Pharmacology of Inhalant Anesthetics Flashcards Preview

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Flashcards in Pharmacology of Inhalant Anesthetics Deck (45):
1

What makes inhalant anesthetics unique from other drugs?

  • 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

2

What is the anesthesia triad?

Anti-nociception > Unconsciousness > Muscle relaxation

3

When and what were the first inhalant anesthetics used?

1840; Chloroform, diethyl ether, nitrous oxide

4

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

4; Isoflurane, Desoflurane, Sevoflurane, and Nitrous oxide

5

Why are physiochemical characteristics important?

  • 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

6

What are some organic compounds for inhalant agents?

Modern inhalants: isoflurane, sevoflurane, desflurane

7

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

Nitrous oxide

8

Modern inhalants are ______ and have an _______

Halogenated; ether bond

9

What is halogenation?

Addition of Cl, Br, or F

10

What are the effects of halogenation?

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

11

What is the effect of the ether bond in inhalants?

Makes them less arrhythmogenic

12

What are the properties determining how inhalants are administered?

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

13

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

  • solubility
  • blood:gas partition co-efficient

14

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

Molecular motion and degree of intramolecular attraction

15

Define gas

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

Example: Nitrous oxide

16

Define vapor

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

17

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

Vapor

Gas

Gaseous

18

What is partial pressure?

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

19

What is Dalton's Law of Partial Pressure?

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

20

What are 3 ways to quantify inhalants?

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

21

Inhalant concentration changes relative to the concentration of what?

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

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?

(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

Define vapor pressure

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

24

Define saturated vapor pressure

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

25

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

Gas: administer from 0-100% concentration

Vapor: maximum delivered concentration depends on its saturated vapor pressure

26

What happens to vapor pressure as temperature decreases and why?

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

27

What is the vapor pressure of isoflurane?

238mmHg

28

What is the vapor pressure of sevoflurane?

157mmHg

29

What is the vapor pressure of Desflurane?

669mmHg

30

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

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

Define gas solubility

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

32

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

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

33

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

True

34

Why is gas solubility important?

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

Why do drugs with lower solubility have faster onset?

 

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

36

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?

 

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

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

 

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

38

What is the Minimum Alveolar Concentration (MAC)?

  • 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

Which gas has the highest MAC?

Desflurane (6-8%)

40

MAC range of Sevoflurane

 

2.2-3%

41

MAC range of Desflurane

6-8%

42

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

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

43

What factors increase MAC?

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

44

What factors decrease MAC?

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

45

Factors that don't affect MAC

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