Inhalant Anesthetics Flashcards Preview

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Flashcards in Inhalant Anesthetics Deck (79)
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1

Why use inhalant anesthetics?

1. Predictable effects
2. Rapid adjustment of anesthetic depth
3. Minimal metabolism
4. Economical

2

Nitrous oxide

- Low blood gas PC (0.47)
- Mild analgesic
- Accumulation in closed gas spaces

3

Xenon

Expensive, used mostly experimentally

4

Solubility

Anesthetic vapors dissolve in liquids and solids

Equilibrium is reached when the PP of the anesthetic is the same in each phase (pressure, not number of molecules)

5

Partition coefficient

Expression of solubility
Concentration ratio of an anesthetic in the solvent and gas phases, describes the capacity of a given solvent to dissolve an anesthetic

6

Blood-gas partition coefficient

Most clinically useful number

Describes amount of anesthetic in the blood vs. alveolar gas at equal partial pressure

7

What does the pressure of anesthetic in the alveolar gas represent?

Brain concentration- location of effect

8

T/F: Anesthetic in blood is pharmacologically active?

False

9

Most to least soluble anesthetics

Halothane= 2.54
Isoflurane= 1.46
Sevoflurane= 0.68
Desflurane= 0.42

10

Low blood-gas PC

1. Less anesthetic dissolved in the blood at an equal PP
2. Shorter time required to attain PP in brain
3. Shorter induction and recovery

Clinically more useful

11

High blood-gas PC

1. More anesthetic dissolved in the blood at an equal PP
2. Longer time required to attain PP in brain
3. Longer induction and recovery

Not very clinically useful

12

Effect of solubility on recovers

The lower the solubility, the faster the recovery

13

Order of inhalant uptake

Vaporizer > breathing circuit > alveoli > arterial blood > brain

14

Partial pressure in the brain is roughly equal to...

Partial pressure in the alveoli

15

Ways to increase partial pressure in the alveoli

1. Increase anesthetic delivery to alveoli
2. Decrease removal from the alveoli

16

Increased alveolar delivery

1. Increase inspired anesthetic concentration
2. Increase alveolar ventilation

17

How do you increase inspired anesthetic concentration?

1. Increase vaporizer setting
2. Increase fresh gas flow
3. Decrease breathing circuit volume

18

How do you increase alveolar ventilation?

1. Increase minute respiration
2. Decrease dead space ventilation

19

Decrease removal from alveoli

1. Decrease blood solubility of anesthetic
2. Decrease cardiac output
3. Decrease alveolar-venous anesthetic gradient

20

Concentration effect

The higher the inspired pressure the more rapidly alveolar pressure approachs inspired pressure

21

As uptake into blood decreases, inspired pressure can...

be decreased

22

A ____ inspired pressure is required at the beginning of gas anesthesia to quickly increase____

High, alveolar pressure

23

Anesthetic elimination

Requres decrease in alveolar concentraions

24

Anesthetic elimination is most effected by:

1. Anesthetic solubility
2. Alveolar ventilation

(same that effect alveolar concentration)

25

How do you quickly decrease alveolar concentration?

1. Turn off vaporizer
2. Disconnect patient and flush O2
3. Turn up O2 rate- dilutes the circuit
4. Increase ventilation (IPPV)- increase fresh gas to alveoli

26

Definition: Minimum Alveolar Concentration (MAC)

Minimum alveolar concentration of an anesthetic that prevents movement in 50% of patients exposed to noxious stimulus

27

Relationship between MAC and potency of an anesthetic

Inversely proportional

High MAC = low potency

28

T/F: Alveolar concentration is NOT the same as the vaporizer setting

True

29

How is MAC measured?

Percent of agent in expired gas

30

MAC: Halothane

Dog- 0.9%
Cat- 1%
Horse- 1%