Inhalation Agents Flashcards Preview

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Flashcards in Inhalation Agents Deck (40):
1

ideal inhalation agent

-poorly soluble
-non-pungent
-non-flammabe
-inexpensive
-easy to produce
-potent
-environmentally safe
-no hepatic metabolism
-not a trigger for malignant hyperthermia
-no emetogenic effects (all Vas do)

2

MAC

alveolar concentration at which 50% of patients wiil move to noxious stimuli

3

prevents movement in 95% of patients on incision

1.5 MAC (with no other meds)

4

1 MAC Halothane

0.76%

5

1 MAC Isoflurane

1.15%

6

1 MAC Sevoflurane

1.85%

7

1 MAC Desflurane

6.0%

8

1 MAC Nitrous Oxide

104%

9

MAC awake

-voluntary response to command
-usually 1/3 MAC
-Iso (38%), Sevo, Des
-MAC awake for N2O 64% (about 2/3)

10

MAC aware

-concentration at which patient can remember events/ loses ability to learn
-below MAC awake
-varies for different agents

11

MAC- BAR

-average alveolar concentration which blunts autonomic response to noxious stimulus
-2.2 MA for Sevo
-addition of Fentanyl decreases MAC BAR by 50%

12

site of action of IA

cell membranes in the CNS

13

goal of inhalational anesthesia

achieve a constant and optimal brain partial pressure (as reflected by PA/ET gas)

14

PA (ET gas) is used as an index of...

-depth of anesthesia
-recovery from anesthesia
-anesthetic equal potency (MAC)
(1 MAC of all IAs are equipotent, but they have their own individual potencies)

15

determinantes of PA

-input minus uptake
- delivery into the alveoli (input) minus loss of drug into the blood (uptake)

16

INPUT

-inhaled partial pressure
-alveolar ventilation and FRC
-characteristics of the anesthetic breathing system

17

UPTAKE

-solubility of the anesthetic in the blood
-cardiac output
-alveolar to venous PP differences (A-vD)

18

overpressure

-high initial Pi to help achieve the desired PA more rapidly, accelerating the rate of rise of PA to PBr
-Pi should be decreased as A-vD decreases to avoid overdose

19

How does hyperventilation effect the rate of rise of PBR?

-delays the rate of rise of PBr
-(no breathing= no uptake)
-(hypoventilation= delay in PBr)

20

IAs effect on ventilation

-dose dependent depression of ventilation

21

Spontaneous Ventilation under GA (IA)

-delivery of IA is decreased as spontaneous ventilation is decreased (protective against excessive anesthetic)

22

Mechanical Ventilation under GA (IA)

-no decrease in ventilations as PA approached FI (no feedback, may easily become too anesthetized)

23

characteristics of the breathing system that will increase the rate of rise of PA

-volume of the external breathing system
-solubility of the inhaled anesthetic in to the components of the breathing system
-FGF

24

as potency decreases, oswald....

-oswald coefficient decreases
-(decreased potency correlates to decreased solubility)

25

increased solubility is _____________ proportional to the rate of rise of PA toward the PI

inversely

26

intermediately soluble

Isoflurane

27

poorly soluble

Sevo, Des, N20

28

soluble

(no modern inhaled anesthetics)

29

95% equilibration of partial pressures b/w blood and tissue phases

3 time constants

30

Brain: Blood equilibration time

-5-15 minutes for volatiles (TCs 2-5 minutes)
-2 minutes for poorly soluble
-5 minutes for intermediately soluble

31

time constant formula

capacity/flow

32

cardiac output and uptake

-inc CO= inc uptake= slow rise in PA, slow inhalation induction
-dec CO= dec uptake= fast rise in PA, rapid induction

33

AvD

-difference between alveolar and venous pressure
-reflects tissue uptake of IA

34

AvD depends on...

-solubility of the agent in the tissue
-tissue blood flow
-arterial-tissue partial pressure differences

(uptake and equilibration within the vessel rich group is rapid- 3 TC, 5-15min)

35

titration of IA based on...

-patient response
-interactions with other medications
-degree of stimulation

36

IA reversible effects on CNS

-immobility (reversible, spinal cord mediated)
-amnesia (higher centers)

37

Meyer-Overton Hypothesis

-the MAC of a volatile anesthetic is inversely proportional to it's lipid solubility (oil: gas coefficient)
-MAC is inversely related to potency

38

5 Angstrom Theory

-proposes that anesthetics exert their effects on two different sites separated by a distance of 5 angstroms (maximal potency is achieved with a molecule 5 carbons long)

39

Multisite Theory of Narcosis

-inhaled anesthetics act by effects at multiple sites

40

Unitary Theory of Narcosis

-anesthetics act on no more than 2 or 3 sites to produce a specific effect