Inhalational Anesthetics principals

Question 1

What is methoxyflurane?

Answer 1

A potent halogenated anesthetic with high solubility and low vapor pressure

Question 2

How was methoxyflurane metabolized?

Answer 2

50% by cytochrome P450 into nephrotoxic compounds

Question 3

What was prolonged anesthesia with methoxyflurane associated with?

Answer 3

Vasopressin resistant, high output renal failure

Question 4

What are the effects of enflurane?

Answer 4

Depressed myocardial contractility
Increased CSF
Decreased CSF output
Seizures

Question 5

What is the ultimate effect of inhalation all anesthetics?

Answer 5

Therapeutic tissue concentration in the brain

Question 6

What is the inspired gas concentration determined by?

Answer 6

The fresh gas flow rate
Breathing circuit volume
Circuit absorption

Question 7

What is the concentration of a gas directly proportional to?

Answer 7

It’s partial pressure

Question 8

Why is the alveolar partial pressure of a gas important?

Answer 8

Because it determines the partial pressure of anesthetic in the blood and ultimately the brain.

Question 9

What is the relationship between uptake and alveolar concentration?

Answer 9

The greater the uptake, the greater the difference between inspired and alveolar concentration and SLOWER rate of induction.

Question 10

What 3 factors affect anesthetic uptake?

Answer 10

Solubility in the blood
Alveolar blood flow
The difference in partial pressure between alveolar gas and venous blood.

Question 11

What does it mean if something is less soluble?

Answer 11

Means that it is not taken up in the blood as avidly, meaning that the alveolar concentration will be higher and induction much faster (nitrous oxide)

Question 12

What is the partition coefficient?

Answer 12

The ratio of the concentrations of the anesthetic gas in each of two phases at steady state

Question 13

What is the blood/gas coefficient of nitrous oxide?

Answer 13

0.47 so the blood has 47% capacity of nitrous oxide as alveolar gas

Question 14

What is the blood/gas coefficient of halothane?

Answer 14

2.4

Question 15

If the blood/gas coefficient is bigger, what does this mean for the anesthetic’s solubility and uptake by the pulmonary circulation?

Answer 15

It means it is more soluble and has higher uptake in the pulmonary circulation meaning that the alveolar partial pressure will take awhile to rise, thereby causing slower induction

Question 16

What is alveolar uptake(blood flow) equal to?

Answer 16

Cardiac output

Question 17

What are the first organs to reach steady state and why?

Answer 17

Brain, heart, liver, kidney, and endocrine because they have the high blood flow

Question 18

How can you increase the alveolar concentration?

Answer 18

By increasing the concentration of inspired gas

Question 19

What is augmented inflow effect?

Answer 19

The absorbed gas has be replaced by an equal volume of the mixed gas to prevent alveolar collapse

Question 20

What is the second gas effect?

Answer 20

A high concentration of one gas will augment its own uptake and another volatile anesthetic (nitrous oxide does this)

Question 21

How does ventilation affect the alveolar partial pressure?

Answer 21

It will increase it by constantly replacing anesthetic that is being taken up

Question 22

What does VQ mismatch doe to alveolar partial pressure?

Answer 22

It increases it, thus making onset faster for soluble agents

Question 23

What happens with the elimination of nitrous oxide?

Answer 23

It diffuses so fast that oxygen and co2 are diluted causing a diffusion hypoxia?

Question 24

How do you treat diffusion hypoxia?

Answer 24

By administering 100% oxygen for 5-10 minutes after stopping nitrous oxide

Question 25

How are inhalational agents cardio protective?

Answer 25

They open the K ATP channel, preventing the influx of calcium and reducing ROS. Therefore reducing ischemia-reperfusion injury

Question 26

What protective property does Xenon have?

Answer 26

An anti-apoptotic effect that may be secondary to its inhibition of calcium ion influx following cell injury

Question 27

What happens to MAC as you age per decade?

Answer 27

The MAC decreases by 6% regardless of volatile anesthetic

Question 28

What is a MAC of 1.3 correlated with in any of the volatile anesthetics?

Answer 28

Prevention of movement in 95% of patients

Question 29

What is a Mac of 0.3-0.4 associated with?

Answer 29

Awakening

Question 30

What factors decrease MAC?

Answer 30

``` Temperature (hypo or hyperthermia) Old Acute alcohol intoxication Hypoxemia Hypercapnia Hypotension Hypercalcemia Hyponatremia Pregnancy ```

Question 31

What factors increase Mac?

Answer 31

``` Hypernatremia Cocaine Ephedrine Chronic alcohol use Young age Temperature over 42 Celsius ```

Question 32

What is the principal mechanism by which halothane decreases blood pressure?

Answer 32

By decreasing cardiac output

Question 33

How do isoflurane, sevoflurane, and desflurane decrease blood pressure?

Answer 33

Through decreasing SVR Cause dose dependent changes in arterial bp, SVR, and co

Question 34

Which anesthetic is metabolized to hexafluoroisopropanolol?

Answer 34

Sevoflurane

Question 35

How is sevoflurane metabolized to hexafluoroisopropanolol ?

Answer 35

Through p450 enzymes

Question 36

How are desflurane, isoflurane, and sevoflurane mainly eliminated?

Answer 36

Unchanged when exhaled out of the lungs

Question 37

What is the order of volatile that undergoes liver metabolism from greatest to least?

Answer 37

Halothane > sevoflurane > isoflurane > desflurane

Question 38

What enzyme family is responsible for volatile metabolism in the liver?

Answer 38

P450 (CYP2E1)

Question 39

What do desflurane and isoflurane get metabolizes to in the liver?

Answer 39

Trifluoroacetic acid

Question 40

What does Trifluoroacetic acid do?

Answer 40

Binds hepatocellular proteins and acts as a happen --> immune response

Question 41

What is a rare complication from isoflurane or desflurane?

Answer 41

Hepatic necrosis and liver failure from subsequent exposure after immune response on first exposure

Question 42

What 2 types of liver injury are associated with halothane?

Answer 42

1. Mild form : free radical formation by reductive metabolism (CYP2A6 and CYP3A4) (under conditions of hypoxia or decreased flow 2. Oxidative metabolism and the immunologic response from TFA

Question 43

What does the rate of rise of the FA:Fi ratio depend on?

Answer 43

The blood gas solubility The inspired concentration of gas Therefore the speed at which the alveolar anesthetic (FA) equilibration with that being delivered to the lungs (Fi).

Question 44

How much inactivation of methionine synthetase do you get from nitrous oxide at 70% for 46 minutes?

Answer 44

50%

Question 45

What does halothane do to catecholamines effects on the heart?

Answer 45

Sensitized the heart to them so causes arrhythmias

Question 46

Which inhalational agents will have a longer induction with one-lung ventilation

Answer 46

Desflurane and nitrous oxide because they have the lowest blood/gas solubility. One lung ventilation creates a shunt. Less blood is there to take the volatile to the brain. The less soluble agents will just stay in the ventilated lung

Question 47

When cardiac output is doubled what happens to the rate of rise of FA/Fi of a soluble agent?

Answer 47

It will slow the rate of rise

Question 48

What happens to rate of rise for insoluble agents in a shunt?

Answer 48

Slow the rise