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2. physics exam 2 (7/13) > study guide for physics exam 2 > Flashcards

study guide for physics exam 2 Flashcards

0
Q
  1. define P50:
  2. what is normal?
  3. what is an example of a left shifted P50?
  4. what is an example of a right shifted P50?
A
  1. p 50 is the pp of oxygen that gives you 50% saturation on the oxy-Hb dissociation curve
  2. normal P50=27 mmHg
  3. left shifted ex: 24
  4. right shifted ex: 30
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1
Q 
calculate arterial oxygen content (CaO2) with a given ABG
ex:
SaO2=97
paO2=100
Hgb=14
A

(1. 34 x Hb x SaO2) + (0.003 x paO2)=
(1. 34 x 14 x .97) + (0.003 x 100)=
18. 2 + .3 =
18. 5

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2
Q

how do you check an oxygen analyzer (modern and galvanic) in the morning?

A

make sure that it reads 21%, then flush it with the flush button (it should read 100%)

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3
Q

why do we place an O2 analyzer in certain positions in the breathing circuit?

A
  1. placed in inspiratory limb d/t less humidity
  2. should be upright or only slightly tilted to decrease moisture gathering
  3. if placed between mask or ETT and circuit, it will INCREASE dead space (unacceptably)
  4. should be upstream of the humidifier
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4
Q

what are the sources of artifact in pulse oximetry?

A
  1. smokers have 8-15% carbon monoxide which gives a fase high
  2. motion
  3. lights
  4. vasoconstriction
  5. cold fingers
  6. volume depleted/ hypotensive
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5
Q
  1. what are brething circuit disconnects and other problems seen as on our monitors?
  2. which ones will alarm first? second?
  3. why?
A
  1. -co2 detector (chemical)
    - —-lowor high PIP or low VT (mechanical)
    - —-saO2
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6
Q
  1. how are various types of VAE detected on our monitors?
  2. what is the difference in responses to small vs. massive PE?
  3. what is the difference in responses to CO2 vs. air embolism?
A
  1. it is detected via ETCO2 monitoring and SaO2 monitoring
    2a. for an massive gas embolism, you will see a decrease in ETCO2;
    2b. for a small embolism (which is a shunt) you may see an increase in N2 (“other” or “balance”)
  2. if co2 embolism, you will see an increase in FiCO2; the monitor may say:
    FiO2=90%
    FiCO2=5% (which is 40mmhg/760mmhg)
    other: 5%
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7
Q

what is the normal relationship between arterial and end tidal CO2?

A
  1. arterial CO2 is usually 6 mmHg higher than ETCO2
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8
Q

what are normal values of various gasses in air, trachea, alveoli, arteries, venous blood?

  1. oxygen:
  2. nitrogen:
  3. co2:
A

O2=21%; Nitrogen=78% of room air

a. atmosphere: O=160 mmhg; N=593; CO2=0
b. trachea: O=150; N=593; CO2=0
c. alveolus: O=102; N=593; CO2=40
d. arterial: O=98; N=593; CO2=40
e. venous: O2=40; N=593; CO2=46

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9
Q

what are the reasons for these capnograph readings:

  1. high co2?
  2. low co?
  3. no co2?
A
  1. high co2: hypoventilation, rebreathing co2 (bad granules or valves), hypermetabolic state
  2. low co2: hyperventilation, hypoperfusion,
  3. no co2: esophageal intubation, patient not breathing
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10
Q

what do these waveforms represent (or what will you see):

  1. if patient is breathing spontaneously?
  2. cardiogenic oscillation?
  3. rebreathing?
  4. hyperventilating?
  5. hypoventilating?
A
  1. spontaneously breathing during ventilation will cause a curare cleft or resumption may be gradual (if not being ventilated)
  2. cardiogenic oscillation is a ripple or zig-zag pattern at the end of the exhalation phase representing the heart cycling blood
  3. rebreathing of co2 will show an elevated ETCO2 that never returns to baseline
  4. hyperventilation will show a lower ETCO2
  5. hypoventilation will show a higher ETCO2 (>40 mmHg) that returns to baseline
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11
Q

what would you do to treat capno waveforms such as:

  1. hypoventilation
  2. hyperventilation
  3. rebreathing
  4. spontaneous
  5. prolonged upstroke (expiration)
A
  1. hypoventilation: increase resp rate; VT
  2. hyperventilatin: decrease resp rate; then VT
  3. rebreathing: increase flows to 6-10 L; then change granules and check valves when case is over (or immediately if increased FGF has no effect).
  4. spontaneous breathing: if mid case, give more paralytic. If end of case, switch to psv pro or simv-pc
  5. prolonged expiration (upper left corner is shaved off at 45 degrees or more): check for obstruction of gas flow (mechanical or d/t bronchospasm, copd etc).
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12
Q

what is the waveform change with an incompetent inspiratory valve?

A

slanted down stroke pattern (instead of dropping straight down)

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13
Q
  1. what is compliance? formula for compliance?
  2. how does a pressure volume loop change when there is increased compliance?
  3. when there is decreased compliance?
A
  1. compliance is the ease of distensibility of the lungs (how easy they inflate); formula is: change in volume /change in pressure.
  2. increased compliance on a PV loop causes the loop to be more upright and needs less pressure to reach max VT
  3. decreased compliance on a PV loop causes the loop to lay more flat (horizontal) and requires more pressure to reach max VT
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14
Q

describe the components of a PV loop:

  1. which direction does it go for spontaneous respirations?
  2. which direcction does it go for ventilated respirations?
  3. which axis is volume? and which is pressure?
  4. what unit is the pressure measured in?
  5. how can you see peep on the PV loop?
A
  1. spontaneous respirations go clockwise
  2. ventilated respirations go counter clockwise
  3. volume is the vertical axis; pressure (PIP) is the horizontal axis
  4. PIP (pressure) is measured in cm H2O
  5. peep is seen as the place on the pressure axis where the waveform starts and ends.
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15
Q
  1. what factors increase compliance?

2. what factors decrease compliance?

A
  1. peep, muscle relaxation
  2. inadequate muscle relaxation, air embolism tumor in lungs, rapid infusion of narcotics (rigid chest), bronchoconstriction, ptx, lateral position, lithotomy, prone, trendelenberg, large abdomen, scoliosis
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16
Q

which type of gas analyzers out of IR, Raman, Mass spectrometer, detect nitrogen directly?

A

mass spectrometry and Raman CAN detect N2O;

-Infrared CANNOT

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17
Q
  1. Why should you disconnect the sidestream sampling port of an IR gas analyzer before giving puffs of albuterol to an intubated patient?
  2. what about with a mass spectrometry unit?
A
  1. they can ruin the gas sampling module (which costs $10,000)
  2. propellents such as (or in) albuterol can be interpreted as VA (isoflurane)-called a transcient effect.
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18
Q

what are some problematic metabolites of sevo and enflorane?

A

compound A and Fl- ions which are toxic to the kidneys

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19
Q
  1. what is the minimal FGF for sevo?

2. why?

A
  1. minimal FGF is 2L for sevo over 2%; 1L if under 2%

2. higher fresh gas flows keep gas flowing fast enough to prevent build up of compound A & florine ions

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20
Q

what are best ways to limit exposure to WAGS (including N2O)?

A
  1. avoid spills
  2. Control leaks (connections, circuit etc.)
  3. Avoid poor mask fit
  4. No gasses e cept oxygen in mask before placed on patient
  5. Dont refill vaporizors when in “on position”
  6. Use low flows
  7. Limit nitrous use
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21
Q
  1. define absolute humidity:

2. define relative humidity:

A
  1. absolute humidity is the MAX amount of water a gas/air can hold at a given temperature
  2. relative humidity is defined as the RATIO of the CURRENT water vapor pressure in the mixture to the MAX water vapor (absolute) at a given temperature. (Expresses as a %)
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22
Q

what ways do patients lose heat in the OR (by rank and percentage)?

A
  1. Radiation(50-60%)-transfering heat into the air or to cool objects
  2. Evaporation(20%)-loss of heat/moisture as vapor into the air
  3. Convection(<20%)-loss of heat into moving air stream
  4. Conduction(negligable)-loss of heat to a cold surroundings
    (R-E-C-C vd*)
    *Vection before duction
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23
Q
  1. how do adults maintain their body temp?

2. how do infants?

A
  1. adults maintain body heat by shivering or behavioral go get a blanket
  2. infants maintain body heat by burning brown fat (non shivering thermogenesis)
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24
Q

how do anesthetic agents (especially volatile) affect normal homeostatic mechanisms?

A

anesthesia blunts the urge to shiver, put on a blanket, causes vasocontriction of skin

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25
Q
  1. how are the various body systems affected by hypothermia?
  2. at what temp is the V-fib thershold reached?
  3. what is the v-fib threshold (in case you wanted to know)?
A
  1. chemical reactions slow down or even stop at cool temperatures
  2. reduction in v-fib threshold occurs at 86 degrees farenheit (30 degrees celcius) (some say 28 degrees celcius (82.4 farenheit))
  3. the point at which cooling prolongs refractory period lowering the threshold making one more prone to arrhythmias
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26
Q
  1. name methods of body temp measurement:

2. what is the best mode used to measure core body temp?

A

a) rectal
b) esophageal
c) tympanic
d) nasal or nasopharyngeal
e) skin
f) core (pulm artery, bladder)
2. core (tip of a pulmonary artery catheter)

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27
Q

what are advantages and disadvantages to rectal temperature measurement?

A

rectal temp:

  1. aesthetic considerations
  2. perforation (in infants)
  3. slow equillibration to core with adults
28
Q

what are advantages and disadvantages to esphageal temperature measurement?

A

esophageal:

  1. must be in distal 1/3 to be accurate (upper esophagus may reflect temp of inspired gasses)
  2. safe to measure
29
Q

what are advantages and disadvantages to tympanic temperature measurement?

A

tympanic:

  1. accurate: close to core and brain temp
  2. risk of perforating tympanic membrane
  3. cerumen can make it inaccurate
30
Q

what are advantages and disadvantages to nasal temperature measurement?

A

nasal:

  1. inaccurate if not intubated
  2. if intubated, accurately reflects brain(core) temp
31
Q

what are advantages and disadvantages to skin temperature measurement?

A

skin:

  1. useful, no risk of measurement
  2. may be useful as a second measuring site (by showing degree of peripheral vasoconstriction)
  3. axillary temp acuracy is relative to placement on axillary artery and whether arm is adducted
32
Q
  1. what are flow and temperature dependence?

2. how do these affect modern vaporizer design?

A
  1. the premise that the gas delivery is dependent on temperature remaining between 20-35 degrees celcius and flows remaining between 200cc-10L/min FGF in order to deliver expected results (what’s on the dial).
  2. a)vaporizers have metal cups around the bases to control temperature
    b) they contain temperature compensation devices that allow for more air flow to pick up gas if the gas becomes cooler (<20 degrees).
    c) they are designed to allow for a percentage of the oxygen/air flow to be divided and diverted toward the gas (chamber flow) while the rest continues on its path (bypass flow), they then converge coming out of the vaporizer (this flow is part of what the temperature compensation device controls).
33
Q

convert a dose of one agent to an equipotent dose of another agent.
for example, your patient is on desflurane at 9%, how do you calculate it?

A
  1. set % of gas being given / mac of the gas being given = X% of gas to be given / mac of gas to be given
  2. cross multiply
  3. divide
    ex: des is at 9% / mac of des is 6% = X% of sevo / mac of sevo is 1.8%
    9/6=x/1.8&raquo_space; 16.2/6&raquo_space; 2.7%
34
Q

if you are giving a gas at x liters/min, what the amount of mL/min given?
ex: desflurane at 6L/min

A
  1. convert L/min to mL/min
  2. multiply this by mac % in decimal form
    ex: at 6 L/min (6000 mL/min) x 1 mac of Des= 6%
    6000 x .06 des = 360 cc of des
35
Q

how do you figure out the percent of fully saturated vapor of a volatile agent?
ex: Isoflurane

A
  1. divide the vapor pressure by the barometric pressure of air
    (vapor pressure of the gas / barometric pressure)
    ex: Isoflurane is 240 mmHg vapor pressure
    240/760 mmHg=0.33
    isoflurane is fully saturated at 33%
36
Q

how does temperature affect the vapor pressure of a VA?

A

if you increase temp, you increase VP

37
Q

why does the stream of gas moving over the surface of the liquid VA cool the liquid?

A

-moving air cools liquids like it cools humans (convection);

It pulls the high energy molecules off the top layer, leaving the slower moving (cooler) molecules behind

38
Q

how do variable bypass vaporizers differ from blenders like the tech 6?

A
  • blenders (tech 6) are heated and NO fresh gas flow enters the vaporizing chamber (as the des is dialed up, it adds more gas to the fresh gas flow)
  • variable bypass allows a percentage of FGF to enter the chamber and pick up the gas, then it re-joins the bypass flow (the gas that didn’t enter the gas chanber).
39
Q

how do changes in FGF affect depth (even when the vaporizer setting is unchanged)?

A

it decreases depth d/t the fact that it slows the rate of gas molecules entering the body (and thus the brain) and d/t redistribution down the concentration gradient, the body “robs” the brain of the gas it needs to maintain depth (remember that the vessel rich group takes 30% of Blood flow).

40
Q

how is low flow anesthesia a good thing for anesthetists?

A
  1. decreases waste of gas by having the patient rebreathe unabsorbed exhaled gasses
  2. maintains tracheal moisture by not blowing in high flow of dry air/oxygen.
41
Q

at what form and percentages does CO2 exist in the blood?

A
  1. carbaminohemoglobin (HbCO2)= 20-30%
  2. CO2 in plasma=5-10%
  3. carbonic acid (H2CO3)=60-70%
42
Q
  1. what is the bohr effect?
  2. what is the haldane effect?
    a) how does it work in the lungs?
    b) how does it work in the tissues?
A
  1. the BOHR effect is the change in the oxyHb dissociation curve that occurs when CO2 leaves the blood and enters the alveoli. The more acidic or higher the co2 levels, the more readily oxygen is released by Hb molecules. External environment dictates affinity (left or right shifts)
  2. the HALDANE effect promotes CO2 transport (and is more important quantitatively than the Bohr effect) because:
    a) at the lungs, the association of oxygen to Hb speeds up the CO2-Hb dissociation (delivering CO2 out of the lungs);
    b) at the tissues, the effect is reversed: the joining of CO2 with Hb causes the dissociation of Hb-O2 (causing delivery of oxygen to the tissues).
    (Internal environment of Hb cell affinity dictates release)
43
Q

for testing purposes, what are normal ABGs?

A

pH: 7.4
paCO2: 40
HCO3-: 24
paO2: 100

44
Q

what is the general formula of Ethers?

A 
R-O-R'
i.e. r group-O-r group
ex: ch3-ch2-o-ch2-ch3 
or
 cf3-ch-f-o-cf2h (isoflurane (forane))
45
Q 
SEVOFLURANE:
what is the:
-mac
-vp
-bgsc
-ogsc

-trade name of SEVO?

A
  • mac: 1.8%
  • vapor pressure: 160
  • blood:gas solubility coeffecient: .60
  • oil:gas solubility coeffecient: 47

aka: ULTANE

46
Q 
DESFLURANE?
what is the:
-mac
-vp
-bgsc
-ogsc
trade name of DES?
A 
mac: 6
vapor pressure: 660
blood:gas solubility coeffecient: .42
oil:gas solubility coeffecient: 19
aka: SUPRANE
47
Q 
ISOFLURANE
what is the:
-mac
-vp
-bgsc
-ogsc
-trade name of ISO?
A 
mac: 1.14%
vapor pressure: 240
blood:gas solubility coeffecient: 1.4
oil:gas solubility coeffecient: 98
Trade name: FORANE
48
Q

what physiological issues does hypothermia cause?

A

pancreatic: inflammation of the pancreas,
resp: fluid in the lungs, pneumonia,
renal: kidney failure
cardiac: heart problems
hepatic: slowed metabolism, liver failure
neurological: weakness, clumsiness, delirium

49
Q
  1. what does latent heat mean?
  2. all anesthetics get their latent heat from what/where?
  3. what is “specific” latent heat?
A
  1. the heat required to vaporize the liquid to a gas (to change somthing from one form to another)
  2. all volatile anesthetics acquire their latent heat of vaporization from the environment as they vaporize
  3. the amount of heat required to convert 1 gram of substance from one phase to another.
50
Q
  1. what is the critical temperature?

2. what happens if you go above the critical temperature?

A
  1. the temperature at which the latent heat of vaporization for a substance becomes zero
  2. above the critical temperature, the substance cannot exisst as a liquid (it becomes gas)
51
Q
  1. Why should you wait before turning down the flows to 2L/min?
  2. what should you do to your flows to maintain depth?
A
  1. The concentration gradient will cause the body to draw VA molecules from the brain as the body concentration falls (lessens depth)
  2. Turn flows from 8 to 4 or 6 for 6-10 minutes
52
Q
  1. 100% at 4000mL/min means how much of the total flow of gas diverted into the gas chamber to pick up VA?
  2. what is the math:
    - saturation of Isoflurane?
    - what percentage does oxygen make up in the mixture when iso is fully saturated?
    - what is the math set up?
A
  1. 100% at 4000 mL/min means 100 ml of gas will be diverted to the gas chamber
  2. the vapor presure of iso is 240 mmHg
    240 mmHg/760mmHg=0.33 (33%)
    -this means that 100 ml of oxygen will make up 67% of the mixture (the other 33% of the mix will be isoflurane)
    -100 mL/67%==x mL/33%
    100mL/67=xmL/33 …[33x100=3300]; [67*x=67x]
    -3300 = 67x
    -=49 ml
53
Q

if the FGF is decreased to 2L/min and the iso is dialed to 1%:

  1. how much oxygen will be sent to the gas chamber?
  2. calculate the amount of iso that will be picked up
  3. do the math on what % (although we already know) will be?
A
  1. 2000 x .025 (because we already know that 2.5% of the gas will be diverted to the gas chamber)
    2000 x 2.5=50 mL
  2. if 50 ml=67%, then the amount of gas is 37%
    50mL/67% = x mL/33%
    33 * 50=1650
    x * 67= 67x
    1650/67= 25 mL of gas
  3. to find the percent of Iso delivered; divide the amount in mL by the total flow (2L or 2000mL):
    25/2000=0.01
54
Q
  1. How much FGF will be diverted to the chamber when you have 2L FGF with 2% iso dialed?
  2. what is the splitting ratio?
  3. what is the moral of this story?
A
  1. 2000 x 0.02=40 mL (gas)
    if 40 mL gas is given and gas is 33%, the air going to the chamber is … x/66=40/33
    67*40/33= …2680 /33= 81 mL
  2. the splitting ratio is 81/2000
    or 0.04 or (around 4%)
  3. the moral is that if you change the dialed concentration, you change the splitting ratio
55
Q 
the dialed agent match the inspired agent:
-The vaporizer is set to 2%
-The inspired agent is only 1.25
-The end tidal is 0.9%
why is this?
A
  • there is some uptake into the circle components
  • there is uptake and elimination of other gasses by the patient
  • FGF (low FGF can alter actual %)
  • air dilution d/t leakage
56
Q
  • if your VE (minute ventilation) is 8L i.e. 800 mL x 10 bpm
    1. if your FGF is 8L, how much of your VE is new gas?
    2. if your FGF is 2L, how much of your VE is new gas?
A
  1. if VE is 8L/min and FGF is 8L/min, everything inhaled is new gas
  2. if your FGF is 2L/min (2/8=.25) therefore 25% of your FGF is new and 75% (or 6L) is rebreathed
  3. How much is actually inspired?
    - [(.25 x 2) + (.75 x .9)]=
    - [0.5 + .675]=1.175
    - 1.8 % is inspired
57
Q

blast from the past:

What is the low pressure circuit?

A
  1. low pressure circuit:
    - flow meters
    - vaporizers
    - flow control valve
    - check valve
    - common gas outlet
58
Q

what is in the intermediate pressure circuit?

A 
-intermediate pressure circuit:
N2O pipeline
-failsafe valve
-O2 supply failure alarm
-second stage O2 pressure regulator
-O2 pipeline supply
59
Q

what is in the high pressure circuit?

A

high pressure circuit:

  • cylinder pressure guage
  • N2O
  • O2cylinders
  • check valve,
60
Q
  1. what is pumping effect?

2. how does the Drager 19 prevent this?

A
  1. in older (non-variable bypass) vaporizers intermittened positive pressure ventilation or flush valve causes oscillation which pushes fresh gas back into the vaporizer (even bypass flow)
    - when the bypass flow re-enters the vaporizer, it picks up more gas leading to overdose
  2. there is a tortuous inlet that will not allow for back flow (back flow would have to push air molecules coming in back up a “zig zag” turnstyle)
    - also there is a temperature compensation bypass valve
61
Q
  1. What is the BEST way to maintain body heat in the OR?

2. What is the most PRACTICAL way?

A
  1. BEST way: warm room

2. MOST PRACTICAL way: forced air, then insulation

62
Q
  1. if you are running FGF at 4 L/min, what is your splitting ratio if your iso is running at 1%?
A

100/4000=.025 (2.5% splitting ratio)

in other words, 2.5% of the fresh gas flow is diverted to the gas chamber

63
Q

What must u have at chamber outlet of vaporizer?

A

100%saturation of VA

64
Q

I u are running Des ans reduce your FGF to 500 m/minL right after intubation, what is your ml of Des/ min?

A

500 cc/min x .06 (6%)= 30 cc/ min

65
Q

How do u calculate relative humidity?

A

Give humidity/L air divided by absolute humidity/L of air

Ex: 8/L divided by 44/L =.18 BUT REMEMBER… Relative humidity is in % so… Answer is 18% (or 18

66
Q

Vaporizers must function at high degree of accuracy since…

A

The VP of anesthetics is greater than what is required to produce anesthesia

67
Q

(Missed ?)

What does massive PE do to ETCO2?

A

Drops to ZERO!!!

68
Q

Missed ?

How to decrease WAGS?

A

Unplug nitrous in AM

2. physics exam 2 (7/13) (2 decks)

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