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Anesthesia Basics > Inhaled Agents > Flashcards

Inhaled Agents Flashcards

1
Q

Isoflurane - blood-gas coefficient

A

1.46

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2
Q

Isoflurane - MAC value

A

1.15

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3
Q

Isoflurane - vapor pressure at 20°C

A

240 mmHg

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4
Q

Isoflurane - cassette color & airway compatibility

A

Purple, pungent/irritating

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5
Q

Isoflurane - brand name

A

Forane

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6
Q

Enflurane - blood-gas coefficient

A

1.9

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7
Q

Enflurane - MAC value

A

1.63

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8
Q

Enflurane - vapor pressure at 20°C

A

172 mmHg

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9
Q

Enflurane - cassette color & airway compatibility

A

Orange, pungent/irritating

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10
Q

Enflurane - brand name

A

Ethrane

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11
Q

Halothane - blood-gas coefficient

A

2.54

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12
Q

Halothane - MAC value

A

0.76

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13
Q

Halothane - vapor pressure at 20°C

A

244 mmHg

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14
Q

Halothane - cassette color & airway compatibility

A

Red, nonpungent

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15
Q

Halothane - brand name

A

Fluothane

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16
Q

Desflurane - blood-gas coefficient

A

0.45

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17
Q

Desflurane - MAC value

A

6.0

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18
Q

Desflurane - vapor pressure at 20°C

A

669 mmHg

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19
Q

Desflurane - cassette color and airway compatibility

A

Blue, pungent/irritating

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20
Q

Desflurane - brand name

A

Suprane

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21
Q

Sevoflurane - blood-gas coefficient

A

0.65

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22
Q

Sevoflurane - MAC value

A

1.85

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23
Q

Sevoflurane - vapor pressure at 20°C

A

160 mmHg

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24
Q

Sevoflurane - cassette color and airway compatibility

A

Yellow, nonpungent

25
Q

Sevoflurane - brand name

A

Ultane

26
Q

Nitrous oxide - blood-gas coefficient

A

0.46

27
Q

Nitrous oxide - MAC value

A

104

28
Q

Nitrous oxide - vapor pressure at 20°C

A

38k mmHg

29
Q

Nitrous oxide - tank color and airway compatibility

A

Blue tank, nonpungent

30
Q

Solubility - lower partition coefficients

A
  • Lower partition coefficients imply decreased solubility, faster equilibration of partial pressure (alveolus ⇔ blood ⇔ brain),
  • Rapid induction
    • ​Ex: desflurane
31
Q

Solubility - higher partition coefficients

A
  • Higher partition coefficients imply increased solubility, slower equilibration as more molecules are dissolved in the blood
  • Prolonged induction
    • Ex: halothane
32
Q

Solubility - partition coefficients

A
  • Partition coefficients express relative solubility of anesthetic gas at equilibrium
  • Tissue:Blood coefficient = time for equilibrium of tissue with arterial blood
33
Q

Cardiac output and induction

A
  • Increased CO results in faster uptake but decreased alveolar concentration (Fa)
  • Prolonged induction
    • More blood passing through the lungs = anesthetic is getting carried away faster
34
Q

Alveolar-venous concentration gradient and induction

A
  • Depends on uptake by desired (brain) and undesired (fat, muscle) tissues
  • Tissue uptake is determined by partition coefficients and regional blood flow
  • Less tissue uptake means blood returns to alveolus with higher partial pressure
    • Fa increases faster
35
Q

Factors that speed rate of induction (increases Fa/Fi)

A
  • Use of agents with low solubility (low partition coefficients)
  • Low CO w/ minimal R→L shunting and preserved CBF
  • Increased alvolar MV, increased conc. of agent, increased FGF rate
    • Replaces anesthetic taken up by the bloodstream)
  • Ex: Pediatric patients
    • Faster induction due to increased alveolar ventilation, decreased FRC, increased % of blood flow to brain
36
Q

Content-sensitive elimination time

A
  • Longer duration of anesthetic is associated with longer time to recovery
    • Over longer time, more anesthetic is deposited in undesired tissues and must be “washed out”
    • Effect is more pronounced with increased solubility of agent
37
Q

Diffusion hypoxia

A
  • High concentrations of relatively insoluble gases (N2O) diffuse out of the blood and enter the alveolus, displacing and replacing alveolar concentration of O2 and CO2
    • Dilution of alveolar O2 can lead to hypoxia
    • Dilution of CO2 can decrease ventilatory drive and worsen hypoxia
  • Administer high flow 100% O2 for 5-10 minutes after discontinuation of N2O
38
Q

MAC

A
  • Reference point (1 MAC) = alveolar conc. at which 50% of patients will not move in response to a standardized surgical stimulus
    • Analogous to ED50
  • MAC is greatest at 1 yr and is reduced by 6% per decade
39
Q

What is MACBAR?

A
  • 1.5 - 2 MAC
  • Concentration which _b_locks adrenergic response to nociceptive stimuli
40
Q

What is MACAware?

A
  • ≈ 0.4 - 0.5 MAC
  • Concentration at which 50% of patients will not be forming long term memory
41
Q

What is MACAwake?

A
  • 0.15 - 0.5 MAC
  • Concentration at which 50% of patients open eyes on command
42
Q

Factors that decrease MAC (increase potency)

A
  • Acidosis
  • Acute alcohol use
  • Advanced age
  • Benzodiazepines
  • Increased altitude
  • Intravenous anethestics
  • Hypotension (severe)
  • Hypoxia
  • Opiates
  • Pregnancy
43
Q

Factors that increase MAC (decrease potency)

A
  • Chronic alcohol use
  • Very young age (closer to 1 y of age)
  • Increased temperature ( >42°C)
  • Decreased altitude
  • Drugs (MAOIs, TCAs, cocaine, acute amphetamine use)
44
Q

Systemic effects of inhaled agents - CV

A
  • All volatile agents are dose-dependent CV depressants, though mechanism of decreased BP differs
  • Heart rate effects vary with MAC and inspired concentration rate of change
45
Q

Systemic effects of inhaled agents - pulmonary

A
  • All agents increase RR with decrease in TV
    • Overall volatile agents cause decrease in MV and increase in PaCO2
  • All agents blunt ventilatory response to hypoxemia, volatile agents decrease response to hypercarbia
  • Volatile agents are potent bronchodilators
  • Minimal inhibition of hypoxic pulmonary vasoconstriction (HPV)
46
Q

Systemic effects of inhaled agents - neurological

A
  • All agents increase** CBF causing **increased ICP and impair autoregulation of vascular tone
  • Volatile agents decrease CMR (N2O may increase)
  • All agents decrease SSEP / MEP signals
47
Q

Systemic effects of inhaled agents - hepatic

A
  • Halothane** causes **both hepatic artery vasoconstriction and decreases portal vein flow
    • Potential for hypoxic hepatic injury
  • Other volatile agents preserve vascular supply better with increase** in hepatic artery flow **compensating** for **decreased portal vein flow
48
Q

Systemic effects of inhaled agents - renal

A
  • All agents decrease RBF, GRF, UO
  • Untreated hypotension can cause acute kidney injury
49
Q

Differential physiological effects of halothane

A
  • HR: ⇔ or slight decrease
  • SVR: ⇔
  • CO: significantly decrease
  • Contractility: significant decrease
  • HBF: significant decrease
50
Q

Differential physiological effects of isoflurane

A
  • HR: slight increase
  • SVR: slight decrease
  • CO: ⇔
  • Contractility: slight decrease
  • HBF: slight decrease
51
Q

Differential physiological effects of sevoflurane

A
  • HR: ⇔
  • SVR: slight decrease
  • CO: ⇔
  • Contractility: slight decrease
  • HBF: slight decrease
52
Q

Differential physiological effects of desflurane

A
  • HR: slight increase
  • SVR: slight decrease
  • CO: ⇔
  • Contractility: slight decrease
  • HBF: slight decrease
53
Q

Differential physiological effects of N2O

A
  • HR: ⇔ or increase
  • SVR: ⇔ or increase
  • CO: ⇔ or increase
  • Contractility: ⇔ or decrease
  • HBF: slight decrease
54
Q

Inhalational anesthetics - N2O

A
  • MAC of 104% precludes use as solo agent for surgical anesthesia
    • Used at 30 - 70% conc. as adjuvant to IV or potent inhaled anesthetics
    • Low solubility = rapid onset / offset of action
  • Nonpungent, has analgesic properties
  • Disadvantages
    • Rapidly diffuses into and expands air-containing cavities → avoid in air embolism, PTX, bowel obstruction, pneumocephalus, middle ear and retinal procedures
    • Prolonged exposure → inhibits B12-dependent enzymes for myelin and nucleic acid synesthes
      • Megaloblastic bone marrow change possible > 12 - 24 h use
    • Nonflammable but does support combustion
    • Increases PONV
    • Sympathomimetic CV effects
55
Q

Inhalational anesthetics - isoflurane

A
  • Inexpensive, slower onset / offset of action
  • Pungent
  • Coronary vasodilator
    • Possibility for coronary “steal” effect → flow diverted away from vessels with fixed lesions
56
Q

Inhalation anesthestics - desflurane

A
  • Most rapid onset / offset among volatiles
  • Very pungent → may be irritant in patients prone to bronchospasm
  • High vapor pressure requires an electrically heated vaporizer → eliminates variations in delivery owing to changes in ambient temp.
  • Rapid increase or high conc. may cause transient but significant sympathetic stimulation
57
Q

Inhalational anesthestics - sevoflurane

A
  • Least pungent (best choice for inhalational induction)
  • Fast onset / offset of action
  • Controversial potential for nephrotoxicity due to metabolic production of fluoride ion and degradation to Compound A
    • Compound A production increases with low FGF, high conc. sevoflurane, desiccated barium lime absorbent
58
Q

Inhalation anesthetics - halothane

A
  • Low pungency
  • Inexpensive
  • Esp. potent bronchodilator
  • Rare but fulminant postop autoimmune hepatitis
  • CV depression and myocardial desensitization to catecholamines (increases vent. dysrhythmias)
59
Q

Inhalational anesthetics - Heliox

A
  • Nonanesthetic gas mixture
    • Commonly 70 - 79% helium and 21 - 30% O2
  • Lower density of gases promotes laminar flow, reduces turbulence in upper airway obstruction
    • Helps decrease the work of SV

Anesthesia Basics (7 decks)

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