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Anesthesia-phar > Dewan (Inhalational) Part 1 - 4 key points > Flashcards

Dewan (Inhalational) Part 1 - 4 key points Flashcards

1
Q

The greater the uptake of an anesthetic agent…

A
  • the greater the difference between inspired and alveolar concentrations
  • slower rate of induction
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2
Q

3 factors that affect anesthetic uptake:

A
  1. solubility in the blood (blood:gas partition coefficient)
  2. pulmonary blood flow / cardiac output
  3. difference in anesthetic partial pressure b/w alveolar gas and venous blood
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3
Q

Low cardiac output states can lead to…

A
  • overdose with soluble agents
  • rate of rise in alveolar concentrations INCREASED since it is not being taken away from the lungs quickly
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4
Q

Factors which speed induction and recovery (7)

A
  1. elimination of rebreathing
  2. high fresh gas flows
  3. low anesthetic circuit volume
  4. low absorption by the circuit
  5. Decreased solubility
  6. high cerebral blood flow
  7. increased ventilation
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5
Q

Meyer Overton Rule

A
  • anesthesia occurs from molecules dissolving at specific lipophilic sites and all share a common MOA at a molecular level

In other words, the anesthetic potency of inhalational agents correlates directly with their lipid solubility

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6
Q

What is MAC? What does it mean?

A

Minimal Alveolar Concentration
alveolar concentration that prevents movement in 50% of patients in response to a standardized stimulus

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7
Q

Complications from prolonged exposure to N2O

A

Bone marrow suppression and neurologic deficiencies

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8
Q

Halothane can cause ____? (rare) and risks

A

“Halothane Hepatitis” - rare
Higher risk:
1. middle age obese women
2. familial predisposition to halothane toxicity
3. personal history of toxicity

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9
Q

Isoflurane can ____ _____ arteries

A
  • *dilate coronary** arteries
  • not as strongly at NTG or adenosine
  • this dilation could divert blood away from fixed stenotic lesions
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10
Q

Desflurane’s ___ solubility causes…

A

Low solubility causes rapid induction and emergence

(blood solubility)

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11
Q

Rapid increase in Desflurane can cause…?

A

tachycardia
HTN
catecholamine release
*esp in those with cardiac disease

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12
Q

Sevoflurane is a good agent for ___ and _____

why?

A

pediatrics and adults

because its nonpungent and allows for rapid alveolar concentration causing rapid and smooth inhalation

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13
Q

What is Fi and factors that affect Fi

A

Fi = inspiratory concentration

  1. fresh gas flow rate
  2. volume of breathing system
  3. absorption by the machine/circuit
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14
Q

How does Fi oppose FA?

A

increased Fi decreases uptake, and at 100% inspired concentration, uptake would not oppose ventilation

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15
Q

What is FA?

A

Alveolar concentration

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16
Q

What is equilibrium?

A

pressure exerted by gas is equal on both sides of the membrane

NO NET MOVEMENT

not an = amount of molecules

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17
Q

What is the goal of induction?

A

reach equilibrium between inspired and alveolar concentration of anesthetics

Fi / FA = 1

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18
Q

What does ventilation do for the Fi/FA?

A

ventilation delivers anesthetics to the lungs and increases FA

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19
Q

Uptake - what does it do for FA/Fi?

A

Increases FA to match Fi towards = 1

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20
Q

Define uptake and its formula

A

Uptake = anesthetic in the blood passes through the lung which OPPOSES ventilation by taking the anesthetic away from the lungs

Uptake = solubility x (Pi-PA)/PB x Cardiac Output

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21
Q

3 factors that affect uptake

A
  1. solubility
  2. cardiac output
  3. difference in partial pressure
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22
Q

Solubility - what is it? how does it affect induction?

A
  • Solubility = blood-gas coefficient, differs one gas from another
  • lower solubility = faster onset and emergence
  • higher = slower
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23
Q

Solubility temp effects

A

hypothermia = higher solubility, slower onset

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24
Q

Solubilities of top 4 gasses in order least to greatest

A
  1. Desflurane 0.42
  2. N2O 0.47
  3. Sevoflurane 0.6
  4. Isoflurane 1.4
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25
Q

cardiac output effects on induction

A

Increased CO decreases induction d/t increase in uptake of drug away from lungs

(better perfusion)

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26
Q

What is the difference in anesthetic partial pressure ?

A

difference between alveolar gas in the lungs and venous blood

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27
Q

order of gas flow

A

vaporizer → inflow → circuit → alveoli → blood → brain → other tissues

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28
Q

determinants of anesthetic transfer from blood to tissues

A
  1. tissue solubility of the agents
  2. tissue blood flow
  3. difference in partial pressure b/w arterial blood and tissue
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29
Q

metabolism of agents

A

metabolism increases uptake

  1. halothane = significantly metabolized
  2. sevoflurane = slightly
  3. desflurane and isoflurane negligible
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30
Q

how does increasing ventilation affect FA/Fi?

A

increase in ventilation will raise FA/Fi

*especially with soluble agents

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31
Q

how does suppressing ventilation affect FA/Fi?

A

anything that depresses ventilation (opiates) decreases the rate in rise of FA which is a negative feedback loop

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32
Q

How can Fi be controlled?

A
  1. high flow rates (time constant)
  2. high % concentration
33
Q

what is minute ventilation and alveolar dead space?

A

Ve = 6L

Anatomic dead space = 2cc/Kg + circuit dead space

34
Q

What is FRC and normal value?

A

Functional residual capacity VA = 4L

35
Q

Why do different agents produce difference FA/Fi?

A

different solubilities

36
Q

What is the time constant?

A

Capacity / flow rate (L/Lpm)

Time it takes to change a gas over

37
Q

Time constant %s

1, 2, and 3

½

A

1 TC = 63%

2 TC = 86%

3 TC = 98%

½ = 50% = 0.7 TC

38
Q

during short cases, where does the anesthetic go?

A

only to the vessel rich group due to the long time constant and low flow rate

39
Q

what is included in the vessel rich group?

% body fat and CO?

A

brain, heart, liver, kidney, endocrine

10% body fat, 75% CO

first to reach steady state d/t small volume limit and solubility

40
Q

second highest perfused group

A

muscle group = muscle and skin

slower uptake yet greater volume capacity which sustains uptake for hours

41
Q

third vessel group?

A

fat group, which is fairly similar to muscle group

42
Q

lowest perfusion group?

A

bones, ligaments, hair, cartilage

insignificant uptake

43
Q

Factors that affect the rate of rise in humans: (4)

A
  • Pungency: with inhalation agents
  • Overpressure: ventilation with high concentration
  • Potency: how many molecules needed for sleep
  • Mechanical factors: small airway closures
44
Q

Oxygenation & Apnea

A

Oxygenation will continue as long as there is a partial pressure gradient

45
Q

Fat/Blood partition coefficients - list in order from least to greatest

A
  • Nitrous oxide 2.3 - least fat soluble
  • Desflurane 27
  • Isoflurane 45
  • Enflurane 46
  • Sevoflurane 48
  • Halothane 67 or 80? – most fat soluble
46
Q

What is the Meyer-Overton concept?

A

vapor potency is directly related to fat solubility

47
Q

why is it harder to wake obsese patients? N2O and sevoflurane equilibrium time?

A
  • fat is a resovoir
  • N2O equilibrium ½ time is 70-80min
  • Sevoflurane equilibrium is over 30 hours
48
Q

Alveolar Gas Equation

A

PAO2 = (760 – 47) x FiO2 – (PaCO2 / 0.8)

49
Q

What is the concentration effect?

A
  • The higher the inspired concentration the less FA is affected by uptake
  • Even if the solubility is the same, the more concentrated the gas, the less uptake
    • FA is reached faster
50
Q

What is the second gas effect?

A
  • 1st gas with high concentration, 2nd gasses uptake is quicker
  • Typical with N2O
51
Q

V/Q mismatch and its affect on anesthetics?

A
  • V/Q mismatching increases the alveolar-arterial difference
  • Mismatch redirects bloodflow – raises pressure in front of restriction, lowers pressure beyond the restriction, and reduced flow through the restriction
    • AKA increases alveolar partial pressure and decrease in arterial partial pressure
    • More with soluble agents
52
Q

Maintenance of anesthetics (flow rate)

A
  • Flow rates reduced to maintain steady state of anesthetic level and provide constant replenishing to the alveolar concentration
  • Higher solubility, higher uptake for long time
53
Q

What is emergence? Factors?

A
  • recovery = lowering concentration in brain tissue
  • cannot overpressure to offset effects of solubility, less adjustable factors, timing is key
  • more rapid recovery with insoluble agents
  • the longer the anesthesia, the longer the washout, and the more deposits in reservoirs with long time constraints
54
Q

4 methods of elimination of anesthetics?

A
  1. biotransformation
  2. transcutaneous loss
  3. exhalation
  4. ALVEOLUS * most important
55
Q

Why does diffusion hypoxia occur?

A
  • Large amounts of N2O is released into the alveoli during the first 5-7min of recovery which dilutes the oxygen → hypoxia
  • N2O is 32-34x more soluble than nitrogen or oxygen even though it is insoluble
56
Q

How to prevent diffusion hypoxia?

A
  • If pt is on N2O preoxygenate with 100% supplemental oxygen for 10 min to prevent the hypoxia
  • Works better with shorter cases. The longer the case, the longer the fat continues to take up anesthetics
57
Q

What is MAC?

A

MAC = minimal alveolar concentration to prevent response with 50% of people

58
Q

What is MAC awake?

A

1/3 MAC = open eyes, safe airway

Lower in elderly and with narcotics, temp changes, acute alcohol use, hypotension, pregnancy, hyponatremia, hypercalcemia.

Decreases 6% per decade

59
Q

When do you get no recall?

A

0.33 MAC

pt may still move, but there is hypnosis

60
Q

What patient population would have faster emergence?

A

Pediatrics

61
Q

List factors that effect the rate of recovery from inhalation anesthetics

A

CO, PP gradient, solubility of coefficient

62
Q

When are tissue solubility coefficients important?

A

?

63
Q

Why do the time constants for the VRG, MG, and FG differ?

A

?

64
Q

What are atoms? ions? charge?

A

Atoms = what compose molecules

Ions = charged atoms

Charge = bonds between atoms

65
Q

Chemical structure of anesthetics?

A

Ethers

R-O-R’

66
Q

Density? How temp affects it?

A

Mass / Volume

IN-Direct relationship b/w temp and density

temp increase → material expands and density decreases

Temp decrease → density increases

67
Q

2 properties of flow?

A

Laminar and Turbulent

Laminar R^4 and Turbulent = Reynolds #

68
Q

Volume

A

Size of container

gas fills to fit containers shape

69
Q

Pressure

A

Force / Unit Area

molecules hitting the membrane

faster movement, higher pressure

70
Q

4 methods of heat transfer?

A

Conduction – cold from the table

Radiation – common in the OR

Convection
Evaporation – pt breathes out

71
Q

What is Vapor?

A

Vapor = gas that exists as a liquid at room temp and 1 ATM = 760mmHg = 101kPa

72
Q

Vapor Pressure?

A
  • saturated vapor pressure = pressure gas exerts in ATM above liquid phase
  • Dependent on temp and agent… temp increase, VP increases
  • maximum pressure exerted by a gas that can also exist as a liquid under standard conditions
  • max PP of vapor at a specific temp
73
Q

What is Latent Heat of Vaporization?

A

Latent Heat of Vaporization = calories req to change 1mL of gas and break the bonds holding it together

74
Q

Boyles Law

A

Temperature Constant

Pressure and Volume INVERSE relationship

V1/V2 = P2/ P1

75
Q

Charles Law

A

Pressure is constant

Temp and Volume have direct relationship

76
Q

Gay-Lussacs Law

A

Volume is constant

Temp and Pressure direct relationship

77
Q

Avogadros #

A
  • 6.02 x 10^23
  • PV = nRT
  • GMW ideal gas occupies 22.4L witih avo # of molecules
78
Q

Dalton’s Law

A
  • Daltons Law; any gas that exerts a partial pressure in a mix of gasses is proportional to the % concentration of the gas
    • 1% of sevoflurane = 7.6 mmHg of 760mmHg
    • At sea level, air is 21% O2, PP of O2 in air = 0.21 x 760mmHg = 159mmHg
79
Q

Henry’s Law

A
  • Henrys Law; constant temp, the amount of a given gas that dissolves in volume is directly proportional to the partial pressure of gas in equilibrium with that liquid
    • As temperature drops gasses are more soluble, longer to reach equilibrium

Anesthesia-phar (18 decks)

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