Inhaled anesthetics 1: pharmacokinetics 3

Question 1

Describe the ways in which inhaled anesthetics are eliminated from the body.

Answer 1

elimination from the alveoli (primary mechanism)
hepatic biotransformation (secondary mechanism)
percutaneous loss (minimal and not clinically significant)

Question 2

Describe how much of sevoflurane is metabolized by the liver.

Answer 2

2% metabolized

Question 3

Describe how much of isoflurane is metabolized by the liver.

Answer 3

0.2% metabolized

Question 4

Describe how much desflurane is metabolized by the liver.

Answer 4

0.02%

Question 5

Describe how much nitrous oxide is metabolized by the liver

Answer 5

0.004% metabolized

Question 6

Sevoflurane metabolism produces

Answer 6

free fluoride ions (theoretical risk of high output kidney failure)

Question 7

Desflurane and isoflurane produce

Answer 7

trifluoroacetic acid (small risk of immune-mediated hepatic dysfunction)

Question 8

Sevoflurane generates ______ when exposed to soda lime

Answer 8

sevoflurane

Question 9

Desflurane & isoflurane produce ______ when exposed to desiccated soda lime

Answer 9

carbon monoxide

Question 10

The halogenated anesthetics undergo metabolism by

Answer 10

the P450 system

Question 11

Up to _____ of halothane undergoes hepatic biotransformation

Answer 11

20%

Question 12

What is the primary mechanism for immune-mediated hepatic dysfunction (halothane hepatitis)

Answer 12

high trifluoroacetic acid (an important metabolic byproduct of halothane metabolism)

Question 13

What is the recommendation by the FDA to prevent compound A buildup inside the breathing circuit?

Answer 13

a minimum FGF of 1 L/min for up to 2 MAC-hrs and 2L/min after 2 MAC hrs
FGF rates <1 L/min are not recommended at any time

Question 14

Which P450 enzyme is chiefly responsible for halogenated anesthetic metabolism in the liver?

Answer 14

CYP2E1

Question 15

Which concept BEST explains why the rate of rise of FA/FI is faster for nitrous oxide than desflurane?
a. concentrating effect
b. augmented inflow effect
c. second gas effect
d. ventilation effect

Answer 15

a. concentrating effect

Question 16

The following alter the speed of anesthetic induction and emergence:

Answer 16

concentration effect
ventilation effect

Question 17

The ______ says that the higher the concentration of inhalation anesthetic delivered to the alveolus (Fa), the faster its onset of action.

Answer 17

concentration effect (also called overpressuring)

Question 18

What are the two components to the concentration effect?

Answer 18

1. concentrating effect
2. augmented gas inflow effect

Question 19

The _______ describes how changes in alveolar ventilation can affect the rate of rise of Fa/Fi

Answer 19

ventilation effect

Question 20

The greater the alveolar ventilation, the _________ of Fa/Fi

Answer 20

the greater the rate of rise

Question 21

The concentration effect only applies to

Answer 21

induction

Question 22

When the patient is breathing room air, _____ is the primary gas in the alveolus

Answer 22

nitrogen

Question 23

Nitrous oxide is _____ more soluble in the blood than nitrogen

Answer 23

34 x

Question 24

When nitrous oxide is introduced into the lung, the volume of nitrous oxide going from the alveolus to the pulmonary blood is _______ than the amount of nitrogen moving in the opposite direction. This causes the alveolus to______, and the ________ in alveolar volume causes a relative increase in Fa.

Answer 24

higher; shrink; reduction

Question 25

The concentrating effect temporarily

Answer 25

reduces alveolar volume

Question 26

On the subsequent breath, the concentrating effect causes an ______ inflow of tracheal gas containing the anesthetic agent to replace the lost alveolar volume. This _______ alveolar ventilation & augments Fa.

Answer 26

increased; increases

Question 27

Assuming that the FRC remains constant, which concept explains a temporary increase in alveolar oxygen concentration when using nitrous oxide for an inhalation induction? A. Concentration effect B. Diffusion hypoxia C. Ventilation effect D. Second gas effect

Answer 27

D. Second gas effect

Question 28

Explain the meaning of the second gas effect.

Answer 28

Administering one gas during induction (nitrous oxide) hastens the onset of a second gas (halogenated agent)

Question 29

What is diffusion hypoxia?

Answer 29

Movement of nitrous oxide from the tissue back into the alveoli during emergence. This dilutes alveolar oxygen and carbon dioxide which can lead to transient hypoxemia and hypocarbia

Question 30

Newer evidence suggests using this during emergence to reduce absorption atelectasis and improve post-operative gas exchange

Answer 30

Lower FiO2

Question 31

How does the second gas effect work?

Answer 31

When nitrous oxide and the second gas are introduced into the alveolus, the rapid uptake of N2O causes the alveolus to shrink temporarily. The reduction in alveolar volume and augmented tracheal inflow causes a relative increase in concentration of the second gas. The partial pressure of alveolar oxygen also increases when the alveolus shrinks transiently. The end result is that the alveolar concentration of the other gases is higher than if they were administered alone.

Question 32

The second gas effect produces a more meaningful benefit with agents of

Answer 32

Higher blood:gas solubility ISO> sevo> des

Question 33

What is the best way to mitigate diffusion hypoxia after nitrous oxide is discontinued?

Answer 33

Increase the FiO2 for 3-5 minutes after you d/c N2O. It doesn’t have to be 100% though

Question 34

A patient has a right to left intracardiac shunt. The rate of rise of FA/FI of which drug will be affected MOST?

Answer 34

Desflurane Agents with low solubility (desflurane) are affected the most

Question 35

How does a right to left shunt affect the onset of volatile agents?

Answer 35

Slower induction with a volatile agent (less soluble agents are affected to a greater extent)

Question 36

How does a right to left shunt affect the onset of intravenous anesthetics?

Answer 36

Faster induction with an IV agent

Question 37

How does a left to right shunt affect the onset of volatile agents?

Answer 37

No meaningful impact on induction with a volatile agent

Question 38

How does a left to right shunt impact the onset of intravenous anesthetics?

Answer 38

Slower induction with an IV agent