Lecture 8 9/10/24

Question 1

Which halogenated ethers are most commonly used in vet med?

Answer 1

-isoflurane
-sevoflurane

Question 2

What are the characteristics of an ideal anesthetic?

Answer 2

-chemically stable
-non-flammable
-environmentally friendly
-inexpensive
-easy delivery
-potent
-low solubility
-minimal metabolism
-minimal toxicity
-minimal side effects
-analgesia

Question 3

Which state are modern inhalants in?

Answer 3

vapors

Question 4

What are the physiochemical properties of solubility?

Answer 4

-dissolved concentration in liquid
-net movement of gas into liquid until equilibrium
-temperature dependent

Question 5

What are the physiochemical properties of partial pressure?

Answer 5

-pressure the gas exerts to escape from solution
-each gas exerts a pressure
-mixture of gases = partial pressure the same for individual gases

Question 6

How do anesthetics travel?

Answer 6

via partial pressure gradient

Question 7

What is the gas partition coefficient?

Answer 7

-concentration ratio of anesthetic in gas vs liquid or between two tissues
-describes capacity of particular solvents/tissues to dissolve anesthetic gas

Question 8

Why is the gas partition coefficient important?

Answer 8

it provides means of predicting speed of induction, recovery, and change in depth

Question 9

How does rate of rise of alveolar partial pressure relate to solubility?

Answer 9

inversely proportional

Question 10

Why do highly soluble anesthetics take a longer time to rise in alveolar partial pressure?

Answer 10

because the anesthetic is rapidly taken up by the blood and held there

Question 11

What does P-alveolar represent?

Answer 11

P-CNS

Question 12

Why do poorly soluble anesthetics have a quick rise in alveolar partial pressure?

Answer 12

the gas passes through the blood and right into the brain

Question 13

Why is a low blood:gas partition coefficient desirable?

Answer 13

it leads to faster induction and recovery

Question 14

What are the characteristics of the oil:gas partition coefficient?

Answer 14

-ratio of anesthetic in oil compared to gas at equilibrium
-more lipid soluble = more rapidly taken up by brain

Question 15

How does oil:gas partition coefficient relate to potency?

Answer 15

direct correlation

Question 16

What is the primary goal of inhalant anesthetic delivery?

Answer 16

ensure adequate partial pressure of anesthetic in the CNS to produce CNS depression and general anesthesia

Question 17

What is important about the pathway in the body that anesthetic inhalants follow?

Answer 17

they do not go to the liver or kidneys; there is no hepatic or renal metabolism

Question 18

What are the characteristics of inhalant uptake?

Answer 18

-PA rapidly equilibrates with arterial partial pressure (Pa)
-Pa rapidly equilibrates with Pbrain
-PA useful indicator of brain partial pressure

Question 19

Which factors affect inhalant uptake?

Answer 19

-delivery to the alveoli
-uptake by the blood

Question 20

What aspects of inspired inhalant concentration impact delivery to the alveoli?

Answer 20

-vaporizer setting
-fresh gas flow
-volume of the anesthesia circuit
-type of anesthetic circuit
-rubber and plastic in the circuit

Question 21

How can the inspired concentration be increased?

Answer 21

-increase vaporizer setting
-increase fresh gas flow
-decrease volume of anesthesia circuit
-changing plastic vs. rubber content

Question 22

What is the overpressure technique?

Answer 22

using high O2 setting and high vaporizer setting to start anesthesia in order to achieve a quick rise in alveolar concentration

Question 23

What are the characteristics of alveolar ventilation?

Answer 23

-improving alveolar ventilation leads to more rapid induction
-want to decrease dead space ventilation

Question 24

Which factors impact blood uptake of inhalant anesthetics?

Answer 24

-solubility
-cardiac output
-alveolar to venous anesthetic partial pressure gradient

Question 25

What are the characteristics of solubility?

Answer 25

-more soluble = slower rise in anesthetic conc. -inversely related to potency

Question 26

How does low cardiac output affect uptake?

Answer 26

-more rapid rise in alveolar conc. -less uptake from alveoli to oppose input -blood becomes concentrated with drug quickly

Question 27

How does high cardiac output affect uptake?

Answer 27

-slower rise in alveolar conc. -increased capacity of blood to hold anesthetic

Question 28

What is the driving force of inhalant uptake and elimination?

Answer 28

-partial pressure gradient -larger gradient = more uptake and longer time to achieve desired PA

Question 29

What are the characteristics of potency?

Answer 29

-amount of drug needed to achieve general anesthesia -inversely related to MAC

Question 30

What is MAC?

Answer 30

alveolar concentration that prevents gross, purposeful movement in 50% of patients in response to noxious stim.

Question 31

What are the MAC values for isoflurane and sevoflurane?

Answer 31

iso: 1.3 sevo: 2.3

Question 32

How is MAC determined?

Answer 32

-using Palveolar expired conc. -without other drugs -in healthy animals

Question 33

Which animals have a variation from the standard MAC values?

Answer 33

cats - MAC values for iso and sevo are about 0.3 higher

Question 34

Why is MAC important?

Answer 34

-anesthetic requirement -compare agents -evaluate pharmacologic effects -want to set vaporizer around MAC value

Question 35

What are the theories behind how inhalant anesthetics work?

Answer 35

-modulation of ion channels** -decreased neuronal excitability -inhibition of action potential -enhanced inhibitory synaptic transmission

Question 36

What are the sites of action for inhalant anesthetics?

Answer 36

-brain -spinal cord

Question 37

What are the advantages of using inhalants?

Answer 37

-tailored to individual -rapid changes in depth -minimal metabolism

Question 38

What are the primary goals of using inhalants?

Answer 38

achieve muscle relaxation and hypnosis

Question 39

What are the disadvantages of using inhalants?

Answer 39

-necessary equipment -airway management -waste gases -side effects

Question 40

What are the effects of inhalants?

Answer 40

-dose dependent hypotension -decreased ventilatory response to CO2 -dose dependent hypoventilation -unconsciousness -decreased cerebral metabolic rate of O2 -increased cerebral blood flow -increased intracranial pressure -decreases in renal blood flow and glomerular filtration rate

Question 41

Why is it important to pre-medicate when using inhalants?

Answer 41

side effects are dose dependent, so we can reduce the dose of inhalants when pre-medicating

Question 42

What are the characteristics of malignant hyperthermia?

Answer 42

-genetic mutation of ryanodine receptor -use of inhalants can result in hyperthermia, muscle rigidity, increased EtCO2, hypocalcemia, and hyperkalemia -reversed with dantrolene -very poor prognosis; nearly always fatal

Question 43

When is trace gas exposure most likely to occur?

Answer 43

-vaporizer filling -leaks -recovery