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Anatomoy 3 > Pharmacology 4 Volatile Agents > Flashcards

Pharmacology 4 Volatile Agents Flashcards

1
Q

Why worry about Anesthesia?

A

BC we give muscle relaxants, which abolish pt’s ability to let us know if they are light - possibility of pt being immobile w normal VS and fully aware but unable to let you know

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2
Q

Ideal VA

A

Rapid onset, rapid and predictable recovery, no residual effects on organs, easy to administer, high safety margin

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3
Q

Woodbridge’s definition of Anesthesia 1950

A

GA is depression of sensory, motor, reflex, and mental fxn.

Analgesia, skeletal muscle relaxation, freedom from reflexes, unconsciousness (hypnosis and amnesia)

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4
Q

Prys-Roberts’ definition of Anesthesia 1970

A

As a result of drug-induced unconsciousness, a state in which the pt neither perceives nor recalls unpleasant stimuli. Increasing dose produces pattern of suppression of responses (somatic easier than autonomic)
Pain - mvmt - breathing - bp/hr - sweating - stress response

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5
Q

Eger’s definition 2002

A

2 qualities apply to VA:
Immobility - what surgeon wants
Amnesia - what pt wants
(reflex suppression and MR are useful, but have nothing to do with anesthetic state, pt can’t tell us anything if amnesia is present)

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6
Q

Stage 1

A

Analgesia and sedation

  • eyes open to command, breathe normally, tolerate mild pain (suturing)
  • airway protective and other reflexes intact
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7
Q

Stage 2

A

Excitement
-rarely see (induction masked d/t IV agents, emergence quick d/t low solubility of VA)
-Muscle mvmt, retching, heightened laryngeal reflexes, disconjugate pupils, increased HR/BP and VE
-Associated w MACawake and amnesia
MACawake = responds to commands but won’t remember

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8
Q

Stage 3

A

Surgical anesthesia

  • associated w MAC
  • no mvmt in response to surgical stimuli
  • no behavioral pain response
  • amnesia
  • reflex depression
  • skeletal muscle relaxation
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9
Q

Stage 4

A

Medullary depression (OD)

  • CV collapse (decreased BP/CO
  • Respiratory collapse (apnea)
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10
Q

Gauging depth - clinical signs - Respiratory

A

-increased depth of VA = increased RR, decreased tidal volume “pant like puppies”
-Changes in character of spontaneous breathing
~excessive depth = rocking boat d/t diaphragmatic breathing only, loss of ICM
-Hard to use in controlled ventilation, NDMR, and opioids

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11
Q

Gauging depth - clinical signs - Eyes

A

-Lacrimation, eye mvmt, disconjugate = light
-Pupils have no direct relationship: opioids = miosis, except meperidine causes mydriasis
mydriasis = increased paCO2 or cerebral hypoxia
all abolished by anti-Ach

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12
Q

Gauging depth - clinical signs - Motor

A

Active expiration = light

Soft abdomen = deep

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13
Q

Gauging depth - electronically - BIS

A

Bispectral Index Monitoring

  • scale of 0 - 100
  • at 60 return to responsiveness
  • Doesn’t work w KETAMINE or N2O
  • NOT a standard of care per ASA or AANA
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14
Q

ASA Practice Advisory on assessing for increased risk of awareness 2005 - Pre-op Eval

A

*review medical records:
-substance abuse
-previous hx of awareness
-hx or anticipated difficult intubation
-chronic pain pts on high doses of opioids
-ASA status of IV or V
-limited hemodynamic reserve
*Interview pt:
-level of anxiety
-other potential risk factors
>cardiac, c/s, trauma, ER, paralysis, use of
MR, N2O, opioids

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15
Q

ASA Practice Advisory on assessing for increased risk of awareness 2005 - Pre-induction phase

A

Adhere to checklist protocol for anesthesia machines and equipment, verify fxn of IV access, pumps, connections
use benzo pre-op

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16
Q

” “ “ - Intra-op monitoring

A
  • Clinical techniques
  • Conventional monitoring
  • Brain fxn monitoring
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17
Q

Gauging depth - electronically - Gas analysis

A

End-tidal agent - monitoring standard

  • dial setting
  • inspired VA
  • expired VA
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18
Q

T or F: Accuracy is most difficult and critical after induction and before incision?

A

True : why?
Too much VA = hypotension d/t lack of stimulus (incision) and vasodilatory effect of VA
Too little VA = salivate, tachycardia, HTN and mvmt on incision

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19
Q

When is inspired amt of VA more than expired?

A

Beginning of the case

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20
Q

What does halogenation do to an agent?

A

Decreases flammability

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21
Q

Using only Fluorine yields what kind of agent?

A

Non-flammable, low solubility, and extreme resistance to metabolism

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22
Q

What current VA degrades in soda lime?

A

Sevo

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23
Q

What VA has the fastest onset?

A

Des < N20 < Sevo < Iso

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24
Q

Lower solubility in blood yields:

A
  • rapid induction
  • more precise control
  • favor prompt recovery
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25
Q

What VA is the cheapest?

A

Iso at 10 cents per ml

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26
Q

What VA is the most expensive?

A

Sevo at 61 cents per ml

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27
Q

N2O

A

Vapor pressure: its a gas, there isn’t one
BGPC: 0.46 (fast onset)
MAC: 104

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28
Q

Iso

A

VP: 240
BGPC: 1.46 (longest next to enflurane)
MAC: 1.17 % (most potent next to N2O)

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29
Q

Des

A

VP: 669
BGPC: 0.42 (fastest onset)
MAC: 6.6 % (least potent)

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30
Q

Sevo

A

VP: 170
BGPC: 0.69
MAC: 1.8 %

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31
Q

Which VA needs a heated vaporizer? Why?

A

Des bc Vapor pressure is 669

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32
Q

What structures do Iso, Des, and Sevo have?

A

Iso - halogenated methyl ethyl ether w Cl-
Des - Completely fluorinated methyl ethyl ether, replacing Cl- on Iso w Fl-
Sevo - Completely fluorinated methyl isopropyl ether

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33
Q

If the VA has a low MAC value…

A

the more potent the agent

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34
Q

Which agent is not stable in soda lime?

A

Sevo, degrades into Compound A

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35
Q

Which agent is the only inorganic compound?

A

Nitrous oxide (N2O)

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36
Q

In what 2 ways is nitrous oxide used?

A

Alone for sedation or in combination w opioids and VA to enhance GA

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37
Q

Is N2O flammable?

A

No, but supports combustion

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38
Q

What are advantages of N2O?

A
  • low solubility so rapid on/off
  • doesn’t depress BP
  • analgesic (10mg of morphine)
  • additive MAC w VA
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39
Q

What are disadvantages of N2O?

A

*supports combustion
*minimal skeletal muscle relaxation
*causes PONV
*high volume of absorption
*decreases immunity r/t ↓ in PMNs
*causes miscarriages r/t ↓ methionine synthetase
*causes polyneuropathy and B12 inactivation =
pernicious anemia

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40
Q

N2O is contraindicated in what surgeries?

A

Some eye surgeries, pneumothorax, belly cases

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41
Q

What VA is an organic alkane?

A

Halothane

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42
Q

Why was is taken off of the market?

A

20% metabolized by the liver = halothane hepatitis

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43
Q

What agents are Ethers?

A

Iso, Des, and Sevo

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44
Q

Iso characteristics

A
  • gold standard
  • most potent w MAC of 1.17%
  • longest onset/offset w solubility of 1.46
  • pungent, so no inhaled induction
  • extreme physical stability
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45
Q

Des characteristics

A
  • Least potent w MAC of 6.6%
  • need heated vaporizer d/t vapor pressure of 669
  • boils near room temp
  • more stable and resistant to metabolism than iso
  • the most rapid onset/offset w solubility of 0.42
  • expensive
  • pungent
  • carbon monoxide generation in soda lime
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46
Q

Sevo characteristics

A

*MAC of 1.8%
*solubility of 0.69
*non pungent
*most expensive
*metabolism 5% potential nephrotoxicity
*degrades in soda lime to compound A =
No FGF < 1 L/min and no 2 MAC hours a low flow

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47
Q

Name brand names for agents

A 
Iso = Forane
Des = Suprane
Sevo = Ultane
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48
Q

MAC values for VA’s are additive

A

True

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49
Q

What are the factors that decrease (modify) MAC?

A

Opioids - decrease MAC significantly
Age - decrease MAC with age
Hypothermia, hyponatremia
Pregnancy, Lidocaine, Alpha-2 agonist

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50
Q

What are some factors that increase MAC?

A

Hyperthermia, Drugs that ↑ CNS (cocaine, MAIOs, anxiety), hyperthermia, hypernatremia

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51
Q

What is VA MOA?

A

unknown

mediated at cord, supraspinally, RAS likely

52
Q

What is the Meyer-Overton theory?

A

correlation btw lipid solubility (oil:gas partition coefficient) and VA potency
causes distortion of ion channels, AP blocked

53
Q

Unlikely that voltage-gated channels plan a role in production of anesthetic state

A

True

54
Q

What is the effect on ligand-gated channels?

A

Glutamate, glycine, and GABA may be important site (role)

55
Q

What are the effects of VA’s on CNS?

A

*No retrograde amnesia
*No prolonged effects
*Luxury perfusion - ↑ CBF and ↓ CMRO2 (risk of ↑
ICP w tumors so hyperventilate, ↓ CO2 to ↓
vasodilation

56
Q

What are the effects on EEG?

A

< 0.4 MAC = VA ↑ freq + voltage
0.4 MAC = shift post to ant, ↓ CMRO2, + amnesia
1 MAC = freq ↓ + max voltage
1.5 MAC = burst suppression
2 MAC = silence/isoelectric
No sz activity (fast freq + high voltage = spikes

57
Q

How does VA effect EP’s?

A

↓ amplitude + ↑ latency

  • Don’t go above 1 MAC
  • Don’t go up and down
  • Usually asked to avoid N2O
58
Q

At what MAC does cerebral vasodilation occur?

A

> 0.6 MAC

59
Q

At what MAC is cerebral autoregulation best preserved?

A

at 1 MAC

60
Q

Do VA’s including N2O enhance CSF production?

A

No, they ↑ reabsorption and ↑ CSF pressure

61
Q

What are the effects of VA’s on MAP and how are they produced?

A

current VA’s ↓ MAP by ↓ SVR (vasodilate)
not N2O
so use some N2O w VA to ↓ drop in MAP

62
Q

What are the effects of VA’s on HR from greatest to least?

A

They ↑ HR - Iso > des > sevo

The more rapid the rise on conc, the more rapid the increase in HR

63
Q

What are the effects of VA’s on RAP?

A

Des, Iso, and N2O ↑ RAP while sevo ↓ RAP

64
Q

What are the effects of N2O on PVR?

A

↑, more pronounced if pre-existing pulm HTN and neonates, congenital heart dz R to L shunt

65
Q

Describe a spontaneously breathing pt w VA’s

A

Higher HR, Lower CO, SVR, BP d/t higher levels of CO2 (vasodilator) and SNS stimulation

66
Q

What is coronary steal, what VA does this, and what must be done in CAD pts?

A

coronary vasodilation and blood is diverted away from ischemic areas, Iso does this
In CAD pt, no ↑ HR or drop in BP

67
Q

How do you control Des and Iso neurocirculatory responses?

A

Don’t stomp on the gas! slower increase in VA, use fentanyl, esmolol, precedex or clonidine

68
Q

List cardiac coexisting dz’s and choices of VA:

A

CHF - no VA, use N2O and fent
CAD - Sevo and fent
Valvular HD - VA good for regurg (full, fast, forward)
VA contraindicated in stenosis!!! Use N2O

69
Q

What are the 3 prominent effects of VA’s on ventilation?

A
  1. Pattern of breathing (↑ RR, ↓ VT) = rapid shallow
  2. ↓ Ventilatory response to CO2 and hypoxemia
    (quality of each breath ↓, so dead space ↑)
  3. ↑ Airway resistance
    (bronchodilator once alseep)
70
Q

Why does pt on vent need great VT?

A

VT augmented bc VQ mismatch, ↓ FRC, ↑ dead
space (d/t lack of diaphragmatic vent)
So assist spontaneous breathers… LMA’s

71
Q

What is the response to hypoxemia in VA?

A
  1. 1 MAC depresses this by 50-70%

1. 1 MAC abolishes response completely

72
Q

All VA’s including N2O ↓ FRC

A

True

73
Q

What are VA hepatic effects?

A

Maintain hepatic BF and venous O2 saturation

74
Q

What agents have metabolites?

A

Iso and des have trifluoroacteic acid but remember, des has almost NO metabolism
Sevo produces hepatotoxic compound A

75
Q

VA produce dose-related decreases in:

A
  • Renal blood flow
  • GFR
  • Urine output (d/t ↓ BF)
76
Q

How do you abolish or lesson these effects?

A

Pre-op hydration

77
Q

How is Compound A formed?

A

When Sevo degrades in CO2 absorbent

78
Q

What makes the degradation of sevo worse?

A

Dry granules, higher absorbent temps

79
Q

What is important to remember about the flow of Sevo?

A

Never use with FGF < 1 L/min, do not exceed 2 MAC hours at 1-2 L/min FGF

80
Q

What are the effects of VA’s on skeletal muscles?

A

Produce some skeletal muscle relaxation
Potentiate MR’s
N2O does not do either!

81
Q

What about MH?

A

All VA’s and Succs can trigger MH, but NOT N2O

82
Q

What are the obstetric effects of VA’s?

A

↓ in uterine BF and uterine smooth muscle tone
modest at 0.5 MAC, substantial at 1 MAC
N2O does NOT do this

83
Q

What is a good cocktail for C/S?

A

0.5 MAC VA + 0.5 MAC N2O

84
Q

Do VA’s cross the placenta?

A

Yes, but rapidly exhaled after birth

85
Q

What do VA’s do to the resistance of infection?

A

All but N2O > VA’s inhibit WBC chemotaxis

86
Q

What are the genetic effects of VA’s?

A

*Not mutagens or carcinogens (-Ames test)
*N2O ↑ abortion/miscarriage (B12 enzyme
methionine synthetase decreased)

87
Q

How do VA’s work w bone marrow fxn?

A

N2O > 24 h = megaloblastic changes
N2O > 4 d = agranulocytosis
Can still give to bone marrow recipients
Avoid in burns/immune depressed = repeated exposure have cumulative effects

88
Q

N2O and peripheral neuropathy

A

Long exposure = nerve degeneration
sensorimotor polyneuropathy
pernicious anemia

89
Q

What do VA’s do to total body O2 needs?

A

VA decrease VO2

90
Q

What makes VA’s resistant to metabolism?

A

Fluorine-carbon bond

91
Q

What is the % of Iso metabolism?

A

0.2%

92
Q

What is the % of Des metabolism?

A

0.02%

93
Q

What is the type of metabolism that they undergo and what metabolite do they have in common?

A

Oxidation by cytochrome P450

Trifluoroacetic acid

94
Q

Carbon monoxide toxicity:

A

Des&raquo_space; Iso DEGRADATION
Caused by strong bases (KOH and NaOH)
Can not detect intraop
Cause CNS disturbances

95
Q

What factors favor carbon monoxide?

A

Dry absorbent (prolonged high FGF)
High absorbent temp (low FGF)
baralyme > sodasorb

96
Q

Metabolism of Sevo:

A

2-5% oxidation by cytochrome P450

97
Q

Degradation of Sevo and causes:

A

produces compound A

  • high absorbent temps
  • dry absorbent
  • baralyme&raquo_space; soda lime
98
Q

Des compensation is used on the Fabius GS bc:

A

Des has characteristics that affect the sensitivity of the Fabius GS flow sensor

99
Q

If this is not done, what will happen?

A

VT readings will be higher than set VT (up to 25%)

100
Q

List physical signs of adequate ventilation in an anesthetized pt:

A

*chest mvmt * BBS * mvmt of bag/bellow * mvmt of unidirectional valves * sounds of vent * moisture in ETT w exhalation

101
Q

List monitors that display signs of adequate ventilation in an anesthetized pt:

A

*Oxygen analyzer * spirometry * airway pressure * exhaled volume on monitor * gas analysis * capnography

102
Q

What are common problems w spirometry?

A

weight/bulk close to face
tubing disconnections/damaged
peds vs adult D Lite sensor

103
Q

List common problems w mechanical ventilation:

A
  • Failure to resume or failure to initiate

* Disconnection* most common - Y piece -

104
Q

How to prevent these problems from occurring:

A
  • Pre-anesthesia checklist
  • Precordial
  • If you turn off vent, keep your finger on the switch
  • Use apnea alarms and DON’T silence them
105
Q

List the umpteen mechanisms of circulatory effects of VA -

A
  • direct myocardial depression
  • decreased SNS
  • peripheral autonomic ganglionic block
  • decreased carotid sinus baroreceptor activity
  • decreased cAMP
  • decreased release of catecholamines
  • decreased calcium ion influx thru slow channels
106
Q

N2O alone or w VA produces mild SNS stim:

A

increased, plasma catecholamines, mydriasis, increased body temp, diaphoresis, increased RAP, systemic and pulmonary vasoconstriction

107
Q

N2O w opiates:

A

more circ depression

decreased bp, co, increased lvedp and svr

108
Q

High risk factors for PONV:

A

3 pts; hx, gyn, breast

109
Q

Medium risk factors for PONV:

A

2 pts: face, ear, neuro, obesity, cross eyed

110
Q

Low risk factors for PONV:

A

1 pt: young, female, anxiety, lap chole, opioids given, case > 1 hr

111
Q

What determines FGF:

A

the vaporizer and flow meter settings

112
Q

What determines FI

A

FGF, circuit vol, circuit absorption

113
Q

what determines FA

A

uptake, ventilation, and conc and second gas effects

114
Q

what determines Fa

A

V/Q mismatch

115
Q

Why do we use PA as a measure of depth?

A

bc Pbr = Pa = FA

116
Q

Why is solubility important?

A

The more poorly blood soluble agent has a faster speed of induction

117
Q

What is a time constant and what are the %?

A 
Capacity / flow
1 = 63%
2 = 86%
3 = 95%
There is circuit, lungs, and brain
118
Q

Uptake =

A

BGSC x Content (A-V) x Q (CO)

119
Q

The higher the uptake….

A

the slower the induction

120
Q

High FA/FI ratio =

A

less difference btw inhaled and exhaled VA

121
Q

The VRG is how much % of body wt and how much % of CO?

A

10 % body wt and 75% CO

122
Q

What organs are in the VRG?

A

Brain, heart, liver, kidneys

123
Q

The greater the VAlv / FRC ratio…

A

the faster induction

5:1 in neonates as compared to 1.5/1 in adults

124
Q

What cases would it be wise to avoid N2O?

A

abdominal, bowel, craniotomies, sitting positions, anytime the wound is higher than the heart

125
Q

The greater the A-V difference of VA…

A

the slower the rate of rise/slower induction

Anatomoy 3 (9 decks)

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