Inhalation Agents

Question 1

ideal inhalation agent

Answer 1

• 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)

Question 2

MAC

Answer 2

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

Question 3

prevents movement in 95% of patients on incision

Answer 3

1.5 MAC (with no other meds)

Question 4

1 MAC Halothane

Answer 4

0.76%

Question 5

1 MAC Isoflurane

Answer 5

1.15%

Question 6

1 MAC Sevoflurane

Answer 6

1.85%

Question 7

1 MAC Desflurane

Answer 7

6.0%

Question 8

1 MAC Nitrous Oxide

Answer 8

104%

Question 9

MAC awake

Answer 9

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

Question 10

MAC aware

Answer 10

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

Question 11

MAC- BAR

Answer 11

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

Question 12

site of action of IA

Answer 12

cell membranes in the CNS

Question 13

goal of inhalational anesthesia

Answer 13

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

Question 14

PA (ET gas) is used as an index of…

Answer 14

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

Question 15

determinantes of PA

Answer 15

• input minus uptake

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

Question 16

INPUT

Answer 16

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

Question 17

UPTAKE

Answer 17

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

Question 18

overpressure

Answer 18

• 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

Question 19

How does hyperventilation effect the rate of rise of PBR?

Answer 19

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

Question 20

IAs effect on ventilation

Answer 20

-dose dependent depression of ventilation

Question 21

Spontaneous Ventilation under GA (IA)

Answer 21

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

Question 22

Mechanical Ventilation under GA (IA)

Answer 22

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

Question 23

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

Answer 23

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

Question 24

as potency decreases, oswald….

Answer 24

• oswald coefficient decreases

- (decreased potency correlates to decreased solubility)

Question 25

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

Answer 25

inversely

Question 26

intermediately soluble

Answer 26

Isoflurane

Question 27

poorly soluble

Answer 27

Sevo, Des, N20

Question 28

soluble

Answer 28

(no modern inhaled anesthetics)

Question 29

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

Answer 29

3 time constants

Question 30

Brain: Blood equilibration time

Answer 30

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

Question 31

time constant formula

Answer 31

capacity/flow

Question 32

cardiac output and uptake

Answer 32

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

Question 33

AvD

Answer 33

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

Question 34

AvD depends on...

Answer 34

- 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)

Question 35

titration of IA based on...

Answer 35

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

Question 36

IA reversible effects on CNS

Answer 36

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

Question 37

Meyer-Overton Hypothesis

Answer 37

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

Question 38

5 Angstrom Theory

Answer 38

-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)

Question 39

Multisite Theory of Narcosis

Answer 39

-inhaled anesthetics act by effects at multiple sites

Question 40

Unitary Theory of Narcosis

Answer 40

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