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Anesthesia > Inhalant Anesthesia > Flashcards

Inhalant Anesthesia Flashcards

1
Q

What was the first used inhaled anesthetic? Why is it no longer used?

A

diethyl ether

  • tracheal and bronchial mucosa irritatino
  • prolonged induction and recovery
  • post-op nausea and vomiting
  • flammable and explosive
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2
Q

What were 3 desirable characteristics of diethyl ether?

A
  1. stable cardiac output, rhythm, and BP
  2. stable respiration
  3. good muscle relaxation
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3
Q

What is the most common inhalant anesthesia in North America? What is it approved for use in?

A

isoflurane

dogs and horses - commonly used in other species

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4
Q

What allows for rapid induction and recovery associated with sevoflurane? What is it approved for use in?

A

low blood:gas partition coefficient —> highly controllable depth

dogs

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5
Q

What is the flammability of inhaled anestehtics like?

A
  • ETHER = flammable and explosive
  • NITROUS OXIDE = supports flammability
  • HALOTHANE and ISO = flammable at extremely high concentrations not normally used in practice
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6
Q

What are the odors of ether, isoflurane, and sevoflurane like?

A

irritant

pungent, animals resent mask induction

acceptable

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7
Q

What are the 3 major effects of inhalent anesthetics?

A
  1. unconsciousness (bind to ligand-gated ion channels and block CNS neurotransmission)
  2. muscle relaxation
  3. dose-dependent cardiovascular and respiratory depression - reduced contractility, systemic vascular resistance (vasodilation)
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8
Q

How do inhaled anesthetics affect blood pressure? What effects fo halothane, sevoflurane, desflurane, isoflurane, and nitrous oxide have?

A

reduce blood pressure (CO x SVR)

  • HALO = reduces contractility, maintains SVR
  • SEVO/DES/ISO = reduce SVR, maintains CO (truly vasodilatory via NO, cyclooxygenase, adenylate cyclase)
  • N2O = used with sevo or iso to attenuate BP reduction
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9
Q

Which inhaled anesthetics have minimal effects on HR? Which ones increase it?

A

halothane and sevoflurane

isoflurane and desflurane cause sympathetic stimulation due to hypotension (can be confused with a too light plane)

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10
Q

How do inhaled anesthetics affect ventilation? What are 4 effects?

A

depressed TV and minute ventilation

  1. increases ratio of dead space to tidal volume
  2. hypoxic pulmonary vasoconstriction response decreases
  3. expiratory muscles effort increases, promoting atelectasis
  4. decreases response to increased CO2 and hypoxia
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11
Q

What inhaled anesthetic attenuates ventilatory decrease?

A

nitrous oxide

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12
Q

What inhaled anesthetics are associated with airway irritation? What is typically added to decrease this? On what patients are these anesthetics avoided?

A

desflurane and isoflurane are pungent, making patients cough and bronchospasm

better tolerated with opioids and sedatives on board

avoided in “light patients” without other drugs due to potential for life-threatening bronchospasm

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13
Q

What inhaled anesthetics are not associated with airway irritation?

A

N2O, sevo, halo —> very little bronchospasm

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14
Q

How do inhaled anesthetics affect intracranial pressure? Which one has the most and least effect?

A

increase intracranial pressure by increasing cerebral blood flow (vasodilation)

  • HALOTHANE = greatest effect
  • SEVOFLURANE = least effect
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15
Q

What effect do inhaled anesthetics have on cerebral oxygen consumption? What is an exception?

A

decreases O2 consumption, but increases cerebral blood flow

N2O - increases cerebral O2 consumption and cerebral blood flow

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16
Q

What are the most common hepatic and renal effects of inhaled anesthetics?

A

HEPATIC = decrease portal vein flow and inhibit metabolism of other drugs

RENAL = dose-dependent reduction in blood flow, GFR, and urine output

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17
Q

How are inhaled anesthetics able to reach the brain?

A

gain entrance via the respiratory tract, where they maintain steady alveolar concentration and enter systemic circulation

  • uptake and distribution
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18
Q

What are 4 theories on molecular targets and anatomic sites of action of inhaled anesthetics?

A
  1. enhance inhibitory receptors, including GABA and glycine receptors
  2. induce an inhibitory effect on excitatory channels like neuronal nicotinic and glutamate receptors
  3. produce immobility by action at the spinal cord
  4. produce amensia by action on supraspinal structures, like the amygdala, hippocampus, and cortex
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19
Q

What is anesthetic potency proportional to? What does it suggest?

A

solubility in olive oil

anesthesia is produced when a certain number of molecules occupy a region of nerve cell membranes, specifically ligand-gated GABA, NMDA, and nACh channels; voltage-gated Kv and BK channels; and background TREK, Kan, and S channels

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20
Q

How do anesthetic liquids travel to the brain and interact with lipid and proteins to induce anesthesia?

A
  • vaporized and mixed with oxygen
  • mixture is delivered to the alveoli via a mask or ET tube
  • mixture diffuses into the bloodstream
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21
Q

What affects the diffusion rate of inhaled anesthetics across alveoli walls? Distribution to tissues?

A

concentration gradient of alveoli and capillaries and lipid solubility of anesthetic gas

blood supply and lipid solubility (brain, heart, and kidney have greater blood flow = quickly saturated)

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22
Q

What is the maintenance of gas anesthesia dependent on?

A

sufficient quantities of anesthetic delivered to and maintained in the alveoli

  • brain levels of inhalant = arterial levels = alveolar levels
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23
Q

What are gas and vapors? Whats the difference?

A

collections of molecules in constant state of motion and bombardment, attraction, and repulsion

  • GAS = agent exists as a gaseous form at room temperature and sea level pressure (N2O)
  • VAPOR = gaseous form of an agent that exists as a liquid at room temperature and seal level pressure (contemporary anesthetics)
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24
Q

What are quantities of inhaled anesthetics measured by?

A

partial pressure - force per unit area created by the constant state of motion

  • concentration in vol %*
  • mass in mg or g
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25
Q

What is vapor pressure? How does this affect the administration of inhaled anesthetics?

A

pressure that vapor molecules exert when the liquid and vapor phases are in equilibrium —> measure of the tendency for molecules in a liquid to evaporate or enter gaseous phase

inhalant anesthetics have very high vapor pressure - too high to be safely given to patients as a liquid

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26
Q

How does temperature affect vapor pressure?

A

as temperature increases, the vapor pressure and concentration increases, meaning more molecules go into the gaseous vs. liquid phases and are available to the patient

  • vaporizers are temperature controlled!
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27
Q

What are volatile agents? How are their vaporizers made?

A

high vapor pressure agents (iso, sevo, des, halo) that evaporate readily and are delivered from unique precision vaporizers to control their delivery

made to delivery only a specific halogenated agent and located OUTSIDE the breathing circuit

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28
Q

What are nonvolatile agents? How are their vaporizers made?

A

low vapor pressure agents (methoxyflurane) that have no need for precision vaporizers

non-precision (liquid in jar) vaporizers, often within the breathing circuit

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29
Q

What are the 3 purposes of vaporizers? What do their dials control?

A
  1. dilute vapor generated by the liquid anesthetic with oxygen
  2. further mixes with bypass oxygen
  3. get safer vapor pressure to deliver to the patient

ratio of bypass oxygen to agent-filled oxygen

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30
Q

Once in the gas/vapor form, what 5 things affect inhalant concentrations getting into the alveolus?

A
  1. inspired partial pressure - high pressure = accelerated induction
  2. alveolar ventilation - high ventilation = increased alveolar uptake
  3. volume of the anesthetic breathing system
  4. solubility of anesthetic in components of the system
  5. gas inflow from anesthetic machine
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31
Q

In what 2 ways can the partial pressure of an inhalant be increased?

A
  1. turn up vaporizer to multiples of MAC
  2. increase oxygen flow
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32
Q

What aspects of ventilation affect anesthetic arriving to the alveolus?

A
  • apnea, hypoventilation (slow, shallow) = delays rate of alveolar anesthetic concentration
  • high tidal volume, hyperventilation = facilitates rate of rise
33
Q

How does the volume of the circuit affect anesthetic arriving at the alveolus? What is recommended for rebreathing circuits?

A
  • larger than required rebreathing bag = decreases speed of induction, recovery, and change in inhalant
  • smaller than required = increases speed of induction, recovery, and change in inhalant

use standard-length circuits, since longer circuits make it difficult to speed changes

34
Q

How do circuit materials affect anesthetic arriving to the alveolus?

A

rubber and plastic parts may absorb certain anesthetics (based on rubber gas partition coefficient and solubility)

  • older agents, like methoxyflurane, have lengthy induction and recovery period because they are highly absorbed (630)
  • isoflurane (62) and sevoflurane (0) are relatively inert
35
Q

What is minimal alveolar concentration? What is it correlated with?

A

vaporizer setting that produces immobility in 50% of patients undergoing surgical stimulus (measure of ED50 = potency)

oil gas partition coefficient
- lower MAC = more potent!

36
Q

Why is it important to know MAC of an anesthetic? When is surgical anesthesia reached?

A
  • measure of potency
  • variability between species is minor

1.2-1.4 x MAC
(0.8-1) x MAC with appropriate meds

37
Q

What are the potencies of isoflurane, sevoflurane and desflurane like?

A
  • iso MAC = 1.5, most potent
  • sevo MAC = 2.1, less potent
  • des MAC = 7.2-10.3, least potent
38
Q

What 7 things can affect MAC of an inhaled anesthetic?

A
  1. age
  2. metabolic activity
  3. body temperature
  4. disease
  5. pregnancy
  6. obesity
  7. use of other agents, like premeds
39
Q

What 3 things affect the transfer of an agent from alveolus to arterial blood?

A
  1. blood-gas coefficient
  2. cardiac output (high = rapid uptake)
  3. alveolar-to-venous partial pressure difference (large difference = rapid uptake)
40
Q

How is solubility in blood and lipid/oil related to potency of an inhaled anesthetic?

A

incerversly

directly

41
Q

How is temperature associated with solubility of inhaled anesthetics?

A

increase in temperature = decreased solubility

decrease in temperature = increased solubility
- hypothermia increases anesthetic dissolving in blood = deeper patient

42
Q

How does a high blood-gas partition coefficient relate to induction, recovery, and change in anesthetic depth?

A

high = SLOWER - blood is considered an inactive reservoir for the inhalants

43
Q

What solubility of an inhaled anesthetic is considered the most important? How does sevoflurane and isoflurane compare?

A

blood gas solubility —> lower = quicker action

SEVO has a lower blood gas solubility, making it much quicker

44
Q

How does cardiac output affect transfer of alveolus to arterial blood?

A

passage of more blood through the lungs removes more anesthetic from the alveoli, thus increased cardiac output slows inhalant onset and recovery

45
Q

At what speeds are hyperthyroid cats and dogs in heart failure induced and recovered? Why?

A

slow to go under and recover from high inhalant concentration —> high cardiac output

induce and recover quickly —> low cardiac output

46
Q

What 3 things affect movement from blood into brain tissue?

A
  1. brain-blood partition coefficient
  2. cerebral blood flow
  3. arterial-to-venous partial pressure difference
47
Q

How do the brain blood partition coefficients vary between agents? How is onset of inhalants hastened? What are 2 exceptions?

A

varies little

maintain cerebral blood flow

neuro and ophtho patients

48
Q

What is the key component to ALL potent anesthetics getting to the brain?

A

blood flow to vessel rich groups

  • brain, kidney, heart, liver
49
Q

What is the vapor pressure, blood-gas partition coefficient, MAC, and rubber solubility of isoflurane?

A

high - requires precision vaporizer

low - rapid induction and recovery

1.3% - 1.2 x MAC = 1.5% = starting setting on vaporizer

low compared to older agents

50
Q

What are 5 effects of isoflurane?

A
  1. maintains cardiac output, heart rate, and rhythm (fewest adverse effects of all inhalants)
  2. depresses the respiratory system
  3. maintains cerebral blood flow
  4. almost completely eliminated through lungs
  5. induces good muscle relaxation
51
Q

Why isn’t isoflurane indicated for ophtho or neuro procedures? Why is it not used to mask patients? What does it produce when exposed to carbon dioxide absorbent?

A

maintains cerebral blood flow

causes profound bronchospasm

carbon monoxide

52
Q

What is the vapor pressure, blood-gas partition coefficient, and MAC of sevoflurane?

A

high - required precision vaporizer

low - very rapid induction and recovery

2.34-2.58% - initial setting at 3-3.5%

53
Q

In what 2 ways is sevoflurane more advantageous than isoflurane?

A
  1. high controllability of depth of anesthesia - useful in exotics and horses, high risk patients, and C-sections
  2. easier to mask patient because it is more pleasant smelling and causes less bronchospasm
54
Q

What are 4 effects of sevoflurane? What can it react with?

A
  1. minimal cardiovascular depression
  2. depresses respiratory system
  3. eliminated by the lungs
  4. induces adequate muscle relaxation

potassium hydroxide (KOH) or sodium hydroxide (NaOH) in dessiccated CO2 absorbent to produce Compound A, which is associated with renal damage

55
Q

What is the blood-gas partition coefficient and MAC of desflurane?

A

lowest - very, very rapid induction and recovery

7.2-9.8% - least potent

56
Q

Why is a special vaporizer required for desflurane?

A

needs a heated electronic precision vaporizer because it boils at room temperature

57
Q

What are 2 important effects of desflurane? What does it react with?

A
  1. strong vapors cause coughing and holding of breath —> very prone to bronchospasm
  2. transient increase in heart rate and blood pressure

spent soda lyme —> carbon monoxide

58
Q

How is halothane different than other inhaled anesthetics?

A
  • heavily (20-46%) metabolized in the liver
  • greatly increases cerebral blood flow
59
Q

In what patients is halothane avoided? What is it a potent trigger for?

A

adrenal or thyroid tumors —> sensitizes heart to catecholamine and induces arrhythmias

malignant hyperthermia —> requires prophylactic Dantrolene

60
Q

What is the carrier of halothane?

A

thymol

  • vaporizers require more cleaning
61
Q

What is the diffusion of nitrous oxide like?

A

extremely high —> preferentially replaces oxygen in the alveolus and can cause diffusion hypoxia or pneumothorax

62
Q

What inhaled anesthetic causes least cardiovascular and respiratory effects? What additional unique effect does it have?

A

nitrous oxide - not very potent, can be given directly from tank as a carrier

analgesia

63
Q

What effect is associated with the use of nitrous oxide?

A

second gas effect = when used with another inhalant, N2O hastens the onset of the second gas and decreases cardiovascular depressant effects

64
Q

What are the most common causes of waste anesthetic exposure?

A
  • vaporizer filling
  • leaks in breathing circuit
  • disconnection of patient
  • masking of patient
  • scavenging patient not working
  • F air canister use
65
Q

Why is waste gas exposure an environmental issue?

A
  • halothane and isoflurane contribute to ozone depletion
  • contribute to greenhouse warming
66
Q

How can waste gas exposure be minimized?

A
  • don’t tank or mask patients with inhalants
  • scavenge appropriately and avoid F air canisters
  • leak test machine daily
  • maintain and service machines regularly
  • turn on vaporizer after patient is connected
  • check cuff inflation
  • empty rebreathing bag into scavenging system prior to disconnecting
  • fill vaporizers at the end of the day
  • use lower flow techniques
  • monitor room
67
Q

By definition, are isoflurane and sevoflurane gases or vapors?

A

vapors

68
Q

Isoflurane gas exposed to sodasorb can be a source of which toxin?

a. carbon monoxide
b. carbon dioxide
c. ether
d. tetraldehyde
e. methemoglobin

A

A

69
Q

Which of the following agents have a low vapor pressure and because of this is used in a non-precision (liquid in jar) type vaporizer (such as the stephens vaporizer)?

a. Desflurane
b. Isoflurane
c. Sevoflurane
d. Halothane
e. Methoxyflurane

A

E

70
Q

All of the following except which will increase inhalant arrival at the alveolus?

a. Increased respiratory rate
b. Reduced rebreathing bag size
c. Shortened rebreathing circuit hoses
d. Increased tidal volume
e. Decreased tidal volume

A

E

71
Q

The MAC of isoflurane in the dog and cat are:

a. 1.5 and 1.6 respectively
b. 1.2 and 1.0 respectively
c. 1.8 and 2.0 respectively
d. 0.8 and 0.6 respectively
e. 2.3 and 2.5 respectively

A

A

72
Q

All modern inhalant anesthetics such as isoflurane and sevoflurane are used in precision, temperature and pressure controlled vaporizers. The temperature control occurs in these vaporizers because of which working mechanical part?

a. The sump
b. The bypass chamber
c. The common gas outlet which controls the atmospheric pressure
d. The bimetallic strip
e. The wick

A

B

73
Q

Which of the following is true regarding the mechanism of inhalant anesthetics

a. The AMPA receptor is likely involved
b. They act by increasing Na conduction
c. Mu opioid receptors mediate their effect
d. It is largely unknown, but postulated to involve lipid solubility and protein changes
e. They act similarly to local anesthetics

A

D

74
Q

A new inhalant anesthetic is developed which has a MAC of 2.0 in the dog and cat. What initial vaporizer setting would you expect to set in order to have a PREMEDICATED canine or feline patient be anesthetized safely and pain free for surgery?

a. 2.4-2.8%
b. 0.6-0.8%
c. 3-3.2%
d. 0.6-1%
e. 1.6-2.0%

A

MAC = 2.0

0.8 x 2 = 1.6
1 x 2 = 2

E

75
Q

Desflurane requires a specialized heated vaporizer because:

a. It boils at room temperature
b. It has a relatively low blood gas partition coefficient
c. It has negligible solubility in rubber
d. It freezes at room temperature
e. It has a relatively high blood gas partition coefficient

A

A

76
Q

When we focus on deliver of inhalant anesthetics to the brain (site of action) which area of the respiratory tract is most important in maintaining a solid level of anesthesia in the brain tissue?

a. larynx
b. alveolus
c. trachea
d. nasopharynx
e. distal airway

A

B

77
Q

All of the inhalant (volatile, gas) anesthesia agents have the following in common with EXCEPTION of which?

a. Cause Bronchoconstriction
b. Cause reduction in sensitivity to C02 levels
c. Cause an increase in intracranial blood flow
d. Cause Dose dependent cardiovascular depression
e. Cause muscle relaxation

A

A

78
Q

Blood gas Solubility coefficients are also known as partition coefficients and are studied to describe the speed of the inhalant agent. Which of the following statements is true regarding blood solubility of the inhalant agents?

a. Solubility of the gas anesthetic in blood is DIRECTLY proportional to the speed of induction and recovery
b. Solubility of the gas anesthetic in blood is INVERSELY proportional to the speed of induction and recovery

A

B

79
Q

N20 is not used as a PRIMARY gas inhalant anesthetic in veterinary patients for all of the following reasons EXCEPT:

a. There is a fear of diffusion hypoxia if it is used
b. Its MAC in veterinary patients is roughly 200%
c. There is a fear of diversion, abuse potential with human employees
d. Its not potent enough
e. It is costly

A

C

Anesthesia (40 decks)

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