fluid can lead to airway and facial edema
Increased ICP and IOP
How does high altitude effect anesthetic delivery?
The delivered concentration of a volatile anesthetic from a variable-bypass vaporizer increases as altitude increases
- delivered partial pressure remains essentially unchanged
Desflurane vaporizers are heated to maintain a constant vapor pressure within the vaporizer
- at higher altitudes, concentration needs to be increased in order to deliver proper partial pressure of anesthetic
