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Foundations- Anesthesia > General Anesthetics: Pharmacology and Clinical Use Part 1 > Flashcards

General Anesthetics: Pharmacology and Clinical Use Part 1 Flashcards

1
Q

why do we use inhalants? (5)

A
  1. use of lungs for delivery and elimination
  2. do not depend on hepatic or renal function
  3. rapid and precise adjustment of anesthetic depth
    -can measure how much giving at any point during anesthetic event
  4. rapid and complete recovery
    -recovery may take longer because have to breathe off all inhalant from body
    -but not as smooth recovery as injectables
  5. control/maintain anesthesia induced by injectables
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2
Q

can you use inhalants alone?

A

yes but not recommended! not super safe to animal or those around and will have an excitatory phase; requires bulky and expensive equipment

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3
Q

how are all inhalants administered?

A

as vapor! some is liquid and some is gas

a gaseous state with a critical temperature greater than room temp

critical temp is the temp above which only gas exists

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4
Q

what is vapor pressure?

A

pressure exerted by a vapor when it exists in equilibrium with its liquid state

measured in mmHg in US

-dalton’s law of partial pressure:
Ptotal= P1+P2+P3…

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5
Q

describe vapor pressure of inhalants

A

relationship between vapor pressure and maximal pressure

vapor pressure/barometric pressure X 100 = vol %

if change altitude, will not affect vapor pressure, but volume % will change! but doesn’t really matter as long as the partial pressure of the brain is the same

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6
Q

describe solubility

A

solids or gases dissolved in liquid; solute + solvent = solution

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7
Q

describe solubility of inhalants

A
  1. inherent property of the vapor/gas
    -temperature dependent
    -defined as total amount of vapor dissolved within a solute at equilibrium (no net movement)
  2. vapors/gases move from areas of higher partial pressure to lower partial pressure (gradient)
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8
Q

describe partition coefficients

A
  1. ratio of the vol% of vapor in one phase compared to the vol% in another phase
  2. blood/gas partition coefficient: relative affinity of an anesthetic vapor for blood compared to alveolar gas
  3. partial pressure is the same in both phases!!
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9
Q

describe MAC/potency

A

the alveolar concentration of an inhalant anesthetic required to prevent movement in 50% of a given patient population when exposed to a noxious stimulus

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10
Q

how is MAC measured?

A

use only the inhalant with the species with the face mask; test

if move, go up, it no move no more, go down, find sweet spot

do again with another animal

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11
Q

what does MAC tell us? how is it used?

A

the lower the MAC, the more potent the anesthetic

used to compare anesthetics:
-rule of thumb (MAC x 1.5) because don’t want to be sitting right at MAC or patient may move in surgery

-ED50 vs ED95

-MAC is additive among multiple inhalants (if using 2 inhalants, can use less of each; not done though)

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12
Q

what is the average MAC for isofluorane and sevofluorane across species?

A

iso: 1.3

sevo: 2.3

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13
Q

what factors increase MAC (make you need more inhalant?)

A
  1. hyperthermia
  2. hypernatremia
  3. increased levels of excitatory neurotransmitters
    -cocaine, amphetamines
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14
Q

what factors decrease MAC? (make you need less inhalant)

A
  1. increased age
    -exception: neonates need less inhalant in first week of life then increase as grow up then decrease when old
  2. hypothermia
  3. hyponatremia
  4. severe hypotension
  5. severe hypercarbia
  6. severe hypoxemia
  7. metabolic acidosis
  8. other anesthetics
  9. pregnancy
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15
Q

what factors do NOT affect MAC?

A
  1. duration of anesthesia
  2. gender
  3. alkalosis
  4. hypertension
  5. anemia
  6. changes in most electrolytes
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16
Q

what characteristic of anesthetic in brain produces anesthesia? describe

A

partial pressure! NOT concentration

brain partial pressure equilibrates quickly with alveolar partial pressure and brain partial pressure always moves TOWARDS alveolar partial pressure

17
Q

describe the alveolar bucket concept

A
  1. the alveoli are like a bucket that are being filled, but have a leak (uptake)
  2. you can increase delivery by:
    -increasing inhaled partial pressure
    -increasing alveolar ventilation: delivers anesthetic from the breathing circuit to alveoli
    –if animal has apnea following propofol, breathe for them!!- hook them up!!
  3. you can decrease the leak/uptake factors by
    -decreasing solubility
    -decreasing cardiac output
    -decreasing the alveolar venous partial pressure difference
18
Q

how do you increase the inhaled anesthetic partial pressure? (3) (to increase delivery)

A
  1. turn up the vaporizer
  2. increase the fresh gas flow
  3. minimize the volume of the breathing circuit
19
Q

describe decreasing solubility to decrease the leak to achieve faster equilibration between alveoli and brain

A

the higher the solubility, the slower the partial pressure rise is going to be, because now has to go through a sponge (dissolve)

20
Q

describe decreasing cardiac output to achieve faster equilibration between alveoli and brain

A

using a facemask technique, you will induce general anesthesia faster in a dog with a LOW cardiac output

the bigger the pool, the more dilute the inhalant, the smaller the pool, the more concentrated the inhalant
-think food dye in a cup of water versus food dye in a bathtub

21
Q

describe decreasing the alveolar-venous partial pressure difference

A

if partial pressure difference is smaller, will get to equilibrium (FA/FI=1) very quickly

lots of movement of anesthetic from alveoli at beginning of anesthetic event but as time goes on, gas will stop moving away from alveoli as reach 1 and settle into equilibrium

22
Q

describe elimination of inhalant anesthetics

A

now want to increase partial pressure difference between brain and alveoli to speed up recovery!

  1. reverse of uptake
    -can’t use over pressure: vapor and oxygen up which increases PP in alveoli very high but can’t deliver less than zero percent??

-can use high fresh gas flows to flush machine so that inhalant wants to flow out

  1. effect of duration: use context sensitive decrement (flushing out the machine using fresh O2)
    -the longer the anesthetic event, the longer it takes to recover from anesthesia (breathe off inhalant)
    -after long enough you reached equilibrium, which will take longer to get rid of
23
Q

describe isoflurane general info

A
  1. most commonly used inhalant
  2. color code is purple
  3. no preservative needed
24
Q

describe isoflurane systemic effects

A

respiratory: dose dependent depression

cardiovascular:
-dose related hypotension
-primarily vasodilation

GI: hepatic metabolism approx 0.2% (not clinically significant)

renal: none

muscular: excellent relaxation

uterus/fetus: crosses placenta, rapidly inhaled

NO ANALEGSIA

25
Q

describe isoflurane clinical use

A

MAC: 1.3% (more potent than sevo)

vaporizer settings:
induction: 3-5%
early anesthesia: 2-3%
maintenance: 1-2.5%

other considerations: depth changes slowest among modern inhalants

26
Q

describe sevoflurane general info

A
  1. very popular
  2. color code: yellow
  3. no preservative needed
27
Q

describe systemic effects of sevoflurane

A

respiratory: dose dependent depressiom

cardiovascular:
-dose related hypotension
-vasodilation

GI: hepatic metabolism approx 5% (not clinically significant)

renal: compound A

muscular: excellent relaxation

uterus/fetus: crosses placenta, rapidly exhaled

NO ANALGESIA

28
Q

describe sevoflurane clinical use

A

MAC 2.3% (less potent than iso)

vaporizer settings:
-induction: 5-7%
-early anesthesia: 2-5%
-maintenance: 1.5-4%

other considerations: depth changes quickly

29
Q

describe desflurane

A
  1. least soluble inhalant available
  2. color code: blue
  3. requires a special vaporizer: heated, pressurized, electronic control
  4. may irritate airway
30
Q

describe systemic effects of desflurane

A

respiratory: dose dependent depression

cardiovascular:
-dose related hypotension
-vasodilation + myocardial depression

GI: not metabolized in anyway!

renal: none

muscular: excellent relaxation

uterus/fetus: crosses placenta, rapidly exhaled

NO ANALGESIA

31
Q

describe desflurane clinical use

A

MAC: 8% (low low potency)

vaporizer settings:
-induction: 15-18%
-early anesthesia: 12-15%
-maintenance: 8-12%

other considerations: depth changes VERY quickly

Foundations- Anesthesia (8 decks)

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