Inhalant General Anesthetics

Question 1

Nitrous oxide does not cause unconsciousness… why is it used?

Answer 1

Excellent analgesic and alleviates anxiety; can also reduce amount of hydrocarbon anesthetic needed

Question 2

all inhalant anesthetics by the early 1950s had at least one of what two major drawbacks

Answer 2

1) explosive when administered with oxygen
2) produce toxic metabolites

Question 3

how do we reduce the flammability of a hydrocarbon

Answer 3

by substituting their hydrogen for a halogen

Question 4

halothane-oxygen mixtures are explosive/non-explosive

Answer 4

non-explosive

Question 5

in general, hepatic and renal toxicity are directly related to the extent at which an inhalant is

Answer 5

metablolized

Question 6

what are the main inhalants used in veterinary medicine today

Answer 6

• isoflurane
• sevoflurane

Question 7

the TI of all hydrocarbons ranges from

Answer 7

2-4

Question 8

why do we not use newer inhalant anesthetics?

Answer 8

they offer little or no advantage over iso or have serious drawbacks

Question 9

To be both safe and effective, general anesthetics must (2)

Answer 9

inhibit cerebrocortical activity while maintaining brainstem function

Question 10

the safety of general anesthetics is dependent on

Answer 10

the extent to which CVS and respiratory functions are impaired at concentrations required to maintain unconsciousness

Question 11

what is the MOA of inhalant anesthetics

Answer 11

not fully understood, but involves GABA facilitation

Question 12

how is inhalant anesthetic absorbed and eliminated

Answer 12

absorbed into blood from lungs; eliminated mainly be exhalation

Question 13

depth of anesthesia is proportional to:

Answer 13

partial pressure of the anesthetic

Question 14

what is partial pressure

Answer 14

the physical pressure exerted by one gas (in a mixture of gases) within a container

Question 15

how do highly soluble gases influence partial pressure and overall effect

Answer 15

highly soluble -> move slowly in tissues (because they form bonds) -> weak partial pressure and weak effect

Question 16

how fast do highly soluble gases get absorbed and eliminated

Answer 16

absorbed quickly; eliminated slowly

Question 17

rate of onset and recovery depends on

Answer 17

partial pressure

Question 18

how do poorly soluble gases influence partial pressure and overall effect

Answer 18

move rapidly in tissues -> high partial pressure -> high overall effect

Question 19

how fast do poorly soluble gases get absorbed and eliminated

Answer 19

slowly absorbed; quickly eliminated

Question 20

will a high or low soluble anesthetic render a patient unconscious more quickly (assuming a high concentration gradient to force the anesthetic into the tissue)

Answer 20

low soluble (because it has a higher partial pressure)

Question 21

will a patient recover more quickly if given an anesthetic with high or low solubility

Answer 21

low

Question 22

how do we overcome the problem of getting a poorly soluble inhalant anesthetic drug into the body

Answer 22

by creating a high concentration gradient between the capillaries and alveoli

Question 23

what is the blood gas parturition coefficient

Answer 23

the relative solubility of drug in tissues vs alvgeolar gas

Question 24

what is the BGPC for:
- sevoflurane
- isoflurane

Answer 24

sevoflurane: 0.68
isoflurane: 1.4

Question 25

how can we determine the concentration of anesthetic that is present in the brain

Answer 25

multiply the concentration of inhalant anesthetic being delivered by the BGPC

Question 26

the BGPC for isoflurane is 1.4, what does this mean?

Answer 26

the concentration of iso in the tissues is 1.4x the concentration in the alveolar air or if you administer 1% iso, the concentration in tissues is 1.4%

Question 27

the onset of unconsciousness and recovery are fast with __________ drugs and slow with __________ drugs

Answer 27

poorly-soluble; highly-soluble

Question 28

how do we utilize the concentration of anesthetic in the inspired air to induce a patient more quickly

Answer 28

can increase (so more enters tissue with each breath) and then decrease once the patient is unconscious

Question 29

T/F we can control the inspired anesthetic concentration using a precision vaporizer

Answer 29

T

Question 30

how does ventilation rate impact the concentration of anesthetic in the brain

Answer 30

the faster the patient breathes, the faster the anesthetic is delivered to and absorbed from the lungs

Question 31

what are 2 factors that influence inhalant anesthetic delivery to the brain that we cannot readily control

Answer 31

1) pulmonary blood flow 2) pulmonary/venous concentration gradient

Question 32

what are 3 factors that influence drug delivery to the brain that we can readily control

Answer 32

1) BGPC 2) concentration of anesthetic in the inspired air 3) ventilation rate

Question 33

inhalant anesthetics are eliminated mainly by

Answer 33

exhalation

Question 34

what are 3 factors that influence the elimination of an inhalant anesthetic

Answer 34

1) solubility in tissues 2) respiratory rate 3) pulmonary blood flow

Question 35

what effect do inhalant anesthetics have on thermoregulation

Answer 35

depress -> cause some degree of hypothermia

Question 36

halothane has ~25-40% metabolism, isoflurane has ~0.2% metabolism and sevoflurane has ~3-5% metabolism place the drugs in order of most to least toxic

Answer 36

halothane, sevoflurane, isoflurane

Question 37

metabolites of inhalant anesthetic metabolism are usually damage to what organs

Answer 37

liver and kidney

Question 38

what are 3 harmful metabolites of inhalant anesthetics

Answer 38

1) trifluoroacetic acid 2) Br- 3) Cl-

Question 39

what is used to compare potency of inhalant anesthetics

Answer 39

MAC

Question 40

what is MAC50

Answer 40

concentration of anesthetic in the inspired air that will prevent 50% of patients from feeling a painful stimulus

Question 41

the MAC for very potent drugs would be relatively (high/low)

Answer 41

low

Question 42

what is used to control the vaporizer setting

Answer 42

MAC50

Question 43

The MAC95 value is about _____% higher than MAC50, so in unpremedicated patients you should set the vaporizer at ____x MAC to start, then adjust

Answer 43

30-40%; 1.3x

Question 44

what do we set the vaporizer to in premedicated patients to start

Answer 44

MAC50 value

Question 45

lines in what species are susceptible to malignant hyperthermia

Answer 45

pigs, dogs and humans

Question 46

malignant hyperthermia is caused by mutations in the

Answer 46

skeletal muscle calcium release channel (RYR)

Question 47

what happens to mutated calcium release channels when exposed to halogenated hydrocarbons

Answer 47

uncontrolled muscle contraction

Question 48

how do we treat malignant hyperthermia

Answer 48

dantrolene

Question 49

why is it important to change out soda lime regularly when using iso as the inhalant anesthetic

Answer 49

it forms CO when exposed to desiccated CO2 absorbents

Question 50

what is a drawback of iso that is only important when the patient is not being stimulated

Answer 50

dose-dependent drop in blood pressure

Question 51

what is isoflurane's only real drawback

Answer 51

pungent odour

Question 52

is it better to use isoflurane or sevoflurane on reptiles and amphibians

Answer 52

sevoflurane (because they can hold their breath for over 20 min)

Question 53

what happens to sevoflurane when exposed to CO2 absorbents

Answer 53

releases Compound A, which is nephrotoxic