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Pharmacology Test 3 > Inhalent Anesthetics (Gatson) > Flashcards

Inhalent Anesthetics (Gatson) Flashcards

1
Q

Inhalent anesthetics

about/general

A

Administered and eliminated through the lungs

Onset and offset doesn’t depend on liver/kidney function

Predictable and rapid titration of anesthesia

Requires specialized device for delivery and carrier gas

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2
Q

3 effects of inhaled anesthetics

A
  1. Antinociception
  2. Muscle Relaxation
  3. Unconsciousness
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3
Q

Hist:

A

1840: ether
1956: Halothane
1980s: Isofulrane
1990s: Sevoflurane

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4
Q

Inhalents used in vet med

A
  1. ISO
  2. SEVO
  3. DES
  4. Nitrous Oxide
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5
Q

Chemical Characteristics

Determine

A

Action and safety

Supply and delivery

Interactions with other substances w/in machine

Equiptment necessary for delivery

Uptake, distribution, elimination

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6
Q

Organic coumpounds:

Aliphatic

Ether

A

Aliphatic hydrocarbon

  • halothane

Ether

  • isoflurane
  • sevoflurane
  • desflurane
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7
Q

Inorganic compounds

A

Nitrous oxide

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8
Q

Halogenation

A

Addition of

  • CL
  • BR
  • F

Halogenation:

  • Dec reactivity
  • Inc potency
  • Makes non-flammable
  • Tox poss (esp w/ F)
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9
Q

Halogenation of Bromide and Chloride

A

Increases potency

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10
Q

Halogenation of Fluorine

A

Improves stability

  • Less natural decomposition
  • Less need for preservatives

Reduces

  • potency
  • solubility
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11
Q

Halothane vs Isofulrane

A

Halothane: Aliphatic hydrocarbon (no ether bonds)

  • requires preservative
  • Cardiac dysrhythmias
    • lack of ether bond
  • more potent (MAC 0.9%)
  • NO LONGER MARKETED

Isoflurane

  • No preservative
  • No arrhythmias (ether)
  • Less potent (MAC: 1.3%)
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12
Q

Properties determining administration of inhalants

A

Vapor pressure

Boiling Point

Liquid Density / Specific Gravity

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13
Q

Properties determining how inhalants travel around the body

A

Solubility

Blood:gas partition co-efficient

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14
Q

Inhalanet classification

Gas vs Vapor

A

Gas

  • exists in gaseous form at room temp and atmospheric temp
  • ex: nitrous oxide

Vapor: majority of our in. anest.

  • Gaseous state of an agent
  • liquid at room temp and atmospheric pressure
  • ex: isoflurane, sevoflurane, desflurane
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15
Q

Vapor physical properties

A

Properties same as gas when in gaseous form

Abide by GAS LAWS

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16
Q

Partial Pressure

A

Pressure an individual gas exerts on walls of a closed container

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17
Q

Dalton’s law of partial pressure

A

Total pressure of a mixture of gases is equal to sum of partial pressure of all the gaseous substances present

18
Q

Three wasy to quantify inhalants

A
  1. Pressure (mmHg) absolute value
  2. Concentration (%) relative value to concentration of whole gas mixture
  3. Mass (grams or milligrams)

*usually reported as concentration

19
Q

Vol %

A
  1. Changes relative to atmospheric pressure
  2. May be different in various body compartments
    * partial pressure is same if inhalant in equilibrium between body compartments
20
Q

Concentration example:

Florida Total Atmospheric pressure: 760mmHg

We want to deliver a PA of Iso = 15mmHg

A

15mmHg/760mmHg = 2%

Higher alveolar pressure in Florida

21
Q

Concentration example:

Colorado total pressure = 630mmHg

We want to deliver a PA of Iso at 15mmHg

A

15mmHg/630mmHg = 2.4%

Lower alveolar pressure in colorado

22
Q
  1. Vapor Pressure
  2. Saturated vapor pressure
A
  1. Pressure vapor molecules exert when the liquid and vapor phases are in equilibrium
  2. Maximum concentration of molecules in the vapor state that exists for a given liquid at a given temperature
23
Q

Vapor pressure can change based off

A

Temperature

24
Q

Temp Decrease

vs

Evaporation

A

Temp Decrease => vapor pressure decreases

Evaporation => cooling => dec vaport pressure => decreased delivered vapor concentration

25
Q

Boiling point

A
  1. Temp at which vapor pressure = atmospheric temp
  2. Boiling point decreases with increasing altitude
  3. Desflurane = boiling point close to room team
    * Only vapor that requires a source of heat
26
Q

Iso in a Sevo vaporizer at 3%….?

A

Iso vapor pressure (238mmHg) > Vapor pressure of Sevo (157mmHg)

Potential anesthetic overdose

Clean by running high concentration O2 for long period of time

27
Q

SOLUBILITY

A

Total number of gas molecules dissolved into a solvent

Amount of gas dissolved depends on

  • Partial Pressure gradient between gas and solvent
  • Chemical nature of gas (molecular weight)
  • Chemical nature of solvent

Solubility changes with temp

28
Q

Solubility expressed as

A

Partition coefficient

Blood : gas partition coefficient = 2.0

  • Blood (pulmonary blood): 2% to Gas (alveoli) : 1%

Blood : gas partition coefficient = 0.5

  • Blood: 1% to Gas: 2%
29
Q

Importance of solubility

A

Blood:gas partition coefficient

  • helps predict speed of anesthetic induction, recovery, change in depth
  • Lower blood:gas partition coefficient = faster onset and recovery
    • Sevo (low blood:gas partition therefore less solubility)
      • faster onset and recovery than iso
30
Q

Summary

A
  1. Most mod. inhalents halogenated organic compounds
  2. Majority mod. inhalents are vaport
  3. Vapor pressure determines how many molecules of inhalant avail. to prod. anesth.
  4. Saturated vapor pressure determines max conc of inhalant that can be delivered
  5. Solubility determines speed of onset and recovery from anesthesia
  • expressed as blood:gas partition coefficient
  • determines percentage of inhalant in blood vs alveoli
  1. Temperature affects vapor pressure and solubility
    * Important in hypothermia = wake up slower
31
Q

Which anesthetic agent has fastest onset time at similar conditions

A

Nitrous Oxide

Lowest blood:gas partition coefficient

32
Q

MOA

A

Three theories

    1. Protein Receptor Hypothesis
      * Inhalants bind to membrane protein and alter structure
    1. Neurotransmitter Availability
      * Inhalants prevent breakdown of GABA
    1. Meyer-Overton Theory
      * Lipid soluble agents occupy hydrophobic regions of molecules in CNS distorting membrane proteins
33
Q

What we know about mechanism of action

A

Principal cites of action

  • Brain (amnesia)
  • Spinal cord (immobility)

Partial pressure of anesthetic in brain/spinal cord produces anesthesia

Less anesthesia required for unconsciousness than immobility

34
Q

Potency

A

Dose required to reach a desired effect

Potency doesn’t equal Efficacy

35
Q

MAC

A

Minimum alveolar concentration of anesthetic that prevents gross, purposeful movement in 50% of exposed patients.

MAC = ED50

Higher the MAC, lower the potency

36
Q

Important MAC values

A

Dog: Iso: 1.14-1.5 / Sevo: 2.1-2.4

Cats: Iso: 1.28-1.6 / Sevo: 2.6-3.1

Horses: Iso: 1.3-1.6 / Sevo: 2.3-2.8

37
Q

Nitrous oxide

A

Human MAC = 100%

Other spp MAC = 200% (not very potent)

Can’t be used alone

Can lower MAC of other agents

38
Q

MAC can change based on

A

Kind of MAC

  • Surgical
  • intubation
  • awake

Determination made in healthy dogs in absence of other drugs

39
Q

Factors that INC MAC

A

Hyperthermia

Hypernatremia

Drugs causing CNS stimulation

Increased levels of excitatory NTs

40
Q

Factors that DEC MAC

A

Other anesthetics

Hyponatremia

Hypotension (MAP < 50 mmHg)

Hypothermia

PaO2 below 40 mmHg

PaCO2 above 90 mmHg

Pregnancy

Inc Age

41
Q

Factors that DON’T affect MAC

A

Gender

Normal resp gas concentrations

Duration of anesthesia

Metabolic acidosis/alkalosis

Mild to moderate anemia

Pharmacology Test 3 (12 decks)

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