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Stanford CA-1 Guide > Inhalational Agents > Flashcards

Inhalational Agents Flashcards

1
Q

4 phases of pharmacokinetics

A

Uptake, distribution, metabolism (minimal), elimination

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2
Q

The ___ of gas in the alveolus determines the effect, NOT the ___

A

Partial pressure

Concentration

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3
Q

At higher altitude, how will the same concentration of gas affect the anesthesia

A

Higher altitude = lower pressures = less anesthesia

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4
Q

How does gas flows affect the inspired concentration of gas compared to the delivered concentration from the machine?

A

Higher gas flows -> closer inspired Fi to machine Fi

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5
Q

Things that increase alveolar concentration of gas

A

INPUT minus UPTAKE

  • Decreased uptake into bloodstream (low solubility, low cardiac output, saturated bloodstream)
  • Higher ventilation of fresh gas into the alveoli (higher flows, higher concentration of inspired gas)
  • Concentration effect
  • Second gas effect
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6
Q

What is the concentration effect? Why?

A

Higher inspired concentrations -> F(A) approaches F(I) faster

Higher inspired concentration means there is more to buffer the uptake into blood vessels, so F(A) won’t drop as quickly

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7
Q

What is the second gas effect?

A

As nitrous oxide is taken up into blood vessels faster than volatile agents, the relative concentration of the volatile agent increases, leading to quicker anesthesia

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8
Q

Right-to-left shunt…how is volatile agent rate of anesthesia affected?

How will it affect IV anesthetics?

A

Higher P(A) but lower P(a), so dilution with non-ventilated blood leads to slower onset

Faster onset, since bypassing some of lungs

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9
Q

Left-to-right shunt…how is volatile agent rate of anesthesia affected?

A

Little effect for inhaled OR IV drugs

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10
Q

Sevo, iso, des, N2O, halo…put in order of solubility

How does this affect F(A)/F(I) over time?

A

Low -> High…
N2O > Des > Sevo > Iso > Halo

More soluble = longer to reach F(A)/F(I) of 1

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11
Q

N2O…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 0.47
  • 39,000
  • 104%
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12
Q

Desflurane…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 0.42
  • 681
  • 6%
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13
Q

Sevoflurane…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 0.69
  • 160
  • 2.15%
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14
Q

Isoflurane…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 1.4
  • 240
  • 1.2%
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15
Q

Halothane…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 2.3
  • 243
  • 0.75%
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16
Q

Enflurane…

  • Blood:Gas Partition Coefficient
  • Partial pressure at 20ºC
  • MAC
A
  • 1.8
  • 175
  • 1.68%
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17
Q

What does blood:gas partition coefficient mean?

A

At steady state, 1mL of blood contains ___ as much gas as 1mL alveolar gas

18
Q

At 50% N2O in inspired gas, how many mL N2O will be in 1mL of blood?

A

0.5mL x 0.47 = 0.235mL N2O in 1mL blood

19
Q

How does increased fat in blood affect induction via gases?

A

Fat:blood partition coefficient is >1, so the gas wants to be in fat more than in blood, so it will SLOW induction

20
Q

How do volatile gases affect the brain?

A
  • Decreased O2 use

- Decreased vascular resistance -> increased CBF and ICP

21
Q

At 0.5 MAC, is CBF higher or lower than normal?

A

NEITHER…at 0.5 MAC, decreased O2 use counteracts vasodilation, so CBF stays constant

22
Q

At 1 MAC, is CBF higher or lower than normal?

A

HIGHER…plateau’d decrease in O2 use, so vasodilation is more prominent -> increased CBF

23
Q

How do gases affect CV?

A

Vasodilation -> decreased MAP, BUT C.O. maintained

24
Q

Which gas has negative effect on cardiac contractility?

A

Halothane

25
Q

How do gases affect lungs?

A
  • Decreased Vt but increased RR, so MV maintained
  • Dose-dependent decreased response to high CO2 and low O2
  • Bronchodilation
26
Q

How do gases affect kidneys?

How do gases affect muscles?

A

Decreased RBF -> decreased GFR

Muscle relaxation (NOT N2O)

27
Q

N2O…

  • Potency
  • Solubility
  • Particularly contraindicated when?
  • Effect on CV?
  • Effect on pulm?
  • Effect on analgesia?
  • Prolonged exposure can lead to what?
  • Effect on muscles?
  • Should periodically do what?
A
  • Low potency (high MAC)
  • Low solubility - rapid uptake and elimination
  • Diffuses into air-filled spaces (pneumothorax, middle ear, bowel, blebs, ETT cuff) and causes expansion
  • Unmasks myocardial depression in CAD or bad hypoT
  • pHTN after prolonged
  • NMDA antagonist -> MAYBE analgesia
  • Prolonged -> bone marrow suppression, peripheral neuropathies
  • NO affect on muscles (no MH, no relaxation)
  • Periodically remove air from ETT cuff
28
Q

Isoflurane…

  • Potency
  • Solubility
  • Why do patients not like it?
  • Effect on CV?
  • Effect on brain?
  • At 2 MAC, produces _____
A
  • High potent (MAC 1.2%)
  • High solubility -> longer onset and elimination
  • VERY pungent
  • Vasodilation -> less perfusion to stenotic coronaries that can’t dilate (coronary steal)
  • Minimal increased CBF (vasodilation) and ICP
  • At 2 MAC -> silent EEG
29
Q

Sevoflurane…

  • Potency
  • Solubility
  • Desiccated CO2 absorbant?
  • Normal CO2 absorbant? So?
A
  • Lower potent (MAC 2.1%)
  • Lower solubility -> pretty quick on and off
  • Desiccated absorbant –> CO –> FIRE
  • CO2 absorbant -> Compound A (nephrotoxic in rats)
  • SO, keep flows above 2 L/min to prevent rebreathing
30
Q

Desflurane…

  • Potency?
  • Vapor pressure? So?
  • Effects if given while awake?
  • Desiccated CO2 absorbant?
  • What to know about changing concentration?
A
  • LOW potency (MAC 6.6%)
  • HIGH vapor pressure, so boils at sea level, so must be kept in heated/pressurized container to regulate concentration
  • Awake –> PUNGENT -> bronchospasm, coughing, coughing, laryngospasm, breath-holding, salivation
  • Desiccated absorbant -> CO -> FIRE
  • Rapidly increased concentration -> increased sympathetics (tachy, hypertension)
31
Q

At equilibrium, ___ partial pressure = ___ partial pressure

A

Alveolar = brain

32
Q

1 MAC = ED__
So, ED95 = __ MAC
What does that mean?

A

50
1.3
At 1.3 MAC, 95% of people will not move to surgical stimulus

33
Q

What determines potency?
What determines solubility?
Rank least to most potent

A

Oil:Gas partition coefficient
Blood:Gas partition coefficient
N2O < Des < Sevo < Iso < En < Halo

34
Q

MAC (aware)
MAC (movement)
MAC (intubation)
MAC (blunt autonomic response)

A
  1. 4 (verbal/tactile stimulation)
  2. 0 (surgical incision)
  3. 3 (intubation, LMA); also ED95 for incision
  4. 6 (no tachy/hyperT to noxious stimuli)
35
Q

How does MAC change with age?

A

Greatest at 6mo old, then declines

6% per decade after 40y/o

36
Q

Things that decrease MAC (meds, physiology, pathology, substances)

A

Meds: Depressants, ketamine, alpha-2 agonists, verapamil, local anesthesia
Physio: Increasing age after 1 y/o
Path: hypothermia, hypoxia, hypercarbia, anemia, sepsis, hyponatremia
Substances: acute EtOH, chronic meth

37
Q

Things that increase MAC (meds, physiology, pathology, substances, genetic)

A 
Meds: amphetamines, L-dopa, ephedrine, TCAs
Physio: Increasing age < 1 y/o
Path: hyperthermia, hypernatremia
Substances: chronic EtOH
Genetic: red hair
38
Q

Things that increase risk of intra-op awareness

What are you aware of?

When during the surgery?

How to manage? (after)

A

Paralytics, children, chronic drugs/EtOH, surgeries requiring light anesthesia

Hearing voices

Induction and emergence

Counseling

39
Q

Signs of light anesthesia

A

Tearing, bucking, coughing, dilated pupils, sweating, movement, tachy/hyperT

40
Q

How to prevent intraop awareness?

A

Premedicate, gas > TIVA, MAC > 0.5-0.7, avoid paralytics, redose IV meds before very stimulating things, increase BP with meds rather than decreasing the gas

Stanford CA-1 Guide (2 decks)

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