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Pharmacology > Pharmacology of Inhalant Anesthetics > Flashcards

Pharmacology of Inhalant Anesthetics Flashcards

1
Q

What makes inhalant anesthetics unique from other drugs?

A
  • Administered & eliminated through the lungs
  • onset & offset does not depend on liver or kidney function
  • predictable & rapid titration of anesthesia
  • requires a specialized device for delivery
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2
Q

What is the anesthesia triad?

A

Anti-nociception > Unconsciousness > Muscle relaxation

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3
Q

When and what were the first inhalant anesthetics used?

A

1840; Chloroform, diethyl ether, nitrous oxide

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4
Q

How many inhalant agents are used in vet med and what are they?

A

4; Isoflurane, Desoflurane, Sevoflurane, and Nitrous oxide

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5
Q

Why are physiochemical characteristics important?

A
  • determines actions & safety
  • determines how they are supplied & delivered
  • determines how they interact with other substances within the anesthetic machine
  • determines equipment used for delivery
  • determines uptake, distribution, & elimination
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6
Q

What are some organic compounds for inhalant agents?

A

Modern inhalants: isoflurane, sevoflurane, desflurane

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7
Q

What’s an example of an inorganic compound in inhalant agents?

A

Nitrous oxide

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8
Q

Modern inhalants are ______ and have an _______

A

Halogenated; ether bond

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9
Q

What is halogenation?

A

Addition of Cl, Br, or F

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10
Q

What are the effects of halogenation?

A

-decreases reactivity, increases potency, makes inhalants non-flammable, toxicity still possible (esp. with F)

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11
Q

What is the effect of the ether bond in inhalants?

A

Makes them less arrhythmogenic

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12
Q

What are the properties determining how inhalants are administered?

A

-vapor pressure -boiling point -liquid density/specific gravity

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13
Q

What are the properties determining how inhalants travel around the body?

A
  • solubility
  • blood:gas partition co-efficient
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14
Q

What does the change in the state of matter depend upon?

A

Molecular motion and degree of intramolecular attraction

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15
Q

Define gas

A

an agent that exists in gaseous form at room temperature and atmospheric pressure

Example: Nitrous oxide

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16
Q

Define vapor

A

Gaseous state of an agent that exists as a liquid at room temperature and atmospheric pressure -example: isoflurane, sevoflurane, desflurane

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17
Q

Inhalants existing as a ____ still have the same physical properties as a _____ when it exists in its ____ form

A

Vapor

Gas

Gaseous

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18
Q

What is partial pressure?

A

The pressure an individual gas exerts on the walls of a closed container; it is an absolute value

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19
Q

What is Dalton’s Law of Partial Pressure?

A

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

20
Q

What are 3 ways to quantify inhalants?

A
  • pressure (mmHg)
  • concentration (%) - most often
  • mass (grams or milligrams)
21
Q

Inhalant concentration changes relative to the concentration of what?

A

The whole gas mixture

  • vol% changes relative to atmospheric pressure
  • vol% may be different in various body compartments while partial pressure is the same if the inhalant agent is in equilibrium b/t body compartments
22
Q

How would you calculate the percent of an agent to be used in a vaporizer, given the total pressure and the alveolar pressure of that agent?

A

(Alveolar pressure (Pa)/total pressure)x100 = % of that gas

Ex:

Total pressure = 760 mmHg

Pa of ISO = 15 mmHg

15mmHg/760mmHg x 100 = 2%

23
Q

Define vapor pressure

A

The pressure vapor molecules exert when the liquid and vapor phases are in equilibrium

24
Q

Define saturated vapor pressure

A

Maximum concentration of molecules in the vapor state that exists for a given liquid at a given temperature

25
Q

What is the practical difference between a gas and a vapor?

A

Gas: administer from 0-100% concentration

Vapor: maximum delivered concentration depends on its saturated vapor pressure

26
Q

What happens to vapor pressure as temperature decreases and why?

A

It decreases; evaporation > cooling > decreased vapor pressure > decreased delivered vapor concentration

27
Q

What is the vapor pressure of isoflurane?

A

238mmHg

28
Q

What is the vapor pressure of sevoflurane?

A

157mmHg

29
Q

What is the vapor pressure of Desflurane?

A

669mmHg

30
Q

What happens if someone pours Isoflurane into a Sevoflurane vaporizer and delivers 3% of the agent?

A

Increased output from the vaporizer > potential anesthetic OVERDOSE (deliver more Iso using Sevo vaporizer) Vapor pressure of Iso (238mmHg) > Vapor pressure of Sevo (157mmHg)

31
Q

Define gas solubility

A

The total number of gas molecules dissolved in a solvent; expressed as a partition coefficient

32
Q

The amount of gas dissolved into a solvent (its solubility) depends on _____

A
  • partial pressure gradient b/t gas and solvent -chemical nature of the gas (molecular weight) -chemical nature of the solvent
33
Q

Each inhalant has a different solubility in blood, True or False?

A

True

34
Q

Why is gas solubility important?

A

Blood:gas partition coefficient can help predict SPEED of anesthetic induction, recovery, and change of depth - lower blood:gas partition coefficient = FASTER onset & recovery - the more soluble a gas is = the SLOWER the onset & recovery

35
Q

Why do drugs with lower solubility have faster onset?

A

Because agents with low solubility quickly saturated the blood, so additional anesthetic molecules are then readily transferred to the brain

36
Q

You are performing isoflurane anesthesia on aortic foxes in the Alaskan wilderness in December. Your team is having a difficult time keeping the foxes anesthetized. What is the problem?

A

The vapor pressure of isoflurane is decreased because of the low ambient temperature -Lower temp > lower saturated vapor pressure > less inhalant will be available for anesthetic

37
Q

What are the principal sites of action of inhalant anesthetics and what are the effects at each site?

A

-Brain (amnesia) -Spinal cord (immobility) - partial pressure of anesthetic in the brain/spinal cord produces anesthesia

38
Q

What is the Minimum Alveolar Concentration (MAC)?

A
  • Minimum alveolar concentration of an anesthetic that prevents gross, purposeful movement in 50% of patients exposed to a noxious stimulus
  • describes the dose of anesthetic being delivered
  • MA = ED50
  • ED95 = 20-40% MAC (humans)
  • Potency = 1/MAC
39
Q

Which gas has the highest MAC?

A

Desflurane (6-8%)

40
Q

MAC range of Sevoflurane

A

2.2-3%

41
Q

MAC range of Desflurane

A

6-8%

42
Q

Why can’t we use Nitrous Oxide as a sole anesthetic?

A
  • It has a very high MAC
  • has half the potency in non-human species
  • usually given concurrently to lower MAC of other agents
43
Q

What factors increase MAC?

A
  • Hyperthermia
  • Hypernatremia
  • Drugs causing CNS stimulation
  • Increased levels of excitatory NTs
44
Q

What factors decrease MAC?

A
  • Other anesthetics
  • Hyponatremia
  • Hypotension (MAP<50mmHg)
  • Hypothermia -PaO2 below 40mmHg
  • PaCO2 above 90mmHg
  • Pregnancy -Inc age
45
Q

Factors that don’t affect MAC

A
  • Gender
  • Normal resp gas concentrations
  • Duration of anesthesia
  • Metabolic acidosis/alkalosis
  • Mild to moderate anemia

Pharmacology (33 decks)

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