Inhalational Agents

Question 1

Potency is directly related to ________.

Answer 1

lipid solubility

Question 2

What is the Meyer-Overton Rule?

Answer 2

an increase in solubility = an increase in potency

Question 3

What provides a “quantitative” measurement of lipid solubility?

Answer 3

the oil (olive): gas partition coefficient

Question 4

What is the definition of a MAC?

Answer 4

the minimum alveolar concentration of an inhalational agent at which 50% of patients do not move in response to skin incision or similar noxious stimulus

Question 5

MAC is inversely related to ________.

Answer 5

potency

Question 6

_______ is another way of representing lipid solubility, and therefore potency.

Answer 6

oil:gas partition coefficent

Question 7

SO DO NOT GET CONFUSED—> SPEED OF UPTAKE is most represented by the _______ coefficient, and POTENCY is most represented by the ________ coefficient.

Answer 7

blood:gas, oil:gas

Question 8

What agent has the highest blood:gas coefficient? What agent has the highest oil:gas coefficient?

Answer 8

HALOTHANE for BOTH

Question 9

In regards to cardiovascular effects, what two IA’s are primarily the same?

Answer 9

isoflurane and desflurane

both have slightly more decrease in BP and SVR than Sevo

Question 10

What volatile anesthetic has no change in SVR?

Answer 10

Halothane

Question 11

What volatile anesthetic can produce none to a 20% increase in HR?

Answer 11

Isoflurane and Desflurane

Question 12

What VA causes a sensitization to catecholamines?

Answer 12

Halothane

Question 13

Which VA has the least effect on BP and SVR?

Answer 13

Sevoflurane

Question 14

The solubility of gas in a liquid ______ as temperature increases.

Answer 14

decreases (opposite of solids)

**More inhalational agent will dissolve if the patient is hypothermic–> LeChatelier’s law

Question 15

What determines the speed at which partial pressure of an agent builds up in the blood and subsequently the brain, and also determines the speed the agent is eliminated from the blood and the brain?

Answer 15

blood solubility, blood:gas partition coefficient

Question 16

\_\_\_\_\_\_ = blood solubility
\_\_\_\_\_\_ = lipid solubility

Answer 16

blood: gas PC
oil: gas PC

Question 17

The _____ the ventilation, the faster the uptake.

Answer 17

greater

Question 18

The ______ the cardiac output, the faster the uptake. (within limits)

Answer 18

lower

Question 19

Easy way to remember the Solubility graph for inhalational agents.

Answer 19

the graph represents the % that the agent is equilibrated after 30 minutes
*remember that Halothane was invented in the 50’s…. then each IA for the next decade… 60’s…. 70s… etc.
Don’t forget that Enflurane will probably not be on the graph, but you must still use it for this to work!!
HE IS Doing Nothing
Halothane is 58% equilibrated after 30 min
Isoflurane is 73% equilibrated after 30 min
Sevoflurane is 85% equilibrated after 30 min
Desflurane is 91% equilibrated after 30 min
N2O is 99% equilibrated after 30 min

Question 20

N2 is _____ times LESS soluble in blood than N2O.

Answer 20

34 times less

Question 21

Compared with N2O, the carrying capacity of the blood for N2 is _____.

Answer 21

POOR;
N2= 0.014 and N2O= 0.470
b\c of this difference, gas spaces change pressure or volume when N2O is turned on and off
*so normally the amount of N2 leaving the blood to the alveoli is the same that enter the blood from the alveoli, but since N2O is more soluble in blood, more can enter, thus more spaces distend

Question 22

The rate of diffusion of gas into or out of the blood is proportional to its blood solubility. Who’s law explains this?

Answer 22

Ficks law of diffusion

Question 23

What law explains why gas bubbles distend when N2O is turned on or collapse when N2O is turned off?

Answer 23

Fick’s law of diffusion

Question 24

Explain the concentration effect.

Answer 24

With N2O turned on, the N2O diffuses into the blood quicker than N2 normal would, so the alveoli shrink in size thus permitting a more rapid uptake of N2O by the blood—> explained by FICK

Question 25

Explain the second gas effect.

Answer 25

two anesthetics with varying onset speeds are given together–> a high concentration of a fast (N2O) with a slower second anesthetic gas…. the second gas achieves anesthetic levels more quickly than if it had been given alone

Question 26

What is the dilutional effect?

Answer 26

it is the opposite of the concentration effect; if you turn off N2O, it readily diffuses from the blood to the alveoli diluting the oxygen CO2 and expanding the alveoli=hypoxia
also termed, diffusional hypoxia