Inhalational Anesthesia

Question 1

Can nitrous oxide alone be used as a general anesthetic?

Answer 1

No, but it can be when combined with things such as opioids.

Question 2

How do isoflurane, desflurane, and sevoflurane relate molecular-ly to diethyl ether? One important functional property that sets them apart?

Answer 2

They are fluorinated / halogenated diethyl ether derivatives (or very similar structures, at least). Unlike ether, they aren’t flammable, which is important when using electrocautery in the OR.

Question 3

What are 4 clinically relevant differences between inhaled anesthetic agents?

Answer 3

Potency
Solubility
Pungency
Cost

Question 4

What are 5 things that you want your general anesthetic to do?

Answer 4

Hypnosis
Amnesia
Immobility / Muscle Relaxation / Akinesia
Blunting of Autonomic Responses

Question 5

What kinetics for inhaled anesthetics are desirable?

Answer 5

Quickly induce anesthetic state, but be readily reversed when the gas is removed.

Question 6

What effects do inhaled anesthetics have on brain metabolism? How about on synchrony?

Answer 6

Decreased metabolism.
Increased synchrony (like sleeping?).

Question 7

How do you achieve a controlled, constant dosage of inhaled drug being delivered to the patient?

Answer 7

By a vaporizer. (not an ether-soaked cloth)

Question 8

What are the 3 compartments into which anesthetic will go? Which can hold the most drug?

Answer 8

Vessel Rich Group (Brain, liver, kidney)
Fat (biggest, lowest blood flow)
Muscle (intermediate blood flow)

Question 9

How are anesthetic gases eliminated from the body?

Answer 9

By exhalation, mainly. Very little metabolic breakdown.

Question 10

What variable that varies between tissue types greatly affects absorption?

Answer 10

Solubility. Inhaled drugs tend to be highly soluble in fat and less soluble in brain.

Question 11

How does solubility in fat affect recovery time?

Answer 11

Less soluble in fat, less recovery time.

Question 12

Three reasons why anesthetic gases that are less soluble perform better?

Answer 12

Less potent - (better? worse? unclear)
Faster onset / “offset”
Less accumulation in tissue / fat

Question 13

How do inhaled anesthetic drugs affect cerebral blood flow?

Answer 13

They increase it.

Question 14

Is the spinal cord affected by inhaled anesthetics?

Answer 14

Yes. Response to stimuli is blocked.

Question 15

4 effects of inhaled anesthetics on respiration?

Answer 15

Bronchodilation
Increased respiratory rate
Decreased tidal volume
Decreased respiratory reflexes (i.e. RR won’t increase in response to low O2 / high CO2)

Question 16

4 cardiovascular effects of inhaled anesthetics?

Answer 16

Decreased BP (vasodilation)
Blood redistributed from core to periphery (vasodilation)
Impairs autonomic reflexes to maintain BP (eg. carotid baroreceptor reflex)
Decreases contractile strength of heart muscle.

Question 17

What’s the MAC? How is it used?

Answer 17

Minimum Alveolar Concentration: % of total gas that must be anesthetic in order to make 50% of patients not move in response to surgical incision.
Used as a starting point from which the dosage is adjusted for the patient.

Question 18

3 factors other than MAC affecting the proper dose of inhaled anesthetic?

Answer 18

Intensity and type of surgical stimulus.
Age and medical condition of patient.
Concurrent use of other anesthetics (opioids, muscle relaxants).

Question 19

What are 4 common problems with inhaled anesthesia?

Answer 19

Nausea and vomiting
Respiratory depression
Cardiovascular collapse
Inhibition of uterine contraction (post-delivery bleeding)

Question 20

2 rare complications seen with inhaled anesthetics?

Answer 20

Malignant hyperthermia

Liver toxicity

Question 21

1 controversial problem with anesthesia?

Answer 21

Neurotoxicity.

Question 22

Are patients the only people who might be adversely affected by inhaled anesthetics?

Answer 22

No. They might harm the environment, esp. the ozone layer. (how about anesthesiologists, surgeons, nurses, and techs?)

Question 23

What’s the mechanism of action of inhaled anesthetics?

Answer 23

Trick question. Nobody knows.

Question 24

What’s the functional outcome of inhaled anesthetics, broadly speaking?

Answer 24

Disrupt normal patterns of neuronal transmission involved in consciousness, which we see on EEG.

Question 25

What does the fact that that these gases work on flies, snakes, fish, and zebras tell us?

Answer 25

It works on evolutionarily ancient, conserved machinery.

Question 26

What do we know about where, cellularly speaking, these drugs go?

Answer 26

They like membranes. It’s probably more about binding to proteins than altering membrane properties, though.

Question 27

Is there just one receptor that inhaled anesthetics bind to?

Answer 27

No. They seem to bind to many.

Question 28

Is there thought to be one receptor to which anesthetic gas binding is most important?

Answer 28

Yes. GABA-A appears to be pretty important.

Question 29

Why are there suspicions that anesthetic gases pose cognitive risks?

Answer 29

Some animal models suggest reduced synapse formation after exposure.
Many anecdotal reports of “not feeling like self” after general anesthesia.