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Pharmacology > Inhalation Anesthesia 2 > Flashcards

Inhalation Anesthesia 2 Flashcards

1
Q

What are the four main components to general anesthesia?

A
  1. Unconsciousness.
  2. Immobility.
  3. Analgesia.
  4. Amnesia
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2
Q

What is the goal of General Anesthesia?

A

To produce and maintain a constant partial pressure of inhalational anesthetic in the brain. The mechanism to accomplish this is to produce a partial pressure in the alveoli (PA), which produces a partial pressure in the blood (Pa), which in turn produces a partial pressure in the brain (Pbr).

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3
Q

Uptake and distribution can be divided into 4 phases, What are they?

A
  1. Developing an inspired anesthetic concentration.
  2. Developing an alveolar anesthetic concentration.
  3. Developing a blood anesthetic concentration.
  4. Distribution of the anesthetic agent from the blood to the tissue.
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4
Q

What is a “wash-in”?

A

Using high flows of delivery gas (o2 and o2/n2o) at 5-10L/min which can precisely control the partial pressure of an anesthetic agent inspired and accomplish what is called a “wash-in”

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5
Q

What is the concentration effect?

A

Initial phenomenon with inhale d anesthetics- pt will increase MV with the addition of anesthetic gas administration.

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6
Q

Why does the concentration effect occur?

A

High concentrations of inspired anesthetics are rapidly removed from the lungs by the blood. This creates a drive to increase MV because of the decrease in fraction of O2 inspired.

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7
Q

How does concentration effect, effect the way we give anesthesia?

A

If doing inhalation induction, the patient will begin to breath faster initially and this will speed up the induction process.

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8
Q

The rate at which the alveolar partial pressure of the anesthetic rises is determined by what 2 factors?

A
  1. Inspired concentration.

2. Alveolar ventilation.

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9
Q

What is the “Second Gas Effect”?

A

When concurrent administration of N2O and another inhaled agent is performed, the N2O will speed up the blood brain barrier crossing of the other gas.

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10
Q

What are the three factors that determine how rapidly anesthetics pass from the inspired gases to the blood?

A
  1. Solubility of the agent in the blood.
  2. Rate of blood flow through the lungs (CO).
  3. Partial pressure of the agents in the arterial/venous blood (Pa)
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11
Q

What formula represents the ratio of anesthetic concentration in the blood to the anesthetic concentration in a gas (alveolar)?

A

Pa/PA.

Anesthetic Blood concentration Anesthetic Alveolar Concentration

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12
Q

How does a high CO effect anesthetic agents effect on the brain?

A

A high cardiac output is moving blood quickly, but it does not give much time for PP to build up in the brain. So CO is inversely related to uptake of anesthetic gas in the brain.

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13
Q

What two things determine the rate at which partial pressure of a given tissue will match partial pressure of the blood going to it?

A
  1. Solubility of the gas in tissues.

2. Tissue blood flow (as blood flow increases, uptake increases)

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14
Q

Describe Stage 3 of Anesthesia:

A 
Breathing pattern more normal.
More eye reflexes are lost.
Laryngeal reflexes start to be blocked.
Wont respond to incision.
Muscular tone begins to be blocked
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15
Q

Describe Stage 1 of Anesthesia:

A

Faster RR, lower TV. Eye lid reflex disappears.

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16
Q

Describe Stage 2 of Anesthesia:

A 
Breathing erratic.
Eye divergence.
Tense/struggling muscle tone.
Secretion of tears increases.
Swallowing/retching/vomitting possible.
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17
Q

Which stage of anesthesia is considered too deep?

A

Stage 4

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18
Q

Which stage of anesthesia do we NEVER extubate in?

A

Stage 2.

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19
Q

Which stage of anesthesia can be extubate in?

A

Stage 1 and Stage 3.

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20
Q

Which stage of anesthesia is sometimes called the “excitatory phase”?

A

Stage 2.

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21
Q

Which stage of anesthesia is vomiting the most possible?

A

Stage 2

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22
Q

Describe the beginning and end of stage 1 of anesthesia?

A

Begins with administration of anesthesia and ends with the loss of consciousness.

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23
Q

Which stage is considered Surgical Stage of Anesthesia?

A

Stage 3

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24
Q

Describe beginning and end of Stage 3 of anesthesia:

A

Movement into this stage is characterized by the return of regular respiration, excitement subsides, pupils become centered. Cough/gag/eyelid reflex are absent.

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25
Q

Describe what is actually happening in the brain in Stage 1 of Anesthesia:

A

Brain gas tension is very low. Dorsal horn activity decreases and there is decreased synaptic transmission in the spinothalamic tract.

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26
Q

Describe beginning and end of Stage 2 of anesthesia?

A

Extends from the loss of unconsciousness to the beginning of surgical anesthesia.

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27
Q

Why is Stage 2 a stage of delirium/excitement?

A

The Pbr rises and there is blockade of inhibitory neurons, which enhances and facilitates synaptic transmission.

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28
Q

Current guideline’s signs of “light” anesthesia?

A 
Increased RR.
Increased BP, HR.
Increased muscle tone.
Swallowing, coughing return.
Tear formation.
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29
Q

Current guideline’s signs of “deep” anesthesia include?

A

Hypotension.
Diaphragmatic breathing (agonal).
Pupils dilate and lack luster.
Bradycardia.

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30
Q

Definition of MAC?

A

The PP of an inhaled agent at 1atm that prevents skeletal muscles movement in response to a surgical skin incision in 50% of the patient population.

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31
Q

What is a reliable indicator of dose and potency of an anesthetic?

A

MAC

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32
Q

What should titration of an inhaled gas go off of on the monitor?

A

The fraction of expired gas (NOT the Mac number)

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33
Q

Does a potent inhaled agent have a higher or lower MAC?

A

Has a lower MAC.

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34
Q

Factors that decrease MAC (will require less agent)?

A 
Hypoxia.
Anemia.
Hypotension.
Drugs-lithium, narcs, sedatives, calcium channel blockers.
Acute Alcohol ingestion.
Pregnancy.
Elderly.
Decreased CBF, CMRO2
35
Q

Factors that increase MAC (will require more agent)?

A

Infants.
Hyperthermia.
Chronic Alcohol, barbs, or narc use.

36
Q

What electrolyte abnormalities effect MAC?

A

Hypercalcemia decreases.
Hypernatremia Increases.
Hyponatremia decreases.

37
Q

Do local anesthetics increase or decrease MAC?

A

Decrease (except cocaine).

38
Q

At 1 MAC, what % of patients will not move?

A

50%

39
Q

At 1.2 MAC, what % of patients will not move?

A

95%

40
Q

At 1.3 MAC, what % of patients will not move?

A

99%

41
Q

Define MAC-Awake:

A

The minimum alveolar concentration at which 50% of subjects will respond to the command “open your eyes”.

42
Q

What MAC value is considered MAC-awake?

A

1/3 MAC

43
Q

Define MAC-BAR:

A

The MAC necessary to block adrenergic response to skin incision.

44
Q

Define MAC-Intubation:

A

Similar to MAC-BAR in that its values exceed the anesthetic requirements for surgical skin incision.

45
Q

MAC deflurane?

A

6

46
Q

MAC isoflurane?

A

1.15

47
Q

MAC Nitrous Oxide?

A

104

48
Q

MAC Sevoflurane?

A

2.2

49
Q

50% N2O and 6% desflurane is how much MAC?

A

1.5MAC

50
Q

1.1% Sevo and 25% N2O is how much MAC?

A

0.75MAC

51
Q

0.6% isoflurane and 50% N2O is how much MAC?

A

1MAC

52
Q

What two ways are anesthetics gases eliminated from the body?

A

Hepatic metabolism and exhaled from lungs

53
Q

Input of anesthetic gas into the alveoli is determined by three things:

A
  1. Inspired partial pressure,
  2. Alveolar Ventilation,
  3. Characteristics of the breathing system
54
Q

Uptake of anesthetic gas into the arterial blood is determined by three things:

A
  1. Solubility or “blood/gas partition coefficient”,
  2. Cardiac Output,
  3. Alveolar to venous partial pressure difference.
55
Q

Transfer of anesthetic gas from the arterial blood to the brain is determined by three things:

A
  1. Brain-blood (oil/blood) partition coefficent,
  2. Cerebral blood flow,
  3. Arterial to venous partial pressure difference.
56
Q

Is a higher or low Pi (inspired partial pressure) required during initial administration of an inhaled anesthetic?

A

A High Pi.

57
Q

Why is a high Pi required during initial administration of a gas?

A

This offsets the impact of uptake into the blood and accelerates the rate of induction.

58
Q

The effect of Pi (inspired partial pressure) is known as what?

A

Concentration effect.

59
Q

Give a clinical example of the use of concentration effect:

A

If you want a fast onset of a drug, increase the % (even above the MAC of the gas)

60
Q

What other effect is the concentration effect related to?

A

Second Gas effect because the N2O is creating a concentration effect.

61
Q

Define Second Gas Effect:

A

The ability of the large-volume uptake of one gas (first gas) to accelerate the rate of increase of the PA (PP of Alveoli) of a concurrently administered companion gas (second gas)

62
Q

Does hyperventilation or hypoventilation facilitate a faster induction?

A

Hyperventilation increases induction and hypoventilation decreases induction

63
Q

At what two time periods are high fresh gas flows usually used during a case?

A

Induction and emergence

64
Q

Define partition coefficient:

A

A distribution ratio describing how the inhaled anesthetic distributes itself between two phases at equilibrium (when the partial pressures in the two phases are identical)

65
Q

What is the blood-gas partition coefficent of N2O?

A

0.46

66
Q

What is the blood-gas partition coefficient of Halothane?

A

2.54

67
Q

What is the blood-gas partition coefficient of sevoflurane?

A

0.65

68
Q

What is the blood-gas partition coefficient of isoflurane?

A

1.46

69
Q

What is the blood-gas partition coefficient of desflurane?

A

0.45

70
Q

What is the Vapor pressure of sevoflurane?

A

160

71
Q

What is the vapor pressure of desflurane?

A

669

72
Q

What is the vapor pressure of isoflurane?

A

240

73
Q

What does a high blood-gas partition coefficient mean?

A

Means a large amount of inhaled anesthetic must be dissolved (undergo uptake) in the blood before equilibrium with the gas phase (in the alveoli) is reached

74
Q

Increased cardiac output will result in increased or decreased induction speed?

A

Decreased induction speed

75
Q

Does a right-to-left intracardiac shunt slow or speed induction?

A

Slows the rate of induction

76
Q

Why does a right-to-left shunt slow induction speed?

A

Because it bypasses the lungs (and therefore bypasses uptake from the alveoli)

77
Q

Complete equilibration of any tissue requires how many time constants?

A

3 time constants

78
Q

Approximately how long does it take for equilibration of anesthetic gases between tissues?

A

After 6-12 minutes, 75% if the returing venous blood flow is at the same partial pressure as the PA

79
Q

What will hypoventilation (or low FGF) during emergence do?

A

Will lead to transfer of anesthetic back into the tissues delaying patient recovery.

80
Q

What two things can be done to speed emergence from an anesthetic?

A

High FGF and hyperventilation

81
Q

What is diffusion hypoxia?

A

Can occur during emergence as a result of N2O abruptly being discontinued. The N2O in the blood diffuses rapidly across capillary/alveoli membrane which dilutes the O2 concentration and can be seen as decrease in PaO2.

82
Q

What can be done to easily avoid diffusion hypoxia?

A

Administering 100% O2 for 5-10 minutes after the N2O has been discontinued.

83
Q

Elimination of all but small amounts of anesthetics must take place for the patient to regain which two coordinated functions?

A
  1. Ability to swallow,

2. Effective respiratory effect.

Pharmacology (9 decks)

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