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Pharmacology Test 3 > Inhalent Anesthetics (Gatson) > Flashcards

Inhalent Anesthetics (Gatson) Flashcards

(41 cards)

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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

Study These Flashcards
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

Study These Flashcards
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 %

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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

Study These Flashcards
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

Study These Flashcards
A

15mmHg/630mmHg = 2.4%

Lower alveolar pressure in colorado

22
Q
  1. Vapor Pressure
  2. Saturated vapor pressure
Study These Flashcards
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

24
Q

Temp Decrease

vs

Evaporation

Study These Flashcards
A

Temp Decrease => vapor pressure decreases

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

25
Boiling point
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
Iso in a Sevo vaporizer at 3%....?
Iso vapor pressure (238mmHg) \> Vapor pressure of Sevo (157mmHg) Potential anesthetic overdose Clean by running high concentration O2 for long period of time
27
**SOLUBILITY**
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
Solubility expressed as
**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
Importance of solubility
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
Summary
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 6. Temperature affects vapor pressure and solubility * Important in hypothermia = wake up slower
31
Which anesthetic agent has fastest onset time at similar conditions
Nitrous Oxide Lowest blood:gas partition coefficient
32
MOA
Three theories * 1. Protein Receptor Hypothesis * Inhalants bind to membrane protein and alter structure * 2. Neurotransmitter Availability * Inhalants prevent breakdown of GABA * 3. Meyer-Overton Theory * Lipid soluble agents occupy hydrophobic regions of molecules in CNS distorting membrane proteins
33
What we know about mechanism of action
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
Potency
Dose required to reach a desired effect Potency doesn't equal Efficacy
35
MAC
Minimum alveolar concentration of anesthetic that prevents gross, purposeful movement in 50% of exposed patients. MAC = ED50 Higher the MAC, lower the potency
36
Important MAC values
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
Nitrous oxide
Human MAC = 100% Other spp MAC = 200% **(not very potent)** Can't be used alone Can lower MAC of other agents
38
MAC can change based on
Kind of MAC * Surgical * intubation * awake Determination made in healthy dogs in absence of other drugs
39
Factors that INC MAC
Hyperthermia Hypernatremia Drugs causing CNS stimulation Increased levels of excitatory NTs
40
Factors that DEC MAC
Other anesthetics Hyponatremia Hypotension (MAP \< 50 mmHg) Hypothermia PaO2 below 40 mmHg PaCO2 above 90 mmHg Pregnancy Inc Age
41
Factors that DON'T affect MAC
Gender Normal resp gas concentrations Duration of anesthesia Metabolic acidosis/alkalosis Mild to moderate anemia

Pharmacology Test 3 (12 decks)

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